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Results on tau physics from HERA

Results on tau physics from HERA. Junpei Maeda (Tokyo Institute of Technology) On behalf of the H1 and ZEUS collaborations. 10th Int. Workshop on Tau Lepton Physics (TAU08) September 22–25, 2008 Novosibirsk, Russia. GeV. HERA: World’s Only ep Collider. e + /e –. p. 27.6 GeV.

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Results on tau physics from HERA

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  1. Results on tau physics from HERA Junpei Maeda (Tokyo Institute of Technology) On behalf of the H1 and ZEUS collaborations 10th Int. Workshop on Tau Lepton Physics (TAU08) September 22–25, 2008 Novosibirsk, Russia

  2. GeV HERA: World’s Only ep Collider e+/e– p 27.6 GeV 920 GeV HERA laid to rest on 30 June 2007. HERA–I (1992~2000) : L~120 pb–1/exp. HERA–II (2002~2007) : L~350 pb–1/exp. – luminosity upgraded – longitudinally polarized lepton beam – detector upgrades 0.5 fb–1 data for each experiment! J.Maeda - Results on tau physics from HERA

  3. H1 and ZEUS detector p p e+/e– e+/e– Liquid Argon Calorimeter Uranium–scintillator Calorimeter good hadronic energy resolution fine granularity, excellent tracking for electrons for electrons for hadrons for hadrons J.Maeda - Results on tau physics from HERA

  4. Tau Production at HERA Tau lepton production is a rare process at HERA! • t+t– pair–production events • Isolated t lepton with missing transverse momentum(PTmiss) events • Double charged Higgs Search • Lepton Flavour Violation Tau lepton is important in exotic search. J.Maeda - Results on tau physics from HERA

  5. Tau Production at HERA • t+t– pair–production events • Leptonic channel ( ) • Semi–leptonic channel ( ) • Hadronic channel ( ) • Isolated t lepton with missing transverse momentum(PTmiss) events • Double charged Higgs Search • Lepton Flavour Violation J.Maeda - Results on tau physics from HERA

  6. t+t– pair–production (only leptonic) @ ZEUS ZEUS–prel–06–017 HERA–II e–p data L=135 pb–1 searched for (leptonic decay) dominant background qm (rad) PT,m (GeV) m– m+ qe (rad) PT,e (GeV) selection criteria PT,miss (GeV) Me, m (GeV) Data agree with SM expectation. J.Maeda - Results on tau physics from HERA

  7. t+t– pair–production (incl. hadronic) @ ZEUS ZEUS–prel–08–009 HERA–II e±p data L=364 pb–1 To study hadronically–decayed t identification, searched for: (BR : ~23%) more statistics than em channel (~6%) (BR : ~42%) Hadrons from t decay is identified by ”jet”. The most difficult thing : separate a t–jet from quark/gluon induced jets s ~ 10 pb (PTt > 5 GeV) There are many kinds of large background… e.g.) diffractive–photoproduction s~300 nb (2 jets w/ ET>4 GeV) J.Maeda - Results on tau physics from HERA

  8. nS(ievent,V) / NS x2 Signal nS(ievent,V) / NS+nB(ievent,V) / NB • Implemented in TMVA #signal events in V #all signal events Discrimination value D(ievent,V) = background #background events in V #all background events x1 test event t–jet ID for t+t– pair–production @ ZEUS had t–ID t–ID using PDE Range Searching (discriminant) ZEUS–prel–08–009 suggested by T.Carli, B.Koblitz. NIMA501(2003)576 • Generalization of one–dimensional PDE approach to n dimensions • Counts number of signal and background events (training sample) in ”vicinity”V of the test event • Implemented in TMVA • 6 variables are inputted to discriminant, then evaluate discrimination value. (next slide) J.Maeda - Results on tau physics from HERA

  9. t–jet ID for t+t– pair–production @ ZEUS had t–ID 6 variables are prepared for discriminant. Rmean, Rrms : 1st and 2nd moment of radial extension Mass : invariant mass of clustered CAL cells Lmean : 1st moment of longitudinal extension jet axis cell Li ai Ei Rtrk : The sum of distance between the jet axis and the tracks associated with the jet Nsubj : Number of subjets (ycut=5×10–4) Outputted discrimination value The highest D in event The second highest D ZEUS–prel–08–009 J.Maeda - Results on tau physics from HERA

  10. Results of t+t– pair–production @ ZEUS ZEUS–prel–08–009 HERA–II e±p data L=364 pb–1 Discriminant threshold is given for each topology. • MC statistics • PHP scale normalization Large uncertainty due to Data are in reasonable agreement with SM expectation. J.Maeda - Results on tau physics from HERA

  11. The highest Mttvisible event (Mttvisible=40 GeV) J.Maeda - Results on tau physics from HERA

  12. t+t– pair–production @ H1 Eur. Phys. J. C48 (2006) 699–714 HERA–I e±p data L=106 pb–1 look for all topologies to be able to identify t+t– events • leptonic(em), semi–leptonic(e–jet, m–jet), hadronic(jet–jet) decay • look at the jets from low PT • exactly required 1 or 3–tracks in the jet • using neural network to identify t–jet • the first measurement of t+t– cross section at ep–collider had t–ID Neural Network based tau–ID • To distinguish hadronic 1–prong, 3–prong t decays from quark/gluon jets (L1–prong, L3–prong) • To distinguish hadronic 1–prong t decays from misidentified electrons/muons (Lvetoe, Lvetom) • – multiplicities of neutral clusters / invariant mass / number of tracks / 1st moment of energy deposits… signal efficiency = 50% misideintifed probability = 0.5% (4%) J.Maeda - Results on tau physics from HERA

  13. stat. syst. smeasured = 13.6±4.4±3.7 pb stheory = 11.2±0.3 pb (GRAPE) Results of t+t– pair–production @ H1 Eur. Phys. J. C48 (2006) 699–714 HERA–I e±p data L=106 pb–1 . Purest final state Phase space definition elastic events with two t leptons of first measurement at HERA !! – pTt > 2 GeV – 20º < qt < 140º good agreement with SM expectation! (acceptance ≈ 1%) J.Maeda - Results on tau physics from HERA

  14. t+t– candidate @ H1 Eur. Phys. J. C48 (2006) 699–714 J.Maeda - Results on tau physics from HERA

  15. Tau Production at HERA • t+t– pair–production events • Isolated t lepton with missing transverse momentum(PTmiss) events • Double charged Higgs Search • Lepton Flavour Violation J.Maeda - Results on tau physics from HERA

  16. tn Isolated tau leptons + PTmiss physics ZEUS : Phys. Lett. B 583 (2004) 41 H1 : H1prelim–07–064 Rare process, but sensitive to new physics – SM signal is single W boson production with subsequent decay W tn.– Main background is CC events with narrow jets.– A complement to isolated e(m) + PTmiss analysis(There is a slight excess for e(m) channel at H1.) Large PTX new physics? PTX > 12 GeV (H1) PTmiss > 20 GeV (ZEUS) An excess at high pTX could be a sign of new physics. single top production via FCNC etc. PTmiss PTX Additional high pT jet J.Maeda - Results on tau physics from HERA

  17. t–ID for Isolated t + PTmiss analysis @ ZEUS HERA–I e±p data L=130 pb–1 Phys. Lett. B 583 (2004) 41 had t–ID t–ID using PDE Range Searching – Same method as t+t- analysis. (see above) – Variable set is different. log(Rtrk) –log(Lrms) Lrms : 2nd moment of longitudinal extension jet axis CAL cell Li ai Ei required D > 0.95 Good separation of signal from background! J.Maeda - Results on tau physics from HERA

  18. Result of isolated t + PTmiss @ ZEUS Phys. Lett. B 583 (2004) 41 Interesting t+PTmiss events at large PTX are observed at ZEUS! New physics signal +0.12 J.Maeda - Results on tau physics from HERA

  19. tn W tn Isolated tau leptons + PTmiss @ H1 H1prelim–07–064 • ZEUS HERA–I result has a slight excess for t + PTmiss events. • H1 analyzed all HERA data. 471 pb–1 had t–ID cut–based tau–ID • look for jet in LAr calorimeter (cone radius = 1.0) PTjet > 7 GeV, 20º < qjet < 120º • Isolation : Distance to other e, m, jet in h–f > 1.0 Radial shower shape (”Jet radius”) < 0.12 (only 1–prong jet) • Njettracks = 1 misidentification probability : < 1% CC events are dominant. Data in good agreement with SM prediction! J.Maeda - Results on tau physics from HERA

  20. t + PTmiss candidate event H1prelim–07–064 J.Maeda - Results on tau physics from HERA

  21. Tau Production at HERA • t+t– pair–production events • Isolated t lepton with missing transverse momentum(PTmiss) events • Double charged Higgs Search • Lepton Flavour Violation J.Maeda - Results on tau physics from HERA

  22. Doubly–charged Higgs search @ H1 Phys. Lett. B 638 (2006) 432 searched for H++ bosons using HERA–I e+p data L=88 pb–1 t– het e+ e+ het H++ t+ g SM signal efficiency p p (X) CDF (MH > 114 GeV) (c.f. hep-ex/0808.2161) had t–ID cut–based tau–ID No evidence for H++ e+t+ decays J.Maeda - Results on tau physics from HERA

  23. Lepton Flavour Violation @ H1/ZEUS searched for Lepton Flavour Violation H1 : Eur. Phys. J. C52 (2007) 833–847 ZEUS : (n) Eur. Phys. J. C44 (2005) 463–479 t Leptoquark(LQ)s couple to both quarks and leptons. t (W±) It carries both leptonic(L) and baryonic (B) numbers. s–channel u–channel SM DIS had t–ID had t–ID t–ID using PDE Range Searching Neural Network based tau–ID like H1 t+t– analysis same discriminant as in ZEUS t+PTmiss search 80% signal efficiency 95% quark/gluon induced jet rejection Required : exactly 1 or 3 tracks in the jet PTjet1 >25GeV, PTjet2 >15GeV DNN>0.8 & … J.Maeda - Results on tau physics from HERA

  24. Limits for LQs in the t channel @ H1/ZEUS Eur. Phys. J. C52 (2007) 833–847 Eur. Phys. J. C44 (2005) 463–479 HERA–I e±p data L=80.2 pb–1 No candidate was found. Limits on LQ were set. No significant deviation from SM found. Limits were set on coupling to LQ leading to Lepton Flavour Violation. HERA–I e±p data L=130 pb–1 No evidence for LFV No evidence for LFV J.Maeda - Results on tau physics from HERA

  25. Summary • Only a few taus have been seen at HERA. • Detecting taus at HERA is a challenging task. • They are an important signature for new physics. • Many tools for the identification of hadronically–decayed taus have been developed by H1 and ZEUS. • Results for t+t– pair–production are in agreement with SM prediction (H1/ZEUS). • New result of isolated t + PTmiss from H1 is in agreement with SM expectation. • ZEUS result using HERA–I data has a slight excess. • No evidence for H++ e+t+ decays (H1) and lepton flavour violation (H1/ZEUS) • HERA data taking ended on June 30 2007 after 15 years successful operation: • Each experiment has collected ~500 pb–1 data. • Tau analyses have not finalized yet, still more to come for the next years! J.Maeda - Results on tau physics from HERA

  26. backup slides

  27. Background control sample for t+t– pair–production @ H1 J.Maeda - Results on tau physics from HERA

  28. Event selection for isolated tau + PTmiss @ H1 CC selection H1prelim–07–064 PTmiss > 12 GeV the ratio of the anti–parallel and parallel components of the hadronic PT Tau–jet selection (cut–based) look for jet in LAr calorimeter (cone radius = 1.0) PTjet > 7 GeV, 20º < qjet < 120º Isolation : Distance to other e, m, jet in h–f > 1.0 Radial shower shape (”Jet radius”) only 1–prong jet (misidentification probability : < 1%) J.Maeda - Results on tau physics from HERA

  29. W tn Isolated tau leptons + PTmiss @ H1 H1prelim–07–064 J.Maeda - Results on tau physics from HERA

  30. Lepton Flavour Violation @ ZEUS J.Maeda - Results on tau physics from HERA

  31. Limits for LQs in the t channel @ H1/ZEUS HERA–I e±p data L=80.2 pb–1 Eur. Phys. J. C52 (2007) 833–847 No significant deviation from SM found. Limits were set on coupling to LQ leading to Lepton Flavour Violation. No evidence for LFV e+p data e–p data HERA–I e±p data L=130 pb–1 No candidate was found. Limits on LQ were set. No evidence for LFV Eur. Phys. J. C44 (2005) 463–479 J.Maeda - Results on tau physics from HERA

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