1. Prospects for quarkonium studies at LHCb
« Quarkonium Production at the LHC » workshop
Patrick Robbe, LAL Orsay, 19 Feb 2010

2. LHCb Detector
Forward Spectrometer Geometry, with angular acceptance 15<q<300 mrad
Performance numbers relevant to quarkonium analyses:
Charged tracks Dp/p = 0.35 % %, s(m)=12-25 MeV/c2
ECAL s(E)/E= 10% E-1/2  1 % (E in GeV)
muon ID: e(mm) = 94 %, mis-ID rate (pm) = 3 %
Vertexing: s(L)=250 mm (Primary Vertex Resolution: 10mm in x/y, 60 mm in z)

3. Introduction Unique acceptance between LHC experiments:
Quarkonium Physics Program:
Measurement of J/y production cross-section in LHCb acceptance (3<h<5, pT<7 GeV/c),
Measurement of J/y polarization
Similar measurements with y(2S), Y(1S), Y(2S), Y(3S).
Production of cc, hc
Extensive studies of Bc, X(3872)

4. Monte Carlo Tools PYTHIA 6.3 for the studies shown here:
Production of J/y through Color Single Model.
PYTHIA 6.4 for the current Monte Carlo productions:
With Color Octet Model added, tuned to reproduce CDF measurements see note CERN-LHCb
EvtGen for decays:
Generator package which allows to have a detailed description of b  J/y X decays.
Also allows correct angular correlations in decays of polarized particles.
PHOTOS for radiative corrections.

5. Monte Carlo J/y Samples
LHCb MC (14 TeV, Pythia 6.3) 3<h<5
In LHCb acceptance (3<h<5, pT<7 GeV/c):
s(pp  prompt J/y X) x Br(J/y  m+ m-) = 2.7 mb
s(pp  (b  J/y X) X') x Br(J/y  m+ m-) = 0.15 mb
NB: the analysis presented here does not depend on the exact spectrum of the J/y.

6. J/y  m+ m- Reconstruction
Selection based on positive muon identification of the two m, cut on the m transverse momentum pT>0.7 GeV/c and on the quality of the m+m- vertex.
Invariant mass plot on fully simulated minimum bias events (with all background included):
Mass resolution: 11.0 ± 0.4 MeV/c2,
S/B=17.6 ± 2.3 in ±3s mass window,
1.3x109 reconstructed after L0 trigger J/y for 1 fb-1 ( =14 TeV)
Or 0.65x106 for 1 pb-1 at = 7 TeV
LHCb Minimum Bias Monte Carlo (14 TeV)

7. Separating prompt J/y from J/y from b
Use pseudo-propertime:
Prompt component characterized by peak at 0,
Exponential decay for J/y from b component,
Long tail due to association of the J/y to a not-related primary vertex.
LHCb Inclusive J/y Monte Carlo (14 TeV)
Combined mass/pseudo-propertime fit will allow to measure both prompt and J/y from b production cross sections in h and pT bins:
4 pseudo-rapidity h bins, 3 < h < 5.
7 transverse momentum bins pT, pT<7 GeV/c.

8. Example: fit on MC at = 14 TeV
Sample corresponding to 0.8 pb-1, = 14 TeV
Signal: Inclusive J/y sample
Background: toy Monte-Carlo reproducing behaviour (mass and pseudo- lifetime) seen on the Minimum Bias sample.
LHCb Inclusive J/y Monte Carlo + Toy MC (14 TeV)
Results (J/y with 3<h<5 and pT<7 GeV/c):
s(prompt J/y) x Br(J/y → m+ m-) = 2597  12 (stat)  24 (eff) nb [Input: 2667 nb]
s(J/y from b) x Br(J/y → m+ m-) = 161  4 (stat)  2 (eff) nb [Input: 153 nb]
Statistical error at maximum 10% in each of the analysis bin, for 5pb-1 of data at = 7 TeV.

9. Systematics from J/y polarization
Acceptance as a function of cosq, q = helicity angle
Large LHCb detector acceptance dependance on assumed initial polarization of J/y.

10. Systematics from J/y polarization
Study the effect of ignoring the polarization dependance of the efficiency (J/y are not polarized in the LHCb Monte Carlo)
a«data»
Measured cross-section, assuming a=0
Input s«data»
2758 nb ± 27 nb
2820 nb +1
2738 nb ± 27 nb
3190 nb -1
2787 nb ± 28 nb
2286 nb
Systematic error up to 25 % when ignoring polarization.
Polarization will be measured (in a second step):
in bins of h and pT,
separating prompt and J/y from b,
With full angular analysis, in different reference frames.

11. y(2S)  m+ m- Similar performances than J/y:
Mass resolution: 13 MeV/c2
S/B = 2
Number of reconstructed y(2S) = 2-4 % of the number of reconstructed J/y.
Measurement of the ratio s(y(2S))/s(J/y), as a function of pT, separating prompt and from b.
Polarization effects complicate also the measurement: systematic error up to 22% on the cross section ratio.

12. LHCb Inclusive Y Monte Carlo (14 TeV)
Y(1S) → m+ m-
Loose muon ID selection, and transverse momentum requirement (pT(m)>1.5 GeV/c).
L0 trigger efficiency: 96 %
Mass resolution: 37 MeV/c2
Similar reconstruction and resolutions will be obtained for the Y(2S) and Y(3S) states: this will allow to separate the 2 Upsilon states.
Goal is to measure cross-sections and polarization for all di-muon states, as a function of pT.
LHCb Inclusive Y Monte Carlo (14 TeV)

13. LHCb Inclusive J/y Monte Carlo (14 TeV)
cc reconstruction
J/y selection, adding a photon detected in the ECAL with pT(g)>500 MeV/c.
Dm=m(J/y g)-m(J/y) distribution obtained on fully simulated events containing on J/y. Since the J/y background is very low, the plot contains a large fraction of the total background.
Dm resolution = 27 MeV/c2.
LHCb Inclusive J/y Monte Carlo (14 TeV)
cc1
cc2

14. LHCb Inclusive Y Monte Carlo (14 TeV)
cb2 reconstruction
Reconstruction of cb2(1P) → Y(1S) g
Photon detected in ECAL, with pT(g) > 500 MeV/c
Mass resolution: 47 MeV/c2
LHCb Inclusive Y Monte Carlo (14 TeV)

15. LHCb Signal Monte Carlo + Toy MC (10 TeV)
hc reconstruction
Besides di-muon states, LHCb detector performances will allow to study other states though hadronic decay modes.
Reconstruction of hc → hc g is difficult (E(g)~500 MeV in the hc rest frame).
Hadronic decay channels look promising: hc → pp, hc → f K+ K-, hc → f p+ p-.
In particular, hc → pp probably visible with first year data, which will give access to s(hc)xBr(hc → pp) relative to s(J/y)xB(J/y → pp).
LHCb Signal Monte Carlo + Toy MC (10 TeV)
Expected pp mass distribution:
Assuming Br(hc → pp) = 0.12 %,
Toy Monte Carlo for background, reproducing background seen on fully simulated minimum bias events,
100 pb-1 at = 10 TeV
J/y
cc0 hc
cc1
cc2
m(pp) (GeV/c2)

16. LHCb Generator Only signal 1++/2-+
X(3872) and Z(4430)
Reconstruction of X(3872) → J/y p+ p- (and the control channel y(2S) → J/y p+ p-), prompt or from b: systematic study of this state.
Expect 1800 reconstructed B → X(3872) K, with 2 fb-1 at = 14 TeV, allowing to disentangle unknown quantum number JPC: 1++/2-+.
Reconstruction of X(3872) → J/y p+ p- (and the control channel y(2S) → J/y p+ p-), prompt or from b: systematic study of this state.
Expect 1800 reconstructed B → X(3872) K, with 2 fb-1 at = 14 TeV, allowing to disentangle unknown quantum number JPC: 1++/2-+.
LHCb Generator Only signal 1++/2-+
Similar studies for B0 → Z(4430)+( → y(2S)p+)K-
About signal events can be selected from 2 fb-1 of data at =14 TeV, assuming B(B0 → Z(4430)+ K-)xB(Z(4430)+→y(2S)p+) = 4.1x10-5
Possible to confirm the Belle discovery with about 100 pb-1 of data at = 7 TeV.

17. Bc
Measurement of mass, lifetime and production cross section using the decay modes:
Bc+ → J/y p+ assuming s(Bc+)=0.4 mb, and Br(Bc+ → J/y p+) =0.13 %, expect 310 signal events for 1 fb-1 of data at = 14 TeV.
Production cross section relative to B+(→ J/y K+)
Bc+ → J/y m+ X: signal yield one order of magnitude larger, production cross section measurement possible with 2010 data.
1 fb-1, 14 TeV

18. Conclusions
LHCb will measure production cross sections and polarization of di-muon states, in the LHCb acceptance: 3 < h < 5, pT<7 GeV/c.
Other quarkonium states will also be looked at: hc, cc, cb, Bc.
LHCb performances will allow to also study associate productions: J/y+J/y, J/y+cc, either reconstructing D or tagging it with a displaced e or m.
Study of « exotic » states: X(3872) and Z(4430).
Similar states can also be searched in (Quarkonium p+ p-) mass spectra: Yb → Y(1S) p+ p-, Bc** → Bc+ p+ p-.