Recent Results from Experiment D0

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Recent Results from Experiment D0

V. Šimák

1_{FZU ACR and FJFI CTU Prague, for D0 Experiment}

Abstract.Brief summary of resent experimental results from experiment D0 at TEVA-TRON in FNAL.

1 Introduction

After 28 years (1983 - 2011) of TEVATRON work in FNAL, particle physics reach high level of understanding of elementary interactions in center of mass energy up to 2 TeV. Two big particle detector, CDF and D0 could analyze all interactions detected with complex of subdetectors in full 4π cover and with magnetic spectrometry for all charged particles.

Briefs summary of some of results achieved at TEVATRON:

1985 - First observation of proton-antiproton collisions by CDF at 1.8 TeV (June 8). 1992 - D0 observes ﬁrst proton-antiproton collision with cms energy 1.8 TeV. 1995 - Experiment CDF ad D0 announce discovery of top quark (March 3th). 1996 - Observation of antihydrogen atoms.

1996 - Observation of exotic charm meson. 1998 - Discovery ofBcmeson.

1999 - Fixed target experiment KTeV observes direct CP violation in the decay of neutral Kaons. 2000 - The DONuT experiment reports ﬁrst evidence for the direct observation of theτneutrino. 2004 - Run II, which started in 2001, achieves a peak luminosity 1032_cm2_sec−1_.

2006 - Discovery of Bs matter-antimatter oscillations 3 trillion times per second. 2007 - Discovery of cascade b-baryon.

2009 - Discovery of single top quark production.

2010 - Tevatron achieves a peak luminosity 4x1032_cm2_sec−1 2011 - Tevatron produces ﬁnal pron-antiproton collisions (sept 30)

Experiments D0 and CDF have collected about 10 f b−1_{of data each.}

The result from both experiment enriched knowledge in particle physics and fulﬁlled some open questions in Standard Model.

The analysis of data will still continue for few next years. DOI: 10.1051/

C

Owned by the authors, published by EDP Sciences, 2014 /2014 007 0

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sl d

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sl d B Factory a

) 68% C.L. >120 (IP sl b A

) 68% C.L. <120 (IP sl b A

Combination Standard Model

Figure 1.Combination of D0 and B factory average forad slandassl.

Following pictures present resent results from experiment D0 divided according the subjects: B-physics, Electroweek B-physics, Quntum Chromodynamics, Top quark B-physics, Higgs boson and New Phenomena. Most of the results are obtained with statistics of events corresponding to 10.4f b−1_.

2 B-physics

Several results in spectroscopy of hadrons from is coming from study of physics of b quark, which could be directly identiﬁed in 60% of events. We present a measurement of the semileptonic mixing asymmetrya=(Γ( ¯A)−Γ(A))/(Γ( ¯A)+Γ(A)) forB0_mesons,_ad

sl. Using two independent decay channels:

B0_→_μ₊_D₊_X_,_D_→_K+_π−_π−_and_B0_→_μ₊_D∗₊_X_,_B0_→_μ₊_D∗₊_X_with_D∗_→_D¯0₊_π−_{, ¯}_D0_→

K+π− (and charge conjugate processes), we have determined the semileptonic mixing asymmetry for B0 _mesons,_ad

sl. We extract the charge asymmetries in these two channels as a function of the

visible proper decay length (VPDL) of the B0 meson, correct for detector-related asymmetries using data-driven methods, and account for dilution from charge-symmetric processes using Monte Carlo simulation. The ﬁnal measurement combines four signal VPDL regions for each channel, yielding:

ad_sl=0.68±0.45 (stat.)±0.14 (syst.)

Combination of measurements ofad_sl(D0 and existing world-average from B factories),as_sl, and the two impact-parameter-binned constraints from the same-charge dimuon asymmetryAb_sl. The bands represent the±1 standard deviation uncertainties on each measurement. The ellipses represent the 1, 2, 3, and 4 standard deviation twodimensional conﬁdence level regions of the combination [1] in Fig.2.

We have measure the time-integrated ﬂavor-speciﬁc semileptonic charge asymmetry in the decays of B0

s mesons that have undergone ﬂavor mixing, alss, using B

0

s( ¯B0s)→ D±s +μ++X decays, with

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Figure 2. Invariant mass distribution ofB0

s candidates withct >200μmfor events in the mass range 1.01 <

M(K+K−)<1.03GeV. A ﬁt to a sum of a GaussianB0

s→J/ψφsignal (dashed-dotted) a quadratic combinatorial

background (dotted), and the reﬂection of the decayB0_→_J/ψK∗_{(892) (dashed), is used to extract the}_B0

syield

(left). Proper decay length distributions forB0_→_J/K0_{candidates, with ﬁt results superimposed (right).}

A ﬁt to the diﬀerence between the time-integratedD−s andDs+mass distributions of theB0sand ¯B0s

candidates yields the ﬂavor-speciﬁc asymmetry

as

ls=−1.08±0.72(stat)±0.17(syst)

which is the most precise measurement and in agreement with the standard model prediction. We have investigated the decayB0

s →J/ψ→K+K−for invariant masses of theK+K−pair in the range

1.35<M(K+K−)<2GeVFig.2.

From the study of the invariant mass and spin of the K+K− system, we ﬁnd evidence for the two-body decay and measure the relative branching fraction of the decays to be [2]Rf2/φ = 0.22± 0.05 (stat)±0.04 (syst). We measure theΛ0_blifetime in the fully reconstructed decayΛ0_b→J/ψΛ0_[3] Fig. 2.

The lifetime of the topologically similar decay channelB0 _→ _J_/ψ_K0

S is also measured [4]. We

obtain τ(Λ0

b)=1.303±0.075(stat.)±0.035(syst.)ps

andτ(B0₎₌₁_.₅₀₈_±₀_.₀₂₅₍_stat_.₎_±₀_.₀₄₃₍_s_y_st_.₎_ps_.

Using these measurements, we determine the lifetime ratio of τ(Λ0

b)/τ(B0)=0.864±0.052(stat.)±0.033(syst.).

We present a measurement of the relative branching fraction, Rf0/φ, of B0s to J/ψf0(980), with

f0(980) → π+π−, to the processB0_s → J/ψφ, withφ → K+K− Fig. 2. TheJ/ψf0(980) ﬁnal state corresponds to a CP-odd eigenstate ofB0

s that could be of interest in future studies of CP violation.

With 8f b−1_{of data recorded with the D0 detector we ﬁnd}

Rf0/φ=0.275±0.041(stat)±0.061(syst).

Using data corresponding to an integrated luminosity of 1.3f b−1_{, we observe a narrow mass state} decaying intoυ(1S)+γ, where theυ(1S) meson is detected by its decay into a pair of oppositely charged muons, and the photon is identiﬁed through its conversion into an electron-positron pair. The signiﬁcance of this observation is 5.6 standard deviations. The mass of the state is centered at 10.551±0.014(stat.)±0.017(syst.)GeV/c2_{, which is consistent with that of the state recently observed} by the ATLAS Collaboration Fig.3 [5].

3 Electroweek Interactions

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Figure 3. Dimuon invariant mass spectrum for opposite-charge pairs passing the muon selection criteria. The solid curve is a ﬁt to the data assuming threeυresonances and a combinatorial background. The relative con-tributions from theυ(1S),υ(2S), andυ(3S) (left). The distribution ofMμμγ-Mμμ+mυ(1S)ﬁt with three signal

functions and the mixed event background (right).

We present a measurement of the W boson mass using data corresponding to 4.3f b−1_{of integrated} luminosity collected with the D0 detector during Run II at the Fermilab Tevatronpp¯collider. With a sample of 1,677,394 decayW → eorμcandidate events, we measureMW =80.367±0.026GeV.

This result is combined with an earlier D0 result determined using an independent Run II data sample, corresponding to 1f b−1_{of integrated luminosity, to yield}_M

W=80.375±0.023GeV[7].

We study the processespp¯ →WZ→ν, +−andpp¯ →ZZ → +−νν¯where=eorμ. Using 8.6 fb−1 _{of integrated luminosity. We measure the}_WZ _{production cross section to be 4}_.₅₀+0.63

−0.66 pb which is consistent with, but slightly above a prediction of the standard model. The ZZ cross section is measured to be 1.64±0.46 pb, in agreement with a prediction of the standard model. Combination with an earlier analysis of theZZ→+−+−channel yields aZZcross section of 1.44+₋0.35₀_.₃₄pb [9].

We study WW and WZ production with lνqq (l = e, μ) ﬁnal states using data corresponding to4.3f b−1_{of integrated luminosity. Assuming the ratio between the production cross sections}_σ₍_WW₎ andσ(WZ) as predicted by the standard model, we measure the total WV (V=W,Z) cross section to beσ(WV) = 19.6+₋3_3.0.2 pb, and reject the background-only hypothesis at a level of 7.9 standard deviations. We also use b-jet discrimination to separate the WZ component from the dominant WW component. Simultaneously ﬁtting WW and WZ contributions, we measureσ(WW) = 15.9+3.7

−3.2pb andσ(WZ)=3.3+4.1

−3.3pb, which is consistent with the standard model predictions [8].

We present a measurement of pp¯ → Zγ → ll+γ,l = e, μproduction with a data sample cor-responding to an integrated luminosity of 6.2f b−1_{. The results of the electron and muon channels} are combined, and we measure the total production cross section and the diﬀerential cross section

dσ/dpγ_T, where pγ_T is the momentum of the photon in the plane transverse to the beamline Fig. 5. The results obtained are consistent with the standard model predictions from next-to-leading order calculations. We use the transverse momentum spectrum of the photon to place limits on anomalous

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LEP-2 80376± 33

World Average 80385± 15

Figure 4.Summary of measurement of W mass as March 2012

and the distribution of the charge-signed photon-lepton rapidity diﬀerence are found to be in agree-ment with the standard model. These results provide the most stringent limits on anomalousWWγ

couplings for data from hadron colliders:−0.4<Δκ_γ<0.4 and−0.08< λ_γ<0.07 at the 95% C.L.

4 QCD Interactions

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Figure 5.A comparison of the measured WW and WZ signals (ﬁlled histograms) to background-subtracted data (points) in the dijet mass distribution (summed over electron and muon channels) for 0, 1, and 2-tag sub-channels after the combined ﬁt to data using the dijet mass distribution [9] (left). Unfoldeddσ/dpγpT distribution with no

Mllγrequirement for combined electron and muon data compared to the NLO prediction (right).

distribution functions. The observable measures the angular correlations of jets and is defined as the number of neighboring jets above a given transverse momentum threshold which accompany a given jet within a given distanceΔRin the plane of rapidity and azimuthal angle. The ensemble average over all jets in an inclusive jet sample is measured and the results are presented as a function of transverse momentum of the inclusive jets, in different regions of !R and for different transverse momentum requirements for the neighboring jets. The measurement is based on a data set corresponding to an integrated luminosity of 0.7f b−1_{. The results are well described by a perturbative QCD calculation} in next-to-leading order in the strong coupling constant, corrected for non-perturbative effects. From these results, we extract the strong coupling and test the QCD predictions for its running over a range of momentum transfers of 50 to 400 GeV [10] Fig. 6.

We present measurements of the diﬀerential cross sectiondσ/dpTγ for the inclusive production

of a photon in association with a b-quark jet for photons with rapidities|y_γ| <1.0 and 30 < pTγ <

300GeV, as well as for photons with 1.5 < |y_γ| < 2.5 and 30 < pTγ < 200GeV, where pTγ is the photon transverse momentum Fig. 8. The b-quark jets are required to havepT>15GeVand rapidity |yjet|<1.5. The results are based on data corresponding to an integrated luminosity of 8.7f b−1. The

measured cross sections are compared with next-to-leading order perturbative QCD calculations using diﬀerent sets of parton distribution functions as well as to predictions based on the kT-factorization QCD approach, and those from the Sherpa and Pythia Monte Carlo event generators [11].

In special runs of D0 experiment with Proton Forward Detector we have meured elastic scattering of pp¯ at √(s) = 1.960T eV. Comparison with other experiments is displayed in Fig. refQCD-3ab [12]. We investigate the decayB0

s → J/ψK+K−for invariant masses of theK+K−pair in the range

1.35< M(K+K−)<2 GeV. The data sample corresponds to an integrated luminosity of 10.4 fb−1of

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NLO pQCD + non-perturb. correct.

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√s = 1.96 TeV L = 0.7 fb-1 DØ

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αs(MZ) = 0.1191 +0.0048 −0.0071 (DØ combined fit to R_Δ_R data)

Figure 6. The measurement ofRΔRas a function of inclusive jetpT for three diﬀerent intervals inΔRand for

four diﬀerent requirements ofpnbr

T min. The inner uncertainty bars indicate the statistical uncertainties, and the total

uncertainty bars display the quadratic sum of the statistical and systematic uncertainties. The theory predictions are shown with their uncertainties (left). The strong couplingαs at large momentum transfers, Q, presented as

αs(Q) (a) and evolved toMZusing the RGE (b). The uncertainty bars indicate the total uncertainty, including

the experimental and theoretical contributions. The newαs results fromRΔR are compared to previous results

obtained from inclusive jet cross section data. Theαs (MZ) result from the combined ﬁt to all selected data

points and the corresponding RGE prediction are also shown (right).

5 TOP quark Physics

The top quark is the heaviest known elementary particle, with a mass about 40 times larger than the mass of its isospin partner, the bottom quark. It decays almost 100%. of the time to aW boson and a

bquark. The summary of cross section production oft_t¯is presented in Fig. 9, with ﬁnal combination: σt¯t=7.65±0.42pb.

We present a measurement of the top quark mass (mt) in pp¯ collisions at √s=1.96 TeV using

t_t¯events with two leptons (ee,eμ, orμμ) and accompanying jets in 4.3f b−1 _{of data collected. We} analyze the kinematically underconstrained dilepton events by integrating over their neutrino rapidity distributions. We reduce the dominant systematic uncertainties from the calibration of jet energy using a correction obtained from t_t¯events with a ﬁnal state of a single lepton plus jets. We also correct jets in simulated events to replicate the quark ﬂavor dependence of the jet response in data. We measuremt =173.7±2.8 (stat)±1.5 (syst) GeV and combining with our analysis in 1 f b−1 of

preceding data we measuremt=174.0±2.4 (stat)±1.4 (syst) GeV. Taking into account statistical and

systematic correlations, a combination with the D0 matrix element result from both data sets yields

mt=173.9±1.9 (stat)±1.6 (syst) GeV [13].

We measure lepton angular distributions int_t¯_→_W+_b,W−b¯ →l+νbl¯−. Using data corresponding to an integrated luminosity of 5.4f b−1_{, we ﬁnd that the angular distributions of} _l− _{relative to} anti-protons andl+relative to protons are in agreement with each other. Combining the two distributions and correcting for detector acceptance we obtain the forward-backward asymmetry

Al_FB=(5.8±5.1(stat)±1.3(syst))

compared to the standard model prediction ofAl

FB(predicted)=(4.7±0.1). This result is further

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s = 1.96 TeV = 0.7

cone

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NLO pQCD

+non-perturbative corrections

CTEQ6.5M

600

DØ, 0.70 fb-1

Figure 7. Inclusive jet cross section measurements as a function of jetpT in six|y|bins. The data points are

multiplied by 2, 4, 8, 16, and 32 for the bins 1.6<|y|<2.0,1.2<|y|<1.6,0.8<|y|<1.2,0.4<|y|<0.8, and|y|<0.4, respectively (left). MC closure test of the method used to extract the inclusive jetpTcross section

for the jet|y|<0.4 bin. The full analysis was repeated treating MC events as data and comparing the result to the input cross section. Good agreement is found within the statistical uncertainties of ﬁts to jet energy scale and resolution, and unfolding present in MC (shaded band), which are much smaller than the systematic uncertainties in data(right).

Al

FB=(11.8±3.2) [14].

We present measurements of thetWbcoupling form factors using information from electroweak single top quark production and from the helicity of W bosons from top quark decays int_t¯events Fig. 10 [15]. We set upper limits on anomaloustWbcoupling.

Combining measurements that simultaneously determine the fractions of W bosons with longitu-dinal (f0_{) and right-handed (}_f+_{) helicities, we ﬁnd}

f0₌₀_.₇₂₂_±₀_._081[_±₀_.₀₆₂₍_stat_.₎_±₀_.₀₅₂₍_s_y_st_._{)] and}

f+=−0.033±0.046[±0.034(stat.)±0.031(syst.)].

Combining measurements where one of the helicity fractions is ﬁxed to the value expected in the standard model, we ﬁnd

f0₌₀_.₆₈₂_±₀_._057[_±₀_.₀₃₅₍_stat_.₎_±₀_.₀₄₆₍_s_y_st_._{)] and}

f+ =−0.015±0.035[±0.018(stat.)±0.030(syst.)] [16]. The results are consistent with standard model expectations. Thet_t¯spin correlation strength C is deﬁned by

d2_σ

tt¯/dcosΘ1dcosΘ2=σ(tt¯) (1−Ccos(Θ1)cos(Θ2))/4,

whereΘ1,Θ2are the angles between the spin-quantization axis and the direction of flight of the down-type fermion from the W boson decay in the respective parenttor ¯trest frame. The fractional difference in the number of events where the top and antitop quark spins are aligned and those where the top quark spins have opposite alignment A is defined asC=A|α1α2|whereαiis the spin analyzing

power of the ﬁnal state parton under consideration. In NLO QCDα_l+ = 1 for the charged lepton

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fact. (Lipatov, Zotov) T k SHERPA, v1.3.1 PYTHIA, v6.420 >15 GeV jet T |<1.5, p jet |y (x0.3) -1 DØ, L = 8.7 fb

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CDF (1.800 TeV) E710 (1.800 TeV) DØ (1.960 TeV)

Figure 8. MC closure test of the method used to extract the inclusive jet pT cross section for the jet|y|<0.4

bin. The full analysis was repeated treating MC events as data and comparing the result to the input cross section. Good agreement is found within the statistical uncertainties of ﬁts to jet energy scale and resolution, and unfolding present in MC (shaded band), which are much smaller than the systematic uncertainties in data (left). dσ/dtdiﬀerential cross section of elastic scattering measured by the D0 Collaboration and compared to the CDF and E710 measurements at√s=1.8 TeV, and to the UA4 measurement at√s=0.546 TeV (scaled by a factor of 100) (right).

=1.96 TeV s cross section (pb) at t

t

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CDF ANN l+jets 7.82 ± 0.38 ± 0.40 pb 4.6 fb-1

0.55 pb

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CDF all-jets 7.21 ± 0.50 ± 1.08 pb 2.9 fb-1

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