Multi Lepton events at HERA

Transcription

1 St. Petersburg, 25/04/2003 DIS03 Conference Multi Lepton events at HERA Andrea Parenti (on behalf of H and ZEUS Collabs.) Padova University and INFN A.Parenti - Multi Lepton Events at HERA p./??

2 Outline Introduction Di muon events at H and ZEUS Multi electron events at H and ZEUS Search for Doubly Charged Higgs at H Conclusions A.Parenti - Multi Lepton Events at HERA p.2/??

3 Introduction Multi lepton production at high proceeds mainly through 2 photon process: BKG to Multi e search: NC DIS (DIS + fake electron) Elastic Compton ( misidentified as ) SM expectation (QED) is well known; DATA MC comparison is a good test for new physics A.Parenti - Multi Lepton Events at HERA p.3/?? p e γ γ e l l + X

4 Multi lepton production at HERA a) b) p e e γ γ p γ γ q d) c) p e γ q q p e+ e γ e+ processes: dominate the cross section a) and b) c) Cabibbo Parisi process (elastic or inelastic): ) order of magnitude below (except at high d) Drell Yan process: negligible GRAPE Monte Carlo simulates a) b) and c) A.Parenti - Multi Lepton Events at HERA p.4/??

5 ! Di Muons at H Data taking: Lumi used: 70.9 pb Muon Selection Track in both CTD and Muon Detector Angular region: For low momentum s: Track + MIP Run Event 8928 Class: Date 6/02/2002 R Z E[GeV] (DCLU) ϕ[degree] η Y X Event Selection Two muons: Invariant mass cut: Muon Isolation: GeV, 5 GeV.0 in (or GeV 0.5 if GeV) [ Details on MC] [ Details on Syst. Uncertainties] A.Parenti - Multi Lepton Events at HERA p.5/??

6 Di Muons at H: Cross section [pb/gev] dσ/dm µ,µ - σ SM ) / σ SM (σ H Muon Pair Analysis 6 H DATA (Prelim.) SM (GRAPE) γ γ (LPAIR) γ γ ττ µµ bb + cc Υ µµ 0 Z µµ [GeV] M µ,µ Total Cross Section: Good Agreement w/ SM: [pb/gev] µ dσ/dp t - σ SM ) / σ SM (σ H Muon Pair Analysis H DATA (Prelim.) SM (GRAPE) γ γ (LPAIR) γ γ ττ µµ bb + cc Υ µµ 0 Z µµ [GeV].3 µ P t 4.7 pb Main contribution: interaction Small contribution to from:, and and decays 46.2 pb A.Parenti - Multi Lepton Events at HERA p.6/??

7 Di Muons at H: Cross section [pb/gev] /dm µ,µ dσ ela - σ SM ) / σ SM (σ H Muon Pair Analysis (ep epµµ) H DATA (Prelim.) SM (GRAPE) [GeV] [pb/gev] /dm µ,µ dσ inel - σ SM ) / σ SM (σ M Elastic µ,µ Inelastic Cross Section: Good Agreement w/ SM: H Muon Pair Analysis (ep eµµ X) H DATA (Prelim.) SM (GRAPE) [GeV] Inelastic 20.8 M µ,µ 0.9 Elastic and Inelastic separated by tagging proton remnant 3.3 pb 2.5 pb A.Parenti - Multi Lepton Events at HERA p.7/??

8 Di Muons at ZEUS Data taking: Lumi used: 05.2 pb Muon Selection Track in CTD ( Angular region: Event Selection Two muons: Muon Isolation: 5 GeV)+ MIP in CAL matched to muon chambers = 0 events ZEUS ZEUS (prel.) GRAPE M µµ (GeV) Good Vertex: 40 cm, 0.5 cm Acollinearity: [ Details on MC] A.Parenti - Multi Lepton Events at HERA p.8/??

9 Multi electrons at H Data taking: Event Selection Lumi used: 5.2 pb Two central ( ), isolated, electrons cut: Event Classification GeV, GeV 2e : Only 2 central electrons 3e/4e : Additional isolated electrons (also Forward and Rear) subsample Just 2 opposite charge electrons: 45 GeV (ie, ) Cleaner sample; scattered electron is lost in beam pipe; both detected electrons come from interaction A.Parenti - Multi Lepton Events at HERA p.9/??

10 Multi electron events at H Different topology for 2e and 3e events: A 2e event: A 3e event: Multi-electron Event M(2)=30 GeV Multi-electron Event M(2)=8 GeV PT=63 GeV PT=6 GeV PT=25 GeV PT=62 GeV PT=20 GeV preliminary preliminary = 20 GeV = 25 GeV, = 62 GeV = 63 GeV, = 30 GeV Harder in 2e = 8 GeV More forward s in 3e A.Parenti - Multi Lepton Events at HERA p.0/??

11 Events Events Multi electrons at H: global variables H Preliminary Multi-electron Analysis H Data 5 pb - 2e GRAPE NC-DIS +Compton 0 50 E-P z (GeV) 3e 0 50 E-P z (GeV) Events Events e 0 20 P miss (GeV) T 3e 0 20 miss (GeV) P T Events Events e P hadrons (GeV) T 3e P hadrons (GeV) T GRAPE: interaction + & conversion NC DIS + Compton: fake 2e 3e events A.Parenti - Multi Lepton Events at HERA p./??

12 Multi electrons at H: electron variables H Preliminary Multi-electron Analysis Events 0 2 2e P e T (GeV) Events 0 2 2e P e2 T (GeV) H Data 5 pb - GRAPE NC-DIS+Compton Events 0 3e Events 0 3e Events 0 3e P e T (GeV) P e2 T (GeV) P e3 T (GeV) Three 2e events with 50 GeV (but low SM expectation) A.Parenti - Multi Lepton Events at HERA p.2/??

13 Multi electrons at H: Mass distributions Events H Preliminary Multi-electron Analysis H Data 5 pb - GRAPE NC-DIS 2e +Compton P T e+p T e2 (GeV) e L MC(GRAPE) 500 L DATA highest Harder = Mass of two electrons for 2e 0-50 At 00 GeV Events M 2 (GeV) 3e M 2 (GeV) P T e+p T e2 (GeV) M 2 (GeV) 3e L MC(GRAPE) 500 L DATA M 2 (GeV) 2e events: 3 found expected 3e events: 3 found expected A.Parenti - Multi Lepton Events at HERA p.3/??

14 Multi electrons at H: Cross Section H Preliminary Multi-electron Analysis dσ/dm 2 (pb/gev) 0-2 H Preliminary SM (GRAPE) Extracted from sample Good Agreement w/ SM Good agreement also for and M 2 (GeV) [ More cross sections] A.Parenti - Multi Lepton Events at HERA p.4/??

15 Multi electrons at H: Overview Selection DATA SM GRAPE NC-DIS + Compton Visible 2e * Visible 3e Visible 4e or more subsample Visible 2e Visible 3e * Statistical Systematic Uncertainty DATA agree with SM at low Excess in DATA at high Possible explanation: doubly charged Higgs? A.Parenti - Multi Lepton Events at HERA p.5/??

16 Multi electrons at ZEUS Data taking: Event Selection Good Vertex : Two central ( 50 cm ) electrons: Lumi used: 30.5 pb GeV, 0 GeV A 2e event A.Parenti - Multi Lepton Events at HERA p.6/??

17 Multi electrons at ZEUS: electron variables events events ZEUS (prel.) GRAPE+NC+QEDC NC+QEDC QEDC ZEUS a) E T, (GeV) c) E T,2 (GeV) events events b) θ e, (rad) d) θ e,2 (rad) Good Agreement A.Parenti - Multi Lepton Events at HERA p.7/??

18 Multi electrons at ZEUS: Mass distribution ZEUS events 0 2 ZEUS (prel.) GRAPE+NC+QEDC NC+QEDC QEDC Two events w/ 00 GeV; expected M 2 (GeV) A.Parenti - Multi Lepton Events at HERA p.8/??

19 Multi electrons at ZEUS: Overview Type Data SM GRAPE NC DIS Compton 2e sample 2e * GeV GeV e sample 3e GeV GeV * Only Statistical Error A.Parenti - Multi Lepton Events at HERA p.9/??

20 Search for at H appears in various extensions to SM couples to level pairs at tree is a possible explanation of H excess in multi search H looked for coupled only to (ie, and = 0) p p p H ++(--) e +(-) h ee γ(z) p,x e -(+) e -(+) e +(-) h H ++(--) ee γ(z) h ee e +(-) H ++(--) γ(z) e -(+) p,x p,x A.Parenti - Multi Lepton Events at HERA p.20/??

21 Search for at H Uses samples and cuts from Multi electron and Di muon analyses Additional Cuts for electron (muon) analysis: Mass window: 0 GeV ( ) Transverse momentum cut: where (electron only) = GeV (keeps 95% of signal) Wrong Charge cut: If ( ), events with ( ) are rejected A.Parenti - Multi Lepton Events at HERA p.2/??

22 at H: Overview (GeV) electron analysis ( 2e + 3e ) muon analysis * From processes, and ** * conversions ** Expected signal if = 0.3 ** The efficiency on signal is high Only of 2e events survives the cuts (none of 3e ) cannot explain H excess in multi search H set limits on production A.Parenti - Multi Lepton Events at HERA p.22/??

23 Search for at H: Limits H Higgs search: H ±± limits σ*br (pb) H preliminary Observed Limit Expected Limit h ee Excluded via Bhabha Scattering SLAC+PETRA H µµ H ee M H (GeV) Left Plot: Limit of Excluded by OPAL LEP I Excluded by OPAL LEP II Pair Production HERA II - fb - Bhabha OPAL Single Production, BR(H ee)=00% OPAL Preliminary H Preliminary HERA II Sensitivity M H (GeV) Right Plot: Exclusion limits on, = 00%. Best results from LEP, but HERA will tell something new with higher luminosity A.Parenti - Multi Lepton Events at HERA p.23/??

24 Conclusions HERA collisions were analysed by H and ZEUS, in the search for di lepton events The major contribution to the process comes from QED: Monte Carlo simulations agree well with data, except 2e and 3e at high mass in H (3+3 events found, expected) production was analysed (and excluded) by H as explanation for the excess A.Parenti - Multi Lepton Events at HERA p.24/??

25 Additional Slides A.Parenti - Multi Lepton Events at HERA p.25/??

26 The H Detector. Liquid Argon CAL Muon Detectors Angular coverage: Thickness: (EM), 5 8 (HAD) Energy Resolution (EM, HAD): Forward Tracking Device Tracking Devices Central Tracking Device Muon Detectors LSTs ( Liquid Ar Calorimeter ): Forward Spectrometer ( Superconducting Coil ): Forward Tracking Device Coverage: Central Tracking Device Coverage: Back Ward Proport. Chamber [ To Multi e][ To Di ][ To ] Coverage: A.Parenti - Multi Lepton Events at HERA p.26/??

27 Monte Carlo samples: H Multi electrons analysis GRAPE: interaction + Cabibbo Parisi, and conversion (no Drell Yan) LPAIR: only in Weizsäcker Williams approximation DJANGO: NC DIS WABGEN: Elastic Compton Di muons analysis Signal simulation in search GRAPE: as above CompHEP computes cross section DIFFVM: LPAIR: resonance CTEQ4L for PDF s DGLAP eqt.s for parton shower AROMA: and decays PYTHIA for hadronization [ Back to Multi e] [ Back to Di ] [ Back to A.Parenti - Multi Lepton Events at HERA p.27/?? ]

28 Systematic Uncertainties at H Multi electron analysis PDF s of proton Cuts used in the generator Tracking Efficiency: 3 5% Energy Scales in CAL: 0.7 3% (EM), 2% (HAD) Trigger Efficiency: 3% Lumi measurement:.5% Di muon analysis Trigger Efficiency: 5.5% Muon ID: 5.8% Lumi measurement [ Back to Multi e] [ Back to Di ] A.Parenti - Multi Lepton Events at HERA p.28/??

29 Electron ID at H Three types of electrons: Central electrons ( track Forward electrons ( Backward electrons ( Isolation cut: Isolation cut: = 0 ): CAL deposit ( ): CAL deposit ( The ID procedure was tested for: Tracking Efficiency Electron Misidentification Photon Conversions ): CAL deposit ( 5 GeV) + CTD matched 0 GeV) 5 GeV) [ Back to Multi electron] A.Parenti - Multi Lepton Events at HERA p.29/??

30 Electron ID at H: Test of Tracking Efficiency NC DIS Selection: (Just) E.M. cluster in CAL, Central Region ( No tracking requirements ) GeV.2 H Multi-electron analysis : Tracking efficiency control.2 Neutral current selection H data (PRELIMINARY) Simulation Efficiency Efficiency P T el (GeV) θ el (degrees) Quite flat, high efficiency; well described by MC A.Parenti - Multi Lepton Events at HERA p.30/??

31 Electron ID at H: Electron Misidentification NC DIS Selection, plus second E.M. Cluster in CAL: Left: No tracking requirements Right: Loose tracking requirements Dominated by Compton Compton is suppressed 0 3 H Multi-electron analysis : No track requirement Fake 2 nd electron control Loose track requirement 0 2 Neutral current selection Events Events 0 H data (PRELIMINARY) NC GRAPE Comptons P T e2 (GeV) P T e2 (GeV) In both cases, BKG described by MC A.Parenti - Multi Lepton Events at HERA p.3/??

32 Electron ID at H: Photon Conversions Compton Enriched Sample: central electron E.M. cluster (photon candidate) No (significant) extra energy in CAL H Multi-electron analysis : Photon conversion control 0 3 Elastic Compton selection H data (PRELIMINARY) Events 0 2 NC GRAPE Comptons Events Number of photon associated tracks Starting radius of photon associated tracks (cm) DATA well described by MC Conversions in tracker walls (peaks in right plot) well described, too A.Parenti - Multi Lepton Events at HERA p.32/??

33 Di electrons at H: GRAPE Vs. LPAIR LPAIR simulates only process Good Agreement (within %) of LPAIR and ( only) GRAPE Effect of GRAPE additional diagrams: 20% total cross section increase 40% cross section increase at low mass ( conversions) and at mass A.Parenti - Multi Lepton Events at HERA p.33/??

34 Multi electrons at H: Cross Section H Preliminary Multi-electron Analysis H Preliminary Multi-electron Analysis dσ/dp T hadrons (pb/gev) H Preliminary SM (GRAPE) dσ/dp T e (pb/gev) H Preliminary SM (GRAPE) P T hadrons (GeV) P T e (GeV) [ Back] A.Parenti - Multi Lepton Events at HERA p.34/??

35 The ZEUS Detector. Central Tracking Detector Barrel Rear Muon Detector Uranium Calorimeter Angular coverage: Thickness: (EM), 4 7 (HAD) Energy Resolution (EM, HAD): Forward Muon Detector Calorimeter Central Tracking Device Angular Coverage: Muon Detectors Forward MUON detector: 25% up to GeV, Barrel Rear MUON: = 30 50% for 50 GeV, [ Back to Multi-e] [ Back to Di- ] A.Parenti - Multi Lepton Events at HERA p.35/??

36 Monte Carlo samples: ZEUS Multi electrons analysis GRAPE: interaction + Cabibbo Parisi, and DJANGO: NC DIS + Inelastic Compton conversion (no Drell Yan) COMPTON2.0: Elastic Compton Di muons analysis GRAPE: as above [ Back to Multi-e] [ Back to Di- ] A.Parenti - Multi Lepton Events at HERA p.36/??

37 Electron ID at ZEUS Three types of electrons: Central electrons ( ( 5 GeV) + DCA < 8 cm Forward electrons ( Backward electrons ( Isolation cut: Isolation cut: = 0, ): CAL deposit ( ): CAL deposit ( ): CAL deposit ( 0 GeV) + CTD track GeV) GeV) 0.3 GeV [ Back to Multi-e] A.Parenti - Multi Lepton Events at HERA p.37/??

38 A 2e event at ZEUS = 34 GeV = 56 GeV, =.34 rad, = 53 GeV, = 0.4 rad A.Parenti - Multi Lepton Events at HERA p.38/??

39 A 3e event at ZEUS = 94 GeV, = 0.76 rad, = 52 GeV, = 36 GeV, =.00 rad, = 0.58 rad = 47 GeV, A.Parenti - Multi Lepton Events at HERA p.39/??