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Heavy quark physics at the LHC and elsewhere

Heavy quark physics at the LHC and elsewhere. Guy Wilkinson University of Oxford Edinburgh, February 2006. B s mixing measurements: tree and loop Probing the weak phase in B s mixing Very rare decays. . Talk Roadmap. Motivation & context. Why quark flavour physics?

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Heavy quark physics at the LHC and elsewhere

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  1. Heavy quark physics at the LHC and elsewhere Guy Wilkinson University of Oxford Edinburgh, February 2006

  2. Bs mixing • measurements: tree and loop • Probing the weak phase in Bs mixing • Very rare decays  Talk Roadmap Motivation & context • Why quark flavour physics? • And why flavour physics in the LHC era? • What is the CKM model, and what state is it in? B-physics: precision tests of the CKM triangle & beyond The Tevatron and the LHC (especially LHCb): We will concentrate on these Super B-factories: potential and prospects Beyond the b’s: flavour physics in the charm & kaon sector

  3. Why are there three generations ? • Why is there an extreme hierarchy in mass (m t ~ 170 GeV !) • What is origin of CP violation ? • Can we understand the cosmic baryon-antibaryon asymmetry ? • Is there a relation between the quark & neutrino mixing matrices? u b d u t s s Why do we care about flavour physics? Quark flavour physics at heart of many of HEP’s big questions: Complementary to direct searches for new physics at the LHC • Powerful way to look for new physics • Elucidate flavour structure of • the new physics when found • (not dissimilar to ILC) new particles?

  4. Unitarity Triangle, Summer 2005 Remarkably self-consistent: certainly the CKM model is the dominant mechanism of CP violation in nature! This conclusion is only possible thanks to work of B factories.

  5. α β  What is the CKM Model ? In Standard Model, charged-current quark-coupling described by the CKM matrix, which has 4 parameters, 1 of which is complex Wolfenstein parameterisation: A, ρ, λ and η. Non-zero value of η is source of all CP violation in the Standard Model. VCKMVCKM* = 1 implies: This is the unitarity triangle

  6. α  β Existing triangle measurements: the essentials A lot of information in these ρ-η plane plots! For clarity lets focus in on most important experimental constraints. ‘B’ ‘G’ In (rough) order of importance: • Side ‘B’ fixed by ratio of b→ul/b→cl (theory limited) • Angle β from measurement of CP asymmetry in Bd→J/ψK0 • Side ‘G’ constrained by measurements (limits) on Bd(s) mixing • Recent B-factory results give first indications on α and 

  7. Good agreement, but hints of inconsistencies Overall consistency of measurements is impressive. A closer look, however, reveals that agreement is not quite perfect…. Indirect 0.791±0.034 Direct 0.687±0.032 >2 sigma difference Although at 1st order the CKM description is vindicated, are there 2nd order corrections from New Physics contributing?

  8. Tree Box Penguin loop b b b d t t b u t d,s d,s We must hunt both Boxes (eg. mixing) & Penguins (eg. B→) Trees still play vital role in global strategy – provide pure CKM benchmark values to compare other measurements against. Example: ‘b→ul/b→cl’ side is tree; sin2β from J/ψK0 is box. Generic Strategy to Hunt for New Physics New heavy particles (eg. sparticles) if they exist, are expected to lurk in box and Penguin processes. Here contributions may be comparable to, or exceed, the Standard Model amplitudes

  9. Time line of B physics facilities and goals B-factories Tevatron Selected list of most important aims (in ~ order of likely achievement): (double existing data set) LHC • Improved measurements of  • Observation of Bs mixing 2008 • Very high precision sin2β 2010 • Precision measurements of  • Measurement of Bs mixing phase Super B-factory • Observation of very rare decays Study prospects in a few of above

  10. Time line of B physics facilities and goals B-factories Tevatron Selected list of most important aims (in ~ order of likely achievement): (double existing data set) • Improved measurements of  LHC • Observation of Bs mixing 2008 • Very high precision sin2β 2010 • Precision measurements of  • Measurement of Bs mixing phase Super B-factory • Observation of very rare decays Study prospects in a few of above

  11. b b t α t d,s d,s  β Bs Mixing Next important constraint on triangle likely to be ‘mixing side’  |Vtd|/|Vts| Vtd,ts Measure Δmd (slow) & Δms (fast!), frequency of oscillations. Ratio of frequencies, with hadronic correction (error ~ 6%) → |Vtd|/|Vts| Δmd known. Present 95% CL limit on Δms is > 16.6 ps-1 (LEP/SLD alone >14.5 ps -1) Standard model expectation

  12. Note both are flavour specific, eg. we know b or b at decay. Bs Mixing: the experimental challenges Bs mixing search now being spear-headed by CDF and D0. Immediate challenge is toaccumulate enough events. Two choices: • Fully hadronic Bs • decays, eg. Bs→Ds • 2)Semi-leptonic, eg. Bs→Dslν But we also need to ‘tag’ Bs, to know flavour at time of birth. Reduces effective statistics by a lot! eg. εeff = 1.6% at CDF. 2) has higher yield and dominates present results; but worse proper time resolution will limit performance at high Δms.

  13. Bs mixing: future prospects Present Tevatron analyses use 400-600 pb-1 of data. More data, and improved analyses, will give real possibility of observation (if within Standard Model region!) soon-ish. If the Tevatron fails, LHC should do the job. eg. LHCb: • Can observe Δms=40 ps-1 • with 1/8 year of running. • Sensitivity up to Δms=68 ps-1 • in one year of running Of course this assumes aligned and understood detector etc Place your bets now for winner! (4-8 fb-1 expected by 2009)

  14. ATLAS CMS B-physics at the LHC B physics advantages of LHC vs Tevatron: LHCb • 10x higher b-production cross-section • Higher luminosity (ATLAS/CMS) • One dedicated B-physics experiment ATLAS/CMS: excellent B-physics for channels involving leptons

  15. B-physics at the LHC vs the B-factories

  16. Dipole magnet VELO ~1 cm B LHCb Spectrometer collision point • Crucial for B physics: • optimised geometry and choice of luminosity • trigger efficient in hadronic & leptonic modes • excellent tracking and vertexing (m, ) • excellent particle ID

  17. BsDs proper time resolution st ~ 40 fs LHCb VELO (Silicon Vertex Locator) VELO is laid out as a series of R and Φ measuring stations approaching 0.8 cm to the beam line, situated in vacuum chamber (inside beam-cavity!) VELO key to LHCb physics programme: • Provides ‘lifetime trigger’ which gives • high efficiency for all decay modes • Gives excellent proper time resolution; • vital for high performance Bs physics

  18. RICH sytem will allow clean separation of different Bhh modes. Not possible elsewhere at hadron colliders. Example of LHCb RICH in action Situation at Tevatron: CDF data BsKK signal Bd signal Bd signal

  19. Towards a precise measurement of  LHCb has a wide variety of strategies for measuring : 1) Tree level methods – vital for benchmarking entire triangle Example: approaches involving B→DK decays 2) Methods involving loops – sensitive to new physics Example: two-body modes Such redundancy is essential in the hunt for new physics! How well do we need to do? Well 1) suggests that we make measurement with precision equal to or better than that from indirect prediction… γ = (61.4 ± 6.5)°

  20. Vub – phase ~  s b u u c c B- b B- D0 s u u u u For decays common to Do and Do we access interference effects which depend on ! Other parameters exist in game (‘rb’, ‘δb’) and need several decays to overconstrain problem. D0  • Many common D0/D0 final states exist • Charged B’s: no flavour tagging or proper time • analysis required. It is merely a counting experiment! B →DK - interfering B diagrams Two interfering tree diagrams (theoretically clean).

  21. B →DK - some specific examples LHCb aspects particularly suited to B→DK: trigger & RICH Statistics in recent B-factory publications Expected annual yield at LHCb Do decay mode CP-self conjugate (‘3-body Dalitz’) Ks (KsKK) ~200 5000 CP-eigenstates (‘GLW’) ~30 8000 KK () Doubly Cabibbo suppressed (‘ADS’) K (K) ~10 2000 Lack of tagging requirement means full statistics can be used!

  22. Belle sees clear difference where it should ! Expected variation of sensitivity in Dalitz space Example of B→DK analysis: D(Ks)K Pioneered by B-factories: look at Dalitz space of D decay products for B+ and B- decays. Rich resonance decay structure allows for reasonable sensitivity with ~200 events. B-factory samples have statistical error of ~ 20o. Scope for 5o LHCb error, but needs good understanding of D decay model Other approaches (eg. ‘ADS’) cleaner and more precise. All DK methods measure same parameters, but have differing systematics → combine for final precision of ~1o ?

  23. B0→ and Bs→KK receive important contributions from Penguin graphs. b→u transitions in tree gives rise to  dependence in the time dependent CP asymmetries. Individually, however, hadronic uncertainties don’t allow Penguin/tree contributions to be decoupled, and hence  to be extracted. u +, K+ d,s +, K+ B0, Bs b d,s b B0, Bs - , K- u - , K- t d,s d,s u u d,s d,s However, B0→ and Bs→KK identical under swapping d↔s (‘U-spin’). Hadronic effects should be same (or very similar) for both. Combined analysis allows to be extracted with high sensitivity to New Physics !  Accessing  with B→hh Decays Penguin Tree (Recall role of RICH in separating modes) ~ 

  24. Accessing  with B→hh Decays For both decays measure ACPd,s = Ad,scosΔmd,st + Bd,ssinΔmd,st Large event yields, RICH and good proper time resolution allow for good precision on all parameters. Bd → Suitable combination of parameters gives  to ±5o Hadronic amplitude which we assume to be same for two cases Enough constraints exist in analysis that stability to U-spin symmetry assumption can be assessed. Comparison with tree-level measurements a very important test! Bs→KK  [degrees]

  25. b b t t d,s d,s Vtd,ts Beyond the triangle 1: the Bs mixing phase Other angles exist beyond those of familiar unitarity triangle ! At order λ3 CKM element Vts is real; at order λ5 it has a very small phase, c , (c  0.02radians). Phase accessible through Bs mixing. Analogous to β measurement in B0 system (~ Vtd). In Bs case, new physics contributions may be much more evident, because of tiny SM signal ! Golden channel for c : Bs→J/ψΦ. Every LHC experiments expect 50-150k events. Vector-vector final state → angular analysis needed to separate CP-odd and even amplitudes. LHCb is sensitive at level of SM expectation, but may need several years for 5σ observation.

  26. Beyond the triangle 2: very rare decays In addition to studying consistency of triangle, we may look for certain B decays heavily suppressed in Standard Model. Clean Standard Model prediction: Br (Bs  μ+μ-) ~ 4 × 10 -9 Large enhancements possible, eg. MSSM: Br ~ tan6β / M2H ! Distinctive leptonic signature good for all experiments

  27. High statistics for precise CKMology • Precise measurements to elucidate • flavour structure of new physics • Very high sensitivity in flavour violating • tau decays, eg.→μ • Particular strengths: ability to reconstruct • modes with neutrinos and EM neutrals Motivation & Prospects for a Super-B Factory Spectacular success of BaBar/Belle demonstrates power of Upsilon(4s) environment. Aim for order in magnitude improvement in precision: Two proposals: SuperKeK & Frascati. Briefly discuss former.

  28. Projections for luminosity at SuperKEKB Design lumi = 4 x 1035 cm-2 s-1 Aim for 100x present yield

  29. SuperBelle detector Aerogel Cherenkov counter + TOF counter g “TOP” + RICH CsI(Tl) 16X0 g pure CsI (endcap) Si vtx. det. 4 lyr. DSSD SC solenoid 1.5T g 2 pixel/striplet lyrs. + 4 lyr. DSSD Tracking + dE/dx small cell + He/C2H6 • remove inner lyrs. Use fast gas m / KL detection 14/15 lyr. RPC+Fe g tile scintillator New readout and computing systems

  30. Dtn etc. B meson beam ! B e- (8GeV) e+(3.5GeV) Υ(4S) p Vub B Charged Higgs full (0.1~0.3%) reconstruction BgDp etc. direct CPV f2(a) isospin analysis Decays with neutrinos,  and 0’s feasible • B decays with neutrinos BgDtn, tn, uln • B decays with g, p0Bg Xsg, p0p0 etc. Not possible at LHCb ! Methods established at BaBar/Belle.

  31. What can a Super B-factory do? Pursue hints of new physics seen at BaBar/Belle which are difficult to pursue at LHC Central values as now, with Super-B precision Example: sin2β measured with J/ψ Ks and ΦKs B0gJ/Ks b→ΦKS has b→s Penguin sin2βJ/ψK0 = 0.69 ± 0.03 sin2βΦK0 = 0.47 ± 0.19 B0gfKs Mode unsuited to LHCb (poor vertex constraint) (0.03 stat error on Δsin2β)

  32. More to quark flavour physics than B’s ! All discussion so far has focused on B decays. Why is this? Because in B system there is a multitude of observables that can be cleanly related to CKM / SM predictions But there is still much to learn from other quark systems: • D0 system: very small mixing and CP violation expected. • New physics may couple differently to up-type quarks ! • Kaon system: historical view is that despite being birthplace • ofCP physics, interpretation of measurements is messy. • Not always true !

  33. New opportunities in charm physics Mixing and CP violation expected to be small in Standard Model, but are coming within range of new experiments, eg. LHCb and SuperBfactory. Clear signatures can be looked for. For instance, for direct CP violation compare D0 and D0 decays to CP eigenstates, such as KK, .  Current precision 10-2. In SM we expect effects of order 10-3. LHCb will accumulate 5 x 108 D*→D0(hh) p.a., >100x Tevatron yields.  Clear discovery potential!

  34. BR(K+p+nn) = (8.0 ± 1.1)×10-11 BR(KLp0nn) = (3.0 ± 0.6)×10-11 K→ and the unitarity triangle Two ultra-suppressed kaon decays provide extremely clean constraints on unitarity triangle. Standard Model predicts: Irreducible theory error on 0 = 1% ; on + = 5%

  35. Prospects for K+→+ p+ K+ n n Decay already observed! 3 events at E787/949 (now defunct) Rate consistent with SM. P-326: proposed CERN experiment (in NA48 hall) Data taking in ~2010 With 100 events ! Reconstruct missing mass. Vetoes vital!

  36. Prospects for K0→0: E391a at KEK First dedicated K0→ experiment. Challenging signature! Requirement for selection: • 2 photons only • Missing pt No events ! missing pt (GeV/c) z position of vertex (cm)

  37. Prospects for K0→0: upgrade for J-PARC E391 aims to reach 10-9 (Grossman-Nir limit) with present data. E391 situated on 12 GeV KEK PS. Upgraded experiment planned for J-PARC (30 GeV protons) → 100x KL flux Intention is to have sensitivity at SM BR. ~3 years of operation

  38. Conclusions and Outlook Now know that observed CP violation is described to first order by CKM model. But still expect new physics to show! Augment existing triangle constraints with new, very precise measurements involving tree and loop: Bs mixing;  (tree and loop) Additional measurements beyond the triangle: Bs mixing phase ; very rare decays (eg. Bs→μμ) LHC studies can be complemented by super-clean, super-B ! Charm and kaon mesons still have role to play.

  39. Backup Slides

  40. LHCb Choice of Geometry and Running Luminosity Forward spectrometer geometry exploits correlated production (excellent for flavour tagging) De-focus beams locally to lower luminosity to ~2 x 1032 cm-2 s-1 Inelastic pp collisions/crossing Optimises fraction of 1-interaction events → cleaner to analyse. Also allows for acceptable occupancy and radiation levels. Forward layout also allows planes of silicon to approach very close to beam

  41. sbb ~ 500 mb, < 1% of inelastic cross-section Use multi-level trigger to select interesting events: high pTelectrons, muons or hadrons vertex structure and pT of tracks full reconstruction Trigger ~ 200 Hzto tape in exclusive decays    30–60%efficiency

  42. Kaon ID: ~88% Pion mis-ID: 3% LHCb Ring Imaging Cherenkov (RICH) System PID mandatory for suppressing same topology backgrounds in many final states, and for adding kaons to flavour tagging. Wide momentum span in PID requirements → 2 RICHes with 3-radiators Cherenkov rings in RICH 1 Good performance for 2<p<100 GeV/c

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