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Carsten Hast, SLACExcursion into Tau Physics, November 2007 1 A rather abbreviated history of the Reconstruction of hadronic decays 3 hadrons (g -2) |v.

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Presentation on theme: "Carsten Hast, SLACExcursion into Tau Physics, November 2007 1 A rather abbreviated history of the Reconstruction of hadronic decays 3 hadrons (g -2) |v."— Presentation transcript:

1 Carsten Hast, SLACExcursion into Tau Physics, November A rather abbreviated history of the Reconstruction of hadronic decays 3 hadrons (g -2) |v us | Mass measurement Lifetime Lepton Universality Lepton Flavor Violation Outlook An Excursion into Physics Carsten Hast Stanford Linear Accelerator Center DESY Hamburg and Zeuthen November 12 th,13 th 2007

2 Carsten Hast, SLACExcursion into Tau Physics, November Back in the early 60s 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 … How to Find a Lepton e + e - l + l -

3 Carsten Hast, SLACExcursion into Tau Physics, November The following is from Yung-Su Tsai (1971) Assuming that the new lepton has the same electro- magnetic and weak interaction as e and Assuming it is heavy, so it will decay into hadrons From decays via CVC Tsai calculated the decay rates of the into different hadrons:, K ( * ),, a 1, cont. and partial and total decay width, lifetime and cross section Characteristics of Lepton Decays W e e u d d = cos c d + sin c s c the Cabibbo angle

4 Carsten Hast, SLACExcursion into Tau Physics, November Characteristics of Lepton Decays lifetime sec) -1 = 310 fsec r e r r had

5 Carsten Hast, SLACExcursion into Tau Physics, November In 1973 MARK I was ready at SPEAR at SLAC Look for events with only 2 charged tracks and missing energy How to Find the First Pair Event W e e uu ds e+e+ e-e- M.L. Perl et al. 75 PRL

6 Carsten Hast, SLACExcursion into Tau Physics, November …it worked out: Martin Perl Nobel Laureate of 1995 Have to give it a name: the third M. Perl, Frederick Reines, King Carl Gustaf 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/ was discovered charm was born 2 families of leptons, 2 families of quarks Nice SU(2) U(1) symmetry Who needs a 3 rd generation! How to Find the First Pair Event … but it helps when you have nice colleagues who find strange electron-muon events as well, like Pluto in 1976, and then…

7 Carsten Hast, SLACExcursion into Tau Physics, November Production of Pairs In the following lets focus on e + e - machines CMS energy from threshold to the Z resonance and beyond

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

9 Carsten Hast, SLACExcursion into Tau Physics, November Initial and final state radiation E E CMS /2 Taus are flying back to back in CMS Each decays to an odd number of charged particles (1, 3, 5, 7…) plus neutral particles ( 0,…) Most (semi)hadronic decays proceed via resonances (a 1,, K*…) Need to identify e,,, K,, 0 Reconstruction of decay vertex is always good 4 detector coverage, high efficiency, etc. Reconstruction of Pairs e+e+ e-e-

10 Carsten Hast, SLACExcursion into Tau Physics, November E CMS = (4s) = GeV Unfortunately with a boost ( E(e-)=9.0GeV and E(e+)=3.1GeV ) Typical Pair: PEP II and BaBar SVT, DCH: charged particle tracking vertex &mom. resolution EMC: electromagnetic calorimetry / 0 / DIRC, IFR, DCH: charged particle ID /K/p, 1.5 T Solenoid Electromagnetic Calorimeter (EMC) Detector of Internally Recflected Cherenkov Light (DIRC) Instrumented Flux Return (IFR) Silicon Vertex Tracker (SVT) Drift Chamber (DCH) e - (9 GeV) e + (3.1 GeV) Typical Event Simulated 1-7 topology event

11 Carsten Hast, SLACExcursion into Tau Physics, November Standard Event Selection of an 1- n topology: 1.In CMS: Demand 1 charged track vs. n charged tracks 2.Net charge of 0 3.Get rid of converted photons 4.Invent good ways to reduce background 1.Cuts on event thrust angle and magnitude 2.Cuts on photons in the event 3.Lepton identification on the tag side 4.Vertexing 5.Missing Energy (neutrinos) 5.Particle identification on signal side 6.Reconstruct (or get rid of) 0 Pair Event Reconstruction e-e- e+e+ tag rec

12 Carsten Hast, SLACExcursion into Tau Physics, November The following is an example of how to do a analysis Most of these decays are quite well measured, except for the rarer ones (Ian Nugent (BaBar) Tau 06 in Pisa, submitted to PRL in July 2007 ) How to: to Three Hadrons

13 Carsten Hast, SLACExcursion into Tau Physics, November Rely on superb particle identification of the B-Factory detectors How to: to Three Hadrons II K K - - K + K - K - K %22.49%4.73%1.02% K %74.87% % K - - K %0.49%59.63%25.54% K - K - K %50.87%

14 Carsten Hast, SLACExcursion into Tau Physics, November How to: to Three Hadrons III ARGUS 1993

15 Carsten Hast, SLACExcursion into Tau Physics, November All modes are related to each other (signal and background) How to: to Three Hadrons IV BR(8.83±0.01± 0.13)% (0.273±0.002± 0.009)% (0.1346±0.0010± )% (1.58±0.10± 0.13) BR DPG (9.02±0.08)%(0.333±0.35)%(0.153±0.10)%<3.5x % CL BaBar arXiv: [hep-ex] Submitted to PRL

16 Carsten Hast, SLACExcursion into Tau Physics, November How to: to Three Hadrons V K - - K + K K - K - K + Mike Roney, Lepton Photon 2007

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

18 Carsten Hast, SLACExcursion into Tau Physics, November heavy enough to decay into hadrons Hadronic Decays for QCD Tests probes the hadronic V-A current e e H 0 probes the hadronic electromagnetic current hadrons W hadrons e+e+ e –e – Isospin

19 Carsten Hast, SLACExcursion into Tau Physics, November Hadronic vacuum polarisation is the largest uncertainty in calculating a (a had )= a few x (others are only x ) Dominant part can be calculated from the 2 spectral functions Hadronic Decays: and (g -2) muon anomalous magnetic moment: Need to measure Br ) and the precise mass spectrum shape Isospin

20 Carsten Hast, SLACExcursion into Tau Physics, November Fudjikava (Belle preliminary) Tau 06 Hadronic Decays: and (g -2) BG subtraction Detector unfolding Radiative corrections Fitting Pion form factor Gounaris-Sakurai parameterization

21 Carsten Hast, SLACExcursion into Tau Physics, November Fudjikava (Belle preliminary) Tau 06 Hadronic Decays: and (g -2) Interference between and a 2 x Belle 0.5(stat.) 3.2(sys.) 2.3(Iso.) Aleph,Cleo 3.2(exp.) 2.3(Iso.) CMD2, Kloe 4.9(exp.) 1.6(rad.) (770) (1400) (1700)

22 Carsten Hast, SLACExcursion into Tau Physics, November x a th = QED Kinoshita-Nio, Passera EW Czarnecki-Marciano-Vainshtein hvp ( ), ( ) e e Davier et al hvp NLO Krause, Hagiwara et al light-by-light Melnikov-Vainshtein, Knech et al = ( ), ( ) e e a exp - a th = 1.3 Davier/Pich Anomalous Magnetic Moment Summary BNL - E821 A = ( )

23 Carsten Hast, SLACExcursion into Tau Physics, November Hadronic Decays: |v us | The route to world best measurements of |v us | and m s Need detailed knowledge of all (strange) BRs and shapes of all (strange) mass spectra |V ud | 2 +|V us | 2 + |V ub | 2 = 1 |V ud | 2 = from nuclear decays and neutron decays (PDG 2006) |V ub | 2 = ( ) x from e.g. inclusive B X u l decays |V us | 2 = Mike Roney, Lepton Photon 2007

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

25 Carsten Hast, SLACExcursion into Tau Physics, November Hadronic Decays: I.Nugent: BaBar preliminary Tau 06 and updated in arXiv: [hep-ex] submitted PRD-RC qqbar BG

26 Carsten Hast, SLACExcursion into Tau Physics, November Hadronic Decays: s 0 B.Shwartz, Belle preliminary Tau 06 and updated in arXiv: [hep-ex] submitted to PLB K* 0 (800)+ K*(892)+ K*(1410)Fit with K* 0 (892) only

27 Carsten Hast, SLACExcursion into Tau Physics, November not in average Br( - K 0 - ) = ( stat syst )% PDG 2007 ( ) % Hadronic Decays: s (cont.)

28 Carsten Hast, SLACExcursion into Tau Physics, November Belle preliminary arXiv: [hep-ex] Hadronic decays with BR is dominated (100%) by

29 Carsten Hast, SLACExcursion into Tau Physics, November Hadronic Decays: |v us | Summary Swagato Banerjee, Kaon 2007

30 Carsten Hast, SLACExcursion into Tau Physics, November Strange Spectral Functions: ALEPH (99) and OPAL (05) |V us |=0.2204± exp ± th ± ms No good solution Need better data to clarify Need B-factories to contribute Moments k,l=0 DHZ05, hep-ph/

31 Carsten Hast, SLACExcursion into Tau Physics, November Decay Branching Ratios Br( - 1-prong 0 neutrals ) = ( )% Br( - e - v e ) = ( )% Br( - - v ) = ( )% Br( - 1h 0 neutrals ) = ( )% Br( - (3h) - 0 neutrals ) = ( )% Br( - (5h) - 0 neutrals ) = ( )% Br( - (7h) - 0 neutrals ) < 2.7 x Sum = ( )% 148 allowed modes + 55 LF, or L, or B violating Impressively well measured!

32 Carsten Hast, SLACExcursion into Tau Physics, November MARK I m = 1.9±0.1 GeV Mass Measurement 1996 BES m = ±0.31 MeV

33 Carsten Hast, SLACExcursion into Tau Physics, November E cm (GeV) B r.c. obs Mass Measurement At threshold (BES 1996) Need detailed knowledge of production cross section, beam energy, luminosity

34 Carsten Hast, SLACExcursion into Tau Physics, November Mass Measurement Pseudo-Mass Technique Pseudo-mass was introduced by ARGUS in 1992 Assume neutrino is mass less direction is approximated by the reconstructed tracks m* 2 =2(E beam – E had )(E had – P had )+m had 2 MC for input masses: GeV GeV GeV MC input mass Fit result BaBar Belle M τ = ± 0.13(stat.) ± 0.32(sys.) MeV (prel.) Mτ + – Mτ – = MeV |Mτ + – Mτ – |/Mτ < 2.8 · 90% CL (CPT-Test)

35 Carsten Hast, SLACExcursion into Tau Physics, November Mass Measurement New preliminary mass from KEDR Collaboration at the VEPP-4M Collider in Novosibirsk (hep-ex/ ) e,,,K, – vs – e -pair events keV

36 Carsten Hast, SLACExcursion into Tau Physics, November 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

37 Carsten Hast, SLACExcursion into Tau Physics, November 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 Decay Length

38 Carsten Hast, SLACExcursion into Tau Physics, November Lifetime The Results PDG ± 1.0 fs DELPHI 2005

39 Carsten Hast, SLACExcursion into Tau Physics, November Test of Lepton Universality (charged current) A.Pich Tau06

40 Carsten Hast, SLACExcursion into Tau Physics, November Test of Lepton Universality Now, lets put everything together and see whether it all works: mass (m ) life time( ) leptonic branching ratios B =(17.36 LEP and B e =(17.84 CLEO (B /B e ) exp = (B /B e ) the = A.Pich Tau06 Standard Model Prediction m = MeV

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

42 Carsten Hast, SLACExcursion into Tau Physics, November Observation of LFV would be a clear signature of new physics Some examples : 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

43 Carsten Hast, SLACExcursion into Tau Physics, November Typical Event Selection e-e- e+e+ tag rec Decay products of Taus are well separated in space (CM) Signal side (Neutrinoless decays) l, lhh (l = e, h =, K) Mass reconstructed from particles = m and their energy = E beam Tag side (1-prong decays) B e e 3-prong decays) hhh for ) /e l l l l h h

44 Carsten Hast, SLACExcursion into Tau Physics, November Event Selection E = E – E beam = 0 smeared by resolution and radiation Signal simulation M EC candidate invariant mass, with energy constrained to beam energy M = M EC –M ~ 0 Signal Region is blinded while developing the analysis

45 Carsten Hast, SLACExcursion into Tau Physics, November Signal from MC and background from Data (excluding ± 3 ) Common Input Variables: Event Missing Mass Event Missing P T Tag side missing mass Tag side momentum helicity angle MC Optimized for different tagging modes electron electron + gamma muon hadron hadron gamma 3 hadrons Event Selection II

46 Carsten Hast, SLACExcursion into Tau Physics, November Results e + e events (L = 232 fb -1) Estimate background from linear fit to M sideband N bkg = 6.2 ± 0.5 N obs = 4 = 9.3 ± 0.6 % B( ) < at 90% C.L. BaBar Phys. Rev. Lett. 95, (2005) What a few signal would look like

47 Carsten Hast, SLACExcursion into Tau Physics, November e Results e + e events L = 232 fb -1 What a few signal would look like B( e ) < at 90% C.L. Estimate background from linear fit to M sideband 1 event in a 2 2 signal box, N bkg = 1.9 ± 0.4, = 4.7 ± 0.3% BaBar Phys. Rev. Lett. 96, (2006)

48 Carsten Hast, SLACExcursion into Tau Physics, November Lepton Flavor Violation Results (BaBar + Belle) S.Banerjee Tau06

49 Carsten Hast, SLACExcursion into Tau Physics, November Estimate background from 2-dimensional fit Total expected number of events: 11.3, N bkg = (depends on channel) Total Observed: 10 events e + e events L = 221 fb -1 B( lhh) < ( ) at 90% C.L. lhh Results (BaBar) BaBar Phys. Rev. Lett. 95, (2005)

50 Carsten Hast, SLACExcursion into Tau Physics, November Lepton Flavor Violation Results (Belle) Recent results on Belle s LFV search (Upper Limit on Br at 90% CL) 42 decay modes This year s publications T. Ohshima Tau06

51 Carsten Hast, SLACExcursion into Tau Physics, November LFV new prelim. Belle lll Belle update to 535 fb-1 increase in lumi by 6.1 fold Efficiency: % : events Total = events Nobs=0 events 90%CL limits: BR lll )<( )x fold improvement over previous limit Mike Roney, Lepton Photon 2007

52 Carsten Hast, SLACExcursion into Tau Physics, November Mike Roney, Lepton Photon 2007 LFV new prelim. BaBar lll BaBar update to 376fb-1 increase in lumi by 4.3 fold Efficiency: % : events Total = events Nobs=6 events 90%CL limits: BR ( lll )<( )x fold improvement over previous limit

53 Carsten Hast, SLACExcursion into Tau Physics, November New Belle Results on lV 0 using 543fb -1 Efficiency: % : events Total = ev Nobs=3 events 90%CL limits: BR(t lV 0 )<(6.1-18)x10 -8

54 Carsten Hast, SLACExcursion into Tau Physics, November New BaBar Results l hep-ex/ PRL (2007) expected background/channel ~ Total expected background=3.1, Observed=2 UL on Br. between 1.1 x and 5.8 x 10 90% CL Lafferty (BaBar preliminary) Tau 2006 … and more Violations …

55 Carsten Hast, SLACExcursion into Tau Physics, November Summary, Conclusions and Outlook The is a clean laboratory to test the standard model Some examples of hadronic tau decay analysis ( g -2) : resonance analysis of hadronic tau decays is currently in a small contradiction with the production measurements More detailed analysis of the strange spectral functions at B-Factories is eagerly anticipated (|v us | and m s ) Mass measurements are already very precise (0.1 per/mille) and will get even better Lifetime measurements from B-Factories are overdue Lepton Universality is tested to the few per/mille level but to e/ Br measurements of B-Factories are overdue Lepton Flavor Violation: no signal at the to -8 level

56 Carsten Hast, SLACExcursion into Tau Physics, November Summary, Conclusions and Outlook Many thanks for your kind invitation! B-Factories in 2008 will have (more/less) 1 ab -1 each Lepton universality O(10 -4 ) (maybe) LFV O(10 -8 ) CPV and CPT test in more systematic fashion |v us | and m s and s (even better) Super-B Factory with 100 ab -1 Lepton universality O(10 -4 ) tough to get errors smaller LFV O( ) CPT test to O( ) CPV in decays: case for (4s) running with polarized beams

57 Carsten Hast, SLACExcursion into Tau Physics, November Additional

58 Carsten Hast, SLACExcursion into Tau Physics, November BELLE (preliminary) Use - K - 0 sample to get - K* - ) through the K *- (892) K - 0 mode using BR( K *- (892) K K* - BELLE ~1.9 lower than PDG 07 (CLEO) BR ( )x10 -4 ( )x10 -4

59 Carsten Hast, SLACExcursion into Tau Physics, November Some intepretations within benchmark models compilation by S. Banerjee (Tau06,hep-ex/ )


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