I.Lokhtin, ''Simulation of jet quenching at RHIC and LHC ''

Transcription

1 Simulation of jet quenching at RHIC and LHC I. Lokhtin, A. Snigirev Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University Thanks for help and discussions to L. Sarycheva, C. Roland, S. Petrushanko, L. Malinina, I. Vardanyan, B. Wyslouch, G. Veres... (CMS Heavy Ion group), T. Sjostrand and A. Morsch Model of jet quenching in heavy ion collisions Jet quenching pattern at RHIC Examples of jet quenching observables at LHC Summary and outlook

2 Monte Carlo models to simulate jet quenching and flow effects in HIC PYQUEN fast code to simulate jet quenchig (modify PYTHIA6.4 jet event), HYDJET merging soft part (with including flow effects) and multijets generated with PYQUEN The codes are included in LHC generator database GENSER I. Lokhtin, A. Snigirev, Eur. Phys. J. C 46 (2006) 211

3 Medium induced partonic energy loss Collisional loss (incoherent sum over scatterings) Bjorken; Mrowzinski; Thoma; Markov; Mustafa et al... Radiation loss (coherent LPM interference) Gylassy Wang; BDMPS; GLV; Zakharov; Wiedemann...

4 Medium induced partonic energy loss General kinetic integral equation: L dp de x x x,e, dx dx E L, E = dx 0 1 dp x = exp x / x dx x 1. Collisional loss and elastic scattering cross section: 1 de = dx 4T t max 2 2s t d d 12 dt dt t, dt C t 2, S = 33 2 N ln t / 2, C =9 / 4 gg, 1 gq, 4 / 9 qq f QCD 2 D 2. Radiative loss (BDMS): 2 s C F de m q =0 = dx L E E LPM ~ g 2D [ ] 2 2 CF D g L 16 4 y d 1 y ln cos 1 1, 1= i 1 y y 2 k ln, k =, 1 =, y=, C F = k y 2 g E 3 dead cone approximation for massive quarks: 1 de de m q 0 = m q =0, 3/2 2 dx dx 1 l l= 2 D 1/3 mq E 4/3

5 Nuclear geometry and QGP evolution impact parameter b O1O2 transverse distance between nucleus centers Space time evolution of QGP, created in region of initial overlaping of colliding nuclei, is descibed by Lorenz invariant Bjorken's hydrodynamics J.D. Bjorken, PRD 27 (1983) 140

6 Monte Carlo simulation of parton rescattering and energy loss in QGP Distribution over jet production vertex V(r cos, r sin ) at im.p. b T A r 1 T A r 2 dn b = 2 d dr r max d rdrt A r 1 T A r Transverse distance between parton scatterings li=( i+1 i) E/pT li dp = 1 i 1 exp 1 i s ds, 1= dl i 0 Radiative and collisional energy loss per scattering E tot, i = E rad, i E col, i Transverse momentum kick 2 per scattering 2 t,i k = E ti 2 m0 i 2 ti E ti 2 p m q p 2 m0 i 2 p

7 Angular spectrum of gluon radiation Medium modified jet fragmentation depends on fraction of partonic energy loss falling outside the jet cone But full treatment of angular spectrum of emitted gluons is sophisticated and model dependent Two simple parameterizations of gluon angular distribution: g dn Small angular radiation: d sin exp g dn Broad angular radiation: d , 0 ~5o

8 PYQUEN (PYthia QUENched) Initial parton configuration PYTHIA6.4 w/o hadronization: mstp(111)=0 Hard parton rescattering and energy loss + emitted gluons PYQUEN rearranges partons to update ns strings: ns call PYJOIN Parton hadronization and final particle formation PYTHIA6.4 with hadronization: mstp(111)=1, call PYEXEC More details on PYQUEN physics can be found in: I.Lokhtin, A.Snigirev, EPJ C45 (2006) 211; ; and references therein.

9 Model for HYDRO flow The final hadron spectrum are given by the superposition of thermal distribution and collective flow assuming Bjorken's scaling. 1. Thermal distribution of produced hadron in rest frame of fluid element f E 0 E 0 E m exp E 0 /T f, 1 cos 0 1, Y max L 2. Space position r and local 4 velocity uμ max 2 2 Y L 2 f max T f r =2 r / R R A, b, 0 r R f, f e, 0 2 ur =sinh Y r / R eff R A, b R A, u t = 1 ur2 cosh, u z = 1 ur2 sinh 3. Boost of hadron 4 momentum pμ in c.m. frame of the event i i 0 p x = p 0 sin 0 cos 0 ur cos [ E 0 u p / ut 1 ], i i p y = p 0 sin 0 sin 0 ur sin [ E 0 u p 0 / u t 1 ], i i p z = p 0 cos 0 u z [ E 0 u p 0 / u t 1 ], i i i i E=E 0 u t u p 0, u p 0 =ur p 0 sin 0 cos 0 u z p 0 cos 0

10 HYDJET (HYDrodynamics + JETs) generates njet NN subcollisions and formation of jet induced state by calling (PYTHIA+PYQUEN) njet times start filling JETSET arrays with npyt lines and HYDJET arrays with nl (corresponding to nl partons) lines calculation of multiplicity of HYDRO induced particles, nhyd=n npyt, and adding new particles in JETSET arrays We are working on improvement of soft part generation: N.S. Amelin, R. Lednisky, T.A. Pocheptsov, I.P. Lokhtin, L.V. Malinina, A.M. Snigirev, Yu.A. Karpenko, Yu.M. Sinyukov, nucl th/ , PRC in press

11 HYDJET: model parameters External input beam and target nucleus atomic weight (A=B) impact parameter (fixed or distributed) total mean multiplicity in central Pb+Pb or Au+Au events (multiplicity for other centralities and atomic weights is calculated automatically) Parameter can be varied by user ytfl - maximum transverse collective rapidity, controls slope of low-pt spectra (0.01<ytfl<3.0, default value is ytfl=1.) ylfl - maximum longitudinal collective rapidity, controls width of -spectra (0.01<ylfl<7.0, default value is ylfl=5.) fpart - fraction of multiplicity proportional to # of participants; (1.-fpart) - fraction of multiplicity proportional to # of NN subcollisions (0.0<fpart<1.0, default value is fpart=1.) ptmin - minimal pt of hard parton-parton scattering in PYTHIA (2 GeV < ptmin < 500 GeV, default value ptmin=10 GeV) Internal sets poison multiplicty distribution thermal particle ratios and freeze-out at Tf=100 MeV

12 HYDJET: output information Output particle information: final hadronic state of the event in JETSET format (common block LUJETS, #150000) parton history of the event in JETSET format (common block HYJETS, #150000) Output global event characteristics: bgen - generated value of impact parameter nbcol - mean # of NN subcollisions at given bgen npart - mean # of nucleon participants at given bgen npyt - multiplicity of jet-induced particles in the event nhyd - multiplicity of HYDRO-induced particles in the event

13 Fit RHIC hadron spectra with HYJDET Fixing multiplicity and Ylmax=3.5 from PHOBOS -spectra (K factor = 2 for PYTHIA jet cross section) Fixing Tf=100 MeV, YTmax=1.25 and ptmin=2.8 GeV/c from PHENIX pt spectra Fixing initial QGP conditions from high pt part: T0=500 MeV, 0=0.4 fm/c and nf=2 Calculating nuclear modification factor RAA and azimuthal correlation function C( )

14 Fit RHIC spectra with HYJDET

15 Reproducing jet quenching pattern at RHIC with HYJDET Nuclear modification factor Azimuthal back to back correlations

16 Jet quenching at LHC (I): jet fragmentation function Jet fragmentation function D(z): probability distribution for leading hadron in the jet to carry fraction z( pth/ptjet) of jet transverse momentum: In the jet induced by heavy quark, the energetic muon can be produced ( b tagging )

17 Medium modified jet fragmentation function measured with leading Pb+Pb (b=0), s=5.5a TeV (T0=1 GeV, 0=0.1 fm/c, nf=0) ETjet > 100 GeV Significant low z enhancement and high z suppression o

18 Jet quenching at LHC (II): + */Z( μ μ )+jet production COMHEP + PYTHIA μ <2.4, ptμ >5 GeV/c jet<3, ETjet,PTμ μ >50 GeV s=5.5 A TeV: (pp μ +μ +jet) 18 pb, (Pb+Pb μ +μ +jet) 0.8 b Events per 1 month: (T= s, L= sm 2s 1) T L (Pb+Pb μ +μ +jet) ~ 103 I. Lokhtin, A. Sherstnev, A. Snigirev, Phys. Lett. B 599 (260) 2004

19 + Invariant mass spectrum of μ μ pairs from */Z+jet production

20 Imbalance of transverse momentum in + */Z( μ μ )+jet channel in HIC Dimuon jet correlation Dimuon jet leader correlation Advantage in using PT imbalance between leading hadron in a jet (but not jet itself) and muon pair: week dependence on dispersion of jet energy determination

21 Summary and outlook The method to simulate jet quenching in heavy ion collisions has been developed. The model is the fast Monte Carlo tool implemented to modify a standard PYTHIA jet event. The full heavy ion event is obtained as a superposition of a soft hydro type state and hard jets. The model is capable of reproducing main features of the jet quenching pattern at RHIC (the momentum dependence of the nuclear modification factor and the suppression of azimuthal back to back correlations). The model was also applied to probe jet quenching in new channels at LHC energy: jets tagged by leading particles and dilepton jet correlations. The further development of the model focusing on a more detailed description of low transverse momentum particle production is in the progress.

22 BACKUP SLIDES

23 Jet quenching in heavy ion collisions (medium induced partonic energy loss) E T03 (temperature), g (number degrees of freedom) EQGP >> EHG LHC, central Pb+Pb: T0, QGP ~ 1 GeV >> T0, HGmax ~ 0.2 GeV, gqgp > ghg EQGP / EHG (1 GeV / 0.2 GeV)3 ~ 102

24 Observation of jet quenching at BNL RHIC (Au+Au & Cu+Cu, s = 200 A GeV) First observation of new phenomena supporting idea of QGP formation (not for d+au collisions, excepting high pt suppression at forward rapidity possible onset of low x initial state effects like nuclear shadowing and CGC) high pt hadron suppression high pt azimuthal anisotropy azimuthal correlations

25 Potential of jet physics at future CERN LHC (Pb+Pb, s = 5500 A GeV) New regime of HI physics where hard and semi hard QCD production dominates over soft background and probes hot and long lived QGP complementary measurements from ALICE & CMS/ATLAS ATLAS ALICE (low pt particle tracking & ID, CMS/ATLAS (high pt particle tracking, central forward (J/ψ, ), multiplicity,...) (J/ψ,, Z), jets with calorimetry & tracker,...) soft probes + selected hard probes hard probes + selected soft probes

26 Dependence of geometry and interaction dynamics on event centrality

27 PYQUEN: gluon radiation spectrum (LHC, central Pb+Pb, T0, QGP = 1 GeV) Number of gluons Gluon energy PYQUEN # of gluons per partonic jet, PYQUENm # of gluons per leading parton

28 PYQUEN: energy loss fluctuations (LHC, central Pb+Pb, T0, QGP = 1 GeV) Single parton loss Partonic jet loss (Rjet=0.5) PYQUEN (PYQUENm) vacuum shower before (after) in medium radiation

29 PYQUEN: mean energy loss dependences (LHC, Pb+Pb, T0, QGP (b=0) = 1 GeV) E dependence L dependence dependence

30 Elliptic flow at RHIC with HYJDET Underestimation at pt<2 GeV/c due to large contribution of h from in medium emitted non perturbative gluons (at low pt HYDRO w/o jets describes better). Increasing ptmin remove discrepancy (LHC case)

31 HYDJET: quenching of particle spectra 30,000 minimum bias Pb+Pb events, s=5.5a TeV (pt, min=10 GeV, ntot=30000) pt distribution distribution PT spectra: strong hardening due to jets and softening due to jet quenching spectra: some broadening due to jets and narrowing due to jet quenching

32 HYDJET: elliptic flow v2(pt) v2( ) v2(pt > 2 GeV): sharp drop due to jets and additional v2 due to jet quenching v2( ): ~30% reduction due to jets and small influence due to jet quenching