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XI GDRE WORKSHOP
Heavy Ions at Relativistic Energies
SUBATECH, Nantes, France
June 29 - July 13, 2011
Pion femtoscopy from ALICE
Jan Pluta
Faculty of Physics
Warsaw University of Technology
ALICE-femto one year ago?
(some results presented during the last GDRE workshop, July 2010)
Pion source size from STAR
STAR, Phys. Rev. C 80 (2009) 24905
STAR, arXiv:1004.0925 [nucl-ex]
Au + Au
Cu + Cu
p+p
(various ways
of fitting)
pT dependence of pion source size similar in nuclear and pp collisions
Dariusz Miskowiec, Particle correlations in ALICE, Physics at the LHC,
3 Hamburg, 10-Jun-2010
Identical pion correlation functions
Bose-Einstein peak clearly visible
Dariusz Miskowiec, Particle correlations in ALICE, Physics at
the LHC, Hamburg, 10-Jun-2010
4
4
Multiplicity and transverse momentum dependence
identical pions
Dariusz Miskowiec, Particle correlations in ALICE, Physics
at the LHC, Hamburg, 10-Jun-2010
unlike-sign pions
baseline has to be treated properly
5
Multiplicity dependence
for comp.: nuclear collisions
M. Lisa, Ann. Rev. Nucl. Part. Sci. 55, 357
Dariusz Miskowiec, Particle correlations in ALICE, Physics at the
LHC, Hamburg, 10-Jun-2010
6
visible dependence in pp 
HBT radii depend on
multiplicity rather than on
collision geometry
Transverse momentum dependence
no significant dependence on
transverse momentum
for comparison: in
nuclear collisions
Dariusz Miskowiec, Particle correlations in ALICE, Physics at
the LHC, Hamburg, 10-Jun-2010
7
7 TeV and new 900 GeV data
identical pion correlations
120 M events at 7 TeV
2.1 M events at 0.9 TeV
Dariusz Miskowiec, Particle correlations in ALICE, Physics at
the LHC, Hamburg, 10-Jun-2010
high-q baseline flatter at 7 TeV
8
π+ π -
correlations at 7 TeV
Coulomb
K0 S
rich resonance structure
ω
ρ
f0
f2
low-q baseline steeper at 7 TeV
 origin: jets
Dariusz Miskowiec, Particle correlations in ALICE, Physics at
the LHC, Hamburg, 10-Jun-2010
high-q baseline flatter at 7 TeV
 origin: momentum cons.
9
one year after …
ALICE – femto papers
Two-pion Bose-Einstein correlations in pp collisions at sqrt(s)=900 GeV.
By ALICE Collaboration (K. Aamodt et al.). Jul 2010. 13pp. Temporary entry
Published in Phys.Rev.D82:052001,2010.
e-Print: arXiv:1007.0516 [hep-th]
Femtoscopy of pp collisions at sqrt{s}=0.9 and 7 TeV at the LHC with two-pion Bose-Einstein
correlations. By ALICE Collaboration (K. Aamodt et al.) CERN-PH-EP-2010-083, Jan 2011. 21pp.
e-Print: arXiv:1101.3665 [hep-ex]
Two-pion Bose-Einstein correlations in central Pb-Pb collisions at $sqrt(s_NN)$ = 2.76 TeV.
By ALICE Collaboration (K. Aamodt et al.). CERN-PH-EP-ALICE-2010-006, Jan 2011. 18pp.
Published in Phys.Lett.B696:328-337,2011.
e-Print: arXiv:1012.4035 [nucl-ex]
Quark Matter’ 2011 - presentations
Examples of correlation functions
…in spherical harmonics
…in Cartesian coordinates
Multiplicity dependence
Momentum - dependence
The energy (in)dependence
of the emission region size
The change of energy almost
one order of magnitude !!!
The non-femtoscopic
background
MC -simulations
Non-identical pions
π+π - pairs
Fitting the
correlation
function
Bowler-Sinyukov formula
Final functional form
B-background fit
Conclusions
•
•
•
•
Linear scaling wit dN/dɳ seen for all energies
kT dependence consistent with hydro
No common scaling for pp and AA
No collision energy dependence of femtoscopic
radii for pp collisions
• Radii in Pb-Pb collisions at LHC 30% larger than
in AuAu collisions at RHIC
• Problem with non-femtoscopic correlations