Probing Modification of the Initial State in Small Systems via Jets Detected in PHENIX

Probing Modification of the Initial State in

Small Systems via Jets Detected in PHENIX

Jonathan Runchey on behalf of the PHENIX Collaboration 5 November 2019

Quark Matter 2019 Wuhan, China

Motivation

•What is a jet?

Motivation

•What is a jet?

• A collimated spray of hadrons originating from a hard scattered parton

•Understanding how partons interact with the QGP provides essential

insight into QCD

•Studies of jet production in small systems are necessary to decouple which

effects observed in A+A data come from:

• Interactions with the medium

• Initial state effects and modifications of the PDFs

•At LO di-jets are produced with ∆φ = π in the transverse plane

• Initial and final state radiation broadens that distribution

•_{We measure the correlation of the “trigger” particle (high pT)} with “associated” particles in the same jet or opposite jet

Two particle correlations

𝜋0_,𝛾

h±

PHENIX detector overview

Δφ

•Two central arms: cover ɸ~π and |η|<0.35

•Finely segmented EM calorimeter: able to measure 𝜋0 _{up to 20 GeV}

•Drift chamber and pad chambers measure

Correlation in p+p collisions

π0_{-hadron correlations}

𝛾-hadron correlations

•𝛾-h shows away-side yields that are consistently smaller than the

corresponding π0_{-h yields because}

π0 _{probes larger Q}2 PhysRevD.98.072004 P T tr ig P_Tassoc

•p_out allows us to separate effects:

•non-perturbative (Gaussian)

•perturbative (non-Gaussian tail)

•Hard gluon radiation in initial or final state

Correlation in p+p collisions (II)

PhysRevD.98.072004 [GeV/c] out p 5 - -4 -3 -2 -1 0 1 2 3 4 5 -1 [GeV/c] out dp dN trig N 1 8 -10 7 -10 6 -10 5 -10 4 -10 3 -10 2 -10 1 -10 1 10 4-5 ) -1 5-7 (x10 ) -2 7-9 (x10 ) -3 9-12 (x10 ) -4 12-15 (x10 [GeV/c] trig T p ± -h 0 p ± -h g PHENIX =200 GeV s p+p <0.5 E 0.1<x |<0.35 h | 𝑝_$%& = |𝑝₎*++$,|𝑠𝑖𝑛Δ𝜙 𝑥3 = − |𝑝₎*++$,| |𝑝₎&567| 𝑐𝑜𝑠Δ𝜙

•_{Fitted Gaussian width as a function of pT}trig

•_{With increasing pT}trig we see:

• Larger Gaussian widths

• Stronger non-perturbative effects

Correlation in p+p collisions (III)

PhysRevD.98.072004 [GeV/c] trig T p 4 6 8 10 12 14

Gaussian Width [GeV/c]

0.4 0.5 0.6 0.7 0.8 0.9 PHENIX =200 GeV s p+p <0.5 E 0.1<x |<0.35 h | ± -h g ± -h 0 p

[GeV/c] out p 6 - -4 -2 0 2 4 6 -1 [GeV/c] out dp dN trig N 1 9 -10 8 -10 7 -10 6 -10 5 -10 4 -10 3 -10 2 -10 1 -10 1 PHENIX = 200 GeV NN s <9 GeV/c trig T 5<p 2 p < f D < 2 p -± -h 0 p <0.15 E 0.1<x ) -1 <0.25 (x10 E 0.15<x ) -2 <0.5 (x10 E 0.25<x ) -3 <1 (x10 E 0.5<x p+Au p+p

𝜋

0

-h correlation in p+Au collisions

•Intra-jet correlation: π0 _{and hadron} fragment from the same hard parton

• Narrower than the away side

• Sensitive only to fragmentation p_T

Near Side Away Side

PhysRevC.99.044912 [GeV/c] out p 6 - -4 -2 0 2 4 6 -1 [GeV/c] out dp dN trig N 1 9 -10 8 -10 7 -10 6 -10 5 -10 4 -10 3 -10 2 -10 1 -10 1 _PHENIX = 200 GeV NN s <9 GeV/c trig T 5<p 3 p 4 < f D < 3 p 2 ± -h 0 p <0.15 E 0.1<x ) -1 <0.25 (x10 E 0.15<x ) -2 <0.5 (x10 E 0.25<x ) -3 <1 (x10 E 0.5<x p+Au p+p 𝑥₃ = −|𝑝) *++$,_| |𝑝₎&567| 𝑐𝑜𝑠Δ𝜙 𝑝_$%& = |𝑝₎*++$,|𝑠𝑖𝑛Δ𝜙

•Near side shows no p_out broadening compared to p+p

• Intra-jet radiation effects are small

•Away side p+Au shows clear p_out broadening

•With this in mind let’s focus on the away side…

PhysRevC.99.044912

Near Side Away Side

𝜋

0

-h correlation in p+Au(Al) collisions

𝑥₃ = − |𝑝)

*++$,_|

|𝑝₎&567| 𝑐𝑜𝑠Δ𝜙 𝑝_$%& = |𝑝₎*++$,|𝑠𝑖𝑛Δ𝜙

•Near side shows no p_out broadening compared to p+p

• Intra-jet radiation effects are small

•Away side p+Au shows clear p_out broadening

•With this in mind let’s focus on the away side…

•These bins in particular

PhysRevC.99.044912

Near Side Away Side

𝜋

0

-h correlation in p+Au(Al) collisions

𝑥₃ = − |𝑝)

*++$,_|

|𝑝₎&567| 𝑐𝑜𝑠Δ𝜙 𝑝_$%& = |𝑝₎*++$,|𝑠𝑖𝑛Δ𝜙

N

coll

dependance p+Au(Al) (away side)

•p_out broadening shows clear N_coll dependence

•Effects that may possibly contribute:

• Multiple scattering of partons inside the nuclear

medium (“Cronin effect region”)

• Additional k_T (initial transverse momentum) for a

parton in the nucleus with respect to p+p

• Path length dependence->hard scattered partonic

energy loss

• v₂ and v₃ systematically ruled out as contributors

PhysRevC.99.044912

𝑥₃ = − |𝑝)

*++$,_|

|𝑝₎&567| 𝑐𝑜𝑠Δ𝜙 𝑝_$%& = |𝑝₎*++$,|𝑠𝑖𝑛Δ𝜙

Correlation yields in d+Au

•Look for modification of away side in d+Au by

studying ratio with p+p

•This quantity can be studied as a function of z_T

𝑧

₎

=

𝑝

) *++$,

𝑝

₎&567

𝐼

_=>

=

𝑌

=>% >

𝑌

_@@>

d+Au away yield ratio

p T / p h T = p T z 0 0.2 0.4 0.6 0.8 1 1.2 dA I 0.4 0.6 0.8 1 1.2 1.4 1.6 < 7 p T 5 < p < 9 p T 7 < p A pp Y A dAu Y = dA Away I -h 0 p dAu, 0-20%, PH ENIX preliminary •_{Suppression at high zT}

•There is a hint of enhancement at low z_T

•Can we improve error bars? Yes!

•_{Let’s look at the double ratio}

𝑅𝐼 = 𝑌=>%

> _/𝑌

=>%C 𝑌_@@> /𝑌_@@C

d+Au comparison of away yield vs. double ratio

•Clear improvement of uncertainties in RI compared to I_dAu

•RI shows small high-z suppression and low-z enhancement in d+Au

•Let’s explore this as a function of centrality…

p T / p h T = p T z 0 0.2 0.4 0.6 0.8 1 1.2 dA I 0.4 0.6 0.8 1 1.2 1.4 1.6 < 7 p T 5 < p < 9 p T 7 < p A pp Y A dAu Y = dA Away I -h 0 p dAu, 0-20%, PH ENIX preliminary p T / p h T = p T z 0.2 0.4 0.6 0.8 1 RI 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 < 7 p T 5 < p < 9 p T 7 < p N pp / Y A pp Y N dAu / Y A dAu Y RI = -h 0 p dAu, 0-20%, PH ENIX preliminary

Central

RI Centrality Dependence

Peripheral p T / p h T = p T z 0.2 0.4 0.6 0.8 1 RI 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 < 7 p T 5 < p < 9 p T 7 < p N pp / Y A pp Y N dAu / Y A dAu Y RI = -h 0 p dAu, 0-20%, PH ENIX preliminary p T / p h T = p T z 0.2 0.4 0.6 0.8 1 RI 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 < 7 p T 5 < p < 9 p T 7 < p N pp / Y A pp Y N dAu / Y A dAu Y RI = -h 0 p dAu, 20-40%, PH ENIX preliminary p T / p h T = p T z 0.2 0.4 0.6 0.8 1 RI 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 < 7 p T 5 < p < 9 p T 7 < p N pp / Y A pp Y N dAu / Y A dAu Y RI = -h 0 p dAu, 60-88%, PH ENIX preliminary

•_{Low-zTenhancement, increasing as a function of centrality}

•_{Indication of high-zTsuppression}

•Theory input will be valuable to interpret these results

•Can we study this effect in another system? Yes, 3_He+Au!

𝜋

0

-h in

3

He+Au: Correlation Functions

0 0.5 1 1.5 2 2.5 3 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 CF 5-7 x 0.6-1 GeV/c 0 0.5 1 1.5 2 2.5 3 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 5-7 x 1-2 GeV/c 0 0.5 1 1.5 2 2.5 3 0.5 1 1.5 2 2.5 = 200 GeV NN S ± -h 0 p 0-20%, 5-7 x 2-3 GeV/c 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 ) f D ( mixed AB N ) f D ( same AB N µ ) f D CF( 5-7 x 3-5 GeV/c 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 6 7 5-7 x 5-7 GeV/c fit to CF ZYAM level He3Au 0 0.5 1 1.5 2 2.5 3 0.7 0.8 0.9 1 1.1 1.2 f D CF 7-9 x 0.6-1 GeV/c 0 0.5 1 1.5 2 2.5 3 0.6 0.8 1 1.2 1.4 1.6 f D 7-9 x 1-2 GeV/c 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 3.5 f D 7-9 x 2-3 GeV/c 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 f D 7-9 x 3-5 GeV/c 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 6 7 8 f D 7-9 x 5-7 GeV/c PH ENIX preliminary pTassoc p T tri g

Double ratio in

3

He+Au

T 0 p /p T h = p T z 0.2 0.4 0.6 0.8 1 I R 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 0.060 ± constant fit: 0.848 : [5-7] GeV/c 0 p T p : [7-9] GeV/c 0 p T p : [0.6-1, 1-2, 3-5, 5-7] GeV/c T h ± p 2 p |< p -f D , Away: | 2 p |< f D Near: | pp Near /Y pp Away Y He3Au Near /Y He3Au Away Y = I R

subtraction not applied

1 v ± -h 0 p = 200 GeV, 0-20%, NN S PH ENIX preliminary

•High-z_Tsuppression illustrated by fit •Similar trend as in d+Au

Comparing

3

He+Au to d+Au

T 0 p /p T h = p T z 0.2 0.4 0.6 0.8 1 I R 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 : [5-7] GeV/c 0 p T He3Au, p : [7-9] GeV/c 0 p T He3Au, p : [5-7] GeV/c 0 p T dAu, p : [7-9] GeV/c 0 p T dAu, p : [0.6-1, 1-2, 3-5, 5-7] GeV/c T h ± p 2 p |< p -f D , Away: | 2 p |< f D Near: | pp Near /Y pp Away Y xAu Near /Y xAu Away Y = I R

subtraction not applied 1 v ± -h 0 p = 200 GeV, 0-20%, NN S _preliminaryPH ENIX

•

Very interesting!

•

How do we explain this?

• _{CNM energy loss?}

Fully reconstructed jets (preview)

•Coming soon! Fully reconstructed jets from

2015 high statistics small systems data sets

•p+p has similar statistics to p+Au (shown)

Conclusions

•_{PHENIX has taken a rich collection of small system measurements}

•We have interesting results from two particle correlations:

• N_coll dependence of momentum broadening in p+A

• Evidence of jet modification in d+Au and 3_He+Au

•We are looking forward to input from theorists!

Hard scattering kinematics

Momentum component of the associated hadron perpendicular to the trigger particle

Longitudinal momentum fraction of the associated hadron with respect to the trigger particle

(proxy for the momentum fraction z)

𝜋0_,𝛾

𝜋

0

-h in p+p: Correlation Functions

pTassoc 0 0.5 1 1.5 2 2.5 3 0.6 0.8 1 1.2 1.4 CF 5-7 x 0.6-1 GeV/c 0 0.5 1 1.5 2 2.5 3 0.2 0.4 0.6 0.81 1.2 1.4 1.6 1.8 2 2.2 2.4 _{5-7 x 1-2 GeV/c} 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 3.5 4 = 200 GeV NN S ± -h 0 p 0-20%, 5-7 x 2-3 GeV/c 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 ) f D ( mixed AB N ) f D ( same AB N µ ) f D CF( 5-7 x 3-5 GeV/c 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 6 7 5-7 x 5-7 GeV/c fit to CF ZYAM level pp 0 0.5 1 1.5 2 2.5 3 0.4 0.6 0.8 1 1.2 1.4 1.6 f D CF 7-9 x 0.6-1 GeV/c 0 0.5 1 1.5 2 2.5 3 0.5 1 1.5 2 2.5 f D 7-9 x 1-2 GeV/c 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 3.5 4 f D 7-9 x 2-3 GeV/c 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 f D 7-9 x 3-5 GeV/c 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 6 7 8 f D 7-9 x 5-7 GeV/c PH ENIX preliminary p T tri g

•Low-z_Tenhancement, increasing as a function of centrality

•Indication of high-z_Tsuppression

RI

z_T z_T z_T z_T

Central

RI Centrality Dependence

T 0 p /p T h = p T z 0.2 0.4 0.6 0.8 1 dAu ) I /(R He3Au ) I (R 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 0.061 ± constant fit: 0.876 : [5-7] GeV/c 0 p T p : [7-9] GeV/c 0 p T p : [0.6-1, 1-2, 3-5, 5-7] GeV/c T h ± p 2 p |< p -f D , Away: | 2 p |< f D Near: | dAu Near /Y dAu Away Y He3Au Near /Y He3Au Away Y = dAu ) I (R He3Au ) I (R

subtraction not applied

1 v ± -h 0 p = 200 GeV, 0-20%, NN S PH ENIX preliminary