Systematic study of high p T hadron production in small collision systems by the PHENIX experiment at RHIC Takao Sakaguchi Brookhaven National Laboratory For the PHENIX Collaboration 1 9/12/2017 T. Sakaguchi, ISMD2017
Quark Gluon Plasma (QGP) Partonic (quarks and gluons) matter believed to have existed in the early Universe. QGP formation by colliding heavy ions at high energies (RHIC, LHC, etc.) Confirmation of its formation by comparing with the system known not to form QGP p + p , p +A collisions Particle flow, high p T hadron suppression, etc. ( ) AA d 3 N / dp 3 R AA = ( N coll / σ inel ) d 3 σ / dp 3 ( ) pp d 3 N p T dp T dyd ϕ ∝ [1 + 2 v 2 ( p T )cos2( ϕ − φ RP ) + ...] 2 PRC82, 011902(R) (2010) 9/12/2017 T. Sakaguchi, ISMD2017
Small system ~was s e~ simple a e and a a b basel eline~ Why were we interested in small system collisions (i.e., p / d / 3 He+Au): To confirm the high-p T hadron suppression in Au+Au is due to final state effects (QGP), and not cold nuclear matter (CNM) effects. CNM effects include: k T broadening, shadowing, CNM energy loss, … 2 d+Au, s = 200 GeV, 0-20% most central Measured R d Au : NN Jets/hadrons and direct photons in minimum 1.5 bias d +Au collisions are consistent with unity dAu 1 R up to high-p T - + (h +h )/2 (PRC 77, 014905) 0.5 As expected from parton distribution function 0 (PRL98, 172302) π (PRL98, 172302) η (EPS09). 0 0 2 4 6 8 10 p [GeV/c] T PRC 87, 054907 (2013) d+Au (MB) virtual 2.5 γ s =200 GeV 0 π -tagging NN Cronin+Isospin 2 Cronin+Isospin+Shadowing Cronin+Isospin+Shadowing+ E ∆ dA 1.5 init R 1 0.5 0 2 4 6 8 10 12 14 16 18 20 p (GeV/c) 3 T PRL 116, 1223011 (2016) 9/12/2017 T. Sakaguchi, ISMD2017
Small system is no longer simple Jets R d A shows strong centrality dependence Suppression in most central, enhancement in most peripheral Strong flow like A+A is seen in most central d +Au collisions Similar observation by the LHC experiments We didn’t anticipate “flow” in a small system like p / d +A PRL 116, 1223011 (2016) PRL114, 192301 (2015) 4 9/12/2017 T. Sakaguchi, ISMD2017
Journey to new worlds Initial state effects, e.g. CGC, will affect to production cross-section of particles and their orientation Mini-QGP production? Final state effects , e.g. hydrodynamics will produce flow- like structure If there is QGP , detail investigation of the interaction of partons with the medium will give insight on its characteristics Systematic study of the leading hadron spectra in small systems will help 5 9/12/2017 T. Sakaguchi, ISMD2017
PHENIX detector and dataset Integrated luminosities, triggered by BBC: Year-3 and -8 d +Au: 2.74 µ b -1 (1.1 pb -1 pp-equiv), 80 µ b -1 (32.1 pb -1 pp-equiv) Year-14 3 He+Au: 25 nb -1 (15 pb -1 pp-equiv) Year-15 p +Au, p +Al: 80 nb -1 (16 pb -1 pp-equiv), 275 nb -1 (7.4 pb -1 pp-equiv.) Particle identification and tracking: π 0 by Electromagnetic Calorimeter in central arm (| η |<0.35) Hadrons by muon arms (3.1<| η |<3.9) p/d/ 3 He Au South North 6 9/12/2017 T. Sakaguchi, ISMD2017
Event trigger and bias PRC 90, 034902 (2014) Min. Bias trigger has inefficiency Measured BBC charge distribution was compared with a Glauber Monte Carlo simulation folded with a negative binomial distribution (NBD) Trigger efficiency is determined as 88%. Same for p / d / 3 He+Au Bias factors (BF) for centrality selection are calculated Bias is coming from auto-correlation between high p T particle in mid-rapidity and backward multiplicity (where centrality is determined) Cent (%) 0-20 20-40 40-60 60-88 0-100 p +Au BF 0.90 0.98 1.02 1.00 0.86 d +Au BF 0.94 1.00 1.03 1.03 0.89 3 He+Au BF 0.95 1.02 1.02 1.03 0.89 7 9/12/2017 T. Sakaguchi, ISMD2017
Nuclear modification factors for min. bias Comparison of the R p / d /He+Au for three collision systems Enhancement at p T = 5 GeV/c indicates a system size dependence Some hint of suppression at higher p T (p T >10GeV/c)? p d Au Au 3 He 8 9/12/2017 T. Sakaguchi, ISMD2017
R p+Au vs centralities Nuclear modification in centralities: Centrality determined similarly as for large systems (PRC90,034902) p +Au results show large centrality dependence 9 9/12/2017 T. Sakaguchi, ISMD2017
R p/d+Au vs centralities Nuclear modification in centralities: Centrality determined similarly as for large systems (PRC90,034902) p +Au results show large centrality dependence d +Au results agree with p +Au at high-p T 10 9/12/2017 T. Sakaguchi, ISMD2017
R p/d/ 3 He+Au vs centralities Nuclear modification in centralities: Centrality determined similarly as for large systems (PRC90,034902) p +Au results show large centrality dependence d +Au results agree with p +Au at high-p T 3 He+Au results agree with p +Au and d +Au at high-p T At moderate p T an ordering is seen as a function of systems 11 9/12/2017 T. Sakaguchi, ISMD2017
Ι ntegrated R AA in d +Au and 3 He+Au At higher N part , d +Au and 3 He+Au show very similar N part dependence At lower N part , d +Au collisions show more enhancement More Cronin effect, or less suppression (energy loss) 12 9/12/2017 T. Sakaguchi, ISMD2017
Ι ntegrated R AA in p / d / 3 He/Au+Au Integrated R AA for p / d/ 3 He/Au+Au R AA from all three systems converge for N part >~12 Similar hot matter is produced? System ordering of R AA is seen for N part <12 is seen; R pAu ~R dAu >R HeAu >R AuAu p +Au @ p T =5GeV/c (0-20, 20-40, 40-60, 60-88%) Au+Au @ p T =5GeV/c (80-93, 70-80, 60-70%) 13 9/12/2017 T. Sakaguchi, ISMD2017
Cold nuclear energy loss? Different energy loss scenarios (no, small or moderate) are comparable to the data at high-p T System dependent enhancement change at low-p T is not reproduced The peak positions are also different Additional parameters to be tuned? PRD 93, 074030, and priv. comm. with I. Vitev 14 9/12/2017 T. Sakaguchi, ISMD2017
Multiple scattering ? HIJING++ simulation shows similar trend between collision systems Ingredient: multiple scattering + shadowing effect HIJING++ predicts the Cronin peak around p T = 1.5-2GeV/c Much lower than in the data (p T ~ 5 GeV/c) based on 1701.08496 private comm. with G. Papp PHENIX Data HIJING++ simulation 1.4 1.4 Y 200 GeV π ± , | η |<0.5 R min. bias ● ● ● ● ● ● ● ● A ● ● ● ● ● ● ● ● 1.2 1.2 ● ● ● ● ● ● ● ● ● ● ● ● N ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● I ● ● ● ● ● ● ● ● ● ● ● ● M ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● R pA ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 1.0 1.0 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● I ● ● ● ● ● ● ● L ● ● ● ● E p+Au ● ● ● ● ● 0.8 0.8 R d+Au ● ● ● ● ● ● ● He+Au ● ● ● ● P ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 0.6 0.6 ● ● ● G.Papp et al, HIJING++ 0 0 1 1 2 2 3 3 4 4 5 5 p T 15 9/12/2017 T. Sakaguchi, ISMD2017
Lessons from model comparison Cold nuclear energy loss alone can’t describe the trend of nuclear modification factors for p / d / 3 He+Au collisions Multiple scattering + shadowing scenario seems to describe the spectra This scenario predicts larger ( smaller ) enhancement in the forward ( backward ) in comparison to mid-rapidity HIJING++ simulation based on 1701.08496 private comm. with G. Papp 1.6 1.6 p+Au@200 GeV → π ± Y R min. bias ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 1.4 1.4 ● ● A ● ● ● ● ● ● ● ● Au-going p-going N ● ● ● ● ● ● ● ● ● ● 1.2 1.2 ● ● ● ● I ● ● ● ● ● ● ● ● M ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● R pAu ● ● R pA ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 1.0 1.0 ● ● I L ● ● E ● ● ● ● [2.2,1.2] 0.8 0.8 ● ● ● ● ● ● ● R ● ● ● ● [ − 0.5,0.5] [ − 1.2, − 2.2] P 0.6 0.6 G.Papp et al, HIJING++ y 0 0 1 1 2 2 3 3 4 4 5 5 p T 16 9/12/2017 T. Sakaguchi, ISMD2017
Looking forward and backward Strong centrality and rapidity dependence of charged hadrons Backward rapidity shows large enhancement Forward rapidity shows suppression Opposite trend compared to HIJING++ prediction 17 9/12/2017 T. Sakaguchi, ISMD2017
Looking forward and backward π 0 point Strong centrality and rapidity dependence of charged hadrons Backward rapidity shows large enhancement Forward rapidity shows suppression Opposite trend compared to HIJING++ prediction 18 9/12/2017 T. Sakaguchi, ISMD2017
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