QCD corrections to excited lepton (pair) production at the LHC

Majhi, Swapan

doi:10.1103/physrevd.88.074028

Cited by 5 publications

(6 citation statements)

References 69 publications

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“…Moreover, the composite Majorana neutrinos of this model can be responsible for baryogenesis via leptogenesis [33,34]. The phenomenology of other excited states has also been discussed in a series of recent papers [31,[35][36][37][38][39][40][41].…”

Section: Introductionmentioning

confidence: 99%

Perturbative unitarity bounds for effective composite models

et al. 2019

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In this paper we present the partial wave unitarity bound in the parameter space of dimension-5 and dimension-6 effective operators that arise in a compositeness scenario. These are routinely used in experimental searches at the LHC to constraint contact and gauge interactions between ordinary Standard Model fermions and excited (composite) states of mass M. After deducing the unitarity bound for the production process of a composite neutrino, we implement such bound and compare it with the recent experimental exclusion curves for Run 2, the High-Luminosity and High-Energy configurations of the LHC. Our results also applies to the searches where a generic single excited state is produced via contact interactions. We find that the unitarity bound, so far overlooked, is quite compelling and significant portions of the parameter space (M, Λ) become excluded in addition to the standard request M ≤ Λ.

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Section: Introductionmentioning

confidence: 99%

Perturbative unitarity bounds for effective composite models

et al. 2019

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“…Here, L T = (ν L , L ) is the ordinary lepton doublet, g and g are the SU(2) L and U(1) Y gauge couplings and W W W µν , B µν are the field strength tensor of the corresponding gauge fields respectively; τ τ τ are the Pauli matrices and Y is the hypercharge, f and f are dimensionless couplings and are expected (and assumed) to be of order unity. Excited states interacting with the SM sector through the model Lagrangians (1.1)-(1.2) and (1.3) have been extensively searched for at high-energy collider facilities and their phenomenology has also been discussed in a series of recent papers [24,25,26,27,28,29,30,31,32,33]. The current strongest bounds are due to the recent LHC experiments.…”

Section: Pos(corfu2019)057mentioning

confidence: 99%

Perturbative unitarity bounds for fermions composite models

Biondini¹,

Leonardi²,

Panella³

et al. 2020

Proceedings of Corfu Summer Institute 2019 "School and Workshops on Elementary Particle Physics and Gravity" — PoS(CORFU2019)

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Perturbative unitarity is a powerful tool for inferring the range of validity of a given effective field theory. Here, we study such a bound in the parameter space of dimension-5 and dimension-6 effective operators that arise in a scenario of fermion compositeness. These operators are routinely used in experimental searches at the LHC to constraint contact and gauge interactions between ordinary Standard Model fermions and excited states of mass M. We derive the unitarity bound for the production process of an excited neutrino, then we implement such bound and compare it with the recent experimental exclusion curves for Run 2, the High-Luminosity and High-Energy configurations of the LHC. The results also applies to the searches where a generic single excited state is produced via dimension-6 contact interactions. The unitarity bound, so far overlooked in these effective models, is quite compelling and can serve as a guide for exploring the parameter space (M, Λ) in addition to the standard request M ≤ Λ.

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“…Only the width of the * resonance and the * production cross section depend on Λ. As long as the width of the * is small compared to the mass resolution of the detector, the signal efficiency is independent of Λ. Mass-dependent next-to-leading order (NLO) k-factors ranging from 1.2 to 1.35 [26] are applied on the signal event yields. Production cross sections for the signals, as well as those of the different decay modes including the corresponding branching fractions are given in Table 2.…”

Section: Decay Modementioning

confidence: 99%

“…The values of the k-factors are taken from Ref. [26]. The case f = − f = 1 does not apply to the * → γ channel.…”

Section: Decay Modementioning

confidence: 99%

Search for excited leptons in proton-proton collisions at s = 8 $$ \sqrt{s}=8 $$ TeV

Khachatryan¹,

Sirunyan²,

Tumasyan³

et al. 2016

J. High Energ. Phys.

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A search for compositeness of electrons and muons is presented using a data sample of proton-proton collisions at a center-of-mass energy of √ s = 8 TeV collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 19.7 fb −1 . Excited leptons ( * ) produced via contact interactions in conjunction with a standard model lepton are considered, and a search is made for their gauge decay modes. The decays considered are * → γ and * → Z, which give final states of two leptons and a photon or, depending on the Z-boson decay mode, four leptons or two leptons and two jets. The number of events observed in data is consistent with the standard model prediction. Exclusion limits are set on the excited lepton mass, and the compositeness scale Λ. For the case M * = Λ the existence of excited electrons (muons) is excluded up to masses of 2.45 (2.47) TeV at 95% confidence level. Neutral current decays of excited leptons are considered for the first time, and limits are extended to include the possibility that the weight factors f and f , which determine the couplings between standard model leptons and excited leptons via gauge mediated interactions, have opposite sign. A Details of the final selection 29The CMS collaboration 35-1 - JHEP03(2016)1251 IntroductionThe standard model (SM) of particle physics describes the observed phenomena very successfully, however it provides no explanation for the three generations of the fermion families. Attempts to explain the observed hierarchy have led to a class of models postulating that quarks and leptons may be composite objects of fundamental constituents [1][2][3][4][5][6][7][8][9]. The fundamental constituents are bound by an asymptotically free gauge interaction that becomes strong at a characteristic scale Λ. Compositeness models predict the existence of excited states of quarks (q * ) and leptons ( * ) at the characteristic scale of the new binding interaction. Since these excited fermions couple to the ordinary SM fermions, they could be produced via contact interactions (CI) in collider experiments, with subsequent decay to ordinary fermions through the emission of a W/Z/γ boson, or via CI to other fermions. Searches at LEP [10][11][12][13], HERA [14], and the Tevatron [15][16][17][18] have found no evidence for excited leptons. At the Large Hadron Collider (LHC) at CERN, previous searches performed by the CMS [19] and the ATLAS collaborations [20] have also found no evidence of excited leptons, obtaining a lower limit on the mass M * < 2.2 TeV for the case M * = Λ.In this paper, a search for excited leptons (e * and µ * ) is presented, using a data sample of pp collisions at a center-of-mass energy √ s = 8 TeV collected with the CMS detector at the LHC in 2012 and corresponding to an integrated luminosity of 19.7 ± 0.5 fb −1 [21].We consider the production of an excited lepton in association with an oppositely charged lepton of the same flavor, with subsequent radiative decays ( * → γ) or neutral current decays ( * → Z). Theory and mod...

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QCD corrections to excited lepton (pair) production at the LHC

Cited by 5 publications

References 69 publications

Perturbative unitarity bounds for effective composite models

Perturbative unitarity bounds for effective composite models

Perturbative unitarity bounds for fermions composite models

Search for excited leptons in proton-proton collisions at s = 8 $$ \sqrt{s}=8 $$ TeV

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