Prompt J/  and b ➝ J/  X production in pp collisions at LHCb Patrick Robbe, LAL Orsay & CERN, 7 Dec 2010 For the LHCb Collaboration KRUGER 2010 Workshop on Discovery Physics at the LHC Kruger National Park – South Africa

The LHCb detector New preliminary results of J/  cross-section measurement with 5.2 pb -1 data at LHCb. Prospects for future LHCb measurements in the quarkonium sector. 2 Outline

Unique acceptance amongst the LHC experiments: can explore production properties in the forward region. 3 The LHCb Detector

4 Level 0: Hardware triggers From Muon system & calorimeters High Level Trigger (HLT) 1: Software triggers Add information from VELO and tracking stations to Level 0 information Find primary vertices, etc. HLT2: Software triggers Use all of the detector information to make inclusive and exclusive selections The LHCb Trigger

5 Data Taking Data used in the J/  cross-section measurement Full data sample (37pb -1 ) will be used for studies for winter conferences.

Double differential cross-section measurement, as a function of the transverse momentum p T and of the rapidity y: – 14 p T bins, p T < 14 GeV/c – 5 y bins, 2<y<4.5 Separately for: – Prompt J/  = direct J/  + J/  from  c feed-down, – J/  from b decays. Use (5.2±0.5) pb -1 of data collected end of September 2010 at LHCb, with two different trigger settings, with pp collisions at center-of- mass energy of 7 TeV: – 2.2 pb -1 with standard muon trigger, – 3 pb -1 with the lifetime unbiased muon trigger lines pre-scaled to cope with instantaneous luminosity increase. 6 J/  cross-section measurement

7 Trigger and Selection Selection: L0 Trigger: Single Muon: Di-Muon: p T >1.4 GeV/c p T,1 >0.56 GeV/c, p T,2 >0.48 GeV/c HLT1 Trigger: Single Muon: Di-Muon: Confirm L0 single Muon and p T >1.8 GeV/c (Pre-scaled in Trigger 2 by 0.2) Confirm L0 Di-Muon and M μμ >2.5 GeV/c 2 HLT1 Trigger:Di-Muon: M μμ >2.9 GeV/c 2 μ tracks: ● well reconstructed tracks identified as muons in muon detector, ● p T > 0.7 GeV/c, ● Track fit quality (χ 2 /nDoF < 4). Reconstructed J/  : ● mass window: 0.15 GeV/c 2, ● vertex fit quality (p(χ 2 )>0.5%). Event: at least one reconstructed Primary Vertex (PV): to compute proper-time

8 J/  Sample N = ± 924 Each mass distributions obtained in the 70 bins are fit with: A Crystal Ball function for the signal to take the radiative tail into account, An exponential function for the background. Crystal Ball function:

Computed as: With: – N(J/  ➝  +  - ): number of reconstructed signal events, separatly prompt and from b. – L: integrated luminosity (5.2 pb -1 ) –  tot : total detection efficiency, including acceptance, reconstruction, selection and trigger efficiencies. – B(J/  ➝  +  - ): (5.94 ± 0.06) % –  y = 0.5,  p T =1: bin sizes. 9 Cross-section Measurement

Fraction of J/  from b is given by fit of t z : 10 Separation prompt J/  / J/  from b PV

11 t z tail Origin of the tail are signal J/  associated with the wrong Primary Vertex. The shape of the tail contribution is determined directly from data, simulating an uncorrelated PV using the one of the next event: Sideband subtracted With “next event” method

12 t z signal and background functions Signal: Convolved by resolution function: Sum of 2 Gaussians Background: fit with function describing the shape seen in the J/  mass sidebands: 3 positive exponentials and 2 negative exponentials.

Fit is performed in all analysis bins to extract number of prompt J/  and of J/  from b. For example, 3<p T <4 GeV/c, 2.5<y<3. 13 t z fit LHCb Preliminary =7 TeV L=5 pb -1

Efficiencies are computed from Monte Carlo and are extensively checked on data, with control samples. Efficiencies are checked in Monte Carlo to be equal for prompt J/  and J/  from b in each (p T,y) bin. Small differences are treated as systematic uncertainties. 14 Efficiencies LHCb Simulation unprescaled trigger prescaled trigger

15 Systematics Source of systematic uncertainties considered:

16 Polarization J/  are not polarized in the LHCb simulation. Different angular distributions because of different polarization lead to very different efficiencies. 3 extreme polarization cases studied, in the helicity frame where the angular distribution of J/  muons is (integrating over  ): Differences between 3% and 30% depending on the bin: quote 3 different results of the prompt J/  cross-section, one for each polarization case. 16  =+1  =0  =-1

Integrated over the acceptance: 17 Results: prompt J/  cross-section Unpolarized J/ 

For the 2 extreme polarization cases considered: 18 Results: prompt J/  cross-section  =+1  =-1

19 Results: J/  from b cross-section Integrated over the acceptance:

Results: bb cross-section From the J/  from b cross-section, extrapolate to the total bb cross-section in 4  :  4  : extrapolation factor computed from P YTHIA 6.4, no uncertainty associated to it. B(b ➝ J/  X  (1.16±0.1)%  measured at LEP, with 9% uncertainty. With Tevatron measured hadronization fractions, we estimate B(b ➝ J/  X  (1.08±0.05)%: assign 2% uncertainty due to hadronization fractions. Result: LHCb published value from b ➝ D 0  X (Phys.Lett.B694 (2010) 209) 20

21 Results: mean p T Mean p T is estimated (for unpolarized prompt J/  ) interpolating the measured cross-section with a cubic B-spline function. J/  from b mean p T 20% higher than prompt J/ .

With full data sample, measure polarization of prompt J/ , in bins of p T and y, taking into account the full angular distribution. Measurement of  c cross-section will be possible (will also allow to know proportion of J/  from feed-down) 22 Prospects for future measurements

With full data sample, measurements of  (2S) and Y(1S), Y(2S) and Y(3S) will be possible, in their decay modes to  +  Other quarkonium states Y(1S), Y(2S), Y(3S)  (2S)

Conclusions New results for J/  cross-section measurement at LHCb with 5 pb -1 of data, as a function of p T and y, extending the range of the first measurement presented at ICHEP Large uncertainties due to unknown J/  polarization: future polarization measurement will address this issue. Measurement of  (2S) and Y(1S), Y(2S), Y(3S) cross- sections will allow to provide a complete picture of quarkonium production in the forward rapidity region. 24