Identification techniques for highly boosted W bosons that decay into hadrons

Abstract

Abstract:In searches for new physics in the energy regime of the LHC, it is becoming increasingly important to distinguish single-jet objects that originate from the merging of the decay products of W bosons produced with high transverse momenta from jets initiated by single partons. Algorithms are defined to identify such W jets for different signals of interest, using techniques that are also applicable to other decays of bosons to hadrons that result in a single jet, such as those from highly boosted Z and Higgs bosons. The efficiency for tagging W jets is measured in data collected with the CMS detector at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb −1 . The performance of W tagging in data is compared with predictions from several Monte Carlo simulators. The CMS collaboration 29 IntroductionThe LHC at CERN probes a new energy regime in particle physics, where searches for physics beyond the standard model (SM) at high mass scale often involve objects with large transverse momenta (p T ). In final states that contain the W ± and Z gauge bosons or Higgs bosons (H), it is possible to achieve a high selection efficiency through the use of hadronic decay channels. At sufficiently large boost above order of p T > 200 GeV, the final state hadrons from the W→ qq decay merge into a single jet, and the traditional analysis techniques relying on resolved jets are no longer applicable. However, in such cases the analysis of jet substructure can be used to identify those jets arising from decays of W, Z or H bosons. Because the values of the mass of the W and Z bosons are rather close to each other, we do not distinguish the two, and refer to such jets collectively as V jets, while the Higgs boson mass is significantly higher and can be distinguished. The focus -1 - JHEP12(2014)017of this paper is solely on the identification of W jets, however, we note that many of the procedures described are equally applicable for handling highly boosted Z and H bosons. Measurements of jet substructure observables related to identification of W bosons have been previously reported by CMS [1,2] and ATLAS [3,4]. Several searches at CMS have employed jet substructure techniques for identifying ("tagging") W jets and Z jets. These include searches in all-jet tt final states [5,6], single and pair produced V bosons in inclusive dijet final states [7,8], and searches in the VV final states, where one of the vector bosons decays leptonically [9,10]. In these searches, a variety of different observables have been used to identify the V jets. This paper aims to compare and measure the performance in 8 TeV pp collisions of various jet substructure techniques that can be used to distinguish V jets from more ordinary quark-and gluon-initiated jets, which we refer to as QCD jets.This paper is organized as follows. The CMS detector is described in section 2. The procedures chosen for the reconstruction of events are described in section 3. The data and simulated events used in our studies as well as the e...

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