Jets Final State Research Articles

Ultra-relativistic heavy-ion collisions - a hot cocktail of hydrodynamics, resonances and jets

Ultra-relativistic heavy-ion collisions at energies of RHIC and LHC are con- sidered. For comparison with data the HYDJET++ model, which contains the treatment of both soft and hard processes, is employed. The study focuses mainly on the interplay of ideal hydrodynamics, final state interactions and jets, and its influence on the devel- opment of harmonics of the anisotropic flow. It is shown that jets are responsible for violation of the number-of-constituent-quark (NCQ) scaling at LHC energies. The inter- play between elliptic and triangular flows and their contribution to higher flow harmonics and dihadron angular correlations, including ridge, is also discussed.

Model-independent probe of anomalous heavy neutral Higgs bosons at the LHC

We first formulate, in the framework of effective Lagrangian, the general form of the effective interactions of the lightest Higgs boson h and a heavier neutral Higgs boson H in a multi-Higgs system taking account of Higgs mixing effect. We regard h as the discovered Higgs boson which has been shown to be consistent with the standard model (SM) Higgs boson. The obtained effective interactions contain extra parameters reflecting the Higgs mixing effect. Next, We study the constraints on the anomalous coupling constants of H from both the requirement of the unitarity of the S matrix and the exclusion bounds on the SM Higgs boson obtained from the experimental data at the 7--8 TeV LHC. From this we obtain the available range of the anomalous coupling constants of H, with which H is not excluded by the yet known theoretical and experimental constraints. We then study the signatures of H at the 14 TeV LHC. In this paper, we suggest taking weak-boson scattering and pp to VH* to VVV as sensitive processes for probing H model independently at the 14 TeV LHC. We take several examples with the anomalous HVV coupling constants in the available ranges to do the numerical study. a full tree-level calculation at the hadron level is given with signals and backgrounds carefully calculated. We impose a series of proper kinematic cuts to effectively suppress the backgrounds. It is shown that, in both the VV scattering and the pp to VH* to VVV processes, H boson can be discovered from the invariant mass distributions of the final state particles with reasonable integrated luminosity. Especially, in the pp to VH* to VVV process, the invariant mass distribution of the final state jets can show a clear resonance peak of H. Finally, we propose several physical observables from which the values of the anomalous coupling constants f_W and f_{WW} can be measured experimentally.

Variable-flavor-number scheme for final state jets in thrust

We present results for mass effects coming from secondary radiation of heavy quark pairs related to gluon splitting in the thrust distribution for ${e}^{+}{e}^{\ensuremath{-}}$ collisions. The results are given in the dijet limit where the hard interaction scale and the scales related to collinear and soft radiation are widely separated. We account for the corresponding fixed-order corrections at $\mathcal{O}({\ensuremath{\alpha}}_{s}^{2})$ and the summation of all logarithmic terms related to the hard, collinear, and soft scales as well as the quark mass at ${\mathrm{N}}^{3}\mathrm{LL}$ order. We also remove the $\mathcal{O}({\mathrm{\ensuremath{\Lambda}}}_{\mathrm{QCD}})$ renormalon in the partonic soft function, leading to an infrared evolution equation with a matching condition related to the massive quark threshold. The quark mass can be arbitrary, ranging from the infinitely heavy case, where decoupling takes place, down to the massless limit, where the results smoothly merge into the well-known predictions for massless quarks. Our results are formulated in the framework of factorization theorems for ${e}^{+}{e}^{\ensuremath{-}}$ dijet production and provide universal threshold corrections for the renormalization group evolution of the hard current, the jet, and the soft functions at the scale where the massive quarks are integrated out. The results represent a first explicit realization of a variable-flavor-number scheme for final-state jets along the lines of the well-known flavor-number-dependent evolution of the strong coupling ${\ensuremath{\alpha}}_{s}$ and the parton distribution functions.

Precise QCD predictions for the production of Higgs + jet final states

We compute the cross section and differential distributions for the production of a Standard Model Higgs boson in association with a hadronic jet to next-to-next-to-leading order in quantum chromodynamics (QCD). In Higgs boson studies at the LHC, final states containing one jet are a dominant contribution to the total event rate, and their understanding is crucial for improved determinations of the Higgs boson properties. We observe substantial higher order corrections to transverse momentum spectra and rapidity distributions in Higgs-plus-one-jet final states. Their inclusion stabilises the residual theoretical uncertainty of the predictions around 9%, thereby providing important input to precision studies of the Higgs boson.

The transverse-momentum spectrum of Higgs bosons near threshold at NNLO

We give next-to-next-to-leading order (NNLO) predictions for the Higgs production cross section at large transverse momentum in the threshold limit. Near the partonic threshold, all radiation is either soft or collinear to the final state jet which recoils against the Higgs boson. We find that the real emission corrections are of moderate size, but that the virtual corrections are large. We discuss the origin of these corrections and give numerical predictions for the transverse-momentum spectrum. The threshold result is matched to the known NLO result and implemented in the public code PeTeR.

Measurement of the forward-backward asymmetry in top quark-antiquark production inpp¯collisions using thelepton+jetschannel

We present a measurement of the forward–backward asymmetry in top quark–antiquark production using the full Tevatron Run II data set collected by the D0 experiment at Fermilab. The measurement is performed in lepton+jets final states using a new kinematic fitting algorithm for events with four or more jets and a new partial reconstruction algorithm for events with only three jets. Corrected for detector acceptance and resolution effects, the asymmetry is evaluated to be AFB=(10.6±3.0)%. Results are consistent with the standard model predictions which range from 5.0% to 8.8%. We also present the dependence of the asymmetry on the invariant mass of the top quark–antiquark system and the difference in rapidities of the top quark and antiquark.3 MoreReceived 23 May 2014DOI:https://doi.org/10.1103/PhysRevD.90.072011© 2014 American Physical Society

ConstrainingCP-violating Higgs sectors at the LHC using gluon fusion

We investigate the constraints that the LHC can set on a 126 GeV Higgs boson that is an admixture of CP eigenstates. Traditional analyses rely on Higgs couplings to massive vector bosons, which are suppressed for CP-odd couplings, so that these analyses have limited sensitivity. Instead we focus on Higgs production in gluon fusion, which occurs at the same order in the strong coupling for both CP-even and -odd couplings. We study the Higgs plus two jet final state followed by Higgs decay into a pair of tau leptons. We show that using the 8 TeV dataset it is possible to rule out the pure CP-odd hypothesis in this channel alone at nearly 95\% C.L, assuming that the Higgs is CP-even. We also provide projected limits for the 14 TeV LHC run.

Search for excited quarks in the [formula omitted] final state in proton–proton collisions at [formula omitted

A search for excited quarks decaying into the γ+jet final state is presented. The analysis is based on data corresponding to an integrated luminosity of 19.7 fb−1 collected by the CMS experiment in proton–proton collisions at s=8 TeV at the LHC. Events with photons and jets with high transverse momenta are selected and the γ+jet invariant mass distribution is studied to search for a resonance peak. The 95% confidence level upper limits on the product of cross section and branching fraction are evaluated as a function of the excited quark mass. Limits on excited quarks are presented as a function of their mass and coupling strength; masses below 3.5 TeV are excluded at 95% confidence level for unit couplings to their standard model partners.

Measurement of the electric charge of the top quark intt¯events

We present a measurement of the electric charge of top quarks using $t\bar{t}$ events produced in $p\bar{p}$ collisions at the Tevatron. The analysis is based on fully reconstructed $t\bar{t}$ pairs in lepton+jets final states. Using data corresponding to 5.3 $\rm fb^{-1}$ of integrated luminosity, we exclude the hypothesis that the top quark has a charge of $Q=-4/3\,e$ at a significance greater than 5 standard deviations. We also place an upper limit of 0.46 on the fraction of such quarks that can be present in an admixture with the standard model top quarks ($Q=+2/3\,e$) at a 95\% confidence level.

Two-loop QCD corrections to Higgs → b + b ¯ $$ \overline{b} $$ + g amplitude

Exclusive observables involving Higgs boson in association with jets are often well suited to study the Higgs boson properties. They are rates involving cuts on the final state jets or differential distributions of rapidity, transverse momentum of the observed Higgs boson. While they get dominant contributions from gluon initiated partonic subprocesses, it is important to include the subdominant ones coming from other channels. In this article, we study one such channel namely the Higgs production in association with a jet in bottom anti-bottom annihilation process. We compute relevant amplitude H → b+ $$ \overline{b} $$ +g up to two loop level in QCD where Higgs couples to bottom quark through Yukawa coupling. We use projection operators to obtain the coefficients for each tensorial structure appearing in this process. We have demonstrated that the renormalized amplitudes do have the right infrared structure predicted by the QCD factorization in dimensional regularization. The finite parts of the one and two loop amplitudes are presented after subtracting the infrared poles using Catani’s subtraction operators.

1-jettiness DIS event shape: NNLL+NLO results

We present results for the complete $\mathrm{NNLL}+\mathrm{NLO}$ ($\ensuremath{\sim}{\ensuremath{\alpha}}_{s}$) 1-jettiness (${\ensuremath{\tau}}_{1}$) event shape distribution for single jet ($J$) production in electron-nucleus (${N}_{A}$) collisions ${e}^{\ensuremath{-}}+{N}_{A}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}+J+X$, in the deep inelastic scattering (DIS) region where the hard scale is set by the jet transverse momentum ${P}_{{J}_{T}}$. These results cover the entire ${\ensuremath{\tau}}_{1}$ spectrum including the resummation (${\ensuremath{\tau}}_{1}\ensuremath{\ll}{P}_{{J}_{T}}$) and fixed-order (${\ensuremath{\tau}}_{1}\ensuremath{\sim}{P}_{{J}_{T}}$) perturbative QCD regions. They incorporate nonperturbative soft radiation effects, the anti-${k}_{T}$ jet algorithm in the fixed-order calculation, and a smooth matching between the resummation and fixed-order perturbative QCD regions. The matching smoothly connects the spectrum in the resummation region, which can be computed without reference to an external jet algorithm, and the fixed-order region where an explicit jet algorithm must be specified. Our code, used for generating the numerical results, is flexible enough to incorporate different jet algorithms for the fixed-order calculation. We also perform a jet-shape analysis, defined within the 1-jettiness framework, which allows one to control the amount of radiation included in the definition of the final state jet. This formalism can allow for detailed studies of jet energy-loss mechanisms and nuclear medium effects. The analysis presented here can be used for precision studies of QCD and as a probe of nuclear dynamics using data collected at HERA and in proposed future electron-ion colliders such as the EIC and the LHeC.

Precision measurement of the top quark mass in lepton + jets final States.

We measure the mass of the top quark in lepton+jets final states using the full sample of pp collision data collected by the D0 experiment in Run II of the Fermilab Tevatron Collider at sqrt[s] = 1.96 TeV, corresponding to 9.7 fb(-1) of integrated luminosity. We use a matrix element technique that calculates the probabilities for each event to result from tt production or background. The overall jet energy scale is constrained in situ by the mass of the W boson. We measure m(t) = 174.98 ± 0.76 GeV. This constitutes the most precise single measurement of the top-quark mass.

Erratum: Photon isolation effects at NLO in γγ + jet final states in hadronic collisions

We present the NLO QCD corrections to pp → γγj production at hadron colliders. Our calculation includes contributions from the fragmentation of a hadronic jet into a highly energetic photon, and consequently allows the implementation of arbitrary infrared-safe photon isolation definitions. We compare different photon isolation criteria and perform a detailed study of the dependence of the γγj cross section on the photon isolation parameters.

Search for pair production of excited top quarks in the lepton + jets final state

A search is performed for pair-produced spin-3/2 excited top quarks (t* t*-bar), each decaying to a top quark and a gluon. The search uses data collected with the CMS detector from pp collisions at a center-of-mass energy of sqrt(s) = 8 TeV, selecting events that have a single isolated muon or electron, an imbalance in transverse momentum, and at least six jets, of which one must be compatible with originating from the fragmentation of a b quark. The data, corresponding to an integrated luminosity of 19.5 inverse femtobarns, show no significant excess over standard model predictions, and provide a lower limit of 803 GeV at 95% confidence on the mass of the spin-3/2 t* quark in an extension of the Randall-Sundrum model, assuming a 100% branching fraction of its decay into a top quark and a gluon. This is the first search for a spin-3/2 excited top quark performed at the LHC.

Measurement of the triple-differential cross section for photon + jets production in proton-proton collisions at $ \sqrt{s} $ = 7 TeV

A measurement of the triple-differential cross section (sigma as a function of the photon pt and eta and the jet eta) in photon + jets final states using a data sample from proton-proton collisions at sqrt(s) = 7 TeV is presented. This sample corresponds to an integrated luminosity of 2.14 inverse femtobarns collected by the CMS detector at the LHC. Photons and jets are reconstructed within a pseudorapidity range of abs(eta) < 2.5, and are required to have transverse momenta in the range 40 < pt(gamma) < 300 GeV and pt(jet) > 30 GeV, respectively. The measurements are compared to theoretical predictions from the SHERPA leading-order QCD Monte Carlo event generator and the next-to-leading-order perturbative QCD calculation from JETPHOX. The predictions are found to be consistent with the data over most of the examined kinematic region.

SU(5)octet scalar at the LHC

Color scalars are salient features of non-minimal SU(5) model, where Higgs sector is extended by 45-dimensional multiplet. We show that gauge coupling unification can be realized in this model with TeV octet scalar and intermediate (~10^6 GeV) color-triplet scalar at scale larger than 10^{15} GeV. We analyze the possible LHC signatures of these TeV octet scalars. We emphasize that multi-(b)-jet final states provide significant signal for direct probe of octet scalars at the LHC.

Search for Z' resonances decaying to top-antitop in dilepton +jets final states in pp collisions at 8 TeV center of mass energy

Search for Z' resonances decaying to top-antitop in dilepton +jets final states in pp collisions at 8 TeV center of mass energy

Preliminary measurement of the top quark pair production in the $\tau$ + jets final state with 20 $fb^{-1}$ of $pp$ collision data recorded at $\sqrt{s} = 8$ TeV with the ATLAS experiment

Preliminary measurement of the top quark pair production in the $\tau$ + jets final state with 20 $fb^{-1}$ of $pp$ collision data recorded at $\sqrt{s} = 8$ TeV with the ATLAS experiment

The quark beam function at two loops

In differential measurements at a hadron collider, collinear initial-state radiation is described by process-independent beam functions. They are the field-theoretic analog of initial-state parton showers. Depending on the measured observable they are differential in the virtuality and/or transverse momentum of the colliding partons in addition to the usual longitudinal momentum fraction. Perturbatively, the beam functions can be calculated by matching them onto standard quark and gluon parton distribution functions. We calculate the inclusive virtuality-dependent quark beam function at NNLO, which is relevant for any observables probing the virtuality of the incoming partons, including N-jettiness and beam thrust. For such observables, our results are an important ingredient in the resummation of large logarithms at N3LL order, and provide all contributions enhanced by collinear t-channel singularities at NNLO for quark-initiated processes in analytic form. We perform the calculation in both Feynman and axial gauge and use two different methods to evaluate the discontinuity of the two-loop Feynman diagrams, providing nontrivial checks of the calculation. As part of our results we reproduce the known two-loop QCD splitting functions and confirm at two loops that the virtuality-dependent beam and final-state jet functions have the same anomalous dimension.

Search for Quantum Black Hole Production in High-Invariant-MassLepton+JetFinal States UsingppCollisions ats=8 TeVand the ATLAS Detector

This Letter presents a search for quantum black-hole production using 20.3 fb-1 of data collected with the ATLAS detector in pp collisions at the LHC at √s = 8 TeV. The quantum black holes are assumed to decay into a final state characterized by a lepton (electron or muon) and a jet. In either channel, no event with a lepton-jet invariant mass of 3.5 TeV or more is observed, consistent with the expected background. Limits are set on the product of cross sections and branching fractions for the lepton+jet final states of quantum black holes produced in a search region for invariant masses above 1 TeV. The combined 95% confidence level upper limit on this product for quantum black holes with threshold mass above 3.5 TeV is 0.18 fb. This limit constrains the threshold quantum black-hole mass to be above 5.3 TeV in the model considered.