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Upsilon Production at LHCb

Quarkonia Workshop, Vienna, 19th April 2011

Giulia Manca, Universita` degli Studi di Cagliari & I.N.F.N.

on behalf of the LHCb collaboration

LHCb-CONF-2011-016

Outline

➡Theory and motivation➡The LHC and LHCb➡Selected quarkonia results

ϒ cross section

➡Conclusions and outlook

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Introduction➡Many quarkonia states

discovered ~30 years ago➡Nevertheless theproduction mechanism is not fully understood➡Expected large cross-sections at

LHC ->among first measurements ➡High rates make quarkonia

central player for detector and software calibration

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Fermilab, Summer 1977

Motivations

➡ The production mechanism in pp collisions still unclear

➡ Several models around : Started with Color singlet(CSM)

Undershoots the data, no polarisation prdiction

Extendend to color octet (COM) mechanisms

Better agreement for cross-section, predicts TRANSVERSE polarisation, not

confirmed by experiments NLO CSM describes cross-section and allows LONGITUDINAL polarisation Other models such as color

evaporation model (CEM), kt factorization, soft color interaction model cannot describe the data or make predictions

➡ New data from LHC experiments will help to resolve this issue

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J/ & ϒ cross section crucial milestone in understanding detector and first step to B cross

section measurement

pT(GeV/c)

Polarisation measurement

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In the Υ(1S) case, the D0 results (black) are incompatible with the CDF results (green) The CDF results are compatible with the NRQCD predictions (yellow) The D0 results are marginally incompatible with NRQCD predictions The curves are the limiting case of the kT factorization predictionsFor J/psi and Psi(2s) the NRQCD and the data disagree.

CERN and the LHC

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p p

NOMINAL (2011) : √s =14 TeVL = 2·1032 cm-2 s-1 (LHCb specific)

pp collider : 2010 :➡ @ √s = 7 TeV➡ L ≈ 1-2·1031 cm-2 s-1

Luminosity @ LHCb

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Mar 2010 July 2010 Nov 2010

➡ LHC running very well!

➡ LHCb efficiency ≈90%

➡ This analysis : L ≈ 35 pb-1 (±10%)

Goal : 1 fb-1 (end

of 2011)

The LHCb detector

collision

Point

Vertex

Locator

VELO

Tracking

System

Muon

SystemRICH

Detector

Calorimeters

p p

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Performance numbers relevant to quarkonium analyses:– Charged tracks p/p = 0.35 % - 0.55%, (m)=10-

25 MeV/c2

– ECAL (E)/E= 10% (E/GeV)-1/2 1 % – Muon ID: () = 97%, mis-ID rate () = 1-3 % – Vertexing: proper time resolution 30-50 fs– Trigger: dominantly software

field regularly reversed to cancel detector

asymmetries

Rapidity Range

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ϒ→ Acceptance

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LHCb

CMS

ATLASCMS

ATLAS

LHCb

ALICE

Total Acceptance≈3-14%ATLAS Acceptance 85%

Total Acceptance≈20%CMS 85%

Total Acceptance≈8%LHCb Acceptance 86%

ϒ production

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€

pp →bb + X

Three for the price of one!

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BR(Y(1S))=(2.48±0.05)%

BR(Y(2S))=(1.93±0.17)%

BR(Y(3S))=(2.18±0.21)%

Trigger and Event Selection

L0 Trigger:Single Muon:

Di-Muon:

pT>1.4 GeV/c

pT,1>0.56 GeV/c, pT,2>0.48 GeV/c

HLT1 Trigger:Single Muon:

Di-Muon:

Confirm L0 single Muon and pT>1.8 GeV/c (Prescaled)

Mμμ>2.9 GeV/c2 or cuts on vertex and track quality

HLT2 Trigger:

μ tracks: ● well reconstructed tracks identified as muons in muon detector, ● pT > 1 GeV/c, ● Track fit quality

Reconstructed : ● mass window: 8.5-11.5 GeV/c2, ● vertex fit quality (p(χ2)>0.5%).

Global Event Cuts (GEC): reject events with very large multiplicities (93% efficiency)

Confirm L0 Di-Muon and Mμμ>2.5 GeV/c2Di-Muon:

Cross Section Measurement Strategy

For a generic resonance A:

a) Nfit = number of events in the mass peak in each pT bin, corrected for acceptance and efficiency

b) c) εtot = total efficiency

d) e) ∆pt, ∆y = bins of pT and y

f) ∫Ldt = integrated luminosity

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€

dσ ( pp → A )dpT dy 2.0< y< 4.5

Br(A →μ +μ −) =N fit

A (pT ,y;ε tot )

Ldt⋅ ΔpT ⋅ Δy∫

a) Number of ϒ(1S) candidates

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• Nfit : function=3 Crystal Balls(CB)+exponential for background. Fixed (=2,n=1) and width (2S,3S) to scale with the masses.

Same function used on

individualbin fits

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Workshop

a) Number of ϒ (1S) candidates• Nfit : extracted from Crystal Ball (CB) part of the fit with CB+ exponential. •Fix width and masses •Only ϒ(1s) considered.

•2.0 < y < 2.5

0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5 5<pT<6

6<pT<7 7<pT<8 8<pT<9

9<pT<10 10<pT<11 11<pT<12

12<pT<13 13<pT<14 14<pT<15

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a) Number of ϒ(1S) candidates

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Efficiency

The efficiency εtot has been broken in three pieces :

εtot = Nϒ(accepted, reconstructed and triggered)/Nϒ generated

Nϒaccepted Nϒreconstructed Nϒtriggered = Nϒgenerated Nϒaccepted Nϒreconstructed

-Nϒgenerated = Total number of ϒ’s generated in the pT-y chosen range

-Nϒaccepted = Number of ϒ’s generated inside the LHCb angular acceptance (10-400 mrad), in the pT-y chosen range

-Nϒreconstructed=Number of ϒ’s accepted, detected and reconstructed in range -Nϒtriggered =Number of ϒ’s accepted, detected, reconstructed in range and triggered

€

dσ ( pp → Υ(nS )dpT dy Δy

• Br(Υ(nS) →μ +μ −) =N fit

Υ(nS )(pT , y;A,ε trig ,ε reco)

Ldt⋅ ΔpT ⋅ Δy∫

b) A c) εreco d)εtrig

from Monte Carlo

from Data and MC

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b) Acceptance Nevts gen with in 0<pT<15,2.0<y<4.5,10<<400mrad A=acceptance of the LHCb geometry cut= Nevts generated with in 0<pT<15,2.0<y<4.5

pT of Y (GeV/c)

y of Y

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c) Reconstruction Efficiency N ϒ’s detected,reconstructed in range Εrec = efficiency for ϒ’s to be detected, reconstructed and matched to MC N ϒ’s generated in angular acceptance in range

pT of Y (GeV/c)

y of Y

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d) Trigger EfficiencyTrigger efficiency: efficiency of the triggers used to select the events ➡ L0 ➡ HLT1➡ HLT2

Calculated in J/ events as a function of (pT1+pT2) and <y>, for independent triggers, then weighed with Lum Since some triggers were prescaled for a portion of the data, an average value is used, weighted by the corresponding luminosity. Several cross checks have been performed to make sure this was correctly handled.

Systematic uncertainty estimated using J/ and ϒ Monte Carlo->later

Applied as a weight to the candidate entering the M() plot N ϒ’s detected,reconstructed,triggered in rangeεtrig= efficiency ϒ’s to be triggered N ϒ’s detected,reconstructed, in range

d) Trigger Efficiency

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➡ Scaled number of candidates to get effect as a function of ϒ pT and y

pT of Y (GeV/c)

y of Y

pT of Y (GeV/c)

Scaled number of ϒ(1S) candidates

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• Nfit : function=3 Crystal Balls(CB)+exponential for background. Fixed (=2,n=1) and width (2S,3S) to scale with the masses.

Scaled for the trigger

efficiency

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Systematic Uncertainties

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Polarisation effect on Calculated reweighting the MC unpolarised events

assuming =±1

= 0 = -1 =+1

α = −1 ->full longitudinal polarisationα = +1 -> full transversepolarization, α = 0 -> no polarisation

α = (σT −2σL)/(σT +2σL)With σT /L cross sections for production of transverse and longitudinal polarised

pT of Y (GeV/c)

pT of Y (GeV/c) pT of Y (GeV/c) pT of Y (GeV/c)

y of Y

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Polarisation effect on reco

➡ Calculated reweighting the MC unpolarised events assuming =±1

α = −1 ->full longitudinal polarisationα = +1 -> full transversepolarization, α = 0 -> no polarisation

α = (σT −2σL)/(σT +2σL)With σT /L cross sections for production of transverse and longitudinal polarised

y of YpT of Y (GeV/c)

Upsilon Cross Section

€

108.3 ± 0.7(stat) -7.9+18.8(pola) ± 22.0(osys) ±10.8(lumi) nb =108.3 ± 0.7(stat) -25.8

+30.9 (syst) nb

Comparison with Theory

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Y. Q. Ma, K. Wang and K. T. Chao, Phys. Rev. Lett. 106 (2011) 042002.

P. Artoisenet, PoS ICHEP 2010 (2010) 192.

J.-P. Lansberg, Eur. Phys. J. C 61 (2009) 693

A. D. Frawley, T. Ullrich and R. Vogt, Phys. Rep. 462 (2008) 125.

Comparison with CMS

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Conclusions

➡ϒ(1S) cross section measured. ϒ(2S) and ϒ(3S) are under way

➡Agreement with theory good!➡Trigger efficiency and polarisation

uncertainty can be improved ➡ϒ polarisation next step➡Should be ready for the summer

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Back up

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ϒ cross section

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G.Bodwin, talk at Berkeley workshop May 2009

ϒ rate ~ 1/100 J/ψ rateLHC rate ~ 50 Tevatron rate

Caveats:1. These plots only include the color-

singlet contributions lower limit2. Branching ratios not included3. Our energies lower than 5 GeV

more events4. Rapidity range different (but flat

y)5. 10 TeV!

Level 0: Hardware triggers From Muon system & calorimeters

High Level Trigger (HLT) 1: Software triggersAdd information from VELO and tracking stations to Level 0 informationFind primary vertices, etc.

HLT2: Software triggersUse all of the detector information to makeinclusive and exclusive selections

The LHCb Trigger

Trigger and Event Selection

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Trigger Efficiency

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• Systematics: difference between e(trig) measured in J/ MC events and the true value in ϒ MC

Caveat: this is the per bin effect, the effect on the cross section is 6-16%

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a) Number of ϒ (1S) candidates• Nfit : extracted from Crystal Ball (CB) part of the fit with CB+ exponential. •Fix width and masses •Only ϒ(1s) considered.

•2.0 < y < 2.5

0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5 5<pT<6

6<pT<7 7<pT<8 8<pT<9

9<pT<10 10<pT<11 11<pT<12

12<pT<13 13<pT<14 14<pT<15

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a) Number of ϒ (1S) candidates• Nfit : extracted from Crystal Ball (CB) part of the fit with CB+exponential. •Fix width,m2S,m3S to 50 MeV. •Only ϒ(1s) considered.

•2.5 < y < 3.0

0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5 5<pT<6

6<pT<7 7<pT<8 8<pT<9

9<pT<10 10<pT<11 11<pT<12

12<pT<13 13<pT<14 14<pT<15

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a) Number of ϒ (1S) candidates• Nfit : extracted from Crystal Ball (CB) part of the fit with CB+exponential. •Fix width,m2S,m3S to 50 MeV. •Only ϒ(1s) considered.

•3.0 < y < 3.5

0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5 5<pT<6

6<pT<7 7<pT<8 8<pT<9

9<pT<10 10<pT<11 11<pT<12

12<pT<13 13<pT<14 14<pT<15

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a) Number of ϒ (1S) candidates• Nfit : extracted from Crystal Ball (CB) part of the fit with CB+exponential. •Fix width,m2S,m3S to 50 MeV. •Only ϒ(1s) considered.

•3.5 < y < 4.0

0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5 5<pT<6

6<pT<7 7<pT<8 8<pT<9

9<pT<10 10<pT<11 11<pT<12

12<pT<13 13<pT<14 14<pT<15

25.2.2011 G.Manca, A&S Week

a) Number of ϒ (1S) candidates• Nfit : extracted from Crystal Ball (CB) part of the fit with CB+exponential. •Fix width,m2S,m3S to 50 MeV. •Only ϒ(1s) considered.

•4.0 < y < 4.5

0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5 5<pT<6

6<pT<7 7<pT<8 8<pT<9

9<pT<10 10<pT<11 11<pT<12

12<pT<13 13<pT<14 14<pT<15