Isolated Leptons in Events with Large Missing Transverse Momentum at HERA

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1 Isolated Leptons in Events with Large Missing Transverse Momentum at HERA J. Ferrando University of Oxford February 2 th, 2008 J. Ferrando Isolated Leptons at HERA / 30

2 Outline 2 Isolated Lepton 3 4 James Ferrando Isolated Leptons at HERA 2 / 30

3 HERA HERA H and ZEUS Isolated Leptons Backgrounds Example Events History HERA collided e ± (27.5 GeV) and protons (820,920,460,575 GeV) at largest s 38 GeV 2 colliding beam experiments ZEUS + H HERA underwent a luminosity upgrade James Ferrando Isolated Leptons at HERA 3 / 30

4 HERA HERA H and ZEUS Isolated Leptons Backgrounds Example Events History Integrated Luminosity (pb ) HERA Luminosity Integrated Luminosity (pb ) ZEUS Luminosity Days of running Days of running James Ferrando Isolated Leptons at HERA 4 / 30

5 H and ZEUS H HERA H and ZEUS Isolated Leptons Backgrounds Example Events History ZEUS Optimised for precision measurement of the scattered lepton Optimised for precision measurement of the hadronic final state James Ferrando Isolated Leptons at HERA 5 / 30

6 Isolated Lepton Production HERA H and ZEUS Isolated Leptons Backgrounds Example Events History e + e + q e + e + q q γ,z W (c) e + W q ν γ,z W W (a) f f (f) W + q q f f e + e + q e + e + q e + f f γ,z W (d) q q e + f f γ,z W (b) q f f e + e + q W ν q (g) W γ,z W (e) e + q f f f f Main SM physics source of isolated leptons in events with missing transverse momentum at HERA is single W production (σ pb) 8 LO Diagrams in EPVEC: (a) and (b) dominant diagrams (c) involves TGC (d) and (e) EM gauge invariance (f) and (g) suppressed (2 nd W ) CC diagrams are similar but σ order of magnitude lower Nucl. Phys. B375 (992) 3 James Ferrando Isolated Leptons at HERA 6 / 30

7 W NLO HERA H and ZEUS Isolated Leptons Backgrounds Example Events History Diagrams for NLO corrections to photoproduction of W γ W γ g W q q g q q q NLO corrections of order 5% calculated in Eur.Phys.J. C (2002) Remaining theoretical cross-section uncertainties 5% Corrections are moderate and may be applied by reweighting LO MC (hep-ex/ ) James Ferrando Isolated Leptons at HERA 7 / 30

8 Backgrounds HERA H and ZEUS Isolated Leptons Backgrounds Example Events History NC DIS CC DIS Dilepton production e (k µ ) e (k µ) e (k µ ) ν (k µ) γ,z o (q µ ) W ± (q µ ) p (p µ ) X p (p µ ) Genuine electron misidentified lepton Genuine µ and fake and fake PT miss due and genuine PT miss PT miss due to to mismeasurement mismeasurement σ 8000 pb σ 40 pb σ 30 pb X James Ferrando Isolated Leptons at HERA 8 / 30

9 e Candidate HERA H and ZEUS Isolated Leptons Backgrounds Example Events History Well isolated electron Large hadronic activity not back-to-back with electron James Ferrando Isolated Leptons at HERA 9 / 30

10 µ Candidate HERA H and ZEUS Isolated Leptons Backgrounds Example Events History ZEUS James Ferrando Isolated Leptons at HERA / 30

11 HERA I results HERA H and ZEUS Isolated Leptons Backgrounds Example Events History Electron Muon e ± p obs./exp. obs./exp. (W ± contribution) (W ± contribution) Full sample /.54 ±.50 (7%) 8 / 2.94 ± 0.50 (86%) H pt X > 25GeV 5 /.76 ± 0.30 (82%) 6 /.68 ± 0.30 (88%) 8.4 pb pt X > 40GeV 3 / 0.66 ± 0.3 (80%) 3 / 0.64 ± 0.4 (92%) In isolated lepton in HERA I data H observed an excess over the SM in both electron and muon channels. Excess was not confirmed by ZEUS in similar analyses In the τ channel ZEUS observed 2/0.2 ± 0.05 (45%) events at PT X > 25 GeV James Ferrando Isolated Leptons at HERA / 30

12 This Seminar HERA H and ZEUS Isolated Leptons Backgrounds Example Events History In this seminar I present recent results on Isolated lepton : H Isolated (e,µ) searches with full HERA luminosity (Hprelim ) ZEUS Isolated (e,µ) searches with full HERA luminosity (ZEUS-prel-07-02) Combined H+ZEUS Isolated Lepton (e,µ) searches ( Hprelim-0762/ZEUS-prel ) In addition: H Single W production results Single top Production at HERA Possible interpretations in terms of RPV SUSY James Ferrando Isolated Leptons at HERA 2 / 30

13 Selection H results ZEUS results H + ZEUS Working Group Results A large amount of work has been done by H and ZEUS analysis teams to ensure compatibility of searches James Ferrando Isolated Leptons at HERA 3 / 30

14 H Results H results ZEUS results H + ZEUS Working Group Results James Ferrando Isolated Leptons at HERA 4 / 30

15 H Results H results ZEUS results H + ZEUS Working Group Results miss + l+p T events at HERA I+II (e p, 294 pb ) miss - l+p T events at HERA I+II (e p, 84 pb ) Events 2 H Data (prelim.) All SM Signal N Data = 4 = 34.5 ± 4.8 N SM Events 2 H Data (prelim.) All SM Signal N Data = 8 = 24.4 ± 3.4 N SM X P T (GeV) e and µ channels X P T (GeV) e and µ channels James Ferrando Isolated Leptons at HERA 5 / 30

16 ZEUS results H results ZEUS results H + ZEUS Working Group Results Events 2 miss - e, µ + P events at ZEUS (e p 206 pb ) T ZEUS (prel.) SM MC W Prod. MC Events X P T (GeV) miss + e, µ + P events at ZEUS (e p 286 pb ) T ZEUS (prel.) SM MC W Prod. MC No excess visible in ZEUS search in either e + p or e p data set SM (dominated by W production) describes data well X P T (GeV) James Ferrando Isolated Leptons at HERA 6 / 30

17 ZEUS results H results ZEUS results H + ZEUS Working Group Results James Ferrando Isolated Leptons at HERA 7 / 30

18 H+ZEUS H results ZEUS results H + ZEUS Working Group Results In 2006 H+ZEUS working groups were formed with a view to producing final combined results on important topics One such group was assembled with a view to producing combined results on searches Comparisons of phase space explored by different experiments were made Having established compatibility of searches, the results were combined James Ferrando Isolated Leptons at HERA 8 / 30

19 Combined results e + p data H results ZEUS results H + ZEUS Working Group Results miss e, µ + P events at HERA I+II (e + p, 0.58 fb ) T miss e, µ + P events at HERA I+II (e + p, 0.58 fb ) T Events 2 H+ZEUS Data (prelim.) All SM Signal N Data N SM = 57 = 53. ± 6.4 Events 2 H+ZEUS Data (prelim.) All SM Signal N Data N SM = 57 = 53. ± X (GeV) P T HERA Exotics Working Group lν (GeV) M T overflow HERA Exotics Working Group James Ferrando Isolated Leptons at HERA 9 / 30

20 Combined results e ± p data H results ZEUS results H + ZEUS Working Group Results Events 2 miss e, µ + P events at HERA I+II (e ± p, 0.97 fb ) T H+ZEUS Data (prelim.) All SM Signal N Data N SM = 87 = 92.7 ±.2 Events 2 miss e, µ + P events at HERA I+II (e ± p, 0.97 fb ) T H+ZEUS Data (prelim.) All SM Signal N Data N SM = 87 = 92.7 ± X (GeV) P T HERA Exotics Working Group lν (GeV) M T overflow HERA Exotics Working Group James Ferrando Isolated Leptons at HERA 20 / 30

21 Combined Results H results ZEUS results H + ZEUS Working Group Results James Ferrando Isolated Leptons at HERA 2 / 30

22 Single Top via FCNC RPV SUSY The results of the searches have implications for: Single W production cross section at HERA Hprelim-076 σ W =.23 ± 0.25 (Stat) ± 0.22 (Sys) pb Single top production at HERA via FCNC FCNC limits Some RPV SUSY models James Ferrando Isolated Leptons at HERA 22 / 30

23 Single Top Production Single Top via FCNC RPV SUSY BSM candidate for excess of high P T isolated leptons at large PT X is single top production via anomalous FCNC v tuz H Preliminary (HERA I+II) Excluded Excl. by ZEUS Excl. by CDF Excl. by L3 κ tcγ = v tcz = 0 m t = 75 GeV κ tuγ LEP and TeVatron are sensitive to these couplings too Phys. Lett. B (2003) Hprelim-0763 James Ferrando Isolated Leptons at HERA 23 / 30

24 RPV SUSY? Single Top via FCNC RPV SUSY 4 e + p t ~ bχ γq Wq 3 3 m 2 χ ± Possible interpretation of excess For many RPV scenarios: [ 4 GeV 2 ] m 2 y m 2 x [4 GeV 2 ] = m 2 t [ (E b p z b )/2E e] 2E e (E b + p z b ) () m 2 χ + Eur. Phys. J. C5 543 (2007) m 2 t ~ [ 4 GeV 2 ] m 2 y m 2 x [4 GeV 2 ] James Ferrando Isolated Leptons at HERA 24 / 30

25 have been performed for isolated leptons in events with large missing transverse momentum using the full HERA data set Excess over the standard model at high PT X observed by H in HERA I data remains in e + p data ZEUS has not confirmed the H excess H and ZEUS have set up a working group to produce final combined results on isolated leptons: W production cross section BSM limits James Ferrando Isolated Leptons at HERA 25 / 30

26 Significance Significance of H excess H Generic Search H Isolated Tau E. Perez Ringberg Oct O. Behnke DESY PRC Oct James Ferrando Isolated Leptons at HERA 26 / 30

27 Significance Significance of H excess H Generic Search H Isolated Tau The highest significance in e + p data taking for the H analysis alone was 3.7σ The e + p preliminary H only has a significance 3.0σ Combining with ZEUS one obtains.7σ! James Ferrando Isolated Leptons at HERA 27 / 30

28 3 4 5 Generic Search Significance of H excess H Generic Search H Isolated Tau Events Events j-j e-j j-j µ-j e-j j-ν µ-j e-ν j-ν e-e e-ν e-µ e-e µ-µ e-µ j-γ µ-µ e-γ j-j-j j-γ e-j-j H General Search, HERA II e + p (78 pb ) e-γ j-j-ν j-j-j e-e-j e-j-j e-e-e j-j-ν e-j-ν e-j-ν µ-j-ν e-j-γ µ-j-ν H Data (prelim.) j-ν-γ j-j-γ SM e-j-j-j e-j-γ j-j-j-ν e-j-j-j j-j-j-j H Data (prelim.) SM j-j-j-ν ) p (59 pb - j-j-j-j-ν H General Search, HERA II e j-j-j-j Hprelim H performed a generic search in final states with 2 high P T obects: e,µ,jets,γ,ν P T > 20 GeV < θ < 40 Classify by final state SM predictions for all HERA processes Good agreement of event yields with SM expectation for most classes James Ferrando Isolated Leptons at HERA 28 / 30

29 Generic Search Significance of H excess H Generic Search H Isolated Tau Number of Event Classes Number of Event Classes + H General Search, HERA II e p (78 pb ) Σ P T Scan H Data (prelim.) MC Experiments log P - H General Search, HERA II e p (59 pb ) Σ P T Scan H Data (prelim.) MC Experiments PT and M all inv distributions checked Distribution of P-values in good agreement with expectation of SM log P James Ferrando Isolated Leptons at HERA 29 / 30

30 H τ Significance of H excess H Generic Search H Isolated Tau τ + P miss + events at HERA I + II (e p, 287 pb ) T τ + P miss - events at HERA I + II (e p, 84 pb ) T Events 2 H Data (prelim.) All SM Signal N Data = N SM =.8 ±.8 Events 2 H Data (prelim.) All SM Signal N Data = N SM = 8.6 ± X X P T / GeV P T / GeV τ sample much less pure than e, µ No excess visible in data James Ferrando Isolated Leptons at HERA 30 / 30