Francesco Barile for the ALICE Collaboration. Università degli Studi di Bari & INFN

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1 Produzione di deutoni e anti-deutoni nelle collisioni centrali Pb-Pb a snn= 2.76 TeV con il rivelatore Cherenkov HMPID nell'ambito dell'esperimento ALICE ad LHC Francesco Barile for the ALICE Collaboration Università degli Studi di Bari & INFN

2 Outline Introduction The ALICE detector PID in ALICE ALICE results with the HMPID contribution Deuteron analysis with HMPID Conclusions SIF The High Momentum Particle Identification Detector 2

3 Introduction Nuclear matter under extreme conditions can be investigated in ultra-relativistic heavy-ion collisions. Collective and thermal properties of the Quark Gluon Plasma inferred from transverse momentum (pt) distributions and integrated yields of identified particles excellent PID needed Heavy Ion collisions dynamical evolution Initial interaction Hydrodynamic flow (radial and elliptic flow) Chemical freezeout (particle ratios) Kinetic freezeout (momentum distribution) Thermalization At LHC energies uu,dd,ss pairs can be easily excited from the quantum vacuum abundant production of strangeness and antimatter (light) nuclei and anti-nuclei: very sensitive to fireball characteristics sensitive to late stage of fireball evolution 3

4 Introduction Nuclei production Thermal model: The key parameter at the LHC energies is the Tchem Nuclei abundance strongly depends on the value of Tchem Large mass Exponential dependence of the yield exp(-m/tchem) A.Andronic, P.Braun-Munzinger, J.Stachel and H.Stoecher, Phys.Lett. B697, 203 (2011), Coalescence model: Nuclei are formed by protons and neutrons which are nearby and have same velocity (after kinetic freeze-out) Nuclei produced at chemical freeze-out Can break apart Created again by final-state coalescence J.I. Kapusta, Phys.Rev. C21, 1301 (1980) 4

5 The ALICE detector The ALICE detector Central barrel ITS HMPID 2π tracking and PID η < 0.9 B= 0.5 T EM cal. ( η < 0.7, Δϕ = 107 ) RICH ( η < 0.5, Δϕ = 57.6 ) EMCAL TRD HMPID ITS TPC TOF TOF PHOS TPC ITS tracking ITS tracking++vertexing vertexing++pid PID(dE/dx) (de/dx) TPC tracking + vertexing + PID (de/dx) TPC tracking + vertexing + PID (de/dx) TOF PID TOF PID (time-of-flight) (time-of-flight) HMPID PID (ring HMPID PID (ringimaging imagingcherenkov) Cherenkov) 5

6 The ALICE detector & PID The ALICE detector ITS TPC TOF & PID HMPID 6

7 Particle Identification: HMPIDdetector detector The HMPID The ALICE-HMPID (High Momentum Particle Identification Detector) performs charged particle track-by-track identification measuring the emission angle of Cherenkov radiation; It consists of seven identical proximity focusing RICH counters. HMPID TPC 5m m fro IP HMPID geometrical acceptance: 5% of the TPC x 20 events to reach a comparable statistic significance wrt TPC, TOF; 7

8 Particle Identification: Cherenkov The HMPID detector Collage of rings! p-pb 5.02 TeV 8

9 Particle Identification: Cherenkov The HMPID detector HMPID contribution in: pp, 2.76 TeV and 7 TeV Pb-Pb collisions, 2.76 TeV p-pb collisions, 5.02 TeV Physics Letters B 736 (2014)

10 ALICE results HMPID Recent results with with HMPID: pi/k/pcontribution Identified particle spectra see R. Nania Nuclear modification factor RAA Particle ratios Physics Letters B 736 (2014)

11 Deuteron HMPID Deuterons in in HMPID HMPID also identifies at higher pt (above 3 GeV/c) deuterons (anti-d) in central Pb-Pb collisions allowing the extension of the p T spectrum of TPC+TOF analysis Performance plot (HMPID specific cuts are used) 11

12 Deuteron HMPID Deuterons in in HMPID TPC + TOF Extraction of the raw yields in 7 pt bins (example of a fit). 12

13 pt-spectrum Deuterons in HMPID Extraction of the raw yields in 7 pt bins. Corrected spectrum (corrected for PID, matching, tracking x geom. acceptance..) in nice agreement with TPC+TOF analysis 13

14 centrality pt-spectra & in Blast-wave Deuterons Pb-Pb Spectra are fitted with the blast-wave function (simplified hydro model) in different centrality bins These fits are used for the extrapolation of the yield to the unmeasured region at low and high p T A hardening of the spectrum with increasing centrality is observed expected in a hydrodynamic description of the fireball as a radially expanding source 14 E. Schnedermann et al., Phys. Rev. C48, 2462 (1993)

15 Anti-d/d ratioratio (0-10% Bar-d/d in Pb-Pbcentr.) The anti-d/d ratio in 0-10% centrality class. The ratio exhibits a constant behaviour as a function of the transverse momentum The average value is in agreement with expectations from thermal / coalescence model; 15

16 Conclusions Conclusions The PID capability of the ALICE detector is unique among the LHC experiments The HMPID contributes to the identification of charged hadron (pi/k/p) in the intermediate momentum range (1.5 6 GeV/c) The limited acceptance of HMPID implies a more difficult analysis process with respect to different detector that covers a wider phase space ( x 20 events to reach a comparable statistical significance wrt TPC, TOF); Recent published physics results with the contribution of the HMPID are presented (spectra, ratio, RAA..) Recent results on deuteron and anti-deuteron in central Pb-Pb collisions are shown. 16

17 Conclusions 17

18 Particle Identification: HMPIDdetector detector The HMPID The ALICE-HMPID (High Momentum Particle Identification Detector) performs charged particle track-by-track identification by means of the measurement of the emission angle of Cherenkov radiation and of the momentum information provided by the tracking devices. It consists of seven identical proximity focusing RICH counters. RADIATOR 15 mm liquid C6F14, n ~ 175nm, bth = 0.77 PHOTON CONVERTER Reflective layer of CsI QE ~ 175 nm. The largest scale (11 m2) application of CsI photo-cathodes in HEP PHOTOEL. DETECTOR - MWPC with CH4 at atmospheric pressure (4 mm gap) HV = 2050 V. - Analogue pad readout 18

19 PID Particle Identification in ALICE 19

20 TPC At low momenta, nuclei are identified using the de/dx measurement in the TPC About 7% resolution in central Pb-Pb collisions 20

21 PID with TOF Velocity measurement with the TOF detector is used to calculate the m 2 distribution Excellent TOF performance ( σtof = 85 ps time resolution in Pb-Pb collisions) 3σ-cut around expected TPC de/dx for deuterons reduces drastically the background from TOF and TPC track mismatch Raw yields extraction from a fit of gaussian function + exponential tail to the m 2 distribution 21

22 ALICE results HMPID Recent results with with HMPID: pi/k/pcontribution Identified particle spectra Low pt (pt < 2 GeV/c): Soft production Non-perturbative physics Bulk properties Intermediate pt (2<pT < 8 GeV/c): baryon/meson enhancement new hadronization mechanisms? parton recombination? High pt (pt > 8 GeV/c): Hard production Perturbative physics Jet quenching Spectra in pp scaled by Ncoll and peripheral Pb-Pb collisions are similar Spectra in central Pb-Pb collisions are lower at high pt and flatter at pt < 2 GeV/c than the ones in pp collisions Physics Letters B 736 (2014)

23 ALICE results HMPID Recent results with with HMPID: pi/k/pcontribution Central Pb-Pb collisions: peak at pt 3 GeV/c higher than at RHIC hydrodinamic (dependent on hadron mass) or recombination (baryon enhancement)? Particle ratios Recombination (Fries et al.) of soft thermal radially flowing partons: describe shape of data Hydro model (Krak.w): describe the rise of the ratios Hydro model + jet quenching (EPOS): qualitatively describes the data but overestimate the peak. pt> 10 GeV/c: agreement between pp and Pb-Pb parton fragmentation (jet chemistry) not modified by the medium Physics Letters B 736 (2014)

24 ALICE results HMPID Recent results with with HMPID: pi/k/pcontribution pt < 8 GeV/c: p less suppressed than π and K Nuclear modification factor RAA pt > 10 GeV/c same suppression for π, K, p -> particle composition and ratios at high pt are the same in medium and in vacuum Physics Letters B 736 (2014)