Multi Lepton events at HERA

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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./??

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/??

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

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/??

! 3.5 7 0-80. -90. 0. 90. -2. 0. 2. 4. Di Muons at H Data taking: 999 00 Lumi used: 70.9 pb Muon Selection Track in both CTD and Muon Detector Angular region: For low momentum s: Track + MIP Run 276837 Event 8928 Class: 8 0 6 20 22 23 24 27 29 Date 6/02/2002 R Z E[GeV] (DCLU) ϕ[degree] 80. -4. 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/??

Di Muons at H: Cross section [pb/gev] dσ/dm µ,µ - σ SM ) / σ SM (σ 0 0-0 -2 0-3 0-4 3 2 0 - H Muon Pair Analysis 6 H DATA (Prelim.) SM (GRAPE) γ γ (LPAIR) γ γ ττ µµ bb + cc Υ µµ 0 Z µµ 0 20 50 00 [GeV] M µ,µ Total Cross Section: Good Agreement w/ SM: [pb/gev] µ dσ/dp t - σ SM ) / σ SM (σ 0 0-0 -2 0-3 3 2 0-46.5 H Muon Pair Analysis H DATA (Prelim.) SM (GRAPE) γ γ (LPAIR) γ γ ττ µµ bb + cc Υ µµ 0 Z µµ 0 20 30 40 50 60 70 80 [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/??

Di Muons at H: Cross section [pb/gev] /dm µ,µ dσ ela - σ SM ) / σ SM (σ 0 0-0 -2 0-3 0-4 3 2 0 - H Muon Pair Analysis (ep epµµ) H DATA (Prelim.) SM (GRAPE) 20 40 60 80 00 20 [GeV] [pb/gev] /dm µ,µ dσ inel - σ SM ) / σ SM (σ M Elastic µ,µ Inelastic Cross Section: Good Agreement w/ SM: 0 0-0 -2 0-3 0-4 3 2 0 - H Muon Pair Analysis (ep eµµ X) H DATA (Prelim.) SM (GRAPE) 20 40 60 80 00 20 [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/??

Di Muons at ZEUS Data taking: 997 00 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 0 2 0 0-0 -2 ZEUS ZEUS (prel.) 97-00 GRAPE 20 40 60 80 00 20 40 60 80 M µµ (GeV) Good Vertex: 40 cm, 0.5 cm Acollinearity: -0.995 [ Details on MC] A.Parenti - Multi Lepton Events at HERA p.8/??

Multi electrons at H Data taking: 994 00 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/??

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/??

Events Events 60 40 20 0 20 0 0 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 0 2 0 0-0 -2 0 0-0 -2 2e 0 20 P miss (GeV) T 3e 0 20 miss (GeV) P T Events Events 0 2 0 0-0 0-2e 0 20 40 P hadrons (GeV) T 3e 0 20 40 P hadrons (GeV) T GRAPE: interaction + & conversion NC DIS + Compton: fake 2e 3e events A.Parenti - Multi Lepton Events at HERA p./??

Multi electrons at H: electron variables H Preliminary Multi-electron Analysis Events 0 2 2e 0 0-0 -2 0 50 P e T (GeV) Events 0 2 2e 0 0-0 -2 0 50 P e2 T (GeV) H Data 5 pb - GRAPE NC-DIS+Compton Events 0 3e Events 0 3e Events 0 3e 0-0 20 40 P e T (GeV) 0-0 20 40 P e2 T (GeV) 0-0 20 P e3 T (GeV) Three 2e events with 50 GeV (but low SM expectation) A.Parenti - Multi Lepton Events at HERA p.2/??

Multi electrons at H: Mass distributions Events 0 2 0 H Preliminary Multi-electron Analysis H Data 5 pb - GRAPE NC-DIS 2e +Compton P T e+p T e2 (GeV) 50 00 2e L MC(GRAPE) 500 L DATA highest Harder = Mass of two electrons for 2e 0-50 At 00 GeV Events 0-2 0 0-0 -2 0 50 00 50 M 2 (GeV) 3e 0 50 00 50 M 2 (GeV) P T e+p T e2 (GeV) 0 50 00 50 0 0 50 00 50 M 2 (GeV) 3e L MC(GRAPE) 500 L DATA 0 50 00 50 M 2 (GeV) 2e events: 3 found 0.25 0.05 expected 3e events: 3 found 0.23 0.04 expected A.Parenti - Multi Lepton Events at HERA p.3/??

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 0-3 20 30 40 50 60 M 2 (GeV) [ More cross sections] A.Parenti - Multi Lepton Events at HERA p.4/??

Multi electrons at H: Overview Selection DATA SM GRAPE NC-DIS + Compton Visible 2e 05 8.2 2.8 * 93.3.5 25.0 5.5 Visible 3e 6 2.6 3.0 2.5 3.0 0. 0. Visible 4e or more 0 0. 0.0 0. 0.0 0.0 0.0 subsample 4 48.3 6. 46.4 6..9 0.9 Visible 2e Visible 3e * Statistical 00 3 0.25 0.05 0.2 0.04 0.04 0.03 00 3 0.23 0.04 0.23 0.04 0.00 0.00 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/??

Multi electrons at ZEUS Data taking: 994 00 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/??

Multi electrons at ZEUS: electron variables events events 0 2 0 0-0 -2 0 2 0 0-0 -2 ZEUS (prel.) 94-00 GRAPE+NC+QEDC NC+QEDC QEDC ZEUS a) 0 20 40 60 80 00 E T, (GeV) c) 0 20 40 60 80 00 E T,2 (GeV) events events 0 2 0 0-0 2 0 0 - b) 0 2 3 θ e, (rad) d) 0 2 3 θ e,2 (rad) Good Agreement A.Parenti - Multi Lepton Events at HERA p.7/??

Multi electrons at ZEUS: Mass distribution ZEUS events 0 2 ZEUS (prel.) 94-00 GRAPE+NC+QEDC 0 0 - NC+QEDC QEDC Two events w/ 00 GeV; expected.2 0. 0-2 0 20 40 60 80 00 20 40 M 2 (GeV) A.Parenti - Multi Lepton Events at HERA p.8/??

Multi electrons at ZEUS: Overview Type Data SM GRAPE NC DIS Compton 2e sample 2e 9 23.9 3.9 * 82.2.2 23.9 3.7 7.8 0.5 30 GeV 6 5.7 0.3 4.4 0.2 0.9 0.2 0.4 0. 00 GeV 2 0.77 0.08 0.47 0.05 0.2 0.06 0.8 0.03 3e sample 3e 26 34.7 0.5 34.7 0.5 - - 30 GeV 2.43 0.08.43 0.08 - - 00 GeV 0 0.37 0.04 0.37 0.04 - - * Only Statistical Error A.Parenti - Multi Lepton Events at HERA p.9/??

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/??

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) = 45 20 GeV (keeps 95% of signal) Wrong Charge cut: If ( ), events with ( ) are rejected A.Parenti - Multi Lepton Events at HERA p.2/??

at H: Overview (GeV) electron analysis ( 2e + 3e ) muon analysis 00 0 0.23 0.46 4.72 0 0.0 0.3 2.25 20 0.09 0.43.77 0 0.0 0.26 0.80 50 0 0.02 0.32 0.37 0 0.0 0.20 0.5 * 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/??

Search for at H: Limits H Higgs search: H ±± limits σ*br (pb) 0.4 0.3 H preliminary Observed Limit Expected Limit h ee Excluded via Bhabha Scattering SLAC+PETRA 0.2 0. 0.09 0.08 0.07 0.06 0.05 0.04 H µµ H ee 80 90 00 0 20 30 40 50 M H (GeV) Left Plot: Limit of 0-0 -2 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 0 50 00 50 200 250 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/??

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, 0.25+0.23 expected) production was analysed (and excluded) by H as explanation for the excess A.Parenti - Multi Lepton Events at HERA p.24/??

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

The H Detector. Liquid Argon CAL Muon Detectors Angular coverage: Thickness: 20 30 (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/??

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/?? ]

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/??

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/??

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 0.8 0.6 0.4 Efficiency 0.8 0.6 0.4 0.2 0.2 0 0 0 20 30 40 50 60 70 80 P T el (GeV) 0 0 20 40 60 80 00 20 40 60 80 θ el (degrees) Quite flat, high efficiency; well described by MC A.Parenti - Multi Lepton Events at HERA p.30/??

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 0 2 0 Events 0 H data (PRELIMINARY) NC GRAPE Comptons 0 0 20 30 40 50 60 70 80 90 00 P T e2 (GeV) 0 0 20 30 40 50 60 70 80 90 00 P T e2 (GeV) In both cases, BKG described by MC A.Parenti - Multi Lepton Events at HERA p.3/??

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 0-0.5 0 0.5.5 2 2.5 3 3.5 4 4.5 Number of photon associated tracks 0 20 30 40 50 60 70 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/??

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/??

Multi electrons at H: Cross Section H Preliminary Multi-electron Analysis H Preliminary Multi-electron Analysis dσ/dp T hadrons (pb/gev) 0-0 -2 H Preliminary SM (GRAPE) dσ/dp T e (pb/gev) 0-0 -2 H Preliminary SM (GRAPE) 0-3 0 5 0 5 20 25 P T hadrons (GeV) 0-3 0 2 4 6 8 20 22 24 P T e (GeV) [ Back] A.Parenti - Multi Lepton Events at HERA p.34/??

The ZEUS Detector. Central Tracking Detector Barrel Rear Muon Detector Uranium Calorimeter Angular coverage: Thickness: 20 25 (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/??

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/??

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/??

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/??

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/??

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