Excited-quark and -lepton production at hadron colliders

Baur, U.; Spira, M.; Zerwas, P.M.

doi:10.1103/physrevd.42.815

Cited by 260 publications

(356 citation statements)

References 16 publications

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“…The current implementation contains gauge interaction production by quark-gluon fusion (processes 147 and 148) or lepton-photon fusion (process 146) and contact interaction production by quark-quark or quark-antiquark scattering (processes 167-169) . The couplings f , f ′ and f s to the SU(2), U(1) and SU(3) groups are stored in PARU(157) -PARU(159), the scale parameter Λ in PARU(155); you are also expected to change the f * masses in accordance with what is desired -see [Bau90] for details on conventions. Decay processes are of the types q * → qg, q * → qγ, q * → qZ 0 or q * → q ′ W ± , with the latter three (two) available also for e * (ν * e ).…”

Section: Excited Fermionsmentioning

confidence: 99%

PYTHIA 6.4 physics and manual

Sjöstrand

Mrenna

Skands

2006

J. High Energy Phys.

9,615

10,151

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The Pythia program can be used to generate high-energy-physics 'events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, with emphasis on those where strong interactions play a rôle, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCDbased models. This physics input is summarized here, for areas such as hard subprocesses, initial-and final-state parton showers, beam remnants and underlying events, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

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Section: Excited Fermionsmentioning

confidence: 99%

PYTHIA 6.4 physics and manual

Sjöstrand

Mrenna

Skands

2006

J. High Energy Phys.

9,615

10,151

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“…Where there is an excess (deficit) in data in a given bin, the significance is plotted as positive (negative). 2 To test the degree of consistency between the data and the fitted background, the p-value of the fit is determined by calculating the χ 2 -value from the data and comparing this result to the χ 2 distribution obtained from pseudo-experiments drawn from the background fit, as described in a previous publication [22]. The resulting p-value is 0.73, showing that there is good agreement between the data and the fit.…”

Section: Comparing the Dijet Mass Spectrum To A Smooth Backgroundmentioning

confidence: 99%

“…The observed dijet mass distribution after all selection cuts is shown in figure 1. Also shown in the figure are the predictions for an excited quark for three different mass hypotheses [1,2]. The m jj spectrum is fit to a smooth functional form, interactions, could be absorbed by the background fitting function, and therefore the m jj analysis is used only to search for resonant effects.…”

Section: Comparing the Dijet Mass Spectrum To A Smooth Backgroundmentioning

confidence: 99%

“…The study of these events tests the Standard Model (SM) at the highest energies accessible at the LHC. At these energies, new particles could be produced [1,2], new interactions between particles could manifest themselves [3-6], or interactions resulting from the unification of SM with gravity could appear in the TeV range [7][8][9][10][11][12]. These collisions also probe the structure of the fundamental constituents of matter at the smallest distance scales allowing, for example, an experimental test of the size of quarks.…”

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confidence: 99%

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ATLAS search for new phenomena in dijet mass and angular distributions using pp collisions at $ \sqrt{s}=7 $TeV

Buanes¹,

Burgess²,

Eigen³

et al. 2013

J. High Energ. Phys.

103

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Mass and angular distributions of dijets produced in LHC proton-proton collisions at a centre-of-mass energy √ s = 7 TeV have been studied with the ATLAS detector using the full 2011 data set with an integrated luminosity of 4.8 fb −1 . Dijet masses up to ∼ 4.0 TeV have been probed. No resonance-like features have been observed in the dijet mass spectrum, and all angular distributions are consistent with the predictions of QCD. Exclusion limits on six hypotheses of new phenomena have been set at 95% CL in terms of mass or energy scale, as appropriate. These hypotheses include excited quarks below 2.83 TeV, colour octet scalars below 1.86 TeV, heavy W bosons below 1.68 TeV, string resonances below 3.61 TeV, quantum black holes with six extra space-time dimensions for quantum gravity scales below 4.11 TeV, and quark contact interactions below a compositeness scale of 7.6 TeV in a destructive interference scenario. The ATLAS collaboration 30At the CERN Large Hadron Collider (LHC), collisions with the largest momentum transfer typically result in final states with two jets of particles with high transverse momentum (p T ). The study of these events tests the Standard Model (SM) at the highest energies accessible at the LHC. At these energies, new particles could be produced [1,2], new interactions between particles could manifest themselves [3-6], or interactions resulting from the unification of SM with gravity could appear in the TeV range [7][8][9][10][11][12]. These collisions also probe the structure of the fundamental constituents of matter at the smallest distance scales allowing, for example, an experimental test of the size of quarks. The models for new phenomena (NP) tested in the current studies are described in section 9. The two jets emerging from the collision may be reconstructed to determine the twojet (dijet) invariant mass, m jj , and the scattering angular distribution with respect to the colliding beams of protons. The dominant Quantum Chromodynamics (QCD) interactions for this high-p T scattering regime are t-channel processes, leading to angular distributions that peak at small scattering angles. Different classes of new phenomena are expected to modify dijet mass distribution and the dijet angular distributions as a function of m jj , creating either a deviation from the QCD prediction above some threshold or an excess of events localised in mass (often referred to as a "bump" or "resonance"). Most models predict that the angular distribution of the NP signal would be more isotropic than that of QCD.Results from previous studies of dijet mass and angular distributions [13][14][15][16][17][18][19][20][21][22][23] were consistent with QCD predictions. The study reported in this paper is based on pp collisions at a centre-of-mass (CM) energy of 7 TeV produced at the LHC and measured by the ATLAS detector. The analysed data set corresponds to an integrated luminosity of 4.8 fb −1 collected in 2011 [24,25], a substantial increase over previously published ATLAS dijet analyses [22, 23].A d...

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“…Shown in Figure 7(b) is the interpretation of the search in terms of the quantum black hole signal. The second such "photon+X" search focuses on searching for excited leptons [26] ( * is limited to e * or μ * ) produced through an effective field theory description [27]. The effective field theory production mechanism requires the emission of an additional Standard Model electron or muon with the excited lepton then decays via emission of a single photon to a Standard Model lepton of the same flavor.…”

Section: Photon+x Signaturesmentioning

confidence: 99%

Exotic Physics at ATLAS

Meehan

2014

EPJ Web of Conferences

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Abstract. A number of proposed explanations to observed phenomena predict new physics that will be directly observable at the LHC. Each new theory is manifested in the experiments as an experimental signature that sets it apart from the many well understood Standard Model processes. Presented here is a summary of a selection of such searches performed using 8 TeV center of mass energy data produced by the LHC and collected with the ATLAS detector. As no significant deviations from the standard model are observed in any search channel presented here, the results are interpreted in terms of constraints on new physics in a number of scenarios including dark matter, sequential standard model extensions, and model independent interpretations depending on the given search channel.

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Excited-quark and -lepton production at hadron colliders

Cited by 260 publications

References 16 publications

PYTHIA 6.4 physics and manual

PYTHIA 6.4 physics and manual

ATLAS search for new phenomena in dijet mass and angular distributions using pp collisions at $ \sqrt{s}=7 $TeV

Exotic Physics at ATLAS

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