Diapositive 1

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Study of short-lived resonances in ALICE
A. Badalà INFN Sezione di Catania- Italy for
the ALICE Collaboration

• Contents
• Physics motivations
• ALICE detector
• Results on strange resonances (K(892),?(1520),?(1
  020),..) from simulated p-p events _at_ 900 GeV
  and _at_14 TeV
• Summary

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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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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
Resonance mass shift and width broadening have
been suggested as a signature of chiral symmetry
restoration
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Resonances from jets
Recently suggestion to study chiral symmetry
restoration by comparing resonance production in
event classes based on azimuthal distribution
respect to jet direction
First attempt has been done studying h(high
pt)-?(1020) correlations
C. Markert, 23rd Winter Workshop on Nuclear
Dynamics Big Sky, Montana, USA
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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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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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 be 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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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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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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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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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.
Recent suggestion by Maiani et al. (Phys. Lett.
B645(2007)138) to use this observable to solve
the problem of the real quark composition of some
resonances as the fo(980)( or
?)
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ALICE ( A Large Ion Collider Experiment)
HMPID PID (RICH) _at_ high pT
TOF PID
EMCAL Jets reconstruction
TRD Electron ID
PMD ? multiplicity
ITS Low pT tracking Vertexing
TPC Tracking, dE/dx
PHOS ?, p0
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Reconstruction of short-lived resonances is
improved by optimal performance on 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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Reconstruction of short-lived resonances is
improved by optimal performance on primary
vertex reconstruction tracking efficiency
ITS TPC
In ALICE Kalman filter strategy allows a good
tracking performance down to very low momenta
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Reconstruction of short-lived resonances is
improved by optimal performance on primary
vertex reconstruction tracking efficiency momentum
resolution
?pt/pt lt0.7 for ptlt2 GeV/c
?pt/pt 3 at 100 GeV/c
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Reconstruction of short-lived resonances is
largely improved by optimal performance
on primary vertex reconstruction tracking
efficiency momentum resolution track impact
parameter particle identification
with ITS and TPC at low momenta
and TOF at high momenta
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Particle Identification
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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Study of short-life resonances in ALICE
Several activities are going on in ALICE
concerning the study of such resonances, both in
pp and AA collisions, with contributions from
several groups. (Other contributions to this
conference from P.Ganoti and D. Tapia-Takaki).
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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• Software code development
• Test distributed analysis of events
• Optimization of reconstruction tools
• Background estimation
• Efficiency evaluation

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Results from p-p events _at_ 900 GeV and 14 TeV

• Events of PYTHIA were generated and fully
  reconstructed using
• Realistic simulation of the detector response for
  the whole ALICE assembly
• Realistic clusters and tracks reconstruction

2 Data Sets
2 x 105 minimum bias p-p PHYTIA events _at_ 900
GeV. Running scenario at LHC startup 1.5 x 106
minimum bias p-p PHYTIA events _at_ 14 TeV (about
0.2 1-year data taking)
PDC06 data, distributed GRID analysis
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Study of the combinatorial background by the
mixed-event technique
Studied dependence on event selection
criteria ?Charged multiplicity ?z-vertex location
Only events with ?mlt5 and ?zv lt 3 cm mixed
Multiplicity
Comparison of the event mixing background to the
true combinatorial backgroung True background
(Signal) (True pairs)
z-vertex
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Like-sign technique also explored
p-p_at_900 GeV
Unlike sign
Like-sign
Comparison of the like-sign background to the
true combinatorial background
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Perfect PID
PID influence on K(892) reconstruction
Realistic PID
True
Found
p-p_at_900 GeV
Maxprob gt 0.7 (K) No PID (p)
Maxprob gt 0.7 (K) Maxprob gt 0.7 (p)
No thresh on maxprob
Perfect PID
Realistic PID
True K 4306 Found K 4139 S/B 0.11 S/vB
20.28
True K 7599 Found K 7488 S/B 0.138 S/vB
30.68
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?(1020) and ?(1520) with realistic PID
p-p_at_900 GeV
?
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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
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K(892)0 pT-analysis with realistic PID
p-p_at_14 TeV
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Correction matrix
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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
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Summary
? Short-lived resonances in pp collisions _at_ LHC
energies could be studied in ALICE from the very
beginning ? With a small sample of events
O(105) _at_ 900 GeV and realistic PID ?
Extraction of yields at least for K(892),
F(1020), ?(1520) ? Rough pT -
distribution for K(892) up to 1.5 GeV/c ?
Particle ratios F/K, ?/K, F/? measurable ?
Analysis of O(106) pp events at 14 TeV fully
reconstructed on the GRID ? Resonance
yields with large statistics ?
pT-analysis ? Correction matrix (y,pT) ?
Extension to other resonances is in progress.
K(892)0
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EXTRA SLIDES