1 / 27

B Physics prospects at LHCb

B Physics prospects at LHCb. Emanuele Santovetti on behalf of the LHCb Collaboration Università di Roma Tor Vergata e INFN. Physics motivations Detector requirements Physics program. Physics motivation.

zaynah
Download Presentation

B Physics prospects at LHCb

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. B Physics prospects at LHCb Emanuele Santovetti on behalf of the LHCb Collaboration Università di Roma Tor Vergata e INFN • Physics motivations • Detector requirements • Physics program DIS2007 Munich 16-20 April

  2. Physics motivation • LHCb is a dedicated B physics precision experiment at LHC to study CP violation and rare decays • Standard Model describes CP violation by a single complex phase in the unitary CKM matrix • We will over constrain the unitarity triangles and search for new physics LHCb precision enough to distinguish unitarity triangles (equal up to the l3 order) • New Physics can manifest through the exchange of a new intermediate particle in box and penguin diagram • compare measurementswhere NP effects are expected with treelevel ones (no loop or penguins) DIS2007 Munich 16-20 April

  3. Pythia production cross section 100 μb 230 μb bb correlation Detector design: B acceptance • Designed to maximize B acceptance (within cost and space constraints) • Forward spectrometer, 1.9 <  < 4.9 • more b hadrons produced at low angles • single arm OK since b-b pairs produced correlated in space • Luminosity tuned (2×1032 cm-2s-1) to maximize the probability of single interaction per x-ing • pT trigger can be lowered up to 2 GeV/c, efficient also for purely hadronic B • 1 year of running = ~2 fb-1 and 1012 b-b events @nominal luminosity DIS2007 Munich 16-20 April

  4. Detector requirements • Time dependent measurements • Reconstruction in the harsh LHC environment • B events ~ few % of the total cross section • Need of a selective trigger • Mass and pointing constraint to reduce background p+,K+ Good vertex spatial resolution to determine proper time K- ~1 cm Good K/p separation K+ Bs SV p+ PV p p Btag B flavor tagging DIS2007 Munich 16-20 April

  5. LHCb detector Muon stations Tracking stations beam VELO RICH system ECAL and HCAL DIS2007 Munich 16-20 April

  6. Momentum resolution dp/p = 0.5% p0 invariant mass spectrum Detector performances + 12C → 0 + X → 2 + X B vertex (0) =4.7 MeV/c2 PV IP Particle Identification Eff. DIS2007 Munich 16-20 April

  7. Flavor tagging Tagging power in ε(1-2ω)2 • Opposite side • Charge of the kaon in the b→ c→ s chain • Charge of the lepton in semi-leptonic decays • Charge of accompanying b jet • Same side • Charge of the K accompanying Bs • Charge of the p from B** → B*p± DIS2007 Munich 16-20 April

  8. LHCb Physics program • Bs mixing parameters: DGs, Dms,fs • a with Bd→p0p+p- • b with Bd → J/Y Ks • g with different methods • Rare decays • Bs → mm to the level of the SM prediction • Radiative penguin Bd → K*g, Bs → fg, Bd → wg • Electroweak penguin Bd → K*mm • and much more, e.g. Bc, charm physics, D0 mixing and CP violation) • .... not exhaustive list ! DIS2007 Munich 16-20 April

  9. ACP(t) - background subtracted sin2b with B0J/KS • One of the first CP measurements • golden mode, very well measured by b-factories • will be an important check of CP analyses and of tagging performance • can search for direct CP violating term  cosDmdt • Expect 240k reconstructed*B0 J/y KS events/2fb-1 • Precision sstat(sin 2b) ~ 0.02 in 2fb-1 of collected data [currently s(sin 2b) ~ 0.03] *after trigger and reconstruction DIS2007 Munich 16-20 April

  10. Measure g • g is the least well measured CKM angle and LHCb has several ways to measure it (independent) • Most promising method is the ADS+GLW applied to B → DK • B+→D(Kp)K+, D(K3p)K+, D(pp,KK)K+ • B+→D*(Kp)K+ • B0→D(Kp)K*0, D(KK)K*0, D(pp)K*0 • BS→DSK • Dalitz analysis for the neutral and charged B → DK decays • B0 → p+p- and Bs → K+K-, sensitive to new physics DIS2007 Munich 16-20 April

  11. Cabibbo favored Cabibbo suppressed The B → DK decays (GLW and ADS method) Consider the following decays (tree level) Color favored Color suppressed • Measuring the three different decay rates (relative) and the c.c. will allow to extract the gamma angle in a clean way, but… • because the color suppression, thetwo amplitudes, A1 and A2, very different → large error • need the D0 tag Decays of D0, D0 to same final state allows the two tree diagrams (theoretically clean!) to interfere. Consider the decay D0 → K-p+ For these decays the reversed suppression of the D decays relative to the B decays results in much more equal amplitudes → big interference effects ~ O(1) Counting experiment: no need for flavor tagging or proper time determination → measure of BR ~ O(10-7) or smaller DIS2007 Munich 16-20 April

  12. (1) 56000* (2) 700 (3) 56000 (4) 700 The B → D(Kp)K decays 4 B± → (Kp)DK± decays *both charges • Interference parameters • From the B decays: g– because have b→u , b→c interference rB – the ratio in magnitude of two diagrams (≤0.1 for DK±) δB – a CP conserving strong phase difference • The D decays introduce: rDK – the ratio in magnitude of two diagrams (0.060) δDK – a CP conserving strong phase difference rates (1) and (3) are favored + CP eigenstate = GLW method rates (2) and (4) are suppressed + another D decay = ADS method but these suppressed rates have order 1 interference term, as rB~rD DIS2007 Munich 16-20 April

  13. B →DK strategy: ADS+GLW • D0→Kp 3 observables from the relative rates of the 4 processes, depend on 4 unknowns g, rB, dB, dDKp • rDKpis already well measured • may benefit from cos(dD) measurements in CLEO-c and/or BES III • Need another D0 decay channel to solve for all unknowns • D0→Kppp (BR ~ 8%): provides 3 observables which depends on 4 unknowns g, rB, dB, dDK3p only dDK3pnew, rDK3pis already well measured • D0→KK/pp each CP mode provides one more observables with no new unknowns DIS2007 Munich 16-20 April

  14. LHCb sensitivity w/o bkgrd δDKp, δDK3p • Toy MC to simulate 2 fb-1 signal data: → fit results return input values • Combine Kp with: • K3p similar yields and identical background level • KK pp4300 B+ and 3300 B- with B/S ~ 2 estimated bkgrd δDKp, δDK3p (HighlightedareRMS quoted from non-Gaussian distribution of fit results due to close ambiguous solutions, will disappear as statistics increase. Global analysis using all modes will also help.) s(g) ~ 5º-15º in 2 fb-1depending on rB, δDK and δDK3 DIS2007 Munich 16-20 April

  15. D0K mass ADS with B →D*K decays • Attractive feature • D*→D0p0 (BR~2/3) – has strong (CP con.) phase δB • D*→D0g (BR~1/3) – strong phase δB+p → if can distinguish the two decays, powerful additional constraint ! • Preliminary studies (without background) show that, including D*K improves precision of previous analyses to s(g) = 2º - 5º (favored mode: 17k/2 fb-1) • However… • Reconstruction efficiency is small for soft g while background is enormous • Non trivial to separate D0p0 and D0g • Fit DK mass shape to get p0 and g components ignoring neutrals Signal/bkgrd Arbitrary norm. B±→D*(D0g)K± 1 bb event here represents 5k/2fb-1 bb sample B± mass Charged reconstruction B±→D*(D0p0)K± B±→D*(D0g)K± DIS2007 Munich 16-20 April

  16. A1 = A(B0 D0K*0): bc transition, phase 0 A2 = A(B0 D0K*0): bu transition, phase + A3 = 2 A(B0 DCPK*0) = A1+A2, because DCP=(D0+D0)/2 GLW method - g from B0 →D0K*0 • Dunietz variant of Gronau-Wyler method makes use of interference between two color-suppressed diagrams interfering via D0 common final states (pp, pK, KK) • Measuring the 6 decay rates, B0D0(Kp,pp,KK)K*0 + CP conjugates, allows g to be extracted without flavor tagging or proper time determination s(g) ~ 7º - 10º (2 fb-1) depending on , δDK and δDK3 *in 2 fb-1, both charges DIS2007 Munich 16-20 April

  17. Bs→ DsK • Interference between tree level decays via BS mixing (s-version of Bd→D*p): time dependent analysis (clean, no penguins) • Measuresg+fS (fS from BS→J/ΨΦ) • Expect 5400 events/2fb-1 • Excellent proper-time resolution (st ~ 40 fs) allows to resolve BS oscillations • s(g) ~ 13°from 2fb-1 data [Dms=17.3 ps–1] • Main background from DSp (BR×10 ) • Suppressed using kaon ID from RICH detector • B/S <1 @ 90% CL • Parallel analysis possible with Bd→Dp± (~790k events/2fb-1 with B/S ~ 0.3, g extraction requires rDp or combined Bs→ DsK U-spin analysis) DIS2007 Munich 16-20 April

  18. g from B0 hh • B0→ pp originally proposed to measure a but the influence of penguin diagrams makes the task difficult From the time dependent CP asymmetry deiq = ratio of penguin and tree amplitude in B→pp d’eiq’ = ratio of penguin and tree amplitude in B→KK Extract four asymmetries Assuming U-spin flavor symmetry (u↔s) d=d’ and q=q’ and taking b from Bd → J/y Ks and c from Bs → J/yf we can solve for g DIS2007 Munich 16-20 April

  19. g from B0 hh • 26k Bd → pp events with 2fb-1, B/S < 0.7 • 37k Bs → KK events, B/S = 0.3 • s(g) ~ 5º + uncertainty from U-spin symmetry breaking • Sensitive to new physics DIS2007 Munich 16-20 April

  20. Summary of performances on g Signal only, no accept. effect Combining all modes, with a nominal year of data (2 fb-1), LHCb will be able to extract g with ~ 4° resolution, and compare the B→DK direct measurement with the indirect determination (B0 +–,Bs  K+K–) to make a stringent test of the SM DIS2007 Munich 16-20 April

  21. ? Bs mixing phase, fs, from Bs→J/y(m+m-) f In the SM fsSM = -2c = -2l2h (small) and from UT fits we get fs= -0.037± 0.002 Direct measurements not very precise: recent D0: -0.79+0.47-0.39 CP violating decay can proceed directly or through mixing. The “mixing box” can have contributions from NP particles, resulting infs = fsSM + fsNP≠ -2l2h Tagged Bs Tagged Bs Measure proper time dependence Measure time-dependent CP asymmetry hf = ± 1 CP DIS2007 Munich 16-20 April

  22. Bs mixing phase, fs, from Bs→J/y(m+m-) f • Because the final state contains two vector particles, it is a mixture of CP odd and CP even • Use qtr angle between m+andnormal to f decay plane to do an angular analysis to identify the states. Total With:2 fb-1 of data Precision on fss(fs) = 0.023 CP even bkgnd From pure CP states Bs → J/yh,s(fs)= 0.059 Combining s(fs)= 0.021 (UT fit value: -0.037) CP odd Simultaneous fit to time and angular distributions DIS2007 Munich 16-20 April

  23. Very small branching ratio in SM: (3.4 ± 0.5) × 10-9 Present limit from Tevatron at 95% CL(1 fb-1): < 7 × 10-8 (expected final limit at 95% CL (8 fb-1): < 2 × 10-8) Sensitive to New Physics through loops Could be strongly enhanced by SUSY. ? ? MSSM Bs→m+m- DIS2007 Munich 16-20 April

  24. LHCb Sensitivity (signal+bkg is observed) BR (×10-9) 5 SM prediction 3 Integrated Luminosity (fb-1) Bs→m+m- • LHCb should have good prospect for significant measurement: 17 SM events/2fb-1 • Difficult to get reliable estimate of expected background • No background events selected in sample of 33M events but estimation limited by statistic • Combinatorial: B to m+X, B to m-X known as the main source of background, addressed by very good mass resolution 18 MeV/c2 • Bd, Bs to pp, pK, KK and mis-id. addressed by particle identification and mass resolution. with L=2fb-1 3s observation if at SM value DIS2007 Munich 16-20 April

  25. Conclusions • LHCb will be ready to collect data with its full detector as LHC turns on. Physics at 14 TeV starting in 2008 • It will make precision measurements that will severely constrain the unitarity triangle fits and probe rare decays • These measurements could either limit New Physics contributions to B decays or, more optimistically, uncover them DIS2007 Munich 16-20 April

  26. The B → DK decays (GLW method) Consider the following diagrams and the c.c. colour suppressed colour favoured • Measuring the three different decay rates (relative) and the c.c. will allow to extract the gamma angle in a clean way, but… • two amplitudes (A1 and A2) very different → large error • need the D0 tag DIS2007 Munich 16-20 April

  27. The ADS method Decays of D0, D0 to same final state allows the two tree diagrams (theoretically clean!) to interfere. Consider the decay D → K-p+ B+→D0K+ (colour suppressed) B+→D0K+ (colour favoured) Cabibbo favoured Cabibbo suppressed For these decays the reversed suppression of the D decays relative to the B decays results in much more equal amplitudes → big interference effects ~ O(1) Counting experiment: no need for flavor tagging or proper time determination → measure of BR ~ O(10-7) or smaller DIS2007 Munich 16-20 April

More Related