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Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 1 Update of Initial Conditions in A Multiple...
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Transcript of Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 1 Update of Initial Conditions in A Multiple...
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 1
Update of Initial Conditions in A Multiple Phase Transport (AMPT) Model
Zi-Wei LinDepartment of Physics
East Carolina UniversityGreenville, NC
Work still in progress
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 2
Outline
Present status of the AMPT model
Need to update the initial conditions
Optimize parameters/functions by fitting dNch/dη data
Outlook
Summary
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 3
What do we needfor simulations of high energy heavy ion collisions?
We need:
Initial particle/energy production
Parton interactions/equation-of-state
Hadronization/QCD phase transition
Hadron interactions
Options:
Soft+hard model, CGC, pQCD, ...
Parton cascade (ZPC, MPC, BAMPS), hydrodynamics, dE/dx, ...
String fragmentation, quark coalescence, independent fragmentation, statistical hadronization, ...
Hadron cascade (ART, RQMD, UrQMD, ...), freezeout temperature, …
The AMPT model includes the components in green.In particular, it can be used to study
coalescence of partons into hadrons, thermalization and flow, dynamical chemical freeze-out and kinetic freeze-out
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 4
ZPC (Zhang's Parton Cascade)
ART (A Relativistic Transport model for hadrons)
A+B
Final particle spectra
Hadrons freeze out (at a global cut-off time);strong-decay all remaining resonances
Hadronization (Lund String fragmentation)
Structure of AMPT v1.xx (default model)
Partons freeze out
HIJING (PDFs, nuclear shadowing): minijet partons, excited strings, spectators
Less partonic interaction
Dominated by hadronicinteractions (at very high densities)
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 5
A+B
Final particle spectra
Hadronization (Quark Coalescence)
Structure of AMPT v2.xx (String Melting model)
HIJING (PDFs, nuclear shadowing): minijet partons, excited strings, spectators
ART (A Relativistic Transport model for hadrons)
Partons freeze out
ZPC (Zhang's Parton Cascade)Partonicinteractionsdominate.
Better describes flow & HBT,
but does not describe wellsingle particle spectra
Melt to q & qbar via intermediate hadrons
Hadrons freeze out (at a global cut-off time);strong-decay all remaining resonances
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 6
AMPT Source Codes
First public release of AMPT codes: ~ April 2004.Detailed physics descriptions in Lin, Ko, Li, Zhang & Pal, PRC 72, 064901 (2005).
Versions v1.21/v2.21 (2008) and v1.11/v2.11 (2004) are available athttps://karman.physics.purdue.edu/OSCAR-old/
http://personal.ecu.edu/linz/ampt/also contains more recent test versions, including
v1.25t3/v2.25t3 (8/2009) v1.25t7/v2.25t7 (9/2011) v1.25t7b/v2.25t7b (2/2012)
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 7
http://personal.ecu.edu/linz/ampt/
looks like this
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 8
A+B
Update Initial Conditions of AMPT
HIJING (PDFs, nuclear shadowing): minijet partons, excited strings, spectators
Final particle spectra
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 9
Similar updates have been done recently:
In HIJING2.0:Deng, Wang and Xu, PRC 83 (2011) & PLB 701 (2011):used GRV (Gluck-Reya-Vogt) parton distribution functions, parameterized functions p0(√sNN) & σsoft(√sNN);new parameters for quark and gluon nuclear shadowing functions are used to reproduce dNch/dη in AA collisions.
In AMPT:Pal & Bleicher, PLB 709 (2012)used HIJING2.0 as initial conditions,smaller value for the gluon shadowing parameter sg
is needed to reproduce dNch/dη in AA collisions at LHC,since rescatterings considerably reduce hadron yields at mid-rapidity
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 10
Rescatterings considerably reduce hadron yields at mid-rapidity
In AMPT:Lund model's a & b values used for pp/HIJINGcan describe SPS dN/dy when final state interactions are turned off.
but this agreement is gone when final state interactions are included.
We have to use different a & b valuesto describe dN/dy of AA collisions.
Lin, Ko, Li, Zhang & Pal, PRC 72 (2005);first shown in PRC 64 (2001).
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 11
1) Need to Use up-to-date parton distribution functions
Duke-Owens Set 1 (1984)used in HIJING1.0 & AMPT significantly under-estimates the gluon density at small-x
It is essential to use up-to-date PDFfor LHC& for heavy flavors (since ~all come from gluons)
LHC RHIC
For this study, we have incorporated into AMPT the CTEQ6M PDF
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 12
2) Need to use up-to-date nuclear shadowing functions RA(x)
PDF in a nucleus
≠ PDF in a nucleon *A
Central Pb+Pb collisions at √sNN=5.5 TeVfrom default AMPT v1.11:shadowing has a large effect
Deng, Wang and Xu, PLB 701 (2011)
For this study, we have incorporated into AMPTthe EPS09 nuclear shadowing
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 13
We follow the following strategy similar to Deng, Wang and Xu, PRC 83 (2011):
At each collision energy √sNN:
• choose different p0 values
• for each p0, determine the σsoft value that reproduces the experimental σpptotal
• run AMPT for each (p0, σsoft) set, then compare with dNch/dη data to find the best (p0, σsoft) value.
Optimize parameters by fitting dNch/dη datawith the default AMPT model (+CTEQ6M & EPS09)
The nucleon-nucleon cross sectionin the eikonal approximation:
In AMPT/HIJING1.0: p0=2.0 GeV/c, σsoft≈57 mb.
Go through all relevant collision energies:p0(√sNN) & σsoft(√sNN)
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 14
Example of the (p0, σsoft) sets
√sNN=200 GeV
√sNN=7 TeV
from PDG
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 15
At √sNN=19.6 GeV:p0=1.0, 1.2, 1.4, 1.6, 1.8 GeV/c.
…
At √sNN=200 GeV:p0=2.0, 2.2, 2.4, 2.6 GeV/c.
…
At √sNN=7 TeV:p0=3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 GeV/c.
Higher p0 gives lower dNch/dη(except for the lowest energy√sNN=19.6 GeV)
AMPT results for different (p0, σsoft) setsvs pp inelastic data
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 16
Fit p0 to inelastic pp data at different energies
√sNN=200 GeVdNch/dη (|η|<0.5) INEL=2.22 ±0.05
p0=2.35 +0.08-0.09 GeV/c
using AMPT results with interpolation
√sNN=2360 GeVdNch/dη (|η|<0.5) INEL=3.77 +0.25-0.12
p0=3.77 +0.18-0.33 GeV/c
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 17
p0 values fitted to inelastic pp data
p0(√sNN) increases with collision energy,
related to more partons at small-x in the new PDF
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 18
Fit p0 to central AA data at different energies
after incorporating EPS09 shadowing functions in AMPT
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 19
AuAu at √sNN=19.6 GeV:p0=1.2, 1.4, 1.6, 1.8 GeV/c.
…
AuAu at √sNN=200 GeV:p0=2.0, 2.2, 2.3, 2.4, 2.6 GeV/c.
PbPb at √sNN=2760 GeV:p0=3.5, 4.0, 4.5 GeV/c.
Higher p0 gives lower dNch/dη/(Npart/2)
AMPT results for different (p0, σsoft) setsvs central AA data
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 20
p0(√sNN) fitted to pp data and to AA data are not consistent This test of the PDF+shadowing update cannot systematically describe
dNch/dη of pp & AA collisions throughout this energy range
Fitted p0 values combined
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 21
Search for consistent p0(√sNN) from fits to pp data and to AA data
Possibilities include:
1) a & b parameters in Lund string fragmentation:
a=0.3 & b=0.8/GeV2 are used in this study,this is one set of the 2009 fit values in PYTHIA 8.1;we can explore the a-b parameter space:e.g. PYTHIA have used a=0.76, b=0.58/GeV2 (2007 fit
values),and used a=0.30, b=0.58/GeV2 before.
2) Alternative nuclear shadowing.
Outlook
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 22
• Work is under way to incorporate into AMPT up-to-date parton distribution functions and nuclear shadowing functions
• CTEQ6M and EPS09 have been tested within AMPT,but the functions p0(√sNN) & σsoft(√sNN)
from fits to pp dNch/dη data and fits to central AA data are not consistent
• We will investigate Lund a,b parameters and alternative nuclear shadowing functions to obtain consistent p0(√sNN) & σsoft(√sNN) from fits to pp and AA data;
that would allow systematic descriptions of dNch/dη in pp & AA collisions throughout a wide energy range.
• May require more significant developments: dynamical quark coalescence in phase space
(instead of space/nearest neighbors),inelastic parton interactions
Summary
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 25
amptsub.f art1f.fhijing1.383_ampt.f hipyset1.35.flinana.f main.f zpc.f
input.ampt
Files in the Source Code include
Fortran routines
EPS09 shadowing function tablefor Au and Pb nucleus
Input parameter values
Update of initial conditions introduces new input data files:
cteq6m.tbl
EPS09LOR_197EPS09LOR_208
CTEQ6M PDF table
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 26
HIJING soft strings + hard minijets
ZPC 2↔2 parton cascade: gg↔gg, gg↔qqbar, gq↔gq, ...
Hadronization Lund string fragmentationor quark coalescence
ART hadron cascade including:
Main Ingredients
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 27
2005 v1.12/v2.12:Freezeout time of spectator projectile and target nucleons should be ~0
but not correctly updated in 'ampt.dat'; now corrected
10/2008 v1.21/v2.21:Added option to turn off φ meson decays at the end of hadron cascade
i.e., at NT=NTMAX
10/2008 test version v1.22/v2.22:Included deuteron(d) interactions in hadron cascade via d+M ↔ B+B
(M or B represents a meson or a baryon), also included elastic collisions of d+M and d+B;similar anti-deuteron interactions are also included.
3/2009 test version v1.23/v2.23:Included a subroutine to enable users to insert user-defined hadrons
before the start of the hadron cascade
Earlier modifications in the AMPT source code
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 28
6/2009 test version v1.25t1/v2.25t1:Added an option of event selection so that each event will have at least 1 minijet parton
above a set Pt value in the initial condition;Added an option to embed a back-to-back high-Pt q/qbar pair in each event;Write out Npart information (spatial coordinates and status of each incoming nucleon);Added option to write complete parton information before and after the parton cascade and the full parton collision history for the string melting version
7/2009 test version v1.25t2/v2.25t2:Added an option to enable users to modify nuclear shadowing smoothly
between no-shadowing and the default HIJING shadowing
5/2011 test version v1.25t4/v2.25t5:Included the finite widths of resonances (K* η ρ ω Φ Δ)
when they are produced from quark coalescence in the string melting version
2/2012 test version v1.25t7b/v2.25t7b:Added option to enable random orientation of reaction plane
Recent modifications in the AMPT source code
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 29
amptsub.f art1f.fhijing1.383_ampt.f hipyset1.35.flinana.f main.f zpc.f
README Makefile exec input.ampt ana/
Files in the Source Code include
Fortran routines
Instructions (including summary of changes)
Script to run AMPT
Input parameter settings
Directory for output data and diagnostics files
update of initial conditions will introduce new input data files:
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 30
Parameters in input.ampt:
New options in red
200. ! EFRM (sqrt(S_NN) in GeV)CMS ! FRAMEA ! PROJA ! TARG197 ! IAP (projectile A number)79 ! IZP (projectile Z number)197 ! IAT (target A number)79 ! IZT (target Z number)2 ! NEVNT (total number of events)0. ! BMIN (mininum impact parameter in fm) 13. ! BMAX (maximum impact parameter in fm, also see below)1 ! ISOFT (D=1): select Default AMPT or String Melting(see below)150 ! NTMAX: number of timesteps (D=150), see below0.2 ! DT: timestep in fm (hadron cascade time= DT*NTMAX) (D=0.2)2.2 ! PARJ(41): parameter a in Lund symmetric splitting function0.5 ! PARJ(42): parameter b in Lund symmetric splitting function1 ! (D=1,yes;0,no) flag for popcorn mechanism(netbaryon stopping)1.0 ! PARJ(5) to control BMBbar vs BBbar in popcorn (D=1.0)1 ! shadowing flag (Default=1,yes; 0,no)0 ! quenching flag (D=0,no; 1,yes)1.0 ! quenching parameter -dE/dx (GeV/fm) in case quenching flag=12.0 ! p0 cutoff in HIJING for minijet productions (D=2.0)3.2264d0 ! parton screening mass in fm^(-1) (D=3.2264d0), see below0 ! IZPC: (D=0 forward-angle parton scatterings; 100,isotropic)0.47140452d0 ! alpha in parton cascade1d6 ! dpcoal in GeV1d6 ! drcoal in fm0 ! ihjsed: take HIJING seed from below (D=0)or at runtime(11)53153523 ! random seed for HIJING8 ! random seed for parton cascade0 ! flag for Ks0 weak decays (D=0,no; 1,yes)1 ! flag for phi decays at end of hadron cascade (D=1,yes; 0,no)0 ! optional OSCAR output (D=0,no; 1,yes; 2,initial parton info)
Initial Conditions/HIJING(e.g. turn on quenching tomimic inelastic energy loss)
Hadron Cascade(e.g. NTMAX=2 turns offhadron cascade but still has full parton cascade & hadronization)
Parton Cascade
Hadronization
Output options
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 31
Output filesampt.dat
1 1 4218 8.0000 84 84 2 82 1 83 2112 0.000 0.000 99.996 0.940 6.00 -4.86 0.23 0.00 2112 0.000 0.000 99.996 0.940 6.78 3.61 0.21 0.00 2212 0.000 0.000 99.996 0.940 5.53 1.48 0.26 0.00 2212 0.000 0.000 -99.996 0.940 -9.31 -2.75 -0.16 0.00 111 0.071 -0.334 -0.376 0.135 1.81 -0.96 -1.18 7.00
Event#Test#
Particle# b(fm) Npart1
Npart2
Particle ID(PYTHIA)
Final momentum mass Final position & time(at kinetic freeze-out)
zpc.datFinal momentum, position & time of all partons (at kinetic freeze-out)
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 32
EPS09 (JHEP 2009) determines the nuclear modification to the free proton PDF from the CTEQ6.1M set in the MS scheme
The CTEQ6.1M set provides a global fit that is almost equivalent in every respect to the published CTEQ6M
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 33
Parton coalescence to hadrons: Currently, a parton can only coalesce after it does not have further interactions (i.e., after kinetic freezeout);Average parton density at coalescence, and effective equation of state of AMPT depends on σp;Need to improve Parton coalescence for better EoS;hadronization condition (~HBT) & parton cross section (~v2) will be decoupled
Needs to Further Develop AMPT
Need to use up-to-date Parton Distribution Functions in nuclei: essential for heavy flavors & LHC
Inelastic partonic interactions
Including color fields in parton phase.
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 34
RRPL2u (19) model predictions of sigma_total for pp collisions (ecm==sqrt_s>=5GeV):
sigma_total=35.45 - 33.34/((ecm^2)^0.5453) + 42.53/((ecm^2)^0.4581) + 0.3079*(-3.364 + Log[ecm^2])^2
Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 35
At √sNN=900 GeV:p0=2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 GeV/c
At √sNN=2360 GeV:p0=2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5 GeV/c
At √sNN=7 TeV:p0=3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 GeV/c
Fitting ALICE INEL>0 pp data