Search Constraints
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Search Results
- Creator:
- Gao, Yongsheng and ATLAS Collaboration
- Description:
- A search is performed for top-quark pairs (t (t) over bar) produced together with a photon (gamma) with transverse energy greater than 20 GeV using a sample of t (t) over bar candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 fb(-1) of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 t (t) over bar gamma candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 +/- 26 and 120 +/- 39 non-t (t) over bar gamma background events, respectively. The production of t (t) over bar gamma events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The t (t) over bar gamma production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is sigma(fid)(t (t) over bar gamma) x BR = 63 +/- 8(stat)(-13)(+17) (syst) +/- 1(lumi) fb per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of 48 +/- 10 fb.
- Resource Type:
- Article
- Identifier:
- Publisher version: dx.doi.org/10.1103/PhysRevD.91.072007
- Campus Tesim:
- Fresno
- Creator:
- Hall, Raymond E. and D0 Collaboration
- Description:
- In this Letter we report on a search for long-lived particles that decay into final states with two electrons or photons. Such long-lived particles arise in a variety of theoretical models, such as hidden valleys and supersymmetry with gauge-mediated breaking. By precisely reconstructing the direction of the electromagnetic shower we are able to probe much longer lifetimes than previously explored. We see no evidence of the existence of such long-lived particles and interpret this search as a quasi model-independent limit on their production cross section, as well as a limit on a long-lived fourth generation quark.
- Resource Type:
- Article
- Identifier:
- Publisher version: dx.doi.org/10.1103/PhysRevLett.101.111802
- Campus Tesim:
- Fresno
- Creator:
- Haight, Katherine G., Striegler, Keith R., Berg, Gregory T., Gump, Barry H., Lake, Chris B., Clary, Carter D., Mayse, Mark A., and Chattan, Ondine
- Resource Type:
- Text
- Identifier:
- 1995_5, Box 2 C-E1, AVF: Proposals - 1996-97
- Campus Tesim:
- Fresno
- Creator:
- Gao, Yongsheng and ATLAS Collaboration
- Description:
- A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy √s = 7 TeV is presented. The measurement covers the pseudorapidity ranges |η|<1.37 and 1.52⩽|η|<2.37 in the transverse energy range 45⩽ET<400 GeV. The results are based on an integrated luminosity of 35 pb−1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.
- Resource Type:
- Article
- Identifier:
- doi: 10.1016/j.physletb.2011.11.010
- Campus Tesim:
- Fresno