Large Transverse Momentum Jets Research Articles

Search for pair production of up-type vector-like quarks and for four-top-quark events in final states with multiple b-jets with the ATLAS detector

A search for pair production of up-type vector-like quarks (T ) with a significant branching ratio into a top quark and either a Standard Model Higgs boson or a Z boson is presented. The same analysis is also used to search for four-top-quark production in several new physics scenarios. The search is based on a dataset of pp collisions at sqrt{s}=13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb−1. Data are analysed in the lepton+jets final state, characterised by an isolated electron or muon with high transverse momentum, large missing transverse momentum and multiple jets, as well as the jets + ETmiss final state, characterised by multiple jets and large missing transverse momentum. The search exploits the high multiplicity of jets identified as originating from b-quarks, and the presence of boosted, hadronically decaying top quarks and Higgs bosons reconstructed as large-radius jets, characteristic of signal events. No significant excess above the Standard Model expectation is observed, and 95% CL upper limits are set on the production cross sections for the different signal processes considered. These cross-section limits are used to derive lower limits on the mass of a vector-like T quark under several branching ratio hypotheses assuming contributions from T → W b, Zt, Ht decays. The 95% CL observed lower limits on the T quark mass range between 0.99 TeV and 1.43 TeV for all possible values of the branching ratios into the three decay modes considered, significantly extending the reach beyond that of previous searches. Additionally, upper limits on anomalous four-top-quark production are set in the context of an effective field theory model, as well as in an universal extra dimensions model.

Search for supersymmetry in final states with missing transverse momentum and multiple b-jets in proton-proton collisions at sqrt{s}=13 TeV with the ATLAS detector

A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino left({tilde{chi}}_1^0right) is reported. It uses LHC proton-proton collision data at a centre-of-mass energy sqrt{s}=13 TeV with an integrated luminosity of 36.1 fb−1 collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing large missing transverse momentum and several energetic jets, at least three of which must be identified as originating from b-quarks. To increase the sensitivity, the sample is divided into subsamples based on the presence or absence of electrons or muons. No excess is found above the predicted background. For {tilde{chi}}_1^0 masses below approximately 300 GeV, gluino masses of less than 1.97 (1.92) TeV are excluded at 95% confidence level in simplified models involving the pair production of gluinos that decay via top (bottom) squarks. An interpretation of the limits in terms of the branching ratios of the gluinos into third-generation squarks is also provided. These results improve upon the exclusion limits obtained with the 3.2 fb−1 of data collected in 2015.

Measurement of the top-quark mass in thett¯dilepton channel using the full CDF Run II data set

We present a measurement of the top-quark mass in events containing two leptons (electrons or muons) with a large transverse momentum, two or more energetic jets, and a transverse-momentum imbalance. We use the full proton-antiproton collision data set collected by the CDF experiment during the Fermilab Tevatron Run~II at center-of-mass energy $\sqrt{s} = 1.96$ TeV, corresponding to an integrated luminosity of 9.1 fb$^{-1}$. A special observable is exploited for an optimal reduction of the dominant systematic uncertainty, associated with the knowledge of the absolute energy of the hadronic jets. The distribution of this observable in the selected events is compared to simulated distributions of ${t\bar{t}}$ dilepton signal and background.We measure a value for the top-quark mass of $171.5\pm 1.9~{\rm (stat)}\pm 2.5~{\rm (syst)}$ GeV/$c^2$.

Search for production of vector-like quark pairs and of four top quarks in the lepton-plus-jets final state in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

A search for pair production of vector-like quarks, both up-type ($T$) and down-type ($B$), as well as for four-top-quark production, is presented. The search is based on $pp$ collisions at $\sqrt{s}=8$ TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 20.3 fb$^{-1}$. Data are analysed in the lepton-plus-jets final state, characterised by an isolated electron or muon with high transverse momentum, large missing transverse momentum and multiple jets. Dedicated analyses are performed targeting three cases: a $T$ quark with significant branching ratio to a $W$ boson and a $b$-quark ($T\bar{T} \to Wb$+X), and both a $T$ quark and a $B$ quark with significant branching ratio to a Higgs boson and a third-generation quark ($T\bar{T} \to Ht$+X and $B\bar{B} \to Hb$+X respectively). No significant excess of events above the Standard Model expectation is observed, and 95% CL lower limits are derived on the masses of the vector-like $T$ and $B$ quarks under several branching ratio hypotheses assuming contributions from $T \to Wb$, $Zt$, $Ht$ and $B \to Wt$, $Zb$, $Hb$ decays. The 95% CL observed lower limits on the $T$ quark mass range between 715 GeV and 950 GeV for all possible values of the branching ratios into the three decay modes, and are the most stringent constraints to date. Additionally, the most restrictive upper bounds on four-top-quark production are set in a number of new physics scenarios.

Production of massless charm jets in pp collisions at next-to-leading order of QCD

We present predictions for the inclusive production of charm jets in proton–proton collisions at 7 TeV. Several CTEQ parton distribution functions (PDFs) of the CTEQ6.6M type are employed, where two of the CTEQ6.6 PDFs have intrinsic charm. At large enough jet transverse momentum and large jet rapidity, the intrinsic charm content can be tested.

Measurement of the top-quark pair production cross-section using final states with an electron or a muon and a hadronically decaying τ-lepton

A measurement of the top-quark pair production cross-section is reported using proton-proton collision data at s=7 TeV recorded by ATLAS experiment at the Large Hadron Collider. Events are extracted from 2.05 fb−1 of data by requiring an isolated electron or muon, a large missing transverse momentum, two or more energetic jets and a hadronically decaying τ-lepton. The measured cross-section, σtt¯=186±13(stat.)±20(syst.)±7(lumi.) pb, is in good agreement with the Standard Model prediction.

Search for supersymmetry inppcollisions ats=7 TeVin final states with missing transverse momentum andb-jets with the ATLAS detector

The results of a search for supersymmetry in events with large missing transverse momentum and heavy-flavor jets using an integrated luminosity corresponding to 2.05 fb−1 of pp collisions at s=7 TeV recorded with the ATLAS detector at the Large Hadron Collider are reported. No significant excess is observed with respect to the prediction for standard model processes. Results are interpreted in a variety of R-parity conserving models in which scalar bottoms and tops are the only scalar quarks to appear in the gluino decay cascade, and in an SO(10) model framework. Gluino masses up to 600–900 GeV are excluded, depending on the model considered.4 MoreReceived 28 March 2012DOI:https://doi.org/10.1103/PhysRevD.85.112006This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.© 2012 CERN, for the ATLAS Collaboration

Studying the underlying event in Drell-Yan and high transverse momentum jet production at the Tevatron

We study the underlying event in proton-antiproton collisions by examining the behavior of charged particles (transverse momentum pT > 0.5 GeV/c, pseudorapidity |\eta| < 1) produced in association with large transverse momentum jets (~2.2 fb-1) or with Drell-Yan lepton-pairs (~2.7 fb-1) in the Z-boson mass region (70 < M(pair) < 110 GeV/c2) as measured by CDF at 1.96 TeV center-of-mass energy. We use the direction of the lepton-pair (in Drell-Yan production) or the leading jet (in high-pT jet production) in each event to define three regions of \eta-\phi space; toward, away, and transverse, where \phi is the azimuthal scattering angle. For Drell-Yan production (excluding the leptons) both the toward and transverse regions are very sensitive to the underlying event. In high-pT jet production the transverse region is very sensitive to the underlying event and is separated into a MAX and MIN transverse region, which helps separate the hard component (initial and final-state radiation) from the beam-beam remnant and multiple parton interaction components of the scattering. The data are corrected to the particle level to remove detector effects and are then compared with several QCD Monte-Carlo models. The goal of this analysis is to provide data that can be used to test and improve the QCD Monte-Carlo models of the underlying event that are used to simulate hadron-hadron collisions.

SIMULATION OF JET QUENCHING OBSERVABLES IN HEAVY ION COLLISIONS AT THE LHC

Large transverse momentum jets provide unique tools to study dense QCD matter in high-energy heavy-ion collisions. Results from RHIC on suppression of high transverse momentum particles in Au + Au collisions indicate a significant energy loss of leading partons in the dense and strongly interacting matter formed in these collisions. The LHC will collide Pb ions at [Formula: see text], where the cross section of hard scattering will increase dramatically. Large production rates, the large acceptance of the CMS calorimeters and tracking system, combined with the capability of triggering on jets, will extend the transverse momentum reach of charged particle spectra and nuclear modification factors up to pT &gt; 200 GeV / c .

Jet properties from dihadron correlations inp+pcollisions ats=200 GeV

The properties of jets produced in p+p collisions at root s=200 GeV are measured using the method of two-particle correlations. The trigger particle is a leading particle from a large transverse momentum jet while the associated particle comes from either the same jet or the away-side jet. Analysis of the angular width of the near-side peak in the correlation function determines the jet-fragmentation transverse momentum j(T). The extracted value, root =585 +/- 6(stat)+/- 15(sys) MeV/c, is constant with respect to the trigger particle transverse momentum, and comparable to the previous lower root s measurements. The width of the away-side peak is shown to be a convolution of j(T) with the fragmentation variable, z, and the partonic transverse momentum, k(T). The is determined through a combined analysis of the measured pi(0) inclusive and associated spectra using jet-fragmentation functions measured in e(+)e(-) collisions. The final extracted values of k(T) are then determined to also be independent of the trigger particle transverse momentum, over the range measured, with value of root =2.68 +/- 0.07(stat)+/- 0.34(sys) GeV/c.

NLO forward–backward charge asymmetries in [formula omitted] production at large hadron colliders

We consider the next-to-leading order corrections, O(αs), to forward–backward charge asymmetries for lepton-pair production in association with a large transverse momentum jet at large hadron colliders. We find that the leading order results are essentially confirmed. Although experimentally challenging and in practice with large backgrounds, these observables could provide a new determination of the weak mixing angle sin2θefflept(MZ2) with a statistical precision for each lepton flavour of ∼10−3 (7×10−3) at LHC (Tevatron), and if b jets are identified, of the b quark Z asymmetry AFBb with a statistical precision of ∼2×10−3 (4×10−2) at LHC (Tevatron).

Large transverse momentum jet production and DIS distributions of the proton

We have calculated the single jet inclusive cross section as measured at Fermilab in next-to-leading order QCD using recent parton distributions of the CTEQ Collaboration. We studied the scheme dependence of the jet cross section by employing the MS and DIS factorization schemes consistently. For E T > 200 GeV, we find that the cross section in the DIS scheme is larger than in the MS scheme yielding a satisfactory description of the CDF data over the whole E T range in the DIS scheme.

Double pomeron jet cross sections

We treat hadron-hadron collisions where the final state is kinematically of the kind associated with double-pomeron-exchange (DPE) and has large transverse momentum jets. We show that in addition to the conventional factorized (FDPE) contribution, there is a nonfactorized (NDPE) contribution which has no pomeron beam jet. Within a simple model we compute DPE-two-jet total and differential cross sections at Tevatron energy scales, and show that the NDPE contribution is dominant.

Production of CP-odd Higgs bosons with large transverse momentum at hadron supercolliders

A two Higgs doublet model is employed to study the production of a CP-odd Higgs boson ( A) associated with a large transverse momentum jet ( j) at hadron supercolliders. The cross section of pp → jA + X is evaluated with four subprocesses: gg → gA, gq → qA, g q → qA and q q → gA . We find that pp → jA + A is a significant source of CP-odd Higgs bosons at future hadron supercolliders.

Measuring nuclear gluon shadowing through three-jet production in electron-nucleus collisions

The possibility of studying the nuclear gluon distribution by looking at large transverse momentum jets in deep inelastic lepton scattering is investigated. Provided that a colliding beam of leptons and nuclei, rather than a fixed nuclear target, can be arranged, a clean measurement of gluon shadowing appears possible.

The polarized gluon distribution and large transverse momentum jets

The Carlitz-Collins-Mueller proposal to measure the polarized gluon distribution in the proton by measuring two-jet events is examined in greater detail. It is shown that an experiment with a proton target at rest in the laboratory cannot be used to measure the polarized gluon distribution. However, one can measure the polarized gluon if a relativistic proton beam is used instead. The resulting jet cross-section is calculable; the gluon contribution to the total cross-section is not − α s /2 π.

Higgs boson production at large transverse momentum in hadronic collisions

Production of Higgs bosons accompanied by a large transverse momentum jet at hadron colliders via a top quark loop is calculated to lowest order QCD. Analytic expressions for the matrix elements, including the decay H → VV → four massless fermions (V = W,Z), are presented. The dependence of the matrix elements on the mass of the top quark exchanged in the loop in all regions of phase space is studied in detail. The Hj signal is compared with the background arising from VVj and V+3 jet production for LHC and SSC energies.

Hadronic production of electroweak vector boson pairs at large transverse momentum

Production of electroweak vector boson pairs accompanied by a large transverse momentum jet at hadron colliders is calculated to lowest order QCD with emphasis on the p T and invariant mass distribution of the gauge boson pair. Analytic expressions for the matrix elements of all possible processes, including decays of W- and Z-bosons into massless fermion final states, are presented. It is found that these processes represent an important source for gauge boson pair production at the LHC and SSC and also constitute a background to new physics signals at these colliders, such as Higgs tagging or pair production of a fourth charged lepton.

Higgs decay to τ+τ−A possible signature of intermediate mass Higgs bosons at high energy hadron colliders

This paper considers the decay of a standard model Higgs boson into a tau pair, as a possible signature at the SSC or LHC for a Higgs boson of mass between 110 and 160 GeV. The production of the Higgs in association with a large transverse momentum jet is considered, since this may aid in reconstructing the Higgs mass. The background from the production of tau pairs via virtual photons and Z's is studied. We comment on the possible use of this process to search for a light Higgs at the Tevatron collider.

Measurement of very large transverse momentum jet production at the CERN [formula omitted] collider

The production of very large transverse momentum hadron jets has been measured in the UA2 experiment at the CERN pp Collider for s = 540 GeV using a highly segmented calorimeter. The range of previously available cross sections for inclusive jet production is extended to p T = 150 GeV and the two-jet invariant mass distribution to m jj = 280 GeV with the largely increased data sample collected during the 1983 running period. The results are compared with the predictions of QCD models.