ALICE Experiment Roman Lietava University of Birmingham Physics
ALICE Experiment Roman Lietava University of Birmingham • • Physics motivation Detectors Observables and Physics Performance Summary UK HEP Forum 1 Roman Lietava, University of Birmingham
ALICE Collaboration 937 members (63% from CERN MS) 77 Institutions, 29 Countries ALICE UK: 6 members University of Birmingham UK HEP Forum 2 Roman Lietava, University of Birmingham
Collision Systems L 0 Collision system √s. NN (Te. V) Run time (s/year) (cm-2 s-1) pp 14. 0 1031 107 April 2007 Pb. Pb 5. 5 1027 106 2007/2008 Year Other collision systems and energies: • p. A, lighter ions (Sn, Kr, Ar, O) • pp @ 5. 5 Te. V UK HEP Forum 3 Roman Lietava, University of Birmingham
Physics Motivation The study of Quantum Chromodynamics: • A-A collisions: - physics of many particles interacting strongly, QCD phase transition • p-p and p-A collisions: - benchmark for AA collisions - specific aspects • Ultra peripheral AA collisions – physics • Cosmic ray physics UK HEP Forum 4 Roman Lietava, University of Birmingham
QCD Phase Diagram Nonperturbative phenomena hep-ph/020516 Lattice QCD PLB 478(2000)447 UK HEP Forum 5 Roman Lietava, University of Birmingham
Space Time Evolution of the Collisions UK HEP Forum 6 Roman Lietava, University of Birmingham
ALICE Physics Goals Degrees of freedom as a function of T hadron ratios and spectra, dilepton continuum, direct photons Global observables: Multiplicities, distributions Early state manifestation of collective effects: elliptic flow Energy loss of partons in quark gluon plasma: jet quenching, high pt spectra, open charm and open beauty Ø Large acceptance Ø Good tracking capabilities Ø Selective triggering Ø Excellent granularity Deconfinement: charmonium and bottomonium spectroscopy Chiral symmetry restoration: neutral to charged ratios, res. decays Fluctuation phenomena - critical behaviour: event-by-event particle comp. and spectra Geometry of the emitting source: HBT, impact parameter via zero-degree energy flow pp collisions in a new energy domain Ø Wide momentum coverage Ø P. I. D. of hadrons and leptons Ø Good sec. vertex reconstr. Ø Photon Detection 7 Use a variety of experimental techniques! Roman Lietava, University of Birmingham UK HEP Forum
Alice Detector • Tracking (B=0. 2 -0. 5 T): - Inner Tracking System (ITS) – pixels, drift, strips - Time Projection Chamber (TPC) - Transition Radiation Detector (TRD) • PID: - TPC - TRD - Time Of Flight (TOF) - High Momentum PID (HMPID) • Muons: dimuon arm • Calorimetry: - PHOton Spectrometer (PHOS) - Electromagnetic Calorimeter (EMCAL) - under discussion UK HEP Forum 8 Roman Lietava, University of Birmingham
Bat 40 ATLAS CMS ALICE UK HEP Forum 9 Roman Lietava, University of Birmingham
ALICE Detector Acceptance Muon arm: 2. 4< <4 PMD 2. 3< <3. 5 FMD: -5. 4< <-1. 6, 1. 6< <3 UK HEP Forum 10 Roman Lietava, University of Birmingham
PT Resolution UK HEP Forum 11 Roman Lietava, University of Birmingham
ALICE PID Øp, K, p identified in large acceptance (2 p * 1. 8 units ) via a combination of d. E/dx in Si and TPC and TOF from ~100 Me. V to 2 (p/K) - 3. 5 (K/p) Ge. V/c ØElectrons identified from 100 Me. V/c to 100 Ge. V/c (with varying efficiency) combining Si+TPC+TOF with a dedicated TRD ØIn small acceptance HMPID extends PID to ~5 Ge. V ØPhotons measured with high resolution in PHOS, counting in PMD, and in EMC p/K TPC+ITS K/p e /p (d. E/dx) p/K e /p TOF K/p p/K HMPID (RICH) 0 TRD PHOS 1 2 3 K/p 4 5 p (Ge. V/c) e /p 0 UK HEP Forum 1 12 10 100 p(Ge. V/c) Roman Lietava, University of Birmingham
ALICE Trigger (Birmingham) Triggering on: • collision centrality • high p. T muons • high p. T electrons • jets ALICE trigger features: • Global trigger selection • Past-Future protection • Different trigger rates for group of detectors • Dynamic suppression of common triggers Rates and pile-up: • Pb-Pb collisions: 8 k. Hz interaction rate L=1027 cm-2 s-1 • 60 % pile-up probability • p-p collisions: 200 k. Hz interaction rate L=3 x 1030 cm-2 s-1 • 100 % pile-up probability • TPC drift time 90 s UK HEP Forum 13 Roman Lietava, University of Birmingham
First ALICE trigger board (LTU) UK HEP Forum 14 Roman Lietava, University of Birmingham
Observables Medium characteristics • • • Particle multiplicities Particle spectra Particle ratios Flow Particle correlation Fluctuations UK HEP Forum Hard probes • Jets • Heavy quark and quarkonium production • Direct photons and dileptons 15 Roman Lietava, University of Birmingham
Multiplicity What multiplicity do we expect? We can extrapolate from RHIC data: ALICE design: d. N/dy=8000 UK HEP Forum d. Nch/d ~ 2500 (from K. Kajantie, K. Eskola) 16 Roman Lietava, University of Birmingham
NA 57 Transverse mass spectra NA 57 Pb-Pb at s=17 Ge. V Transverse mass spectra Freeze out temperature Transverse flow 5% most central events UK HEP Forum 17 Roman Lietava, University of Birmingham
Hadron Ratios Degree of chemical equlibrium: Constraint on timescales of flavour production mechanism 18 Roman Lietava, University of Birmingham
• One year of ALICE running (107 events) Ls up to pt = 12 Ge. V/c • Topological signature, not reliant on identification of daughters % L Detection % of rec. Ls vs pt pt (Ge. V/c) L Yield Entries S/B 1 5. 5 L/event Reconstructed pt spectrum M(pp) (Ge. V/c 2) UK HEP Forum 19 pt (Ge. V/c) Roman Lietava, University of Birmingham
Hard Processes Modified by the Medium • Jet quenching: – energy degradation of leading hadrons, pt dependence; – modification of genuine jet observables; – energy imbalance in dijet events • Open charm/beauty production • c’onium & b’onium bound states production Final state (medium) interaction versus initial state (Cronin, shadowing) interaction p-p and p-A measurement are mandatory UK HEP Forum 20 Roman Lietava, University of Birmingham
High p. T Suppression · RAB = d 2 N/dp Td TABd 2 spp/dp. Td Number of coll AA coll pp coll STAR results: d-Au, Cronin effect Au-Au, jet quenching • High pt particles suppressed in Au-Au relative to pp, d-Au. UK HEP Forum J. Adams et al. , Phys. Rev. Lett. 91, 072304 (2003). 21 Roman Lietava, University of Birmingham
Di-jets Mini-jets in Au+Au at RHIC (STAR) In central Au-Au events, although trigger jet is clearly visible, “away-side” jet is not visible, as predicted from strong absorption in a high colour charge density volume, e. g. that produced in a QGP Missing jet UK HEP Forum 22 Roman Lietava, University of Birmingham
Jets Reconstruction in ALICE • Jets are produced copiously. 20 2 100/event 100 200 pt (Ge. V) 100 K/year • Jets are distinguishable from the HI underlying event. I event t je V e G 0 10 UK HEP Forum +H 23 Roman Lietava, University of Birmingham
Heavy Quarks • Initially produced quarks experience the full collision history: – Short time scale for production: t 1/m. Q – Production suppressed at larger times: m. Q» T – Long time scale for decay tdecay» t. QGP • The large masses of c and b quarks make them qualitatively different probes ( massless partons) Observables: UK HEP Forum • Total production rate • transverse momentum distribution • correlation between quark and antiquark 24 Roman Lietava, University of Birmingham
Heavy Quarks D 0 K-p+ reconstruction in ALICE cuts depend on D 0 pt D 0 K-p+ ct = 123. 7 0. 8 m BR: (3. 83 0. 09) % Affected by main vertex resolution in p+p case UK HEP Forum 25 Roman Lietava, University of Birmingham
Heavy Quarks D 0 K-p+ reconstruction in ALICE Pb. Pb: p. T>1 Ge. V/c pp: p. T>0 Ge. V/c UK HEP Forum 26 Roman Lietava, University of Birmingham
Heavy Quarkonia J/Y and via Dielectrons Mass resolution for : 100 Me. V (B = 0. 4 T) J/Y: : Acceptance down to pt = 0 Ge. V/c ! UK HEP Forum 27 Roman Lietava, University of Birmingham
Motivation for pp Study • First insight in pp collisions in new energy domain ( s 14 Te. V), study of evolution of soft hadronic physics • Contribution to knowledge of underlying minimum bias (background) pp events to complement other LHC physics programmes (Higgs search, B physics, etc. ) • Provide pp data as a reference for study of other collision systems (p-A, A-A) • Low multiplicity data to commission and calibrate various components of ALICE UK HEP Forum 28 Roman Lietava, University of Birmingham
ALICE Features for pp ¨ Excellent particle identification (TOF and HMPID) ¨ pt cut-off · Magnetic field (but this could be lowered) · Material thickness (hard to change) ¨ ATLAS and CMS have better -coverage UK HEP Forum 29 Roman Lietava, University of Birmingham
Summary Permanent closure of L 3 door in RB 26 (05/03/04) ALICE experiment is getting ready: - the detectors are being built -the software is getting ready - the understanding of the physics potential grows … UK HEP Forum . . . and so does the number of people involved 30 Roman Lietava, University of Birmingham
ALICE Setup ITS TOF PMD HMPID TRD TPC MUON SPEC. PHOS FMD UK HEP Forum 31 Roman Lietava, University of Birmingham
Low pt Physics Examples Entries Resonances: K* • Decay channel K* K+p • Invariant mass distribution. STAR for. Preliminary 550 events Au+Au minimum bias · p. T 0. 2 Ge. V/c |y| 0. 5 Statistical error only UK HEP Forum STAR data shows clear K* on background · Other resonances (r, w, f 0. . . ) are being extracted 32 Roman Lietava, University of Birmingham
HBT • Single event • Raw correlation function – Uncorrected for Coulomb – R = 8 fm, l = 0. 5 – Tracking with ITS+TPC, B = 0. 2 T C(Qinv) Event-by-Event p+p+ HBT Qinv (Ge. V) C(p 1, p 2)= d 6 N d 3 p 1 d 3 p 2 d 3 N d 3 p 1 d 3 p 2 Resolution for B=0. 2 T UK HEP Forum 33 Roman Lietava, University of Birmingham
Number of Participants Npart p. A: Spectators Npart=n+1 AA: UK HEP Forum 34 Roman Lietava, University of Birmingham
UK HEP Forum 35 Roman Lietava, University of Birmingham
d. N/d Charged Particle Multiplicity 130 Ge. V Au. Au 200 Ge. V Au. Au Ntot = 4100 ± 210 Ntot = 4960 ± 250 0 -6%cent 25 -35%cent 45 -55%cent UK HEP Forum 36 Roman Lietava, University of Birmingham
EMCAL => trigger and g-jet, + improve resolution on Ejet Proposed EMCAL | |<0. 7 Df ~ 120 o TPC g-jet with PHOS+EMCAL + TPC jet Collision axis 8% UK HEP Forum PHOS+EMCAL 2% 37 Roman Lietava, University of Birmingham
Elliptic flow scaled with n(quarks) STAR Preliminary d. N(p. T, b, y, )=A(1 + 2 v 1(p. T, b, y) cos( ) + 2 v 2(p. T, b, y)cos(2 ) +…) - the angle relative to reaction plane • v 1=0 at y=0 by symmetry • v 2 – information about the equation of state UK HEP Forum 38 Roman Lietava, University of Birmingham
Why is elliptic flow interesting? Raimond Snellings coordinate space • Coordinate space configuration anisotropic (almond shape) however, initial momentum distribution isotropic (spherically symmetric) • Only interactions among constituents generate a pressure gradient, which transforms the initial coordinate space anisotropy into a momentum space anisotropy (no analogy in pp) • Multiple interactions lead to thermalization -> limiting behavior ideal hydrodynamic flow y x Momentum space py px UK HEP Forum 39 Roman Lietava, University of Birmingham
Elliptic flow as a function of centrality Non-flow considerable for central and peripheral events 40 STAR Nucl. Phys. A 698 (2002) 193 Roman Lietava, University of Birmingham UK HEP Forum
1+2 Experiments T=LQCD 0 1 Qs 2 10 100 pt (Ge. V/c) Hard processes Modified by the medium Bulk properties ALICE PID CMS&ATLAS UK HEP Forum 41 Roman Lietava, University of Birmingham
High pt RHIC Results • RAA clearly different between mesons and baryons • Importance of PID at high pt • p+p baseline measurement! UK HEP Forum 42 Roman Lietava, University of Birmingham
Heavy Quarks Open Charm via Hadronic Decays Pb+Pb: pt > 1 Ge. V/c d. N/dpt Significance p+p: pt > 0 Ge. V/c ! Significance = UK HEP Forum d. N/dpt Significance 43 Roman Lietava, University of Birmingham
Heavy Quarks Open Charm via Hadronic Decays • Input to simulation – cc: PYTHIA, tuned to NLO calculations, with CTEQ 4 L and nuclear shadowing EKS 98 – Background: HIJING • Reconstruction effects included • PID with TOF Pb+Pb System ( s) Pb-Pb (5. 5 Te. V) pp (14 Te. V) Signal for 107(109)evts 13000 20000 S/B 11 % 50 % Significance for 107(109)evts 37 84 Pb. Pb: p. T>1 Ge. V; pp: p. T>0 UK HEP Forum sminv = 12 Me. V (B = 0. 4 T) 44 Roman Lietava, University of Birmingham
Parton Energy Loss - Reduction of single inclusive high pt particles • Parton specific (stronger for gluons than quarks) • Flavour specific (stronger for light quarks) • Measure identified hadrons (p, K, p, L, etc. ) + partons (charm, beauty) at high pt - p+p and p+A measurements crucial UK HEP Forum – Suppression of mini-jets • same-side / away-side correlations – Change of fragmentation function for hard jets (pt >> 10 Ge. V/c) • Transverse and longitudinal fragmentation function of jets • Jet broadening reduction of jet energy, dijets, -jet pairs 45 Roman Lietava, University of Birmingham
Parton Energy Loss UK HEP Forum 46 Roman Lietava, University of Birmingham
UK HEP Forum 47 Roman Lietava, University of Birmingham
UK HEP Forum 48 Roman Lietava, University of Birmingham
Permanent closure of L 3 door in RB 26 (05/03/04) UK HEP Forum 49 Roman Lietava, University of Birmingham
c/b Quarkonia via dimuons • 1 month statistics of Pb. Pb √s. NN=5. 5 Te. V; Y J/ 104 2 3 4 | | < 2. 4 UK HEP Forum 9 d. N/d =8000 J/ d. N/d =5000 Events/100 Me. V Events/25 Me. V 105 10 11 M + - Y 103 102 0 (Ge. V) 5 2. 5 < 10 <4 50 Roman Lietava, University of Birmingham 15
ALICE Pb-Pb central event UK HEP Forum 51 Roman Lietava, University of Birmingham Nch(-0. 5< <0. 5)=8000
The LHC facility • Running conditions: Collision system √s. NN (Te. V) L 0 <L>/L 0 (cm-2 s-1) pp 14. 0 5. 5 1034* 1027 April 2007 Pb. Pb End 2007 Early 2008 *Lmax(ALICE) = 1031 (%) Run time (s/year) sgeom (b) 70 -50 107 106 * * 0. 07 7. 7 ** Lint(ALICE) ~ 0. 7 nb-1/year • + other collision systems: p. A, lighter ions (Sn, Kr, Ar, O) & energies (pp @ 5. 5 Te. V). UK HEP Forum 52 Roman Lietava, University of Birmingham
Experimental Conditions @ LHC • pp commissioning start April 2007 • wish list of the HI community for the LHC • Initial few years (1 HI ‘year’ = 106 effective s, ~like at SPS) – 2 - 3 years Pb-Pb L ~ 1027 cm-2 s-1 – 1 year p - Pb ‘like’ (p, d or a ) L ~ 1029 cm-2 s-1 – 1 year light ions (e. g. Ar-Ar) L ~ few 1027 to 1029 cm-2 s-1 plus, for ALICE (limited by pileup in TPC): – reg. pp run at s = 14 Te. V L ~ 1029 and < 3 x 1030 cm-2 s-1 • Later: different options depending on Physics results • Heavy Ion running part of LHC initial program, early pilot run expected by end of 2007 UK HEP Forum 53 Roman Lietava, University of Birmingham
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