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B hadron cross-section via single muons in pp collisions at 14 TeV

This article provides an overview of the ALICE detector and its motivations for studying heavy ion collisions at LHC. It discusses the method and results of measuring the B hadron cross-section via single muons in pp collisions. The text language is English.

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B hadron cross-section via single muons in pp collisions at 14 TeV

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  1. B hadron cross-section via single muons in pp collisions at 14 TeV • Heavy ion collisions @ LHC • ALICE detector overview • Motivations • Method • Results • Summary L. Manceau for the ALICE collaboration (LPC Clermont-Ferrand) manceau@clermont.in2p3.fr

  2. Heavy ion collisions@LHC Central Pb-Pb (Au-Au) σc(LHC)= σc(RHIC) × 10 σb(LHC)= σb(RHIC) × 100 σW(LHC)= σγ(RHIC) × 10 σZ(LHC)= σγ(RHIC) LHC: unprecedented conditions to study QCD matter K. Safarik manceau@clermont.in2p3.fr

  3. HMPID PMD PHOS ALICE@LHC • Designed to measure large multiplicity (8000 charged particles per unit of rapidity at mid-rapidity) • Central barrel (-0.9 ≤ η≤ 0.9): (di-)electrons, photons, hadrons • Muon spectrometer (-4 ≤ η≤ -2.5): (di-)muons • Backward, forward small acceptance detectors: multiplicity, centrality, luminosity manceau@clermont.in2p3.fr

  4. ALICE muon spectrometer - 4 ≤ η ≤ -2.5 • Tracking: • Position resolution < 100 μm (bending plane) • →ΔM < 100 MeV/c² @ 10 GeV/c² • 1.1 M read-out channels • Trigger: • Time resolution < 2 ns • Rate < 1kHz • Decision in < 800 ns • 21000 read-out channels manceau@clermont.in2p3.fr

  5. B hadron cross-section in p-p: motivations • Testing NLO pQCD with heavy flavours Charm Beauty hep-ph/0601164 • Large theoretical uncertainties on cross-sections • Measurement of σ(B) [σ(D)] in p-p is mandatory for understanding: • σ(B) [σ(D)] in p-A: shadowing & anti-shadowing • σ(B) [σ(D)] in A-A: energy loss • Measurement of σ(B) in p-p is mandatory for understanding: • σ(Υ) in p-p, p-A & A-A: production, absorption, suppression, recombination (?) • σ(J/ψ) in p-p (→ p-A & A-A): N(B→J/Ψ)/N(direct J/Ψ) ~ 20% in 4π manceau@clermont.in2p3.fr

  6. B hadron cross-section via single muons: method • Extract N(  B) from “data” • Correct for integrated luminosity, detection efficiency, acceptance & decay kinematics • Get differential inclusive B hadron cross-section Eur.Phys.J.C49 :149-154 (2007), ALICE-INT-2006-021 (2006) μ←c: 0. ≤ pt ≤ 3. GeV/c μ←b: 3. ≤ pt ≤20. GeV/c μ←W: 20. ≤pt ≤80. GeV/c manceau@clermont.in2p3.fr

  7. Method widely used and well documented 1. 1.UA1: collisions @ , single muons & dimuons C. Albajar et al., PLB 213 (1988) 405 2.CDF: collisions @ , single electrons F. Abe et al., PRL 71 (1993) 4 3.D0: collisions @ , single muons & dimuons B. Abbott et al., PLB 487 (2000) 264-272 2. 3. ALICE : 4. collisions @ , single electrons F. Antinori et al., ALICE-INT-2006-015 5. collisions @ , single electrons • F. Antinori et al., ALICE-INT-2005-33 6. collisions @ , single muons & dimuons • R. Guernane et al., ALICE-INT-2005-018 4. 5. 6. manceau@clermont.in2p3.fr

  8. Simulation input • Physics Data Chalenge 2006: PDC06 • Full simulation on grid: generation → reconstruction • Detector configuration: MUON+ITS+TOF+T0+V0+FMD+ZDC+PMD+PHOS • 1·107 single muonevents (14000 CPU days, 32 TB with raw data) • Efficiency correction for muon detection in the acceptance • Hypothesis: μ←πΚ is perfectly subtracted • Charm/bottom crossing point ~ 6 GeV/c manceau@clermont.in2p3.fr

  9. Statistics estimates • L=1030 cm-2 s-1 , T=106 s • L=3.1030 cm-2 s-1,T=106 s • L=3.1030 cm-2 s-1 ,T=107 s (Nominal) • Large yield over a broad pt range (even in scenario 1 !) • Beyond 20 GeV/c W ± stick out manceau@clermont.in2p3.fr

  10. Extraction of N(µ←B) Combined fit: (T-B) (fc+R·fb) • T: total number of muons • B: number of muons from B → free parameter • fc (fb) shape distribution of muons from D (B) → from Pythia distributions • R: number of muons from B over number of muons from D → free parameter fixed within 30% (Pythia) Chi2/ddl=0.07 µ←B off by 0.5% µ←D off by 0.3% manceau@clermont.in2p3.fr

  11. Systematic uncertainties Charm Beauty 2. Biased shapes for µ distribution 1. Hadrons hep-ph/0601164 3.Systematic 1. Theoretical predictions for D & B 2. Get μ dN/dpt & Fit μ dN/dpt → biased shapes fc & fb 3. Investigate systematics Chi2/ddl=36 Chi2/ddl=7 µ←B off by 19% µ←B off by 22% • Systematic errors • →17% to 22% on integrated yield • Chi2 → constrain systematics Chi2/ddl=19 Chi2/ddl=13 µ←B off by 17% µ←B off by 17% manceau@clermont.in2p3.fr

  12. → muons pt 2-3 GeV/c F(μ←B) = 39.83 ptmin = 2.4 GeV/c ptmin Decay kinematics corrections F(μ←B) • F(µ←B): Pythia simulation • 90% of B → μ in the acceptance have a transverse momentum larger than ptmin • ptmin: minimisation of the correction dependence on shape distributions used in Pythia 90% manceau@clermont.in2p3.fr

  13. Inclusive differential B hadron cross-section • Input distribution well reconstructed • Statistical errors negligible • Statistical errors from F(μ←B) from 0.4% to 15% at high ptmin • Systematic errors from F(μ←B) negligible • Systematic errors from fit ~20% • Error from normalisation ~5% (not included) Allow to constrain model manceau@clermont.in2p3.fr

  14. Transverse Plane Inclusive differential B hadron cross-section via single electrons TRD TPC ITS • Strategy: • Electron identification: dE/dx TPC, TRD • Impact parameter cut d0: ITS • cτof B ~ 500µm → displaced vertex for electrons ~100 µm. • (π0 background reduction → loss of statistics) • Different method → different stat. & different syst. → cross-check C. Bombonati et al., PWG3, March 07 ALICE-INT-2006-015 manceau@clermont.in2p3.fr

  15. Summary B hadron cross-section from single muons (and electrons) is a very promising channel: • Measuring B cross-section in p-p is mandatory for a large physics program • The method for measuring B cross-section via single muons is widely used and well documented • This method allows us to extract B cross-section for 2. ≤ ptmin ≤ 20. GeV/c, statistical errors are negligible, systematic errors are about 20% ( impose constrains on model parameters) • D hadron cross-section can be extracted simultaneously (work in progress) • As the method is totally different, measuring B & D cross-sections via single electrons is a good cross-check • Measuring B & D cross-sections should allow to compute new ratios to understand energy loss manceau@clermont.in2p3.fr

  16. Back up manceau@clermont.in2p3.fr

  17. B hadron cross-section in p-p: motivations (II) • New ratio to understand energy loss →mass, color charge • R(D)/h color charge dependence • R(B)/h mass dependence • RB/D isolate mass dep. N. Armesto et al., Phys. Rev. D 71 (2005) 054027 J. Phys. G 35 (2008) 054001 • Measurement of σ(B) in p-p is mandatory for understanding: • σ(Υ) in p-p, p-A & A-A: production, absorption, suppression, recombination (?) • σ(J/ψ) in p-p (→ p-A & A-A): N(B→J/Ψ)/N(direct J/Ψ) ~ 20% in 4π → Informations on the thermodynamical state of QCD medium : Ec, Tc manceau@clermont.in2p3.fr

  18. Understanding E loss with heavy flavours • Traditional ratios: • New ratios: 1 nominal year: 107 central Pb-Pb events, 109 p-p events Statistics: bars, systematics: bands Sensitivity to color charge dependence Sensitivity to mass dependence J. Phys. G 32 (2006) 1295, nucl-ex/0609042 manceau@clermont.in2p3.fr

  19. Electrons in central barrel C. Bombonati et al., PWG3, March 07 ALICE-INT-2006-015 manceau@clermont.in2p3.fr

  20. PDC08 22000 evnts p-p @ 14 TeV manceau@clermont.in2p3.fr

  21. Realistic dN/dpt PDC06 • L=1030 cm-2 s-1, T=7.2 105 s (J.P. Revol@Erice05) • L=1030 cm-2 s-1 , T=106 s • L=3.1030 cm-2 s-1 , T=107 s • (Nominal) • L=3.1030 cm-2 s-1, T=106 s Scaling & Extrapolation • Charm underestimated (factor ~ 2). • 106 single muon events. • 2 GeV/c <pt<10 GeV/c. • NLO calculation: • M.L. Mangano, P. Nason and G. Ridolfi, • Nucl. Phys. B 373 (1992) 295 • 4 statistics scenarii. • 2 GeV/c <pt<20 GeV/c. manceau@clermont.in2p3.fr

  22. Systematic uncertainties (I) D hadron B hadron D hadron B hadron Hera LHC • Pythia is tuned to reproduce « Hera LHC » predictions on D and B hadron production cross-section:hep-ph/0601164 manceau@clermont.in2p3.fr

  23. Systematic uncertainties (II) Beauty Charm Beauty 1 Hadrons 2 Muons 3 Fit • Get μ dN/dpt from D & B • Fit μ dN/dpt • Investigate systematics manceau@clermont.in2p3.fr

  24. Flavor creation Flavor exitation Gluon Splitting Unravel NLO processes manceau@clermont.in2p3.fr

  25. Systematic error on decay kinematics & acceptance correction 90% 60% 20% 90% 60% 20% Systematic error is negligible manceau@clermont.in2p3.fr

  26. μ←πΚ Background (I) PDC06 PDC08 Software trigger pt>0.5 GeV/c at generation on muons: μ←πΚ underestimated Realistic μ←πΚ manceau@clermont.in2p3.fr

  27. Point where πΚ are absorbed za zv z=0 I.P.= vertex Origin Absorber μ←πΚ Background (II) D. Stocco et al. ALICE-INT-2006-27 • Due to I.P. displacement πK cover different distances in different events: • I.P. closer to absorber → - probability to decay before absorption → - µ produced • I.P. further to absorber → + probability to decay before absorption → + µ produced manceau@clermont.in2p3.fr

  28. μ←πΚ Background (II) z=zv-za 1. Correcting each pt slices of d²Nµ/dptdz for vertex smearing. 2. linear dependence: slope → muons from πK decay z=0 extrapolation → muons from b & c 1. 2. 2. 1. manceau@clermont.in2p3.fr

  29. path length L Gluonsstrahlung probability w Q kT l in medium, dead cone implies lower energy loss Heavy Quark Energy Loss  C.Salgado (BDMPS) Energy loss depends on: colour coupling factor: 4/3 for q, 3 for g medium transport coefficient “Dead cone” effect for heavy quarks: in vacuum, gluon radiation suppressed at q < mQ/EQ Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291. Salgado, Wiedemann, PRD 68(2003) 014008. Dokshitzer and Kharzeev, PLB 519 (2001) 199. Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003.

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