Diapositive 1

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Study of short-lived resonances in ALICE
A. Badalà INFN Sezione di Catania

• Contents
• Physics motivations
• Some SPS and RHIC results
• ALICE detector performance
• Some results from simulated p-p events _at_14 TeV
• Summary

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A. Badalà- Convegno Naz. Fisica ALICE- LNF
12-14/11/07
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Why short-lived resonances?
Resonances may give information on the dynamics
and on the chiral property of the hot and dense
matter which is produced in the collision
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Resonances as a probe of chiral symmetry
restoration
The best probes are resonances reconstructed by
their leptonic decay channel since leptons are
less likely to rescatter in the hadronic medium.
However regenerated resonances from the late
hadronic phase feed down into this signal
To study chiral symmetry restoration in terms of
mass shift and width broadening, resonance decays
from the early stage of the medium need to be
extracted
Hadronic decay channel probes late stages of the
collision
Leptonic decay channel probes all stages of the
collision
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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NA60 results
A significant excess of ??- pairs is observed
above the yield expected from neutral meson
decay. Its shape is consistent with a
contribution from ??- ? annihilation
Models based on in-medium ? broadening scenario
seem able to reproduce data, while moving mass
models seem ruled out
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Resonances from jets
Recently suggestion to study chiral symmetry
restoration by comparing resonance production
(reconstructed by their hadronic decay) in event
classes based on azimuthal distribution respect
to jet direction
C. Markert, 23rd Winter Workshop on Nuclear
Dynamics Big Sky, Montana, USA and SQM07, Levoca
(Slovakia)
High pT resonances from the away side jet could
be modified by the partonic medium, but they are
so fast to have low probability to be affected by
the hadronic medium
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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?(1020) from same/away side in/out of plane
near - side
side1

• Trigger particle
• hadron pT gt 4.0 GeV/c
• Associated particle
• resonance ?(1020)
• ltpTgt 0.9 GeV/c

away- side
side2
No mass shift or width broadening visible
Next step ? with higher pt
C. Markert, SQM07, Levoca (Slovakia)
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Interactions of resonances in hadronic nuclear
medium

• The yields of resonances detected by their
  hadronic decay can be influenced by effects of
  rescattering and regeneration which depends on
• the time between the chemical and the thermal
  freeze-out
• the lifetime of the resonances
• the interaction cross-section of the decay
  particles.

Due to the rescattering , resonances may not be
reconstructed
Pseudo-elastic collisions may regenerate
resonances
Rescattering
Regeneration
No interaction
The resonances may probe the timescale between
the chemical and the kinetic freeze-out
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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pp and AuAu _at_ ?sNN 200 GeV
Resonance/non-resonance ratio
B.I. Abelev (Star Collaboration) nucl-ex 0604019
At RHIC energies thermal models are able to
reproduce the ratios of stable particles Deviation
s from these ratios have been used to estimate
the time interval between thermal and chemical
freeze-out
?? (UrQMD) 133 fm/c
Suppression of K and ?
Lower limit (??lt4 fm/c, T160 MeV) from measured
K/K and ?/? ratio by a thermal model with a
rescattering phase (G. Torrieri and J. Rafelski,
Phys. Lett. B509 (2001) 239 and C. Market, J.
Phys. G. Nucl. Part. Phys. 31 (2005) 1045)
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Main observables concerning the study of
resonances in pp and AA collisions
() Extraction of the signal/yields () Mass and
widths of resonances () Transverse momentum and
transverse mass spectra () Particle
ratios Elliptic flow Nuclear modification
factors RCP and RAA
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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K(892) ? p K B.R. 1 c? 4 fm
STAR Preliminary
STAR Preliminary
vsNN 200 GeV
vsNN 200 GeV
vsNN 200 GeV
vsNN 62 GeV
STAR Preliminary
STAR collaboration, Phys. Rev. C71, 64902 (2005)
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S(1385) ? ? ? B.R. 0.88 c? 5.5 fm
?(1520) ? pK B.R. 0.45 c? 12.6 fm
dAu vsNN200 GeV
dAu vsNN200 GeV
STAR Preliminary
pp vsNN200 GeV
AuAu vsNN200 GeV
Star collaboration, Phys. Rev. Lett.
96(2006)132301
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F(1020) ? K K- B.R. 0.49 c? 44 fm
AuAu vsNN62 GeV
dAu vsNN200 GeV
PHENIX
STAR Preliminary
AuAu vsNN200 GeV
PHENIX
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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F(1020) ? ee- B.R. 0.000296 c? 44 fm
dAu vsNN200 GeV
PHENIX
PHENIX
S. Huang DIS2007, Munich,Germany
AuAu vsNN200 GeV
PHENIX
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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?0(770) ? p p- B.R. 1 c? 1.3 fm
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Mass and widths of resonances

• Even in the absence of the phase transition,
  temperature and density dependent modifications
  of the mass, width and shape of short-lived
  resonances are predicted. Possible explanations
  are
• Dynamical interactions with the surrounding
  matter (M. Bleisher and H. Stocker, J. Phys.
  G30(2004)S111, E. V. Shuryak and G.E. Brown,
  Nucl. Phys. A717(2003)322)
• Phase-space distortions
• (S. Pratt and W. Bauer, Phys. Rev.
  C68(2003)064905, R. Rapp Nucl.Phys.
  A725(2003)254)

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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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K ? Mass and Width

• K0 ? pT lt 1 GeV ? mass shift of 10 MeV observed
• K and K0 ? pT gt 1 GeV ? mass agrees with PDG
  for all systems within errors
• Width agrees with PDG for all systems within
  errors

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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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F ? Mass and Width
STAR Preliminary

• pT gt 1 GeV ? mass and width agree with MC and PDG
  for all systems
• pT lt 1 GeV ? mass agrees with MC for all systems
  within errors
• pT lt 1 GeV ? width higher than MC for all systems
  ? real physics or detector effect?

PDG
STAR Preliminary
PDG
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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? mass and width
dAu vsNN200 GeV
AuAu vsNN200 GeV
AuAu vsNN62 GeV

• Mass and width of ? meson reconstructed by KK
  channel do not depend on centrality
• Mass and width in agreement with PDG for all
  system

S. Huang , DIS2007, Munich Germany
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Transverse spectra

• Particle production in pp collisions dominated by
  two mechanisms
• soft, thermal-like processes at low pT
  (exponential shape)
• Hard, parton-parton processes at high pT
  (power-law shape)

A unique (Levy) function is used to parametrize
the overall shape
STAR Coll, PRC71(2005)064902
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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K0 Transverse Momentum Spectra
STAR PRELIMINARY
STAR PRELIMINARY
STAR PRELIMINARY
AuAu _at_62 GeV
S. Dash SQM07
K0 spectra fitted by an exponential function

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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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??KK- Spectra
STAR Preliminary

• Change of F spectra from exponential in central
  AuAu collisions to Levy function shape in
  peripheral AuAu ? Matter formed in peripheral
  AuAu collisions favors hard F production

STAR Preliminary
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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SPS ? puzzle NA49NA50
NA50 reported a ? yield measured via dileptons
larger than yield determined by NA49 in KK-
channel. Further, the mT spectra exhibit a
different inverse slope parameter
PbAu _at_E/A158 GeV
NA45 has studied the leptonic and the kaon decay
modes of the ? meson.

• Yield and inverse slope parameter agree in both
  decay modes
• Results are in agreement with the NA49 results

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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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SPS results for ????- (NA60)
NA60 In-In (pT lt 1.6 GeV/c) NA49 Pb-Pb(pTlt1.6
GeV/c) NA50 Pb-Pb(pTgt1.2 GeV/c)
Difference between NA50 and NA49 was not due to
different decay channel
Agreement with NA49 when the fit is performed in
the same range. T value grows with the
centrality of the collision
NA60 In-In (pT gt 1.1 GeV/c) NA49 Pb-Pb(pTlt1.6
GeV/c) NA50 Pb-Pb(pTgt1.2 GeV/c)
Lower T values and flatter distribution if the
fit is performed in the same pT range of
NA50. This hints for the presence of radial flow
? blast wave analysis
M. Floris, SQM07
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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F Production ? KK- and ee-
ee-
KK-
A. Kozlov (Phenix coll.),QM2005

• The leptonic channel yield is a little higher
  than hadronic channel
• More accurate measurement is required to confirm
  if there is branching ratio modification

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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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F ? KK- STAR-PHENIX comparison
STAR
AuAu _at_ vsNN 200 GeV

• F production ? there is a factor of 2 difference
  between PHENIX and STAR

PHENIX
STAR PHENIX
J. Rafelski et al.,Phys.Rev. C72 (2005) 024905
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Resonance suppression (system size dependence)
C. Markert, SQM07
Suppression scales with dNch/dy system size
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Resonance suppression (energy dependence)
Life-time fm/c K(892) 4.0 ? (1020)
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S. Dash SQM2007
For K seems less re-scattering at lower energies
in peripheral collisions Lower density ?
smaller interactions cross section? Shorter
hadronic lifetime ? less hadronic interactions ?
C. Markert, SQM07
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Elliptic flow
Baryons
For KET gt1 GeV, mesons and baryons scale
separately
Mesons
S. Adare et al. (Phenix coll.) nucl-ex 0608033
Universal scaling is observed for mesons and
baryons when quark number scaling is employed
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Elliptic flow for resonances
Measurement of flow for meson and baryon
resonances is of great interest to further
validate the picture sorting of this scaling i.e.
that partonic collectivity dominates the
transverse expansion dynamics.
Au-Au _at_200 GeV
Mass ? meson Mass proton
v2 of ? mesons confirms this universal scaling
S. Afanasiev et al. (PHENIX Coll. ) nucl-ex
0703024
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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K(892) elliptic flow
Using the deviations of the measured flow
coefficient v2 from the scaling law given by the
quark recombination formalism to probe the amount
of hadronic final state interactions

• Partonic generation ? resonances are produced in
  a hadronizing QGP ? v2 scales with n2
• Hadronic generation ? resonances are produced in
  the hadronic final state via hadron-hadron
  scattering ?v2 scales with n4 (KK?22)

C. Nonaka, et al., Phys.Rev.C69031902,2004
AuAu _at_ 200 GeV
Most of K are produced in partonic phase and
only a small quantity is originated in
rigeneration (Need more precise measurements)
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Nuclear Modification Ratios (RCP) for resonances
RHIC results have shown as, in the intermediate
pt region, nuclear modification factors depend on
the constituent quarks rather than on particle
mass.
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Nuclear Modification Ratios (RCP) for resonances
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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ALICE performance on primary vertex reconstruction
Primary vertex in ALICE is reconstructed by means
of tracklets in the two innermost pixel layers
and by a Kalman vertex procedure for p-p events
?lt 40 ?m
? 5 ?m
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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ALICE performance on track impact parameter
Pb-Pb
p-p
? lt60 ?m _at_ ptgt 1GeV/c
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Tracking efficiency
In ALICE Kalman filter strategy allows a good
tracking performance down to very low momenta
Momentum resolution
?pt/pt()
pt(GeV/c)
pt(GeV/c)
?pt/pt lt0.7 for ptlt2 GeV/c
?pt/pt 3 at 100 GeV/c
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ALICE performance on particle identification
with ITS and TPC at low momenta
and TOF at high momenta
stable hadrons (p, K, p) 100 MeV lt p lt 5 GeV
(few 10 GeV) dE/dx in silicon (ITS) and gas
(TPC) Time-of-Flight (TOF) Cerenkov
(RICH) decay topology (K0, K, K-, L) K and L
decays up to at least 10 GeV leptons (e, m),
photons, p0, h electrons in TRD p gt 1 GeV,
muons p gt 5 GeV, p0 in PHOS 1 lt p lt 80 GeV
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Mass resolution
K(892)
?(1020)
Mass resolution 1.3 MeV/c2
Mass resolution 3 MeV/c2
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Short-lived resonances in ALICE
Pb-Pb events studied for PPR
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Study of short-life resonances in ALICE
Now several activities are going on in ALICE
concerning the study of such resonances in pp
collisions (using PDC06 events). In particular,
resonances reconstructed by their hadronic decay
are studied in PWG2. Reconstruction of ?(1020)
by its ee- decay has also been probed. Catania
people have expecially worked on reconstruction
of
Resonance K(892)
F(1020) ?(1520) Decay channel
(B.R.) K? (100) KK-
(49) N K (45) Width
MeV/c2 50.8
4.5 15.6
Life time fm/c
3.9 44
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Started study of ??- correlations

• Software code development
• Test distributed analysis of events
• Optimization of reconstruction tools
• Background estimation
• Efficiency evaluation

In next talk results obtained in p-p simulated
events at 900 GeV and 14 TeV
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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F(1020) signal
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Background estimation
For K(892)0 BAD agreement between background
estimated by event-mixing technique and true
background
?1
?2
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A. Badalà- Convegno Naz. Fisica ALICE- LNF
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Summary

• Many interesting results on short-lived
  resonances from SPS and RHIC
• ALICE performances (tracking and PID) give us the
  possibility to do well this kind of physics
• We are working to be ready to analyze first data

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EXTRA SLIDES
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K(892)0 pT-analysis with realistic PID
p-p_at_14 TeV
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Resonance yield
Overall number of particles antiparticles
generated by PYTHIA_at_900 GeV ?1.34
K(892)/event ?0.08 ?(1520)/event ?0.23
F(1020)/event
A. Badalà- SQM07- Levoca 24/06/-29/06/07
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?(780)
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K(892)0
1 GeV/cltptlt2 GeV/c
2 GeV/cltptlt3 GeV/c
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Signal extraction (unlike-sign)
Inside same event, correlations between K and p-
candidates K- and p candidates Evaluate
invariant mass spectrum
Example K(892) ? Kp (100)
Mixed-event technique
Combinatorial background
Like-sign technique
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ALICE PID
A common BAYESIAN approach is adopted by every
ALICE detector performing PID The probability
w(is) to be a particle of type i (i e,?, ?, K,
p...) if a signal s (dE/dx, TOF,...) is detected,
is
r(si)(Detector response function) conditional
probability density functions to get a signal s
in a detector, if a particle of i-type hits the
detector
Ci (particle concentration) a priori probability
to find a particle of type i in the detector
Probability to be a particle of i-type (i e, ?,
?, K, p, ), if we observe a vector S sITS,
sTPC, sTOF, of PID signals in different
detectors is
Combinated response function
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Temperature and lifetime from ?(1520) /? and K/K
G. Torrieri and J. Rafelski, Phys. Lett. B509
(2001) 239
Dependence of the two ratios K/K and ?(1520)/?,
on the chemical freeze-out temperature and time
interval between chemical and kinetic freeze-out.
Model termally produced particle yields
rescattering phase. Then regeneration is not
taken into account.
preliminary
0-20 most central AuAu
C. Market, J. Phys. G. Nucl. Part. Phys. 31
(2005) 1045.
?(1520)/? 0.034 ? 0.011 ? 0.013
K(892)/K 0.19 ? 0.05
results between T 175 MeV gt ?? 4-6
fm/c ?? 0 fm/c gt T 110-130 MeV
?? gt 4 fm/c for T160 MeV
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Results for p-p collisions _at_14 TeV
1.5 x 106 PYTHIA events
Detailed analysis for K(892)0 on PID perfomances
Found K(2?)89182 True K(2?)85360
K
Mass resolution 3MeV
A. Badalà- SQM07- Levoca 24/06/-29/06/07
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?(1020) and ?(1520) with realistic PID
p-p_at_14 TeV
Mass resolution 1.2 MeV
?(1020)
?(1520)
?(1020)
?(1520)
True ?3879 Found ?3649
True ?4893 Found ?4967
A. Badalà- SQM07- Levoca 24/06/-29/06/07
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pp- Invariant Mass Distribution from Monte Carlo

• HIJING events with a realistic simulation of
  detector response

STAR Preliminary
?0(770) ? p p-
?sNN 200 GeV
?0

• Use ? and K0 shape from HIJING to fit the
  data
• K0 signal is fixed using STAR measurement
  

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K(892)0 like-sign / true background
Good agreement in all bins of pT
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K(892)0 event mixing / true background
BAD agreement except for bins of very small pT
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f1f2 correlations for pK pairs

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?0 ? Mass
STAR Preliminary

• Mass shift observed for all systems
• Systematic errors shown for Minimum Bias dAu 200
  GeV

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? signal
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Formation of hadronic resonances (from jets) in
a chiral medium
Formation time arguments a.) General
pQCD Formation time fm/c pT GeV Formation
time fm/c 1/mass b.) Specific string
fragmentation (PYTHIA) formalism Gallmeister,
Falter, PLB630, 40 (2005) Intermediate pT
resonances form early c.) Vitev et al.
(hep-ph/0611109) High pT heavy particles and
resonances form early
Low pt High pt
Near side No medium or late hadronic medium No medium
Away side Late hadronic medium Partonic or early hadronic medium (depend on formation time) CSR ?
Side 1 2 Late hadonic medium Early hadronic medium
Need to determine the right momenta for trigger
and resonance particle