Single Jet Inclusive Cross Section Research Articles

NNLO QCD corrections in full colour for jet production observables at the LHC

Calculations for processes involving a high multiplicity of coloured particles often employ a leading colour approximation, where only the leading terms in the expansion of the number of colours Nc and the number of flavours nf are retained. This approximation of the full colour result is motivated by the 1/ {N}_c^2 suppression of the first subleading terms and by the increasing complexity of including subleading colour contributions to the calculation. In this work, we present the calculations using the antenna subtraction method in the NNLOjet framework for the NNLO QCD corrections at full colour for several jet observables at the LHC. The single jet inclusive cross section is calculated doubly differential in transverse momentum and absolute rapidity and compared with the CMS measurement at 13 TeV. A calculation for dijet production doubly differential in dijet mass and rapidity difference is also performed and compared with the ATLAS 7 TeV data. Lastly, a triply differential dijet cross section in average transverse momentum, rapidity separation and dijet system boost is calculated and compared with the CMS 8 TeV data. The impact of the subleading colour contributions to the leading colour approximation is assessed in detail for all three types of observables and as a function of the jet cone size. The subleading colour contributions play a potentially sizable role in the description of the triply differential distributions, which probe kinematical configurations that are not easily accessed by any of the other observables.

Single-jet inclusive cross section and its definition

We investigate some well-known problematic aspects of the single-jet inclusive cross-section, specifically its non-unitarity and the possibly related issue of apparent perturbative instability at low orders. We study and clarify their origin by introducing possible alternative weighted definitions of the observable which restore unitarity. We show that the perturbative instability of the standard definition is an accidental artefact of the smallness of the NLO $K$ factor which only manifests itself for values of the jet radius in the range $R\sim 0.3-0.6$, and that its non-unitarity is necessary in order to ensure cancellation of logs of the momentum cutoff used in the jet definition. We also show that alternative unitary definitions do not have better perturbative properties compared to the conventional non-unitary definition, while suffering from lack of cancellation of large logs.

Infrared sensitivity of single jet inclusive production at hadron colliders

Jet production at hadron colliders is a benchmark process to probe the dynamics of the strong interaction and the structure of the colliding hadrons. One of the most basic jet production observables is the single jet inclusive cross section, which is obtained by summing all jets that are observed in an event. Our recent computation of next-to-next-to-leading order (NNLO) QCD contributions to single jet inclusive observables uncovered large corrections in certain kinematical regions, which also resulted in a sizeable ambiguity on the appropriate choice of renormalization and factorization scales. We now perform a detailed investigation of the infrared sensitivity of the different ingredients to the single jet inclusive cross section. We show that the contribution from the second jet, ordered in transverse momentum pT, in the event is particularly sensitive to higher order effects due to implicit restrictions on its kinematics. By investigating the second-jet transverse momentum distribution, we identify large-scale cancellations between different kinematical event configurations, which are aggravated by certain types of scale choice. Taking perturbative convergence and stability as selection criteria enables us to single out the total partonic transverse energy ĤT and twice the individual jet transverse momentum 2 pT (with which ĤT coincides in Born kinematics) as the most appropriate scales in the perturbative description of single jet inclusive production.

Single Jet Inclusive Production for the Individual Jet $p_{\rm T}$ Scale Choice at the LHC

We study the single jet inclusive cross section up to next-to-next-to leading order in perturbative QCD, implemented in the parton-level event generator NNLOJET . Our results are fully differential in the jet transverse momentum and rapidity and we apply fiducial cuts for comparison with the available ATLAS 7 TeV 4.5 fb$^{-1}$ data for jet radius $R=0.4$. For the theoretical calculation we employ the antenna subtraction method to reliably cancel all infrared divergences present at intermediate stages of the calculation. We present all results using the individual jet transverse momentum $\mu_{R}=\mu_{F}\sim p_{T}$ as the renormalization and factorization scale for each jet's contribution to the single jet inclusive cross section. Finally, we consider the differences between our predictions using this scale choice to those for the leading jet transverse momentum scale choice, $\mu_{R}=\mu_{F}\sim p_{T_{1}}$, used in [14], with reference to the ATLAS data.

Weak corrections to four-parton processes

We report on a calculation of the ‘mixed’ strong and (purely) weak corrections through the order αS2αW to parton–parton processes in all possible channels at hadron colliders entering the single jet inclusive cross section. At both Tevatron and LHC, such effects are always negligible (below permille level) in the total integrated cross section whilst they become sizable in differential rates. Specifically, if such corrections are defined with respect to the full leading-order result of O(αS2+αSαEW+αEW2), we find that, at the FNAL accelerator, they can reach the −5% benchmark in the jet transverse energy (at the kinematical limit of the machine, rendering their detection quite difficult). At the CERN collider, in the same observable, they exceed the −10% level already at 1 TeV and can reach −40% at 4 TeV, kinematic regions where such corrections will be comfortably observable for standard luminosity. In addition, such corrections are somewhat sensitive to the factorisation/renormalisation scale choice.

AGK cutting rules and multiple scattering in hadronic collisions

We discuss the AGK rules for the exchange of an arbitrary number of reggeized gluons in perturbative QCD in the high energy limit. Results include the cancellation of corrections to single jet and double jet inclusive cross sections, both for hard and soft rescattering contributions.

Combining QCD matrix elements at next-to-leading order with parton showers in electroproduction

We present a method to combine next-to-leading order (NLO) matrix elements in QCD with leading logarithmic parton showers by applying a suitably modified version of the phase-space-slicing method. The method consists of subsuming the NLO corrections into a scale-dependent phase-space-slicing parameter, which is then automatically adjusted to cut out the leading order, virtual, soft and collinear contributions in the matrix element calculation. In this way a positive NLO weight is obtained, which can be redistributed by a parton shower algorithm. As an example, we display the method for single-jet inclusive cross sections at $\mathcal{O}({\ensuremath{\alpha}}_{s})$ in electroproduction. We numerically compare the modified version of the phase-space-slicing method with the standard approach and find very good agreement on the percent level.

Effects of higher-order threshold corrections in high-ETjet production

Results for higher-order threshold enhancements in high-${E}_{T}$ jet production in hadron-hadron collisions are presented. Expressions are given for the next-to-next-to-leading order (NNLO) threshold corrections to the single-jet inclusive cross section at next-to-leading logarithmic (NLL) accuracy. The corrections are found to be small for the specific choice of ${E}_{T}/2$ for the factorization and renormalization scales, and the corrected cross section shows a substantial reduction of the scale dependence. A comparison to experimental results from the Fermilab Tevatron is presented.

Resummation of threshold corrections for single-particle inclusive cross sections

We derive threshold resummations for single-particle and single-jet inclusive cross sections, thus generalizing previous results at fixed invariant mass to a wider class of cross sections with phenomenological interest. We confirm the structure of our resummed expressions by comparison with explicit one-loop calculations for direct photons and heavy quarks.

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.

Parton distributions: a study of the new HERA data, αs, the gluon and [formula omitted] jet production

New data, especially HERA measurements of the proton structure function at small x, allow the opportunity to improve our knowledge of the gluon and quark distribution functions. We perform a global analysis which incorporates these new precise data, and which extends down to Q 2 = 1.5 GeV 2. We discuss the sensitivity to the value of α s and the improvement in the determination of the gluon. We compare the predictions of the single jet inclusive cross section with recent measurements from the Fermilab Tevatron.

Inclusive jet production at HERA: Next-to-leading order QCD corrections to the resolved and direct photon contribution

We have calculated high transverse energy single-jet inclusive cross sections for γp-collisions at next-to-leading order superimposing direct and resolved photoproduction. The dependence on the scale and the scheme for the factorization of the photon structure is studied quantitatively. The accuracy of the predictions due to variations of all scales is investigated.

Single jet photoproduction at HERA in next-to-leading order QCD

We present results for next-to-leading order calculations of single jet inclusive cross sections by resolved photons inep-collisions at HERA. The dependence on the jet recombination cut and on the choice of the renormalization and factorization scales is studied in detail.

The single jet inclusive cross section in γγ processes at e +e − colliders as a means of measuring the gluon distribution of the photon

We examine the possibility of using the single jet inclusive cross section in γγ processes at e +e − colliders such as TRISTAN and LEP in order to get reliable measurements of the parton distributions of the photon and in particular of the gluon distribution. We find that if it is possible to tag the two spectator jet fragments from the two photons, and thereby reliably identifying the double resolved contribution to the cross section, then unambiguous measurement of the gluon content of the photon is possible if, in addition, it is assumed that the quark distributions are reliably known. An O( α s 3) next-to-leading order calculation of this contribution, which is very much less sensitive to renormalisation/factorisation scale uncertainties, is performed which reinforces this conclusion.

The single jet inclusive cross section at HERA in next-to-leading order QCD

We present the first next-to-leading order calculation of the single jet inclusive cross section at the ep collider HERA. Both the “resolved” and “direct” contributions are calculated to this order. We verify that our results are much less sensitive to the choice of renormalisation/factorisation scales than the leading order results. We examine the possibility of using this cross section to measure the parton distribution functions of the photon, in particular the poorly known gluon distribution.

Axigluon production in hadronic collisions.

Recently proposed chiral-color models predict the existence of a massive color octet of vector bosons, the axigluon. In this paper we investigate axigluon production in hadronic collisions. We compute the single-jet inclusive cross section and the two-jet invariant-mass distribution for the CERN collider, the Fermilab Tevatron, and the Superconducting Super Collider. We use CERN data to exclude axigluon masses between 125 and 275 GeV, subject to a mild constraint on the width.

LargeP T photoproduction in the hard scattering expansion

LargepT photoproduction is studied in the hard scattering expansion, including both three- and four-jet processes. The higher twist corrections (∝p T −6 andp T −8 ) to the basic QCD hard scattering process (∝p T −4 ) are estimated using the constituent interchange model and the various terms compared. Both single jet inclusive cross sections and single particle inclusive π0 cross sections are evaluated, the latter using scale violating fragmentation functions. We find that the higher twist terms are significant at present energies, particularly for three-jet events, though the four-jet anomalous photon contribution can be measured. Three-jet QCD processes require considerably higher energies to provide a significant contribution to the cross section. Methods of separating the different processes experimentally are discussed.