The performances of the ALICE Time Of Flight detector are presented, based on the 2010 data taking. Hardware status, time resolution and PID capability are shown and compared with the design values. First results in Pb-Pb at √sNN = 2.76TeV are reported

Agostinelli, A.

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DOI 10.1393/ncc/i2011-11102-xColloquia: IFAE 2011IL NUOVO CIMENTO Vol. 34 C, N. 6 Novembre-Dicembre 2011The performance of the ALICE TOF detectorA. Agostinelli on behalf of the ALICE CollaborationDipartimento di Fisica, Universita` di Bologna and INFN, Sezione di Bologna - Bologna, Italy(ricevuto il 29 Luglio 2011; pubblicato online il 21 Dicembre 2011)Summary. — The performances of the ALICE Time Of Flight detector are pre-sented, based on the 2010 data taking. Hardware status, time resolution and PIDcapability are shown and compared with the design values. First results in Pb-Pbat√sNN = 2.76TeV are reported.PACS 29.40.Cs – Gas-filled counters: ionization chambers, proportional, andavalanche counters.1. – IntroductionALICE is an experiment at CERN LHC designed and optimized to study Pb-Pb col-lisions with√sNN = 5.5TeV. The investigation of colored deconfined matter, the socalled Quark Gluon Plasma, is its main goal. To achieve this it has been designed withan excellent tracking system and very high particle identification (PID) performance.Time Of Flight system is one of the main ALICE detectors for particle identification [1].This detector covers a cylindrical surface of about 150m2, with an inner radius of 3.7m.It has full azimuthal acceptance (with a segmentation in 18 sectors) and a polar ac-ceptance of |η| ≤ 0.9. In each sector 91 Multigap Resistive Plate Chamber (MRPC)have been installed. The MRPCs have an active area of 7.4× 120 cm2, with ten 250μmwidth gas gaps delimited by 400μm tick soda-lime glasses which are grouped into twostacks, placed on both side around a central anode. External electrodes are obtainedfrom 550μm tick glasses with a specially developed acrylic paint loaded with metal oxy-des, giving an average surface resistivity between 2 and 25MΩ/. The strips work inavalanche mode regime, with E ∼ 100 kV/cm. Measurements at test beam for a sampleof mass-production MRPCs have shown an efficiency MRPC > 99% and a time resolu-tion σMRPC < 50 ps, at a working voltage of 13 kV [2]. Without beam operations, onaverage, the MRPC strips draw a current less than 1 nA. Finally, each strip is dividedinto 96 readout channels of about 10 cm2 of active area. During 2010 data taking thesystem used on average 96% of its 157248 readout channels.c© CERN on behalf of the ALICE Collaboration under CC BY-NC 3.0 251252 A. AGOSTINELLI on behalf of the ALICE COLLABORATIONFig. 1. – Top: measured resolution during Pb-Pb data taking. Bottom: mass distribution ofparticle which reached TOF from a single Pb-Pb collision.2. – Results from 2010 data takingFirst results on identified particle spectra in p-p collisions at 900GeV have beenpublished in [3]. Here selected results from last year heavy ions runs are shown. Themeasure of global time resolution (σtot) is reported in fig. 1. For each track, the quantitytmeasured − texpected is related to the TOF time resolution (σTOF ), the time zero of asingle Pb-Pb collision (σt-Zero) and the time resolution due to tracking (σt-Track). InPb-Pb, with σt-Zero and σt-Track typical values of 10 and 20 ps respectively, σTOF isabout 80 ps, as from design value. These distributions will be improved by single channeltime-slewing corrections and time-walk inside a pad. Considering an expected timeresolution of 90 ps, TOF allows π/K (and K/p) separation better than 2σ up to about3.0GeV/c (4.4GeV/c). Mass distribution for the particles with a measured time of flightfrom TOF detector in just a single Pb-Pb event is also shown. Particle identification atan event by event level becomes in this way a straight and amazing reality for the TOFdetector.REFERENCES[1] ALICE Collaboration, J. Phys. G: Nucl. Part. Phys., 32 (2006) 1295.[2] CERN/LHCC 2000-012, ALICE TDR, 8 (2000) ALICE TOF Technical Design Report.[3] ALICE Collaboration, Eur. Phys. J. C, 71 (2011) 1655.

The performance of the ALICE TOF detector

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The performance of the ALICE TOF detector

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