Motivation:

It is observed that the near-side jet peak distribution differs from central and peripheral d+Au collisions.

Here the jet centrality dependence is studied by Pythia simulation.

Three processes are analyzed in Pythia:

  - Soft QCD Minbias with Multiple Parton Interaction (MPI) on

  - Soft QCD Minbias with Multiple Parton Interaction (MPI) off

  - Hard QCD with Multiple Parton Interaction (MPI) on
 
  - Hard QCD with Multiple Parton Interaction (MPI) off

Method

Dihadron correlations are projected on Δη for near-side (Δφ~0) and away-side (Δφ~π) separately. The near-side distribution is fitted with a Gaussian + Pedestal.

The fit parameters are: Gaussian area Y, Gaussian width σ, Pedestal C.

The dihadron correlation below shown is ZYAM subtracted.

Both trigger and associate particles are global tracks in TPC |η|<1 acceptance. 1<pT<3 GeV/c.

The centrality classes are categorized by:
1. number of particles in the FTPC East acceptance -3.8<η<-2.8.
2. number of particles in the TPC |η|<1.

The dN/dη used in X-axis is the number of particles in the |η|<0.5.
 

More about process in PYTHIA:  http://home.thep.lu.se/~torbjorn/pythia81html/QCDProcesses.html.
 
  - SoftQCD:minBias         for minimum bias

  - HardQCD:all                 for QCD jet production above some minimum pT threshold

Data set:

PYTHIA simulation used starsim.C.

  - Soft QCD Minbias with Multiple Parton Interaction (MPI) on

SoftQCD:minBias = on

  - Soft QCD Minbias with Multiple Parton Interaction (MPI) off

SoftQCD:minBias = on
PartonLevel:MPI = off
 
 - Hard QCD with Multiple Parton Interaction (MPI) on

HardQCD:all = on
 
 - Hard QCD with Multiple Parton Interaction (MPI) off

HardQCD:all = on
PartonLevel:MPI = off
 
1<pT<3

|η|<1

pion, kaon and proton(antiproton) are used.

Event selection: mutliplicity in -3.8<η<-2.8.
 

Results:

FTPC centrality

1. Soft process with MPI on

TPC mutliplicity |η|<0.5 vs FTPC multiplicity -3.8<η<-2.8.

Gaussian area Y_jetlike  and  Pedestal C.
 

2. Soft process with MPI off

TPC mutliplicity |η|<0.5 vs FTPC multiplicity -3.8<η<-2.8.

Gaussian area Y_jetlike  and  Pedestal C.

 

3. HardQCD with MPI on

TPC mutliplicity |η|<0.5 vs FTPC multiplicity -3.8<η<-2.8.

Gaussian area Y_jetlike  and  Pedestal C.

4. HardQCD with MPI off

TPC mutliplicity |η|<0.5 vs FTPC multiplicity -3.8<η<-2.8

Gaussian area Y_jetlike  and  Pedestal C.

 

TPC centrality:

1. Soft process with MPI on

TPC mutliplicity |η|<0.5 vs FTPC multiplicity -3.8<η<-2.8.

Gaussian area Y_jetlike  and  Pedestal C.

2. Soft process with MPI off

TPC mutliplicity |η|<0.5 vs FTPC multiplicity -3.8<η<-2.8.

Gaussian area Y_jetlike  and  Pedestal C.

First point: fit failed.