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An Excursion into t Physics Carsten Hast Stanford Linear Accelerator Center

An Excursion into t Physics Carsten Hast Stanford Linear Accelerator Center. A rather abbreviated history of the t Reconstruction of hadronic t decays t 3 hadrons n t (g -2) m |v us | Mass measurement Lifetime Lepton Universality Lepton Flavor Violation Outlook.

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An Excursion into t Physics Carsten Hast Stanford Linear Accelerator Center

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  1. An Excursion into t PhysicsCarsten HastStanford Linear Accelerator Center • A rather abbreviated history of the t • Reconstruction of hadronic t decays • t3 hadrons nt • (g-2)m • |vus| • Mass measurement • Lifetime • Lepton Universality • Lepton Flavor Violation • Outlook DESY Hamburg and Zeuthen November 12th,13th 2007 Excursion into Tau Physics, November 2007

  2. e+e-l+l- How to Find a t Lepton • Back in the early 60’s there was no standard model. People were still trying to sort out why there are electrons and muons. Quarks were suggested in ’64. How to find more, for example more leptons? • One way of doing that is pair production in e+e- scattering • Accelerators want to be build, meaning: • need to know how, where, persuade people for money and finally do it… • SPEAR was proposed in 1964 • MARK I was proposed in 1971 • First events in 1974 • In between there was quite some time for people to make up, what the future standard model would be and what features a new, heavy lepton would have … Excursion into Tau Physics, November 2007

  3. W- e- m- dq t- nt dq = cos qc d + sin qc s qc the Cabibbo angle p-m-nm ne nm u Characteristics of t Lepton Decays • The following is from Yung-Su Tsai (1971) • Assuming that the new lepton has the same electro-magnetic and weak interaction as e and m • Assuming it is heavy, so it will decay into hadrons • From p decays via CVC Tsai calculated the decay rates of the t into different hadrons: • t pnt , t K(*)nt , t rnt , t a1nt , t cont. nt • and partial and total decay width, lifetime and cross section Excursion into Tau Physics, November 2007

  4. Characteristics of t Lepton Decays t-lifetime = 1/323 (1010 sec)-1 = 310 fsec Br(te) ≈ Br(tm) ≈ 64.6(63)/323 ≈20%, Br(thad) ≈60% Excursion into Tau Physics, November 2007

  5. e+ W- t+ u u ne nm e- m- d s t- e- t- nt How to Find the First t Pair Event • In 1973 MARK I was ready at SPEAR at SLAC • Look for events with only 2 charged tracks and missing energy M.L. Perl et al. 75 PRL 35 1489 Excursion into Tau Physics, November 2007

  6. …it worked out: Martin Perl Nobel Laureate of 1995 … but it helps when you have nice colleagues who find strange electron-muon events as well, like Pluto in 1976, and then… Have to give it a name: triton“the third” M. Perl, Frederick Reines, King Carl Gustaf How to Find the First t Pair Event • And then you have to convince yourself and your colleagues… • In early 70th there were only 3 quarks (uds), but then in 1974 the J/Y was discovered  charm was born • 2 families of leptons, 2 families of quarks • Nice SU(2) Ä U(1) symmetry • Who needs a 3rd generation! Excursion into Tau Physics, November 2007

  7. Production of t Pairs • In the following let’s focus on e+e- machines • CMS energy from threshold to the Z resonance and beyond Excursion into Tau Physics, November 2007

  8. Experimental Luminosities • LEP • Clean event environment • Low systematic errors • Excellent for large branchingfractions • B-Factories: t cross section at U(4s) is 0.919 nb ≈1M t pairs/fb Very good for rare and forbidden decays Working hard to get the systematic errors down • Number of t pairs per experiment: • ARGUS 0.5M • Cleo 14M • LEP 0.1M/experiment • Belle/BaBar 650M/440M Excursion into Tau Physics, November 2007

  9. g e+ t+ g/Z0 g e- t- Reconstruction of t Pairs • Initial and final state radiation • Et ≤ECMS/2 • Taus are flying back to back in CMS • Each t decays to an odd number of charged particles (1, 3, 5, 7…) • plus neutral particles (p0,…) • Most (semi)hadronic decays proceed via resonances (a1, r, K*…) • Need to identify e, m, p, K, g, p0 • Reconstruction of t decay vertex is always good • 4p detector coverage, high efficiency, etc. Excursion into Tau Physics, November 2007

  10. ECMS=U(4s) = 10.46 GeV • Unfortunately with a boost ( E(e-)=9.0GeV and E(e+)=3.1GeV ) 1.5 T Solenoid Electromagnetic Calorimeter (EMC) Detector of Internally Recflected Cherenkov Light (DIRC) e+ (3.1 GeV) “Typical Event” Simulated 1-7 topology event e- (9 GeV) Drift Chamber (DCH) Instrumented Flux Return (IFR) Silicon Vertex Tracker (SVT) SVT, DCH: charged particle tracking Þ vertex &mom. resolution EMC: electromagnetic calorimetry Þg/p0/h DIRC, IFR, DCH: charged particle ID Þp/K/p,m Typical Pair: PEP II and BaBar Excursion into Tau Physics, November 2007

  11. e+ ttag trec e- t Pair Event Reconstruction • Standard Event Selection of an 1- n topology: • In CMS: Demand 1 charged track vs. n charged tracks • Net charge of 0 • Get rid of converted photons • Invent good ways to reduce background • Cuts on event thrust angle and magnitude • Cuts on photons in the event • Lepton identification on the tag side • Vertexing • Missing Energy (neutrinos) • Particle identification on signal side • Reconstruct (or get rid of) p0 Excursion into Tau Physics, November 2007

  12. How to: t to Three Hadrons • The following is an example of how to do a t analysis • Most of these decays are quite well measured, except for the “rarer” ones • t-  p-p-p+nt • t-  K-p-p+nt • t-  K-p-K+nt • t-  K-K-K+nt • t-  FK-(p-)nt (Ian Nugent (BaBar) Tau 06 in Pisa, submitted to PRL in July 2007 ) Excursion into Tau Physics, November 2007

  13. How to: t to Three Hadrons II Rely on superb particle identification of the B-Factory detectors Excursion into Tau Physics, November 2007

  14. ARGUS 1993 KKp Kpp How to: t to Three Hadrons III Excursion into Tau Physics, November 2007

  15. How to: t to Three Hadrons IV All modes are related to each other (signal and background) BaBar arXiv:0707.2981 [hep-ex] Submitted to PRL Excursion into Tau Physics, November 2007

  16. How to: t to Three Hadrons V K--+ --+ K--K+ K-K-K+ Mike Roney, Lepton Photon 2007 Excursion into Tau Physics, November 2007

  17. Br (t-  Fp-nt ) =(3.49±0.55±0.32) x 10-5 BaBar Br (t-  FK-nt )=(3.48±0.20±0.26) x 10-5 preliminary fK Belle Phys.Lett.B643:5-10,2006 Br (t-  FK-nt ) =(4.05±0.25±0.26) x 10-5 fp How to: t to Three Hadrons VI First observation of tau to phi decays Br (t-  Fp-nt ) =(3.42±0.55±0.25) x 10-5 BaBar (July 2007) Br (t-  FK-nt )=(3.39±0.20±0.28) x 10-5arXiv:0707.2981v1 (acc. PRL) Excursion into Tau Physics, November 2007

  18.  e+  W  hadrons e– hadrons Hadronic t Decays for QCD Tests t heavy enough to decay into hadrons probes the hadronic V-A current e+ e- H0probes the hadronic electromagnetic current Isospin Excursion into Tau Physics, November 2007

  19. Hadronic t Decays:t- p-p0ntand (g-2)m muonanomalous magnetic moment: Hadronic vacuum polarisation is the largest uncertainty in calculating am s(amhad)= a few x 10-10 (others are only 0.3-04 x 10-10 ) Dominant part can be calculated from the 2p spectral functions Isospin Need to measure Br(t-p-p0nt) and the precise mass spectrum shape Excursion into Tau Physics, November 2007

  20. Hadronic t Decays:t- p-p0ntand (g-2)m Fudjikava (Belle preliminary) Tau 06 BG subtraction Detector unfolding Radiative corrections Fitting  Pion form factor Gounaris-Sakurai parameterization Excursion into Tau Physics, November 2007

  21. Hadronic t Decays:t- p-p0ntand (g-2)m Fudjikava (Belle preliminary) Tau 06 r(770) r’(1400) r’’(1700) Interference between r’ andr” am(2p) x 1010 Belle 459.8±0.5(stat.)±3.2(sys.)±2.3(Iso.) Aleph,Cleo 464.0±3.2(exp.)±2.3(Iso.) CMD2, Kloe 450.2±4.9(exp.)±1.6(rad.) Excursion into Tau Physics, November 2007

  22. 1010 x amth=11 658 471.81  0.02QEDKinoshita-Nio, Passera + 15.4  0.2EWCzarnecki-Marciano-Vainshtein +698.2  9.7hvp (711.0  5.8)t, (690.9  4.4)e+e-Davier et al - 9.8 0.1hvp NLOKrause, Hagiwara et al + 12.0 3.5light-by-light Melnikov-Vainshtein, Knech et al = 11 659 187.6  10.3(11 659 200.4  6.8)t , (11 659 180.3  5.6)e+e- amexp - amth = 1.3 s 0.8 s 3.4 s m Anomalous Magnetic Moment Summary Davier/Pich BNL - E821 Am= (11 659 208.0±6.0) 10-10 Excursion into Tau Physics, November 2007

  23. Hadronic t Decays:|vus| The route to world best measurements of |vus| and ms Need detailed knowledge of all (strange) BRs and shapes of all (strange) mass spectra |Vud|2 +|Vus|2 + |Vub|2 = 1 |Vud|2 = 0.97377 + 0.00027 from nuclear b decays and neutron decays (PDG 2006) |Vub|2 = (4.40 + 0.34) x 10-3 from e.g. inclusive B Xuln decays |Vus|2 = 0.2275 + 0.0012 Mike Roney, Lepton Photon 2007 Excursion into Tau Physics, November 2007

  24. Strange and non-Strange -Decays From weighted spectral functions… one can calculate the flavour breaking difference Mike Roney, Lepton Photon 2007 Excursion into Tau Physics, November 2007

  25. Hadronic t Decays:t-K-p0nt t BG qqbar m+m- I.Nugent: BaBar preliminary Tau 06 and updated in arXiv:0707.2922 [hep-ex] submitted PRD-RC Excursion into Tau Physics, November 2007

  26. Hadronic t Decays:t-Ks0p-nt B.Shwartz, Belle preliminary Tau 06 and updated in arXiv:0706.223 [hep-ex] submitted to PLB Fit with K*0(892) only K*0(800)+ K*(892)+ K*(1410) Excursion into Tau Physics, November 2007

  27. not in average Hadronic t Decays:t-K*-(Ksp-)nt (cont.) Br(-K0-) = (0.808  0.004stat0.026syst)% PDG 2007 (0.90  0.04) % Excursion into Tau Physics, November 2007

  28. Hadronic t decays with h Belle preliminaryarXiv:0708.0733[hep-ex] BR t- K-p0nt is dominated (100%) byt- K*hnt Excursion into Tau Physics, November 2007

  29. Hadronic t Decays:|vus| Summary Swagato Banerjee, Kaon 2007 Excursion into Tau Physics, November 2007

  30. No good solution • Need better data to clarify • Need B-factories to contribute |Vus|=0.2204±0.0028exp±0.0003th±0.0001ms Strange Spectral Functions: ALEPH (‘99) and OPAL (‘05) DHZ05, hep-ph/0507078 Moments k,l=0 Excursion into Tau Physics, November 2007

  31. t Decay Branching Ratios Br(-1-prong ³ 0 neutrals ) = (85.330.08)% Br(-e-ve) = (17.840.05)% Br(-m-vm) = (17.360.05)% Br(-1h ³ 0 neutrals ) = (50.130.11)% Br(-(3h)-³ 0 neutrals ) = (14.590.08)% Br(-(5h)-³ 0 neutrals ) = (0.1020.004)% Br(-(7h)-³ 0 neutrals ) < 2.7 x 10-7 Sum = (100.02 0.11)% 148 allowed modes + 55 LF, or L, or B violating Impressively well measured! Excursion into Tau Physics, November 2007

  32. t Mass Measurement 1977 MARK I mt = 1.9±0.1 GeV 1996 BES mt = 1776.96±0.31 MeV Excursion into Tau Physics, November 2007

  33. B r.c. obs Ecm (GeV) t Mass Measurement • At threshold (BES 1996) • Need detailed knowledge of • production cross section, beam energy, luminosity Excursion into Tau Physics, November 2007

  34. Pseudo-Mass Technique • Pseudo-mass was introduced by ARGUS in 1992 • Assume neutrino is mass less • t direction is approximated by the reconstructed tracks • m*t2=2(Ebeam – Ehad)(Ehad – Phad)+mhad2 Belle BaBar MC for input masses: 1.767 GeV1.777 GeV1.787 GeV Fit result MC input mass t Mass Measurement Mτ = 1776.77 ± 0.13(stat.) ± 0.32(sys.) MeV (prel.) Mτ+ – Mτ– = 0.050.27 MeV |Mτ+ – Mτ–|/Mτ < 2.8 · 10-4 @ 90% CL (CPT-Test) Excursion into Tau Physics, November 2007

  35. t Mass Measurement New preliminary t mass from KEDR Collaboration at the VEPP-4M Collider in Novosibirsk (hep-ex/0611046) keV enn,mnn,pn,Kn,rn – vs – ennt-pair events Excursion into Tau Physics, November 2007

  36. t Lifetime • Very precise results from all 4 LEP experiments are published • Will describe one measurement technique: “Decay Length Measurement” • A.Lusiani (BaBar preliminary) 80/fb • 1 vs. 3 topology • One prong tagged as lepton • Rigorous event selection criteria to reduce BG • Reconstruct the 3 prong vertex • Measure distance to beam spot Excursion into Tau Physics, November 2007

  37. Decay Length t Lifetime • The needed precision makes this type of analysis all but trivial • Fighting detector effects in the real detector and in the simulation • Understanding BG sources and their bias towards the measurement Excursion into Tau Physics, November 2007

  38. PDG 2006 290.6 ± 1.0 fs DELPHI 2005 t Lifetime The Results Excursion into Tau Physics, November 2007

  39. Test of Lepton Universality (charged current) A.Pich Tau06 Excursion into Tau Physics, November 2007

  40. Test of Lepton Universality Now, let’s put everything together and see whether it all works: mass (mt) life time(tt) leptonic branching ratios Bm=(17.36±0.05)% LEP and Be=(17.84±0.05)% CLEO (Bm /Be)exp= 0.9725 ± 0.0039 (Bm /Be)the= 0.972564 ± 0.000010 Standard Model Prediction mt=1776.99+0.29-0.26 MeV A.Pich Tau06 Excursion into Tau Physics, November 2007

  41. Lepton Flavor Violation • Lepton Flavor is conserved in the Standard Model • SM extended to include non zero n mass and n mixing predicts Lepton Flavor Violation Quite tough for the current experimental sensitivity… … but: Excursion into Tau Physics, November 2007

  42. Theoretical Predictions of SM Extensions • Many SM extensions include LF violation • Some models predict LFV up to existing experimental limits • Neutrinoless 2 and 3 body decays have different sensitivity Some examples: Observation of LFV would be a clear signature of new physics Excursion into Tau Physics, November 2007

  43. l l m/e l h g l h Typical Event Selection e+ ttag trec e- • Decay products of Taus are well separated in space (CM) • Signal side (Neutrinoless decays) lg (po,h), lhh (l = e, m h = p, K) • Mass reconstructed from particles = mt and their energy = Ebeam • Tag side (1-prong decays) B(t p nt, rnt, enent, m nmnt) ~ 85 % • (3-prong decays) B(t  hhh(p0) nt) ~ 15% (formg) Excursion into Tau Physics, November 2007

  44. Signal Region is blinded while developing the analysis t mgEvent Selection t mgSignal simulation MEC= t candidate invariant mass, with energy constrained to beam energy DE = Et – Ebeam = 0 smeared by resolution and radiation DM = MEC –Mt ~ 0 Excursion into Tau Physics, November 2007

  45. t mgEvent Selection II • Signal from MC and background from Data (excluding ± 3s) • Common Input Variables: • Event Missing Mass • Event Missing PT • Tag side missing mass • Tag side momentum • m helicity angle • MC Optimized for different tagging modes • electron • electron + gamma • muon • hadron • hadron gamma • 3 hadrons Excursion into Tau Physics, November 2007

  46. t mgResults 207106 e+e-→ t+t- events (L = 232 fb-1) What a few 10-7 signal would look like • Estimate background from linear fit to DM sideband • Nbkg = 6.2 ± 0.5 Nobs = 4 e = 9.3 ±0.6 % BaBar Phys. Rev. Lett. 95, 041802 (2005) B(t → mg) < 6.8  10-8 at 90% C.L. Excursion into Tau Physics, November 2007

  47. t egResults Estimate background from linear fit to DM sideband 1 event in a 2s2ssignal box, Nbkg =1.9 ± 0.4, e = 4.7 ± 0.3% 207106 e+e-→ t+t- events L = 232 fb-1 What a few 10-7 signal would look like BaBar Phys. Rev. Lett. 96, 041801 (2006) B(t → eg) < 1.1  10-7 at 90% C.L. Excursion into Tau Physics, November 2007

  48. t Lepton Flavor Violation Results (BaBar + Belle) S.Banerjee Tau06 Excursion into Tau Physics, November 2007

  49. Estimate background from 2-dimensional fit Total expected number of events: 11.3 , Nbkg =0.1- 3.0 (depends on channel) Total Observed: 10 events t lhhResults (BaBar) 197106 e+e-→ t+t- events L = 221 fb-1 BaBar Phys. Rev. Lett. 95, 191801 (2005) B(t → lhh) < (0.7-4.8)  10-7 at 90% C.L. Excursion into Tau Physics, November 2007

  50. t Lepton Flavor Violation Results (Belle) 42 decay modes Recent results on Belle’s LFV search (Upper Limit on Br at 90% CL) 535 86 401 154 87 281 158 158 535 86 401 154 281 158 This year’s publications T. Ohshima Tau06 Excursion into Tau Physics, November 2007

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