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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 Lin Department of Physics East Carolina University Greenville, NC Work still in progress

Zi -Wei Lin Department of Physics East Carolina University Greenville, NC

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Zi -Wei Lin Department of Physics East Carolina University Greenville, NC. Update of Initial Conditions in A Multiple Phase Transport (AMPT) Model. Work still in progress. Outline. Present status of the AMPT model Need to update the initial conditions - PowerPoint PPT Presentation

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Page 1: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 2: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 3: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 4: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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)

Page 5: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 6: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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)

Page 7: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 7

http://personal.ecu.edu/linz/ampt/

looks like this

Page 8: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 9: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 10: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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).

Page 11: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 12: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 13: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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 σpp

total

• 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)

Page 14: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 15: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 16: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 17: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 18: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 19: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 20: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 21: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 22: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 23: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 23

Thank you!

Page 24: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 24

Backup Slides

Page 25: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 26: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 27: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 28: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 29: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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 settingsDirectory for output data and diagnostics files

update of initial conditions will introduce new input data files:

Page 30: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 31: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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) Npart1Npart2

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)

Page 32: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 33: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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.

Page 34: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 35: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

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

Page 36: Zi -Wei Lin Department of Physics East Carolina  University Greenville, NC

Zi-Wei Lin (ECU) 28th WWND, Puerto Rico April 10, 2012 36