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chi_b production study

chi_b production study

Sasha Mazurov

June 06, 2013
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  1. 1
    Study of χ
    b
    production
    at √s=7 and 8 TeV
    Sasha Mazurov
    Ferrara University, CERN
    68th LHCb week
    6 June 2013

    View full-size slide

  2. 2
    Motivation
    bb system, which can be produced in different spin configurations, is ideal laboratory
    ̄
    for QCD tests. It is like a hydrogen atom in QCD.
    States with paralell quark spins (S=1):

    S-wave ϒ state

    P-wave χ
    b
    states, composed by 3 spin
    states χ
    b(0,1,2)
    .
    ● ϒ can be readily produced in the radiative
    decays of χ
    b
    .

    χ
    b
    (3P) state recently observed by ATLAS, D0 and
    LHCb
    Study of χ
    b
    production:

    Measurement for ϒ(1,2,3S) cross sections in
    χ
    b
    decays as a function of p
    T
    (ϒ)

    Measurement of χ
    b(0,1,2)
    (3P) mass.

    Measured mass

    Mass from theory

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  3. 3
    Previous analysys in LHCb

    “Measurement of the fraction of ϒ(1S) originating from χ
    b
    (1P ) decays
    in pp collisions at s=7 TeV”, arXiv:1209.0282,
    √ L =32 pb−1

    “Observation of the χ
    b
    (3P) state at LHCb in pp collisions at s=7 TeV”,

    LHCb-CONF-2012-020, L=0.9 fb−1

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  4. 4
    Cross sections formula

    Calculate for each ϒ(nS), n=1,2,3 and χ
    b
    (mP), m=1,2,3

    Get N from fits: N
    ϒ
    from invariant mass fit of m
    µ+µ-
    and N
    χb→ϒγ
    from mass difference fit of [m
    µ+µ- γ
    – m
    µ+µ-
    ] (better resolution)

    Compute efficiency ε from Monte-Carlo simulation
    Measure differential cross section ratio in bins of p
    T
    (ϒ)
    for 2.5 < y
    ϒ
    < 4

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  5. 5
    Content

    Data and Monte-Carlo samples

    Event Selection criteria

    Determination of ϒ yields

    Determination of the χ
    b
    yields in χ
    b
    → ϒ(1S) γ decay

    Data — Monte-Carlo comparison

    Preliminary results for ϒ(1S) cross section

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  6. 6
    Data and Monte-Carlo samples
    ● √s=7 TeV: Reco14, Stripping 20r1, WGBandQSelection3,
    BOTTOM.MDST. L=1089 pb-1
    ● √s=8 TeV: Reco14, Stripping 20, WGBandQSelection3,
    BOTTOM.MDST. L=2011 pb-1

    Monte Carlo: MC11a, Reco12a, inclusive χ
    b0,1,2
    (1,2,3P) decays.
    5E+5 events for each χ
    b
    state and magnet direction.
    — χ
    b0,1,2
    (2,3P) could not be generated directly, so they are
    defined as χ
    b1,2
    (1P), but with redefined mass and decay
    channels.

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  7. 7
    Event Selection criteria
    |m
    µ+µ−
    - m
    ϒ(1S), pdg
    | < 0.2 GeV/c2
    χ2 of d.t.f in [0, 4]
    Muons min(∆logL] > 0
    Angle of γ direction cos θ
    γ
    > 0
    p
    T
    (γ] > 0.6 GeV/c
    γ confidence level > 0.01
    Use only TOS events (trigger on ϒ]:
    L0 (Muon | DiMuon).*Decision
    HLT1 (DiMuon | SingleMuonHighPT | MuonTrack).*Decision
    HLT2 (DiMuon | SingleMuonHighPT).*Decision

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  8. 8
    Determination of ϒ yields
    ϒ(1S)
    ϒ(2S)
    ϒ(3S)
    Y(1S) signal: f*CB
    Y(1S)(1)

    Y(1S)
    , σ
    Y(1S)
    , α, n] + (1-f)CB
    Y(1S)(2)

    Y(1S)
    , σ
    Y(1S)
    , -α, n]
    Y(2S) signal: CB
    Y(2S)

    Y(2S)
    , σ
    Y(2S)
    , α, n]
    Y(3S) signal: CB
    Y(3S)

    Y(3S)
    , σ
    Y(3S)
    , α, n]

    Floating parameters: f, µ
    Y(1,2,3S)
    , σ
    Y(1S)
    , τ, a
    1

    Constant parameters: α, n

    Constraints: σ
    Y(2S)
    = σ
    Y(1S)
    * (µ
    Y(2S)

    Y(1S)
    ], σ
    Y(3S)
    = σ
    Y(1S)
    * (µ
    Y(3S)

    Y(1S)
    ]
    Signal: the sum of Crystal Ball
    functions, one for each of the Y(2S),
    Y(3S) and two for Y(1S).
    Background: e-τx *(a
    1
    x)
    √s=8 TeV
    p
    T
    (ϒ) > 6 GeV/c
    6.5e+5
    2e+5
    1.1e+5
    α 1.28
    n 4
    B 1314200 ± 1500
    N1S 651760 ± 969
    f 0.749 ± 0.001
    N2S 197750 ± 597
    N3S 112670 ± 482
    dm2s 0.56421 ± 0.00018
    dm3s 0.89588 ± 0.00024
    µ
    Y(1S)
    9.4677 ± 0.00076
    a
    1
    0.1098 ± 0.0092
    σ
    Y(1S)
    0.045809 ± 0.000065
    τ -0.548 ± 0.011

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  9. 9
    Determination of the χ
    b
    yields in χ
    b
    → ϒ(1S) γ decay
    χ
    b(1P)
    Signal: 6 Crystal Ball functions
    Background: e-τx *(a
    1
    x+a
    2
    x2+a
    3
    x3)

    Fit mean and width of χ
    b1
    (1P) Crystal Ball, and means of χ
    b1
    (2P), χ
    b1
    (3P)

    Use MC to scale all other widths to the χ
    b1
    (1P) width.

    Fix means of χ
    b2
    states by using

    PDG: mass differences between χ
    b1
    (1P) and χ
    b2
    (1P), χ
    b1
    (2P) and χ
    b2
    (2P)

    MC: mass differences between χ
    b1
    (3P) and χ
    b2
    (3P)

    For each sum of χ
    b1
    and χ
    b2
    fix a relation:
    N[χ
    b1,2
    (mP)] = α
    frac
    N[χ
    b1
    (mP)] + (1-α
    frac
    )N[χ
    b2
    (mP)], m=1,2,3; α
    frac
    fixed at 0.5

    Systematic uncertainties due to relative contributions of χ
    b1
    and χ
    b2
    states ~ 5% on yields (see backup]
    P
    T
    (ϒ(1S)]>14
    χ
    b(2P) χ
    b(3P)
    χ
    b1(1P)
    χ
    b2(1P)
    4.7e+3
    1e+3
    2e+2
    B 31979 ± 324
    N1P 4725 ± 202
    N2P 1.084 ± 92
    N3P 207 ± 73
    mean_b1_1p 0.42989 ± 0.00076
    mean_b1_2p 0.7922 ± 0.0035
    mean_b1_3p 1.074 ± 0.035
    sigma_1P 0.02167 ± 0.00087

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  10. 10
    Data — Monte-Carlo comparison
    Compare decay variables distributions:
    Get the distributions from sPlots on data and from
    matched events in MC.
    No big difference expected in ϒ variables (as already
    seen in other analyses)

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  11. 11
    p
    T
    (ϒ) χ
    b
    (1P)
    χ
    b
    (2P)
    χ
    b
    (3P)
    p
    T
    (ϒ)
    p
    T
    (ϒ)
    p
    T

    b
    (1P))
    p
    T

    b
    (2P))
    p
    T

    b
    (3P))
    — Monte-Carlo
    — Data

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  12. 12
    p
    T
    (γ) χ
    b
    (1P)
    p
    T
    (γ)
    p
    T
    (γ)
    χ
    b
    (2P)
    χ
    b
    (3P)
    On data the background form depends on p
    T
    (γ], so
    the difference in p
    T
    (γ] distributions are due to the
    sPlot technique.
    For other variables we observe nice agreement
    between data and MC, so we can trust the MC to
    compute efficiencies.

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  13. 13
    Preliminary Results (1)

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  14. 14
    Preliminary Results (2)

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  15. 15
    Systematic uncertainties

    In fit models
    ―For χb
    model (Done]
    ―For ϒ model [In progress]

    Data — Monte-Carlo agreement [To be done, should be small]

    γ reconstruction
    (use previous studies LHCb-INT-2012-001)

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  16. 16
    ToDo

    Finalize systematic uncertainties

    Documentation

    Study of ϒ(2,3S) fractions

    Measurement for rapidity bins

    Precise measurement of χb
    (3P)
    mass

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  17. 18
    Systematic uncertainties
    Constraint N[χ
    b
    (1P)]
    change(%)
    N[χ
    b
    (2P)]
    change(%)
    N[χ
    b
    (3P)]
    change(%)
    N[χ
    b
    (2P)]/N[χ
    b
    (1P)]
    change(%)
    N[χ
    b
    (3P)]/N[χ
    b
    (1P)]
    change(%)
    α
    frac

    b
    (1P)] = 0 3 3 3 0 1
    α
    frac

    b
    (1P)] = 1 3 3 3 0 1
    α
    frac

    b
    (2P)] = 0 2 -2 1 -4 0
    α
    frac

    b
    (2P)] = 1 0 -1 0 -1 0
    α
    frac

    b
    (3P)] = 0 0 0 -1 0 -1
    α
    frac

    b
    (3P)] = 1 0 0 0 0 0
    Fix max PDG mass diff between
    χ
    b1
    (1P) and χ
    b2
    (1P)
    2 -4 7 -6 -8
    Fix max PDG mass diff between
    χ
    b1
    (2P) and χ
    b2
    (2P)
    0 0 0 0 0

    Systematic uncertainties due to relative contributions of χ
    b1
    and χ
    b2
    states

    Other systematic uncertainties are under study.

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  18. 19
    χ
    b
    (1P)
    χ
    b
    (2P)
    χ
    b
    (3P)
    min[p(µ+) , p(µ−)]

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  19. 20
    Data — Monte-Carlo comparison

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  20. 21
    χ
    b
    (1P)
    χ
    b
    (2P)
    χ
    b
    (3P)
    min[pT(µ+) ,pT(µ-)] χ2 for decay tree
    fitter
    χ
    b
    (1P)
    χ
    b
    (2P)
    χ
    b
    (3P)

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  21. 22
    χ
    b
    (1P)
    χ
    b
    (2P)
    χ
    b
    (3P)
    min[p(µ+) , p(µ−)]

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  22. 23
    χ
    b
    (1P)
    χ
    b
    (2P)
    χ
    b
    (3P)
    Muon
    identification
    χ2 for decay vertex
    fitter

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  23. 24
    χ
    b
    (1P)
    χ
    b
    (2P)
    χ
    b
    (3P)
    χ
    b
    rapidity

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