Production of χb at√

s =7 and 8 TeV

Vanya Belyaev, Concezio Bozzi, Hans Dijkstra, Sasha Mazurov

ICHEP approval session6 June 2014

1/23

Motivation

Bound bb̄ states, which can be produced in different spin configurations, are anideal 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 statesχb(0,1,2).Υ can be readily produced in the radiative decaysof χb.χb(3P) state recently observed by ATLAS, D0 andLHCb.

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-Octetmatrix elements.

2 Measurement of χb(3P) mass.

2/23

Previous analysis

“Production of Υ(1S) mesons from χb decays in pp̄ 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 ppcollisions 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(1ϒT

p6 7 8 9 10 11 12 13 14 15

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3/23

In this study

The results in this study extend the statistical precision of previous LHCbmeasurements and add considerably more decays and higher transversemomentum 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)× εΥ(nS)

εχb(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 ε from Monte-Carlo simulation

4/23

Content

1 Datasets2 Determination of Υ yields3 Determination of χb yields in the following decays:

χb(1, 2, 3P)→ Υ (1S)γχb(2, 3P)→ Υ (2S)γχb(3P)→ Υ (3S)γ

4 Measuring of χb1(3P) mass5 Monte-Carlo efficiencies6 Systematic uncertainties7 Results

5/23

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

The Υ selection

Almost the same cuts as are used in the study “Measurement of Υ productionin pp collisions at

√s = 2.76 TeV”, arXiv:1402.2539

Description Requirement

Υ rapidity 2.0 < yΥ < 4.5Track fit quality χ2/ndf < 4

Track pT > 1 GeV/cµ+µ− vertex probability > 0.5%

Luminous region |zPV | < 0.5m and x2PV + y2

PV < 100mm2

Kullback-Leibler distance > 5000

Muon and hadron hypotheses ∆ logLµ−h > 0Muon probability ProbNN > 0.5

Trigger lines:L0 L0DiMuon

HLT1 Hlt1DiMuonHighMassHLT2 HLT2DiMuonB

7/23

The Υ fit model

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GeV/c2]

√s = 7 TeV

6 < pµ+µ−

T < 12 GeV/c

Υ (1S)

Υ (2S)

Υ (3S)

µ+µ− transverse momentum intervals, GeV/c6 – 40

√s = 7 TeV

√s = 8 TeV

NΥ (1S) 283,300 ± 600 659,600 ± 900NΥ (2S) 87,500 ± 400 203,300 ± 600NΥ (3S) 50,420 ± 290 115,300 ± 400015

3 Double Crystal Ball functions for signal yields. Tails’ parameters arefixed from simulation.

Exponential function for combinatorial background.

8/23

χb selection

In this study photons reconstructed using the calorimeter information.Another approach uses photon conversions in e+e− pairs — this methodhas better invariant mass resolution, but requires more statistics.Cuts on γ:

Transverse momentum of γ pT(γ) > 600 MeV/cPolar angle of γ in the µ+µ−γ rest frame cos θγ > 0Confidence level of γ CL(γ) > 0.01

Dimuon mass windows:

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mµ+µ−[

GeV/c2]

9/23

χb1,2(1, 2, 3P)→ Υ (1S)γ fit model (1)

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mµ+µ−γ

− mµ+µ− + mPDG

Υ (1S)

[GeV/c2

]

√s = 7 TeVχb(1P)

χb(2P)

χb(3P)χb1 χb2

One Crystal Ball (CB) for each χb1,2(1P, 2P, 3P) state: 6 CB in totalExclude the study of χb0 due to its low radiative branching ratio.Product of exponential and linear combination of polynomials forcombinatorial background.

10/23

χb1,2(1, 2, 3P)→ Υ (1S)γ fit model (2)

Free parameters: yields and backgroundparameters.

Fixed parameter: µχb1(1P) to the valuemeasured on combined 2011 and 2012datasets.Linked parameters for χb1 and χb2signals:

µχb2(jP) = µχb1(jP) + ∆mPDGχb2(jP), j=1,2

µχb2(3P) = µχb1(3P) + ∆mtheoryχb2(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/c14 – 40

√s = 7 TeV

√s = 8 TeV

Nχb(1P) 2090 ± 80 5070 ± 130Nχb(2P) 450 ± 50 1010 ± 80Nχb(3P) 150 ± 40 220 ± 60

11/23

χb fits

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mµ+µ−γ − mµ+µ− + mPDGΥ (1S)

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mµ+µ−γ − mµ+µ− + mPDGΥ (3S)

[GeV/c2

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12/23

Mass of χb1(3P) in χb → Υ (3S)γ decay

10.5 10.6 10.70

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[GeV/c2

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LHCb√s = 7 and 8 TeV

The measured on the combined 2011 and 2012 datasetsmχb1(3P)=10,510± 2 (stat)± 6 (syst) MeV/c2 is consistent with the massmeasured 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 formχb2 − 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

Data — Monte Carlo comparison

A comparison of the distribution of the relevant observables used in thisanalysis was performed on real and simulated data, in order to assess thereliability of Monte Carlo in computing efficiencies

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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]

Arb

itrar

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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

Monte-Carlo photon reconstruction efficiency

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pΥ (2S)T [ GeV/c]

χb(3P)→ Υ(2S)γ√

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χb(3P)→ Υ(3S)γ√

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χb(3P)→ Υ(1S)γ√

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pΥ (2S)T [ GeV/c]

χb(2P)→ Υ(2S)γ√

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χb(2P)→ Υ(1S)γ√

s =7 TeV√

s =8 TeV

Photon is more energetic as pT(Υ)increases so it is reconstructed moreefficiently.

15/23

Systematic uncertainties

Since this analysis measures the fraction of Υ(nS) particles originating from χb decays, mostsystematic 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 invariantmasses, while the ones on the efficiency are due to the photon reconstruction and the unknowninitial polarization of χb and Υ particles.

The uncertainty related to the Υ fit model estimated by the previous study “Production of J/ψ andΥ 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/γreconstruction efficiency with 2011 data”, LHCb-INT-2012-001.

Υ fraction uncertainties common to all χb decays (%)

Υ fit model ±0.7γ reconstruction ±3

16/23

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 wasestimated 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 analyticalcalculations in HERA “Production of the Charmonium States χc1 and χc2in 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

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

Υ fractions in χb → Υγ decays

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χb(1P)→ Υ (1S)γ

χb(2P)→ Υ (1S)γ

χb(3P)→ Υ (1S)γ

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χb(2P)→ Υ (2S)γ

χb(3P)→ Υ (2S)γ

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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

Υ(1S) fractions in χb(1P)→ Υ (1S)γ decays

In agreement with the previous LHCb result.

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s =8 TeV√

s =7 TeV (2010)

Outer error bars show statistical and systematics errors, inner error bars — only statistical errors.

20/23

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 wasperformed for the first time.

This analysis improves significantly the statistical precision of theprevious 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

Backup

22/23

Υ yields as function of pT

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pT(Υ) [ GeV/c]

Υ (3S)

Eve

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pT(Υ) [ GeV/c]

Υ (1S)

Eve

nts

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 productioncross-sections, which are expected to be about 10% larger.

23/23