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Exploring Rare B and τ Decays: A Pathway to New Physics

This presentation by Roger Barlow from Manchester University delves into the study of rare B and τ decays as potential indicators of new physics beyond the Standard Model. Utilizing data from B-factory experiments like Belle and BaBar, the talk highlights the innovative techniques developed to measure extremely rare branching ratios, while addressing the significant challenges posed by background noise. Barlow discusses the implications of these rare decays for understanding physics at high-energy colliders, including the possibility of new particle contributions through virtual loops.

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Exploring Rare B and τ Decays: A Pathway to New Physics

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  1. Rare B and  decays and searches for New Physics Roger Barlow Manchester University and New (preliminary) results, mostly but not entirely from the B factory experiments Belle and BaBar.

  2. b + H+ u  Why look for Rare Decays? Our chance to see them is when the Standard Model amplitudes are small: Rare decays If new particles are to appear on-shell at high energy colliders, they must appear in virtual loops and affect amplitudes Roger Barlow: Rare B and tau Decays and New Physics

  3. What made it possible? Measuring Branching ratios of ~10-6 needs millions of events Physics progress possible thanks to machine physicists at SLAC and KEK • designed and built B factories operating in a new high-current regime, • continually faced and overcame new problems and challenges. • design luminosities met and exceeded. Roger Barlow: Rare B and tau Decays and New Physics

  4. “Finding a needle in haystack.” Huge backgrounds from other Bs and e+e-qq E(GeV) Use of E=EB-Ei and MES=EB2-(pi)2 Use data sidebands (rather than Monte Carlo) to estimate background “Blind Analysis” Tune cuts without looking in the MES-E ‘signal box’ MES(GeV/c2) (taken from Sekula’s talk. One of many) Roger Barlow: Rare B and tau Decays and New Physics

  5. Other Experimental techniques Continuum suppression from combined information from shape variables “Single-B beam” technique: Reconstruct one “tag” B in a common decay mode (hadronic or semileptonic). Remaining particles must also form a B Limits from N= S + b N small Uncertainties on , b Roger Barlow: Rare B and tau Decays and New Physics

  6. Contents • B decays • Leptonic • Radiative • bs  and bs l + l - • bd  and bd l + l - • Hadronic Charmless • Branching Fractions • Charge Asymmetries • Polarisation • Tau decays Roger Barlow: Rare B and tau Decays and New Physics

  7. W + b u,c,t  b b W + + - W+ H+ d,s u u   B Decays to leptons Proceeds through one or two weak bosons with strong CKM suppression – door open for NP particles to contribute Free of hadronic uncertainties in final state Plus many other diagrams b + ~  d,s - Roger Barlow: Rare B and tau Decays and New Physics

  8. B  CP, Rare decays, CKM V Browder (Belle) Sekula (BaBar) Important as W (suppressed by Vub) can be replaced by charged Higgs, etc Difficult due to neutrinos in the final state tag with fully reconstructed B mesons (180 channels) Tag with BD(*)l SM prediction (1.59 0.40) x 10-4 (depends on fB and Vub) Roger Barlow: Rare B and tau Decays and New Physics

  9. CP, Rare decays, CKM V Browder (Belle) Sekula (BaBar) B  Identify possible  in common decay mode Look at extra calorimeter energy (validate with for D*ln) H+? Extra E(GeV) Extra E(GeV) Roger Barlow: Rare B and tau Decays and New Physics

  10. Results (revised). 3.5  significance (new) BF(B++)= (0.88 0.11) x10-4 BR< 1.80 10-4 @ 90%CL +0.68 -0.67 Belle and BaBar results are similar. Agree within errors Can be combined (R. Faccini) to give (1.36  0.48)x10-4 BF(B++) Roger Barlow: Rare B and tau Decays and New Physics

  11. CP, Rare decays, CKM V Browder (Belle) Impact Limits on e.g. 2 Higgs doublet model: W.S.Hou, PRD 48, 2342 (1993) SM prediction enhanced/reduced by factor rH Or: Within the SM, use the value of BF(B++) to give a measurement of fB Roger Barlow: Rare B and tau Decays and New Physics

  12. CP, Rare decays, CKM V Sekula (BaBar) B   and e   Helicity Suppressed Use hadronic tags: B fully reconstructed as B to D(*) X Lepton is monoenergetic in signal-B rest frame Limits (@ 90% CL) <7.9 x10-6 for e(SM ~ 10-12) <6.2 x10-6 for   (SM ~ 10-7) Lepton momentum in B frame (GeV/) Roger Barlow: Rare B and tau Decays and New Physics

  13. CP, Rare decays, CKM V Sekula (BaBar) B0 to l l FCNC and helicity suppressed, but an initial state photon allows helicity flip SM predictions of order 10-10 (10-15, 10-11 respectively without the  ) See 0 events for e, 3 events for  (but compatible with background) Limits (at 90% CL) BR(Bee)< 0.7 x 10-7 BR(Bmm)< 3.4 x 10-7 (simulated) Roger Barlow: Rare B and tau Decays and New Physics

  14. CP, Rare decays, CKM V Browder (Belle) B  K*  Tag on other B Identify K* Look for extra energy SM prediction ~1.3 x 10-5 Signal is BK* + missing mass. (Could be light dark matter particle: publications by M. Pospelov et al.) Extra Calorimeter Energy (GeV) (at 90% C.L) Roger Barlow: Rare B and tau Decays and New Physics

  15. CP, Rare decays, CKM IV-V Farrington (CDF) Strauss (DØ) Sivoklokov (ATLAS) Langenegger (CMS) Ruf (LHCb) B0  +- SM predicts Bs:(3.40.5)x10-9 Bd:(1.00.1)x10-10 NP can boost this by ~100 B0s +-B0d +- LHC experiments will do this very precisely DØ analysis not yet complete. Combines Bs and Bd. Expect limit ~ 2 10-7 Have result on BR(B ) BR < 4.1 x10-6 @ 95% Roger Barlow: Rare B and tau Decays and New Physics

  16. Radiative B decays FCNC process suppressed in SM: sensitive to new particles in loops bs Inclusive and many exclusive measurements bsl+l -: More information from kinematics bd : strongly suppressed but open to different physics bd l+l-: on the way Roger Barlow: Rare B and tau Decays and New Physics

  17. HFAG average (3.55  0.24  0.03) x10-4 +0.09-0.10 Heavy Quark Physics I &III Hurth (Theory) Convery (BaBar) B  s  inclusive ‘Fully Inclusive’ and ‘sum of exclusives’ (38 modes) Branching Fraction now well measured. Theory and experimental error similar +0.37 -0.49 NLO calculation (3.61 ) x10-4 result: (Eg >1.9GeV) = (3.67 0.29  0.34  0.29) x10-4 Not much room for New Physics here Constrains model builders Roger Barlow: Rare B and tau Decays and New Physics

  18. B  s  exclusive Heavy Quark Physics III Limosami (Belle) • Lots of channels • Branching Fractions measured • CP violating asymmetries measured If nonzero these would be a signature of New Physics Example: B K0s0 t(ps) Roger Barlow: Rare B and tau Decays and New Physics

  19. CP, Rare decays, CKM VI Kovalskyi (BaBar) BSM VI Hamel de Monchenault B  Kl l B  K*l l Standard Model Amplitudes have 3 parts with different kinematics. Check out each separately through Wilson Coefficients: Photon C7 Vector EW C9 Axial EW C10 CKM factors x  Ci(q2) x local operators BKll (46 events) Dilepton mass q2 MES(GeV/c2) E(GeV) Roger Barlow: Rare B and tau Decays and New Physics

  20. CP, Rare decays, CKM VI Kovalskyi (BaBar) Angular variables e.g.*: angle of l l pair in their rest frame. C10 interferes with C7/C9 to give asymmetry K*ll Asymmetry as a function of q2 Roger Barlow: Rare B and tau Decays and New Physics

  21. B++ B00 B d CP, Rare decays, CKM VI Kovalskyi (BaBar) First observation of B++ MES(GeV/c2) Roger Barlow: Rare B and tau Decays and New Physics

  22. +0.018 -0.021 +0.017 -0.014 |Vtd/Vts|=0.171 Compare with BK* CP, Rare decays, CKM VI Kovalskyi (BaBar) Same CKM elements as mixing – but a non-trivial test W d,s b t t W b d,s ds t Roger Barlow: Rare B and tau Decays and New Physics

  23. B l +l - CP, Rare decays, CKM VI Kovalskyi (BaBar) Prediction: few 10-8 Measure B + +l +l - and B0 0l + l - with l =e or  (and e - ) Total limit 7.9 x 10 -8 at 90% CL for B+ ( twice B0) Amazing to be probing at this level E(GeV) E(GeV) MES(GeV/c2) MES(GeV/c2) Roger Barlow: Rare B and tau Decays and New Physics

  24. Charmless Hadronic Decays • Many modes • Will present collected branching ratios • Will present measurements of time-integrated CP violation ACP: they follow on directly from differences in charge conjugate decay states • from the B+/B- difference - trivial • From self-tagged neutral modes – trivial • From C part of CP+mixing fit – nontrivial but standard Roger Barlow: Rare B and tau Decays and New Physics

  25. Heavy Quark Physics I Dragic (Belle) Bona (BaBar) Examples MES(GeV/c2) MES(GeV/c2) E(GeV) Roger Barlow: Rare B and tau Decays and New Physics

  26. Heavy Quark Physics I Dragic (Belle) Bona (BaBar) 2 body -K combinations Results on many other decays. See talks by Dragic, Bona, Latham and Schümann in Heavy Quark Physics Session I Roger Barlow: Rare B and tau Decays and New Physics

  27. Roger Barlow: Rare B and tau Decays and New Physics

  28. CP, Rare decays, CKM IV Di Marco (BaBar) Unno (Belle) B K+- /K-+ Direct CP violation Experiments agree: BaBar: ACP=-0.108 0.0240.007 Bel ACP=-0.093 0.0180.008 Roger Barlow: Rare B and tau Decays and New Physics

  29. Direct CP in K  Competing amplitudes with different strong and weak phases ACP should be the same for K+- and K+0 (Gronau: hep-ph 0508047) Current averages (HFAG) ACP (K+-)=-0.093  0.015 ACP (K+0)=+0.047  0.026 Difference 0.14  0.03 – a long way from zero Maybe colour-suppressed trees are responsible Maybe New Physics Roger Barlow: Rare B and tau Decays and New Physics

  30. Lipkin Sum Rule RLipkin=2(B+K+0)+(B0K00) (B+K0+)+(B0K+-) From isospin and assuming the b s penguin diagram dominates R should be 1+O(10-2) Obtain (HFAG average) RLipkin=1.06  0.05 (Was 1.25  0.10 in 2003) Roger Barlow: Rare B and tau Decays and New Physics

  31. Heavy Quark Physics I Dragic (Belle) BK  ratios Can form many ratios, especially (A Buras, R Fleischer et al, Phys J C 45 (701-710) 2006) Rn=(K+-)Rc=2 (K+0) 2 (K00) (K0+) Obtain (HFAG averages) Rn=0.99  0.07 Rc=1.11  0.07 Agree with each other And with SM predictions The “K puzzle” is no more Roger Barlow: Rare B and tau Decays and New Physics

  32. The Polarisation Puzzle B V V decays are spin 0 to spin1+spin1 Should be 100% longitudinally polarised (if tree or penguin dominates) Measurements confute this – for heavier V especially Needs to be understood – affects CP decomposition More data now available Roger Barlow: Rare B and tau Decays and New Physics

  33. CP, rare decays, CKM III Telnov (BaBar) B 00 See 98 22 events - 3  significance BR (1.16 0.27)10-6 +32 -31 +0.36 -0.37 E(GeV) Fit longitudinal polarisation fl= 0.86  0.05 Measurement needed for B 0+- , used for alpha Informs penguin uncertainty in  determination MES(GeV/c2) +0.11 -0.13 Roger Barlow: Rare B and tau Decays and New Physics

  34. Heavy Quarks I Bona (BaBar) B  K* and f(980)K* fL around 0.5, as in B  K* as opposed to ~1 from simple models Roger Barlow: Rare B and tau Decays and New Physics

  35. CP, rare decays, CKM VI Bussey (CDF) More on B to V V CDF measure longitudinal polarisation in  K*,  K* Confirm BaBar and Belle results that polarisation is not 100%  on the way M(K) (GeV) Roger Barlow: Rare B and tau Decays and New Physics

  36. BSM VI Hayasaka Rare Tau Decays Search for New Physics in decays with Lepton Flavour Violation The B factories are also  factories (+  -) = 0.89 nb ats = M() Total sample of ~1.5 billion tau leptons Roger Barlow: Rare B and tau Decays and New Physics

  37. BSM VI Hayasaka Compendium of results Roger Barlow: Rare B and tau Decays and New Physics

  38. m signal event g t e e t generic t decay General techniques Divide event into two hemispheres ‘Tag side’ usual 1prong (e, , , ) or 3 prong  decay. Different analyses use different tags, trading purity for numbers. ‘Signal side’ with no neutrinos. Powerful energy/momentum constraint. Roger Barlow: Rare B and tau Decays and New Physics

  39. BaBar result Excluded region Belle result BSM VI Hayasaka l  l K0 l is  or e. Theoretical predictions vary from ~10-40 for SM (with  mixing) upwards New 90% CL limits Br ( - e -g ) < 12 x 10-8 Br (-m-g ) < 4.1 x 10-8 Br (t- e -KS) < 5.6 ×10-8 Br (-m -KS) < 4.9 ×10-8 (hep-ex/0605025) Tan  Roger Barlow: Rare B and tau Decays and New Physics

  40. BSM VI Hayasaka  - -,  K -, -,  K – Look for B-L conserved processes as allowed in the Standard Model Look for B-L violating processes as Baryogenesis may need them E(GeV) Decays to non-strange baryons ruled out through proton lifetime measurements Roger Barlow: Rare B and tau Decays and New Physics

  41. % % g % g % g BSM VI Hayasaka  •  in  and 3 modes • Limit 1.6 x10-7 @ 90% CL (BaBar) • 0.65 x10-7 @ 90% from Belle MSSM prediction Tan  MA(GeV/c2) Roger Barlow: Rare B and tau Decays and New Physics

  42. BSM VI Besson(CLEO) Y(1S) CLEO result on Lepton flavour violation Detect  through decay to e  pe/Ebeam (e) BR< 6.2 10-6 LFV Scale >1 TeV p/Ebeam Roger Barlow: Rare B and tau Decays and New Physics

  43. BSM VI Hamel de Monchenault Putting it all together An example: MSSM parameter space Isidori and Paradisi hep-ex 0605012 One set of Parameters {,AU, sparticle masses} Restrictions on MH, Tan Due to bs Bs  g-2 MB B Tan  M(H+) Roger Barlow: Rare B and tau Decays and New Physics

  44. Conclusion BaBar and Belle are probing physics at the TeV scale, exploring parameter spaces of proposed New Physics models Limits on Higgs Masses, Tan , SUSY particles. Precision Frontier and Energy Frontier are Complementary. LHC results will benefit from Rare Decay information. Standard Model beginning to be heavily stressed A SuperB factory would stress it even further Roger Barlow: Rare B and tau Decays and New Physics

  45. Many more results at next year’s conference(s) We look forward to welcoming you to Manchester next year Roger Barlow: Rare B and tau Decays and New Physics

  46. Backup slides Roger Barlow: Rare B and tau Decays and New Physics

  47. Exp. Needs: single B beams Lots of modes have several n and need beams with a single, monochromatic B: Btn, Bnn, BKnn,… Fully reconstruct one of the Bs and study the remaining of the event  closed kinematics,missing energy reconstruction Tag types Semileptonic D(*)l(np) 5K/fb-1 Hadronic D(*) X 3K/fb-1 purity efficiency X=np+mp0+pK+qKs Pioneered by BaBar Roger Barlow: Rare B and tau Decays and New Physics

  48. CP, Rare decays, CKM IV Farrington (CDF) New Physics Implications SO(10) model Dermisek et al hep-ph/0507233 (GeV) M1/2(GeV) Roger Barlow: Rare B and tau Decays and New Physics

  49. What is a rare decay? Experimental definition: One which has not been seen, or only just been seen for the first time Theoretical definition: One which, in the standard model, is either absolutely forbidden or strongly suppressed: FCNC, helicity, small CKM element. (bc is big, so everything else is small) Roger Barlow: Rare B and tau Decays and New Physics

  50. HFAG ACP Roger Barlow: Rare B and tau Decays and New Physics

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