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Physics with muons in the ALICE experiment at the LHC

Physics with muons in the ALICE experiment at the LHC. Z Buthelezi for the ALICE Collaboration iThemba LABS, Cape Town, South Africa. Outline Introduction – Heavy Quarks in QGP medium ALICE status and performance Results in the forward rapidity region of ALICE

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Physics with muons in the ALICE experiment at the LHC

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  1. Physics with muons in the ALICE experiment at the LHC Z Buthelezi for the ALICE Collaboration iThemba LABS, Cape Town, South Africa Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  2. Outline • Introduction – Heavy Quarks in QGP medium • ALICE status and performance • Results in the forward rapidity region of ALICE • proton-proton collisions • PbPb collisions • Outlook on new study : W  production in the forward rapidity region of ALICE Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  3. Heavy quarks in QGP medium Diagnostic tool for the formation of the QGP • Heavy quarks are produced at the beginning of the collisions (high Q2) • Pass through the medium and interact with it, losing energy by gluon radiation and elastic collisions - energy loss mechanisms • parton mass (Dead cone effect) • colour charge (Casimir factor) • Compare heavy / light flavour observables - Probe medium properties ΔEg > ΔEu,d ,s > ΔE c > ΔE b RAA() < RAAD < RAAB Medium density & size Yu. Dokshitzer and D.E. Kharzeev, Phys.Lett. B 519, 199‐206 (2001). Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003. Djordjevic, Gyulassy, Horowitz, Wicks, NPA 783 (2007) 493. Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa 3

  4. Quarkonia, heavy ions and the QGP? machine SPS RHIC sN (GeV) 17 200 History: • J/ψ suppression as a QGP signature (1986, Matsui and Satz- Phys. Lett. B178 (4): 416) • NA38, NA50, NA60 @ SPS – PHENIX, STAR @ RHIC Left open questions: –J/ψ suppression “anomalously” similar @ RHIC & SPS – Sequential suppression (’, c) only – cold nuclear matter effect - still weakly constrained – statistical hadronization, recombination? that could be answered by the LHC enhanced J/ production yields @ LHC Thews et al. Phy. Rev. C 63(5):054905 (2001) Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  5. sLHC → best conditions to study QGP(S. Abreu, et al. arXiv:0711.0974) Access hard probe production cross sections • Muon sources @ LHC - Light mesons decays: , K, - Charm decays: D, mesons (J/ +-) (~ 20 x RHIC) - Beauty decays: B, mesons (+-) (~100 x RHIC) - W / Z decays • Muon pt distribution in HI is sensitive to b-quark energy loss effects  RAA reduction due to nuclear shadowing of PDF • W / Z yields expected to scale with <Ncoll> in parton-parton scattering  calibration for HF RAA & test of the binary scaling assumptions HF muon production @ the LHC? machine SPS RHIC LHC sNN (GeV) 17 200 2760 Z.Conesa del Valle et al., arXiv:0712.0051v1  5 Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  6. The ALICE Detector Size: 16 x 26 meters Weight: 10,000 tons Detectors:18 - HI collisions: measure all known observables to characterise the medium formed in the collisions - pp collisions: baseline for A-A and intrinsic interest, test pQCD models J. Instrum. 3, S08002 (2008) Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  7. (charged particles) ALICE Acceptance • Central barrel: -0.9 < h < 0.9 • 2 p tracking, PID (ITS, TPC, TRD, TOF) • single arm RICH (HMPID) • single arm em. calo (EMCAL ) • PHOS • Quarkonia: e+e- channel • Heavy flavour: hadronic channel, semi-leptonic decays (e+/-) • Forward muon arm: 2.5<y<4  Probe small Bjorken-x (10-5 – 10-3) • Resolution (ΔP/P) goal: 1% @ 20 GeV/c, 4% @ 100 GeV/c • absorber, 3 Tm dipole magnet10 tracking + 4 trigger chambersQuarkonia: +- channel • Heavy flavour: semi-leptonic decays (+/-) • Backward + Forward small acceptance detectors: multiplicity, centrality, luminosity & triggering Reduced acceptance µ arm J. Instrum. 3, S08002 (2008) Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  8. Results from proton-proton collisions @ 7 TeV in 2.5<y<4.0 Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  9. cross section vs pt and y Invariant mass distribution Yield vs multiplicity • Highest charge multiplicity (dNch/d  30) reached. • linear increase of the yield vs multiplicity  test interplay between hard & soft interactions in multi-partonic interactions and/or underlying event. Inclusive J/ measurements Polarization vs pt • First J/Ψ polarization measurement @ LHC. • - θ in HF - longitudinal polarization @ low pt which tends to vanish with increasing pt. • CSF it is constant with polarisation • λφ is constant with 0. • Results can be used as stringent constraint to tune QCD models (NRQCD) for heavy quark production • Comparison with other LHC exp: • ALICE covers large rapidity range. • Good agreement with LHCb data. • Data well described by the NRQCD calculations Phys. Let. B 704 (2011) 442455 Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa ArXiv:1111.1630, Phys. Rev Lett., in press

  10. Low-mass dimuons Upsilon () production arXiv:1112.2222v1 [nucl-ex] • Member of B-quark family • Preliminary plot of the invariant mass distribution • Analysis is ongoing… • Dimuon mass spectrum given as resonance (, ) decays into muons and semi-leptonic decays of charmed mesons • Tune models to data especially for hadrons containing u, d, s quarks • Give insight soft QCD processes (multi-parton interactions, pile up), which affects the high pt studies. Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  11. Production of HF single muons • Background (,K) subtracted using MC after normalization to data @ low pt. • Differential cross-sections are well described according to FONLL( pQCD). • Muon from beauty decay dominate for pt >~6 GeV/c. arXiv:1201.3791, accepted by Phys. Lett. B Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  12. Results from Pb-Pb collisions @ 2.76 TeV in 2.5<y<4.0 Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  13. Inclusive J/RAA • Little to no dependence on centrality. • Less suppression observed at LHC than @ RHIC in the forward rapidity region. •  more shadowing @ LHC but nuclear absorption is less to none. Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  14. Exclusive J/ production - ultra peripheral collisions • - Two ions (or protons) pass each other with impact parameters, b > 2R • Electromagnetic interactions are possible • Number of photons scale as Z2 for single source • ⇒ exclusive particle production in HI dominated by electromagnetic interaction • - In Pb+Pb collisions at 5.5 TeV: (hadronic) ~ 8b • R. Bruce et al., Phys.Rev. 12 071002 (2009) (e+e-) ~ 281 b • (EMD) ~ 226 b • - Allow access to information on the gluon density • - Nuclear gluon shadowing • - Coherent (J/ + A production in UPC) - MUON in coincidence with V0C, but V0A vetoed. - Veto activity on V0C outside muon acceptance. - 2 good tracks in the muon acceptance, both tracks match the trigger. - At least one track has a pt > 1 GeV/c. Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  15. J/ elliptic flow azimuthal distribution of particles in the plane  to the beam axis, z Y. Liu, N. Xu, P. Zhuang, Nucl.Phys.A834 (2010) 317c • E - energy of particle, • P - momentum, • pt - transverse momentum, • y – rapidity, • - azimuthal angle, • R - reaction plane angle • n- Fourier coefficient, lowest order terms: • 1- direct flow • 2- elliptic flow • Regeneration / combination of c quarks for J/ production will dominate the J/ flow @ LHC compared to those at low energies • Various methods are being investigated for v2J/ elliptic flow. • Analysis is in progress . High statistics sample from 2011 PbPb runs will allow to measure J/ flow from pt = 0GeV/c. Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  16. Production of HF single muons • Background from , K decays were not subtracted. • Muons from HF decays dominate for pt > 4 GeV/c. • Suppression of a factor ~2.5 in the most central collision. TAA – nuclear overlap function Grey – normalization error: ratio <TAA>peripheral /<TAA>central Red box: systematic errors dN/dpt Bars: statistical errors Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  17. Outlook on new study: W± production via single muon channel in the forward rapidity region of ALICE: 2.5 < y < 4.0 Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  18. Motivation • Initial study“W production in pp, PbPb & pPb collisions @ LHC energies: W± detection in the ALICE Muon Spectrometer” Z.Conesa del Valle et al.,  Eur. Phys. J. C61 (2009) 729-733 • Scientific motivation: • - W muons have a high pt ~ MW /2  W± as reference for observing QGP induced effects on QCD probes, e.g. suppression of high pt heavy quarks • Probe PDF in the Bjorken-x: • x (10-4–10-3)  2.5 < y < 4.0 @ Q2 ~ M2W± • - study nuclear modification of quark distribution, validate binary scaling MW = 80.398 ± 0.25 GeV/c2, electric charge: ±1 e, spin = 1 weak interactions  change generation of a particle (quark flavour change) Measurements in the forward rapidity region of ALICE: 2.5 < y < 4.0 , pt>1 GeV/c, P > 4 GeV/c will be complimentary to those done by ATLAS & CMS @ central rapidity || 2.5, with large pt > 3-4 GeV/c Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  19. Predictions with PYTHIA Process: 2  1, initial and final state radiation Decay channels : W → +  (10.57 ± 0.15%), W  cX ... Y (33.6 ± 2.6 %) PbPb collisions @ s = 5.5 TeV: pp, nn & np combinations. PDF  EKS98 shadowing parameterization K.J Eskola et al Euro. Phys. J. C, 9:61, 1999 Differential cross section - FrixioneandMangano, Hep-ph/0405130 <L>PbPb~5·1032 cm-2s-1 for t = 107 s (~ 0.5 nb-1) G. Martinez, hep-ex/0505021v1 (2005), F. Carminati et al. J. Phys G30, 1517, 2004 (W)PYTHIA x BRW→ = 17.3 nb , spectra normalised to NLO calculations: th(W)NLO x BRW→ = 20.9 nbLai et al, arXiv:hep-ph/9060399v2,10 Aug 996 Lowest & 2nd order diagrams for W production in hadron-hadron collisions W muons have a high pt MW /2  30 – 50 GeV/c. It is estimated that @ pt =(30, 50) GeV/c the reconstructed yield, NW = 6.9x103the forward rapidity range: 2.5 < y < 4.0 . Z Conesa del Valle et al., arXiv:0712.0051v1 19 Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  20. Recent PbPb runs @ the LHC http://lpcc.web.cern.ch/LPCC/index.php?page=luminosity_charts Increase in luminosity  statistics increase by ~ 18 times more than in 2010. High pt reach for HF muon production, e.g. W and Z decay muons ? 20 Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  21. Strategy for W±± production in PbPb collisions with ALICE • Measure differential cross sections as function of pt and y in forward region: 2 <  < 9   2.5 < y < 4, pt >1 GeV/c, P > 4 GeV/c • Subtract background in the pt region below pt  MW / 2  30–50 GeV/c. • Use high level trigger to reject background. J. Phys: Conf. Series 219 (2010) 02244 • Compare single muons ratios: + / -  charge asymmetry. • Extract RAA, RCP. • Compare with theoretical predictions. Z Conesa del Valle et al., arXiv:0712.0051v1 Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa 21

  22. Summary • ALICE has measured inclusive J/, low mass dimuons and HF single muon cross sections in pp collisions at 7 TeV. Good progress also on analysis at 2.76 TeV. • Upsilon analysis at 7 TeV is in progress. • Data show a suppression of HF decays in PbPb collisions is seen in RCP. • It is observed that suppression increases with increasing centrality. • For the J/ case, the observed suppression is almost constant wrt centrality. • Exclusive J/ measurements in ultra-peripheral PbPb collisions in the forward rapidity region of ALICE are also underway. • Statistics from the 2011 PbPb runs should allow to study W production in the forward rapidity region of ALICE. Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  23. Back up slides Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  24. Cross Section evaluation The same procedure adopted for the 7TeV paper has been followed Where: NMB ~ 22.5 106 NMB ~ 1.4 104 N-MB ~ 4.2 105 number of CINT1B triggers. After physics selection, a small decrease is expected (was ~1-2% in LHC10e) Number of single  with pT>1GeV/c, surviving standard cuts, in CINT1B (NMB) or CMUS1B (N-MB ) trigger Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  25. Centrality measurements in PbPb collisions @ 2.76 TeV Events: - MB trigger events Centrality class: 0-80% determined by V0 Glauber model analysis of large-η V0 scintillator amplitudes :V0A : 2.8 < η < 5.1, V0C : -3.7 < η < -1.7 Phys. Rev. Lett. 106, 032301 (2011) Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  26. HF muon cross sections in different pt bins, pp collisions @ 7TeV arXiv:1201.3791, accepted by Phys. Lett. B Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

  27. Comparison of theoretical prediction for W production at the LHC (Anastasiou et al, hep-ph/0312266v2)

  28. PbPb collisions @ 2.76 TeV: J/Psi RCPmeasurements in 2.5<y<4.0 ALICE data exhibits less suppression @ forward rapidity and low pt compared to ATLAS TAA – nuclear normalisation factor Exploring QCD Frontiers: from RHIC and LHC to EIC, 29 Jan - 3 Feb 2012, Stellenbosch, South Africa

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