Production Of Excited Quarks Research Articles

Signature of theγ+jetand dijet production mediated by an excited quark with QCD next-to-leading order accuracy at the LHC

We present a detailed study of the production and decay of the excited quark at the QCD next-to-leading order (NLO) level at the Large Hadron Collider, using the narrow width approximation and helicity amplitudes method. We find that the QCD NLO corrections can tighten the constraints on the model parameters and reduce the scale dependencies of the total cross sections. We discuss the signals of the excited quark production with decay mode $q^{\ast}\rightarrow q\gamma$ and $q^{\ast}\rightarrow qg$, and present several important kinematic distributions. Moreover, we give the upper limits of the excited quark excluded mass range and the allowed parameter space for the coupling constants and the excited quark mass.

Search for anomalous production of highly boosted Z bosons decaying to [formula omitted] in proton–proton collisions at [formula omitted

Results are reported from a search for the anomalous production of highly boosted Z bosons with large transverse momentum and decaying to μ+μ−. Such Z bosons may be produced in the decays of new heavy particles. The search uses pp collision data at s=7 TeV, corresponding to an integrated luminosity of 5.0 fb−1 recorded with the CMS detector. The shape of the observed transverse momentum distribution of Z bosons is consistent with standard model expectations. Constraints are obtained on models predicting the production of excited quarks decaying via electroweak processes. Assuming a compositeness scale that is equal to the excited quark mass as well as transition coupling strengths between Z bosons and excited quarks that are equal to standard model couplings to quarks, masses of excited quarks below 1.94 TeV are excluded at the 95% confidence level. For excited quark production via a novel contact interaction, masses below 2.22 TeV are excluded, even if the excited quarks do not couple to gluons.

Search for excited quarks in ep collisions at HERA

A search for excited quarks is performed using the full e±p data sample collected by the H1 experiment at HERA, corresponding to a total integrated luminosity of 475 pb−1. The electroweak decays of excited quarks q∗→qγ, q∗→qZ and q∗→qW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for first generation excited quark production is found. Mass dependent exclusion limits on q∗ production cross sections and on the ratio f/Λ of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited quark searches.

Search for a heavy resonance decaying into aZ+jetfinal state inpp¯collisions ats=1.96 TeVusing the D0 detector

We have searched for a heavy resonance decaying into a Z+jet final state in p (p) over bar collisions at a center of mass energy of 1.96 TeV at the Fermilab Tevatron collider using the D0 detector. No indication for such a resonance was found in a data sample corresponding to an integrated luminosity of 370 pb(-1). We set upper limits on the cross section times branching fraction for heavy resonance production at the 95% C.L. as a function of the resonance mass and width. The limits are interpreted within the framework of a specific model of excited quark production.

Search for new particles in the two-jet decay channel with the DØ detector

We present the results of a search for the production of new particles decaying into two jets in p p collisions at sqrt[s]=1.8 TeV, using the DO 1992–1995 data set corresponding to 109 pb-1. We exclude at the 95% confidence level the production of excited quarks (q*) with masses below 775 GeV/c2, the most restrictive limit to date. We also exclude standard-model-like W′ (Z′) bosons with masses between 300 and 800 GeV/c2 (400 and 640 GeV/c2). A W′ boson with mass <786 GeV/c2 has been excluded by previous measurements, and our lower limit is therefore the most stringent to date.

Search for excited quarks with the ATLAS experiment at the CERN LHC:W/Z+jet channel

Resonant production of excited quarks at the CERN LHC by the quark gluon fusion process and their subsequent decay to ordinary quarks and weak gauge bosons W and Z is investigated. Event selection cuts are applied to separate the signal from background. At an integrated luminosity of $3\ifmmode\times\else\texttimes\fi{}{10}^{5}{\mathrm{pb}}^{\mathrm{\ensuremath{-}}1},$ the mass reaches of 7 TeV for qW, and 4.5 TeV for qZ channel are achieved.

Excited quark production at the CERN LHC

We study the production of excited quarks ${q}^{\ensuremath{\star}}$ of spin-1/2 predicted by composite models. Production rates, signatures, and backgrounds are discussed for the CERN LHC. We estimate the discovery mass reach for the excited quarks decaying to jet+photon.

Excited quark production at polarized hadronic colliders

We study the production of excited quarks at hadronic colliders when one of the proton beams is longitudinally polarized. We show that the single spin asymmetry allows to pin down the chirality nature of the interaction.

A search for new intermediate vector bosons and excited quarks decaying to two-jets at the CERN p̄p collider

The two-jet invariant mass spectrum as measured in the UA2 experiment is used to search for additional heavy vector bosons decaying to two-jets. The mass of an additional W boson that couples to fermions with a V+ A form is constrained to be greater than 261 GeV to the 90% confidence level. A limit on the production cross section of additional W and Z bosons is given as a function of the boson mass. A limit on the production of excited quarks is also given as a function of the excited quark mass.

Excited quark production at ep and γp colliders

We study the production of excited quarks q ∗ of spin- j predicted by composite models at ep and γp colliders HERA, LEP-LHC and UNK-VLEPP. The production of excited quarks of spin j = 1 2 at the γp collider based on the ep collider UNK-VLEPP is also considered. The effect of the longitudinal polarization of the electron beam is analyzed and the standard model background is estimated. We show that excited quarks with masses of the order of 1–2 TeV can be studied, and that ep (γp) colliders have additional capabilities in experiments exploring the structures of interactions of q ∗, in comparison with hadron colliders.

Search for excited quarks in e +e − interactions with the cello detector

The production of excited quarks has been looked for in e +e − interactions at PETRA at center of mass energies up to 46.8 GeV using the CELLO detector. The different final state topologies considered are four-jets, two-jets and two-photons, three-jets, two-jets and one-photon. No deviation from standard QCD predictions is observed, thus yielding limits on the coupling constants and the masses of these possible quark states.