Search for Di-electron + Photon Production at CDF In Run II

Heather Gerberich and Ashutosh Kotwal

Results as of February 5, 2004:

  • Introduction
  • Background Prediction
  • Contact Interaction Model Total Signal Acceptance
  • Gauge Mediated Model Total Signal Acceptance
  • eegamma Candidate Events
  • Results
  • Contact Interaction Model Results
  • Gauge Mediated Model Results
  • Introduction

    This signature based search with a resonance in the e gamma channel is geared toward the production of excited or exotic electron as in the following reaction p + pbar --> e* + e --> e gamma + e. Excited electrons are expected in many compositeness models. We use a model for excited fermions based on their coupling to quarks and leptons via contact interaction that is described by an effective four-fermion Lagrangian (Baur, U. Phys Rev D 42, 3). The cross section for this model depends on both the e* mass and the compositeness scale, Lambda.

    Link to contact interaction Feynmann diagram eps file

    Additionally we search for the production of excited electrons via gauge mediated interaction (Baur, U. Phys Rev D 42, 3). Again, the cross section depends on both the e* mass and the compositeness scale, Lambda.

    Link to gauge mediated Feynmann diagram eps file

    We have searched ~200 pb-1 of CDF Run 2 data (Feb, 2002-Sep, 2003) for evidence of e* production.

    Background Prediction

    A benefit of searching for eegamma production is the absense of significant background. The primary sources of background are Zgamma, Z+jet (where a jet fakes a photon), WZ (where an electron is misidentified as a photon, W+jets (where one jet fakes a photon and one jet fakes electrons), multijet background (where one jet fakes a photon and two jets fake electrons), and diphoton+jet (where a jet fakes an electron). We use U. Baur's ZGAMMA program to predict the Zgamma contribution and PYTHIA for WZ and diphoton+jet. We have calculated and applied the fake rates needed for the processes involving jets. This link has the integrated background number of events prediction as a function of the three body masss. Additionally, we plot two distributions: the number of M(e+gamma) entries and the number of events as a function of M(e+e+gamma).

    Link to stacked backgrounds for M(e+gamma) eps file

    Link to background prediction with error band for M(e+gamma) eps file

    Link to stacked backgrounds for M(e+e+gamma) eps file

    Link to background prediction with error band for M(e+e+gamma) eps file

    Total Signal Acceptance

    Contact Interaction Model Total Signal Acceptance

    We estimate the total acceptance for the production of excited electrons via contact interactions using PYTHIA and then full reconstruction through CDF run II simulation.

    Link to contact interaction total acceptance eps file

    Gauge Mediated Model Total Signal Acceptance

    We estimate the total acceptance for the production of excited electrons via gauge mediated interaction using CompHEP and then full reconstruction through CDF run II simulation.

    Link to gauge mediated interaction total acceptance eps file

    eegama Candidate Events

    We search ~200/pb of data for events which pass our selection requirements. We find three candidate events.

  • Run 144674 event 4143240
  • Run 147806 event 1167222
  • Run 167866 event 443088
  • Run 144674 event 4143240

    Run 144674 event 4143240 is had a central electron (e1) and two plug EM objects (p1 and p2). Details for this event are found in the following table and event displays. The met, calculated from the beam constrained track vertex of the electron, is 21 GeV.

    e p1 p2
    Et (GeV) 37 71 48
    det eta -0.87 1.48 -1.47
    eta -1.01 1.27 -1.65
    phi 0.62 4.05 2.02
    M(e+p1) (GeV) M(e+p2) (GeV) M(p1+p2) (GeV) M(e+p1+p2) (GeV)
    176 61 257 318

    Link to COT display eps file for Run 144674 event 4143240. track pt cut 0.5 GeV.

    Link to physics towers LEGO display eps file for Run 144674 event 4143240. tower et cut 0.5 GeV.

    Run 147806 event 1167222

    Run 147806 event 1167222 has two central electrons (e1 and e2) and one EM plug object (p1). Details for this event are found in the following table and event displays. The event met is 13 GeV, as calculated from the beam constrained vertex of electron (e1). This event also has a fourth EM object, a plug object (p2) with et=26 GeV, eta_d = 1.51, eta=1.53, and phi=5.08. This object almost passes the plug EM object selection criteria with associated identification variables isolation ratio= 0.107, PEM chi^2=9.1, and Had/EM = 0.02.

    e1 e2 p1 p2
    Et (GeV) 44 42 46 26
    det eta 0.81 -0.19 1.46 1.51
    eta 0.83 -0.17 1.46 1.53
    phi 3.64 1.96 0.92 5.08
    M(e1+e2) (GeV) M(e1+p1) (GeV) M(e2+p1) (GeV) M(e+p1+p2) (GeV)
    78 92 92 152
    M(e1+p2) (GeV) M(e2+p2) (GeV) M(p1+p2) (GeV) M(e1+e2+p2) (GeV) M(e1+p1+p2) (GeV) M(e2+p1+p2) (GeV) M(e1+e2+p1+p2) (GeV)
    51 91 60 131 121 143 194

    Link to COT display eps file for Run 147806 event 1167222Run. track pt cut 0.5 GeV.

    Link to physics towers LEGO display eps file for Run 147806 event 1167222. tower et cut 0.5 GeV.

    Run 167866 event 443088

    Run 167866 event 443088 has two central electrons (e1 and e2) and one central photon (gamma). Details of this event can be found in the following table and the events displays. The event has met = 11 GeV, as calculated from the beam constrained track vertex of the maximum et electron (e1). There is fourth jet in the event with E_T ~ 25 GeV, eta_d=-0.42, and phi=3.16.

    e1 e2 gamma
    Et (GeV) 165 96 73
    det eta 0.05 0.53 -0.32
    eta -0.03 0.46 -0.29
    phi 1.72 5.00 5.02
    M(e+p1) (GeV) M(e+p2) (GeV) M(p1+p2) (GeV) M(e+p1+p2) (GeV)
    256 220 64 344

    Link to COT display eps file for Run 167866 event 443088. track pt cut 0.5 GeV.

    Link to physics towers LEGO display eps file for Run 167866 event 443088. tower et cut 0.5 GeV.

    Integrated Background Prediction

    The following plot shows the integral of predicted background events from high mass to low mass, at each three-body mass value. Overlaid are the observed events. Black for Run=147806 Event=1167222, blue for Run=144674 Event=4143240, and magenta for Run=167866 Event=443088..

    Link to integrated background prediction of number of events as a function of the three body mass. The following plot shows the integral of predicted background events from high mass to low mass, at each three-body mass value. Overlaid are the observed events. Black for Run=147806 Event=1167222, blue for Run=144674 Event=4143240, and magenta for Run=167866 Event=443088..

    Link to integrated background prediction of number of events as a function of the e-gamma invariant mass.

    Results

    We use a Bayesian approach to estimate the 95% confidence level upper limit on the number of expected events, and thus the upper limit on the cross section. Because the excited electron cross section depends on two parameters, we show an exclusion region.

    Contact Interaction Results

    There are currently no published limits for this model. For the case Me*=Lambda, Me*>889 GeV. The expected limit was 889 GeV.

    Link to contact interaction Lambda = Me* limit eps file

    2-D exclusion region: The contact interaction model is valid for Me* less than Lambda, so we plot Me*/Lambda vs Me*.

    Link to Lambda vs M exclusion region eps file

    Gauge Mediated Results

    For the case Me*=Lambda, the CDF Run II preliminary limit is Me*>208 GeV. The expected limit was 224 GeV.

    Link to gauge mediated Lambda = Me* limit eps file

    There are published limits for the gauge mediate model. The convention is to plot f/Lambda vs Me*. Below we show the results from H1 and ZEUS with the CDF Run II results overlaid. Although not plotted, L3 has set limits on f/Lambda ranging from 10^(-4) to 10^(-1)/GeV in the mass range from 100 to ~210 GeV (The L3 Collaboration, Search for Excited Leptons at LEP, June 2003, hep-ex/0306016 v1). The H1 results reference is (Adloff, C. et al, Search for Excited Electrons at HERA, July 2002, hep-ex/0207038 v1). The ZEUS results reference is (The ZEUS Collaboration, Searches for excited fermions in ep collisions at HERA, October, 2002, hep-ex/0109018 v2).

    Link to M/Lambda vs M exclusion region eps file