Open Charm and Charmonium Production: First Results from LHCb

1. Open Charm and Charmonium Production: First Results from LHCb Zhenwei YANG @Tsinghua Univ. on behalf of the LHCb collaboration 21-24, October, 2010 IHEP, Beijing, China

2. Outline • Physics ambition of LHCb • LHCb detector and performance • Physics interests on charm • First results on charmonium and open charm • Summary and perspectives

3. ➢ Successful running in 2009 @ 2.36 TeV ➢ First collisions @ 7 TeV on March 30, 2010 ➢ Integrated Lumi ~ 20? pb-1 (20 Oct, 2010) Geneva CERN LHC Tunnel

4. 730 members 54 institutes 15 countries

5. Physics Aims of LHCb “dedicated to heavy flavour physics at the LHC” • New PhysicsCP violation: precision measurements of CKM angles(see talk of Patrick Spradlin tomorrow afternoon)rare decays of beauty and charm hadrons • Heavy Flavour PhysicsB productionBc , b-baryon physicscharm decays (e.g. D-mixing)tau lepton flavour violation......

6. bb production at LHC • bb pair production correlated • σbb ~ 300-500 µb (@7-14 TeV) • 15<<300 mrad, unique acceptance • Average design Luminosity ~ 21032 cm-2s-1 • Maximize probability of a single interaction per crossing • 2 fb-1 per nominal year (107 s), ~1012 bb pairs per year 

7. LHCbDetector μ+ beam 2 beam 1 μ- b hadron Muon System (M1-M5) μ-id： e(mm) ~94(97) %, mis-id: e (pm) ~ 3(2) % Silicon strip detector σx/y ~ 10(15.5) μm σz ~ 60(91) μm σIP ~ 21(25) μm @2GeV/c Tracking System (TT,T1-T3) Efficiency ~ 95(94.3)% Ghost ~ 5(7.7)% Δp/p~ 0.5(0.55)%(long tracks) *long tracks: tracks passing trough VELO,TT,T1-T3

8. LHCb Data Taking to be updated to be updated • Stable data taking with high efficiency in all systems, • globallyincreasing with time.

9. Detectors’ Efficiency • Extremely high efficiency for all subdetectors

10. Physics Interests on Charm 1) J/ cross-section (and polarization) • Production mechanism still not well understood, theoretical interests on direct J/ • Three main sources of J/1) Direct J/2) Decay from heavier charmonium3) Decay from b-hadrons • fractions of heavier charmonia are helpful 2) Essentially related to many investigations of CP violation and rare decays 3) Understanding of charm is fundamental for later analyses Prompt J/ J/from b

11. Measurement of J/ cross section • Cross section (both prompt J/ and J/ from b) • Separate “prompt J/” from “J/ from b” by fitting pseudo-proper time tz • σ( incl. J/) • σ( J/ from b)

12. Measurement of J/ cross section • good approximation of average b lifetime • well described by exponential distribution (J/ from b)

13. Mass fit Signal: Crystal Ball function Background: 1st order polynomial Fit results (2.5<y<4, pT<10 GeV/c): Signal = 2872 ± 73 S/B = 1.3 μ= (3088 ± 0.4) MeV/c2 σ = (15.0 ± 0.4) MeV/c2

14. tz Fit Result 1)Background from invariant mass sidebands 2)Crosscheck with a binned fit gives consistent results χ2/ndof=1.6

15. Total Efficiency and Polarization Effect • ε depends strongly on polarization • treated as systematic error for first measurement With more statistics, a direct measurement of polarization with full angular analysis, in different reference frames and bins of y and pT, is foreseen.

16. Preliminary Results Systematic errors mainly come from data/MC discrepancy. Dominant contributions from trigger and tracking efficiencies. ( see CERN-LHCb-CONF-2010-010 )

17. Perspectives with More Data • Much more data since ICHEP several 100k events/pb-1 • Will measure also polarization • Region of measurement (y, pT) will be extended with more data, some overlap with CMS/ATLAS

18. c • ccJ/y(mm) g DM = M (J/yg) - M(J/y) 1) Already seen c peak 2) With more statistics, we will measure (c1+c2)/(J/) separately for prompt c and c from b This will help us to interpret J/ cross section.

19. (2s) (2s)μ+μ- (2s)J/ 1)Well reconstructed through two decay channels 2)With more statistics, we will measure separately cross sections of prompt (2S) and (2S) from b 3)No feed-down contribution from heavier charmonia, easier to interpret

20. X(3872) • Mass fixed to PDG value MX=3871.560.22 MeV/c2 • (2S) could be used as calibration channel • Mass measurement when O(0.1) MeV/c2 stat. uncertainty is reached ~ 3 pb-1 To be approved

21. Open Charm Production • First measurements at √s=7 TeV. • Measure cross section vs y, pT in 2 nb-1, with open trigger. • Use impact parameter to separate prompt D and those from b-hadrons • Good agreement with expectations!

22. Mass Peaks of Open Charm D0→ K-p+ D*+→ (D0→K-p+ )p+ D+→K-p+p+ Ds→ (f→K-K+)p+

23. D0 cross section MC et al.: M. Cacciari, S. Frixione, M. Mangano, M. Nason, G. Ridollfi BAK et. al: B. A. Kniehl, G. Kramer, I. Schienbein, H. Spiesberger

24. D+ cross section

25. D* cross section

26. Ds cross section • (D+)/(Ds+)=2.320.27 0.26 • Consistent with PDG: f(cD+)/f(cDs+)=3.080.70

27. Summary and Perspectives • LHCb producing physics quality measurements • Cross sections of prompt J/ and J/ from b measured separately • Cross sections of D0,D*,D+,Ds+ are measured, good agreement with theor. expectations • Heavier charmonia well reconstructed and waiting for more statistics • (bb) determined in forward region @ 7 TeV

28. Thank you

29. back up

30. Event Selection of J/ Data Sample • (14.15 ± 1.42) nb-1 (low pile-up conditions) Event selection • 2 muons • with fully reconstructed tracks (VELO + Tracker) • identified bymuon system • good vertex reconstructed • pT > 700 MeV/c • Mass window for signal definition: (MJ/ψ± 390) MeV/c2 • Trigger L0 • single muon, pT > 480 MeV/c • HLT: • single muon, pT > 1.3 GeV/c .OR. muon pair with Mμμ > 2700 MeV/c2

31. Efficiencies: ε = εacc x εrec x εtrig • 0<PT<10 GeV/c divided into 10 bins • integrate over 2.5<y<4 due to low statistics • plenty of cross check with data

32. Measurement of σ(pp → bbX) Idea: using B→D0Xμν measure right-sign D0 μ- pairs using tracks not pointing at primary vertex, but which form a common vertex Example: only mode used • From PDG • b in B±/B0/Bs/b-baryon admixture →D0 l νX :BR = 6.82% ±0.35% • Br(D0 → K π) = (3.91 ± 0.01)% production fractions taken from Heavy Flavor Averaging Group (LEP) D0 mesons produced are not only produced in B-decays - but also “prompt”

33. Measurement of σ(pp → bbX) Using log(IP) to separate direct D-meson and D meson from b Open (microbias trigger): 2.9 nb-1 RS Prompt from B WS Muon (1 Muon) trigger: 12.2 nb-1

34. Measurement of σ(pp → bbX) σ( pp → Hb X, 2 < η(Hb) < 6) = 75.3 ± 5.4 ± 13 μb Extrapolation: total bb production cross section at √s = 7 TeV σ( pp → bbX) = 284 ± 20 ± 49 μb (assuming LEP frag. fractions)

35. LHCbDetector (2) μ+ beam 2 beam 1 b hadron μ- RICH1&RICH2 π/Kid： e(KK) ~95(96) %， mis-id ~ 5(7) %， ECAL:s(E)/E= 10% E-1/2 1 % (E in GeV) HCAL: s(E)/E= (695)% E-1/2 (9  2) % (E in GeV)

36. Data Set of J/ (1)

37. Data Set of J/ (2)

38. Selections of D0 & D* D0→ K-p+ and D*+→ (D0→K-p+ )p+ K,p : c2(track)/DoF < 9 c2(IP) > 9 pT > 700 MeV/c K : DLL(K-p) > p : DLL(K-p) D0 : c2(vertex) <9 c2(flight) > 16 c2(IP) < 9 q < 12 mrad K,p : c2(track)/DoF < 10 K,pD : c2(IP) > 9 K : DLL(K-p) > 0 p : DLL(p-K) > 0 D0 : c2(vertex) <9 ct > 90 mm c2(IP) < 9 D*+ : c2(vertex)< 9

39. Selections of D+ and Ds D+→K-p+p+ and Ds→ (f→K-K+)p+ K,p : Prob(c2(track)) > 10-4 pT > 200 MeV/c p > 3.2 GeV/c c2(IP) > 3.0 2 daugthters: pT > 400 MeV/c c2(IP) > 10 1 daughter: c2(IP) > 50 K : DLL(K-p) > 3.3 p : DLL(p-K) > -10 D+ : c2(vertex) <8 q < 14 mrad • c2(flight) > 90 • t < 0.01 ns K,p:c2(track)/DoF<4 K : c2(IP) > 2 p : c2(IP) > 10 K : DLL(K-p) > 9 p : DLL(p-K) > -2 f : |DM|<20MeV/c2 Ds : c2(vertex)/DoF<5 Ds : c2(flight)> 67

40. Measurement of J/ cross section • Cross section(both prompt J/ψ and J/ψ from b) • Measurements restricted to: 2.5<y J/ψ <40<pT J/ψ <10 GeV/c because of the small statistics available • Results on: • dσ/dpT ( incl. J/ψ) in 10 bins of pT J/ψ , 0<pT J/ψ <10 • σ( incl. J/ψ) • σ( J/ψ from b)