Fisica del B ai collider adronici: presente e futuro Marta Calvi Università di Milano Bicocca and INFN IFAE 2005 Catania
B Physics now and in the LHC era Outstanding results from B-Factories provide a successful test the CKM paradigm of flavour structure and CP violation. However present knowledge is still incomplete. (from CKM-fitter ) New Physics could still be hidden in box and in penguin diagrams, realm of indirect discoveries. If NP will be found in direct searches, B Physics measurements will have to sort out how the flavour problem is really solved in these theories.
B Physics at Hadron Colliders The reason for going at hadron colliders: • Huge bb cross section: sbb~500 mb @14 TeV (~1nb @Y(4S) ) • Access to all b-hadrons: Bd,Bu, Bs, b-baryons and Bc The challenge: • Presence of underlying event. High particle multiplicity. • High rate of background events (sbb/sinel~10-3). Experimental requirements • Trigger (also on fully hadronic decays) • Excellent tracking and vertexing (mass resolution, proper time resol.) • Excellent PID (exclusive selections, flavour tagging)
The present: CDF/D0 Excellent mass resol. PID: dE/dx,TOF Silicon vetex trigger Excellent m and track coverage Results from CDF and D0 at Tevatron have demonstrated that precision B physics is possible at hadron machines. LbJ/y L An example: b-baryons Data on tape 600 pb-1/experiment. Used for present results 220-450 pb-1
The future: ATLAS-CMS pTvsh for detected B hadrons • B physics mainly in the first two years with ℒ=1-2x1033 cm–2s-1 10-20 fb-1 /year. • At high luminosity ( >20 piled-up interaction) pursue very rare B decays. B-physics program will depend on trigger strategy and allocated bandwidth. “Classical” scenario: B events triggered by high-pTm or mm. CMS: also exploit online tracking for exclusive B events selection at HLT. Good results from studies on some benchmark channels. ATLAS: maximize B-physics capabilities with reduced detector at start-up with a flexible trigger strategy (start with a mm trigger, add further triggers in the beam-coast and for low-luminosity fills.)
The future: LHCb 10-300 mrad Forward peaked production of b hadrons at LHC pp interactions/crossing Luminosity locally tuned (by defocusing beams) to limit pile up of pp interaction per bunch crossing: ℒ =2x1032 cm–2s-11012 bb produced per year (taking 1 year=107 s) Should be available from day one
LHCb trigger detector 40 MHz L0, L1, L0*L1 efficiency high pT (m,e,g,h) [hardware, 4 ms latency] 1 MHz high IP, high pT tracks [software,1 ms] 40 kHz HLT: software using complete event [10 ms] 2 kHz storage Systematics from data
e-, m- Opposite side Qvertex ,QJet K- B0opposite D PV Bs0signal K- Same side K + K+ B Flavour Tagging Several algorithms used to determine the flavour of the signal B meson at production. Tagging power D2 = (1-2w)2 (in %) Kaon tagging most powerful for LHCb.LHCb combined power for Bs~6%. Lower for B0 (~4%) due to reduced same-side tagging power (p).Recent Neural-Net based studies achieved 9% for Bs (not used here).
A complete program on B Physics would include: • Precise measurement of B0s-B0s mixing: Dms, DGs and phase fs. • Precise determinations of angle gincluding from processes only at tree-level, in order to disentangle possible NP contributions. • Several other measurements of CP phases in different channels for over-constraining the Unitarity Triangles. • Search for effects of NP appearing in rare exclusive and inclusiveB decays. • Studies on b-baryons and Bc physics, studies of bb production …
t s b Bs0 W W Bs0 t s b ( r,h ) a Rb g b B0s-B0s mixing DGs = GL - G H Dms = MH-M L • Precise constraint from Dmq ratio: From CKM fits: Dms=20.5±3.2 ps-1. If Dms>30 ps-1 NP at 3s. • Large decay width difference in SM: (cf DGd /Gd = O(1%) ) DGs/Gs= O(10%) • Small mixing phase in SM: fs = -2 arg (VtsVtb*) =-2 l2 h -0.04 Contributions from new particles can affect both the amplitude and the phase of mixing.
CDF: Bs mixing in Semileptonics Opposite side flavour tags (e,m,jet charge)eD2=(1.43±0.09)% Limit: Dms>7.7 ps-1 @95%CL
CDF: Bs mixing in Bs Dsp Opposite side flavour tags (e, m, jet charge):eD2=(1.12±0.18)% s(t)100 ps Low sensitivity for hadronic only. Combined limit: Dms>7.9 ps-1 @95% CL
Bs mixing, Tevatron perspectives • Improve statistics from: • Better flavour tagging (same side K tag) Add more channels More integrated luminosity • Improve proper time resolution. DO limit, semileptonics: Dms>5.0 ps-1 @95% CL DO projections: Semileptonics dominate now, hadronic modes matter more for large Dms Scans dominated by statistics now, at large Dms proper time resolution is the limiting effect. CDF expects sensitivity 15-16 ps-1 from improvements, on same data set.
Bs mixing at LHC Best mode Bs0Ds-p+ LHCb: 1 year 80k events, S/B3 Control of mistag rate,resolution, backgroundand acceptance is important. Plot made for Dms=20 ps-1 st~ 40 fs proper time resolution (fs) LHCb: 5 observation of Bsoscillation for Dms<68 ps-1 (1 year) Once observed, precision to measure Dms ~0.01ps-1 ATLAS: 5 s observation forDms< 22 ps-1 (10 fb-1). Most recent CMS sensitivity is lower due to trigger restriction.
G=(GL+GH)/2 and DG=GL-GH Γs from BsJ/f D0 Preliminary Use untagged BsJ/f events. VV decay: mixture of CP-even and CP-odd components. Fit distributions of mass, proper decay length and transversity angle to measure relative contribution of CP states, D0 Preliminary D0 Preliminary
Γs from BsJ/f DG/G 0.21 1/G=t(ps) 1.39 R 0.17±0.10 +0.33 – 0.45 +0.25 – 0.33 0.65 1.40 +0.15 – 0.16 +0.15 – 0.13 0.13±0.08 CP-odd fraction at t=0 Including constraint from w.a. Bs lifetime to flavour specific decay channels: tfs=1.43±0.05 ps DG/G= 0.23 +0.16 – 0.17
fsandΓs with BsJ/f (h) BsJ/f is the Bs counterpart of the golden mode B0J/yKS, measuring fd. Fit angular distributions of tagged events, as a function of proper time, to measure DGs and thephase fs of Bs oscillation. LHCb: 100k BsJ/(mm)f events/year, S/B>3 fs Similar sensitivity on fs reached also using BsJ/y()h, with 7k events per year, pure CP state. ATLAS/CMS achieve similar sensitivieties for 20 fb-1
from BsDsK • Exploit Interference between two tree diagrams via Bs mixing: BsDsK and BsDsK • Time-dependent CP asymmetries measureg + fs (and strong phase D) extract g taking fs from BsJ/f. • Very little theoretical uncertainty, insensitive to NP. BsDsK BsDs Need excellent PID for K/p separ. 5400 events/ yr S/B>1.0 at 90%CL () =14º (1 year) 5 yrs of data, ms= 20 ps -1 • New analysis: combination of BsDs(*)K and B0D(*)p using U-spin symmetry. Expected sensitivity ~5º in 5years.
from B DK* • Measure 6 time integrated decay rates: B0D0K*0, D0K*0 and DCPK*0 (+ CP conjugates), where DCP K+K- (or p+p-). • Decays are self-tagging through K*0 K+p-. Appropriate construction of amplitudes allows both gand strong phase D to be extracted (Gronau & Wyler, Dunietz) Similar to B± D0K± but here two colour suppressed diagrams and |A(BD0K*)| / |A(BD0K*)| ~0.4 LHCb annual yields for g = 65,D = 0) • s(g) ~ 8 (55<g<105, -20<D<20)
CDF Bhh Kinematics and dE/dx to separate contributions 1.4 sfor K/p separation hypothesis BR(Bdpp) / BR(BdKp) =0.24±0.06±0.05 BABAR: 0.26 ± 0.036 ± 0.015 Direct ACP(BdKp) = -0.04±0.08±0.01 BABAR: -0.133±0.03±0.009 fs·BR(BsKK) / fd·BR(BdKp) = 0.50±0.08(stat)±0.07(syst)
/K /K Bd/s Bd/s /K /K from Band BsKK Large penguins contributions in both decays Measure time-dependent CP asymmetry for B and BsKK. Exploit U-spin symmetry for P/T ratio (Fleischer). Use RICH detectors for K/p separ. Bd+- without RICH Knowing fs, fd can solve for g . B (95%CL) d sM=17 MeV BsKK (95%CL) B 26 k events/yrBK+135 k BsKK 37 k () 5º (1 year) g (º) +(U-spin)
afrom B r +p- Quinn & Snyder: Time dependent analysis of Dalitz distribution allows a clean determination of a independently from penguin contributions M(p0p-) M(p0p+) poreconstr. eff. 11-parameters fit to a, T and P amplitudes, strong phases, resonant and non-resonant background Mergedpo Resolved po LHCb: 14k events/yr S/B>1.3 sa< 10o (1 year)
bsss penguin decays B-Factories measure 3.7s between sin2b from charmonium and from bsss penguin modes(fKs,h’Ks). If related to NP it is important to examine also other channels involving bsss penguins. ACP(B+fK+)=-0.07±0.17stat±0.03syst BR(Bsff)=(14±6stat±6syst)x10-6 Large samples of Bsff, Bs KK ...,will be reconstructed at LHC, and also Bsfg , BK*g …
B0 K*0 +- BR(B0K*+-)SM=(1.20.4)x10-6 BR(s) AFB(s) Forward-backward asymmetry sensitive to NP via non-standard values of Wilson coeff. C7,C9,C10. Zero point known in SM at 5%. s=M(+-)2 [GeV2] AFB(s) ^ LHCb: 4400 evts/year S/B>0.4 (BR) ~ 2-3% (BR) ~ 2-3% (ACP) ~ 2-3% 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
Bs +- at Tevatron BR(Bs0+-)SM = (3.50.1)x10-9 Good sensitivity to NP. Can be strongly enhanced in SUSY: BR(Bs+-)~(tanb)6, for large tanb. 2005 D0 limit (300 pb-1) 2004 CDF limit (171 pb-1) SUSY SO(10) (Dermisek, Rabi et al.) Excluded by Bsm+m- 4 events observed, expected bg: 4.3±1.2
Bs +- at LHC LHCb:17 eventsBs0+- in 1 year at 2x1032cm-2s-1 Background study requires additional MC statistics, no events selected from full background sample, but only corresponds to S/B > 2 (MBs)=18 MeV/c2 ATLAS/CMS: can exploit also high luminosity runs (clear signature) yields for 100 fb-1 (1 year at 1034 cm-2s-1) Background estimates (from 1999) differ significantly, update awaited. Significant BR measurement, even for SM value!
Bc at Tevatron Original observation: BcJ/yln(CDF'98) New CDF: first observation in fully recon-structed hadronic decays Bc+J/yp+ M(Bc)= 6287.0±4.8stat±1.1syst MeV/c2 D0: observation in inclusive semileptonic decays Bc+J/y m+X t(Bc)=0.448 ±0.121 ps +0.123 – 0.096 M(Bc) = 5.95 ± 0.14 ± 0.34GeV/c2
Bc at LHC 109- 5x1010 Bc produced per year at 2x1032 -1034 cm-2s-1 LHCb: 14k events/year S/B>1.3 Bc+J/y(mm)p+ reconstructed Precision measurements of mass and lifetime M( J/y p+ ) Quarkonium-like Bc mesons allow to study the interplay of strong and weak interactions: Heavy-Quark Expansions, Non-Relativistic QCD, Factorization… Fleisher,Wiler : g measurements with Bc+ Ds+D0 using triangle relations
Conclusions Extensive program on B-Physics being developed by CDF/D0 at Tevatron. Experiments at the LHC expect to take B-Physics a significant step further than the B factories: access to otherb hadron species and high statistics. LHCb combines excellent vertexing and particle ID with flexible trigger, dedicated to B physics. ATLAS and CMS will also contribute significantly. Competitive for modes with muons and small BR. Performances at LHC have been studied on several benchmark channels. Suggestion from theory on new channels are also important in order to fully exploit the opportunities of Bs system, b-baryons and Bcmesons.
sin(2b) from B0J/y Ks • Gold plated channel for b, used at B-Factories. ACP(t) direct CPV=0 in SM sin (2b) • LHC will bring high statistics which can be used to measure also Adir LHCb: B0J/y()Ks 216k evts/yr, B/S<0.8 (sin2b)~0.022 1 year ATLAS 3 years at 1033cm-2s-1