Transcript Document

Reduction of strange quark
suppression and strange hadron
production in p-p and A-A collisions
at RHIC and LHC
Sheng-Qin Feng
China Three Gorges University (CTGU)
IOPP, Wuhan China
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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 PRC
Sa, 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
important ingredient in understanding the nature of
QGP 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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LHC new experimental results
The differential transverse momentum yields (
central rapidity of K 0
S





pT
spectra) and integrated yields at
 

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
collisions at sqrt(s) = 0.9 TeV has been selected with triggers combining several
fast detectors .
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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B. Andersson, G. Gustafson, G. Ingelman and T. Sjiistrand, Phys. Rep. 97
(1983) 31.
Strangeness suppression
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. Originally, the suppression of s quark
pair production compared with u(d) pair production is
assumed to be a ‘constant’ in the LUND string
fragmentation scheme (PYTHIA).
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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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Tai,A and Sa, B-H PLB409(1997)393-397
Sa, B-H and Tai, A, Phys. Rev. C 55 (1997) 2010.
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.
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 We use the transport model PACIAE to
study the strangeness production in pp
collisions:
STAR@ s  200 GeV
ALICE@ s  900 GeV
The relation between
CMS@ s  0 .9 , 7TeV
K/π ratio and reaction
 Prediction:
energies.
ALICE@ s  2 .36 , 7 , 14 TeV
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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: 333-346
SA 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 Benhao.Phys.Rev. C, 2012, 81: 044914;
Zhou Dai-mei, Yan Yu-liang, Dong Bao-guo, Li Xiao-mei, Wang Du-juan, Cai Xu, Sa Benhao. Nucl.Phys. A, 2011, 860: 68
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Sketch for pp dynamic simulation
(PYTHIA & PACIAE.641)
Final state
radiation
Initial state
radiation
Remnant
3
p
h
4
1
2
p
fi ( x)
parton distribution
function
fk
d
p
f j ( x)
…
hadron
rescattering
h
fl
dtˆ
h
Decay
p
Remnant
h
parton Hadronization
rescattering
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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.
qq
In the PYTHIA model it is assumed that the
pair produce with probability
 m 2
exp 




 pT2
 exp 









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In this work, the dependence of effective string
tension on increasing reaction energy
introduced in PLB409-393 are used to
discussed the strangeness production of p-p
collisions in the RHIC and LHC energy
regions
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The PACIAE
 eff   0 1   

where  0 is the string tension of the pure qq
string assumed to be 1 ～GeV/fm
 
  T2 max
ln 

s0

 s 

ln 
s 
 0 





2
  Tj
ln 
j 2
 s
 0
n 1




represents the deviation scale of the multigluon string from the pure string.
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3、Strangeness productions of p-p and A-A interactions
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Strange particles rapidity densities at s  200GeV
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).
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)
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Transverse momentum
distribution of strange
particles in NSD (nonsingle-diffractive) p-p
collisions at s  200GeV .
Long,HY, Feng, S-Q, Zhou,D-M, Yan, Y-L, Ma H-L
and Sa, B-H, Physical Review C 84, 034905 (2011)
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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 particles rapidity densities at mid-rapidity in inelastic pp collisions at s  900GeV
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Transverse
momentum
distribution
of strange
particles in
INEL pp
collisions at
s  900GeV.
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The strange particles rapidity densities at
midrapidity in pp collisions at s  0.9TeV
and s  7TeV .
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The strange particle
rapidity distributions in
NSD pp collisions at s  0.9TeV
and s  7TeV .
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The strange particle
transverse momentum
distributions in NSD pp
collisions at s  0.9TeV
and s  7TeV.
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The PACIAE results at s
=2.36, 7, and 14 TeV
indicate that the K/π
ratio as a function of
first grows up from s
0.2TeV to 0.9TeV and
then turns to saturation.
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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.
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