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Advancing B Physics at Future Hadron Facilities: LHC Perspective

Explore the progress of B physics at the LHC beyond the B factories, delving into experimental setups, tracking high multiplicities, vertex detection, particle ID methods, and flavor tagging for future projects.

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Advancing B Physics at Future Hadron Facilities: LHC Perspective

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  1. B Physics of Future Hadron Facilities Roger Forty (CERN) • Extracting the physics • B physics sensitivities Workshop on the Unitarity Triangle (CKM 2005) San Diego, 17 March 2005

  2. Introduction • Until last month, “B physics of future hadron facilities” would have included both the LHC and Tevatron • Results from CDF/D0 at Tevatron have demonstrated that precision B physics is possible at hadron machines.They were to be followed by a dedicated B experiment • BTeV was a direct competitor for LHCb at the LHCWe benefited in LHCb from the fruitful exchange of ideas(for example on triggering strategy) • However, BTeV has now been cancelled, so this talk becomes “B physics at the LHC” How can B physics at the LHC progress beyond the impressive results of the B factories? Roger Forty B Physics at Future Hadron Facilities

  3. LHC experiments LHCb (that will do B physics) roughly to scale ATLAS/CMS are general purpose experiments,optimized for high pT discovery physics LHCb is a dedicated B physics experiment ATLAS CMS Roger Forty B Physics at Future Hadron Facilities

  4. LHC environment • pp collisions at s = 14 TeV, bunch crossing rate = 40 MHzLarge b cross section sbb ~ 500 mb (but ~ 0.5% of total) • At high luminosity, pile-up of pp interactions per bunch crossing: • LHCb chooses L ~ 2 1032 cm-2s-1(tuneable by defocusing beams)Should be available from day one107 s taken as nominal “year” = 2 fb-1 1012 bb produced/year • ATLAS/CMS expect L ~ 1–2 1033for the first two years  10–20 fb-1/yearthen 1034 cm-2s-1(> 20 piled-up interactions!) • LHC machine had a problem with cryogenic plumbing, now resolved: first beam expected in 2007 pp interactions/crossing Roger Forty B Physics at Future Hadron Facilities

  5. LHCb p p I will focus on LHCb, quoting results from ATLAS/CMS where relevantForward peaked production of b hadrons at LHC LHCb is a forward spectrometer (10–300 mrad) pTvsh for detected B hadrons 100 mb 230 mb Roger Forty B Physics at Future Hadron Facilities

  6. Tracking High multiplicities~ 30 long tracks/event (PYTHIA+GEANT simulation) MC truth Typical B decay length ~ 10 mm 100 mm 10 mm Roger Forty B Physics at Future Hadron Facilities

  7. Tracking MC truth Reconstructed High multiplicities~ 30 long tracks/event (PYTHIA+GEANT simulation) MC truth Typical B decay length ~ 10 mm Full pattern recognition implementedTrack finding efficiency > 95%(for B decay tracks) Roger Forty B Physics at Future Hadron Facilities

  8. Vertex detection • Vertex detector has silicon microstrips with rf geometryapproaches to 8mm from beam (inside secondary vacuum) Impact parameterresolution Momentum resolution(full spectrometer) sIP ~ 30 mm Dp/p~ 0.4% Roger Forty B Physics at Future Hadron Facilities

  9. Vertex detection • Vertex detector has silicon microstrips with rf geometryapproaches to 8mm from beam (inside secondary vacuum) Beam Proper time resolution ~ 40 fs(BsDs-p+,LHCb) cf ~ 50–70 fs (ATLAS/CMS) Roger Forty B Physics at Future Hadron Facilities

  10. Particle ID • RICH system uses novel photodetectors: Hybrid Photo Diodes ~ 500 tubes, each with 1024 pixels 2.5×2.5 mm2 p–K separation e + p test beam Unique feature of LHCb Roger Forty B Physics at Future Hadron Facilities

  11. Neutral reconstruction Merged Resolved • Use calorimeter clusters unassociated to charged tracks • Reasonable efficiency for p0achieved for B0 p+p-p0 study Resolved (separate clusters) or merged (using cluster shape) • KS p+p- efficiency ~ 75% if in vertex detector, lower otherwiseModes with multiple neutrals will be challenging… Recent study of h p+p-p0 (resolved) Mass resolution ~ 12 MeV Roger Forty B Physics at Future Hadron Facilities

  12. Trigger detector 40 MHz ATLAS/CMS ~ 10 Hz to storage for B triggers: mostly mm and high-pTm high pT (m,e,g,h) [hardware, 4ms latency] 1 MHz high IP, high pT tracks [software, 1ms] 40 kHz HLT: software using complete event [10ms] 2 kHz storage Roger Forty B Physics at Future Hadron Facilities

  13. Flavour tagging • Kaon tagging most powerful for LHCb(K± from the “opposite side” b c s) • Combined power for Bs~6% (LHCb)(cf ~ 1% at CDF/D0, ~ 30% at B Factories)Lower for B0 (~ 4%) due to reduced same-side tagging powerRecent Neural-Net based studies achieved 9% for Bs tagging (not used here) Tagging power eD2 = e(1-2w)2 (in %) Roger Forty B Physics at Future Hadron Facilities

  14. B physics sensitivity • All b hadron species are produced: B0, B+, Bs, Bc, b-baryonsExpected fractions ~ 40 : 40 : 10 : 0.1 : 10 % • One of the first physics goals (if CDF/D0 don’t beat us to it): observation of Bs–Bs oscillation • Best mode: Bs Ds-p+ • Plot made for 1 year of data (80k selected events, LHCb) for Dms = 20 ps-1 (SM preferred) • Control of mistag rate,resolution, backgroundand acceptance important Roger Forty B Physics at Future Hadron Facilities

  15. B physics sensitivity • All b hadron species are produced: B0, B+, Bs, Bc, b-baryonsExpected fractions ~ 40 : 40 : 10 : 0.1 : 10 % • One of the first physics goals (if CDF/D0 don’t beat us to it): observation of Bs–Bs oscillation • Best mode: Bs Ds-p+ • Plot made for 1 year of data (80k selected events, LHCb) for Dms = 20 ps-1 (SM preferred) • Control of mistag rate,resolution, backgroundand acceptance important Roger Forty B Physics at Future Hadron Facilities

  16. B physics sensitivity • All b hadron species are produced: B0, B+, Bs, Bc, b-baryonsExpected fractions ~ 40 : 40 : 10 : 0.1 : 10 % • One of the first physics goals (if CDF/D0 don’t beat us to it): observation of Bs–Bs oscillation • Best mode: Bs Ds-p+ • Plot made for 1 year of data (80k selected events, LHCb) for Dms = 20 ps-1 (SM preferred) • Control of mistag rate,resolution, backgroundand acceptance important Roger Forty B Physics at Future Hadron Facilities

  17. B physics sensitivity • All b hadron species are produced: B0, B+, Bs, Bc, b-baryonsExpected fractions ~ 40 : 40 : 10 : 0.1 : 10 % • One of the first physics goals (if CDF/D0 don’t beat us to it): observation of Bs–Bs oscillation • Best mode: Bs Ds-p+ • Plot made for 1 year of data (80k selected events, LHCb) for Dms = 20 ps-1 (SM preferred) • Control of mistag rate,resolution, backgroundand acceptance important Roger Forty B Physics at Future Hadron Facilities

  18. B physics sensitivity • All b hadron species are produced: B0, B+, Bs, Bc, b-baryonsExpected fractions ~ 40 : 40 : 10 : 0.1 : 10 % • One of the first physics goals (if CDF/D0 don’t beat us to it): observation of Bs–Bs oscillation • Best mode: Bs Ds-p+ • Plot made for 1 year of data (80k selected events, LHCb) for Dms = 20 ps-1 (SM preferred) • Control of mistag rate,resolution, backgroundand acceptance important Roger Forty B Physics at Future Hadron Facilities

  19. Dms • Details of LHCb performance study available in TDR (9/9/03) • Measurement of Dms using Bs Ds-p+ decaysSignal/Background (from 107 inclusive bb events) ~ 3Plot uncertainty on amplitude of fitted oscillation vsDms: • 5s observation of Bs oscillationfor Dms < 68 ps-1 (in one year) LHCb could exclude full SM range Once observed, precise value is obtained:sstat(Dms) ~ 0.01 ps-1 • For ATLAS, 5s observation for Dms < 22 ps-1 (for 10 fb-1)Most recent CMS sensitivity is lower due to trigger restriction Roger Forty B Physics at Future Hadron Facilities

  20. sin 2b • Measurement of sin 2b is not a central physics goal of LHCb (since so well measured by B factories) But will be an important check of CP analyses + can search for direct CP violating term  cos Dmdt • Expect 240k reconstructed B0 J/yKS events/year Precision sstat(sin 2b) ~ 0.02in one year for LHCb • ATLAS/CMS expect similar sensitivity for 30 fb-1 B0 mass resolution (MeV) ACP(t) (background subtracted) Roger Forty B Physics at Future Hadron Facilities

  21. fs and DGs • Bs  J/f is the Bs counterpart of the golden mode B0  J/KSCP asymmetry measures fs, the phase of Bs oscillation • In Standard Model fs is small: fs = -2l2h ~ -0.04  sensitive probe for new physics • Final state is admixture of CP-even and odd contributions angular analysis of decay products requiredL(t) = (1-R-) L+(t) (1+cos2qtr)/2 + R- L-(t) (1-cos2qtr)Fit for sinfs, R- and DGs/Gs • 120k signal events/year in LHCbs(sinfs) ~ 0.06, s(DGs/Gs) ~ 0.02(Dms = 20 ps-1)Including Bs  J/h will increase sensitivity:only ~ 7k events/year, but pure CP state • ATLAS/CMS achieve similar sensitivities for 20 fb-1 Roger Forty B Physics at Future Hadron Facilities

  22. g from Bs DsK • Bs Ds-K+ and Bs Ds+K-(b  u transition, BR ~ 7 × lower)both tree decays, which interfere via Bs mixing • CP asymmetry measures g + fsVery little theoretical uncertainty, insensitive to new physicsfs will be determined using Bs J/yf decays  extract g • Bs Ds-p+ gives background to DsK (BR ~ 12  higher)Suppress using PID residual contamination only ~ 10% • 5400 signal events/year (LHCb)S/B (from bb) > 1 (at 90% CL)(only 1 bkg event in wider MB window) Roger Forty B Physics at Future Hadron Facilities

  23. g from Bs DsK • Allow for strong phase difference D between the two diagramsFit two time-dependent asymmetries: • Phase of Ds+K- = D - (g + fs)Phase ofDs-K+ = D + (g + fs)extract both D and(g + fs) • s(g) ~ 14 in one year (LHCb)but expect it to be statistically limited • Discrete ambiguities in gcan be resolved by comparisonwith B0  D-p+ decays[Fleischer, see talk of Wilkinson] Asymmetries (5 years data) Roger Forty B Physics at Future Hadron Facilities

  24. g from B0 D0K*0 • Measure 6 decay rates: B0 D0K*0, D0K*0 and D0CPK*0(+ CP conjugates), where D0CP  K+K- (or p+p-) • Appropriate construction of amplitudes allows both g and strong phase D to be extracted [Gronau & Wyler, Dunietz] • Decays are self-tagging (through K*0  K+p-) and time integrated LHCb annual yields(for g = 65, D = 0) s(g) ~ 8(55 < g < 105,-20 < D < 20) Roger Forty B Physics at Future Hadron Facilities

  25. g from B  h+h- d g() • Time-dependent CP asymmetries for B0 p+p- and Bs K+K-ACP(t) = Adir cos(Dmt) + Amix sin(Dmt)Adir and Amix depend on weak phases g and fd (or fs), and on ratio of penguin to tree amplitudes = d eiq • Under U-spin symmetry [Fleischer](interchange of d and s quarks)dpp=dKK and qpp=qKK 4 measurements, 3 unknowns (taking fs & fd from other modes)  can solve for g • 26k B0 p+p-events/year (LHCb)37k Bs K+K- s(g) ~ 5 • Uncertainty from U-spin assumptionSensitive to new physics in penguins Bs KK B   Roger Forty B Physics at Future Hadron Facilities

  26. a from B0 p+p-p0 M2(p0p-) M2(p0p+) • Time-dependent Dalitz plot analysis of B0 rp  p+p-p0 permits extraction of a along with amplitudes + strong phases[Snyder & Quinn, see talk of Deschamps] • Annual yield ~ 14k events, S/B ~ 1.3 (LHCb)Complicated 11-parameter fit, studied with toyStatistical precision of s(a) ~ 10 achievable in one yearSystematic uncertainties under study, eg from mirror solutions: Roger Forty B Physics at Future Hadron Facilities

  27. a from B0 p+p-p0 M2(p0p-) M2(p0p+) • Time-dependent Dalitz plot analysis of B0 rp  p+p-p0 permits extraction of a along with amplitudes + strong phases[Snyder & Quinn, see talk of Deschamps] • Annual yield ~ 14k events, S/B ~ 1.3 (LHCb)Complicated 11-parameter fit, studied with toyStatistical precision of s(a) ~ 10 achievable in one yearStudy of B0 rr has started, few 102r0r0 /year (for BR = 10-6) Roger Forty B Physics at Future Hadron Facilities

  28. B0 K*0m+m- AFB(s) • Suppressed decay (DB = 1 FCNC), BR ~ 10-6 • Forward-backward asymmetry in the mm rest-frame AFB(s) is sensitive probe of new physics [Ali et al] ^ AFB(s) LHCb: 4400 events/year, S/B > 0.4 AFB(s) reconstructed using toy MC (two years data, background subtracted)Zero point located to ±0.04 ATLAS: 2000 events, S/B = 7 (30 fb-1) ^ ^ s = (mmm/mB)2 Roger Forty B Physics at Future Hadron Facilities

  29. Bs m+m- • Rare decay: BR(Bs m+m-) = 3.5  10-9 in Standard ModelSensitive to new physics, can be strongly enhanced in SUSY • LHCb expect 17 selected signal events/year for SM BRProblem to estimate the background: no events selected from full background sample, but only corresponds to S/B > 2 • ATLAS/CMS yields from 100 fb-1 (1 year at 1034 cm-2s-1) Background estimates (from 1999) differ significantly, update awaited Prospect of significant BR measurement, even for SM value Roger Forty B Physics at Future Hadron Facilities

  30. Other channels Bs  f  • B0fKS is challenging for the triggerExpect ~ 1000 signal events/year in LHCb • However, if new physics is showing up in B0fKS, important to also examine other b  s penguin decays: Bs ff, KK, fg…LHCb will reconstruct large samples of each • Not yet systematically explored: Bc and b-baryon physics • Recent assignment of high rate output streams from the HLT opens possibility of charm physics: > 108 reconstructed D*/year,and inclusive b trigger (eg on single m) should give the equivalent of ~ 109 perfectly tagged b-hadron decays/year • Although detector is under construction, still room to adjust trigger to select channels of topical interest —proposals welcome!  ~ 65 MeV Roger Forty B Physics at Future Hadron Facilities

  31. Systematics • Some potential sources of systematic uncertainty: • B/B production asymmetry • Charge-dependent detection efficiencies • Background asymmetries • Trigger bias (eg for flavour tag, proper-time acceptance) • Some experimental handles available: • Control channels (eg J/yK* for J/yKS, etc) • Regular reversal of spectrometer B field • Simultaneous fit of signal and background (eg DsK/Dsp) • Analysis of tagging performance in separate categories(eg triggered on B signal/triggered on other tracks) • High rate HLT unbiased samples will allow study using data Roger Forty B Physics at Future Hadron Facilities

  32. LHCb installation status The LHCb pit 4 March 2005 Muon filter Dipole magnet (completed) Calorimeter frame Installation will be completed in 2006 Roger Forty B Physics at Future Hadron Facilities

  33. Conclusions • Experiments at the LHC expect to take B physics a significant step further than the B factories:access to other b hadron species + high statistics • LHCb combines excellent vertexing and particle IDwith flexible trigger, dedicated to B physics Various channels studied, differing sensitivity to new physics • ATLAS and CMS will also contribute significantlyCompetitive for modes with muons and small BR • Comparison with a Super B factory is interesting… but construction of LHC experiments is progressing fast: we expect to be taking data in two years’ time the case for a Super B factory should be made relative to the sum of the B factories + LHC Roger Forty B Physics at Future Hadron Facilities

  34. LHCbyields and background Nominal year = 1012 bb pairs produced (107 s at L=21032 cm2s1 with bb=500 b) Yields include factor 2 from CP-conjugated decays Branching ratios from PDG or SM predictions Roger Forty B Physics at Future Hadron Facilities

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