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Charged Leptons as Probes of the Standard Model

Charged Leptons as Probes of the Standard Model. J. Michael Roney University of Victoria ( B A B AR Collaboration Member). Lepton-Photon Symposium Daegu, South Korea August 13-18, 2007. What Standard Model sectors can we probe with charged leptons and how useful is that probing?.

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Charged Leptons as Probes of the Standard Model

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  1. Charged Leptons as Probes of the Standard Model J. Michael Roney University of Victoria (BABAR Collaboration Member) Lepton-Photon SymposiumDaegu, South Korea August 13-18, 2007

  2. What Standard Model sectors can we probe with charged leptons and how useful is that probing? • Appropriate questions, especially for the LEPTON-photon symposium… • There are recent very high precision measurements at low energy of interest but nothing new for LP07 (see Sven Heinemeyer’s review from Monday morning) • the tension between data and SM persists in muon g-2 • PRL 97, 030801(2006) Odom et al electron g-2: defines a to 0.7ppb • EDMs: continue to heavily constrain any physics beyond the SM • Lets start with the basics where new results are in: • Quantum Field Theory has CPT invariance built into it: translates into equal masses & lifetimes for each particle and antiparticle … • SM silent on particular masses, but foundations crumble if e.g. m+ and m- have different masses or lifetimes • charged leptons are the only bare fermions allowing such probes J.M.Roney, Victoria

  3. SM is silent on actual values of the masses and lifetimes • Some are used to define the SM parameter space because of their high precision whereas the absolute values are required for less foundational probing… such as the assumption of charged current universality • Present new results on • m+ lifetime • t masses and CPT tests J.M.Roney, Victoria

  4. Precision m+ lifetime at PSI byMuLan CollaborationPhys. Rev. Lett. 99, 032001 (2007) • “Defines” GF : fundamental SM parameter • GF a MZ 9ppm 0.0007ppm 23ppm weak int’n loop corrections e.g. van Ritbergen & Stuart full 2-loop QED corrections (1999) allow determination of GF from m lifetime at 0.3ppm level (Nucl.Phys.B564:343-390,2000) J.M.Roney, Victoria

  5. (from D. Hertzog, Moriond’07) J.M.Roney, Victoria

  6. J.M.Roney, Victoria (from D. Hertzog, Moriond’07)

  7. CPT test from m lifetime Dominated by lifetime of m- =2.197025(155)ms (Bardin 94) don’t expect much improvement on testing CPT J.M.Roney, Victoria

  8. CPT • what about t Lifetime: 1st CPT on lifetime from BABAR (Lusiani, TAU04) THIS TEST WOULD BENEFIT FROM HIGH STATISTICS AS MANY SYSTEMATICS WOULD CANCEL J.M.Roney, Victoria

  9. CPT t Mass: BELLE published using 5.8x106t-pair events:tnn; t3p n in 414/fb of data PRL 99,011801(2007) (hep-ex/0608046) J.M.Roney, Victoria

  10. CPT • t Mass: future? A SuperB factory with ~100/ab would yield a statistical error of 0.023MeV on the mass difference ~ 6 x smaller than 0.14MeV systematic error BELLE now quotes. (Reach 0.15MeV at 2.3/ab) To fully exploit 100/ab, would need charge asymmetric momentum scales controlled at 10-5 level. VERY CHALLENGING DETECTOR SYSTEMATICS PROBLEM Would get CPT test to 2x10-5 level of sensitivity and would be most sensitive CPT mass difference test after K0(10-18), proton and electron (10-8). J.M.Roney, Victoria

  11. New preliminary t mass from KEDR Collaboration at the VEPP-4M Collider in Novosibirsk (hep-ex/0611046) using enn,mnn,pn,Kn,rn – vs - ennt-pair events J.M.Roney, Victoria

  12. The t mass is needed for probes of charged current universality involving the t but …to probe the SM in m-t and e-m universality further requires higher precision measurements of BR(tenn)and BR(tmnn) and improved t lifetime measurements J.M.Roney, Victoria

  13. Charged Current Lepton universality • Charged current universality: tau decays J.M.Roney, Victoria

  14. Lepton universality in Kaon Decays New results from KLOE at Frascati’s DAFNE phi factory for LP07 can have deviations from SM from e.g. multi-Higgs effects inducing an effective pseudoscalar interaction up to the few % level in K decays (A. Masiero, P. Paradisi, R. Petronzio, PRD74 (2006) 011701) J.M.Roney, Victoria

  15. KLOE Universality results • Using 1.7fb-1 at the f • Compare RK to a SM calculation (M. Finkemeier, PLB 387 (1996) 391) which includes internal brem photons (IB) and ignores contributions from structure-dependent direct photon emission (DE). Requires care! IB IB+DE J.M.Roney, Victoria

  16. KLOE Universality results J.M.Roney, Victoria

  17. Probing the CKM Matrix with t leptons • CKM Unitarity implies: • strange decays of t provides an additional way of probing |Vus | with a technique having uncorrelated experimental and theoretical errors J.M.Roney, Victoria

  18. Strange and non-Strange -Decays J.M.Roney, Victoria

  19. Extracting |Vus| The weighted spectral functions may be written as: When one takes the flavour breaking difference: the D=0 terms cancel leaving D 2. So: J.M.Roney, Victoria 19

  20. BABAR Branching Ratio for -K-0(uses230/fb) t-t+ qq -+ arXiv:0707.2922 [hep-ex] submitted PRD-RC J.M.Roney, Victoria

  21. not in average BELLE:BR, Mass & Width: - KS- J.M.Roney, Victoria arXiv:0706.223[hep-ex] submitted to PLB

  22. BELLE: BR-K-h,-K-0h (K*-h ); -p-0h  • preliminary: • decays with h arXiv:0708.0733[hep-ex] J.M.Roney, Victoria

  23. BELLE (preliminary)Use -K-0h sample to get B(- K*-h ) through the K*-(892)K-0modeusing BR(K*-(892)K-0 )=1/3 J.M.Roney, Victoria

  24. BABAR Branching Ratios for-h-h-h+ i=Channels Selected j=Decay Mode J.M.Roney, Victoria arXiv:0707.2981 [hep-ex] Submitted PRL

  25. BABAR Branching Ratios for-h-h-h+ --+ K--+ K--K+ K-K-K+ J.M.Roney, Victoria

  26. Some Updates to |Vus| from t UPDATED -K-0 arXiv:0707.2922 [hep-ex] -K--+ arXiv:0707.2981 [hep-ex] -K0- arXiv:0706.2231 [hep-ex] J.M.Roney, Victoria

  27. Some Updates to |Vus| from t UPDATED -K-0 arXiv:0707.2922 [hep-ex] -K--+ arXiv:0707.2981 [hep-ex] -K0- arXiv:0706.2231 [hep-ex] J.M.Roney, Victoria

  28. About the t tension… • Comment 1: B-factory experimental program to measure all strange decays of the t in progress: many modes still to be measured by BABAR and BELLE, |Vus| analysis assumed modes not yet measured are negligibly small… • Comment 2:Theory errors for R00 require some care (Maltman & Wolfe hep-ph/0603215): poor convergence properties of the integrated D=2 OPE series for R00 argues for better behaved weighted spectral functions – even so, difference is not diminished using ALEPH spectral functions re-scaled with B-factory BRs even with better behaved weighted SF • Comment 3: The updated |Vus| analysis doesn’t yet include the new -K-h,-K-0h (K*-h ) results from Belle… these lower values will increase the tension further • very active area for both experimentalists and theorists J.M.Roney, Victoria

  29. Lepton Flavour Violation:A bit of history…the importance of being earnest in seeing nothing 1947: muon established as lepton, excited electron ruled out by absence ofe 1958: G. Feinberg: “leptonic GIM” argument establishes two neutrino types: Early weak theory: BR(e)~10-4 expected but BR(e)<10-5 1950’s: first -Ne-N conversion experiments Ee=m-Binding Energy~105MeV and eee searches J.M.Roney, Victoria

  30. History of e-muon LFV Searches B(μeγ) < 1.2x10-11 (MEGA/LAMPF) Brooks et al PRL 83 1521 (1999) μTieTi < 4x10-12 MEG ‘MECO’(?) hadronic decays J.M.Roney, Victoria

  31. Pham EPJ C 8 (1999) 513 By beginning of 21st Century: Lepton Flavour Violation established! SNO, SuperK, K2K: all see neutrino mixing implying massive neutrinos We even have parts of the mixing matrix q12, q23… experiments, such as T2K, preparing to measure q13 So the SM extended to include massive neutrinos predicts LFV in the charged lepton sector as well: well below any conceivable experimental sensitivity… OPPORTUNITY: CHARGED LFV IS UNAMBIGUOUS SIGNAL OF NEW PHYSICS J.M.Roney, Victoria

  32. Many SM extensions predict observable Charged LFV • If see-saw mechanism responsible for small n mass, natural to get large Charged LFV • Heavy Neutrinos • Supersymmetry • … e.g.SO(10) inspired model with SUSY imbedded in GUT Calibbi et al PRD 74(2006) univ. gaugino mass J.M.Roney, Victoria

  33. (requires ~107m/sec) J.M.Roney, Victoria

  34. The present status of the MEG experiment (T. Mori) Liquid Xenon Gamma-Ray Detector: All phototubes installed inside the cryostat; final preparations to start operation toward the end of August Timing Counters: Final assembly in Italy; Installation planned at the end of August Drift Chambers: Installed and ready at the beam line; cosmic ray test soon J.M.Roney, Victoria

  35. STATUS of MEG The whole MEG detector will be ready in September 2007 Plan to start an engineering run with muons after calibration runs in October. Expect to start taking some physics data toward the end of the year J.M.Roney, Victoria

  36. Focus on Lepton Flavour Violation in tdecays • lepton-mass dependent couplings • parameter space in some models touch current limits • different sensitivity to 2-body & 3-body decays – which mode will be discovered first is unknown (e.g. some mSUGRA+Seesaw (PRD66) has parameters having tμγ: tmmm: tμh = 1.5:1.0:8.4) • Well motivated searches: complementary to potential LHC discoveries: Limits (or discovery!) will better constrain theories J.M.Roney, Victoria

  37. e+e-  +-  clean environment +- back-to-back (CM frame), jet-like easy BB bkgd rej through event shape variables • Event easily divided in 2 hemispheres in CM: signal and tag decay • Signal (LFV) decay is neutrinoless: no missing momentum • Tag (SM) tau decay: 1- or 3- prong (+ 1 or 2 ) (depending on signal and dominant non  bkgd) Signal decay LFV: no pmiss CM frame SM  decay (1- or 3- prong) (1 or 2 ) General approach in Search for LFV @ e+e- colliders Lab frame J.M.Roney, Victoria

  38. Signal: no neutrinos  powerful mass and beam energyinformation • mass: mμ  = mt • Babar uses beam energy constrained mass & •  vertex at μpoint of closest approach to beamspot in x,y • (MEC)~9MeV (cf no mass or vertex constraint ~24MeV) • Beam Energy: • E = E  -Ebeam ~ 0 •  (E)~50MeV signal region typically defined as 2 box or ellipse J.M.Roney, Victoria

  39. Summary of tγ,  J.M.Roney, Victoria

  40. BaBar New Babar (prelim) & Belle (prelim) results ont optimize event selections for each signal mode separately accounting for different background compositions J.M.Roney, Victoria

  41. New prelim Belle result ont Belle update to 535fb-1 increase in lumi by 6.1 fold Efficiency:6.0-12.5% <Bkgnd>:0.01-0.40 events Total <Bkgnd>=0.590.31ev Nobs=0 events 90%CL limits: BR(t)<(2.0-4.1)x10-8 5-7 fold improvement over previous limit J.M.Roney, Victoria

  42. New prelim BABAR results ont BABAR update to 376fb-1 for LP07 increase in lumi by 4.3 fold • Background PDF • shapes from • MC or control • samples • PDFs summed • and fit to data • in sidebands • <Bkgd> from • integral of PDF • over signal box J.M.Roney, Victoria

  43. New prelim Babar results ont Efficiency:5.5-12.4% <Bkgnd>:0.3-1.3 events; total=4.20.8 events Total Nobs=6 events 90%CL limits: BR(t)<(3.7-8.0)x10-8 2-5 fold lower limits over previous Babar results J.M.Roney, Victoria

  44. New Belle results ontV0 using 543fb-1 Efficiency:2.5-4.0% <Bkgnd>:0.0-0.2 events Total <Bkgnd>=0.780.29ev Nobs=3 events 90%CL limits: BR(tV0)<(6.1-18)x10-8 J.M.Roney, Victoria

  45. BaBar NEW tp0/h/h’ hep-ex/0610067 PRL 98.061803 (2007) expected background/channel ~ 0.1-0.3 Total expected background=3.1, Observed=2 J.M.Roney, Victoria

  46. Some intepretations within benchmark models compilation by S. Banerjee (Tau06,hep-ex/0702017) J.M.Roney, Victoria

  47. LFV in tau decays: How far we can go? It depends on “irresidual background” levels… not currently a limiting factor tg:future sensitivity will be affected by e+e-t+t-g t+tag t-  m-nng irreducible background. When that limit hit, sensitivity will scale as 1/sqrt(Lumi) . For ~75/ab as with SuperB might expect O(10-9) level , hh’:sensitivity not likely limited by irreducible backgrounds so might expect sensitivity to scale as 1/Lumi .For SuperB might expect O(10-10) level J.M.Roney, Victoria

  48. Summary • Charged leptons are probing many sectors of the SM • CPT • CC Universality • LFV • CKM unitarity with |Vus| - watch this space • EDM • g-2 – possible hint of something beyond SM? • Look forward to more precision data from MEG, MuLan, Babar, Belle, KEDR, BES, KLOE J.M.Roney, Victoria

  49. Additional Slides J.M.Roney, Victoria

  50. Extracting |Vus| from -Spectral Function Strange and non-strange Hadronic Width May be written in terms of the spectral density function or in terms of the 2 point correlator function J.M.Roney, Victoria 50

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