Searches for Isolated Leptons, Multileptons and Leptoquarks at HERA

1. Searches for Isolated Leptons, Multileptons and Leptoquarks at HERA Judith Katzy (DESY)

2. 20.3.07 Polarised e± 2000 2003 HERA 30.6.07 189pb-1 • Total luminosity collected: • H1: 478 pb-1 • 294 pb-1 e+ • 184 pb-1 e- • Zeus: 492 pb-1 • 286 pb-1 e+ • 206 pb-1 e- 170pb-1 105pb-1 14pb-1 ~ 1 fb-1 1992

3. PTmiss Hadronic system (X) isolated electron Events with isolated e or m and PTmiss HERA I: H1 observed 11 events at PTX>25 GeV at SM expectation 3.5±0.6 ZEUS in agreement with SM expectation Both experiments performed search in complete HERA data set

4. Standardmodel prediction Real W production in photoproduction with W decay into leptons main process for this event topology Hadronic system with typically low pTX sW ~ 1.3 pb-1 W decay branching ratio into e or m ~20% Other signal processes: CC W production ~7% Cabbibo-Parisi Z0 production ~3% (only e channel) Modelled using EPVEC generator with NLO QCD correction: Modifies cross section by ~10%, reduces theoretical uncertainty to ~15% Selection cuts For m only: PTX>12GeV >12GeV >10GeV

5. Background processes e: Neutral Current e,m: Charged Current m: Lepton Pair Production Real electron and fake PTmiss from mismeasurement Misidentified e or m and real PTmiss Real m and fake PTmiss from mismeasurement

6. e+ e- H1 isolated leptons 5<ql<140O Excess at high pTX Agreement with SM

7. ZEUS isolated leptons 15o < l < 120o 41 events observed in 492 pb-1 of data Good agreement between data and Standard Model for both data sets No Excess seen at high PTX as seen by H1

8. H1 and Zeus combined 15<ql<120O 87/92.7+-11.2 events with isolated leptons and PTmiss observed in 0.97fb-1 Excess in e+ data has significance of 1.8 s based on data of both experiments (2.9s H1 data only)

9. Cross section measurements H1 data only branching ratio W->e,m ~21% subtract Z0 processes Both measured cross sections are in good agreement with the SM

10. Measurement of W polarisation fraction right left longitudinal polarisation fraction Fit H1 measured cross section to dN/dcosq* and extract F0 and F- simultanously

11. W polarisation fraction Good agreement with the SM found compatible with Single top production within 1s Single parameter fit (other parameter at SM value)

12. l n Anomalous single top production SM single top production s<1fb-1 Top production via flavor changing NC in BSM Candidate process for excess But: same rate for e+ and e- Search for FCNC based on isolated lepton events of HERAI+II additional good top quark reconstruction and positive lepton charge requirement (if possible) Isolated lepton PTmiss High PTX 24 events selected, 26 events SM prediction No significant signal found using multi variant analysis (preliminary)

13. Single top results Limits on FCNC cross section derived using maximum likelihood: s(ep->etX) < 0.16 (95% CL) HERA 1 results: H1: s(ep->etx) < 0.55 pb Zeus: s(ep->etX)<0.23 pb Upper bound on the anomalous coupling: ktug < 0.14 New limit extends into region of phase space uncovered by other colliders

14. Isolated t leptons + pTmiss Look for events with PTmiss and a narrow hadronic jet in complete HERA data set PTmiss • 45% of t decay into 1 charged particle (“1-prong-decay”) giving a • narrow, pencil like jet • main (and large!) background CC events with narrow jets • complementary results to those in electron and muon channel • enhanced t production above SM predicted by some Rp violating SUSY models • HERA I data ZEUS observed 3 events over SM expectation 0.4±0.12, • 2 events at PTX>25GeV, SM expectation 0.2±0.05

15. t results 20 events observed Good agreement with the SM prediction for e+ and e- data set Only 1 event at high PTX – in the e-p data! Dominated by background processes – only 14% signal (other channels up to 85%)

16. Multi-Leptons Search for topologies with 2 or 3 high pT leptons pT1l>10GeV, pT2l>5GeV, 20O<q<160O Third lepton: Ee>5GeV or pTm>2GeV, 5<q<175 ZEUS: ee, eee H1: ee, em, mm, eee, emm

17. QED processes with multi-lepton final state Cabbibo-Parisi Z0 production ~3%, only in electron channel gg process dominant CC W production (7%)

18. 2 lepton results 446 evts 185 evts 201 evts Overall good agreement with SM H1: 3 ee events observed at M>100GeV (all hera1 e+p data) ZEUS: 2 ee event observed at M>100GeV

19. 3 lepton event

20. 81 events 102 events 3 eee events Observed in hera 1 e+p 102 events 2 emm events observed in Hera 2 e+p H1 3 lepton results Overall good agreement with SM Data slightly exceed SM prediction at high mass

21. Zeus 3 lepton results 2 events at high mass

22. Results on 2+3 leptons 4 events with high SPT 3 ee events with M>100 GeV 1 emm event with M12>100GeV SM expectation 1.9±0.4 3 events with high SPT SM expectation 1.58+0.16-0.12

23. e+ hel l+ l- H±± search H1 HERA I data hel’ H++/H-- exists in some left-right symmetric extensions to SM and SUSY models Search for resonances in mass spectra of multi lepton sample Additional charge and PT cut for ee, em channel, PTmiss cut for t

24. Limit on H±± cross section H±±->et H±±->ee H±±->em Best sensitivity for H±±->em: sH±±->em<0.05pb

25. Limits on H±± mass H1 sets most stringent limits on MH for H±±coupling to em and et at coupling of electromagnetic strength: hem=0.3 MH>141 GeV het=0.3 MH>112 GeV

26. Leptoquarks at HERA Leptoquarks: color triplet boson with leptonic and baryonic quantum number: Fermion number: F=L+3B F=2 (e-p) F=0 (se+p) Buchmüller-Rückl-Wyler (BRW) model: LQ classified into 14 types (7 vector, 7 scalar) depending on spin, isospin, chirality LQ at HERA: single production from incoming particles MLQ >300 GeV Contact interaction region MLQ< 300 GeV LQ decay lepton flavor conserving (LFC): LQ->eq, nq or lepton flavor violating (LFV): LQ->mq, tq H1 and ZEUS search for LQ in inclusive NC and CC event sample of 2004/05 data

27. Comparison with LEP and Tevatron ~ factor 2 more lumi to be added using full HERA II data

28. e-p, 30 pb-1 Limits on 1st generation MLQ e-p, 60 pb-1 No enhancement No evidence for LQ signal At l~0.3 exclude MLQ>276-304 GeV

29. Heavy Leptoquarks • Possible new interaction between • e and q can modify DIS cross section • at high Q2 via virtual effects • Search for virtual LQ exchange • using 4 fermion eeqq contact • interaction method • ->report by P.Schleper in Alternatives Lower limits on MLQ/l derived for all LQ MLQ>>300 excluded for all LQ for l ~ 1

30. Limits on LFV Leptoquarks Signature ep->mX Low background, good sensitivity Typical selection: Back-to-back topology, PTcalo>20GeV Assume: No evidence for Signal found Exclude MLQ>300 GeV for l~0.3

31. Summary • Results for isolated leptons with pTmiss shown for complete hera data sample and for the first time with h1+zeus combination ~1fb-1: • In e+p data: H1 observed 21 events where 8.9 were expected • ZEUS observed 6 events where 7.4 expected • H1+ZEUS combined observes 23 events where 14.6 were expected • e- data and e++e- combined sample fully agree with SM prediction • Measured W production cross section and polarisation fractions • Limits on anomalous single top production in FCNC • All HERA data analysed by H1 and ZEUS multi-lepton events • At high SPT H1 observes 4 events, expectation is 1.9±0.4 ZEUS observes 3 events, expectation is 1.58+0.12-0.16 • Combined results expected soon • Limits on H±± • Limits for LQ updated – improvement with full hera data sample to come

32. extras

33. Isolated lepton event selection

34. Multi-lepton event yields at Mll>100GeV H1 preliminary HERA I+II ZEUS preliminary HERA I+II e+p e-p

35. 2 leptonmass spectra, H±± search(backup) H1 HERA I data, H±±preselection 35 evts 125 evts 6 evts 6 evts obs. 0.53±0.06 expt. 1 event after final selection (charge+ PT cuts)

36. Leptoquark search all mass spectra

37. e+ hel l+ l- H±± production H1 HERA I data

38. CC and NC cross section