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Search for Lepton + Photon + MET + b and
for ttbar+Photon Event at CDF
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We present a search for Lepton + Photon + MET + b (ttbar + photon
events) produced in p pbar collisions at sqrt(s)= 1.96 TeV using 929
pb-1 of data taken with the CDF detector in Run II at the
Tevatron. The experimental signature for this search is a high
energy lepton, a high energy photon, at least one high energy
b-tagged jet, and large missing transverse momentum. This signature
is possible in models based on gauge-mediated Supersymmetry and
other extensions of the Standard Model. The ttbar+photon is a
control sample for ttbar+Higgs production at the LHC and is a direct
probe of the charge of top quark. In the signature of 15
Lepton+Photon+MET+b events we observe versus a standard model
expectation of 14.3 +- 1.6 events. We find 10
Lepton+Photon+MET+b with H_T > 200 GeV events versus an expectation of 7.2 +- 1.0
events and we find 7 ttbar+Photon events (H_T > 200 GeV and N_jets > 2)versus an expectation of 3.6+- 0.8
events
We have estimated the background due to events with jets misidentified as lepton+photon+MET+b signature by studying the total P_T of tracks in a cone in eta-phi space of radius R=0.4 around the lepton track (track isolation). We compared distribution of track isolation in our signal sample to that of the Zee and Zmumu samples (for the electron and the muon channels, respectively) and to that of the QCD background sample (generic jet sample, dominated by light-flavor jets).
The number of "jet faking photon" events expected in the lepton+photon+MET+b signature is determined by measuring the jet E_T spectrum in lepton+jet+MET+b samples, and then multiplying by the probability of a jet being misidentified as a photon, which is measured in data samples triggered on jets.
The number of "electron faking photon" events expected in the lepton+photon+MET+b signature is determined by measuring the photon E_T spectrum in lepton+electron+MET+b samples, and then multiplying by the probability of an electron being misidentified as a photon, which is measured in Zee events in which one of the electrons radiates a high-E_T photon.
To estimate the size of the mistag background, each jet in the lepton+photon+MET+pretagged jet sample is weighted by its mistag rate. The mistag rate per jet is measured using a large inclusive-jet data sample.
Tau faking photon background is estimated from ttbar pythia sample by selecting tau -> hadrons -> photon events using MC information and then applying same analysis cuts as for data.
The production of semileptonic ttbar+photon with one of the W bosons decaying leptonically (e, mu and tau channels), and another hadronically is estimated from the MadGraph MC. The production of dileptonic ttbar+photon with both W bosons decaying leptonically (e, mu and tau channels) is also estimated from the MadGraph MC. The SM background from a production W boson and a photon, accompanied by QCD production of heavy flavor quarks in the processes Wbbar+photon, Wccbar+photon, and Wc+photon, is estimated from MadGraph MC.
Backgrounds from WW, ZZ, single top + photon are estimated to be negligible.
| Lepton + Photon + Missing Transverse Energy + B-jet Table | |
|---|---|
| A comparison of the numbers of events predicted by the
Standard Model and the observations for the
Lepton+Photon+Missing Transverse Energy + b search.
PS or PDF or JPG, |
| Lepton + Photon + Missing Transverse Energy + B-jet Plots | |
| The distributions for events in the Lepton+Photon+Missing
Transverse Energy + b sample (points) in a) the E_T of the
lepton, b) the Missing Transverse Energy, c) the E_T of the
b-jet, and d) the E_T of photon. The histograms show the
expected SM contributions, including estimated backgrounds from
misidentified photons and leptons.
PS or PDF or JPG, |
| Lepton + Photon + Missing Transverse Energy + B-jet H_T Plot | |
| The distributions in Number of Jets and H_T, observed
in the Lepton+ Photon+MET+B-jet inclusive search. The histograms
show the expected SM contributions. We apply the same cuts to
the ttbar+Photon events as to the
Lepton+Photon+Missing Transverse Energy + b with two
additional cuts H_T > 200 GeV and N_jets > 2
PS or PDF or JPG, |
| Lepton + Photon + Missing Transverse Energy + B-jet with H_T > 200 GeV Table | |
| A comparison of the numbers of events predicted by the
Standard Model and the observations for the
Lepton+Photon+Missing
Transverse Energy + b with H_T > 200 GeV search.
PS or PDF or JPG, |
| Lepton + Photon + Missing Transverse Energy + B-jet with H_T > 200 GeV Plots | |
| The distributions for events in the Lepton+Photon+Missing
Transverse Energy + b with H_T > 200 GeV
sample (points) in a) the E_T of the lepton, b) the Missing
Transverse Energy, c) the E_T of the b-jet, and d) the E_T of
photon. The histograms show the expected SM contributions,
including estimated backgrounds from misidentified photons and
leptons.
PS or PDF or JPG, |
| The distributions in H_T and Number of Jets, observed
in the Lepton+ Photon+MET+B-jet inclusive search with H_T > 200 GeV.
The histograms
show the expected SM contributions.
PS or PDF or JPG, |
| TTbar + Photon Table | |
| A comparison of the numbers of events predicted by the
Standard Model and the observations for the
ttbar+Photon search.
PS or PDF or JPG, |
| Suggested Slide | |
| Suggested slide for ttbar+Photon Search
PS or PDF or JPG, |
