The ALICE Experiment Event by Event fluctuations ALICE TOF Calibration 30th November 2007Chiara Zampolli1

Collisions between heavy nuclei (such as 208 Pb 82+ ) at a very high energy (such as ~1150 TeV, the maximum available so far) are expected to produce a “new world”, the Quark-Gluon-Coloured-World (QGCW) LHC CERN. In such collisions, many QCD open-colour states may be produced, much more than the number of baryons and mesons. Totally unexpected events are likely to be detected!! Event-by-Event physics becomes crucial. 30th November 20072Chiara Zampolli

ATLAS CMS Designed for high p T physics in p-p collisions ALICE Dedicated LHC HI experiment ~ 9 km CERN LHC 30th November 20073Chiara Zampolli

-Multiplicities & Et distributions, -HBT Correlations, elliptic and transverse flow, -hadron ratios and spectra, -Evt-by-Evt fluctuations -… Heavy ion observables in ALICE -Charmonium and Bottomonium states, -strangeness enhancement, resonance modification, -jet quenching and high pt spectra, -open Charm and Beauty -thermal  radiation,… Probes of deconfinement & chiral symmetry restoration Global characteristics of the fireball (Evt by Evt) p-p and p-A physics in ALICE Physics of ultra-peripheral heavy ion collisions Contribution of ALICE to cosmic-ray physics 30th November 20074Chiara Zampolli

Thanks to the very high charged particle multiplicity expected per event, E-by-E studies will be feasible with the ALICE detector for many observables:  Temperature  Mean p T  Particle Ratios  Multiplicity  Conserved Quantities (Charge)  HBT radii  Balance Function  Flow  DCC ... ALICE PPR II Particle IDentification plays a crucial role! 30th November 20075Chiara Zampolli

3  2  (dE/dx) 30th November 20076Chiara Zampolli

contamination efficiency  K p 0.15 < p T < 4 GeV/c Efficiencycontamination  Kp  Kp 98%78%92%3%20%4% 30th November 20077Chiara Zampolli

Generated Identified (w) Identified (t + w)  K p 30th November 20078Chiara Zampolli

 Event by event fitting procedure for p T spectra: exponential function,T = slope parameter, connected to the  Correction of the identified spectra taking into account:  Limited acceptance and reconstruction efficiency of the detectors: ε acc  Transverse momentum reconstruction efficiency: ε p  PID efficiency: ε PID  PID contamination: C PID kinetical freeze-out temperature 30th November 20079Chiara Zampolli

Temperature (MeV)  Kp 186 ± 2208 ± 8319 ± 13 Fit range: 0.25 < p T < 2 GeV/c  K Generated Reconstructed i.e. corrected! p 30th November Chiara Zampolli

 = 182 MeV  T = 3 MeV = 226 MeV  T = 13 MeV = 303 MeV  T = 21 MeV  T /T ~ 0.5%  T /T ~ 6%  T /T ~ 7% K p 30th November Chiara Zampolli

K/π: R = σ R = R = σ R = p/ π : R = σ R = R = σ R = σ R /R ~ few % 30th November Chiara Zampolli

 K p = 451 MeV  p T = 6 MeV = 578 MeV  p T = 24 MeV = 744 MeV  p T = 50 MeV  p T /p T ~ 1%  p T /p T ~ 4%  p T /p T ~ 7% 30th November Chiara Zampolli

A more “technical” work has been carried on concerning the ALICE TOF detector calibration. Corrections to be introduced, wrt two main sources of uncertainty: Online Calibration TIME DELAYS: Online Calibration an equalization of the channels of the TDCs is necessary because of the delays introduced by the electronics (mainly cable lengths and pulse line lengths). Offline Calibration TIME SLEWING : Offline Calibration time slewing is caused by the finite amount of charge necessary to trigger the discriminator → charge fluctuations generate a time walk. TOF channel status to be determined (from HW map, pulser runs, noise runs). 30th November 2007Chiara Zampolli14

30th November 2007Chiara Zampolli15 Determine the relative delays for each TOF channel using the t TOF -t exp spectra t TOF = time measured by TOF t exp = expected time of flight, from TOF geometry, assuming β = 1 and a straight line trajectory Sharp edge expected at the delay value from fastest particles ( β ~ 1) No delay, ~ 0

30th November 2007Chiara Zampolli16 Dependence of the measured times vs time over threshold used. To unfold the time spread due to the momentum spectra, to the particle types, and to the different track length, the algorithm is based on the comparison between the times of the reconstructed tracks (from track length and momentum measurements) and the measured times (t EXP -t TOF ). The identity of the particle (needed to choose the proper t EXP ) is determined via a combinatorial algorithm.

30th November 2007Chiara Zampolli17 Profiling and fitting procedure – 5 th order polynomial function ToT  amplitude of the signal Test beam results used in simulation

30th November 2007Chiara Zampolli18 σ a = 92.7 psσ b = ps σ c = 93.2 ps decalibration calibration σ cal = ~ 10 ps Results obtained with 500 tracks from 2 HIJING central Pb-Pb ev; simulated time delay = 2 ns.

30th November 2007Chiara Zampolli19 Event by event fluctuations Event by event fluctuations studies are an important tool to explore the QCD phase diagram, searching for the QGP, and the QCD critical point. PID capabilities Thanks to its very high particle yield per event, and to the excellent PID capabilities, ALICE will be able to study fluctuations measuring the identified particle spectra ( π, K, p) and the particle ratios (K/ π, p/ π ) on an Event-by-Event basis. calibration As data taking is approaching (a first cosmics run period is foreseen for December), the calibration tools have to be ready within ALICE framework to comply with the experiment requirements. A lot of work is ongoing, both from the analysis point of view and as more technical software development, waiting for LHC data...

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