PYQUEN event generator

Transcription

1 PYQUEN event generator Igor Lokhtin PYQUEN team: I.Lokhtin, A.Snigirev (SINP MSU) HYDJET team: I.Lokhtin, A.Snigirev,(SINP MSU), K.Tywoniuk (Universidad de Santiago de Compostela) HYDJET++ team: I.Lokhtin, L.Malinina, A.Snigirev, S.V.Petrushanko (SINP MSU), I.Arsene (Oslo University),K.Tywoniuk (Universidad de Santiago de Compostela) 1

2 PYQUEN and HYDJET/HYDJET++ PYQUEN medium induced partonic energy loss model (modifies PYTHIA6.4 jet event), latest version 1.5 (2007) HYDJET merging two independent components: soft hydro type part and hard multi parton part generated with PYQUEN, latest version 1.6 (2009) I. Lokhtin, A. Snigirev, Eur. Phys. J. C 46 (2006) 211 HYDJET++ continuation of HYDJET (more detailed treatment of soft part including resonance decays and separate treatment of chemical & thermal freeze outs), first version 2.0 (2008), version 2.1 is about completed (2009) I.Lokhtin, L.Malinina, S.Petrushanko, A.Snigirev, I.Arsene, K.Tywoniuk, CPC 180 (2009) 779 2

3 Medium-induced partonic energy loss in PYQUEN General kinetic integral equation: L E L, E = 0 dx dp dx 1. Collisional loss and elastic scattering cross section: de dx = 1 t max dt d 4T 2 D dt 2. Radiative loss (BDMS): de dx m q =0 = 2 s C F L E 2 E LPM ~ g D t, x x de dx x, E, [ ] = y2 d 1 y 2 ln cos 1 1, 1 i 1 y C F dead cone approximation for massive quarks: de dx m 0 = 1 de q 1 l 3/ 2 2 dx m =0, l= q 2 D dp dx x = 1 x y2 3 k ln 16 k, k= 2 D g 1/3 m 4/ 3 q E exp x/ x d dt C 2 2 s t 12, t 2 S = 2, C=9/ 4 gg,1 gq, 4/ 9 qq 33 2N f ln t / QCD 1 y, = L 1, y= 2 g E, C = 4 F 3 3

4 Angular spectrum of gluon radiation Three option for angular distribution of in-medium emitted gluons: Collinear radiation Small-angular radiation (default) Broad-angular radiation =0 dn g d sin exp 0 2 dn g d , 0 ~5 o 4

5 Nuclear geometry and QGP evolution impact parameter b O 1 O 2 - transverse distance between nucleus centers (r 1,r 2 ) T A (r 1 ) T A (r 2 ) (T A (b) - nuclear thickness function) 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 5

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

7 PYQUEN (PYthia QUENched) Initial parton configuration PYTHIA6.4 w/o hadronization: mstp(111)=0 Parton rescattering & energy loss (collisional, radiative) + emitted g PYQUEN rearranges partons to update ns strings: ns call PYJOIN Parton hadronization and final particle formation PYTHIA6.4 with hadronization: call PYEXEC Three model parameters: initial QGP temperature T 0, QGP formation time τ 0 and number of active quark flavors in QGP N f (in central Pb+Pb) (+ minimal p T of hard process Ptmin and other PYTHIA parameters) 7

8 PYQUEN: mean energy loss ( s=5.5 A TeV, Pb+Pb, T 0, QGP (b=0) = 1 GeV, 0 =0.1 fm/c ) E-dependence L-dependence -dependence 8

9 PYQUEN: energy loss fluctuations ( s=5.5 A TeV, Pb+Pb, T 0, QGP (b=0) = 1 GeV, 0 =0.1 fm/c ) 9

10 HYDJET & HYDJET++ (HYDrodynamics + JETs) Calculating the number of hard NN sub-collisions Njet (b, Ptmin, s) with Pt>Ptmin around its mean value according to the binomial distr. Selecting the type (for each of Njet) of hard NN sub-collisions (pp, np or nn) depending on number of protons (Z) and neutrons (A-Z) in nucleus A according to the formula: Z=A/( A 2/3 ) Generating the hard part by calling PYTHIA/PYQUEN njet times If nuclear shadowing is switched on, the correction for PDF in nucleus is done by the accepting/rejecting procedure for each of Njet hard NN sub-collisions: by comparision of random number generated uniformly in the interval [0,1] with shadowing factor S 1, which is taken from the adapted impact parameter dependent parameterization based on Glauber-Gribov theory (K.Tywoniuk et al.,, Phys. Lett. B 657 (2007) 170). Generating the soft part according to the corresponding thermal model (for b 0 mean multiplicty is proportional to # of N-participants) Junction of two independent event outputs (hard & soft) to event record 10

11 HYDJET++: rapidity spectra vs. event centrality at RHIC Width of the spectra allows one to fix η max =3.3, Centrality dependence of multiplicity allows one to fix ptmin=3.4 GeV/c 11

12 HYDJET++: transverse momentum spectra at RHIC PYQUEN energy loss model parameters: T 0 (QGP)=300 MeV, τ 0 (QGP)=0.4 fm/c, N f =2 12

13 HYDJET++: hadron spectra at LHC 1000 events Pb+Pb (0-5 % centrality) at s=5.5 A TeV (default parameters, ptmin=7 GeV/c) 13

14 HYDJET++: hadron spectra at LHC 1000 events Pb+Pb (0-5 % centrality) at s=5.5 A TeV (default parameters, ptmin=10 GeV/c) 14

15 Examples of jet quenching observables at the LHС (PYQUEN, Pb+Pb) ~10 6 events with jet energy E T jet > 100 GeV per «1 year» (10 6 sec) at the integral luminosity L=0.5 nb -1 Nuclear modification factor for jet hadrons Nuclear modification factor for jets (R=0.5) Medium-modified jet fragmentation function Azimuthal anisotropy of hard hadrons and jets 15

16 Summary Partonic energy loss MC model PYQUEN (PYthia QUENched) is available via Internet: Corresponding code versioning is provided (latest version is 1.5) PYQUEN is incorporated in full heavy ion event generators HYDJET and HYDJET++ (HYDrodynamics plus JETs; superposition of two independent components: hard multiparton fragementation and soft hydro type state) Corresponding code versioning is provided (latest versions are HYDJET_1.6 and HYDJET++_2.0; v. 2.1 is about completed). 16

17 BACKUP SLIDES 17

18 HYDJET: simple (but fast) model for soft hadroproduction The final hadron spectrum (π, K, p) 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 0 2 m 2 exp E 0 /T f, 1 cos 0 1, Space position r and local 4-velocity u μ f r =2r/R f 2 R A, b, 0 r R f, f e Y L max 2 3. Boost of hadron 4-momentum p μ in c.m. frame of the event 2 Y L max 2, 0 2 u r =sinh Y T max r/ R eff R A,b R A, u t = 1 u r 2 cosh, u z = 1 u r 2 sinh p x = p 0 sin 0 cos 0 u r cos [E 0 u i p 0 i / u t 1 ], p y = p 0 sin 0 sin 0 u r sin [E 0 u i p 0 i / u t 1 ], p z = p 0 cos 0 u z [E 0 u i p 0 i / u t 1 ], E=E 0 u t u i p 0 i, u i p 0 i =u r p 0 sin 0 cos 0 u z p 0 cos 0 18

19 HYDJET: output information Output particle information: event record in PYTHIA/JETSET format (common block HYJETS, #150000) copy of event record in adopted for high multiplicites JETSET arrays (common block LUJETS, #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 njet number of hard parton parton scatterings with pt>ptmin in event sigin total inelastic NN cross section at given c.m.s. energy sigjet hard scattering NN cross section at given ptmin and energy 19

20 HYDJET: model parameters External input beam and target nucleus atomic weight (A=B) c.m.s. energy per nucleon pair impact parameter (fixed or distributed) total mean multiplicity of soft part in central Pb+Pb 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=1.5) ylfl maximum longitudinal collective rapidity, controls width of spectra (0.01<ylfl<7.0, default value is ylfl=4.) Tf hadron freeze out temperature (0.08 <Tf < 0.2, Tf(default)=0.1 GeV) 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.) some parameters and flags of parton energy loss model PYQUEN flags to switch on/off jet production, jet quenching and nuclear shadowing ptmin=ckin(3) minimal pt of parton parton scattering in PYTHIA Internal sets for soft part poison multiplicty distribution thermal particle ratios (π, K and p only) 20

21 HYDJET++: more detailed (and still fast) model for soft hadroproduction Soft (hydro) part of HYDJET++ is based on the adapted FAST MC model: Part I: N.S.Amelin, R.Lednisky, T.A.Pocheptsov, I.P.Lokhtin, L.V.Malinina, A.M.Snigirev, Yu.A.Karpenko, Yu.M.Sinyukov, Phys. Rev. C 74 (2006) Part II: N.S.Amelin, R.Lednisky, I.P.Lokhtin, L.V.Malinina, A.M.Snigirev, Yu.A.Karpenko, Yu.M.Sinyukov, I.C.Arsene, L.Bravina, Phys. Rev. C 77 (2008) fast (but realistic) HYDJET-inspired MC procedure for soft hadron generation multiplicities are determined assuming thermal equilibrium hadrons are produced on the hypersurface represented by a parameterization of relativistic hydrodynamics with given freeze-out conditions chemical and kinetic freeze-outs are separated decays of hadronic resonances are taken into account (360 particles from SHARE data table) with home-made'' decayer written within ROOT framework (C++) contains 15 free parameters (but this number may be reduced to 9) 21

22 HYDJET++ (soft): input parameters 1-5. Thermodynamic parameters at chemical freeze-out: T ch, {µ B, µ S, µ C,µ Q } (option to calculate T ch, µ B and µ s using phenomenological parameterization µ B ( s), T ch ( µ B ) is foreseen). 6. Strangeness suppression factor γ S 1 (the option to use phenomenological parameterization γ S (T ch, µ B ) is foreseen) Thermodynamical parameters at thermal freeze-out: T th, and µ π - effective chemical potential of positively charged pions Volume parameters at thermal freeze-out: proper time τ f, its standard deviation (emission duration) Δτ f, maximal transverse radius R f. 12. Maximal transverse flow rapidity at thermal freeze-out ρ u max. 13. Maximal longitudinal flow rapidity at thermal freeze-out η max. 14. Flow anisotropy parameter: δ(b) u μ = u μ (δ(b),φ) 15. Coordinate anisotropy: ε(b) R f (b)=r f (0)[V eff (ε(0),δ(0))/v eff (ε(b),δ(b))] 1/2 [N part (b)/n part (0)] 1/3 For impact parameter range bmin-bmax: V eff (b)=v eff (0)N part (b)/n part (0), τ f (b)=τ f (0)[N part (b)/n part (0)] 1/3 22

23 HYDJET++: elliptic flow at RHIC dn dn = (1 + v2 cos2ϕ + 2v4 cos4ϕ +...) 2 d p dy 2πp dp dy t t t 23