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Selected highlights from LHCb

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  1. Selected highlights from LHCb Neville Harnew On behalf of the LHCb Collaboration University of Oxford Discrete 2012, Lisboa December 6th 2012

  2. Outline • The LHCb detector and running conditions • Selected physics highlights Focus on new measurements from LHCb: mostexamples are based on 1 fb-1 of 2011 pp collision data. • Parameters of the CKM matrix • Studies of CPV in the Bssystem • CP violation in charm • Rare B decays • Summary and Outlook

  3. 10 – 300 mrad p p LHCb- forward spectrometer • Forward-peaked production → LHCb is a forward spectrometer (operating in LHC collider mode) • bb cross-section = 284 ± 53 mb at s = 7 TeV [PLB 694 209] → ~ 100,000 bb pairs produced/second (104B factories) [PYTHIA] JINST 3:S08005 (2008)

  4. What the doomsayers said • “Hadron colliders are too dirty an environment for flavour-physics” • “Impossible to trigger efficiently on non-leptonic final states” • “It will take a long time to understand detector performance, and so physics output will take years to emerge”

  5. But if anyone was still left in any doubt… B+→(K+π-)Dπ+ D+,D+s→KKπ Phys Lett B712 (2012) 203 LHCb-PAPER-2012-026 ...and even with photons B+→(KSππ)DK+ B0→K*γ LHCb-PAPER-2012-027 LHCb-CONF-2012-004

  6. LHCb data taking • Nominal luminosity = 2 × 1032 cm-2 s-1 : however, LHCb has learned to run at >2 times this. • Continuous (automatic) adjustment of offset of colliding beams allows luminosity to be levelled • 37 pb-1 collected in 2010 • 1 fb-1 in 2011 • So far >2 fb-1recorded in 2012 – on track for 2.5 fb-1 before the long • shutdown

  7. LHCb 2012 data-taking in numbers

  8. Vertex reconstruction performance • Impact parameter resolution = 12 mm for high pT tracks from VELO detector. • Proper-time resolution: st = 45 fs • Bs–Bs oscillations measured: cf CDF: 17.77 ± 0.10 ± 0.07 ps-1 (st = 87 fs) [PRL 97 242003] Prompt J/y Bs J/y f LHCb-CONF-2011-50 LHCb-CONF-2011-49

  9. PID performance arXiv:1211.6759 • Allows strong suppression ofcombinatorial backgroundeg for f  K+K- • Kaon identification efficiency > 90%for pion misidentification < 5%over a large momentum range (2 < p < 100 GeV/c ) Calibration data Without RICH With

  10. arXiv:1211.3055 The LHCb trigger performance • Hardware level (L0): • 4 μs latency @ 40MHz • high-pT μ, e, γ, hadron candidates, typically • pT(μ)>1.4; ET(e/γ)>2.7; ET(hadron)>3.6 [GeV] • Software level (HLT): • ~30000 tasks in parallel on ~1500 nodes • Combined efficiency (L0+HLT): • ~90 % for di-muon channels • ~30 % for multi-body hadronic final states • Offline processing: • ~1010 events, 700 TB recorded per year • ~800 “stripping” selections to reduce to samples with 0(107) events for analyses

  11. Selected physics highlights • Parameters of the CKM matrix • Studies of CPV in the Bs system • CP violation in charm • Rare B decays

  12. Unitarity triangle : CKM fitter • The CKM describes all the flavour-changing processes in the SM • Amazing progress in the last 20 years; the SM remains intact, but still a whole lot still to learn http://ckmfitter.in2p3.fr 1995 2012 2004

  13. And now LHCb in the game … sin(2β) from B0→J/ψK0S LHCb-PAPER-2012-035 SJ/ψKs = 0.73 ± 0.07 (stat) ± 0.04 (syst) CJ/ψKs = 0.030 ± (stat) ± 0.012 (syst) 0.089 0.091 World average : sin(2β) = 0.667 ± 0.023 ± 0.012

  14. A measurement of g from B±  DK± and Dp± • Four methods, comprising 14 B± decays included in a combined fit See parallel talk of Laurence Carson “GGSZ” Phys Lett B718 (2012) 43 “K3p” : LHCb-CONF-2012-030 “ADS” Phys Lett B712 (2012) 203 “GLW” Phys Lett B712 (2012) 203

  15. B±  DK± andB±  Dπ± ADS & GLW modes B-  (p-K+)DK- B+  (p+K-)DK+ ADS modes B-  (p-K+)Dp- B+  (p+K-)Dp+ B-  (K+K-)DK- B+  (K+K-)DK+ GLW modes B+  (K+K-)Dp+ B-  (K+K-)Dp-

  16. B±  DK± andB±  Dπ± GGSZ & K(3π) modes GGSZ mode B+ B- (KSpp )D B-  (p-K+p+p-)DK- B+  (p-K+p+p-)DK+ K(3p) modes B-  (p-K+p+p-)Dp- B+  (p-K+p+p-)Dp+

  17. LHCb g combination LHCb-CONF-2012-032 • World average (before LHCb): g = 66o ± 12o • More data eagerly awaited BDK and BDp BDK only + 16.7 + 7.1 17 http://ckmfitter.in2p3.fr

  18. CP violation in Bp+p- & Bs K+K- (angle a/g) See parallel talk of Denis Derkach • 0.6 fb-1 : ~5.4k B0p+p- events • First time-dependent CP asymmetry plot of B0p+p- at a hadron collider • Also first ever time-dependent asymmetry seen in BsK+K- LHCb-CONF-2012-007

  19. Selected physics highlights • Parameters of the CKM matrix • Studies of CPV in the Bs system • CP violation in charm • Rare B decays

  20. See parallel talk of Jeroen van Leerdam Bs weak mixing phase fs in Bs J/y f • Analogue of 2b(phase of B0 mixing) in the Bs system is expected to be very small, and precisely predicted: fs = -0.036 ± 0.002 • VV final state: mixture of CP-odd and CP-even componentsSeparated using an angular analysis J/ψ rest frame frest frame • Golden mode for this study is Bs J/y f [f is vector meson] • First measurements from the Tevatron indicated large values for fsdiscrepancy with SM reaching ~3s LHCb-CONF-2012-002 Perform BsJ/Y f angular analysis Use opposite side tag: Power=(2.29 ± 0.07 ± 0.26)%

  21. Bs J/y f: fit projections CP-even CP-odd

  22. Results correlated with DGs= width difference of the Bsmass eigenstates plotted as contours in (fsvsDGs) plane LHCb-CONF-2012-002 Most significant direct measurement of fs&DGs DGs= 0.116 ± 0.018 ± 0.006 ps-1 fs = ‒0.001 ± 0.101 ± 0.027 rad Add in BsJ/Y ppfs= ‒0.002 ± 0.083 ± 0.027 Not much room for new physics, will continue to improve precision arXiv:1204.5675

  23. CP-violating asymmetry assl in Bs decays See parallel talk of Thomas Bird • CPV in mixing • First step to resolving the issue of the D0 di-muon asymmetry anomaly. • LHCb preliminary result for assl • D0 not confirmed nor ruled out (1.8s from LHCb result). More coming soon Phys. Rev. D 84, 052007 (2011), Phys. Rev. D 86, 072009 (2012) LHCb-CONF-2012-022

  24. Selected physics highlights • Parameters of the CKM matrix • Studies of CPV in the Bs system • CP violation in charm • Rare B decays

  25. Mixing and CP-violation in charm decays See parallel talk of Artur Ukleja

  26. Charm mixing measurement • Charm mixing has been confirmed by BaBar, Belle & CDF, but no clear observation in a single experiment. • LHCb measure the time-dependent ratio of D0 decays to Wrong Sign to Right Sign • Use the sign of the slow pion from D*+Dop+sandD*- Dop-s to tag the initial D0flavour The no mixing hypothesis is now excluded at the 9.1s level in a single experiment arXiv:1211.1230

  27. Signal window Signal window Phys. Rev. Lett. 108 (2012) 111602 First evidence for CP violation in charm Measure D0/D0(bar) decay asymmetries – charge of p from D* determines production state of the D0 In the Standard Model these asymmetries should be close to zero The quantity DACP= AK - Aπ is measured (since systematics largely cancel) DACP=[-0.82±0.21(stat)±0.11(sys)]% 3.5s different from zero • (Note also recent preliminary CDF result: [-0.62 +- 0.21 +- 0.10]% [CDF note 10784] )

  28. Selected physics highlights • Parameters of the CKM matrix • Studies of CPV in the Bs system • CP violation in charm • Rare B decays

  29. g, g, SM + New physics contributions FCNC decay B0 K*0m+m- See parallel talk of Konstantinos Petridis • LHCb BR = (1.22+0.38-0.32) x 10-6 agrees to within ~30% of SM • But forward-backward asymmetry AFB(q2) in the  rest-frame is a sensitive NP probe • LHCb has largest sample in world, as clean as the B Factories! 900 ± 34 events arXiv:1210.4492

  30. B0 K*m+m- continued • Previous results hinted at discrepancy • First measurement of zero crossing point: q2 = 4.9+1.1-1.3 GeV2 • AFB measured by LHCb consistent with Standard Model [arXiv:1101.0470] SM

  31. But not all is quite as expected … • Expected to be ~zero in SM • Significant deviation emerging (4.6s from zero). Requires further studies and better theoretical understanding • No similar effects seen in BK*m+m- • LHCb measure “isospin asymmetry” JHEP 7 (2012) 133

  32. B+ → π+μ+ μ–rare penguin decay • B+ → π+μ+ μ– First observation – (rarest B decay ever observed that has >5s significance) arXiv: 1210.2645 25±6 events 5.2 σ significance • SM prediction: (2.0 ± 0.2)x10−8 • BR measured (2.4±0.6±0.2) 10-8 PRD77 (2008) 014017

  33. Rare decay Bsm+m- See parallel talk of Serena Oggero • Decay strongly suppressed in SM • Predicted BR = (3.5 ± 0.3)  10-9 • Very sensitive to new physics- MSSM • But it’s a bit like looking for a needle in a haystack arXiv:1208:0934 & PRL 109 041801 (2012)

  34. LHCb m+m- mass spectrum LHCb-CONF-2012-025 B0s→m+m-? 5.4

  35. LHCb Bsm+m- candidate 35

  36. Bsm+m- limits prior to Nov 2012 • LHCb selection based on multivariate estimator (BDT) combining vertex and geometrical information • ATLAS/CMS/LHCb combined @95%CL • BR(Bs→ +-) < 4.2 10-9 • SM (Bs→ +-) = (3.5 ± 0.3)  10-9 • BR(Bd→ +-) < 8.1 10-10 LHCb 2011 limits (1 fb-1) Phys. Rev. Lett. 108 (2012) 231801

  37. Results based on 2011/12 data: 2.1 fb-1 : blinded analysis • The known B masses and widths are fixed in the fit • Cut on BDT>0.5 New 3.5 s LHCb-CONF-2012-043

  38. Constraints on new physics models Status in June 2012 (LCC combination) Status in November 2012 (LHCb only) Straub Moriond 2012 (http://phys.davidstraub.de/files/dstraub-moriond12.pdf)

  39. Summary and Outlook • LHCbis a huge success : the detector works spectacularly well • So far all in good agreement with the Standard Model → New physics is becoming constrained in the flavour sector → CP violation in charm may (or may not) be the first evidence of NP. • Up to 2017 we expect 7-8 fb-1 of data in total, and much of this at ~double the current heavy-flavour production cross-section (since √s: 8→14 TeV) • But still much room for new physics, higher precision required …

  40. See parallel talk of Stephan Eisenhardt Outlook: LHCb Upgrade • Main limitation that prevents exploiting higher luminosity is the Level-0 (hardware) trigger • To keep output rate < 1 MHz requires raising thresholds  hadronic yields reach plateau • Proposed upgrade is to remove hardware trigger: read out detector at 40 MHz (bunch crossing rate). Trigger fully in software in CPU farm. Requires replacing front-end electronics • Will allow to increase luminosity by factor ~ 10 to 1–2 × 1033 cm-2 s-1 • Framework TDR submitted to the LHCC: Physics case enthusiastically endorsed, detector R&D underway Upgrade of LHCb detector planned for 2019 to take at least 10× more data: 50 fb-1

  41. Upgrade sensitivities 50 fb-1 LHCb-PUB-2012-009

  42. Spare slides from here on

  43. Flavour tagging Tagging of production flavour (B or B) important for mixing and CP analyses.Performance calibrated using control channels such as B+→ J/y K+ Current opposite side tagging power: e (1-w)2 = (2.29 ± 0.06 ± 0.22)% LHCb-CONF-2012-026 Tagging variable

  44. The sign of DGs PRL 108 (2012) 241801 • To resolve ambiguity(fs, DGs , d , d)  (p-fs, -DGs , 2p-d , -d) study strong phase difference ds=ds -dbetween K+K- P-wave and S-wave amplitudes as a function of m(K+K-) around the f(1020) • P-wave: f(1020), going through resonance→ expect rapid positive phase shift • S-wave: non-resonant and tail from f0(980)→ expect no fast variation of phase • Analysis based on 0.37 fb-1 • Determine ds in four K+K- mass bins Solution corresponding to DGs> 0 preferred with 4.7s significance

  45. Charm CPV combination

  46. [LHCb-CONF-2012-007] preliminary Time-dependent CPV in B0(s) →h+h-

  47. CP violation in BKp and BsKp

  48. See parallel talk of Artur Ukleja talk Charm mixing

  49. Ks L PID calibration samples • Impressive calibration purity → samples allow PID calibrations in efficiency and purity to be evaluated with data D from D* f

  50. Away from flavour: W/Z production LHCb’s unique forward and low pT acceptance equips it to perform EW / QCD measurements which are highly complementary to those of mid-rapididty GPDs Studies of W/Z production [JHEP 6 (2012) 58] alongside ATLAS/CMS gives complete picture Unique kinematical acceptance ATLAS/ CMS LHCb