Tracking down hyper-boosted top quarks

Journal of High Energy Physics, Jun 2015

Abstract The identification of hadronically decaying heavy states, such as vector bosons, the Higgs, or the top quark, produced with large transverse boosts has been and will continue to be a central focus of the jet physics program at the Large Hadron Collider (LHC). At a future hadron collider working at an order-of-magnitude larger energy than the LHC, these heavy states would be easily produced with transverse boosts of several TeV. At these energies, their decay products will be separated by angular scales comparable to individual calorimeter cells, making the current jet substructure identification techniques for hadronic decay modes not directly employable. In addition, at the high energy and luminosity projected at a future hadron collider, there will be numerous sources for contamination including initial- and final-state radiation, underlying event, or pile-up which must be mitigated. We propose a simple strategy to tag such “hyper-boosted” objects that defines jets with radii that scale inversely proportional to their transverse boost and combines the standard calorimetric information with charged track-based observables. By means of a fast detector simulation, we apply it to top quark identification and demonstrate that our method efficiently discriminates hadronically decaying top quarks from light QCD jets up to transverse boosts of 20 TeV. Our results open the way to tagging heavy objects with energies in the multi-TeV range at present and future hadron colliders.

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Tracking down hyper-boosted top quarks

Received: March Tracking down hyper-boosted top quarks Andrew J. Larkoski 0 1 3 Fabio Maltoni 0 1 2 Michele Selvaggi 0 1 2 B- 0 1 Louvain-la-Neuve 0 1 Belgium 0 1 0 Open Access , c The Authors 1 Universit ́e catholique de Louvain , Chemin du Cyclotron 2 2 Centre for Cosmology , Particle Physics and Phenomenology, CP3 3 Centre for Theoretical Physics, Massachusetts Institute of Technology The identification of hadronically decaying heavy states, such as vector bosons, the Higgs, or the top quark, produced with large transverse boosts has been and will continue to be a central focus of the jet physics program at the Large Hadron Collider (LHC). At a future hadron collider working at an order-of-magnitude larger energy than the LHC, these heavy states would be easily produced with transverse boosts of several TeV. At these energies, their decay products will be separated by angular scales comparable to individual calorimeter cells, making the current jet substructure identification techniques for hadronic decay modes not directly employable. In addition, at the high energy and luminosity projected at a future hadron collider, there will be numerous sources for contamination including initial- and final-state radiation, underlying event, or pile-up which must be mitigated. We propose a simple strategy to tag such “hyper-boosted” objects that defines jets with radii that scale inversely proportional to their transverse boost and combines the standard calorimetric information with charged track-based observables. By means of a fast detector simulation, we apply it to top quark identification and demonstrate that our method efficiently discriminates hadronically decaying top quarks from light QCD jets up to transverse boosts of 20 TeV. Our results open the way to tagging heavy objects with energies in the multi-TeV range at present and future hadron colliders. Contents 1 Introduction 2.1 2.2 3.1 Observables and methodology Jet finding and definition Track-based observables Detailed studies at fixed pT Mass distributions Substructure observables A Parametrised detector simulation A.1 Tracking A.2 Calorimetry B pT scan and results Introduction couple to heavy bosons and the top quark. applies to the heavy bosons of the SM. standard tools for jet analysis at ATLAS and CMS. separate them from background, or resolve combinatorics. pp → tt¯tt¯ pp → Z0 → tt¯ (mZ0 = 3 TeV) pp → Z0 → tt¯ (mZ0 = 15 TeV) pp → Z0 → tt¯ (mZ0 = 30 TeV) pp → t˜t˜ → tt¯+ E/ T (mt˜ = 1 TeV) pp → t˜t˜ → tt¯+ E/ T (mt˜ = 5 TeV) pp → t˜t˜ → tt¯+ E/ T (mt˜ = 10 TeV) pp → g˜g˜ → tt¯tt¯+ E/ T (mg˜ = 2 TeV) pp → g˜g˜ → tt¯tt¯+ E/ T (mg˜ = 5 TeV) pp → g˜g˜ → tt¯tt¯+ E/ T (mg˜ = 10 TeV) pT > 1 TeV pT > 5 TeV pT > 10 TeV Omitted entries have cross sections which are too small to be relevant. sections with final state W, Z, H bosons and top quarks can found in ref. [43]. approximately given by to the jet mass an amount greater than the mass of the top quark. I. Global-jet calorimetric information: distribution inside the jet is not. II. Inner-jet charged track information: sensitive to the internal structure of the jet only using charged particle tracks. III. Dynamic contamination removal: quark, for a fixed jet radius more perturbative QCD radiation is emitted as the pT the jet pT . This is similar to the variable R jet algorithm [45], with the important difference that in our method the clustering metric is not modified. plots of top tagging results for a wide range of jet pT . Observables and methodology colour-singlet bosons, in this work we will focus on top quark identification. Jet finding and definition the jet radius by the jet pT . The contribution from ISR (or UE) to the pT of the jet scales like R2 (proportional energy of the top, its effect on the jet mass m is approximately given by ' mt2op + pT pITSRR2 . direction of the W , in a region scaling like the characteristic angular size of the decay, mW /pT . increasing pT Rd.c. ∼ top quark when (simpler and possibly more robust) approach. and the dead-cone effect suppresses FSR in a region of angular size mtop/pT . radius to: applications are [27, 28, 48–50]. R = C from ISR as of the top quark decay products.3 We note that this coefficient should be optimised in products as possible. kT class of algorithms [51, 56–60] is modified to be dij = min[p2Tni, p2Tnj ]Ri2j , seeded cone jet algorithm with a radius that scales inversely with pT . Track-based observables fraction of final state radiation was captured into the jet. mtrk, R = 1.0 mtrk, R = 4 mtop / pT mtrk pT / ptTrk , R = 4 mtop / pT 2.5 TeV < pT < 5.0 TeV mtrk, R = 1.0 mtrk, R = 4 mtop / pT mtrk pT / ptTrk , R = 4 mtop / pT 100 200 300 400 500 100 200 300 400 500 mass [GeV/c2] mass [GeV/c2] reconstructed jet mass as m = momentum of the tracks. We will also compare observables measured on current and projected future calorimetry to the track-based measurements. track version of the HEPTopTagger [61, 62] of ref. [63] (...truncated)


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Andrew J. Larkoski, Fabio Maltoni, Michele Selvaggi. Tracking down hyper-boosted top quarks, Journal of High Energy Physics, 2015, pp. 32, Volume 2015, Issue 6, DOI: 10.1007/JHEP06(2015)032