Paper approval

Paper approval

8231885873e2149e491d180073311049?s=128

Sasha Mazurov

June 06, 2014
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  1. Production of χb at √ s =7 and 8 TeV

    Vanya Belyaev, Concezio Bozzi, Hans Dijkstra, Sasha Mazurov ICHEP approval session 6 June 2014 1/23
  2. Motivation Bound b¯ b states, which can be produced in

    different spin configurations, are an ideal laboratory for QCD tests. It’s like a hydrogen atom in QCD. States with parallel quark spins (S=1): S-wave Υ state. P-wave χb states, composed by 3 spin states χb(0,1,2) . Υ can be readily produced in the radiative decays of χb. χb (3P) state recently observed by ATLAS, D0 and LHCb. This study: 1 Measurement of Υ(NS) (N=1, 2, 3) fraction originating from χb decays as function of pT (Υ). Provides valuable information on Color-Octet matrix elements. 2 Measurement of χb (3P) mass. 2/23
  3. Previous analysis “Production of Υ(1S) mesons from χb decays in

    p¯ p collisions at √ s = 1.8 TeV” at CDF, arXiv:hepex/9910025. “Observation of a new χb state in radiative transitions to Υ(1S) and Υ(2S) at ATLAS”, arXiv:1112.5154 “Measurement of the fraction of Υ(1S) originating from χb(1P) in pp collisions at √ s =7 TeV”, arXiv:1209.0282, L = 32 pb−1 “Observation of the χb(3P) state at LHCb in pp collisions at √ s =7 TeV”, LHCb-CONF-2012-020, L = 0.9 fb−1. ) c (GeV/ ) S (1 ϒ T p 6 7 8 9 10 11 12 13 14 15 ) (%) P (1 b χ ) from S (1 ϒ Fraction of 0 10 20 30 40 50 60 70 80 90 100 LHCb = 7 TeV s ) 2 c ) (GeV/ − µ + µ m( − ) γ − µ + µ m( 0 0.5 1 1.5 2 2 c Candidates / 20 MeV/ 0 50 100 150 200 250 300 LHCb preliminary = 7 TeV s -1 0.9 fb 0 0.5 1 1.5 2 Pull -4 -2 0 2 4 χb(3P) 3/23
  4. In this study The results in this study extend the

    statistical precision of previous LHCb measurements and add considerably more decays and higher transverse momentum regions. The measurement of Υ(3S) fraction in radiative χb(3P) decay was performed for the first time. In each pT(Υ) bin calculate: σ(pp→χb(mP)X)×Br(χb(mP)→Υ(nS)γ) σ(pp→Υ(nS)X) = Nχb(mP)→Υ(nS)γ NΥ(nS) × Υ(nS) χb(mP)→Υ(nS)γ for each Υ(nS), n = 1, 2, 3 and χb(mP), m = 1, 2, 3 Get N from fits: NΥ from m(µ+µ−) and Nχb→Υγ from [m(µ+µ−γ) − m(µ+µ−)] (for better resolution) Compute efficiency from Monte-Carlo simulation 4/23
  5. Content 1 Datasets 2 Determination of Υ yields 3 Determination

    of χb yields in the following decays: χb (1, 2, 3P) → Υ(1S)γ χb (2, 3P) → Υ(2S)γ χb (3P) → Υ(3S)γ 4 Measuring of χb1(3P) mass 5 Monte-Carlo efficiencies 6 Systematic uncertainties 7 Results 5/23
  6. Datasets Full 2011 dataset at √ s =7 TeV. L

    = 1 fb−1 Full 2012 dataset at √ s =8 TeV. L = 2 fb−1 Monte-Carlo simulation of χb inclusive decays, generated 62 × 106 events. 6/23
  7. The Υ selection Almost the same cuts as are used

    in the study “Measurement of Υ production in pp collisions at √ s = 2.76 TeV”, arXiv:1402.2539 Description Requirement Υ rapidity 2.0 < yΥ < 4.5 Track fit quality χ2/ndf < 4 Track pT > 1 GeV/c µ+µ− vertex probability > 0.5% Luminous region |zPV| < 0.5m and x2 PV + y2 PV < 100mm2 Kullback-Leibler distance > 5000 Muon and hadron hypotheses ∆ log Lµ−h > 0 Muon probability ProbNN > 0.5 Trigger lines: L0 L0DiMuon HLT1 Hlt1DiMuonHighMass HLT2 HLT2DiMuonB 7/23
  8. The Υ fit model 9 10 11 0 5000 10000

    15000 20000 25000 30000 Candidates/(40 MeV/c2) mµ+µ− GeV/c2 √ s = 7 TeV 6 < pµ+µ− T < 12 GeV/c Υ(1S) Υ(2S) Υ(3S) µ+µ− transverse momentum intervals, GeV/c 6 – 40 √ s = 7 TeV √ s = 8 TeV NΥ(1S) 283,300 ± 600 659,600 ± 900 NΥ(2S) 87,500 ± 400 203,300 ± 600 NΥ(3S) 50,420 ± 290 115,300 ± 400015 3 Double Crystal Ball functions for signal yields. Tails’ parameters are fixed from simulation. Exponential function for combinatorial background. 8/23
  9. χb selection In this study photons reconstructed using the calorimeter

    information. Another approach uses photon conversions in e+e− pairs — this method has better invariant mass resolution, but requires more statistics. Cuts on γ: Transverse momentum of γ pT(γ) > 600 MeV/c Polar angle of γ in the µ+µ−γ rest frame cos θγ > 0 Confidence level of γ CL(γ) > 0.01 Dimuon mass windows: 9 10 11 0 5000 10000 15000 20000 25000 30000 35000 Candidates/(12 MeV/c2) mµ+µ− GeV/c2 9/23
  10. χb1,2 (1, 2, 3P) → Υ(1S)γ fit model (1) 10

    10.5 0 200 400 600 800 1000 -4 -2 0 2 4 Candidates/(20 MeV /c2) m µ+µ−γ − m µ+µ− + mPDG Υ (1S) GeV /c2 √ s = 7 TeV χb(1P) χb(2P) χb(3P) χb1 χb2 One Crystal Ball (CB) for each χb1,2(1P, 2P, 3P) state: 6 CB in total Exclude the study of χb0 due to its low radiative branching ratio. Product of exponential and linear combination of polynomials for combinatorial background. 10/23
  11. χb1,2 (1, 2, 3P) → Υ(1S)γ fit model (2) Free

    parameters: yields and background parameters. Fixed parameter: µχb1(1P) to the value measured on combined 2011 and 2012 datasets. Linked parameters for χb1 and χb2 signals: µχb2 (jP) = µχb1 (jP) + ∆mPDG χb2 (jP) , j=1,2 µχb2 (3P) = µχb1 (3P) + ∆mtheory χb2 (3P) Nχb = λNχb1 + (1 − λ)Nχb2 (λ is fixed to 0.5) σχb2 = σχb1 Other linked parameters: µχb1 (2P) = µχb1 (1P) + ∆mPDG χb1 (2P) µχb1 (3P) = µχb1 (1P) + ∆mχb1 (3P) (∆mχb1 (3P) measured in this study) Fixed parameters from MC study: σχb1 (1P) , σχb1(2P) σχb1(1P) ,σχb1(3P) σχb1(1P) α and n parameters of CB. Υ(1S) transverse momentum intervals, GeV/c 14 – 40 √ s = 7 TeV √ s = 8 TeV Nχb(1P) 2090 ± 80 5070 ± 130 Nχb(2P) 450 ± 50 1010 ± 80 Nχb(3P) 150 ± 40 220 ± 60 11/23
  12. χb fits 10 10.5 0 200 400 600 800 1000

    Candidates/(20 MeV/c2) mµ+µ−γ − mµ+µ− + mPDG Υ (1S) GeV/c2 LHCb √ s = 7 TeV 10 10.5 0 500 1000 1500 2000 2500 Candidates/(20 MeV/c2) mµ+µ−γ − mµ+µ− + mPDG Υ (1S) GeV/c2 LHCb √ s = 8 TeV 10.2 10.4 10.6 10.8 11 0 50 100 150 200 250 Candidates/(20 MeV/c2) mµ+µ−γ − mµ+µ− + mPDG Υ (2S) GeV/c2 LHCb √ s = 7 TeV 10.2 10.4 10.6 10.8 11 0 100 200 300 400 500 600 Candidates/(20 MeV/c2) mµ+µ−γ − mµ+µ− + mPDG Υ (2S) GeV/c2 LHCb √ s = 7 TeV 10.5 10.6 10.7 0 5 10 15 20 25 30 Candidates/(20 MeV/c2) mµ+µ−γ − mµ+µ− + mPDG Υ (3S) GeV/c2 LHCb √ s = 7 TeV 10.5 10.6 10.7 0 10 20 30 40 50 60 70 80 Candidates/(20 MeV/c2) mµ+µ−γ − mµ+µ− + mPDG Υ (3S) GeV/c2 LHCb √ s = 8 TeV 12/23
  13. Mass of χb1 (3P) in χb → Υ(3S)γ decay 10.5

    10.6 10.7 0 20 40 60 80 100 Candidates/(20 MeV/c2) mµ+µ−γ − mµ+µ− + mPDG Υ (3S) GeV/c2 LHCb √ s = 7 and 8 TeV The measured on the combined 2011 and 2012 datasets mχb1(3P)=10,510 ± 2 (stat) ± 6 (syst) MeV/c2 is consistent with the mass measured in another study with converted photons — 10,515.7 ± 3.1 (stat)+1.5 −2.1 (syst) MeV/c2 (very preliminary results). ATLAS measured χb1 and χb2 mass barycenter for mχb2 − mχb1 = 12 MeV/c2 and λ = 0.5: mχb(3P) = 10,530 ± 5 (stat) ± 9 (syst) MeV/c2 D0: mχb(3P) = 10,551 ± 14 (stat) ± 17 (syst) MeV/c2 13/23
  14. Data — Monte Carlo comparison A comparison of the distribution

    of the relevant observables used in this analysis was performed on real and simulated data, in order to assess the reliability of Monte Carlo in computing efficiencies 0 0.2 0.4 0.6 0.8 1 0 0.01 0.02 0.03 0.04 0.05 0.06 0 0.2 0.4 0.6 0.8 1 0 0.01 0.02 0.03 0.04 0.05 0.06 0 0.2 0.4 0.6 0.8 1 -0.02 0 0.02 0.04 0.06 0.08 0.1 0 2 4 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0 2 4 0 0.02 0.04 0.06 0.08 0 2 4 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0 10 20 30 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0 10 20 30 0 0.02 0.04 0.06 0.08 0.1 0 10 20 30 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 15 20 25 30 35 0 0.01 0.02 0.03 0.04 0.05 0.06 15 20 25 30 35 0 0.02 0.04 0.06 0.08 0.1 15 20 25 30 35 0 0.05 0.1 0.15 0.2 γ confidence level γ confidence level γ confidence level χ2 of decay tree fitter χ2 of decay tree fitter χ2 of decay tree fitter pT [χb(1P)] GeV/c2 pT [χb(2P)] GeV/c2 pT [χb(3P)] GeV/c2 pT [Υ(1S)] GeV/c2 pT [Υ(1S)] GeV/c2 pT [Υ(1S)] GeV/c2 Arbitrary units Arbitrary units Arbitrary units Arbitrary units Arbitrary units Arbitrary units Arbitrary units Arbitrary units Arbitrary units Arbitrary units Arbitrary units Arbitrary units χb(1P) χb(2P) χb(3P) χb(1P) χb(2P) χb(3P) χb(1P) χb(2P) χb(3P) χb(1P) χb(2P) χb(3P) The agreement is generally very good. 14/23
  15. Monte-Carlo photon reconstruction efficiency 20 30 40 0 5 10

    15 20 25 30 Efficiency, % pΥ(2S) T [ GeV/c] χb(3P) → Υ(2S)γ √ s =7 TeV √ s =8 TeV 20 25 30 35 40 0 5 10 15 20 25 Efficiency, % pΥ(3S) T [ GeV/c] χb(3P) → Υ(3S)γ √ s =7 TeV √ s =8 TeV 10 20 30 40 0 5 10 15 20 25 Efficiency, % pΥ(1S) T [ GeV/c] χb(3P) → Υ(1S)γ √ s =7 TeV √ s =8 TeV 20 30 40 0 5 10 15 20 25 Efficiency, % pΥ(2S) T [ GeV/c] χb(2P) → Υ(2S)γ √ s =7 TeV √ s =8 TeV 10 20 30 40 0 5 10 15 20 25 30 Efficiency, % pΥ(1S) T [ GeV/c] χb(1P) → Υ(1S)γ √ s =7 TeV √ s =8 TeV 10 20 30 40 0 5 10 15 20 25 30 Efficiency, % pΥ(1S) T [ GeV/c] χb(2P) → Υ(1S)γ √ s =7 TeV √ s =8 TeV Photon is more energetic as pT(Υ) increases so it is reconstructed more efficiently. 15/23
  16. Systematic uncertainties Since this analysis measures the fraction of Υ(nS)

    particles originating from χb decays, most systematic uncertainties cancel in the ratio and only residual effects need to be taken into account. Systematic uncertainties on the event yields are mostly due to the fit model of Υ and χb invariant masses, while the ones on the efficiency are due to the photon reconstruction and the unknown initial polarization of χb and Υ particles. The uncertainty related to the Υ fit model estimated by the previous study “Production of J/ψ and Υ mesons in pp collisions at √ s = 8 TeV”, arXiv:1304.6977 Systematic due to photon reconstruction taken from the previous works based on “Study of π0/γ reconstruction efficiency with 2011 data”, LHCb-INT-2012-001. Υ fraction uncertainties common to all χb decays (%) Υ fit model ±0.7 γ reconstruction ±3 16/23
  17. Systematic uncertainties — Polarization The Υ polarization is expected to

    be small. “Measurement of the Υ(1S), Y2S and Υ(3S) polarizations in pp collisions at √ s = 7 TeV”, arXiv:1209.2922. The uncertainty related to the unknown polarization of χb mesons was estimated using the prescription described in the LHCb paper “Measurement of the relative rate of prompt χc0, χc1 and χc2 production at √ s = 7TeV” (thanks to Edwige Tournefier) that is based on the analytical calculations in HERA “Production of the Charmonium States χc1 and χc2 in Proton Nucleus Interactions at √ s = 41.6-GeV” In the previous study the uncertainty due to polarization is dominated ≈ 20%. This study shows that this uncertanty is less than 9%. 17/23
  18. Summary of systematic uncertainties Summary of Υ fraction systematic uncertainties

    (%) (maximum deviations that were found in pΥ T bins): χb fit model χb polarization χb(1P) → Υ(1S)γ +4.3 −5.8 +5.1 −4.0 χb(2P) → Υ(1S)γ +4.8 −6.2 +5.8 −6.8 χb(3P) → Υ(1S)γ +19.6 −16.6 +6.9 −6.7 χb(2P) → Υ(2S)γ +2.3 −7.0 +8.7 −7.8 χb(3P) → Υ(2S)γ +19.7 −19.9 +4.5 −4.2 χb(3P) → Υ(3S)γ +20.9 −27.6 +6.4 −7.5 18/23
  19. Υ fractions in χb → Υγ decays 10 20 30

    40 0 5 10 15 20 25 30 35 40 45 50 Υ(1S) fraction, % pΥ(1S) T [ GeV/c] √ s =7 TeV √ s =8 TeV χb(1P) → Υ (1S)γ χb(2P) → Υ (1S)γ χb(3P) → Υ (1S)γ 10 20 30 40 0 10 20 30 40 50 60 Υ(2S) fraction, % pΥ(2S) T [ GeV/c] √ s =7 TeV √ s =8 TeV χb(2P) → Υ (2S)γ χb(3P) → Υ (2S)γ 10 20 30 40 0 10 20 30 40 50 60 70 80 90 100 Υ(3S) fraction, % pΥ(3S) T [ GeV/c] √ s =7 TeV √ s =8 TeV χb(3P) → Υ (3S)γ Outer error bars show statistical and systematics errors, inner error bars — only statistical errors. Unexpected huge fraction of Υ(3S) (≈ 50%) originated from χb(3P) 19/23
  20. Υ(1S) fractions in χb (1P) → Υ(1S)γ decays In agreement

    with the previous LHCb result. 10 20 30 40 0 5 10 15 20 25 30 35 40 45 50 Υ(1S) fraction, % pΥ(1S) T [ GeV/c] χb(1P) → Υ(1S)γ √ s =7 TeV √ s =8 TeV √ s =7 TeV (2010) Outer error bars show statistical and systematics errors, inner error bars — only statistical errors. 20/23
  21. Summary Measured fractions of Υ(1, 2, 3S) originated from χb

    decays. About 40% of Υ come from χb, with mild dependence on Υ transverse momentum. The measurement of Υ(3S) fraction in radiative χb(3P) decay was performed for the first time. This analysis improves significantly the statistical precision of the previous work and adds more decays and transverse momentum regions. Measured mass of χb(3P) is 10, 510 ± 2 (stat) ± 6 (stat) MeV/c2, consistent with another determination which uses converted photons. Request approval to go to paper Thanks to our referees Mikhail Shapkin and Olivier Deschamps Documentation: TWiki page Analysis Note: LHCb-ANA-2014-004 Paper draft available 21/23
  22. Backup 22/23

  23. Υ yields as function of pT 0 10 20 30

    40 50 2 10 3 10 4 10 5 10 6 10 0 10 20 30 40 50 2 10 3 10 4 10 5 10 6 10 0 10 20 30 40 50 2 10 3 10 4 10 5 10 6 10 Events pT(Υ) [ GeV/c] Υ(3S) Events pT(Υ) [ GeV/c] Υ(1S) Events pT(Υ) [ GeV/c] Υ(2S) √ s =7 TeV √ s =8 TeV √ s =7 TeV √ s =8 TeV √ s =7 TeV √ s =8 TeV Yields normalized by bin width and luminosity. The small difference between 7 and 8 TeV data is due to the production cross-sections, which are expected to be about 10% larger. 23/23