at PHENIX RHIC Backtoback jets in Jiangyong Jia

at PHENIX RHIC Back-to-back jets in Jiangyong Jia n n n Introduction The method Intermediate p. T jet correlation n Columbia University, Nevis Labs Jet shape Reaction plane dependence high p. T jet correlation 9/6/2021 1

Jet Probes the s. QGP (A+A) Leading hadron Q 2 Induced gluon Radiation nucl-th/0302077 § ~collinear but broadened § “Softened” fragmentation 9/6/2021 decreases Jiangyong Jia 2

Jet “quenched” by the medium near • Medium-induced energy loss 0 x 4 -5 suppression away Medium p. T>3, 4 Ge. V/c • Energy loss depends on path length 9/6/2021 Jiangyong Jia 3

Di-jet correlation are also strongly modified Higher p. T → Away-side suppression p. T(assoc) > 2 Ge. V/c Lower p. T → Away-side enhancement p. T(assoc) > 0. 15 Ge. V/c Pedestal&flow subtracted How opaque is the medium? What is the fate of very high p. T jets? Correlation of high p. T jets 9/6/2021 How the energy is distributed to the medium? Detailed study of intermediate and low p. T correlation Jiangyong Jia 4

Jet properties via two particle correlation p+p 1 d. N Ntrig d 1) Jet shape 2) Jet Yield 3) Underlying event 9/6/2021 Jiangyong Jia 5

Underlying event in Au. Au 1 d. N combinatorial background is large in Au+Au! flow+jet Ntrig d And is not constant! flow elliptic flow causes another correlation in them: jet l(1+2 v 2(p. Ttrig)v 2(p. Tassoc)cos(2 )) CF = J( ) + l(1+2 v 2 tv 2 a cos 2 ) 9/6/2021 Jiangyong Jia 6

Intermediate p. T Jet shape 9/6/2021 Jiangyong Jia 7

The Correlation function 0 -5% C( ) 2. 5 -4 x 3 -5 Ge. V/c 2. 5 -4 x 1 -2. 5 Ge. V/c PHENIX Preliminary Flat or slight dip at the away side! Small jet signal! (1/50) Shape can’t be pure di-jet broadening 9/6/2021 Jiangyong Jia 8

Now subtract the v 2 CF = J( ) + l(1+2 v 2 tv 2 a cos 2 ) n n n v 2 background is scaled to match the correlation function (ZYAM). l 2 v 2 tv 2 a ~ few %, thus the change in B only slightly affect subtracted away side jet shape. Sensitive to the v 2 systematic. 9/6/2021 Jiangyong Jia 9

Centrality dependence of the jet shape PHENIX preliminary 9/6/2021 Jiangyong Jia 10

Centrality dependence of the jet shape PHENIX preliminary 9/6/2021 Jiangyong Jia 11

Centrality dependence of the jet shape D D PHENIX preliminary Away side: splitting Near side : broadening 9/6/2021 Jiangyong Jia 12

Near side width Trigger p. T = 2. 5 -4 x 2 -3 Ge. V/c p 0 -hadron-hadron Broadening is seen for pairs at intermediate p. T Energy loss effect? Or baryon/meson difference? 9/6/2021 Jiangyong Jia 13

D parameter D D Splitting Parameter D increasing with centrality Turn on in rather peripheral bins Similar trend for all systems and energies 9/6/2021 Jiangyong Jia 14

Mach Cone? the dip? n Jet broadening from large angle gluon emission (I. Vitev) n n n The dipness of the dip? n Sensitive to flow Deflection of jets by subtraction the flowing medium n Fill up can happens at both 1 and . Armesto, Salgado, Wiedemann. n Part of the jet is in ‘Underlying event’, has Cherenkov gluon radiation in medium been subtracted out. Koch, Majumder, X. -N. Wang nucl-th/0406018 Stoecker hep-ph/0411315 Casalderrey-Solana, Shuryak, Teaney n n n Sound excitation at angle of cos(q)=cs/c independent of p. T Cone narrows as p. T increases Number of particles in the cone not calculated yet. 9/6/2021 Jiangyong Jia 15

Di-jet w. r. p to reaction plane 9/6/2021 Jiangyong Jia 16

RP dependence n Study (di)jet correlations vs angle of trigger h relative to reaction plane n J. Bielcikova et al, Phys. Rev. C 69: 021901, 2004 a is proportional to the N triggers in the bite The mixed events gives C( ) = = x(1+b/a cos 2 ) x accounts for the difference in normalization factor, in dependent of trigger direction and is close to 1. The only free parameter 9/6/2021 Jiangyong Jia 17

The six trigger windows used n 6 bins from 0 to /2 9/6/2021 Jiangyong Jia 18

Check • Constrain v 2 of trigger hadron and associated hadron simultaneously • The extracted v 2 is consistent with the RP v 2 Verification of the method! 9/6/2021 Jiangyong Jia 19

PHENIX preliminary 0 -5% x is fixed !! v 4 not included. PHENIX preliminary 9/6/2021 Jiangyong Jia 20

V 2 subtracted jet yield in each trigger direction n n Can study dependence of modification on overlap geometry Can constrain the v 2 Clearly the systematics dependence on trigger direction 9/6/2021 Jiangyong Jia 21

PHENIX Preliminary 30 -40% PHENIX Preliminary 9/6/2021 Jiangyong Jia 22

RP dependence of the yield n Flow change dramatically vs trigger bin n However, the subtracted distribution agrees in errors n Shoulder and dip seen in all bins n 9/6/2021 Split caused by small v 4 and small remaining v 2 Jiangyong Jia 23

Difference of di-jet yield in/out plane Bin 1 - Bin 6 PHENIX preliminary • Differences can almost be described by the harmonics Mainly due to residual v 2 and v 4 • Path length dependence of the modification should cause the asymmetry between 0 and . • We see hint of this for 30 -40% bin. 9/6/2021 Jiangyong Jia 24

Let’s look at the dip again Look in bin #4 PHENIX Preliminary n n For PHENIX reaction plane resolution & chosen bin sizes, trigger bin 4 has smallest effect from v 2. Even without subtracting flow contribution, a dip is seen for central collisions. 9/6/2021 Jiangyong Jia 25

Jet correlation at High p. T 9/6/2021 Jiangyong Jia 26

Evolution of away-side jet shape 9/6/2021 Jiangyong Jia 27

Evolution of away-side jet shape 9/6/2021 Jiangyong Jia 28

Evolution of away-side jet shape n n n Jet like peak clearly visible Near side jet yield is constant with centrality. Suppression of awayside peak increases with centrality Look at much better data from STAR! 9/6/2021 Jiangyong Jia 29

STAR: Di-jets at higher p. T 8 < p. T(trig) < 15 Ge. V/c p. T(assoc)>6 Ge. V/c STAR Preliminary Clear emergence of jet structure at the away-side No background subtraction! 9/6/2021 Jiangyong Jia 30

Di-jets and the interaction mechanism 8 < p. T(trig) < 15 Ge. V/c p. T(assoc)>6 Ge. V/c Measuring Low z is necessary n n 9/6/2021 Away side jet shape not modified! Away side jet fragmentation function is not modified but overall yield is suppressed! Jiangyong Jia 31

n Jet reappears, but still should still have significant distortion at low p. Tassoc. 9/6/2021 Jiangyong Jia 32

Put things together Higher p. T → Away-side suppression p. T(assoc) > 2 Ge. V/c Lower p. T → Away-side enhancement p. T(assoc) > 0. 15 Ge. V/c Pedestal&flow subtracted Surface emissions (again? ) 9/6/2021 Interaction of the jet with the flowing medium Jiangyong Jia 33

Summary n We studied the jet shape at intermediated p. T n n Reaction plane dependence at intermediate p. T n n n Near side jet is broadened Away side jet developed shoulder and dip structure (not likely due to jet broadening. ) Requires novel mechanism? Supporting the away side jet shape. Slight modification of the jet function from in plane to out of plane High p. T correlation n Jet shape and fragmentation function not modified (need soft region) But the jet yield is reduced by factor of 5 in central Au. Au collisions. A puzzle for the community 9/6/2021 Jiangyong Jia 34

To determine B n Opposite/same sign correlation n n Identical away side strength Different near side strength v 2 contribution is identical ZYAM will find different B in two cases. n n +- -+ ++ -- But the true background should be same Assuming jet width is same in same sign and opposite sign then we can determine B absolutely 9/6/2021 Jiangyong Jia 35

STAR and PHENIX “converges” n n STAR’s measurement imposing PHENIX acceptance. Agrees within systematics. The main difference comes from the assumed v 2 values. 0 -5% 9/6/2021 Jiangyong Jia 36

d-Au/p-p, - h, Correlations d-Au p-p PHENIX preliminary 1 -2 Ge. V/c 0. 4 -1 Ge. V/c p. T, trig > 5 Ge. V/c 2 -3 Ge. V/c 3 -5 Ge. V/c Underlying event yield drops quickly, negligible >2 Ge. V/c 9/6/2021 Jiangyong Jia 37

n The away side jet yield associated with the leading hadron has a much flat p. T distribution than single inclusive 200 Ge. V Trigger pion 5 -10 Ge. V/c 63 Ge. V bg shape 9/6/2021 Jiangyong Jia 38

Where the cross happens PHENIX Preliminary n n Cross happens at the right locations /4, ± /4 The vertical values are different at the near and far side!! n 1. 02 vs 1. 03 9/6/2021 Jiangyong Jia 39

9/6/2021 Jiangyong Jia 40

Jet yield in different regions n Study jet structure in three regions: n n n Near | |<p/3. Away dip | -p|<p/6, Away peaks p/2 < -p<5 p/6, 7 p/6 < -p<3 p/2 9/6/2021 Jiangyong Jia 41

Jet yield 9/6/2021 Jiangyong Jia 42

Ratio to the near side peaks 9/6/2021 Jiangyong Jia 43

Jet yield ratio to the peripheral bins 9/6/2021 Jiangyong Jia 44

Underlying event study from CDF From Rick Field, ISMD 2004 Leading Jet 9/6/2021 Jiangyong Jia 45

Initial/ final state radiation from Pythia Fixed trigger! (>5 ) Near n Far Initial radiation: Near side: enhanced yield at large p. T, assoc n Far side: small change Due to initial k. T + trigger bias effect? ztrig decrease, and zassoc increase n n Final radiation : n n Near side: small change. Energy available: (1 -z. Trig)EJet Far side: enhanced yield at low p. T, assoc. Full jet energy available: EJet 9/6/2021 Jiangyong Jia 46

RP dependence n Study (di)jet correlations vs angle of trigger h relative to event plane n J. Bielcikova et al, Phys. Rev. C 69: 021901, 2004 a is proportional to the n trig in the bite The mixed events gives x accounts for the difference in normalization factor, and is close to 1. C( ) = = x(1+b/a cos 2 ) d. Npairs/d 9/6/2021 Jiangyong Jia 47

Difference of jet per trigger yield Between “max in plane” and “max out of plane” 9/6/2021 Jiangyong Jia 48