B-Physics at the LHC P J Dornan Imperial College, London

1. B-Physics at the LHC • P J Dornan • Imperial College, London P J Dornan - Imperial College London

2. Why b-physics at the LHC • Millions of b’s • With full luminosity, 1034, gives 5.1013 bb pairs per year • But events much too difficult to analyse, ~25 interactions per crossing • So - need to run at lower luminosities for most b-physics • In the early period max luminosity expected ~ 1033 - ATLAS/CMS • but will eventually be able to exploit full luminosity for certain rare decays • LHCb currently plan to run at 2.1032 by detuning the beam Signal/Background improves with increasing energy sinel = 80 mb, sbb = 500 mb All b-species produced, B+, B0, Bs, Bc, b-baryons At these energies b’s are getting ‘light’ Thus bb pairs produced dominantly forward - backward - - P J Dornan - Imperial College London

3. The Experiments • General Purpose • ATLAS, CMS – 4p ‘standard’ colliding beam detectors • Main aim to search for new states - Higgs and those from BSM so will always aim to run at maximum luminosity, 1033 -> 1034 • Specialised • LHCb – forward spectrometer (10 – 300 mrads), designed specifically for b-physics. Will always run at low luminosity, nominally 2.1032 • General Purpose and LHCb operate in complementary kinematic regions b qb b No P J Dornan - Imperial College London

4. Experimental Requirements • An excellent vertex detector • B-states identified by displaced secondary vertices • Good K-p separation • Difficult for general purpose detector - a weakness of ATLAS/CMS • An essential feature of LHCb • A good trigger for interesting b-physics • Far too many b’s produced to trigger on all of them. Therefore trigger must reject many b-states and concentrate on those from which CP/CKM physics will result • This is probably the greatest challenge for a hadronic b-experiment • -- and has caused failures in the past P J Dornan - Imperial College London

5. ATLAS P J Dornan - Imperial College London

6. ATLAS Tracker Pixel Detector Tracker Pixel Detector designed for b-physics Radius of inner layer = 5 cm. 3 layers, but middle willnot be available at start-up P J Dornan - Imperial College London

7. ATLAS Pit Today P J Dornan - Imperial College London

8. CMS P J Dornan - Imperial College London

9. CMS Tracker CMS Silicon Tracker Pixel Detector All Silicon 2 Pixel Layers Radii 4 and 7 cm Low luminosity Radii 7 and 11 cm high luminosity P J Dornan - Imperial College London

10. CMS Today Tracker being assembled In the pit P J Dornan - Imperial College London

11. LHCb P J Dornan - Imperial College London

12. LHCB – VELO P J Dornan - Imperial College London

13. LHCb - VELO Proper time resolution ~ 40 fs P J Dornan - Imperial College London

14. LHCb - RICH1 RICH1 detector Vertex locator P J Dornan - Imperial College London

15. LHCb – RICH1&2 P J Dornan - Imperial College London

16. LHCb RICH performance P J Dornan - Imperial College London

17. Triggers • Vital - Still Evolving - Algorithms depend upon important physics channels • Basic philosophy LHCb much better for hadronic B-decays All comparable for B -> J/y decays ATLAS/CMS better for Rare Decays ->mm(X) P J Dornan - Imperial College London

18. Bd0  p+ p- Bd0  rp BS0  DS p Bd0  DK*0 BS0  DSK Bd0  p+p-, BS0K+K- Bd0  D*p BS0  J/y f Bd0  J/yKS0 Bs(d) mm, mmX, b  sg What physics channels? • Must be interesting and extractable at the trigger level Unitarity Triangles Rare Decays P J Dornan - Imperial College London

19. p+ p- B0 B0 D K- l b B0 d b d p+ u u Flavour Tagging • In many cases need to know the flavour of the B when produced • Use Decays of the other B state - Opposite Side tag • Lepton b -> e, m • Kaon b -> c -> s • Or from the accompanying p/K with the signal B – Same Side tag • Or use vertex charge Prelim. LHCb with Opposite side only Obtain eD2 = 6.4% P J Dornan - Imperial College London

20. Expected unmixed BsDs sample in one year of data taking (fast MC) Bs Oscillation - Dms • With Dmd yields Vtd • Oscillation is fast (>14.4 ps-1) • Need excellent momentum and position resolution, i.e. a fully resconstructable final state and excellent vertex resolution • Use Bs-> Dsp • (LHCb) Obtain ~80,000 fully reconstructed/year, S/B ~3. Proper time resolution ~40fs Expect to make a 5s measurement in 1 year to 68 ps-1 P J Dornan - Imperial College London

21. sin2b - B0 -> J/y Ks • Classic channel for CP violation study • Still important for LHC experiments to measure with the best possible precision. • Measure time dependent asymmetry • Amix yields sin2b • Adir direct CP violation - BSM • Assuming Adir = 0 • ATLAS quote s(sin2b) = 0.013 after 3 years at 1033 • LHCb quote s(sin2b) = 0.022 after 1 year at 2.1032 LHCb P J Dornan - Imperial College London

22. Sin2a - B0 -> p+p= • Actually measure p-b-g • pp a very good channel for LHCb • High pT hadron to give trigger • RICH is essential • But Penguins complicate the analysis Can reach 5° < s(a) < 10° in one year if P/T known to 10% P J Dornan - Imperial College London

23. Sin2a - B0 -> rp • Three final states • r+p-, r0p0, r-p+ p+p-p0 • Requires time dependent Dalitz plot analysis • But needs detailed understanding of the acceptance • An analysis is being developed • -- looks promising P J Dornan - Imperial College London

24. g - LHCb • Will be a major result for LHCb - relies on the hadronic trigger • Many ways • But none are simple - involve measuring low decay rates, time dependent analyses in the Bs system, theoretical uncertainties • Many approaches necessary to check consistency 4 time dep rates yields g-2dg Relate with U-spin yields g 4 time dep rates yields 2b+g 6 decay rates yields g P J Dornan - Imperial College London

25. BsDs BsDsK BsDsK BsDs Features of LHCb for g Determination • Vertex Resolution - Time Dependent Bs Asymmetries • Separation Bs-> Dsp/Bs -> DsK - RICH particle ID and mass cuts P J Dornan - Imperial College London

26. Bs KK Separation With RICH Bd D0 K*0 signal RICH minimises background P J Dornan - Imperial College London

27. LHCb Expected performance for g 2400 events per year 3° < s(g-2dg) < 16° 5000 events per channel per year 3° < s(g-2dg) < 16° ~500,000 events per year. s(2b+g) ~ 10 Some BR’s very small, 10-7 -> 10-8 s(g) ~ 10 ° per year P J Dornan - Imperial College London

28. Bs Mixing phase fs= -2dg • Use Bs -> J/yf • Bs analogue of golden channel, B0 -> J/y Ks • Asymmetry very small in SM, fs ~ -0.04 • so very sensitive to new physics • But two vectors in final state • therefore need a time dependent angular analysis Sensitivity depends on Dms For Dms = 20, Expect s(dg) ~ 2° per year Analysis also yields Gs and DGs P J Dornan - Imperial College London

29. channel BR signal BG Bd0 10-7 222 950 Bd0K* 1.5x10-6 1995 290 Bd0 10-6 411 140 Bs,d -> mmX • Atlas/CMS can here use the high luminosity, so can do better than LHCb Bs -> mmX Bs -> mm s = 46 MeV Full Tracker ATLAS statistics with 30 fb-1 F-B Asymmetry sensitive to some SUSY scenarios CMS – Mass resolution Need 30 fb-1 for a 5s observation P J Dornan - Imperial College London

30. Production less peaked forward Better for ATLAS/CMS For Bc -> J/y p Bc p (GeV) Expect between 5 – 10K Bc -> J/ y p for each of ATLAS, CMS & LHCb per year ATLAS, s(M(Bc) = 74 MeV Also Bc -> J/y mn gives Vbc P J Dornan - Imperial College London

31. An Event in LHCb P J Dornan - Imperial College London

32. The major problem - Triggering • B-rates at the LHC are very high • The final states of interest are a very small proportion • For highest efficiency, the High Level Triggers (HLT)) must focus very directly on the predicted properties of the final states of interest and aim to distinguish them from the predicted backgrounds using the predicted properties of the detector • Predictions in the forward area depend upon knowledge of the pdf’s at very low x where they are least reliable • The simulation will not be perfect! • The performance of the trigger is key to the success of the experiment • Planned on the simulation • Too loose -> low efficiency • Too tight -> potential bias P J Dornan - Imperial College London

33. Triggering LHCb • Dimuon Triggers • Much physics, J/y X decays, rare decays • Strong signature, low rates • Safe for LHCb and ATLAS & CMS, • Triggers for hadronic final states • Much of the physics is here - quite probably any new physics will at the few % level - probing this is the justification for LHCb • But rates are low - or very low • Need • Statistical precision -> highly efficient trigger • Systematic precision -> minimal biases and these must be accurately quantified • Highly demanding for the trigger P J Dornan - Imperial College London

34. The Problem • Crossing rate at LHC = 40 MHz • Running at 2.1032 and a 25 nsec bunch spacing expect crossings with interactions at 10 MHz • - of which 200kHz will have bb pairs! • But those useful for CP/CKM physics and having all decay products in the detector is very much less • e.g. For B0J/y(mm)Ks(p+p-) it is 0.02 Hz – or 1 per minute. • For Bs0  mm it is ~1 per week P J Dornan - Imperial College London

35. Current LHCb Plan • 3 Level Trigger • Level 0 - reduce rate from 10 Mhz to 1 Mhz • Pile-up veto, a high pt hadron, electron, muon, photon • Increases b purity from 1% to 3% • Level 1 – reduce rate from 1 Mhz to 40 kHz • Demand tracks with finite impact parameter and high pt • Divide bandwidth between generic and specific, cuts for special channels, electron, photon, dimuon • b-purity now at 9% • High Level trigger – reduce rate from 40 kHz to 200 Hz to tape • Fast reconstruction, using all detectors except RICH – so far Bandwidth Division at Level1 To maintain efficiency at this rate, HLT must use tight ‘offline’ type cuts. Efficiency for channels not used to define HLT can be low P J Dornan - Imperial College London

36. Possible Improvement • Keep present philosophy but add a new inclusive stream with simple cuts and a high output rate • To be based on detection of just a single muon with minimal pt and impact parameter cuts - small modification of level 1 bandwidth • This would be • Inclusive - trigger on the ‘other’ b • Yields tagged events • Robust • Use to reduce/estimate systematic • uncertainties • Access to states not chosen for HLT optimisation ff, fKs …. • Output rate- whatever can be handled - would be 2 – 5 kHz with ~50% events with bb • Under active investigation - Current 200 Hz stream would be preserved - now Hot Stream • Inclusive stream to be reconstructed at many sites Possible future Level 1 bandwidth P J Dornan - Imperial College London

37. The LHC • Status • Delays due to problems with the cryolines • Poor quality control by the company charged with installation of work by its sub-contractors • First collisions are still scheduled for ‘summer’ 2007 • Great pressure to maintain this date • Components • Almost all ontime • Cryodipoles, which were a problem now stacking up on the surface waiting for the repair of the cryolines P J Dornan - Imperial College London

38. Summary • The LHC has great potential to make major advances in precision CPV b-physics • All species of b-hadron state are produced • Thousands of events for many important channels with small branching ratios make measurements at the few % level possible. • But • The hadronic environment will be difficult • still a lot of background - mostly from uninteresting b-states • Efficient, well understood triggering will be all important P J Dornan - Imperial College London