Study of short-lived resonances in ALICE A. Badal à – INFN Sezione di Catania- Italy for the ALICE Collaboration Contents Physics motivations ALICE detector Results on strange resonances (K*(892),  (1520),  (1020),..) from simulated p-p 900 GeV TeV Summary

Why short-lived resonances? Resonances are strongly decaying particles which have lifetimes of about a few fm/c (i.e  resonance ~  fireball ) Resonances c  (fm)  (770)   +  f 0 (980)   +  K*(892) 0  K  3.9  (1520)  Kp 13  (1020)  K + K - 44  Modifications of properties of resonances (peak,width) Partial chiral symmetry restoration Interaction of the resonances and/or their daughters with fireball medium Resonances may give information on the dynamics and on the chiral property of the hot and dense matter which is produced in the collision A. Badalà- SQM07- Levoča – 24/06/-29/06/07 2

Resonances as a probe of chiral symmetry restoration Resonance mass shift and width broadening have been suggested as a signature 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 A. Badalà- SQM07- Levoča – 24/06/-29/06/07 R. Arnaldi et al. (NA60 Collaboration) Phys. Rev. Lett. 96(2006) 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 NA60 RESULTS 158AGeV 3

Resonances from jets High p T 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 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 p t )-  (1020) correlations C. Markert, 23 rd Winter Workshop on Nuclear Dynamics Big Sky, Montana, USA A. Badalà- SQM07- Levoča – 24/06/-29/06/07 4

Interactions of resonances in hadronic nuclear medium No interaction Rescattering Due to the rescattering, resonances may not be reconstructed Regeneration Pseudo-elastic collisions may regenerate resonances 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. The resonances may probe the timescale between the chemical and the kinetic freeze-out A. Badalà- SQM07- Levoča – 24/06/-29/06/07 5

p+p and  s NN =200 GeV Suppression of K* and  * A. Badalà- SQM07- Levoča – 24/06/-29/06/07 Resonance/non-resonance ratio B.I. Abelev (Star Collaboration) nucl-ex At RHIC energies thermal models are able to reproduce the ratios of stable particles Deviations from these ratios have be used to estimate the time interval between thermal and chemical freeze-out  (UrQMD) = 13±3 fm/c Lower limit (  <4 fm/c, T=160 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 ) 6

(*) Extraction of the signal/yields (*) Mass and widths of resonances (*) Transverse momentum and transverse mass spectra (*) Particle ratios Elliptic flow Nuclear modification factors: R CP and R AA Main observables concerning the study of resonances in pp and AA collisions 7

Elliptic flow Baryons Mesons For KE T >1 GeV, mesons and baryons scale separately Universal scaling is observed for mesons and baryons when quark number scaling is employed A. Badalà- SQM07- Levoča – 24/06/-29/06/07 S. Adare et al. (Phenix coll.) nucl-ex

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. Mass  meson ~ Mass proton v 2 of  mesons confirms this universal scaling S. Afanasiev et al. (PHENIX Coll. ) nucl-ex GeV A. Badalà- SQM07- Levoča – 24/06/-29/06/07 9

Nuclear Modification Ratios (R CP ) for resonances RHIC results have shown as, in the intermediate p t 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 f o (980)( or ?) A. Badalà- SQM07- Levoča – 24/06/-29/06/07 10

ALICE ( A Large Ion Collider Experiment ) ITS Low p T tracking Vertexing TPC Tracking, dE/dx TRD Electron ID TOF PID HMPID PID high p T PHOS γ, π 0 PMD γ multiplicity MUON-ARM μ-pairs MUON-ARM μ-pairs A. Badalà- SQM07- Levoča – 24/06/-29/06/07 EMCAL Jets reconstruction 11

Reconstruction of short-lived resonances is improved by optimal performance on: vertex reconstruction Pb-Pb p-p 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  < 40  m  ~ 5  m A. Badalà- SQM07- Levoča – 24/06/-29/06/07 12

In ALICE Kalman filter strategy allows a good tracking performance down to very low momenta ITS + TPC A. Badalà- SQM07- Levoča – 24/06/-29/06/07 13

 p t /p t ~ 3 % at 100 GeV/c  p t /p t (%) p t (GeV/c)  p t /p t <0.7% for p t <2 GeV/c A. Badalà- SQM07- Levoča – 24/06/-29/06/07 14

with ITS and TPC at low momenta… and TOF at high momenta… A. Badalà- SQM07- Levoča – 24/06/-29/06/07 15

stable hadrons ( , K, p): 100 MeV < p < 5 GeV (few 10 GeV) dE/dx in silicon (ITS) and gas (TPC) + Time-of-Flight (TOF) + Cerenkov (RICH) decay topology (K 0, K +, K -,  ) K and  decays up to at least 10 GeV leptons (e,  ), photons,  0,  electrons in TRD: p > 1 GeV, muons: p > 5 GeV,  0 in PHOS: 1 < p < 80 GeV Particle Identification A. Badalà- SQM07- Levoča – 24/06/-29/06/07 16

Resonance K*(892) Φ (1020)  *(1520) Decay channel (B.R.) K  (~100%) K + K - (49%) N K (45%) Width [MeV/c 2 ] Life time [fm/c] 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). Software code development Test distributed analysis of events Optimization of reconstruction tools Background estimation Efficiency evaluation Study of short-life resonances in ALICE A. Badalà- SQM07- Levoča – 24/06/-29/06/07 17

Results from p-p 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 10 5 minimum bias p-p PHYTIA 900 GeV. Running scenario at LHC startup 1.5 x 10 6 minimum bias p-p PHYTIA 14 TeV (about 0.2% 1- year data taking) PDC06 data, distributed GRID analysis A. Badalà- SQM07- Levoča – 24/06/-29/06/07 18

Studied dependence on event selection criteria ●Charged multiplicity ●z-vertex location Study of the combinatorial background by the mixed-event technique Multiplicity z-vertex Comparison of the event mixing background to the “true” combinatorial backgroung ‘True’ background = (Signal) – (True pairs) Only events with Δm<5 and Δz v < 3 cm mixed A. Badalà- SQM07- Levoča – 24/06/-29/06/07 19

Like-sign technique also explored K* Comparison of the like-sign background to the “true” combinatorial background GeV A. Badalà- SQM07- Levoča – 24/06/-29/06/07 Unlike sign Like-sign 20

Perfect PID Realistic PID PID influence on K*(892) reconstruction True K* = 7599 Found K* = 7488 S/B = S/√B = True K* = 4306 Found K* = 4139 S/B = 0.11 S/√B = Maxprob > 0.7 (K) No PID (π) Maxprob > 0.7 (K) Maxprob > 0.7 (π) No thresh on maxprob True Found Perfect PID Realistic PID GeV

 (1020) and  *(1520) with realistic PID True  (± 2σ) = 186 Found  (±2σ) = 168 S/B = 2.87 S/√B =   GeV A. Badalà- SQM07- Levoča – 24/06/-29/06/07 True Λ (± 2σ) = 146 Found Λ (± 2σ) = 128 S/B = 1.23 S/√B = 19.5 ** ** 22

Results for p-p TeV Detailed analysis for K*(892) 0 on PID perfomances 1.5 x 10 6 PYTHIA events Mass resolution ~ 3MeV/c 2 K* A. Badalà- SQM07- Levoča – 24/06/-29/06/07 Found K*(±2  )=89182 True K*(±2  )=

K*(892) 0 p T -analysis with realistic PID p T = p T = p T = TeV A. Badalà- SQM07- Levoča – 24/06/-29/06/07 24

Correction matrix A. Badalà- SQM07- Levoča – 24/06/-29/06/07 25

 (1020) and  *(1520) with realistic PID TeV  (1020)  (1520) Mass resolution 1.2 MeV/c 2 A. Badalà- SQM07- Levoča – 24/06/-29/06/07 True  =4893 Found  =4967 True  *=3879 Found  *=

● Short-lived resonances in pp LHC energies could be studied in ALICE from the very beginning ● With a small sample of events [O( GeV and realistic PID: ● Extraction of yields at least for K*(892), Φ(1020), Λ*(1520) ● Rough p T - distribution for K*(892) up to 1.5 GeV/c ● Particle ratios Φ/K*, Λ*/K*, Φ/Λ* measurable ● Analysis of O(10 6 ) pp events at 14 TeV fully reconstructed on the GRID ● Resonance yields with large statistics ● p T -analysis ● Correction matrix (y,p T ) ● Extension to other resonances is in progress. Summary K*(892) 0 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

EXTRA SLIDES

K*(892) p t 900 GeV p T -spectrum for realistic PID 2 x 10 5 events  3500 K* Practical limit for 2 x10 5 events A. Badalà- SQM07- Levoča – 24/06/-29/06/07

Overall number of particles + antiparticles generated by GeV:  1.34 K*(892)/event  0.08  (1520)/event  0.23 Φ(1020)/event Resonance yield Exp.data PYTHIA K*(892) yield A. Badalà- SQM07- Levoča – 24/06/-29/06/07

 (780)

 (1020)

K*(892) 0 1 GeV/c<p t <2 GeV/c 2 GeV/c<p t <3 GeV/c

Inside same event, correlations between K + and π - candidates K - and π + candidates Evaluate invariant mass spectrum Combinatorial background: Signal extraction (unlike-sign) Mixed-event technique Like-sign technique Example: K*(892)  Kπ (~100%)

ALICE PID A common BAYESIAN approach is adopted by every ALICE detector performing PID; The probability w(i|s) to be a particle of type i (i = e, , , K, p...) if a signal s (dE/dx, TOF,...) is detected, is: r(s|i)(Detector response function) conditional probability density functions to get a signal s in a detector, if a particle of i-type hits the detector C i (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

Mass resolution ~4000 HIJING events Mass resolution ~3 MeV

preliminary Temperature and lifetime from  (1520) /  and K*/K results between : T= 175 MeV =>  = 4-6 fm/c  = 0 fm/c => T= MeV 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. G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239 C. Market, J. Phys. G. Nucl. Part. Phys. 31 (2005)  (1520)/  =   K*(892)/K = 0.19  0.05  > 4 fm/c for T=160 MeV 0-20% most central Au+Au

Identified particle spectra ALICE has unique capabilities to reconstruct and to identify particles: Global tracking (ITS-TPC-TRD) (  p t /p t ~ 3% at 100 GeV/c) + dE/dx (low p T + relativ. rise), TOF, HMPID, PHOS, … Reconstruction by invariant mass and topological decay , K, p: <p t < 50 GeV/c p T (GeV/c) PID in the relativistic rise  K p Estimated p t range for particle identification for 10 7 central Pb-Pb events (1-year data taking) Weak or strong decaying particles: up to GeV/c 14

Pb-Pb p-p  1GeV/c A. Badalà- SQM07- Levoča – 24/06/-29/06/07

K*(892) ± K S 0 + π ± B.R. ~ 33% π + + π - B.R. ~ 69% Total B.R. ~ 23 % Preparation of tools for K * (892) ± analysis GeV K *+

Nuclear Modification Ratios (R CP ) for resonances RHIC results have shown as, in the intermediate p t region, nuclear modification factors depend on the constituent quarks rather than on particle mass. L. Maiani et al., Phys. Lett. B645(2007)138 A two components recombination/fragmentation model shows clear distinction for the Rcp of the f 0 (980) resonance with or content. A. Badalà- SQM07- Levoča – 24/06/-29/06/07