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LHCb at LHC: Forward Region, Heavy Quark Production, and Results

LHCb is a detector at the LHC that covers the forward region and exploits heavy quark production. It has a large beauty and charm cross-section, high-resolution detectors, and a powerful trigger system. LHCb has collected a significant amount of data and has published several papers and conference contributions. It has made measurements in the charm sector, including time-integrated CP asymmetries and the search for direct CP violation.

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LHCb at LHC: Forward Region, Heavy Quark Production, and Results

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  1. LHCb Umberto Marconi, INFN Bologna CSN1, 22/11/2011

  2. LHCb at LHC • LHCbcovers the forward region at the LHC, in a unique rapidity range: 2 < η < 5. • LHCb exploits the strongly forward peaked heavy quark production: covering only 4% of solid angle, the acceptance ofthe beauty quark production cross section is 40%. • Large beauty cross section: σ(bb) = 284 ± 53 μbμb at 7 TeV, about 0.5% of total [PLB 694 209]. • Large charm cross section: σ(cc) = 6100 ± 930 μb at 7 TeV.

  3. The LHCb detector Time resolution Δt: 30÷50 fs Momentum resolution δp/p = 0.35÷0.55% Mass resolution Δm = 10÷20 MeV Muon ID: ε(μ→μ) = 95%, mis-ID ε(π→μ) = 1÷3% RICH ID: π/K: ε(K→K) = 95%, mis-ID ε(π→K) ~10%

  4. ∂ Events shape Calorimetri Rivelatore dimuoni RICH-2 Camere traccianti T1,T2,T3 Magnete Camere traccianti TT RICH-1 VELO K Bs Primary vertex K K Ds ECAL HCAL d≈1 cm 

  5. LHCb Trigger • First Level (L0) • High-pTμ, e,γ, hadroncandidates (ECAL, HCAL, Muon) :~1 MHz • Software level (High Level Trigger, HLT) • Access all detector data • Farm with ~15000 CPU cores on multi-processor commodity boxes. • HLT1: Confirm L0 candidate with more complete info, add impact parameter and lifetime cuts: ~30 kHz • HLT2: global event reconstruction + selections: ~3 kHz 40 MHz L0 m L0 had L0 e, g Level -0 1 MHz ECAL Alley Had. Alley Muon Alley HLT1 High-Level Trigger 30 kHz Global reconstruction HLT2 Inclusive selections m, m+track, mm Exclusive selections 3kHz Storage: Event size ~35kB

  6. Luminosity leveling L ~ 3.5×1032 cm-2s-1 Tested: 4. ×1032 cm-2s-1twice the design luminosity. Average pileup ~ 1.5 Data taking efficiency above 90% Offline data quality 99% Integrated luminosity in 2011: 1.1 fb-1 It was 35 pb-1 in 2010.

  7. Integrated Luminosity by 2017 • LHCb upgrade LOI: the equivalent of 5 fb-1 at √s=14 TeV collected by the date. • In the meanwhile we proved LHCb can run at L=4.× 1032 cm-2s-1: LHCb can collect more than 2 fb-1/year. • Plan is to run one year at √s=7 TeV to then move up to √s=14 TeV, for three years, until 2017. • The final integrated luminosity should be therefore greater than 7 fb-1equivalent to √s=14 TeV.

  8. LHCb results • “LHCb Conference Contributions”, public notes describing preliminary results submitted to conference:58 notes on different physics subjects in 2011. • Size of the data samples used for analysis so far ranges from 30 pb-1 up to 600 pb-1. • Published or submitted papers at present: 14 • It is a rapidly evolving scenario.

  9. Observables LHCb

  10. The charm sector Prompt charm is much more abundant because of the LHC charm cross-section is about 20 time higher than the B cross-section Charm produced in B decays [B(B->DX) > 50%]

  11. Time integrated CP Asymmetry D0 → K+K−, π+π-

  12. LHCb time-integrated asymmetries in D0 → h+h− • Measure the difference between two asymmetries: ΔACP ≡ ARAW (K−K+) − ARAW (π−π+) = ACP (K−K+) − ACP (π−π+) • Where for any D*-tagged decay D0→f LHCb-CONF-2011-023

  13. Dataset with 580 pb-1 The blue lines indicate the signal window [1844,1884] MeV/c2 K-K+ π-π+ δm ≡ m(h+h+π+)-m(h+h-)-m(π+), 0<δm<15 MeV/c2 1.44 ×106 in the tagged K-K+ sample 0.38 ×106 in the tagged π-π+ sample

  14. LHCb result on ΔACP (580pb-1) ΔACP = [−0.82 ± 0.21(stat.) ± 0.11(sys.)]% Indirect CP violation suppressed in the difference (Δ<t>/τ=9.8±0.9%),so if a genuine effect this is mostly direct CPV. Taking existing HFAG world-average values for ΔACP and AΓ and propagating them to the LHCb lifetime acceptance we get: Time dependence stability check

  15. Measurement of AΓ Search for non-zero value of AΓ is one of most important ways to search of CP-violation in charm mixing. Preliminary AΓ measurement available from LHCb using 28 pb-1 of 2010 data, using D*→D0π, D0→K+K- decays. Two main challenges in time- dependent charm studies at LHC: Understand ‘pollution’ to prompt charm sample coming from B→DX Understand lifetime trigger acceptance: obtained event-by-event in data: Swimming algorithm Preliminary result: AΓ = (- 5.9 ± 5.9 ± 2.1) x 10-3 WAHFAGAΓ = (0.12±0.25)% LHCb-CONF-2011-046 Belle: AΓ = (0.1 ± 3.0±1.5)×10−3Phys.Rev.Lett. 98 (2007) 211803 BaBar: AΓ = (2.6 ± 3.6±0.8)×10−3Phys.Rev. D78 (2008) 011105

  16. Direct CPV search with D+→K- K+ π- Search for direct CPV inCabibbo suppressed D+→K-K+π- events Control signal (Cabibbo favoured → no CPV expected) 370k decays Signal K0(892) φ Look for statistically significant difference in D+vs D- bin contents. Method based on PRD 80 (2009) 096006 Normalise D+vs D- to remove production asymmetries Compare with 43k events in BABAR 80 fb-1 study [PRD 71 (2005) 091101 (R)]

  17. Direct CPV search with D+→K-K+π+ • No evidence of CPV in any binning. • Paper presents results with two adaptive (motivated by resonances) and two uniform binning schemes. arXiv:1110.3970, submitted to PRD Control modes (D+Kππ, DSKKπ) used to check for biases: none found

  18. B mesons mass resolutions B+ J/ψK+ 10.5 MeV B J/ψ K* 7.7 MeV BSJ/ψ φ 7.0 MeV BJ/ψ KS 8.6 MeV All values close to Monte Carlo expectations

  19. BS J/ψφ Search for new physics in BS mixing BS J/ψf0

  20. Bs J/ψ(μμ)φ(KK) Measure CP violation through interference of decays with and without mixing: φS = φM-2φD BS J/Ψ ϕ BS Precise Standard Model prediction Penguin contribution βS=0.018±0.001 [A. Lenz, arXiv: 1102.4274]

  21. Status before LP2011 CDF • CDF 5.2 fb‐1, ~6500 events, σ(φs)~0.5 • D0 9.0 fb‐1, ~5000 events, σ(φs)~0.35 • LHCb 37 pb‐1, ~800 events, σ(φs)~0.7 Theory prediction D0

  22. Describing BS J/ψK+K- • Need flavour-tagged, time-dependent angular analysis. • BS →J/ψK+K- is a mixture of four states: three K+K- P-waves (A0, A⊥, A||) and one S-wave (AS). • Can be described in 4D space using three angles (θ, φ, γ) and the decay proper time τ(BS). • Decay widths depend on: • Angular amplitudes and strong phases. • φS, ΔΓS, ΔmS, ΓS • Additional information: description of background, efficiency, resolution, mistag probability.

  23. Time evolution (for reference) + for BS - for BS-bar Major source of sensitivity to φS

  24. Separating CP eigenstates • Different CP eigenstates are statistically separated in the maximum likelihood fit using angular information. CP even CP odd S wave Relative variation of the angular efficiency < 5%. Accounted for according to full MC simulation.

  25. Tagging • Initial flavor of B can be inferred from: • Opposite Side: products of the other B meson • Same Side: fragmentation particles associated to signal B • Currently use OS, fully optimized and calibrated on data • SS tagging will be used in next round of analysis. LHCb-CONF-2011-049 εtag = (27.0 ± 0.4)% Average dilution factor D = (27.7 ± 0.28)% Effective tagging power εtag D2= (2.08 ± 0.41)% Wrong tagging probability calibrated with B+ → J/ψK+

  26. Time resolution • Time resolution model obtained from prompt events. • Effective proper time resolution 50 fs. LHCb-CONF-2011-049 Time resolution can be compared to the BS oscillation period of about 350 fs. LHCb-CONF-2011-050 LHCb: ΔmS = 17.725 ± 0.041 ± 0.026 ps-1 CDF (1/fb): ΔmS = 17.77 ± 0.10 ± 0.07 ps-1 Efficiency as a function of proper time obtained from data.

  27. Fit projections for BS J/ψK+K- 8276 ±94 BS signals Goodness-of-fit: p-value 0.44 based on point-to-point dissimilarity test. [M. Williams, JINST 5 (2010) P09004]

  28. φS results from BS J/ψK+K- SM prediction [arXiv:1102.4274] Two solutions: (φS , ΔΓS) (π-φS , -ΔΓS) LHCb-CONF-2011-049 World’s most precise measurement of φS φS = 0.15 ± 0.18 (stat) ± 0.06 (sys) 4σ evidence for ΔΓS≠0 ΔΓS = 0.123 ± 0.029 (stat) ± 0.008 (sys) ps-1 ΓS = 0.656 ± 0.009 (stat) ± 0.008 (sys) ps-1

  29. D0, CDF and LHCb on φS

  30. Systematic errors analysis

  31. Perspectives on φS from BS J/ψK+K- • OS effective tagging 2%. The SSK tagger, not used yet, will add ~2% • With L=7 fb-1 the size of the tagged sample should increase by a factor: 2. × 7000./340.×4./2. ~ 80 (selection efficiency +20% not included). • Statistical error should therefore reduce to: 0.18/√80 = 0.02 • Systematic errors dominated by the uncertainties on the angular acceptance, amounting to 0.04.We expect eventually a reduction of a factor two on the systematic error. • Conclusion: φS=xxx ± 0.02 (stat.) ± 0.02 (syst.)

  32. CP violation in BS J/ψf0 ~1400 events LHCB-CONF-2011-051 Angular distribution consistent with scalar f0(980) ππ, S wave f(980) region Using ΓS and ΔΓS from BS J/ψφ π±π± φS = -0.44 ± 0.44 ± 0.02 ambiguous solution

  33. BS J/ψφS and BS J/ψf0combination • Simultaneous fit of BS→ J/ψφand BS→ J/ψf0φS = 0.03 ± 0.16 (stat) ± 0.06 (sys) and ambiguous solution. • Cautions are needed with the combination: • Hadronic nature of f0 is not completely clear. • Different hadronic effects possible in the two channels. [R. Fleischer, R. Knegjens, G. Ricciardi, [arXiv:1109.1112)] LHCb-CONF-2011-056

  34. φS from other channels • The channel, adds to the golden mode: • BSJ/ψf0 , 15% • BSJ/ψ(ee)φ, 14% • BSψ’(μμ)φ, 10% • BSDSDS and Bs->DS(*)DS(*)Trigger and reconstruction efficiencies are rather small on these multi-track channels.

  35. SEARCH FOR NEW PHYSICS IN bs LOOP DECAY PROCESSES BS μμ B0 K*μμ BS φφ, K*K* BS φγ

  36. BS→μ+μ- Predicted to be rare in the SM: BR(Bs→μμ) = (3.2±0.2) × 10-9 BR(Bd→μμ) = (0.10±0.01)×10-9 Large sensitivity expected to NP, eg SUSY. • CDF recently reported on a new result based on 7 fb-1, where they observe an excess of events over the background-only hypothesis: • BR(Bs→μμ) CDF = (1.8+1.1-0.9 ) × 10-8 • BR(Bs→μμ) CDF < 4.0 × 10-8 @95% CL

  37. Analysis strategy. • Discriminating signal and background using two variables: • Invariant mass of μ+μ-: parameterization from data. • Output of a Boosted Decision Tree (BDT): Built on nine kinematical and topological variables. Trained on MC. Shape of the BDT output obtained on B→hh (signal) and B mass sideband (background) • Normalization: • Using B+→ J/ψK+ , BS→ J/ψφ and Bd → Kπ • LHCbfS/fd = 0.267+0.021-0.020Phys. Rev. D, Phys. Rev. Lett. 107, 211801 (2011) [arXiv:1111.2357v1] • Assessing the BR and setting limits: • For a given BR, compare observed and expected numbers of events in 6×4 bins of m(μ+μ-) and BDT output, for signal+bkg and bkg hypotheses. • Calculate CLS [A. Read, J. Phys. G 28 (2002) 2693] • Exclude the BR at 1-α C.L. if CLS < α. • The highest BR which is not excluded is the CLS limit at 1-α C.L.

  38. BS→μ+μ-(370 pb-1) Four bins in BDT output. B mass search window of 120 MeV divided into 6 bins Bs/Bdmass window: ±60MeV/c2 LHCb-CONF-2011-037

  39. BS→μ+μ-(370 pb-1) LHCb-CONF-2011-037 Combinatorial background Peaking background SM signal expectation

  40. BS→μ+μ-candidate? Decay length 11.5 mm mμμ = 5.357 GeV/c2

  41. Updated results (November 2011) BR limits at 95%CL expected (*) observed CLb Bs → μμ 1.4×10-8 1.6×10-8 0.95 Bd→ μμ 3.2×10-9 3.6×10-9 0.68 2σ signal hint! 370 pb-1 2011 data expected (*) observed CLb Bs → μμ 1.3×10-8 1.4×10-8 0.93 Bd → μμ 3.0×10-9 3.2×10-9 0.61 submitted to PLB Adding 37 pb-1 of 2010 data (*) bkg+SM hypothesis for Bs, bkg only hypothesis for Bd

  42. Extrapolated sensitivity Upper limit extrapolation in the presence of SM signal Observation: a 3 sigma evidence of SM signal is possible within the end of 7 TeV run...

  43. LHCb limit of BR(BS→μ+μ-) The signal hypothesis is excluded at the confidence level 1-α when: CLS < α 90% CL 95% CL Expected distribution of CLS in dashed black line under the hypothesis to observe a combination of background and signal events according to the SM rate. The green area covers the ±1σ of compatible observations. The observed distributions of CLS as a function of the assumed branching ratio as dotted blue line.

  44. CMS and LHCb combined limits. LHCb-CONF-2011-047 CMS-PAS-BPH-11-019 BR(BR(BS→μ+μ-)) <1.08 ×10-8 95% CL BR(BR(BS→μ+μ-)) <0.90 ×10-8 90% CL 95% C.L. limit is 3.4 times SM expected value. p-value (1-CLb) for background-only hyp. : 8% p-value for background plus SM signal: 57%

  45. Long term prospect LEPS ~ 2. × LEPS(LHCb): CMS sample at the time was equivalent to the LHCb one. 15 LEPS corresponds to 8 fb-1 taken at 7 TeV or 4 fb-1 taken at 14 TeV. By 2017 LHCb will reach a 5σ signal observation, assuming the BR is SM.

  46. Extrapolated sensitivity arXiv:1108.3018 ... but what matters is the precision to which one can constrain constributions exceeding the SM 0 3 6 9 L(fb-1) end of 2012: ≥ 2 fb-1 2 more years at 14 TeV: 6-7 fb-1 (equivalent) As soon as Bs → μμis measured, we can also start constraining Bd/Bs ratio, which is of prime interest for the MFV scenario.

  47. Bs,d→μμ upper limit: summer 2011 BR limits at 95%CL The past 13 years LHCb: 1.6×10-8 L~300 pb-1 LHCb-CONF-2011-037 CMS: 1.9×10-8 L~1.1 fb-1 Phys. Rev. Lett. 107 (2011) 191802 LHCb+CMS: 1.1×10-8 LHCb-CONF-2011-047 CMS PAS BPH-11-019 CDF: 4.0×10-8 L~7 fb-1 Phys. Rev. Lett. 107 (2011) 191801 D0: 5.1×10-8 L~6.1 fb-1 Phys. Lett. B693 (2010) 539  CDF EPS ★ LHCb EPS L (pb-1)

  48. B0→ K*μ+μ- • FCNC b→s decays, sensitive to NP in loops. • Decay can be described by three angles (θL, θK, φ) and μ+μ- invariant di-muon mass q2 • Many observables: particularly lepton forward-backward asymmetry AFB(q2) SM diagrams

  49. Intriguing behavior of AFB(q2) Beauty Factories and CDF results A more precise determination of AFB is of particular interest as, in the 1 < q2 < 6 GeV2/c4 region, measurements favor an asymmetry with the opposite sign to that expected in the SM.

  50. AFB, FL and BR as function of q2 • AFB:Forward –Backward asymmetry for muons • FL: longitudinal polarization of the K* • Simultaneous fit of ql and qKin q2 bins 323.0 ± 21.4

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