B LHC. A. Sarti LNF - INFN

Transcription

1 B LHC A. Sarti LNF - INFN

2 Why B physics? If NP is not completely decoupled from TeV scale, flavour sector should be affected! B meson system is a natural place where to look Bd system constrained from B factories: Bs mesons (and Bd, Bc, b,..) LHC with large statistics! b s transitions can be studied in detail (Rare decays, precise CP violation analyses) CKM sector can be further constrained ( from trees, NP free, and from loops where, again, NP can sneak in...) B p machine (TeV scale) is doable ms = 17.77±0.10 (stat)±0.07(syst) ps 1 PRL 97 (2006) SM studies. E.g. D0 and CDF measurement of ms NP studies. E.g. D0 and CDF Bs mixing measurement constraint in vs s plane 2

3 B LHC pt of B hadron Pythia production cross section bb correlation 230 µb of B hadron B pp interactions/crossing pp 14 TeV: (bbar) ~ 500 b : 104 L = experiments involved (1 dedicated, LHCb) Huge background from pp to be suppressed Becomes difficult when Lumi increases: pp interaction /crossing 1 23 from to ATLAS & 1033 n=0 LHCb 100 µb Large gain from lower pt thr. n=1 3

4 For detector details see talks in tomorrow session ATLAS & CMS pt resolution in the silicon tracker (muons) General purpose detectors <2.5 and full B physics using trigger with large pt Good resolution in tracker and spectrometer High rec (E.g. CMS >98% for <2.4) and trig pt resolution ~ 1 2% IPT resolution ~ 10 m 4

5 For detector details see talks in tomorrow session Detector LHCb (tracking) optimized for B physics studies σp/p = 0.3% 0.5% depending on p High efficiency (>95%) for long tracks from B decays and ~4% Ghosts for pt>0.5 GeV/c Impact parameter resolution IP ~ 30 m Typical B resolutions Proper time ~ 40 fs Mass ~ MeV/c2 High Multiplicity Environment (~30 charged particles per bb ) 5

6 LHCb (Particle ID) MisID probability vs p (GeV/c) High efficiency (> 95% in full range from 3GeV) Measured on data using: generic (50 Hz), Prompt J/ψ µµ (< 2 Hz) and J/ψ µµ from B (0.3 Hz) misid ( 1%, p>10 GeV/c) measured using decays Good,K separation in GeV range (2 RICH!) Hadron samples to calibrate,k and measure misid: No PID D*+ D0(K π+)π+ (16 Hz of hadrons) Hadrons from B hh (0.02 Hz) (E.g. misid in Bs µµ analysis) Efficiency vs p (for pt > 1 GeV/c) K K, p π e, µ, π ππ invariant mass With PID Red: D* calibration Blue: MC truth π K, p K e, µ, π Kπ invariant mass 6

7 LHC First level (Hrdw) CMS & ATLAS L1: Outp rate <100kHz. Info from μ chambers and calorimeters LHCb L0: Outp rate = 1 MHz. Info from pileup system, ECAL, HCAL and MUON: select minimum pt h, µ, e, γ, π0 trig for J/ channels > 80%, other channels ~40% HLT (Sftw, after full readout) Avoid hard cuts on CMS & ATLAS HLT: Outp rate displacement (unbiased selection ~200Hz. (10% useful for B crucial for proper time studies)! phys) LHCb HLT: Outp rate ~2 khz. Several trigger lines: µ, µ+h, h, ECAL, (start with L0 confirmation). Then inclusive and exclusive selections 7

8 Bs J/ Measure s= 2 s counterpart of d=2 d [sin 2 d = 0.668±0.028] s [SM] = arg(vts2) = 2λ2η = ± [CKMfitter, sum. 07] and hence sensitive probe of NP High BR ~ and good exp. signature ( trigger effective!) Time dependent CP asym. used to measure φs J/ is not a pure CP eigenstate: angular analysis is needed to determine even ( f = 1) and odd ( f =1) states NP suggested by M. Bona et al. (arxiv: , combines CDF and D0 results) 8

9 Key ingredients: tagging and proper time Data samples. Assume ¼ nominal year: 2.5fb 1 ATLAS, CMS and 0.5 fb 1 LHCb (feasible by 2009). Tagging: Measuring tagging on data From 34M bb events (~13 minutes) Clean B+ D0π+ signal LHCb: e,, K, vertex charge (OS) + pion (B0) or kaon (Bs) (SS). εd2 = 6.6% ATLAS: e,, Qjet (OS). εd2 = 4.6% CMS: not yet done... Proper Time: Bs oscillation has to be well resolved good that ms is not too big! resolution function must be well understood measuring lifetimes, oscillation plot with Dsπ etc. ATLAS στ [fs] 83 CMS 77 Entries per 0.02 ps B mass (GeV/c2) Bs Ds+π rate in 0.5 fb 1 (signal only) Bbb/S < 0.05 at 90% CL σt ~ 40 fs LHCb 36 Reconstructed proper time [ps] 9

10 Mass resolution, B/S, yields Bs mass resolutions and Background/Signal ratios σm [MeV/c2] B/S ATLAS 16.5 ) 0.18 CMS 14 ) 0.25 b J/ψ K*0 b J/ψ X comb. LHCb 14+) 0.12 with J/ψ mass constraint +) without mass constraint, improves bkg control ) Numbers of reconstructed J/ and those effectively flavour tagged (¼ year) Nrec Nreceff-tag ATLAS CMS LHCb 23 k 27k 33 k 1.0 k 2.2 k 10

11 Measuring s From Z. Ligeti et al hep-ph/ Allowed regions CL > 0.90, 0.32, 0.05 With 2009 data σ(φs) σ( Γs)/ Γs ATLAS CMS o LHCb LHCb: BSM effect down to the level of SM can be excluded/ discovered with the 2009 data (J/ψ η, ηc φ, Ds+Ds can be added. No angular analysis, but smaller statistics) With > 2009 data measurement 90o σs 0o Allowed region NP/SM = hse2i s hs 180o φs= 0.04± o ATLAS and CMS: ( s) 0.04 with L dt = 30 fb 1 data LHCb By ~2013, SM prediction of s tested to a level of ~ with first ms σs LHCb, L=2fb-1 0o hs 11

12 Bs Bs very rare Effective FCNC +Helicity suppression ~ (mm/mb)2 SM predictions B(Bs ) = (3.5±0.5) x 10 9 B(Bd ) = (1.0±0.2) x [G. Isidori e P. Paradisi Phys Lett. B639, 499 (2006)] Very sensitive to NP with large tan MSSM ~ tan6 /M4A Large tan favoured by b s, (g 2), B etc. Upper limit on BR(Bs ) plays crucial role [1] CDF BR < % 2fb 1 [2] arxiv: v1 29/05/08[hep-ex] A. Sarti [2] D0 BR < % HCPCL 08 [1] arxiv: v1 [hep-ex] 12

13 Bs analysis Analysis Strategies LHCb Combine geometrical information into a likelihood (GL); Divide (GL, Mass, PID) space in N bins and evaluate expected events/bin for signal, signal+bkg ATLAS + CMS: cut on isolation, pointing, decay length. CMS counts events in ±2.3 mass window, ATLAS perform bayesian estimate of # of events Trigger LHCb ~1.5 khz inclusive μ ; CMS ~ 0.9kHz, di μ; ATLAS 20 Hz B phys trigger Performances Di μ mass resolution: LHCb σ ~20 MeV/c2 ; CMS ~ 43 MeV/c2 and ATLAS ~ 67 MeV/c2 13

14 Yields (S,B) Background Main background (b μ,b μ, b μ, b c μ ) B hh, small compared with b μ,b μ Bc+ J/Ψμν dominant of exclusive, but still small Event yields [1 nominal year of data taking] : LHCb: S ~30, B ~ 2fb 1 CMS: S~ 6, B ~ 10fb 1 ATLAS: S ~ 7, B ~ 10fb 1 Normalization channel: B+ J/ K+ 2M 2fb 1 (LHCb) Control channels: Signal description: B hh ~200 2fb 1 background Bs μμ Bs KK (from sidebands) Mass (MeV) 14

15 Results 2009 data BR (x10 9) 90% CL imit on BR (only bkg is observed) Expected final CDF+D0 limit Uncertainty in background prediction SM prediction no sy ste ma ti Integrated luminosity (fb 1) SM wit cs hs yst em atic s LHCb potential With 0.1 fb 1 measure BR 9(15) 10 9 at 3(5) With 0.5 fb 1 measure BR 5(9) 10 9 at 3(5) Exclusion: 0.1 fb 1 BR < fb 1 < SM SM agreement 2 fb 1 3σ evidence 6 fb 1 5σ observation ATLAS and CMS are contributing with performances comparable to Tevatron exp. 15

16 b sll decays Inclusive decay difficult to access at hadron collider. Good prospects for excl decays (B Kℓℓ, K*ℓℓ ). Hadronic uncertainty reduced in: Forward backward asymmetry AFB and s0 Transversal asymmetries Ratio of µµ and ee modes Suppressed loop decay in SM. NP could contribute at the same levels, could modify BR and angular distributions: sensitivity to SUSY, gravitation exchange, extra dimensions. E.g. in SM [Beneke et al hep ph/ ]: BR(Bd K*µµ)=( ) x10 6 and zero crossing of AFB (s0) s0= s0(c7,c9)= GeV2 16

17 Bd K*µµ AFB as a function of the µµ invariant mass. Determine s0, the m2µµ for which AFB=0. CMS studies just started... AFB(s) Measure 200 evts in 2.5 fb 1 With L= 0.5 fb 1 1.8k evts 2ab evts.) 30 fb-1 SM prediction s = m2µµ [GeV2] LHCb : Bbb/S = 0.2 ± 0.1 (ignoring nonresonant Kπµµ events for the time being). L= 2fb 1 σ(s0) = ±0.46 GeV2 L=10 fb 1 σ(s0) = ±0.27 GeV2 at the level of present theoretical precision 17

18 measurement Several independent ways to LHCb: trees and loops B DK : ADS/GLW and GGSZ strategies are pursued. Dependence on D strong phases affect sensitivity Bs DsK : clean measurement using interference of b u and b c transitions via Bs mixing Decay B,+ D(Kπ)K,+ favoured B,+ D(Kπππ)K,+ favoured B,+ D(Kπ)K,+ supp. B,+ D(Kπππ)K,+ supp. B,+ D(hh)K,+ 2 fb 1 yield 28k 28k k Bbb/S >2 >2 2 18

19 measurement (trees) B mode D mode Method tagged, A(t) σ(γ) 2fb-1 Bs DsK KKπ 10º B+ D K+ Kπ+ K3π +KK/ππ counting, ADS+GLW B+ D*K+ Kπ counting, ADS+GLW B+ D K+ Ksππ Dalitz, GGSZ B+ D K+ KKππ 4 body Dalitz 18º B+ D K+ Kπππ 4 body Dalitz Under study B0 D K*0 Kπ + KK + ππ counting, ADS+GLW 9º B ππ,kk Tagged, A(t) 10º 5º - 13º Under study 7-12º Combined LHCb sensitivity to γ with tree decays only (educated guess): σ(γ) ~ fb 1 σ(γ) ~ fb 1 γ with loops decays only Impact of LHCb 10fb 1 19

20 (bbar) Predicted to be 500 b with large errors (extrapolations from 1.8 TeV using NLO QCD). Measurement can be used to: Tests MC descriptions, NLO QCD calculations and PDF knowledge Know precisely the bkg for NP processes Approach Inclusive and exclusive (B+ J/ΨK+): use µ trigger + b jet tagging (ATLAS & CMS) or J/Ψ events to measure b production rate Requires µ trigger (high pt) and jets with ET>50(30)GeV/c in CMS (ATLAS) L1 εtrig ~ 15%. εbtag on HLT Total selected ev ~ 60% Performances (preliminary) Largest sys are from fragmentation and jet energy scale σ(stat)~ 1% in ATLAS with 100pb 1 (1month of 1032) in LHCb with 50nb 1 ( ) CMS (in pt bins): with 10fb 1~O(10%) 10fb 1 Systematic Statistical 20

21 Conclusions LHC program is proceeding without major delays Expect first beam in August and first collisions soon afterwards 3 experiments are getting ready for the B physics challenge: with the expected performance they will be able to test SM and BSM effects trough the analysis of (Golden) b s observables, that can cleanly reveal NP effects: e.g. Bs BR down to SM and Bs mixing 0.04 level with 2009 data b sll decays: with few years of data taking can go at the level of present theoretical uncertainty uncertainty down to 10 expected with 2009 data Cross section for bbar production: few % results with early data and full pt scan (@ 10%) with 2009 data.. and many more important items left outside (see LHCb physics page!) Few months before the LHC startup: stay tuned! Thanks to U. Langenegger (CMS) and A.Policicchio (ATLAS) for help preparing the talk 21

22 Spares

23 J/ comparison in 1 slide 23

24 Bs 24

25 Radiative decays Bd K*γ ACP < 1% in SM, up to 40% in SUSY Can measure at <% level. Reference channel for all radiative decays. Bs φγ No mixing-induced CP asymmetry in SM, up to 50% in SUSY. Sensitivity for ACP(t) measurement under study. Decay Yield 2 fb 1 Bbb/S Bd K*γ 68k 0.60 Bs φγ 11.5k < 0.55 Λb Λ(1116)γ 0.75k < 42 Λb Λ(1670)γ 2.5k < 18 Λb Λγ Right-handed component of photon polarization O(10%) in SM. Can be higher BSM. Measure photon asymmetry αγ from angular distributions of γ and hadron in Λb Λ(pπ,pK)γ decays. 3σ evidence of right-handed component to 21% with 10 fb 1 25

26 measurement 26

27 from loops 27

28 LHCb physics reach 0.5 fb fb 1 yield 0.5 fb 1 stat. sensitivity Rough stat. break-even point with competition * Bd J/ψ(μμ)KS 59k σ(sin(2β)) = fb 1 Bs Ds π+ 35k σ( ms) = ps fb 1 Bs Ds K± 1.6k σ(γ) = 21 deg Bs J/ψ(μμ)φ 33k σ(φs) = fb 1 Bd φks 230 σ(sin(2βeff)) = fb 1 Bs φφ 780 σ( φnp) = 0.22 B+ D(hh)K± B+ D(KSππ)K± 16k 1.3k σ(γ) = deg 0.3 fb 1 Bd π+π 8.9k σ(s, C) = 0.074, fb 1 Bs K+K 9.0k σ(s, C) = 0.088, Bd ρπ π+π π0 3.5k α 2 fb 1 Bd K*0γ 15k ACP 0.4 fb 1 Bs φγ 2.9k ACP(t) Bd K*0μ+μ 1.8k σ(q20) = 0.9 GeV2 0.1 fb 1 18 BRSM at 90%CL 0.05 fb 1 Decay mode Bs μ+μ * Assuming naive 1/ N scaling of stat. uncertainty of existing results at Tevatron ( 16 fb 1) or current B factories ( 1.75 ab 1) For many measurements based on Bs, or untagged B0, B+ decays only few 0.1 fb 1 are necessary to produce the world s best results 28

29 LHCb sensitivities 29

30 LHCb contribution to CKM fit 30

31 Bs mumu strategies 31

32 Comparison of strategies 32