LHCb Physics Summary Burkhard Schmidt CERN on behalf
LHCb - Physics Summary Burkhard Schmidt, CERN on behalf of the LHCb Collaboration Hadron Collider Physics Symposium Kyoto, November 12 -16, 2012
LHCb physics results § Search for potential effects of physics beyond the Standard Model in CP violation and rare decays using charm and beauty hadrons § CP violation in B system (B+, B 0, Bs) : ▪ Measurement of γ in tree-level processes S. Ricciardi in HF session ▪ Measurement of γ in loop-mediated processes (charmless B decays) ▪ CP violation in Bs mixing, φs phase M. Versterinen in HF session § Charm studies ▪ CP violation and mixing in charm § Rare decays ▪ B 0 d, s μ+μ- , K 0 s μ+μ- , D 0 μ+μ▪ B 0 K*0 μ+μ- , τ μ μ μ, etc. § A. Di Canto in HF session J. Albrecht in HF session and T. Blake in SUSY session The physics programme includes also: § Quarkonium studies ▪ Production and spectroscopy of heavy flavour § Soft QCD physics § Electroweak physics B. Schmidt A. Contu in QCD session K. Rinnert in EW session HCP 2012 - Kyoto, November 12 -16, 2012 2
Selection of LHCb Physics results § Outline of this talk: § CP violation in B system (B+, B 0, Bs) : ▪ Measurement of γ in tree-level processes § Charm studies ▪ Observation of D 0 - Do mixing § Rare decays ▪ B 0 d, s μ+μ- , ▪ K 0 s μ+μ-, B 0 K*0 μ+μ§ Electroweak physics New result, next talk ▪ Z→ ττ production cross section § Soft QCD physics Recent result ▪ p. A test run LHCb obtained many more exciting results not covered in this talk – apologies. 78 papers submitted to journals and >100 conference contributions up to now http: //cdsweb. cern. ch/collection/LHCb%20 Papers? ln=en Unless otherwise stated, the results are based on 1/fb of data collected in 2011 at 7 Te. V center of mass energy. B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 3
CP violation in the B system and measurement of γ B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 4
CP violation phenomenology CP violation in decay (direct) Asymmetry in decay amplitudes for a process and its conjugate: | Af / A f | ≠ 1 CP violation in mixing (indirect) If transitions B 0 are allowed CP violation if | q / p | ≠ 1 The only possibility for charged mesons Rate of B 0 differs from B 0 CP violation in interference between mixing and decay (indirect) Even if | Af / Af | = 1 and | q / p | = 1 , CP is violated if Can be measured in the time dependent asymmetry: B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 5
CKM measurements: current status § § Area of CKM triangle is proportional to the amount of CP violation in the model. All CP violation phenomena in SM are the result of a single phase in the CKM matrix. § Precision of some measurements are much worse than the others. Notably, γ, is the least well-measured angle of the Unitarity Triangle. § γ can be measured in tree- and loop-level decays. Tree-level decay: SM benchmark measurement of γ Loop-level decays: Measurement of γ sensitive to NP LHCb can do all of them B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 6
CP violation in B DK: SM benchmark γ v § § Measurement of partial width of B DK decays allows to determine γ Sensitivity to γ from interference between the 2 diagrams Only requirement: D 0 and D 0 decay to the same final states Decay modes used: § D in CP eigenstates (D 0 K+K-, π+π-) [PLB 712 (2012) 203] Gronau -London- Wyler (GLW) [PLB 265, 172 (1991)] § Cabibbo allowed (D 0 K- π+) and double Cabibbo suppressed states (D 0 K+ π- and D 0 K+ π- π+π- ) New Atwood-Dunietz-Soni (ADS) [PRL 78, 3257 (1997)] § D in 3 -body decays (D 0 Ks π+π-) New Giri-Grossmann-Soffer-Zupan (GGSZ, Dalitz) B. Schmidt [LHCb-CONF-2012 -030] [PLB 718 (2012) 43] [ PRD 68, 054018 (2003] HCP 2012 - Kyoto, November 12 -16, 2012 7
Measurable parameters § Measured ratios and asymmetries for GLW: § For ADS modes additional amplitude r. D and phase δD enter from D decay: § GGSZ analysis: Fits distribution of events in the D Ks 0 hh Dalitz plot: K±i– flavour tagged yield in the ith bin, ci, si CLEO inputs Each analysis measures different parameters containing complementary information about γ. B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 8
CP violation in B DK, D hh’ decays Suppressed B+ D 0 K+ followed by allowed D 0 K-π+ interferes with allowed B+ D 0 K+ 0 - + [PLB 712 (2012) , 203] followed by suppressed D K π decay B+ D 0 K+ and B+ D 0 K+ followed by D K+K- decay 4. 5σ B. Schmidt 4. 0σ HCP 2012 - Kyoto, November 12 -16, 2012 9
CP violation in B DK, D K 3π decays Suppressed ADS B± D(π± K π+ π-) / K± π± mode ± § [LHCb-CONF-2012 -030] pl First observation of suppressed ADS B± D(π± K π+ π-) K± mode: 40 candidates (5. 1 σ) § First observation of suppressed ADS B± D(π± K π+ π-) π± mode: 155 candidates (> 10 σ) § Hints of asymmetries in both modes RKADS = (1. 24 ± 0. 27) % RπADS = (0. 369 ± 0. 036) % AKADS = (-42 ± 22) % Aπ ADS = (13 ± 10) % § B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 10
GGSZ analysis: B DK, D K 0 shh § § Model-independent Dalitz plot analysis of D Ks 0 h+h- from B DK Divide phase space into bins and work with the number of events in each bin Binning scheme chosen to maximise sensitivity to γ Strong phase variation from correlated D-D pairs measured at CLEO-c [PLB 718 (2012) 43] [PRD 82 (2012) 112006] v § Candidates after the selection: ~690 D K 0 sππ B. Schmidt ~110 D K 0 s. KK HCP 2012 - Kyoto, November 12 -16, 2012 11
GGSZ analysis: B DK, D K 0 hh § Count number of events in binned plots (separately for B+ and B-) in D K 0 sπ π and D K 0 s. KK plots. § Asymmetry in the number of events in bins manifests CP-violation Maximum likelihood fit to obtain x± and y± x_ = (0. 0 ± 4. 3 ± 1. 5 ± 0. 6) x 10 -2 x+ = (2. 7 ± 5. 2 ± 0. 8 ± 2. 3) x 10 -2 y_ = (-10. 3 ± 4. 5 ± 1. 8 ± 1. 4) x 10 -2 y+ = (-0. 9 ± 3. 7 ± 0. 8 ± 3. 0) x 10 -2 x± = r. B cos(±γ+δB) B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 y± = r. B sin(±γ+δB) 12
γ combination result [LHCb-CONF-2012 -032] § Combination of B DK modes with 1/fb gives: +16. 1 )o γ = ( 71. 1 -15. 7 [43. 9 o – 98. 8 o ] @ 95% C. L. § Comparable to individual results of Babar and Belle § World average: γ = (66 ± 12)o (CKMFitter 2012) § Further 2/fb will be in hand by the end of 2012 § Additional information will come from the determination of γ in time dependent analyses. B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 13
Charm studies: B. Schmidt 0 D – 0 D mixing HCP 2012 - Kyoto, November 12 -16, 2012 14
Measurement of D 0 – D 0 mixing Very interesting because it probes NP which couples to up-quarks. So far evidence for charm mixing in Ba. Bar, Belle and CDF, but observation greater than 5σ only when results are combined. § This result: Observation of D 0 – D 0 oscillations with ‘wrong sign’ D*+ D 0( K+π-) π+ decays [ar. Xiv 1211. 1230] Subm to PRL § § § WS events through either direct DCS decays or mixing followed by CF § RS events dominated by CF § Assuming |x| , |y| << 1 , and negligible CPV: ; x= Δm/Γ y=Δ Γ/2Γ B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 15
D 0 – D 0 mixing – D* yields § Time integrated D 0πs mass distributions for RS and WS candidates ~8. 4 M RS B. Schmidt ~36 k WS HCP 2012 - Kyoto, November 12 -16, 2012 16
D 0 – D 0 mixing – Analysis details § § Count WS and RS events in 13 decay time bins Fit the ratio of yields as function of the decay time § Fit strategy: § Tight cut on D 0 mass § Fit first clean RS sample to determine signal shape § Then fit WS sample with the signal shape fixed by RS sample § Calculate WS/RS ratio R § Systematics: § Relevant sources are those which could bias observed time-dependence on R: ▪ Secondary D-mesons and bkg. from mis-ID charm decays peaking in M(D 0πs) B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 17
D 0 – D 0 mixing – Result First observation of D 0 - D 0 mixing § Mixing parameters: RD = (0. 352 ± 0. 015)% y’ = (0. 72 ± 0. 24)% x’ 2 = -(0. 009 ± 0. 013)% § p-value = 5. 67 x 10 -20 No mixing hypothesis excl. at 9. 1σ § Comparison with other experiments: Experiment ar. Xiv Ref. Ba. Bar 0703020 v 1 0. 303± 0. 019 Belle 0703036 v 2 CDF LHCb B. Schmidt RD (%) y’ (%) x’ 2 Significance 0. 97± 0. 54 -0. 022± 0. 037 3. 9σ 0. 364± 0. 017 0. 06± 0. 4 0. 018± 0. 022 3. 2σ 0712. 1567 0. 304± 0. 055 0. 85± 0. 76 -0. 012± 0. 035 3. 8σ 1211. 1230 0. 352± 0. 015 0. 72± 0. 24 -0. 009± 0. 013 9. 1σ HCP 2012 - Kyoto, November 12 -16, 2012 18
Rare decays B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 19
Rare Decays – Introduction § Flavour physics observables have sensitivity to new particles at high mass scales via their indirect effects in loop diagrams § B 0 s μ+μSM: NP: FCNC, helicity suppressed SM expectation: (3. 54± 0. 30) x 10 -9 [ar. Xiv 1208. 0934 and ar. Xiv: 1204. 1737] § Sensitive to NP contributions MSSM: BR (B 0 s μ+μ-)~tan 6 /M 4 A B 0 K*0 μ+μ- SM: NP: FCNC, BR (PDG) = (1. 05± 0. 15)x 10 -6 Angular observables sensitive to modification of the helicity structure B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 20
Update on search for B 0(s) μ+μ§ § § New analysis using 1. 1/fb of the 2012 data set plus 1/fb from 2011 Same analysis strategy as in 2011 [PRL 108 (2012) 231801] with only minimal changes Improvements: [Subm to ar. Xiv and PRL today] § Refined estimate of the exclusive backgrounds § BDT output calibrated on exclusive B(s) h+h- (instead of inclusive) Analysis will be presented by J. Albrecht B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 21
Update on search for B 0(s) μ+μ§ § § New analysis using 1. 1/fb of the 2012 data set plus 1/fb from 2011 Same analysis strategy as in 2011 [PRL 108 (2012) 231801] with only minimal changes Improvements: [Subm to ar. Xiv and PRL today] § Refined estimate of the exclusive backgrounds § BDT output calibrated on exclusive B(s) h+h- (instead of inclusive) Analysis will be presented by J. Albrecht New result First evidence of B 0 s μ+μ- B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 22
Search for K 0 s μ+μ[arxiv: 1209. 4029 v 2, Subm. JHEP] Yet unobserved FCNC decay with BR (SM) = (5. 0± 1. 5) x 10 -12 § The current 90% CL experimental limit dates from 1973: BR < 3. 2 x 10 -7 § μμ hypothesis ππ hypothesis K 0 π+π Peaking background from Ks 0 π+π- decays is shifted due to μ - π mass difference. § Good mass resolution helps containing it. § § Discrimination through a BDT (geometrical and kinematic), trained on data and calibrated on Ks 0 π+π- data B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 23
Search for K 0 s μ+μ§ Normalisation to translate number of signal decays into a branching fraction: § Use CLs method to determine an upper limit on the branching fraction BR (Ks 0 μ+μ-) < 9(11) x 10 -9 at 90 (95) % CL 35 times better than previous result Summary of all neutral flavoured mesons to μ+μ- decays: B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 24
Isospin asymmetry in B K(*) μ+μ[JHEP 07 (2012) 133] § The isospin asymmetry in B K(*) μ+μ- is defined as: It is predicted to be very small in the SM § § [JHEP 01 (2003) 074] Integrated over q 2 , over 4σ deviation from zero for B K μ+μ 2012 data should allow errors to be halved. B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 25
Analysis of B+→K+μ+μ− FCNC process, sensitive to modifications of the helicity structure § Decay rate can be expressed in terms of the angle θl between the μ- and the K+ in the dimuon rest frame: § Event yield 1232 ± 40 of B+→K+μ+μ in 1. 0 fb-1 Differential branching fraction, using B+ J/ψ K+ as normalisation channel. § Consistently below SM prediction at low q 2. § § Integrating d. B/dq 2 gives BR(B+→K+μ+μ ) = (4. 36 ± 0. 18) x 10 -7 [arxiv: 1209. 4284, Subm. JHEP] B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 26
B+→K+μ+μ− angular analysis [ar. Xiv: 1209. 4284, Subm. JHEP] • • AFB expected to be zero in the SM, can be up to 0. 15 in NP models FH also close to zero in the SM, can be up to 0. 5 in NP models AFB and FH are determined from a simultaneous fit to mass and cos(θl) The results are consistent with the SM B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 27
Other topics - Electroweak physics - Soft QCD physics - Upgrade potential B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 28
Z→ ττ production cross-section § Z-production cross-section is an important verification of SM predictions § Inclusive W, Z μμ production cross-sections published earlier this year (from 37/pb data taken in 2010) [JHEP 06 (2012) 058] § New result: inclusive Z ττ cross section based on 2011 data set of 1/fb Signal topologies and channels [ar. Xiv 1210. 6289, Subm. JHEP] Observed : 124 o. Bkg : 42 o. Signal : 82 B. Schmidt σpp Z τ τ = 71. 4 ± 3. 5 (stat. ) ± 2. 8 (syst. ) ± 2. 5 (lumi. ) pb HCP 2012 - Kyoto, November 12 -16, 2012 29
p. A collisions in LHCb § § § Test run with p. A collisions on September 13 in all 4 LHC experiments Several hours of data taking with L ~ 5 x 1025 cm 2/s with stable conditions No problem of multiplicities in the detector, similar to pp collisions § § KS and Λ peaks reconstructed offline Good expectations for the January (p. A, Ap) run B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 30
LHCb sensitivity to key flavour channels [LHCb-PUB-2012 -009] • Unique potential Bs / b baryon sector • Charged particle final states far in excess of other facilities B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 31
Conclusions § A measurement of γ from a combination of B Dh± analyses has been o reaches the precision of the presented. The obtained value of γ = (71. 1 +16. 6 ) -15. 7 B-factories. Good prospects for precision measurement in the future. § LHCb observed D 0 -D 0 mixing. The no mixing hypothesis is excluded with a significance ff 9. 1σ. The measurement agrees wit the one of other experiments, but has substantially better precision. § LHCb observes an excess of Bs μμ candidates with respect t 0 the background expectations. § The upper limit on K 0 s has been improved by 35 times since the previous measurement, entering the region where constraint becomes interesting – though SM is still a long way to go. § Measurements presented here use (mainly) the 2011 dataset of 1. 0/fb. By the end of 2012, expect to triple the dataset, looking forward to new exciting results next spring. B. Schmidt HCP 2012 - Kyoto, November 12 -16, 2012 32
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