Color Reconnection(CR) effect on particle yeild

Introduction

Pythia8 divide QCD process into two groups, one is Hard QCD the other one is Soft QCD

Soft QCD include non-diffractive elastice and single-diffractive and double-diffractive

in this plot we generate 2M events, we can see the elastic process dominate in low pt hat and the non-diffractive process dominate in high pt.

Pythia8 divide the generated Level into two groups, one is Parton Level and the other one is Hardronization Level, in the Parton Level there is a CR switch which used to control the CR effect on Parton shower.

now there are four kinds of CR modes in Pythia8, the default one is MPI model, the second one is New QCD model In this Twiiki we try to investigate the CR effect on the difference of spectra yield.

we select the Lambda ,Kshort, proton and pi spectrum as a the measurements and pythia8

Firstly we Study the CR effect on Inclusive and UE baryon/meson ratio ,and Then study the Different CR model effect on Hard/Soft QCD process on inclusive baryon/meson ratio.

1. CR effect on Inclusive and UE baryon/meson ratio

We use the pythia 8 with Tune 4C generate 0.5M events in 8 pt hard bins ( 5,11,21,36,57,84,117,159,Inf) and set the Hard QCD process on to select with CR on/off

Generator : pythia 8, version 8029

CR model : MPI

Process : Open all Hard QCD process (HardQCD:all = on)

Tune : Tune 4C

Events : 0.5M per pt hard bin

Special Cut: Decay time less than 10 mm/c (ParticleDecays:tau0Max = 10)

Jet : R=0.4, anti-kt, |eta| <0.5

The UE Estimation: Band Method, we select the particles in the region which have a relation to leading jet with pi /3 <DeltaPhi < 2pi/3 and |eta| less than 0.9 as UE particles,It's a rectangle in eta-phi

1.1 Inclusive baryon/meson ratio

Please Check the 2.2 and 2.3 below

1.2 UE - Band Method

Estimate UE in the band region have a relation : pi /3 <DeltaPhi < 2pi/3 and eta less tjhan 0.9

2.Two CR mode effect in Soft and Hard QCD

2.1 Configure

Pythia8, Tune 4C, energy 8TeV, 0.5M Events in soft QCD ,and 0.5M Events in each pt hard bin in Hard QCD

CR : MPI / New QCD

Generator : pythia 8, version 8029

Process : Hard QCD : open all Hard QCD process (HardQCD:all = on) / Soft QCD :open all soft QCD process(SoftQCD:all=on)

Tune : Tune 4C

Events : 0.5M events per pt hard bin for HardQCD / 0.5M events for SoftQCD

Special Cut: Decay time less than 10 mm/c (ParticleDecays:tau0Max = 10) which used to select Lambda/kshort

2.2 Inclusive proton/pion Ratio w/ and w/o CR

These four plots show the Information about inclusive proton/pion Ratio w/ and w/o CR

The first two plots show the inclusive spectra of proton and pi, Soft QCD w/ a pt <5GeV/c cut and Hard QCD w/ a pt <10GeV/c

The third one is the inclusive proton/pion Ratio w/ and w/o CR, and the last one is the ratio with CR on over CR off

2.3 Inclusive Lambda/Kshort Ratio w/ and w/o CR

These four plots show the Information about inclusive Lambda/Kshort Ratio w/ and w/o CR

The first two plots show the spectra of inclusive lambda and kshort, Soft QCD w/ a pt <5GeV/c cut and Hard QCD w/ a pt <10GeV/c

The third one is the inclusive Lambda/Kshort Ratio w/ and w/o CR, and the last one is the ratio with CR on over CR off

3 Conclusion

Different CR modes have a large influence in lower pt than high pt, in baryon/meson plots