Study of short-lived resonances in ALICE A. Badal à – INFN Sezione di Catania Contents Physics motivations Some SPS and RHIC results ALICE detector performance Some results from simulated p-p TeV Summary A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 1

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- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 2

Resonances as a probe of chiral symmetry restoration 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 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 ρ0ρ0 ρ0ρ π-π- π+π+ ρ0ρ0 - + ρ0ρ0 ρ0ρ0 π-π- π+π+ π+π+ π-π- Leptonic decay channel probes all stages of the collision Hadronic decay channel probes late stages of the collision A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 3

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 R. Arnaldi et al. (NA60 Collaboration) Phys. Rev. Lett. 96(2006) AGeV A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 4

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 (reconstructed by their hadronic decay) in event classes based on azimuthal distribution respect to jet direction C. Markert, 23 rd Winter Workshop on Nuclear Dynamics Big Sky, Montana, USA and SQM07, Levoca (Slovakia) A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 5

 (1020) from same/away side in/out of plane side1 side2 near away No mass shift or width broadening visible side2 side1 near - side away- side Trigger particle: hadron p T > 4.0 GeV/c Associated particle: resonance  (1020) ~ 0.9 GeV/c C. Markert, SQM07, Levoca (Slovakia) A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 6 Next step:  with higher p t

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- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 7

p+p and  s NN =200 GeV Suppression of K* and  * 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 been 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 ) A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 8

(*) 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 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 9

K * (892)  π K B.R. ~1 c  = 4 fm STAR Preliminary √s NN = 200 GeV √s NN = 62 GeV STAR Preliminary STAR collaboration, Phys. Rev. C71, (2005) √s NN = 200 GeV 10

Σ(1385)  Λ  B.R c  = 5.5 fm Λ(1520)  pK B.R c  = 12.6 fm Star collaboration, Phys. Rev. Lett. 96(2006) STAR Preliminary d+Au √s NN =200 GeV p+p √s NN =200 GeV Au+Au √s NN =200 GeV 11

Φ(1020)  K + K - B.R c  = 44 fm STAR Preliminary PHENIX d+Au √s NN =200 GeV PHENIX Au+Au √s NN =200 GeV Au+Au √s NN =62 GeV A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 12

Φ(1020)  e + e - B.R c  = 44 fm p+p √s NN =200 GeVd+Au √s NN =200 GeV Au+Au √s NN =200 GeV PHENIX S. Huang DIS2007, Munich,Germany A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 13

ρ 0 (770)  π + π - B.R. ~1c  = 1.3 fm 20-40% dAu 0.6 ≤ p T < 0.8 GeV/c STAR Preliminary √s NN = 200 GeV % dAu 0.6 ≤ p T < 0.8 GeV/c STAR Preliminary √s NN = 200 GeV 40-80% Au+Au 0.6 ≤ p T < 0.8 GeV/c STAR Preliminary √s NN = 62 GeV 0-20% dAu 0.6 ≤ p T < 0.8 GeV/c STAR Preliminary √s NN = 200 GeV A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 14

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) A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 15

K*  Mass and Width K* 0  p T < 1 GeV  mass shift of ~10 MeV observed K* ± and K* 0  p T > 1 GeV  mass agrees with PDG for all systems within errors Width agrees with PDG for all systems within errors PDG K* 0 PDG K* ± PDG STAR Preliminary MC A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 16

Φ  Mass and Width STAR Preliminary PDG p T > 1 GeV  mass and width agree with MC and PDG for all systems p T < 1 GeV  mass agrees with MC for all systems within errors p T < 1 GeV  width higher than MC for all systems  real physics or detector effect? A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 17

 mass and width  Mass and width of  meson reconstructed by KK channel do not depend on centrality  Mass and width in agreement with PDG for all system d+Au √s NN =200 GeV Au+Au √s NN =200 GeV S. Huang, DIS2007, Munich Germany Au+Au √s NN =62 GeV A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 18

Particle production in pp collisions dominated by two mechanisms: a)soft, thermal-like processes at low p T (exponential shape) b)Hard, parton-parton processes at high p T (power-law shape) STAR Coll, PRC71(2005) A unique (Levy) function is used to parametrize the overall shape Transverse spectra A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 19

K* 0 Transverse Momentum Spectra GeV GeV 200 GeV STAR PRELIMINARY K* 0 spectra fitted by an exponential function S. Dash SQM07 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 20

 →K + K - Spectra STAR Preliminary Change of Φ spectra from exponential in central Au+Au collisions to Levy function shape in peripheral Au+Au  Matter formed in peripheral Au+Au collisions favors hard Φ production A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 21

SPS  puzzle NA49%NA50 NA45 - PRL 96 (2006) ] NA50 reported a  yield measured via dileptons larger than yield determined by NA49 in K + K - channel. Further, the m T spectra exhibit a different inverse slope parameter 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 GeV A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 22

SPS results for  →  +  - (NA60) NA60 In-In (p T < 1.6 GeV/c) NA49 Pb-Pb(p T <1.6 GeV/c) NA50 Pb-Pb(p T >1.2 GeV/c) M. Floris, SQM07 NA60 In-In (p T > 1.1 GeV/c) NA49 Pb-Pb(p T <1.6 GeV/c) NA50 Pb-Pb(p T >1.2 GeV/c) A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 23 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 Lower T values and flatter distribution if the fit is performed in the same p T range of NA50. This hints for the presence of radial flow → blast wave analysis

Φ Production  K + K - and e + e - The leptonic channel yield is a little higher than hadronic channel More accurate measurement is required to confirm if there is branching ratio modification e+e-e+e- K+K-K+K- A. Kozlov (Phenix coll.),QM2005 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 24

Φ  K + K - STAR-PHENIX comparison J. Rafelski et al.,Phys.Rev. C72 (2005) Φ production  there is a factor of ~2 difference between PHENIX and STAR STAR PHENIX STAR + PHENIX √s NN = 200 GeV A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 25

Suppression scales with dN ch /dy ~ system size STAR preliminary Resonance suppression (system size dependence) C. Markert, SQM07 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 26

For K* seems less re-scattering at lower energies in peripheral collisions Lower density  smaller interactions cross section? Shorter hadronic lifetime  less hadronic interactions ? STAR preliminary Resonance suppression (energy dependence) Life-time [fm/c] K(892) = 4.0  (1020) = 45 S. Dash SQM2007 STAR preliminary C. Markert, SQM07 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 27

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 S. Adare et al. (Phenix coll.) nucl-ex A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 28

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- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 29

K*(892) elliptic flow 200 GeV C. Nonaka, et al., Phys.Rev.C69:031902,2004  Partonic generation → resonances are produced in a hadronizing QGP → v2 scales with n=2  Hadronic generation → resonances are produced in the hadronic final state via hadron-hadron scattering → v2 scales with n=4 (K*=K+  =2+2) Most of K* are produced in partonic phase and only a small quantity is originated in rigeneration (Need more precise measurements) Using the deviations of the measured flow coefficient v 2 from the scaling law given by the quark recombination formalism to probe the amount of hadronic final state interactions A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 30

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. K*(892) and  (1020), (mass ~ mass proton), have R CP values close to the kaon ones. A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 31

Nuclear Modification Ratios (R CP ) for resonances Recent suggestion by Maiani et al. to use this observable to solve the problem of the real quark composition of some resonances as the f o (980)( or ?) L. Maiani et al., Phys. Lett. B645(2007)138 A two components recombination/fragmentation model A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 32

ALICE performance on primary 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- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 33

ALICE performance on track impact parameter Pb-Pb p-p  1GeV/c A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 34

In ALICE Kalman filter strategy allows a good tracking performance down to very low momenta ITS + TPC Tracking efficiency  p t /p t (%) p t (GeV/c) Momentum resolution  p t /p t <0.7% for p t <2 GeV/c  p t /p t ~ 3 % at 100 GeV/c p t (GeV/c) 35

ALICE performance on particle identification with ITS and TPC at low momenta… and TOF at high momenta… 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 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 36

Mass resolution Mass resolution ~3 MeV/c 2 0.6<p t <0.8 GeV/c1.0<p t <1.1 GeV/c 1.6<p t <1.8 GeV/c2.0<p t <2.1 GeV/c K*(892)  (1020) Mass resolution ~ 1.3 MeV/c 2 A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 37

   Invariant mass (GeV/c 2 ) K*(892) 0 Invariant mass (GeV/c 2 )  Short-lived resonances in ALICE Pb-Pb events studied for PPR A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 38

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] 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 e+e- decay has also been probed. Catania people have expecially worked on reconstruction of: Software code development Test distributed analysis of events Optimization of reconstruction tools Background estimation Efficiency evaluation Study of short-life resonances in ALICE Started study of  +  - correlations In next talk results obtained in p-p simulated events at 900 GeV and 14 TeV A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 39

Φ (1020): signal

Background estimation For K*(892) 0 BAD agreement between background estimated by event-mixing technique and true background Jet-like azimuthal correlations in  -K pairs generated in PYTHIA events at 14 TeV. A. Badalà- Convegno Naz. Fisica ALICE- LNF – 12-14/11/07 40 11 22

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

EXTRA SLIDES

K*(892) 0 p T -analysis with realistic PID p T = p T = p T = TeV

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)

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

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

Results for p-p TeV Detailed analysis for K*(892) 0 on PID perfomances 1.5 x 10 6 PYTHIA events Mass resolution ~ 3MeV K* A. Badalà- SQM07- Levoča – 24/06/-29/06/07 Found K*(±2  )=89182 True K*(±2  )=85360

 (1020) and  *(1520) with realistic PID TeV  (1020)  (1520) Mass resolution 1.2 MeV A. Badalà- SQM07- Levoča – 24/06/-29/06/07 True  =4893 Found  =4967 True  *=3879 Found  *=3649

HIJING events with a realistic simulation of detector response Use ω and K* 0 shape from HIJING to fit the data K* 0 signal is fixed using STAR measurement ρ 0 (770)  π + π - STAR Preliminary ρ0ρ0  s NN = 200 GeV K0S  π+ π-K0S  π+ π- K0SK0S ω(782)  (π + π - ) π 0 and π + π - ω η  (π + π - ) π 0 and (π + π - )  η’  (π + π - ) η and (π + π - ) ρ 0 η + η’ K*(892) 0  K π with K misidentified as π K *0 + K *0 misidentified π + π - Invariant Mass Distribution from Monte Carlo

K*(892) 0 : like-sign / “true” background Good agreement in all bins of p T

K*(892) 0 : event mixing / “true” background BAD agreement except for bins of very small p T

φ 1 φ 2 correlations for πK pairs

ρ 0  Mass Mass shift observed for all systems Systematic errors shown for Minimum Bias d+Au 200 GeV STAR Preliminary

Λ* signal

Formation of hadronic resonances (from jets) in a chiral medium side 1 side 2 near away Low ptHigh pt Near sideNo medium or late hadronic medium No medium Away sideLate hadronic mediumPartonic or early hadronic medium (depend on formation time) CSR ? Side 1 & 2Late hadonic mediumEarly hadronic medium Formation time arguments: a.) General pQCD: Formation time [fm/c] ~ p T [GeV] Formation time [fm/c] ~ 1/mass b.) Specific string fragmentation (PYTHIA) formalism: Gallmeister, Falter, PLB630, 40 (2005) Intermediate p T resonances form early c.) Vitev et al. (hep-ph/ ): High p T heavy particles and resonances form early Need to determine the right momenta for trigger and resonance particle