Sheng-Qin Feng China Three Gorges University (CTGU)

IOPP, Wuhan China 1

Reduction of strange quark suppression and strange hadron production in p-p and A-A collisions at RHIC and LH

C

Sheng-Qin Feng

China Three Gorges University (CTGU)

IOPP, Wuhan China 2

Outline 1、Motivation

2、 PACIAE and strangeness production mechanisms

3、 strangeness productions of p-p and A-A interactions

4、 Summary

Based on:Long,HY, Feng, S-Q, Zhou,D-M, Yan, Y-L, Ma H-L and Sa, B-H, Physical Review C 84, 034905 (2011)Ren, X-W and Feng, S-Q, Chinese Physics C 38, 054102 (2014)Ren, X-W and Feng, S-Q submitted to PRCSa, Ben-Hao et al, Computer Physics Communications 183 (2012) 333–346

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1、Motivation

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1、Motivation

The investigation of strange hadron productions is an i

mportant ingredient in understanding the nature of QG

P in relativistic heavy ion collisions .

As the strange quark is heavier than up and down quarks,

production of strange hadrons is generally suppressed

relative to hadrons containing only up and down quarks. The

amount of strangeness suppression is an important research

topics.

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The differential transverse momentum yields ( spectra) and integrated yields at

central rapidity of have been measured by the

ALICE experiment during the commissioning phase of the LHC (December 2009)

with the very first proton-proton collisions. A sample of 250 k minimum bias pp c

ollisions at sqrt(s) = 0.9 TeV has been selected with triggers combining several fast

detectors .

Tp

0SK

LHC new experimental results

Strange particle production in proton-proton collisions at sqrt(s) = 0.9 TeV with ALICE at the LHC. ALICE collaboration, ， Eur.Phys.J.C71,2011:1594, arXiv:1012.3257

Strange Particle Production in pp Collisions at sqrt(s) = 0.9 and 7 TeV,The CMS Collaboration， JHEP 05 (2011) 064 , arXiv:1102.4282

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Pb-Pb Collisions at LHC

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Strangeness suppression

As the strange quark is heavier than up and down qua

rks, production of strange hadrons is generally suppre

ssed relative to hadrons containing only up and down

quarks. Originally, the suppression of s quark pair pr

oduction compared with u(d) pair production is assum

ed to be a ‘constant’ in the LUND string fragmentation

scheme (PYTHIA).

B. Andersson, G. Gustafson, G. Ingelman and T. Sjiistrand, Phys. Rep. 97 (1983) 31.

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Strangeness suppression

The mechanism of reduction of strange quark suppression has been studied in the early paper.

Later experiments during SPS have shown this suppression decreases with increasing collision energy.

Tai,A and Sa, B-H PLB409(1997)393-397

Sa, B-H and Tai, A, Phys. Rev. C 55 (1997) 2010.

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The effective string tension was introduced in PLB409-393 and assumed it to be increased with increasing reaction energy. Hence the strange quark production increases with increasing reaction energy.

It was assumed further that the effective string tension varies with reaction energy can be considered by the effective string tension as a function of the number and hardening of gluons in the string.

Tai,A and Sa, B-H PLB409(1997)393-397

Sa, B-H and Tai, A, Phys. Rev. C 55 (1997) 2010.

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We use the transport model PACIAE to study the strangeness production in pp collisions:

STAR@

ALICE@

CMS@ Prediction:

ALICE@

GeVs 200

GeVs 900

TeVs 7,9.0

TeVs 14,7,36.2

The relation between K/π ratio and reaction energies.


2、 PACIAE and strangeness production mechanisms

References:Sa Ben-hao, Zhou Dai-mei, Yan Yu-liang, LI Xiao-mei, Feng Sheng-qin, CAI Xu. Comput. Phys. Commun, 2012,183: 333-346SA Ben-hao, ZHOU Dai-mei, DONG Bao-guo, YAN Yu-liang, MA Hai-liang, LI Xiao-mei. J. Phys. G: Nucl. Part.Phys., 2009, 36: 025007; Yan Yu-liang, Zhou Dai-mei, Dong Bao-guo, Li Xiao-mei, Ma Hai-liang, Sa Ben-hao.Phys.Rev. C, 2012, 81: 044914; Zhou Dai-mei, Yan Yu-liang, Dong Bao-guo, Li Xiao-mei, Wang Du-juan, Cai Xu, Sa Ben-hao. Nucl.Phys. A, 2011, 860: 68


Remnant

Remnant Initial state radiation

Final state radiation

Hadronization

kf

lf

hadronrescattering

Decay

)(xf pi

)(xf pj

h

p

…

ˆd

dt

Sketch for pp dynamic simulation (PYTHIA & PACIAE.641)

p partonrescattering

parton distribution function

1

2

34

h

h

h


The PACIAE

PACIAE is a parton and hadron cascade model which consist of four stages of the parton initiation, parton re-scattering, hadronization,and hadron re-scattering.

In the PYTHIA model it is assumed that the pair produce with probability

22

expexp Tpm

qq


In this work, the dependence of effective string

tension on increasing reaction energy introduc

ed in PLB409-393 are used to discussed the str

angeness production of p-p collisions in the R

HIC and LHC energy regions


The PACIAE

where is the string tension of the pure string assumed to be 1 ～GeV/fm

represents the deviation scale of the multi-gluon string from the pure string.

0

10eff

1

20

2

0

0

2max

lnln

ln

n

j

Tj

T

ss

s

s

qq


3、 Strangeness productions of p-p and A-A interactions


Strange particles rapidity densities at midrapidity (|y| <0.5) in NSD pp collisions at with adj1(31)=0.18(D=0.1), adj1(32)=0.4 (D=0.3), and adj1(33)=0.5(D=0.4).

GeVs 200

Long,H-Y, Feng, S-Q, Zhou,D-M, Yan, Y-L, Ma H-L and Sa, B-H, Physical Review C 84, 034905 (2011)


Transverse momentum distribution of strange particles in NSD (non-single-diffractive) p-p collisions at . GeVs 200

Long,HY, Feng, S-Q, Zhou,D-M, Yan, Y-L, Ma H-L and Sa, B-H, Physical Review C 84, 034905 (2011)


GeVs 900Strange particles rapidity densities at mid-rapidity in inelastic pp collisions at

Strange particle production in proton-proton collisions at sqrt(s) = 0.9 TeV with ALICE at the LHC. ALICE collaboration, ， Eur.Phys.J.C71,2011:1594, arXiv:1012.3257


Transverse momentum distribution of strange particles in INEL pp collisions at

.GeVs 900


The strange particles rapidity densities at midrapidity in pp collisions at and . TeVs 7

TeVs 9.0


The strange particle

rapidity distributions in

NSD pp collisions at and .

TeVs 9.0

TeVs 7


The strange particle transverse momentum distributions in NSD pp collisions at and .

TeVs 9.0

TeVs 7


The PACIAE results at =2.36, 7, and 14 TeV indicate that the K/π ratio as a function of first grows up from 0.2TeV to 0.9TeV and then turns to saturation.

s

s









Summary

In summary, these results might indicate the un-negligible effect of the reduction of strange quark suppression mechanism.

Until now, we find that PACIAE can fit well

the strangeness productions in RHIC and LHC data. but for the multi-strangeness production, we still need to improve the fit results.

Documents

Sheng-Qin Feng China Three Gorges University (CTGU)