Search

This Report summarizes the results of the first 10 months' activities of the LHC Higgs Cross Sections Working Group. The main goal of the working group was to present the status-of-art on Higgs Physics at the LHC integrating all new results that have appeared in the last few years. The Report is more than a mere collection of the proceedings of the general meetings. The subgroups have been working in different directions. An attempt has been made to present the first Report from these subgroups in a complete and homogeneous form. The subgroups' contributions correspondingly comprise the main parts of the Report. A significant amount of work has been performed in providing higher-order corrections to the Higgs-boson cross sections and pinning down the theoretical uncertainty of the Standard Model predictions. This Report comprises explicit numerical results on total cross sections, leaving the issues of event selection cuts and differential distributions to future publications. The subjects for further study are identified.

We consider QCD radiative corrections to standard model Higgs-boson production in association with a W boson in hadron collisions. We present a fully exclusive calculation up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. To perform this NNLO computation, we use a recently proposed version of the subtraction formalism. Our calculation includes finite-width effects, the leptonic decay of the W boson with its spin correlations, and the decay of the Higgs boson into a bb¯ pair. We present selected numerical results at the Tevatron and the LHC.

We consider the production of a generic system of non-strongly interacting particles with a high total invariant mass M in hadron collisions. We examine the transverse-momentum (q) distribution of the system in the small-q region (q≪M), and we present a study of the perturbative QCD contributions that are enhanced by powers of large logarithmic terms of the type ln(M2/qT2). These terms can be resummed to all orders in QCD perturbation theory. The partonic production mechanism of the final-state system can be controlled by quark-antiquark (qq¯) annihilation and/or by gluon fusion. The resummation formalism for the qq¯ annihilation subprocess is well established, and it is usually extrapolated to the gluon fusion subprocess. We point out that this naïve extrapolation is not correct, and we present the all-order resummation formula for the q distribution in gluon fusion processes. The gluon fusion resummation formula has a richer structure than the resummation formula in qq¯ annihilation. The additional structure originates from collinear correlations that are a specific feature of the evolution of the colliding hadrons into gluon partonic states. In the q cross section at small values of q, these gluon collinear correlations produce coherent spin correlations between the helicity states of the initial-state gluons and definite azimuthal-angle correlations between the final-state particles of the observed high-mass system.

We consider the transverse-momentum (q_T) distribution of Drell--Yan lepton pairs produced in hadron collisions. At small values of q_T, we resum the logarithmically-enhanced perturbative QCD contributions up to next-to-next-to-leading logarithmic accuracy. At intermediate and large values of q_T, we consistently combine resummation with the known next-to-leading order perturbative result. All perturbative terms up to order alpha_S^2 are included in our computation which, after integration over q_T, reproduces the known next-to-next-to-leading order result for the Drell--Yan total cross section. We show and discuss the reduction in the scale dependence of the results with respect to lower-order calculations, estimating the corresponding perturbative uncertainty. We present a preliminary comparison with Tevatron Run II data., Comment: Additional details shown in Fig.3. Note added on the quantitative effect of the coefficient A^{(3)}

This is the summary and introduction to the proceedings contributions for the Les Houches 2009 "Tools and Monte Carlo" working group., Comment: 144 Pages. Workshop site http://wwwlapp.in2p3.fr/conferences/LesHouches/Houches2009/ . Conveners were Butterworth, Maltoni, Moortgat, Richardson, Schumann and Skands

We consider the production of W bosons in hadron collisions, and the subsequent leptonic decay W->lnu_l. We study the asymmetry between the rapidity distributions of the charged leptons, and we present its computation up to the next-to-next-to-leading order (NNLO) in QCD perturbation theory. Our calculation includes the dependence on the lepton kinematical cuts that are necessarily applied to select W-> lnu_l events in actual experimental analyses at hadron colliders. We illustrate the main differences between the W and lepton charge asymmetry, and we discuss their physical origin and the effect of the QCD radiative corrections. We show detailed numerical results on the charge asymmetry in ppbar collisions at the Tevatron, and we discuss the comparison with some of the available data. Some illustrative results on the lepton charge asymmetry in pp collisions at LHC energies are presented., Comment: 37 pages, 21 figures

We present updated predictions for Higgs boson production at the Tevatron and the LHC and we review their corresponding uncertainties. We report on a study of the impact of QCD radiative corrections on the Higgs boson search at the Tevatron., Comment: 7 pages, no figures. Invited talk given at the 9th International Symposium on Radiative Corrections, RADCOR 2009, Ascona, Switzerland, October 2009

We consider the production of a generic system of non-strongly interacting particles with a high total invariant mass M in hadron collisions. We examine the transverse-momentum (q_T) distribution of the system in the small-q_T region (q_T << M), and we present a study of the perturbative QCD contributions that are enhanced by powers of large logarithmic terms of the type ln (M^2/q_T^2). These terms can be resummed to all orders in QCD perturbation theory. The partonic production mechanism of the final-state system can be controlled by quark-antiquark (qqbar) annihilation and/or by gluon fusion. The resummation formalism for the qqbar annihilation subprocess is well established, and it is usually extrapolated to the gluon fusion subprocess. We point out that this naive extrapolation is not correct, and we present the all-order resummation formula for the q_T distribution in gluon fusion processes. The gluon fusion resummation formula has a richer structure than the resummation formula in qqbar annihilation. The additional structure originates from collinear correlations that are a specific feature of the evolution of the colliding hadrons into gluon partonic states. In the q_T cross section at small values of q_T, these gluon collinear correlations produce coherent spin correlations between the helicity states of the initial-state gluons and definite azimuthal-angle correlations between the final-state particles of the observed high-mass system., Comment: 27 pages, no figures

We present updated predictions for the total cross section for Higgs boson production by gluon--gluon fusion in hadron collisions. Our calculation includes the most advanced theoretical information available at present for this observable: soft-gluon resummation up to next-to-next-to-leading logarithmic accuracy, the exact treatment of the bottom-quark contribution up to next-to-leading order, and two-loop electroweak effects. We adopt the most recent parametrization of parton distribution functions at next-to-next-to-leading order, and we evaluate the corresponding uncertainties. In comparison with our previous central predictions, at the Tevatron the difference ranges from +9% for m_H=115 GeV to -9% for m_H=200 GeV. At the LHC the cross section is instead significantly increased. The effect goes from +30% for m_H=115 GeV to +9% for m_H=300 GeV, and is mostly due to the new parton distribution functions. We also provide new predictions for the LHC at sqrt{s}=10 TeV., Comment: 7 pages, no figures, references added

We consider the production of W and Z bosons in hadron collisions. We present a selection of numerical results obtained through a fully exclusive calculation up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. We include the $\gamma$--$Z$ interference, finite-width effects, the leptonic decay of the vector bosons and the corresponding spin correlations. The calculation is completely realistic, since it allows us to apply arbitrary kinematical cuts on the final-state leptons and the associated partons, and to compute the corresponding distributions in the form of bin histograms., Comment: Invited talk given at the XVII International Workshop on Deep-Inelastic Scattering and Related Subjects DIS 2009, 26-30 April 2009, Madrid

We consider the transverse-momentum distribution of colourless high-mass systems (lepton pairs, vector bosons, Higgs particles...) produced in hadronic collisions. We briefly review a formalism for the all-order resummation of the logarithmically-enhanced contributions at small transverse momenta, and we present an illustrative selection of numerical results obtained by using our method., Comment: Invited talk given at the XVII International Workshop on Deep-Inelastic Scattering and Related Subjects DIS 2009, 26-30 April 2009, Madrid

We consider QCD radiative corrections to the production of W and Z bosons in hadron collisions. We present a fully exclusive calculation up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. To perform this NNLO computation, we use a recently proposed version of the subtraction formalism. The calculation includes the gamma-Z interference, finite-width effects, the leptonic decay of the vector bosons and the corresponding spin correlations. Our calculation is implemented in a parton level Monte Carlo program. The program allows the user to apply arbitrary kinematical cuts on the final-state leptons and the associated jet activity, and to compute the corresponding distributions in the form of bin histograms. We show selected numerical results at the Tevatron and the LHC., Comment: 7 pages, 3 ps figures

These proceedings collect the presentations given at the first three meetings of the INFN "Workshop on Monte Carlo's, Physics and Simulations at the LHC", held at the Frascati National Laboratories in 2006. The first part of these proceedings contains pedagogical introductions to several basic topics of both theoretical and experimental high pT LHC physics. The second part collects more specialised presentations., Comment: 157 pages, 136 figures; contribution by M. Grazzini has been added

We consider Standard Model Higgs boson production by gluon--gluon fusion in hadron collisions. We present a calculation of the next-to-next-to-leading order QCD corrections to the cross section in the H->WW->lnu lnu and H->ZZ->4l decay channels. The calculation is implemented in the parton level Monte Carlo program HNNLO and allows us to apply arbitrary cuts on the final state leptons and the associated jet activity. We present selected numerical results for the signal cross section at the LHC, by using all the nominal cuts proposed for the forthcoming Higgs boson search., Comment: References added. Version published on JHEP

We consider transverse-momentum (q_T) resummation for Drell--Yan lepton pair production in hadron collisions. At small values of q_T, the logarithmically-enhanced QCD contributions are resummed up to next-to-leading logarithmic accuracy. At intermediate and large values of q_T, resummation is consistently combined with the fixed-order perturbative result. We present numerical results for e^+e^- pairs from the decay of Z bosons produced at Tevatron energies. We perform a detailed study of the scale dependence of the results to estimate the corresponding perturbative uncertainty. We comment on the comparison with the available Tevatron data., Comment: 24 pages, 12 ps figures, added comments and references; results unchanged

We consider Higgs boson production through gluon--gluon fusion in hadron collisions. We present a numerical program that computes the cross section up to NNLO in QCD perturbation theory. The program allows the user to apply arbitrary cuts on the momenta of the partons and of the photons or leptons that are produced in the final state. We present selected numerical results at the Tevatron and the LHC., Comment: Presented at the XLIIIth Rencontres de Moriond, QCD and hadronic interactions, La Thuile, Italy, March 8-15 2008

Report of the Working Group on Higgs Bosons for the Workshop, ``Physics at TeV Colliders'', Les Houches, France, 11-29 June, 2007., Comment: 102 pages, 68 figures

We consider Higgs boson production through gluon--gluon fusion in hadron collisions. We present a numerical program that computes the cross section up to NNLO in QCD perturbation theory. The program includes the decay modes H->gamma-gamma, H->WW->lnulnu, H->ZZ->4leptons, and allows the user to apply arbitrary cuts on the momenta of the partons and of the photons or leptons that are produced in the final state., Comment: 6 pages, to appear in the proceedings of the 8th International Symposium on Radiative Corrections, RADCOR 2007, Florence, Italy

We consider higher-order QCD corrections to the production of colourless high-mass systems (lepton pairs, vector bosons, Higgs bosons,...) in hadron collisions. We propose a new formulation of the subtraction method to numerically compute arbitrary infrared-safe observables for this class of processes. To cancel the infrared divergences, we exploit the universal behaviour of the associated transverse-momentum (q_T) distributions in the small-q_T region. The method is illustrated in general terms up to the next-to-next-to-leading order (NNLO) in QCD perturbation theory. As a first explicit application, we study Higgs boson production through gluon fusion. Our calculation is implemented in a parton level Monte Carlo program that includes the decay of the Higgs boson in two photons. We present selected numerical results at the LHC., Comment: References added

We consider Higgs boson production by gluon fusion in hadron collisions. We study the doubly-differential transverse-momentum (q_T) and rapidity (y) distribution of the Higgs boson in perturbative QCD. In the region of small q_T (q_T << M_H, M_H being the mass of the Higgs boson), we include the effect of logarithmically-enhanced contributions due to multiparton radiation to all perturbative orders. We use the impact parameter and double Mellin moments to implement and factorize the multiparton kinematics constraint of transverse- and longitudinal-momentum conservation. The logarithmic terms are then systematically resummed in exponential form. At small q_T, we perform the all-order resummation of large logarithms up to next-to-next-to-leading logarithmic accuracy, while at large q_T (q_T ~ M_H), we apply a matching procedure that recovers the fixed-order perturbation theory up to next-to-leading order. We present quantitative results for the differential cross section in q_T and y at the LHC, and we comment on the comparison with the q_T cross section integrated over y., Comment: References added

Non resonant production of WW pairs is the most important background in the Higgs search in the range 155 \ltap M_H \ltap 170 GeV at the LHC. We consider QCD corrections to WW pair production in hadron collisions and present a calculation which consistently combines NLO corrections with soft-gluon resummation at small transverse momenta of the WW pair. Spin correlations are fully taken into account in our calculation. We study the impact of the resummation on the leptonic observables and perform a comparison with results obtained at NLO and with the MC@NLO event generator., Comment: 4 pages, 5 figures, presented at the XLIst Rencontres de Moriond, QCD and Hadronic interactions, La Thuile, Italy

This Report summarises the activities of the "SM and Higgs" working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. On the one hand, we performed a variety of experimental and theoretical studies on standard candles (such as W, Z, and ttbar production), treating them either as proper signals of known physics, or as backgrounds to unknown physics; we also addressed issues relevant to those non-perturbative or semi-perturbative ingredients, such as Parton Density Functions and Underlying Events, whose understanding will be crucial for a proper simulation of the actual events taking place in the detectors. On the other hand, several channels for the production of the Higgs, or involving the Higgs, have been considered in some detail. The report is structured into four main parts. The first one deals with Standard Model physics, except the Higgs. A variety of arguments are treated here, from full simulation of processes constituting a background to Higgs production, to studies of uncertainties due to PDFs and to extrapolations of models for underlying events, from small-$x$ issues to electroweak corrections which may play a role in vector boson physics. The second part of the report treats Higgs physics from the point of view of the signal. In the third part, reviews are presented on the current status of multi-leg, next-to-leading order and of next-to-next-to-leading order QCD computations. Finally, the fourth part deals with the use of Monte Carlos for simulation of LHC physics., Comment: 234 pages, 173 figures. Web page of the workshop (with links to the talks): http://lappweb.in2p3.fr/conferences/LesHouches/Houches2005

We present QCD predictions for the transverse momentum (q_T) distribution of the Higgs boson at the LHC. At small q_T the logarithmically-enhanced terms are resummed to all orders up to next-to-next-to-leading logarithmic accuracy. The resummed component is consistently matched to the next-to-leading order calculation valid at large q_T. The results, which implement the most advanced perturbative predictions available at present for this observable, show a good stability with respect to theoretical uncertainties. The numerical program HqT, used to perform the calculation, is briefly discussed., Comment: 4 pages, 2 figures, to appear in the Proceedings of the International Europhysics Conference on High Energy Physics, July 21st - 27th 2005, Lisboa, Portugal

We consider the transverse-momentum (q_T) distribution of generic high-mass systems (lepton pairs, vector bosons, Higgs particles, ....) produced in hadron collisions. At small q_T, we concentrate on the all-order resummation of the logarithmically-enhanced contributions in QCD perturbation theory. We elaborate on the $b$-space resummation formalism and introduce some novel features: the large logarithmic contributions are systematically exponentiated in a process-independent form and, after integration over q_T, they are constrained by perturbative unitarity to give a vanishing contribution to the total cross section. At intermediate and large q_T, resummation is consistently combined with fixed-order perturbative results, to obtain predictions with uniform theoretical accuracy over the entire range of transverse momenta. The formalism is applied to Standard Model Higgs boson production at LHC energies. We combine the most advanced perturbative information available at present for this process: resummation up to next-to-next-to-leading logarithmic accuracy and fixed-order perturbation theory up to next-to-leading order. The results show a high stability with respect to perturbative QCD uncertainties., Comment: 48 pages, 13 postscript figures

We consider QCD radiative corrections to WW pair production in hadron collisions. We perform a calculation that consistently combines next-to-leading order predictions with soft-gluon resummation valid at small transverse momenta ptWW of the WW pair. We present results for the ptWW distribution at the LHC up to (almost) next-to-next-to-leading logarithmic accuracy, and study the effect of resummation on the charged-lepton distributions. Soft-gluon effects are typically mild, but they can be strongly enhanced when hard cuts are applied. The relevant distributions are generally well described by the MC@NLO event generator., Comment: 15 pages, 12 postscript figures. Error corrected in NLO plot for WW transverse-mass distribution. Results unchanged

We propose a framework for the implementation of a subtraction formalism at NNLO in QCD, based on an observable- and process-independent cancellation of infrared singularities. As a first simple application, we present the calculation of the contribution to the e+e- dijet cross section proportional to C_F T_R, Comment: 42 pages Latex; 7 figures included. Modifications to the text, and references added; the results are unchanged

A simulation of the search for the Standard Model Higgs boson at the LHC, in the channel gg -> H -> WW -> lnu lnu, is described. Higher-order QCD corrections are taken into account by using a reweighting procedure, which allows us to combine event rates obtained with the PYTHIA Monte Carlo program with the most up-to-date theoretical predictions for the transverse-momentum spectra of the Higgs signal and its corresponding WW background. With this method the discovery potential for Higgs masses between 140 and 180 GeV is recalculated and the potential statistical significance of this channel is found to increase considerably. For a Higgs mass of 165 GeV a signal-to-background ratio of almost 2:1 can be obtained. A statistical significance of five standard deviations might already be achieved with an integrated luminosity close to 0.4 fb^{-1}. Using this approach, an experimental effective K-factor of about 2.04 is obtained for the considered Higgs signature, which is only about 15 % smaller than the theoretical inclusive K-factor., Comment: 16 pages, 8 eps figures, comparison of jet veto efficiencies between PYTHIA and HERWIG added, to appear on JHEP

This report documents the results obtained by the Working Group on Quantum Chromodynamics and the Standard Model for the Workshop `Physics at TeV Colliders'', Les Houches, France, 26 May - 6 June 2003. After a Monte Guide description, the first contributions report on progress in describing multiple interactions, important for the LHC, and underlying events. An announcement of a Monte Carlo database, under construction, is then followed by a number of contributions improving parton shower descriptions. Subsequently, a large number of contributions address resummations in various forms, after which follow studies of QCD effects in pion pair, top quark pair and photon pair plus jet production. After a study of electroweak corrections to hadronic precision observables, the report ends by presenting recent progress in methods to compute finite order corrections at one-loop with many legs, and at two-loop., Comment: 119pp

This paper describes a comparison of most of the available predictions for the cross section and transverse momentum distribution for a 125 GeV mass Higgs at the LHC, including those from the PYTHIA and HERWIG parton shower Monte Carlos and from four resummation calculations., Comment: 7 pages, submitted to proceedings of the Workshop on Physics at TeV Colliders, Les Houches 2003

Theoretical progress in Higgs boson production and background processes is discussed with particular emphasis on QCD corrections at and beyond next-to-leading order as well as next-to-leading order electroweak corrections. The residual theoretical uncertainties of the investigated processes are estimated in detail. Moreover, recent investigations of the MSSM Higgs sector and other extensions of the SM Higgs sector are presented. The potential of the LHC and a high-energy linear e+e- collider for the measurement of Higgs couplings is analyzed., Comment: 169 pages, Proceedings 3rd Les Houches Workshop: Physics at TeV Colliders, Les Houches, France, 26 May - 6 Jun 2003

We present perturbative predictions for the transverse momentum (q_T) distribution of the Higgs boson at the LHC. At small q_T the logarithmically-enhanced terms are resummed to all orders up to next-to-next-to-leading logarithmic accuracy. The resummed component is consistently matched to the next-to-leading order calculation valid at large q_T. The results, which implement the most advanced perturbative information that is available at present for this observable, show a good stability with respect to perturbative QCD uncertainties., Comment: 6 pages, 3 figures, presented at the XXXIXth Rencontres de Moriond, QCD and Hadronic interactions, La Thuile, Italy

We consider the back-to-back region in the energy--energy correlation in e^+e^- collisions. We present the explicit expression of the O(as^2) logarithmically enhanced contributions up to next-to-next-to-leading logarithmic accuracy. We study the impact of the results in a detailed comparison with precise LEP and SLC data. We find that, when hadronization effects are taken into account as is customarily done in QCD analysis in e^+e^- annihilations, the extracted value of as(M_Z) is in good agreement with the current world average., Comment: 15 pages, 8 figures

We consider QCD corrections to Higgs boson production through gluon--gluon fusion in hadron collisions. We compute the cross section, performing the all-order resummation of multiple soft-gluon emission at next-to-next-to-leading logarithmic level. Known fixed-order results (up to next-to-next-to-leading order) are consistently included in our calculation. We give phenomenological predictions for Higgs boson production at the Tevatron and at the LHC. We estimate the residual theoretical uncertainty from perturbative QCD contributions. We also quantify the differences obtained by using the presently available sets of parton distributions., Comment: 44 pages, 17 postscript figures

We consider the transverse-momentum (q_T) distribution of Higgs bosons produced at hadron colliders. We use a formalism that uniformly treats both the small-q_T and large-q_T regions in QCD perturbation theory. At small q_T (q_T << M_H, M_H being the mass of the Higgs boson), we implement an all-order resummation of logarithmically-enhanced contributions up to next-to-next-to-leading logarithmic accuracy. At large q_T (q_T \gtap M_H), we use fixed-order perturbation theory up to next-to-leading order. The resummed and fixed-order approaches are consistently matched by avoiding double-counting in the intermediate-q_T region. In this region, the introduction of unjustified higher-order terms is avoided by imposing unitarity constraints, so that the integral of the q_T spectrum exactly reproduces the perturbative result for the total cross section up to next-to-next-to-leading order. Numerical results at the LHC are presented. These show that the main features of the q_T distribution are quite stable with respect to perturbative QCD uncertainties., Comment: 9 pages, 2 postscript figures

We consider QCD corrections to Higgs boson production through gluon-gluon fusion in hadron collisions. We compute the cross section, performing the all-order resummation of multiple soft-gluon emission at next-to-next-to-leading logarithmic level. Known fixed-order results (up to next-to-next-to-leading order) are consistently included in our calculation. We give phenomenological predictions for Higgs boson production at the Tevatron and at the LHC. We estimate the residual theoretical uncertainty from perturbative QCD contributions. We also quantify the differences obtained by using the presently available sets of parton distributions