High Transverse Energy Jets Research Articles

Optimal choice of factorization scales for the description of jet production at the LHC

To obtain more precise parton distribution functions (PDFs) it is important to include data on inclusive high transverse energy jet production in the global parton analyses. These data have high statistics and the NNLO terms in the perturbative QCD (pQCD) description are now available. Our aim is to reduce the uncertainty in the comparison of the jet data with pQCD. To ensure the best convergence of the pQCD series it is important to choose the appropriate factorization scales, mu _mathrm{F}. We show that it is possible to absorb and resum in the incoming PDFs and fragmentation function (D) an essential part of the higher alpha _mathrm{s}-order corrections by determining the ‘optimal’ values of mu _mathrm{F}. We emphasize that it is necessary to optimize different factorization scales for the various factors in the cross section: indeed, both of the PDFs, and also the fragmentation function, have their own optimal scale. We show how the values of these scales can be calculated for the LO (NLO) part of the pQCD prediction of the cross section based on the theoretically known NLO (NNLO) corrections. After these scales are fixed at their optimal values, the residual factorization scale dependence is much reduced.

The ATLAS jet trigger performance in LHC Run I and Run II updates

The Large Hadron Collider (LHC) provides proton-proton collisions with a nominal rate of 40 MHz, and the ATLAS trigger performs the first event selections online during data- taking. The ATLAS jet trigger is an important element of the ATLAS trigger system, selecting collision events containing high transverse energy jets, to provide data samples for studies ranging from Standard Model physics to searches for new physics at the LHC. During LHC Run I, the first LHC operation period from 2010 to 2012, the ATLAS jet trigger system improved as experience developed with triggering in a high luminosity and high event pileup environment. For the next LHC operation period, Run II, the system is being updated for further improved performance and stability. In this contribution, performance and improvements of the ATLAS jet trigger in Run I are presented. Updates for Run II are also shown.

Search for New Fermions (“Quirks”) at the Fermilab Tevatron Collider

We report results of a search for particles with anomalously high ionization in events with a high transverse energy jet and large missing transverse energy in 2.4 fb⁻¹ of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron pp collider. Production of such particles (quirks) is expected in scenarios with extra QCD-like SU(N) sectors, and this study is the first dedicated search for such signatures. We find no evidence of a signal and set a lower mass limit of 107, 119, and 133 GeV for the mass of a charged quirk with strong dynamics scale Λ in the range from 10 keV to 1 MeV and N=2, 3, and 5, respectively.

Diffractive photoproduction of dijets at ZEUS

The diffractive photoproduction of dijets has been studied using 77.6 pb −1 of data taken by the ZEUS detector at HERA. The measurements have been made in the kinematic range 0.2< y <0.85 and x IP < 0.035 , where y is the inelasticity and x IP is the fraction of the proton momentum taken by the diffractive exchange. The jets are reconstructed using the k T algorithm. The two highest transverse energy jets are required to satisfy E T > 7.5 and 6.5 GeV, respectively, and to lie in the pseudorapidity range −1.5< η <2.0. Differential cross sections have been measured and are confronted with the predictions from leading order Monte Carlo models and next-to-leading order QCD calculations.

Jet production in deep inelastic scattering at HERA

A small number of recent results from the wealth of precision HERA data on high transverse energy jet production in deep inelastic scattering are reviewed. These measurements are confronted with predictions from next-to-leading order (NLO) Quantum Chromodynamics and allow the extraction of the strong coupling constant, α s . Detailed studies of the underlying subprocess illustrate some areas of current interest.

Jet cross sections at HERA - current issues

Since the start of HERA operation there has been considerable progress in the understanding of jet production in ep collisions. QCD calculations are now able to accommodate the hadronic structure of the virtual photon. The luminosities delivered by HERA are now sufficient to allow studies of final states in which more than two high transverse energy jets are produced. The transition between jet processes in photoproduction and in deep inelastic scattering has been studied in some detail. These advances are highlighted here.

Probing hard color-singlet exchange in [formula omitted] collisions at [formula omitted] = 630 GeV and 1800 GeV

We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at s =630 GeV and 1800 GeV using the DØ detector. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, separation in pseudorapidity between the two highest transverse energy jets, and proton-antiproton center-of-mass energy. The results are consistent with a color-singlet fraction that increases with an increasing fraction of quark-initiated processes and inconsistent with two-gluon models for the hard color-singlet.

Discovery limits for a new contact interaction at future hadronic colliders with polarized beams

The production of high-transverse energy jets in hadron-hadroncollisions is sensitive to the presence of new contact interactions between quarks. If proton polarization were available, the measurement of some parity violating spin asymmetries in one-jet production at large transverse energy would complement the usual search for deviations from the expected QCD cross section. In the same time, a unique information on the chirality structure of the new interaction could be obtained. In this context, we compare the potentialities of various $pp$ and $p\bar p$ colliders that are planned or have been proposed, with the additional requirement of beam polarization.

Heavy top-quark searches in the dilepton mode at the Fermilab Tevatron.

We present the results of a detailed study of the effects of $b$-tagging on the heavy top-quark signal and backgrounds for the modes of the di-lepton plus two high transverse energy jets at the Fermilab Tevatron. The general characteristics of the heavy top-quark signal events are also discussed so that a comparison can be made between $b$-tagging and imposing stringent kinematical cuts to eliminate backgrounds.