衝突エネルギー走査により QCD相構造に迫る試み

Baryon vs Proton Number
Fluctuations
MK, Asakawa, PRC85,021901C(2012); PRC86, 024904(2012)


are experimentally observable
Proton # Cumulants @ STAR-BES
STAR,QM2012
Something
interesting??
Nucleon Isospin as Two Sides of a Coin
N
p
n
Nucleons have
two isospin states.
MK, Asakawa,2012
Nucleon Isospin as Two Sides of a Coin
a coin
N
p
n
Nucleons have
two isospin states.
Coins have two sides.
MK, Asakawa,2012
Slot Machine Analogy
=
+
P (N)
N
P (N)
N
Extreme Examples
Fixed # of coins
Constant probabilities
N
N
N
N
Reconstructing Total Coin Number
P (N )=
P (N )B1/2(N ;N )
:binomial distr. func.
Nucleon Isospin in Hadronic Medium
 Isospin of baryons can vary after chemical freezeout
via charge exchange reactions mediated by D(1232):
cross section
200mb=20fm2
D(1232)
cross sections of p
2
1:2
1
2:1
3
decay rates of D
D(1232)
cross sections of p
2
1:2
1
2:1
3
decay rates of D
D(1232)
cross sections of p
2
1:2
1
2:1
3
decay rates of D
Lifetime to create D+ or D0
BW for s & thermal pion
10~20fm
mesons
time
kinetic f.o.
chem. f.o.
hadronize
Nucleons in Hadronic Phase
• rare NN collisions
• no quantum corr.
baryons
• many pions
Probability Distribution


Detector
binomial distribution func.
 for any phase space in the final state.
Difference btw Baryon and Proton Numbers
(1)
deviates from the equilibrium value.
(2) Boltzmann (Poisson) distribution for
genuine info.
For free gas
noise
Summary
 Baryon and proton number fluctuations are different in
nonequilibrium medium. To see non-thermal contribution,
baryon number is better.
 Formulas to reveal baryon # cumulants in experiments.
 Experimental analysis of baryon # fluctuations may verify
 signals of QCD phase transition
 speed of baryon number diffusion in the hadronic stage.
Future Work
 Refinement of the formulas to incorporate
nonzero isospin density / low beam energy region
 Discussion on time evolution of fluctuations @STAR

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