Measurement of Jet Modification at RHIC/STAR

Measurement of Jet Modification at RHIC/STAR
– OUTLINE – motivation analysis results summary Fuqiang Wang Purdue University 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

相对论重离子碰撞与低能强子物理讨论会, 威海
Physics motivation Quantum Chromodynamics predicts phase transition between hadrons and Quark-Gluon Plasma (a state of thermalized partons) at high energy density. phase diagram of matter T r/r0 5-10 ~200 MeV Quark-Gluon Plasma early universe Few msec after the Big Bang the entire Universe may be in a QGP state. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Lattice QCD prediction:
Physics motivation The goal of RHIC is to create QGP – a state of deconfined, thermalized quarks and gluons Lattice QCD prediction: F. Karsch, Nucl. Phys. A698, 199c (2002) TC ~ 170  8 MeV eC ~ 0.5 GeV/fm3 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

To create the QGP T r/r0 5-10 ~200 MeV Quark-Gluon Plasma 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Heavy ion collisions QCD Vacuum (1) energy density? (2) thermalization? 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Bjorken energy density estimate
Boost invariant hydrodynamics: Bjorken Estimate of Initial Energy Density t ~1 fm/c 30xr0 nucl-ex/ PRL 87 (01) 52301 Cold nuclear matter: r0 ~ 0.16 GeV/fm3 Low bound: t likely is smaller at RHIC. ET drops with time. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

To probe energy density
self-generated, penetrating probe: large pT hadrons, jets Gluon bremsstrahlung Jet quenching: X.-N. Wang et al. they are generated early (by hard-scatterings); they need time to escape the collision zone; during this time, a QGP (or whatever medium) is formed; they interact with the medium, losing energy, thus giving us information about the medium. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Inclusive high pT yield – suppressed
Large pT hadrons are mainly from jets produced by initial hard-scattering. Small cross-sections, scale with number of binary collisions. If no nuclear effect, AA = binary-scaled pp; AA binary-scaled pp  nuclear effect. 130 GeV 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Initial state effect? Control experiment d+Au! Phys. Rev. Lett. 91, No. 7, August 15, 2003 ? Maybe initial state suppression? e.g. PDF different in Au and deuteron 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

High pT suppression suppression of high pT hadron yield suppression of back side angular correlation no suppression in d+Au  Final state interaction in Au+Au, consistent with energy loss by high pT particles – jet quenching. strong absorption 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Energy density inferred from models
X.-N. Wang, PLB 579 (04) 299 pQCD calculations: x30 gluon density x100 energy density in central Au+Au collisions ~ Bjorken estimate 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

“Pre-hadronic” and hadronic rescattering
Gallmeister, Greiner, Xu, PRC67, (2003) Cassing,Gallmeister, and Greiner, hep-ph/ p Suppression factor <L/l> 1 r 2 3 tf Calculations use: 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

To measure energy loss possible… by going to low pT. S. Pal, S. Pratt, PLB574 (2003) 21. X.-N. Wang, PLB 579 (2004) 299, nucl-th/ C.A. Salgado, U.A. Wiedemann, hep-ph/ M. Gyulassy, I. Vitev, X.-N. Wang, B.-W. Zhang, nucl-th/ …… Pal, Pratt, PLB 574 (2003) 21 How is energy distributed? amount of energy loss? contribution from medium? 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Reconstructing low pT associated particles
Df (1/Ntrig) dN/d(Df) STAR Preliminary background Signal p+p Jet-like structures Au+Au top 5% Select a leading particle 4<pT<6 GeV/c, |h|<0.75. Associate other particles (0.15<pT<4 GeV/c,|h|<1.1) with the leading particle. Form Df,Dh correlations. Background from mix- events. v2 modulation on background. Normalize in <|Df|<1.3. Efficiency corrections are applied to associated particles. Take difference and normalize per trigger. High pT particle p+p High pT particle Au+Au 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Azimuth angular correlations
High pT: 1/Ntrigger dN/d(Df) D f (radians) Low pT: M.G. Albrow et al. NPB145, 305 (1978) p+p, 53 GeV near side: |Df|<1.1, |Dh|<1.4 away side: |Df-p|<2, |h|<1.1 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

“Jet” sizes STAR Preliminary near: |Df|<1.1, |Dh|<1.4 away: |Df-p|<2, |h|<1.1 Au+Au top 5% bkgd subt. RMS (1/Ntrig) dN/d(Df) s Df near (1/Ntrig) dN/d(Dh) With increasing centrality: Near side broadens in h but not f. Away side modest increase in size. Dh 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Longitudinal broadening
N.Armesto, C.A.Salgado, U.A.Wiedemann, hep-ph/ long. flow S.A. Voloshin, nucl-th/ p + p radial flow 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

“Jet” charge multiplicity and “energy”
STAR Preliminary p+p With the same final leading particle, we are selecting a larger energy jet in central AA than in pp. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Medium contribution? Total scalar pT: Initial parton energy + medium contribution? TPC acceptance of away side partner? 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Jet quenching model X.-N. Wang, PLB 579 (2004) 299, nucl-th/ with energy loss without energy loss DE = 1.4 – 2.2 GeV } Caution: cannot be readily compared to data yet 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Thermal-shower recombination
Hwa, Yang, nucl-th/ In this model, the thermal- shower recombination is the largest contribution to high pT particles. One mechanism for energy contribution from medium. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Thermalization? Thermalization in the final state: Final state low pT hadron distributions look thermal. Event-by-event <pT> variation is small: every event looks thermal. Hadron compositions described by thermal models. TChemical ~ 160 MeV ~ TC. Necessary but not sufficient condition for early thermalization. NA49, PRC 68 (2003) 34903 Early state thermalization? First time at RHIC elliptic flow at low pT described by hydro: zero mean free path  max. possible v2. SPS v2 lower than hydro, however energy density may be not much lower. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

To probe thermalization
Put two sources of particles together: one from jet fragmentation that are initially hard. the other from bulk medium that are soft. and see how they become at end of the day. Leading hadrons Medium jet medium 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Associated particles pT distributions
STAR Preliminary: Quark Matter 2004 Away side: energy from the initial parton is redistributed to low pT energy loss in medium! Near side: Overall enhancement from pp to AA larger initial parton energy (and modest energy loss) Away syst. error Near softening in spectra: partial equilibration with medium 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Partial approach toward thermalization
STAR Preliminary: QM 2004 Leading hadrons Medium In central Au+Au, the balancing hadrons are greater in number, softer in pT, and distributed broadly in angle, relative to pp or peripheral Au+Au.  away-side products seem to approach equilibration with bulk medium traversed, making thermalization of the bulk itself quite plausible. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Summary high enough energy density? High pt suppressed. Models require x30 normal nuclear gluon density. Statistical reconstruction of “complete” jets. Same pT leading particles from larger energy jets in AA than pp. Potential for experimental measure of energy loss. parton thermalization? Broader angular distribution, larger multiplicity, softer pT. Partial thermalization with bulk medium. High degree of thermalization in medium itself plausible. Have we created a new form of matter? Definitely! It’s dense, strongly interacting, opaque. Is it a QGP? Xin-nian said yes. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

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Are leading particles from jets?
PHENIX, PRL 91, (2003) p / p ~ 0.9 in central p / p ~ 0.3 in peripheral ISR QM’04 non-frag. p / p ~ 0.6 non-frag. p / Nch ~ 0.3 pT=3-4 GeV/c: ~30% are probably from other sources. B. Alper, NPB 87 (1975) 41 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Coalescence / recombination models
Fries et al, PRC 68 (03) 44902 Greco et al, PRC 68 (03) 34904 Hwa et al, nucl-th/ Coalescence / recombination models predict a range of non-fragmentation contributions. All predict a rapid drop of non-fragmentation contribution above 4 GeV/c. pT>4 GeV/c: may mainly come from jets, or related to jets. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Fries et al, PRC 68 (03) 44902 Greco et al, PRC 68 (03) 34904 Hwa et al, nucl-th/ Coalescence / recombination models predict a range of non-fragmentation contributions. All predict a rapid drop of non-fragmentation contribution above 4 GeV/c. 4<pT<6 GeV/c: may mainly come from jets, or related to jets, but transition region according to models. pT>6 GeV/c: a lot cleaner. Study two pT regions: 4<pT<6 GeV/c and pT>6 GeV/c 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

What we know from previous measurements…
Suppression phenomena in central Au+Au are due to final-state interactions. Parton-parton hard-scatterings are initially present. RCP 10% 60-92% pT > 4 GeV/c region is mainly from jet fragmentation. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Baryon/meson 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

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Broadened distribution and thermalization
e.g. a thermal fluctuated large pT particle (or a mono-jet) would produce an away side excess due to momentum conservation. Borghini et al. PRC 62, (2000):  HIJING all h STAR |h| < 0.5 p+p 0.23 0.26 Au+Au 5% 0.31 0.50 assoc. particle pT (GeV/c) cos strength per particle STAR, PRL90, (2003) (1/Ntrig) dN/d(Df) STAR Preliminary: Y. Guo poster P25 Df (1/Ntrig) dN/d(Df) Df STAR Preliminary p+p Au+Au 5% Fit to near side: const. + gaussian + Borghini-cos(fixed) stat. mom. conserv. Borghini et al. free fit trigger particle pT (GeV/c) cos strength per particle STAR, PRL90, (2003) (1/Ntrig) dN/d(Df) STAR Preliminary: Ying Guo poster Df STAR Preliminary p+p Au+Au 5% Fit to near side: const. + gaussian + Borghini-cos(fixed) stat. mom. conserv. Borghini et al. free fit the final state away excess has a similar shape to a stat. distr. from momentum conservation. near side is mostly a jet, and initially no mono-jet at mid-rapidity. No punch-through for 6 < pTtrig < 10 GeV/c. the away side excess is approaching equilibration with the medium, consistent with the pT spectra results. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Broadened distribution and thermalization
(1/Ntrig) dN/d(Df) Df STAR Preliminary p+p Au+Au 5% Fit to near side: const. + gaussian + Borghini-cos(fixed) stat. mom. conserv. Borghini et al. free fit the away excess has a similar shape to a stat. distr. from momentum conservation. Borghini et al. PRC 62, (2000):  HIJING all h STAR |h| < 0.5 p+p 0.23 0.26 Au+Au 5% 0.31 0.50 Cannot distinguish: (1) the full event participates in momentum balance. (2) Only a handful particles: e.g. jet-jet production. the away side excess approaching equilibrium with the medium! 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Cos-coefficient vs centrality
p+p 80-60% 60-40% 40-30% 30-20% 20-10% 10-5% 5-0% cos coeff. Nch 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

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d+Au results d+Au data set has larger statistics than the p+p data set, allowing a study of jet spectra as a function of trigger pT. near away Hardening of spectra with increasing trigger pT. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Raito of d+Au spectra 6<pT<10 GeV/c 4<pT<6 GeV/c Associated pT (GeV/c) d+Au spectra ratio Associated pT (GeV/c) Au+Au / p+p If initial parton energy was larger in AA than pp, then a hardening of spectra is expected. No hardening is observed in AA; may indicate contribution of soft hadrons from energy loss. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

d+Au yield and total pT p+p trigger pT near mult. away mult. p+p trigger pT near sum pT away sum pT Consistency between p+p and d+Au results. d+Au no much different from p+p. Increase of associated multiplicity and sum pT with increasing trigger pT. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

d+Au yield and total pT 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

d+Au vector pT away/near ratio

“z” distributions Backup Slides 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

z distributions 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

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---New results--- 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Azimuth angular correlations
High pT: Low pT: M.G. Albrow et al. NPB145, 305 (1978) p+p, 53 GeV near side: |Df|<1.0, |Dh|<1.4 away side: |Df-p|<2.15, |h|<1.0 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

“Jet” charge multiplicity and “energy”
STAR Preliminary p+p With the same final leading particle, we are selecting a larger energy jet in central AA than in pp. 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Higher pT trigger 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Medium contribution? Total scalar pT: Initial parton energy + medium contribution? TPC acceptance of away side partner? 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Away side <pT> away side associated
particle <pT> decreases with centrality, approaching medium hadron <pT> in central collisions equilibration between the two sources of particles 4<pT<6 GeV/c 6<pT<10 GeV/c 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

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Compare to pp, pA pT (GeV/c) dN/dpT2 [a.u.] PRELIMINARY p+p STAR Preliminary p+p pT (GeV/c) <ztrigger> G. Boca et al. ZPC49, 543 (1991) p+A 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

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Df distribution 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Dh distributions 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Near side distributions

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AA/pp vs IAA Peripheral: AA/pp=1.01 IAA=0.84 - broadening in h - pp reference - v2 - model difference Central: AA/pp=1.66 IAA=1.25 Df Df 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

IAA < 1 in peripheral ? STAR Preliminary pp reference 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

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Hijing (no quenching) 4 < pTtrig < 6 GeV/c 2 < pT < 4 GeV/c 0.15 < pT < 4 GeV/c Df Df 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Like-sign and unlike-sign
STAR Preliminary 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Unlike vs like (top 10%) Unlike-sign Like-sign Back-to-back paper |Dh|<0.5 |Dh|>0.5 1.2 |Dh|<0.5 + |Dh|>0.5 1.0 (Unlike-like)/unlike = 0.1 1-1.5 |Dh|<0.5 - |Dh|>0.5 Df 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

pp (left) AuAu top 5% (right)
Unlike-sign Like-sign Unlike-sign Like-sign 0.15 0.7 |Dh|<0.5 -0.03 0.5 0.15 0.7 |Dh|>0.5 -0.03 0.5 0.15 |Dh|<0.5 + |Dh|>0.5 1.3 -0.03 1.0 |Dh|<0.5 - |Dh|>0.5 0.15 0.1 -0.03 -0.05 Df Df 相对论重离子碰撞与低能强子物理讨论会, 威海 4/7/2019

Measurement of Jet Modification at RHIC/STAR

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