Measurement of the CP-violating weak phase φ_s and the decay width difference Δ⌈_s using the Bº_s →J/ψφ(1020) decay channel in pp collisions at √s=8 TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Measurement

of

the

CP-violating

weak

phase

φ

_s

and

the

decay

width

difference

_s

using

the

B

0

_s

→

J/ψ φ (1020)

decay

channel

in

pp

collisions

at

√

s

=

8 TeV

.

CMS

Collaboration

CERN,Switzerland

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received 27 July 2015

Received in revised form 11 March 2016 Accepted 16 March 2016

Available online 23 March 2016 Editor: M. Doser

Keywords:

CMS Physics B-physics CP violation

The CP-violating weak phase φs of the B0s meson and the decay width difference s of the B0s

lightand heavy masseigenstates are measuredwith theCMS detectoratthe LHCusingadata sam-ple ofB0

s→J/ψ φ (1020)→

μ

+

μ

−K+K− decays.The analysed data set corresponds to an integrated luminosity of 19.7 fb−1 collected in pp collisions at a centre-of-mass energy of 8 TeV. A total of 49 200 reconstructedB0

s decays are used toextract the values ofφs and s by performinga time-dependentand flavour-taggedangularanalysisofthe

μ

+

μ

−K+K− finalstate.Theweakphaseis mea-sured to be φs= −0.075

±

0.097(stat)

±

0.031(syst) rad, and the decaywidth difference is s= 0.095_±0.013(stat)±0.007(syst)ps−1_.

©2016CERNforthebenefitoftheCMSCollaboration.PublishedbyElsevierB.V.Thisisanopenaccess articleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Whilenodirectevidenceofphysicsbeyondthestandardmodel (SM)hasyetbeenfoundattheCERNLHC,theB0_s mesonprovides arich source ofpossibilities to probeits consistency. In this Let-ter,ameasurementoftheweakphase

φ

softheB0s mesonandthe decaywidthdifference

sbetweenthelightandheavyB0s mass eigenstatesis presented,usingthedata collectedby theCMS ex-perimentinppcollisionsattheLHCwithacentre-of-massenergy of8TeV,correspondingtoanintegratedluminosityof19.7fb−1.

The CP-violating weak phase

φ

s originates from the

interfer-ence betweendirect B0_s meson decays into a CP eigenstate ccss and decays through B0s–B0s mixing to the same final state.

Ne-glectingpenguin diagram contributions [1,2],

φ

s isrelatedto the

elementsoftheCabibbo–Kobayashi–Maskawaquarkmixingmatrix by

φ

s

−

2βs,where

β

s

=

arg(

−

VtsV_tb∗

/

VcsV_cb∗

).

Thepredictionfor

2βs, determined via a global fit to experimental data within the

SM, is 2βs

=

0.0363₋+0₀._.0016₀₀₁₅ rad [3]. Since the value predicted by

theSM isvery precise,anysignificant deviationofthe measured value fromthispredictionwouldbe particularlyinteresting, asit wouldindicate apossiblecontributionofnew,unknown particles to the loop diagrams describing B0

s mixing. The theoretical pre-dictionforthedecaywidthdifference

s betweenthelight and

_{E-mailaddress:[email protected].}

heavyB0_s masseigenstatesBLandBH,assumingnonewphysicsin

B0_s–B0_s mixing,is

s

=

L

−

H

=

0.087

±

0.021 ps−1[4].

Theweak phase

φ

s was firstmeasured bytheTevatron

exper-iments [5–8], and then at the LHC by the LHCb and ATLAS ex-periments[9–13],usingB0

s

→

J/ψ φ(1020),B0s

→

J/ψf0

(980),

and

B0

s

→

J/ψ

π

+

π

−decaysto + −h+h−,where denotesamuonin

thepresentanalysisandhstandsforakaonorapion.Finalstates thatdonothaveasingleCPeigenvaluerequireanangularanalysis to disentangle the CP-odd and CP-even components. The time-dependent angular analysis can be performed by measuring the decayanglesofthefinal-stateparticles + −h+h−andtheproper decay time of the B0s multiplied by the speed of light [14], re-ferredtoasctinwhatfollows.InthisLetter,theB0_s

→

J/ψ φ(1020) decaytothefinalstate

μ

+

μ

−K+K−isanalysed,andpossible ad-ditional contributions to the result from the nonresonant decay B0_s

→

J/ψK+K− aretakenintoaccountbyincludingatermforan additionalamplitude(S-wave)inthefit.

In this measurement the transversity basis is used [14]. The three angles

=

(θ

T

,

ψ

T

,

ϕ

T

)

of the transversity basis are

illus-tratedinFig. 1.Theangles

θ

Tand

ϕ

T arethepolarandazimuthal

angles,respectively,ofthe

μ

+intherestframeoftheJ/ψ where thexaxisisdefinedbythedirectionofthe

φ (1020)

mesoninthe J/ψrestframe,andthex–yplaneisdefinedbythedecayplaneof the

φ (1020)

→

K+K−.Thehelicityangle

ψ

TistheangleoftheK+

in the

φ (1020)

restframe with respectto the negative J/ψ mo-mentumdirection.

http://dx.doi.org/10.1016/j.physletb.2016.03.046

[image:2.612.34.553.91.218.2]

Table 1

Angular and time-dependent terms of the signal model.

i gi(θT, ψT,ϕT) Ni ai bi ci di

1 2 cos2

ψT(1−sin2θTcos2ϕT) |A0(0)|2 1 D C −S

2 sin2ψT(1−sin2θTsin2ϕT) |A(0)|2 1 D C −S

3 sin2_ψ

Tsin2θT |A⊥(0)|2 _{1 −D C S}

4 −sin2ψTsin 2θTsinϕT |A(0)||A⊥(0)| Csin(δ⊥−δ) Scos(δ⊥−δ) sin(δ⊥−δ) Dcos(δ⊥−δ)

5 _√1

2sin 2ψTsin 2

θTsin 2ϕT |A0(0)||A(0)| cos(δ−δ0) Dcos(δ−δ0) Ccos(δ−δ0) −Scos(δ−δ0)

6 _√1

2sin 2ψTsin 2θTsinϕT |A0(0)||A⊥(0)| Csin(δ⊥−δ0) Scos(δ⊥−δ0) sin(δ⊥−δ0) Dcos(δ⊥−δ0)

7 23(1−sin 2

θTcos2ϕT) |AS(0)|2 1 −D C S

8 1

3 √

6 sinψTsin2θTsin 2ϕT |AS(0)||A(0)| Ccos(δ−δS) Ssin(δ−δS) cos(δ−δS) Dsin(δ−δS)

9 1

3 √

6 sinψTsin 2θTcosϕT |AS(0)||A⊥(0)| sin(δ⊥−δS) −Dsin(δ⊥−δS) Csin(δ⊥−δS) Ssin(δ⊥−δS)

10 43 √

3 cosψT(1−sin2θTcos2ϕT) |AS(0)||A0(0)| Ccos(δ0−δS) Ssin(δ0−δS) cos(δ0−δS) Dsin(δ0−δS)

Fig. 1.Definition of the three angles θT, ψT, and ϕTdescribing the decay topology

of B0

s→J/ψ φ(1020). See text for details.

ThedifferentialdecayrateofB0_s

→

J/ψ φ(1020) isrepresented usingthefunction f

(,

ct

,

α

)

asinRef.[15]:

d4

B0_s

d

d

(

ct

)

=

f

(,

ct

,

α

)

∝

10

i=1

Oi

(

ct

,

α

)

gi

(),

(1)

where Oi aretime-dependent functions, gi areangularfunctions, and

α

isasetofphysicsparameters.

Thefunctions Oi(ct

,

α

)

are:

Oi

(

ct

,

α

)

=

Nie−ct/cτ

aicosh

st

2

+

bisinh

st

2

+

cicos

(

mst

)

+

disin

(

mst

)

,

where

msisthemassdifferencebetweentheheavyandlightB0s masseigenstates,c

τ

isdefinedastheproductofthelifetimeand thespeedoflight,thefunction gi()andthetermsNi,ai,bi,ci, anddiaregiveninTable 1.

ThetermsC,S,andD aredefinedas:

C

=

1

− |

λ

|

2

1

+ |

λ

|

2

,

S

= −

2

|

λ

|

sin

φ

s

1

+ |

λ

|

2

,

D

= −

2

|

λ

|

cos

φ

s 1

+ |

λ

|

2

,

using the same sign convention as the LHCb experiment [10]. Equation(1)representsthemodelforB0

s.ThemodelforB0s is

ob-tainedbychangingthesignoftheciandditerms.Theparameters

|

A_⊥

|

2_,

_|

_A

0

|

2,and

|

A

|

2arethemagnitudessquaredofthe

perpen-dicular,longitudinal,andparallel P-waveamplitudes,respectively;

|

AS

|

2 is the magnitude squared of the S-wave amplitude repre-sentingthefractionofnonresonantdecayB0

s

→

J/ψK+K−;the

pa-rameters

δ

_⊥,

δ

0,

δ

,and

δS

aretheircorrespondingstrongphases. Thecomplexparameters

λ

f aredefinedas

λ

f

=

(

q

/

p

)(

Af

/

Af

),

wheretheamplitudesAf

(

Af

)

describethedecayofaB0s (B0s)

me-sontoafinalstate f,andtheparameters pandqrelatethemass andflavoureigenstatesasBH

=

pB0s

−

qBs0 andBL

=

pB0s

+

qB0s [16].

Assumingpolarisation-independentCP-violationeffects,

λ

f canbe

simplifiedas

λ

f

=

η

f

λ,

where

η

f istheCPeigenvalue.Theamount ofCPviolationinmixingisassumedtobenegligible[17].Thus,no

|

q

/

p

|

termsareusedinEq.(1)whengoingfromtheB0

s modelto theB0_s model.SincedirectCPviolationisexpectedtobesmall the-oretically[3]andismeasuredtobesmall[9],

|

λ

|

issetto1.0.

2. TheCMSdetector

ThecentralfeatureoftheCMSapparatusisa13 m long super-conductingsolenoidof6 m internaldiameter,providingamagnetic field of3.8 T. Withinthe solenoidvolumeare a siliconpixeland strip tracker,a lead tungstatecrystalelectromagneticcalorimeter, andabrassandscintillatorhadroncalorimeter,eachcomposedof a barrel and two endcap sections. Muons are measured in gas-ionisationdetectorsembeddedinthesteelflux-returnyokeoutside thesolenoid.Extensiveforwardcalorimetrycomplementsthe cov-erageprovidedbythebarrelandendcapdetectors.

The main subdetectors used for the present analysis are the silicon tracker and the muon detection system. The sili-contrackermeasures chargedparticles withinthe pseudorapidity range

|

η

|

<

2.5.Itconsistsof66million100

×

150μm2_silicon

pix-elsandmorethan9millionsiliconstrips.Fornonisolatedparticles oftransversemomentum1

<

pT

<

10GeV and

|

η

|

<

1.4,thetrack

resolutionsaretypically1.5%in pT and25–90(45–150)μminthe

transverse(longitudinal)impactparameter[18].

Muons are measured in the pseudorapidity range

|

η

|

<

2.4, withdetectionplanesmadeusing threetechnologies:drift tubes, cathode strip chambers, and resistive plate chambers. The rel-ative pT resolution for low transverse momentum muons with pT

<

10GeV isbetween0.8%and3.0%dependingon

|

η

|

[19].

Thefirstlevel(L1)oftheCMStriggersystem,composedof cus-tom hardware processors,uses informationfromthecalorimeters andmuondetectorstoselectthemostinterestingeventsinafixed timeintervaloflessthan4μs.Thehigh-leveltrigger(HLT) proces-sor farm furtherreduces theevent ratefromaround 100 kHz to around 400 Hz,beforedatastorage.At theHLTstagethereis full accesstoall theeventinformation,includingtracking,and there-foreselectionssimilartothoseappliedofflinecanbeused.

AmoredetaileddescriptionoftheCMSdetector,togetherwith a definitionofthecoordinatesystemusedandtherelevant kine-maticvariables,canbefoundinRef.[20].

3. Eventselectionandsimulatedsamples

A trigger optimised for the detection of B hadrons decaying to J/ψ is used to collect the data sample. The L1 trigger used in this analysis requires two muons, each with pT greater than

3 GeV and

|

η

|

<

2.1.The HLTrequires aJ/ψ candidatedisplaced from the luminous region. Each muon pT is required to be at

greaterthan 6.9 GeV.The J/ψ candidates are reconstructedfrom themuon pairsselectedbythetriggerintheinvariantmass win-dow2.9–3.3 GeV. The three-dimensional(3D) distanceof closest approachofthetwomuonstoeachotherisrequiredtobesmaller than 0.5 cm. The two muon trajectoriesare fittedto a common decayvertex.The transversedecaylength significance Lxy/

σ

Lxy is

requiredtobe greaterthan 3,whereLxy isthe distancebetween thecentreoftheluminousregionandthesecondaryvertexinthe transverseplane, and

σ

Lxy isthe Lxy uncertainty.The

secondary-vertexfitprobability,calculatedusing the

χ

2 _{andthenumberof}

degreesof freedom of the vertex fit, must be greater than 10%. Theangle

ρ

betweenthedimuontransverse momentumandthe Lxydirectionisrequiredtosatisfycos

ρ

>

0.9.

Offline selection criteria are applied to the sample. The indi-vidual muon candidates are required to lie within a kinematic acceptance region of pT

>

4 GeV and

|

η

|

<

2.1. Two oppositely

chargedmuoncandidatesarepairedandrequiredtooriginatefrom acommonvertex.Dimuon candidateswithinvariantmass within 150 MeV of the world-average J/ψ mass [21] are selected. Can-didate

φ (1020)

mesonsarereconstructedfrompairsofoppositely chargedtracks withpT

>

0.7GeV,afterremovingthe muon can-didatetracksforming the J/ψ.Eachselected trackis assumedto beakaon,andtheinvariantmassofatrackpairisrequiredtobe within10 MeV oftheworld-average

φ (1020)

mass[21].

TheB0s candidatesare formed bycombining J/ψ and

φ (1020)

candidates.A kinematic fit ofthe two muon andtwo kaon can-didatesisperformed,withacommonvertex,andthedimuon in-variantmass is constrained to the nominal J/ψ mass [21]. A B0_s candidateisretainediftheJ/ψ φ(1020)pairhasaninvariantmass between5.20 and 5.65 GeV and the

χ

2 _{vertex fit probability is}

greaterthan2%.

Multiple pp collisions can occur in the same beam crossing (pileup).Theaveragenumberofprimaryverticesinaneventis ap-proximately16,andeachselectedeventisrequiredtohaveatleast one reconstructed primary vertex. If there are multiple vertices, theonethatminimisestheanglebetweentheflightdirectionand themomentumoftheB0

s isselected.Theselectedprimary vertex isusedtomeasurect.Thequantityctiscalculatedfromthe

trans-versedecaylengthvector oftheB0s, L

B0 s

xy,asct

=

mB

0 s

PDGL B0

s xy

·

pT

/

p2T,

wheremB0s

PDG isthe world-average B0s mass [21] and pT isthe B0s transversemomentumvector.Thedecaylengthiscalculatedinthe transverseplanetominimiseeffectsduetopileup.

Simulatedeventsareproduced usingthepythiav6.424Monte Carloeventgenerator[22].TheBhadrondecaysaremodelledwith theevtgensimulation package[23].FortheB0_s signalgeneration, theevtpvvcplh_{moduleisused,whichsimulatesthedoublevector} decaytakinginto accountneutralmesonmixingandCP-violating time-dependent asymmetries. Final-state radiation is included in evtgen _throughthe photos _{package[24,25].The eventsare then} passed through a detailed Geant4-based simulation [26] of the CMSdetector.Thepredicteddistributionsfromsimulationofmany kinematic and geometric variables are compared to those from data and found to be in agreement. The simulated samples are used to determine the signal reconstruction efficiencies, and to studythebackgroundcomponentsintheB0_s signalmasswindow.

The main backgroundfor the B0_s

→

J/ψ φ(1020) decays origi-natesfromnonprompt J/ψ mesonsfromthe decayofB hadrons, suchasB0_,B±_,

b,andBc.SincetheBccrosssectionissmall[21]

comparedtothat ofthe B0_s [21],the Bc decays canbe neglected.

Thecontributionofthe

b

→

J/ψX channelstotheselectedevents

isalsofoundtobesmall,anditsmassdistributionintheselected massrangeisobservedtobeflat.Theeffectofbackgroundwitha similarsignalsignatureonthephysicsobservablesisstudiedusing simulatedevents, andfound to be negligible. The mass

distribu-Fig. 2.The J/ψK+K−invariant mass distribution of the B0

scandidates. The solid line

is a fit to the data (solid markers), the dashed line is the signal component and the dot-dashed line is the background component.

tioninthesignalregionisshowninFig. 2,andthedistributionof ctanditsuncertainty

σ

ct inFig. 3.

Efficiencycorrectionsowingtothedetectoracceptance,trigger selection, and selection criteria applied in the data analysis are taken into account in the modelling of the angular observables. The angular efficiency

()

is calculated using a fully simulated sample ofB0_s

→

J/ψ φ(1020)

→

μ

+

μ

−K+K− decays. Inthis sam-ple,the

sparameterissettozerotoavoidcorrelationsbetween

thedecay timeandthe angularvariables.The

()

is fittedtoa 3D function of

to properly account forthe correlation among theangularobservables.

Thetriggerincludesadecaylengthsignificancerequirementfor the J/ψ candidates.Accordingly, thevalue ofct is requiredtobe greaterthan200 μminordertoavoidalifetimebiascomingfrom theturn-oncurveofthetriggerefficiency.Theefficiencyhistogram ofct isthenfittedwithastraightlineplusasigmoidfunction.

4. Flavourtagging

The flavour of each B0

s candidate atproduction time is deter-minedwithanopposite-side(OS)flavourtaggingalgorithm.Since b quarks are produced as b¯b pairs, the flavour of the signal B0

s mesonatproductiontimecan beinferredfromtheflavour ofthe other B hadron in the event. The tagging algorithm used in this analysisrequiresanadditionalmuonorelectronintheevents con-taining a reconstructed B0

s

→

J/ψ φ(1020) decay. The additional

lepton is assumed to originate froma semileptonic decay ofthe OSB hadron,b

→

ν

X decay, with

=

e,

μ

.Forallthe eventsin whichanOStagleptonisfound thealgorithmprovidesatag de-cision

ξ

basedon thecharge ofthelepton:

ξ

= +

1 forsignalB0

s, and

ξ

= −

1 forsignalB0_s.

[image:3.612.334.540.69.261.2]

di-Fig. 3.The ct distribution (top) and its uncertainty σct (bottom) of the B0s

candi-dates. The solid line is a fit to the data (solid markers), the dashed line is the signal component and the dot-dashed line is the background component. For the ct dis-tribution the pull, defined as the difference between the observed events and the fit function applied to the sum of the signal and background, divided by the statis-tical uncertainty in the observed events, is displayed in the histogram in the lower panel.

lutionfactorD

=

(1

−

2

ω

).

Thevalueof

ω

isestimatedfromdata onaper-eventbasis,asdescribedbelow.

Thetaggingalgorithm isoptimised bymaximisingthe tagging power

P

tag

=

ε

tag

(1

−

2

ω

)

2,which representstheequivalent

effi-ciencyofa sample withperfecttagging (

ω

=

0).The term

ε

tag is

thetaggingefficiency,definedasthefractionofeventstowhicha tagdecisionisfoundbythetaggingalgorithm.

Opposite-sidemuonsandelectrons arereconstructed withthe particle-flow algorithm [27,28]. In each event, the muons (elec-trons) that are not part of the reconstructed B0

s

→

J/ψ φ(1020)

decay are required to be identified withloose identification cri-teria.Iftherearemultiplemuons(electrons)intheevent,theone withthehighest pT is chosenatthisstage. Thetag lepton

selec-tionsarethenoptimisedseparatelyformuonsandelectronsusing simulatedsignalsamplesofB0

s

→

J/ψ φ(1020)decays.Acut-based

opposite-side lepton selection is applied to reduce the number ofleptons not originatingfromB-hadron decays.To optimise the selection, severalvariables arestudied, anda setof five

discrim-inating variables (pT,

η

, dxyz,

R,

Isolation) is identified. A total

number of more than four million alternative cut configurations have been tested to determine the configuration that maximises the tagging power, independently for muons and electrons. The tag muon is thus required to have pT

>

2.2 GeV, the3D impact

parameterdxyzwithrespecttotheprimaryvertexassociatedwith the signal B0_s isrequired tobe smaller than 0.1 cm, andthe an-gular separation,

R

=

(φ)

2

₊

₍

_η

₎

2_{, betweenthemuon and}

thesignalB0_s isrequiredtobegreaterthan0.3,where

φ

and

η

are the azimuthal angle and pseudorapidity differences between the directions of the tag muon and the B0_s candidate. Electrons are requiredtohave pT

>

2.0GeV,dxyz

<

0.1 cm,and

R

>

0.2. Inaddition,amultivariatediscriminator(MVAe−π)tunedto

sepa-rategenuineelectronsreconstructedbytheparticle-flowalgorithm from pions and photons is applied to tag electrons by requiring thatthediscriminatorisgreaterthan0.2[28].

Amultilayerperceptronneuralnetwork(MLP-NN)oftheTMVA toolkit [29] is usedto further separate theright- and wrong-tag leptons. Training and testing is performed using approximately 24 000 and 20 400 simulated B0s

→

J/ψ φ(1020) events for the

muon andelectronMLP-NNs,respectively,andtwoindependently optimised setsofvariables.Halfofeach sampleis usedfor train-ing andtheother halffortesting.Theinput variablescommonto bothMLP-NNsare pT,

η

,anddxyz ofthetaglepton,andtwo vari-ables related toactivity ina cone around thelepton direction: a particle-flowrelativeisolationvariable[28]anda pT-weighted

av-erageofthechargesoftheparticlesinthecone.Specificvariables are further introducedin theMLP-NNs separately formuonsand electrons.Formuons,thepTrelativetotheaxisofthejet

contain-ingthemuonisused,whileforelectronstheMVAe₋π isexploited.

Themistagprobabilitiesareobtainedfromdatausingthe self-tagging channel B±

→

J/ψK±, where the charge of the recon-structedkaondeterminestheflavouroftheB±and,intheabsence ofmixing,oftheopposite-sideBhadronaswell.Themistag prob-abilitiesareparametrisedseparatelyformuonsandelectronswith analytic functions ofthe MLP-NN discriminatorsin orderto pro-vide a per-eventvalue ofthepredictedmistagprobability

ω

.The functional forms of the parametrisations are obtained from the simulated B0

s sample. The candidate B± mesons are required to pass a selectionassimilar aspossible tothat applied forthe re-construction of the signal B0s candidates. The same trigger and J/ψ reconstruction requirements as forthe B0

s signal sample are applied. A charged particle with pT

>

2 GeV, assumed to be a

kaon,iscombinedwiththedimuonpairinakinematicfit.An un-binned extended maximum-likelihoodfit to the invariant J/ψK± massisperformed,yieldingatotalof

(707

±

2)

×

103 reconstructed B±

→

J/ψK± events. The tagging efficiency evaluated with the B±

→

J/ψK± data sample is

(4.56

±

0.02)% and

(3.92

±

0.02)% formuonsandelectrons,respectively,wheretheuncertainties are statistical.

Themistagparametrisationcurvesevaluated withtheB± con-trolchannel for muonsandelectrons are showninFig. 4,where the parametrisations for the B± and B0_s simulated samples are shownforcomparison.

Most tagged events have only a single electron or muon tag. If both tags are available fora specific event (about 3.5% of the cases), thetag leptonwith thegreatestvalue of thedilution fac-torisretained,andthetagdecisionandtheestimatedmistagare takenfromthistaglepton.The overallleptontaggingefficiencyis

(8.31

±

0.03)%, asmeasured in data withthe B±

→

J/ψK± data sample.

To correctfor potential effects induced by thedependence of the tagging algorithm on the B0

s

→

J/ψ φ(1020) simulation, the

[image:4.612.47.267.73.472.2]

[image:5.612.68.272.67.470.2]

Fig. 4.The mistag probabilities ω, defined as the ratio of the number of wrongly

tagged events divided by the total number of tagged events, as a function of the MLP-NN discriminators for muons (top) and electrons (bottom). The data points (solid markers) are placed at the average weighted value of the events in each bin. The vertical bars show the statistical uncertainties and the horizontal bars the bin width. The solid line represents the parametrisation curve extracted from the background-subtracted B±_{data; the dashed and dot-dashed lines refer to the} parametrisations extracted from the simulated B0

sand B±samples, respectively.

data control channel. This is then fit to the function

ω

meas

₌

p0

+

p1

(

ω

−

ω

),

chosentolimitthecorrelationbetweenthe

func-tionparameters p0 and p1. Theparameter

ω

is fixedto a value

roughlycorrespondingtothemeanofthecalculatedmistag prob-ability,

ω

=

0.35. The resulting calibration parameters are p0

=

0.348

±

0.003 and p1

=

1.01

±

0.03, and their uncertainties are

propagatedasastatisticaluncertaintyintheOStagger.

Thesystematic uncertainties relatedto the calibration param-eters p0 and p1 are dominated by the dependenceof these

pa-rameters on the flavour of the signal-side B hadron. The uncer-taintiesareestimatedfromB± dataandsimulatedsamplesofB0

s andB± events.Systematicuncertaintiesoriginatingfrompossible variationsinthe CMSdata-takingconditions,thesignal B hadron kinematics,theanalytic formofthemistag parametrisation func-tions,andthemodelusedtofittheB±invariantmassdistribution aretestedandfoundtobenegligible.

The overall tagging power of the OS lepton tagger, mea-suredwith a sample of B±

→

J/ψK± events, is

P

tag

=

(1.307

±

0.031

(stat)

±

0.007

(syst))%,

correspondingtothecombinedmistag probability

ω

=

(30.17

±

0.24

(stat)

±

0.05

(syst))%.

5. Maximum-likelihoodfit

Anunbinnedmaximum-likelihoodfitto thedataisperformed by includingtheinformationon theB0

s invariant mass(mB0 s), the three decay angles () of the reconstructed B0_s candidates, the flavour tag decision (ξ), ct, and

σ

ct, obtained by summing in quadraturethedecaylengthuncertaintyandtheuncertaintyinthe transversemomentum. Thefit isappliedto thesample of70500 events,outofwhich5650 aretaggedevents,selectedinthemass range 5.24–5.49 GeV andct

=

200–3000μm. From this multidi-mensional fit,the physics parameters of interest

s,

φ

s, theB0s mean lifetime c

τ

,

|

A_⊥

|

2,

|

A0

|

2,

|

AS|2, and the strong phases

δ

,

δ

⊥,and

δS

⊥ are determined, where

δS

⊥ is definedas the differ-ence

δS

−

δ

_⊥.The P-waveamplitudes arenormalised to unityby constraining

|

A

|

2 to1

− |

A_⊥

|

2

− |

A0

|

2.Thefitmodelisvalidated

with simulated pseudo-experimentsand with simulated samples withdifferentparametersets.

Thelikelihoodfunctioniscomposedofprobabilitydensity func-tions(pdf)describingthesignalandbackgroundcomponents.The likelihood fit algorithm is implemented using the RooFit pack-age from the ROOT framework [30]. The signal and background pdfs are formed as the product ofpdfs that modelthe invariant mass distribution andthe time-dependent decayrates of the re-constructed candidates. In addition, the signal pdf also includes the efficiencyfunction. The eventlikelihood function

L

is repre-sented as:

L

=

Ls

+

Lbkg

,

Ls

=

Ns

˜

f

(,

ct

,

α

)

⊗

G

(

ct

,

σ

ct

)

()

×

Ps

(

mB0

s

)

Ps

(

σ

ct

)

Ps

(ξ ),

Lbkg

=

NbkgPbkg

(

cos

θ

T

,

ϕ

T

)

Pbkg

(

cos

ψ

T

)

Pbkg

(

ct

)

×

Pbkg

(

mB0

s

)

Pbkg

(

σ

ct

)

Pbkg

(ξ ),

whereLsandLbkgarethepdfsthatdescribetheB0s

→

J/ψ φ(1020)

signal andbackgroundcontributions, respectively. Thenumber of signal(background)eventsisNs (Nbkg).Thepdf

˜

f

(,

ct

,

α

)

isthe

differentialdecayratefunction f

(,

ct

,

α

)

definedinEq.(1), mod-ified to include the flavour tagging information and the dilution term

(1

−

2

ω

),

whichare applied toeach ofthe ci anddi terms oftheequation.Inthe

˜

f expression,thevalueof

δ

0issettozero,

following ageneral convention. Thefunction

()

isthe angular efficiency and G

(

ct

,

σ

ct

)

isa Gaussian resolution function, which makesuseoftheevent-by-eventdecaytimeuncertainty

σ

ct,scaled byafactor

κ

.The

κ

factorisafunctionofct andisintroducedas a correctionto take careofresidual effectswhen thedecaytime uncertaintyisusedtomodelthect resolution.The function

κ

(

ct

)

is measured using simulated samples and, on average, its value equals1.0towithinafewpercent.Theaveragedecaytime uncer-taintyincludingthe

κ

(

ct

)

factorequals23.4 μm.Alltheparameters of the pdfs are left free to float in the final fit, unless explicitly statedotherwise. The value of

s is constrainedto be positive,

basedonrecentmeasurements[31]. Thesignalmasspdf Ps

(

m_B0

s

)

isthesumofthreeGaussian func-tions witha common mean; the two smaller widths, the mean, andthefractionofeachGaussian functionarefixed tothevalues obtainedinaone-dimensionalmassfit.Thebackgroundmass dis-tribution Pbkg

(

mB0

s

)

is described by an exponential function. The background decay time component Pbkg

(

ct

)

is described by the

sumoftwo exponentialfunctions. Theangularparts ofthe back-groundspdfs Pbkg

(cosθ

T

,

ϕ

T

)

and Pbkg

(cos

ψ

T

)

aredescribed

[image:6.612.87.229.99.211.2]

Table 2

Results of the fit to the data. Uncertainties are statistical only.

Parameter Fit result φs[rad] −0.075±0.097

s[ps−1] 0.095±0.013 |A0|2 0.510±0.005 |AS|2 0.012+₋00..009007 |A⊥|2 0.243±0.008 δ[rad] 3.48+0.07

−0.09

δS⊥[rad] 0.37+₋00..2812

δ⊥[rad] 2.98±0.36

cτ[μm] 447.2±2.9

andsinusoidalfunctionsfor

ϕ

T.Forthe cosθT and

ϕ

T variablesa

two-dimensional pdf isused to take intoaccount the correlation amongthevariables.

Thesignal decaytime uncertaintypdf Ps

(

σ

ct

)

isa sumoftwo Gammafunctions,withalltheparametersfixed tothevalues ob-tained by fitting a sample of background-subtracted events. The backgrounddecaytimeuncertaintypdf Pbkg

(

σ

ct

)

isrepresentedby aGammafunction.Alltheparameters arefixed tothevalues ob-tainedby fitting the B0

s invariant masssideband regions, defined bythemassrangesm_B0

s

=

5.24–5.28GeV and 5.45–5.49 GeV.The functions Ps

(ξ )

and Pbkg

(ξ )

are the tag decision

ξ

pdfs, which

havebeenobtainedfromthedata.

6. Resultsandsystematicuncertainties

The results of the fit are given in Table 2, where the quoted uncertainties are statistical only. The corresponding correlation matrix forthe statistical uncertainties in the physics fit

parame-ters is showninTable 3. Sincethe likelihood profiles of

δ

,

δS

⊥, and

|

AS

|

2 are not parabolic, the statistical uncertainties quoted for these parameters are found from the increase in

−

log

L

by 0.5. In the fit, the value of

ms is allowed to vary following a

Gaussian distribution with mean and standard deviation set to

(17.69

±

0.08)

×

1012_h

_¯

_/s

_{[32].Asacross-check,the}

_m

s valueis

alsoleftfreetofloatanditsbestfitvalueisfoundtobein statis-ticalagreementwiththe setvalue.The variousdatadistributions and the fit projections are shown in Figs. 2, 3, and 5. The drop inthecos

θ

T distributionattherangelimitsisidentified asbeing

causedby close-by,high-angle kaontracks.Thecentral valueand the68%,90%,and95%confidencelevel(CL)likelihoodcontoursof thefitinthe

s–φsplaneareshowninFig. 6.

Severalsourcesofsystematicuncertaintiesintheprimary mea-sured quantities are investigated by testing the various assump-tions made in the fit model and those associated with the fit procedure.

The systematic uncertaintyassociated withthe assumption of aconstantefficiencyasafunctionofctisevaluatedbyfittingthe datawithanalternativect efficiencyparametrisation,whichtakes into account a small contribution of the decay time significance requirement at small ct and first-order polynomial variations at highct.Thedifferencesfoundinthefitresultswithrespecttothe nominalfitareusedassystematicuncertainties.

The uncertainties associatedwith the variables cos

θ

T

,

ϕ

T,and

cos

ψ

T ofthe3D angularefficiencyfunctionarepropagatedtothe

fit results by varying the corresponding parameters within their statisticaluncertainties,accountingforthecorrelationsamongthe parameters. The maximum variation of the parameters extracted fromthefitistakenasthesystematicuncertainty.Thesystematic uncertaintyowingtoasmalldiscrepancyinthekaonpT spectrum

[image:6.612.37.552.447.722.2]

betweendataandsimulationisevaluatedbyweightingtheevents tomakethesimulatedkaonpTspectrummatchthatindata.

Table 3

Correlation matrix for the statistical uncertainties in the physics fit parameters.

|A0|2 |AS|2 |A⊥|2 δ δS⊥ δ⊥ cτ s φs

|A0|2 +1.00 +0.19 −0.64 −0.08 −0.18 −0.02 +0.38 +0.70 +0.11

|AS|2 – +1.00 −0.02 −0.32 −0.79 −0.10 −0.16 +0.01 +0.03

|A⊥|2 – – +1.00 −0.27 +0.03 −0.06 −0.50 −0.77 −0.11

δ – – – +1.00 +0.26 +0.21 +0.11 +0.03 −0.02

δS⊥ – – – – +1.00 +0.06 +0.11 −0.04 −0.06

δ⊥ – – – – – +1.00 +0.03 +0.01 +0.01

cτ – – – – – – +1.00 +0.55 +0.10

s – – – – – – – +1.00 +0.10

φs – – – – – – – – +1.00

Fig. 5.The angular distributions (cosθT, cosψT, ϕT) of the B0s candidates from data (solid markers). The solid line is the result of the fit, the dashed line is the signal

[image:7.612.64.271.69.275.2]

Fig. 6.The CMS measured central value and the 68%, 90%, and 95% CL contours in

the sversus φsplane, together with the SM prediction[3,4]. Uncertainties are

statistical only.

Theuncertaintyinthectresolutionassociatedwiththe

κ

factor ispropagatedtotheresults.Asetoftestsamplesisproducedwith the

κ

(

ct

)

factor varying within their uncertainty, assumed to be Gaussian.Onestandarddeviationofthedistributiondescribingthe differencebetweenthectresolutionwiththenominalfitandwith a varying

κ

(

ct

)

is takenas the systematicuncertainty. Since the

κ

(

ct

)

factorisobtainedfromsimulation,theassociatedsystematic uncertaintyis assessed by using a sample of prompt J/ψ decays obtainedwithanunbiasedtriggerandcomparingthemtosimilarly processed simulateddata. In this way the decay time resolution forct

≈

0 isobtained.The

κ

(

ct

)

factorisvariedwithin thevalues observed in data and simulation. The resulting variations of the physicsparametersaretakenassystematicuncertainties.

Although the likelihood function makes use of a per-event mistagparameter,itdoesnot containapdf modelforthemistag distribution. The associated systematic uncertainty is estimated bygeneratingsimulatedpseudo-experimentswithdifferentmistag distributionsforsignalandbackgroundandfittingthemwiththe nominalfit.

The dominant tagging systematic uncertainty originates from theassumption that thesignal andcalibrationchannels havethe sametaggingperformance.Itisevaluatedusingacalibrationcurve, obtainedfromsimulatedsamples,thatdescribesthemistag prob-abilityof B0_s asfunction of the mistag probability of B±. The fit

tothe dataisrepeated, re-calibratingthemistagprobability with the B0_s–B± calibration curve, andthe differencesfound in the fit resultswithrespecttothenominalfitareusedasthesystematic uncertainties.

Possiblebiasesintrinsictothefitmodelarealsotakeninto ac-count. The nominalmodel function is testedby using simulated pseudo-experiments, andtheaverage ofthepulls(defined asthe differencebetweentheresultoffittothepseudo-experiment sam-pleandthenominalvalue)isusedasasystematicuncertaintyifit exceedsonestandarddeviationstatisticaluncertainty.

Thevarioushypothesesthathavebeenassumedwhenbuilding thelikelihoodfunctionaretestedbygeneratingsimulated pseudo-experiments with different hypotheses and fitting the samples withthenominallikelihoodfunction.Theobtainedpullhistograms ofthephysicsvariablesarefittedwithGaussianfunctions,andthe averageofthepullisusedasasystematicuncertaintyifthe differ-encewithrespect to the averageexceeds one standard deviation statisticaluncertainty.Concerningthe modellingoftheJ/ψK+K− invariant mass distribution, the background model ischanged to a Chebyshev function from the nominal exponential pdf. The ct backgroundpdfis changedtothesumofthreeexponential func-tions insteadofthetwo exponentialfunctionsofthe nominalfit. Theangularbackgroundpdfisgeneratedbyusingthebackground simulationangularshapesinsteadofthefitones.Theeffectofnot includingthe angularresolution isalso tested, usingtheresidual distributions obtained from simulations. The RMS of the angular resolutions were found to be 5.9, 6.3, and 10 mrad, for cos

θT

, cos

ψT

,and

ϕ

T respectively.Thecontributiontothesystematic un-certaintyfromthebackgroundtaggingasymmetryisnegligible.

The hypothesis that

|λ|

=

1 is tested by leaving that param-eter free in the fit. The obtained value of

|

λ

|

is consistent with 1.0within onestandarddeviation.Thedifferencesfoundinthefit resultswithrespecttothenominalfitareusedassystematic un-certainties.

Thealignment systematicuncertaintyaffectsthevertex recon-structionandthereforethedecaytimes.Thateffectisestimatedto be1.5 μm fromstudiesofknownBhadronlifetimes[33].The sys-tematic effectowing to the very small numberof B0

s originating fromB+_c

→

B0

s

π

+feed-down,whichwouldbereconstructedwith largevaluesofct,hasbeenfoundtobenegligible.

The measured values for the weak phase

φ

s and the decay

widthdifference

s are:

φ

s

= −

0

.

075

±

0

.

097

(

stat

)

±

0

.

031

(

syst

)

rad

,

s

=

0

.

095

±

0

.

013

(

stat

)

±

0

.

007

(

syst

)

ps−1

.

ThesystematicuncertaintiesaresummarisedinTable 4.The uncer-taintiesinthe

φ

sand

s resultsaredominatedbythestatistical

uncertainties.

Table 4

Summary of the uncertainties in the measurements of the various B0

s parameters. If no value is reported, then the systematic uncertainty is negligible with respect to the

statistical and other systematic uncertainties. The total systematic uncertainty is the quadratic sum of the listed systematic uncertainties.

Source of uncertainty φs[rad] s[ps−1] |A0|2 |AS|2 |A⊥|2 δ[rad] δS⊥[rad] δ⊥[rad] cτ[μm]

ctefficiency 0.002 0.0057 0.0015 – 0.0023 – – – 1.0

Angular efficiency 0.016 0.0021 0.0060 0.008 0.0104 0.674 0.14 0.66 0.8 KaonpTweighting 0.014 0.0015 0.0094 0.020 0.0041 0.085 0.11 0.02 1.1

ctresolution 0.006 0.0021 0.0009 – 0.0008 0.004 – 0.02 2.9

Mistag distribution modelling 0.004 0.0003 0.0006 – – 0.008 0.01 – 0.1

Flavour tagging 0.003 0.0003 – – – 0.006 0.02 – –

Model bias 0.015 0.0012 0.0008 – – 0.025 0.03 – 0.4

pdf modelling assumptions 0.006 0.0021 0.0016 0.002 0.0021 0.010 0.03 0.04 0.2

|λ|as a free parameter 0.015 0.0003 0.0001 0.005 0.0001 0.002 0.01 0.03 –

Tracker alignment – – – – – – – – 1.5

[image:7.612.40.565.618.747.2]

7. Summary

Using pp collision data collected by the CMS experiment at a centre-of-mass energy of 8 TeV and corresponding to an inte-grated luminosity of 19.7 fb−1, 49 200 B0_s

→

J/ψ φ(1020) signal candidateswere usedtomeasurethe weakphase

φ

s andthe

de-cay width difference

s. The analysiswas performed by using

opposite-side lepton tagging of the B0_s flavour atthe production time.Bothmuonandelectrontagswereused.

Themeasured valuesfortheweak phaseandthedecaywidth difference between the B0

s mass eigenstates are

φ

s

= −

0.075

±

0.097

(stat)

±

0.031

(syst)

rad and

s

=

0.095

±

0.013

(stat)

±

0.007

(syst)

ps−1_{, respectively. The measured values are}

consis-tent with those obtained by the LHCb Collaboration using B0

s

→

J/ψK+K− decays[34].

Ourmeasured valueof

φ

s agrees withtheSM prediction.Our

resultconfirms

s to be nonzero, witha value consistent with

theoreticalpredictions.Theuncertaintiesinour

φ

s and

s

mea-surements are dominated by statisticaluncertainties. Ourresults provideindependentreferencemeasurements of

φ

s and

s,and

contribute to improving the overall precision of these quantities andtherebyprobingtheSMfurther.Sinceourmeasurement preci-sionisstill limitedbystatisticaluncertainty,substantial improve-mentisexpectedfromLHC

√

s

=

13TeV high-luminosity running thatwillbeavailableoverthenextfewyears.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technicalandadministrativestaffs atCERN andatother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentresand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythe computinginfrastructureessential to ouranalyses. Finally, we acknowledge the enduring support for the construc-tionandoperation oftheLHCandthe CMSdetectorprovidedby thefollowingfundingagencies:BMWFWandFWF(Austria);FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES(Bulgaria);CERN;CAS,MOST,andNSFC(China);COLCIENCIAS (Colombia);MSESandCSF(Croatia);RPF(Cyprus);MoER,ERCIUT andERDF(Estonia);Academy ofFinland,MEC,andHIP(Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM(Malaysia); CINVESTAV, CONACYT,SEP,andUASLP-FAI(Mexico);MBIE(NewZealand);PAEC (Pakistan);MSHEandNSC(Poland);FCT(Portugal);JINR(Dubna); MON,RosAtom,RASandRFBR(Russia);MESTD(Serbia);SEIDIand CPAN(Spain);SwissFundingAgencies(Switzerland);MST(Taipei); ThEPCenter,IPST,STARandNSTDA(Thailand);TUBITAKandTAEK (Turkey);NASUandSFFR(Ukraine); STFC(United Kingdom);DOE andNSF(USA).

Individuals have received support from the Marie-Curie pro-grammeandthe European ResearchCouncil andEPLANET (Euro-peanUnion);theLeventisFoundation;theAlfredP.Sloan Founda-tion; the Alexander von Humboldt Foundation; the Belgian Fed-eral Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technolo-gie (IWT-Belgium); the Ministry of Education, Youth and Sports (MEYS)oftheCzechRepublic;theCouncilofScienceandIndustrial Research,India;theHOMING PLUSprogrammeoftheFoundation forPolishScience,cofinancedfromEuropean Union,Regional De-velopment Fund;the Compagnia di SanPaolo (Torino); the

Con-sorzio per la Fisica (Trieste); MIUR project 20108T4XTM (Italy); theThalisandAristeiaprogrammescofinancedbyEU-ESFandthe Greek NSRF; the National Priorities Research Program by Qatar NationalResearch Fund;theRachadapisekSompot Fund for Post-doctoral Fellowship,Chulalongkorn University (Thailand);andthe WelchFoundation.

References

[1] B. Bhattacharya, A. Datta, D. London, Reducing penguin pollution, Int. J. Mod. Phys. A 28 (2013) 1350063, http://dx.doi.org/10.1142/S0217751X13500632. [2] S. Faller, R. Fleischer, T. Mannel, Precision physics with B0

s→J/ψφ at the

LHC: the quest for new physics, Phys. Rev. D 79 (2009) 014005, http://dx.doi. org/10.1103/PhysRevD.79.014005, arXiv:0810.4248.

[3] J. Charles, O. Deschamps, S. Descotes-Genon, R. Itoh, H. Lacker, A. Menzel, S. Monteil, V. Niess, J. Ocariz, J. Orloff, S. T’Jampens, V. Tisserand, K. Tra-belsi, Predictions of selected flavour observables within the standard model, Phys. Rev. D 84 (2011) 033005, http://dx.doi.org/10.1103/PhysRevD.84.033005,

arXiv:1106.4041.

[4]A.Lenz,U.Nierste,Numericalupdatesoflifetimesandmixingparametersof Bmesons,in:T.Gershon(Ed.),Proceedingsofthe6thInternationalWorkshop ontheCKMUnitarityTriangle,UniversityofWarwick,UnitedKingdom,2010, arXiv:1102.4274.

[5] T. Aaltonen, et al., CDF Collaboration, First flavor-tagged determination of bounds on mixing-induced CP violation in B0

s→J/ψφdecays, Phys. Rev. Lett.

100 (2008) 161802, http://dx.doi.org/10.1103/PhysRevLett.100.161802, arXiv: 0712.2397.

[6] V.M. Abazov, et al., D0 Collaboration, Measurement of B0

s mixing parameters

from the flavor-tagged decay B0

s→J/ψφ, Phys. Rev. Lett. 101 (2008) 241801, http://dx.doi.org/10.1103/PhysRevLett.101.241801, arXiv:0802.2255.

[7] T. Aaltonen, et al., CDF Collaboration, Measurement of the CP-violating phase βJs/ψ φin B0s→J/ψφ decays with the CDF II detector, Phys. Rev. D 85 (2012)

072002, http://dx.doi.org/10.1103/PhysRevD.85.072002, arXiv:1112.1726.

[8] V.M. Abazov, et al., D0 Collaboration, Measurement of the CP-violating phase φJs/ψ φusing the flavor-tagged decay B0s→J/ψφin 8 fb−1of pp collisions, Phys.

Rev. D 85 (2012) 032006, http://dx.doi.org/10.1103/PhysRevD.85.032006, arXiv:

1109.3166.

[9] LHCb Collaboration, Measurement of the CP-violating phase φs in B0s →

J/ψπ+π− decays, Phys. Lett. B 736 (2014) 186, http://dx.doi.org/10.1016/ j.physletb.2014.06.079, arXiv:1405.4140.

[10] LHCb Collaboration, Measurement of CP violation and the B0

s meson

de-cay width difference with B0

s →J/ψK+K− and B0s →J/ψπ+π− decays,

Phys. Rev. D 87 (2013) 112010, http://dx.doi.org/10.1103/PhysRevD.87.112010,

arXiv:1304.2600.

[11] LHCb Collaboration, Measurement of the CP-violating phase φs in B0s →

J/ψπ+π− decays, Phys. Lett. B 713 (2012) 378, http://dx.doi.org/10.1016/ j.physletb.2012.06.032, arXiv:1204.5675.

[12] ATLAS Collaboration, Time-dependent angular analysis of the decay B0 s→

J/ψφ and extraction of s and the CP-violating weak phase φs by ATLAS,

J. High Energy Phys. 12 (2012) 072, http://dx.doi.org/10.1007/JHEP12(2012)072,

arXiv:1208.0572.

[13] ATLAS Collaboration, Flavor tagged time-dependent angular analysis of the B0

s→J/ψφdecay and extraction of δγsand the weak phase φsin ATLAS, Phys.

Rev. D 90 (2014) 052007, http://dx.doi.org/10.1103/PhysRevD.90.052007. [14] A.S. Dighe, I. Dunietz, R. Fleischer, Extracting CKM phases and B0

s− ¯Bsmixing

parameters from angular distributions of non-leptonic B decays, Eur. Phys. J. C 6 (1999) 647, http://dx.doi.org/10.1007/s100529800954, arXiv:hep-ph/9804253.

[15] A.S. Dighe, I. Dunietz, H.J. Lipkin, J.L. Rosner, Angular distributions and life-time differences in B0

s→J/ψφdecays, Phys. Lett. B 369 (1996) 144, http://dx. doi.org/10.1016/0370-2693(95)01523-X, arXiv:hep-ph/9511363.

[16]G.Branco,L.Lavoura,J.Silva,CPViolation,Int.Ser.Monogr.Phys.,vol. 103, ClarendonPress,Oxford,1999.

[17] LHCb Collaboration, Measurement of the flavour-specific CP-violating asymme-try asslin B0s decays, Phys. Lett. B 728 (2014) 607, http://dx.doi.org/10.1016/ j.physletb.2013.12.030, arXiv:1308.1048.

[18] CMS Collaboration, Description and performance of track and primary-vertex reconstruction with the CMS tracker, J. Instrum. 9 (2014) P10009,

http://dx.doi.org/10.1088/1748-0221/9/10/P10009, arXiv:1405.6569.

[19] CMS Collaboration, Performance of CMS muon reconstruction in pp collision events at √s=7 TeV, J. Instrum. 7 (2012) P10002, http://dx.doi.org/10.1088/ 1748-0221/7/10/P10002, arXiv:1206.4071.

[20] CMS Collaboration, The CMS experiment at the CERN LHC, J. Instrum. 3 (2008) S08004, http://dx.doi.org/10.1088/1748-0221/3/08/S08004.

[21] Particle Data Group, K.A. Olive, et al., Review of particle physics, Chin. Phys. C 38 (2014) 090001, http://dx.doi.org/10.1088/1674-1137/38/9/090001. [22] T. Sjöstrand, S. Mrenna, P.Z. Skands, PYTHIA 6.4 physics and manual, J. High

Energy Phys. 05 (2006) 026, http://dx.doi.org/10.1088/1126-6708/2006/05/026,

[23] D.J. Lange, The EvtGen particle decay simulation package, Nucl. Instrum. Meth-ods Phys. Res., Sect. A, Accel. Spectrom. Detect. Assoc. Equip. 462 (2001) 152,

http://dx.doi.org/10.1016/S0168-9002(01)00089-4.

[24] E. Barberio, B. van Eijk, Z. Was, PHOTOS – a universal Monte Carlo for QED ra-diative corrections in decays, Comput. Phys. Commun. 66 (1991) 115, http://dx. doi.org/10.1016/0010-4655(91)90012-A.

[25] E. Barberio, Z. W ˛as, PHOTOS – a universal Monte Carlo for QED radiative cor-rections: version 2.0, Comput. Phys. Commun. 79 (1994) 291, http://dx.doi.org/ 10.1016/0010-4655(94)90074-4.

[26] S. Agostinelli, et al., GEANT4 Collaboration, GEANT4—a simulation toolkit, Nucl. Instrum. Methods Phys. Res., Sect. A, Accel. Spectrom. Detect. Assoc. Equip. 506 (2003) 250, http://dx.doi.org/10.1016/S0168-9002(03)01368-8.

[27] CMS Collaboration, Particle–flow event reconstruction in CMS and performance for jets, taus, and Emiss

T , CMS Physics Analysis Summary CMS-PAS-PFT-09-001, http://cdsweb.cern.ch/record/1194487, 2009.

[28] CMS Collaboration, Commissioning of the particle-flow event reconstruction with the first LHC collisions recorded in the CMS detector, CMS Physics Anal-ysis Summary CMS-PAS-PFT-10-001, http://cdsweb.cern.ch/record/1247373,

2010.

[29] H. Voss, A. Höcker, J. Stelzer, F. Tegenfeldt, TMVA, the toolkit for multivari-ate data analysis with ROOT, in: XIth International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT), 2007, p. 40,

http://pos.sissa.it/archive/conferences/050/040/ACAT_040.pdf, arXiv:physics/ 0703039.

[30] I. Antcheva, et al., ROOT — A C++ framework for petabyte data storage, sta-tistical analysis and visualization, Comput. Phys. Commun. 180 (2009) 2499,

http://dx.doi.org/10.1016/j.cpc.2009.08.005.

[31] LHCb Collaboration, Determination of the sign of the decay width differ-ence in the B0

s system, Phys. Rev. Lett. 108 (2012) 241801, http://dx.doi.org/ 10.1103/PhysRevLett.108.241801, arXiv:1202.4717.

[32] Particle Data Group, J. Beringer, et al., Review of particle physics, Phys. Rev. D 86 (2012) 010001, http://dx.doi.org/10.1103/PhysRevD.86.010001.

[33] CMS √ Collaboration, Measurement of the 0b lifetime in pp collisions at s=7 TeV, J. High Energy Phys. 07 (2013) 163, http://dx.doi.org/10.1007/ JHEP07(2013)163.

[34] LHCb Collaboration, Precision measurement of CP violation in B0 s →

J/ψk+k−decays, Phys. Rev. Lett. 114 (2015) 041801, http://dx.doi.org/10.1103/ PhysRevLett.114.041801, arXiv:1411.3104.

CMSCollaboration

V. Khachatryan,

A.M. Sirunyan,

A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam,

E. Asilar,

T. Bergauer,

J. Brandstetter,

E. Brondolin,

M. Dragicevic,

J. Erö,

M. Flechl,

M. Friedl,

R. Frühwirth

1

,

V.M. Ghete,

C. Hartl,

N. Hörmann,

J. Hrubec,

M. Jeitler

1

,

V. Knünz,

A. König,

M. Krammer

1

,

I. Krätschmer,

D. Liko,

T. Matsushita,

I. Mikulec,

D. Rabady

2

,

B. Rahbaran,

H. Rohringer,

J. Schieck

1

,

R. Schöfbeck,

J. Strauss,

W. Treberer-Treberspurg,

W. Waltenberger,

C.-E. Wulz

1

InstitutfürHochenergiephysikderOeAW,Wien,Austria

V. Mossolov,

N. Shumeiko,

J. Suarez Gonzalez

NationalCentreforParticleandHighEnergyPhysics,Minsk,Belarus

S. Alderweireldt,

T. Cornelis,

E.A. De Wolf,

X. Janssen,

A. Knutsson,

J. Lauwers,

S. Luyckx,

S. Ochesanu,

R. Rougny,

M. Van De Klundert,

H. Van Haevermaet,

P. Van Mechelen,

N. Van Remortel,

A. Van Spilbeeck

UniversiteitAntwerpen,Antwerpen,Belgium

S. Abu Zeid,

F. Blekman,

J. D’Hondt,

N. Daci,

I. De Bruyn,

K. Deroover,

N. Heracleous,

J. Keaveney,

S. Lowette,

L. Moreels,

A. Olbrechts,

Q. Python,

D. Strom,

S. Tavernier,

W. Van Doninck,

P. Van Mulders,

G.P. Van Onsem,

I. Van Parijs

VrijeUniversiteitBrussel,Brussel,Belgium

P. Barria,

H. Brun,

C. Caillol,

B. Clerbaux,

G. De Lentdecker,

H. Delannoy,

G. Fasanella,

L. Favart,

A.P.R. Gay,

A. Grebenyuk,

G. Karapostoli,

T. Lenzi,

A. Léonard,

T. Maerschalk,

A. Marinov,

L. Perniè,

A. Randle-conde,

T. Reis,

T. Seva,

C. Vander Velde,

P. Vanlaer,

R. Yonamine,

F. Zenoni,

F. Zhang

3

UniversitéLibredeBruxelles,Bruxelles,Belgium

K. Beernaert,

L. Benucci,

A. Cimmino,

S. Crucy,

D. Dobur,

A. Fagot,

G. Garcia,

M. Gul,

J. Mccartin,

A.A. Ocampo Rios,

D. Poyraz,

D. Ryckbosch,

S. Salva,

M. Sigamani,

N. Strobbe,

M. Tytgat,

W. Van Driessche,

E. Yazgan,

N. Zaganidis

GhentUniversity,Ghent,Belgium

S. Basegmez,

C. Beluffi

4

,

O. Bondu,

S. Brochet,

G. Bruno,

R. Castello,

A. Caudron,

L. Ceard,

V. Lemaitre,

A. Mertens,

C. Nuttens,

L. Perrini,

A. Pin,

K. Piotrzkowski,

A. Popov

6

,

L. Quertenmont,

M. Selvaggi,

M. Vidal Marono

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

N. Beliy,

G.H. Hammad

UniversitédeMons,Mons,Belgium

W.L. Aldá Júnior,

G.A. Alves,

L. Brito,

M. Correa Martins Junior,

M. Hamer,

C. Hensel,

C. Mora Herrera,

A. Moraes,

M.E. Pol,

P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas,

W. Carvalho,

J. Chinellato

7

,

A. Custódio,

E.M. Da Costa,

D. De Jesus Damiao,

C. De Oliveira Martins,

S. Fonseca De Souza,

L.M. Huertas Guativa,

H. Malbouisson,

D. Matos Figueiredo,

L. Mundim,

H. Nogima,

W.L. Prado Da Silva,

A. Santoro,

A. Sznajder,

E.J. Tonelli Manganote

7

,

A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahuja

a

,

C.A. Bernardes

b

,

A. De Souza Santos

b

,

S. Dogra

a

,

T.R. Fernandez Perez Tomei

a

,

E.M. Gregores

b

,

P.G. Mercadante

b

,

C.S. Moon

a

,

8

,

S.F. Novaes

a

,

Sandra S. Padula

a

,

D. Romero Abad,

J.C. Ruiz Vargas

a_{UniversidadeEstadualPaulista,SãoPaulo,Brazil} b_{UniversidadeFederaldoABC,SãoPaulo,Brazil}

A. Aleksandrov,

R. Hadjiiska,

P. Iaydjiev,

M. Rodozov,

S. Stoykova,

G. Sultanov,

M. Vutova

InstituteforNuclearResearchandNuclearEnergy,Sofia,Bulgaria

A. Dimitrov,

I. Glushkov,

L. Litov,

B. Pavlov,

P. Petkov

UniversityofSofia,Sofia,Bulgaria

M. Ahmad,

J.G. Bian,

G.M. Chen,

H.S. Chen,

M. Chen,

T. Cheng,

R. Du,

C.H. Jiang,

R. Plestina

9

,

F. Romeo,

S.M. Shaheen,

J. Tao,

C. Wang,

Z. Wang,

H. Zhang

InstituteofHighEnergyPhysics,Beijing,China

C. Asawatangtrakuldee,

Y. Ban,

Q. Li,

S. Liu,

Y. Mao,

S.J. Qian,

D. Wang,

Z. Xu,

W. Zou

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

C. Avila,

A. Cabrera,

L.F. Chaparro Sierra,

C. Florez,

J.P. Gomez,

B. Gomez Moreno,

J.C. Sanabria

UniversidaddeLosAndes,Bogota,Colombia

N. Godinovic,

D. Lelas,

I. Puljak,

P.M. Ribeiro Cipriano

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,

M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,

K. Kadija,

J. Luetic,

S. Micanovic,

L. Sudic

InstituteRudjerBoskovic,Zagreb,Croatia

A. Attikis,

G. Mavromanolakis,

J. Mousa,

C. Nicolaou,

F. Ptochos,

P.A. Razis,

H. Rykaczewski

M. Bodlak,

M. Finger

10

,

M. Finger Jr.

10

CharlesUniversity,Prague,CzechRepublic

M. El Sawy

11

,

12

,

E. El-khateeb

13

,

T. Elkafrawy

13

,

A. Mohamed

14

,

A. Radi

12

,

13

,

E. Salama

12

,

13

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

B. Calpas,

M. Kadastik,

M. Murumaa,

M. Raidal,

A. Tiko,

C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,

J. Pekkanen,

M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Härkönen,

T. Jarvinen,

V. Karimäki,

R. Kinnunen,

T. Lampén,

K. Lassila-Perini,

S. Lehti,

T. Lindén,

P. Luukka,

T. Mäenpää,

T. Peltola,

E. Tuominen,

J. Tuominiemi,

E. Tuovinen,

L. Wendland

HelsinkiInstituteofPhysics,Helsinki,Finland

J. Talvitie,

T. Tuuva

LappeenrantaUniversityofTechnology,Lappeenranta,Finland

M. Besancon,

F. Couderc,

M. Dejardin,

D. Denegri,

B. Fabbro,

J.L. Faure,

C. Favaro,

F. Ferri,

S. Ganjour,

A. Givernaud,

P. Gras,

G. Hamel de Monchenault,

P. Jarry,

E. Locci,

M. Machet,

J. Malcles,

J. Rander,

A. Rosowsky,

M. Titov,

A. Zghiche

DSM/IRFU,CEA/Saclay,Gif-sur-Yvette,France

I. Antropov,

S. Baffioni,

F. Beaudette,

P. Busson,

L. Cadamuro,

E. Chapon,

C. Charlot,

T. Dahms,

O. Davignon,

N. Filipovic,

A. Florent,

R. Granier de Cassagnac,

S. Lisniak,

L. Mastrolorenzo,

P. Miné,

I.N. Naranjo,

M. Nguyen,

C. Ochando,

G. Ortona,

P. Paganini,

P. Pigard,

S. Regnard,

R. Salerno,

J.B. Sauvan,

Y. Sirois,

T. Strebler,

Y. Yilmaz,

A. Zabi

LaboratoireLeprince-Ringuet,EcolePolytechnique,IN2P3-CNRS,Palaiseau,France

J.-L. Agram

15

,

J. Andrea,

A. Aubin,

D. Bloch,

J.-M. Brom,

M. Buttignol,

E.C. Chabert,

N. Chanon,

C. Collard,

E. Conte

15

,

X. Coubez,

J.-C. Fontaine

15

,

D. Gelé,

U. Goerlach,

C. Goetzmann,

A.-C. Le Bihan,

J.A. Merlin

2

,

K. Skovpen,

P. Van Hove

InstitutPluridisciplinaireHubertCurien,UniversitédeStrasbourg,UniversitédeHauteAlsaceMulhouse,CNRS/IN2P3,Strasbourg,France

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

S. Beauceron,

C. Bernet,

G. Boudoul,

E. Bouvier,

C.A. Carrillo Montoya,

R. Chierici,

D. Contardo,

B. Courbon,

P. Depasse,

H. El Mamouni,

J. Fan,

J. Fay,

S. Gascon,

M. Gouzevitch,

B. Ille,

F. Lagarde,

I.B. Laktineh,

M. Lethuillier,

L. Mirabito,

A.L. Pequegnot,

S. Perries,

J.D. Ruiz Alvarez,

D. Sabes,

L. Sgandurra,

V. Sordini,

M. Vander Donckt,

P. Verdier,

S. Viret,

H. Xiao

UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS-IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France

T. Toriashvili

16

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze

10