Download Physics at NICA , the view from LPI RAS

NICA round table III
06.11.08
Physics at NICA: the view from LPI RAS
A.V. Leonidov
Big goals:
• Qualitative and quantitative description of deconfined
matter and associated features of multiparticle production
• Description of the features of particle production related
to dense strongly interacting medium present
in nucleus-nucleus collisions and not present in
proton-proton and proton-nucleus ones.
• Remarks on “elementary” particle source its generalization
on high density case.
• Rescattering of “elementary” sources and transverse and
longitudinal spectra in pA and AB collisions.
• Event-by-event fluctuations of transverse momenta
Is the produced dense strongly interacting
matter homogeneous on the event-by-event basis?
• Gross features of multiparticle production at moderate energies
such as transverse spectra and particle yields equivalent in
ee
and pp
• Transverse spectra are of “thermal” form with a “temperature”
T=160-200 MeV.
• Same value as a coefficient in the Hagedorn spectrum
 (m) exp(m / T )
• Simplified description: hadronic string with hand-made
rules for its breaking and creation of transverse momentum
Quantitative picture
D. Kharzeev, K. Tuchin (2005)
P. Castorina, D. Kharzeev, H. Satz (2007)
• Fundamental mechanism of particle production is
a Hawking-Unruh radiation through the confinement
horizon – an interface between open color and hidden
phases.
• Based on close relations between Unruh radiation and
Schwinger pair creation mechanism
• Particle production through quantum tunneling
A fundamental challenge for theory is a generalization of the PKS
approach to dense deconfined sources and description of their
coexistence with hidden color hadronic phase.
At NICA energies: a quark-junction matter?
Gluon strings in baryons structured as a junction (have a “Mercedes” form)
Rescattering and transverse and longitudinal spectra in pA and AB
collisions
A.L., M. Nardi, H. Satz (1997)
Particle spectrum of a fireball at rest:
d 3 N0
V0

E cosh  y  exp  E cosh  y  T 
3
2
dydp d 2  2 
sinh  y   pl E
E  p2  m2
Particle spectrum of a moving fireball:
d 3 N0
V0

E cosh  y  
3
2
dydp d 2  2 

exp   E cosh(  )cosh Y  y   p sinh(  )cos      T
sinh     p m

Multiparticle production proceeds through creation of a string
of “elementary” sources shifted in transverse direction due to
rescattering
 p sinh    
d 3N
V0 E

d  dY  F Y ,    I 0 

3 
2
dydp 2  2 
T


 E cosh Y  y  cosh    

YL dY cosh Y  y   exp 
T

YL
F Y ,    g Y   f   
: cluster distribution function
in longitudinal and transverse
rapidity
Longitudinal cluster distribution
g Y    Y  Yl   Y  Yl 
Yl
yin
yin  coth  yin   1 sinh  yin 
ln

s mp

Works quite well for AB collisions at SPS energies
for protons and pions
Pion and nucleon rapidity spectra, Au-Au collisions
Cluster distribution in transverse rapidity
1/ 2
 4 
f AB      2 
  AB 
Distribution width controlled by
0
 2 
exp  2 
  AB 
2
 AB
  N A  NB  2   0
: fixed by reproducing pA transverse spectra


NA
3
2 rp2 RA n0
4
RA
1.12  A1/ 3
: number of rescatterings
n0  0.17 fm3
Pion and nucleon transverse momentum spectra, Au-Au collisions
• Reproduces pion and proton transverse spectra
in pA and AB collisions at SPS energies very well
with T=150 MeV.
• Problems with kaon transverse spectra
• Are the kaon spectra anomalous already at pA level?
• Aren’t we we putting in some flow by hand by using
the random walk in transverse rapidity? Random walk
in transverse momentum looks more natural from
the point of view of Regge phenomenology.
Event-by-event fluctuations in transverse momentum
A.L., M. Gazdzicki, G. Roland (1999)
Measure of event-by event fluctuations:
N
Z z
i 1
• Value of
i
and
 p 
Z2
N
 z2
zi  pi  p
events
 p calculated in LNZ approach too large at
SPS energies in nuclear collisions
• Fluctuation patterns are much more sensitive to genuine
nucleus-nucleus phenomena than spectra
• What is an event-by-event pattern in transverse momentum
fluctuations in pA ?
c
a
l
c
u
l
a
Is the produced dense strongly interacting matter
homogeneous on the event-by-event basis?
Early stage of high energy nuclear
collisions is inevitably inhomogeneous on
the event-by-event basis due to
“deconfined” degrees of freedom.
M. Guylassy, D. Rischke, B. Zhang (1997)
Such a hot-spot structure means that transverse energy density is
•
random
•
strongly correlated
Event-by-event versus averaging:
Inclusive averaging can be dangerous!
M. Kirakosyan, A.L. (2008)
Energy loss: spraying of WW proper field modes (e.g. of
a constituent quark) due to their interaction with the medium =>
medium-induced radiative loss
Main challenge:
Realistic microscopic description of domains of
deconfined dense strongly interacting matter as
created in nuclear collision and its incorporation
in the MC generators