Top Jets at the LHC

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We investigatethe reconstruction of high pT hadronically-decaying top quarksat the Large Hadron Collider. One of the main challenges in identifying energetictop quarks is that the decay products become increasingly collimated. This reducesthe efficacy of conventional reconstruction methods that exploit the topology of thetop quark decay chain. We focus on the cases where the decay products of the topquark are reconstructed as a single jet, a"top-jet." The most basic"top-tag" methodbased on jet mass measurement is considered in detail. To analyze the feasibility ofthe top-tagging method, both theoretical and experimental aspects of the large QCDjet background contribution are examined. Based on a ... continued below

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47

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Almeida, L.G.; Lee, S.J.; Perez, G.; Sung, I. & Virzi, J. October 6, 2008.

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We investigatethe reconstruction of high pT hadronically-decaying top quarksat the Large Hadron Collider. One of the main challenges in identifying energetictop quarks is that the decay products become increasingly collimated. This reducesthe efficacy of conventional reconstruction methods that exploit the topology of thetop quark decay chain. We focus on the cases where the decay products of the topquark are reconstructed as a single jet, a"top-jet." The most basic"top-tag" methodbased on jet mass measurement is considered in detail. To analyze the feasibility ofthe top-tagging method, both theoretical and experimental aspects of the large QCDjet background contribution are examined. Based on a factorization approach, wederive a simple analytic approximation for the shape of the QCD jet mass spectrum.We observe very good agreement with the Monte Carlo simulation. We consider high pT tt bar production in the Standard Model as an example, and show that our theoretical QCD jet mass distributions can efficiently characterize the background via sideband analyses. We show that with 25 fb-1 of data, our approach allows us to resolve top-jets with pT _> 1 TeV, from the QCD background, and about 1.5 TeV top-jets with 100 fb-1, without relying on b-tagging. To further improve the significancewe consider jet shapes (recently analyzed in 0807.0234 [hep-ph]), which resolve thesubstructure of energy flow inside cone jets. A method of measuring the top quarkpolarization by using the transverse momentum of the bottom quark is also presented.The main advantages of our approach are: (i) the mass distributions are driven byfirst principle calculations, instead of relying solely on Monte Carlo simulation; (ii) for high pT jets (pT _> 1 TeV), IR-safe jet shape variables are robust against detectorresolution effects. Our analysis can be applied to other boosted massive particlessuch as the electroweak gauge bosons and the Higgs.

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47

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  • Journal Name: Physical Review Letter

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  • Report No.: LBNL-1364E
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 946061
  • Archival Resource Key: ark:/67531/metadc900892

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  • October 6, 2008

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  • Sept. 27, 2016, 1:39 a.m.

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  • Oct. 3, 2016, 4:24 p.m.

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Almeida, L.G.; Lee, S.J.; Perez, G.; Sung, I. & Virzi, J. Top Jets at the LHC, article, October 6, 2008; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc900892/: accessed January 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.