We include a resummation of large transverse momentum logarithms in the next-to-leading order (NLO) Balitsky-Kovchegov equation. The resummed evolution equation is shown to be stable, the evolution speed being significantly reduced by NLO corrections. The contributions from NLO terms that are not enhanced by large logarithms are found to be numerically important close to phenomenologically relevant initial conditions. We numerically determine the value for the constant in the resummed logarithm that includes a maximal part of the full NLO terms in the resummation.
Novel PDFs taking into account resummation-improved matrix elements, albeit only in the fit of a reduced data set, allow for consistent NLO+NLL calculations of slepton pair production at the LHC. We apply a factorisation method to this process that minimises the effect of the data set reduction, avoids the problem of outlier replicas in the NNPDF method for PDF uncertainties and preserves the reduction of the scale uncertainty. For Run II of the LHC, left-handed selectron/smuon, right-handed and maximally mixed stau production, we confirm that the consistent use of threshold-improved PDFs part…
Using parton density functions (PDFs) with threshold-resummation improvement, we consistently calculate higgsino/gaugino and slepton pair production at next-to-leading order and next-to-leading logarithmic accuracy at the LHC. The smaller PDF uncertainty of the global PDF sets is exploited with a factorisation method, which also avoids complications arising in the refitting of threshold-resummation improved PDF replicas in Mellin space. We explicitly take into account the reduction of the scale uncertainty due to the resummation. We show that the resummation contributions in the PDF fits parti…
We discuss the GENEVA Monte Carlo framework, which combines higher-order resummation (NNLL) of large Sudakov logarithms with multiple next-to-leading-order (NLO) matrix-element corrections and parton showering (using PYTHIA8) to give a complete description at the next higher perturbative accuracy in alpha_s at both small and large jet resolution scales. Results for e+e- -> jets compared to LEP data and for Drell-Yan production are presented.
In electroweak-boson production processes with a jet veto, higher-order corrections are enhanced by logarithms of the veto scale over the invariant mass of the boson system. In this paper, we resum these Sudakov logarithms at next-to-next-to-leading logarithmic (NNLL) accuracy and match our predictions to next-to-leading order (NLO) fixed-order results. We perform the calculation in an automated way, for arbitrary electroweak final states and in the presence of kinematic cuts on the leptons produced in the decays of the electroweak bosons. The resummation is based on a factorization theorem fo…
We consider the $HZ$ associated production at the $14~{\rm TeV}$ LHC in the littlest Higgs model (LHM) and study the corrections of the transverse momentum resummation and threshold resummation at the next-to-leading logarithmic (NLL) accuracy and the fixed-order prediction at the QCD next-to-leading order (NLO) including the contribution from the one-loop-induced $gg$-fusion channel. The QCD NLO+NLL effects on the integrated cross section and the distributions of transverse momentum and invariant mass of the $HZ$ system for the $HZ$ production in the LHM are discussed. The distributions of tr…
We present a first and extensive study of threshold resummation effects for supersymmetric (SUSY) particle production at hadron colliders, focusing on Drell-Yan like slepton-pair and slepton-sneutrino associated production. After confirming the known next-to-leading order (NLO) QCD corrections and generalizing the NLO SUSY-QCD corrections to the case of mixing squarks in the virtual loop contributions, we employ the usual Mellin N-space resummation formalism with the minimal prescription for the inverse Mellin-transform and improve it by resumming 1/N-suppressed and a class of N-independent un…
We present an extension of the Monte Carlo Event Generator Whizard which includes chargino production at the ILC at NLO. We include photons using both a fixed order and a resummation approach. While the fixed order approach suffers from negative event weights, the resummation method solves this problem and automatically includes leading higher order corrections. We present results for cross sections and event generation for both methods and evaluate the systematic errors due to soft and collinear approximations. In the resummation approach, the residual uncertainty can be brought down to the p…
We make use of recently released parton density functions (PDFs) with threshold-resummation improvement to consistently calculate theoretical predictions for neutralino and chargino pair production at next-to-leading order and next-to-leading logarithmic accuracy. The updated cross sections have been computed for experimentally relevant higgsino and gaugino search channels at the ongoing Run II of the LHC. A factorisation method is applied to exploit the smaller PDF uncertainty of the global PDF sets and to avoid complications arising in the refitting of threshold-resummation improved PDF repl…
The resummed differential thrust rate in e+e- annihilation is calculated using Soft-Collinear Effective Theory (SCET). The resulting distribution in the two-jet region T~1 is found to agree with the corresponding expression derived by the standard approach. A matching procedure to account for finite corrections at T < 1 is then described. There are two important advantages of the SCET approach. First, SCET manifests a dynamical seesaw scale q = p^2/Q in addition to the center-of-mass energy Q and the jet mass scale p ~ Q ~ sqrt(1 - T). Thus, the resummation of logs of p/q can be cleanly distin…
We perform threshold resummation of soft gluon corrections to the total cross section and the invariant mass distribution for the process $pp \to t\bar{t}H$. The resummation is carried out at next-to-next-to-leading-logarithmic (NNLL) accuracy using the direct QCD Mellin space technique in the three-particle invariant mass kinematics. After presenting analytical expressions we discuss the impact of resummation on the numerical predictions for the associated Higgs boson production with top quarks at the LHC. We find that NLO+NNLL resummation leads to predictions for which the central values are…
We thoroughly investigate both transverse momentum and threshold resummation effects on scalar-pseudoscalar pair production via quark-antiquark annihilation at the $13~ \text{TeV}$ Large Hadron Collider at QCD NLO+NLL accuracy. A factorization method is introduced to properly supplement the soft-gluon (threshold) resummation contribution from parton distribution functions to the resummed results obtained by the Collins-Soper-Sterman resummation approach. We find that the impact of the threshold-resummation improved PDFs is comparable to the resummation effect of the partonic matrix element and…
We perform a global parton fit to DIS and related data, including next-to-leading logarithmic (NLL) BFKL resummations in both the massless and massive sectors. The resummed fit improves over a standard next-to-leading order (NLO) DGLAP fit, with a positive definite gluon at the input scale as opposed to the negative gluon seen at NLO. Furthermore, the predicted longitudinal structure function is free of perturbative instability at small x, and the reduced cross-section shows a turnover at high y (absent in the NLO fit) consistent with the HERA data.
The moments of the single inclusive momentum distribution of hadrons in QCD jets, are studied in the next-to-modified-leading-log approximation (NMLLA) including next-to-leading-order (NLO) corrections to the alpha_s strong coupling. The evolution equations are solved using a distorted Gaussian parametrisation, which successfully reproduces the spectrum of charged hadrons of jets measured in e+e- collisions. The energy dependencies of the maximum peak, multiplicity, width, kurtosis and skewness of the jet hadron distribution are computed analytically. Comparisons of all the existing jet data m…
We perform threshold resummation of soft gluon corrections to the total cross sections and the invariant mass distributions for production of a top-antitop quark pair associated with a heavy electroweak boson $V = W^+$, $W^-$ or $Z$ in $pp$ collisions at the Large Hadron Collider. The resummation is carried out at next-to-next-to-leading-logarithmic (NNLL) accuracy using the direct QCD Mellin space technique in the three-particle invariant mass kinematics. It is found that for the $t\bar t Z$ process the soft gluon resummation introduces significant corrections to the next-to-leading order (NL…
We examine the soft-gluon resummation effects, including the exact spin correlations among the final state particles, in the search of the Standard Model Higgs boson, via the process $gg\to H\to WW/ZZ \to 4 leptons, at the Tevatron and the LHC. A comparison between the resummation and the Next-to-Leading order (NLO) calculation is performed after imposing various kinematics cuts suggested in the literature for the Higgs boson search. For the $H\to ZZ$ mode, the resummation effects increase the acceptance of the signal events by about 25%, as compared to the NLO prediction, and dramatically alt…
We investigate the QCD effects in the associated production of the chargino and the neutralino, $\tildeχ^\pm_{1}$ and $\tildeχ^0_{2}$, in the Minimal Supersymmetric Standard Model (MSSM) at both the Fermilab Tevatron and the CERN Large Hadron Collider (LHC). We include the next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) and the threshold resummation effects. Our results show that, compared to the NLO predictions, the threshold resummation effects can increase the total cross sections by 3.6% and 3.9% for the associated production of $\tildeχ^+_{1}\tildeχ^0_{2}$ and $…
We perform a threshold resummation calculation for the associated production of squarks and electroweakinos at the LHC to the next-to-leading logarithmic (NLL) accuracy. Analytical results for the process-dependent soft anomalous dimension and the hard matching coefficient are presented. The resummed results are matched to fixed-order predictions at next-to-leading order (NLO) in QCD, which are generalised to scenarios with non-universal squark masses and mixings. Numerically, the NLL contributions increase the total NLO cross section by $2\%$ to $6\%$ for squark masses ranging from 1 TeV to 3…
QCD resummation predictions for the production of new charged ($W'$) and neutral ($Z'$) heavy gauge bosons decaying leptonically are presented. These results are obtained with our resummation code at next-to-leading order and next-to-leading logarithmic (NLO+NLL) accuracy. Our predictions are compared to PYTHIA at leading order (LO) supplemented with parton showers (PS) and FEWZ at NLO and next-to-next-to-leading order (NNLO) for the $p_T$-differential and total cross sections in the Sequential Standard Model (SSM) and general SU(2)$\times$SU(2)$\times$U(1) models. We show that the importance …
We extend the lowest-order matching of tree-level matrix elements with parton showers to give a complete description at the next higher perturbative accuracy in alpha_s at both small and large jet resolutions, which has not been achieved so far. This requires the combination of the higher-order resummation of large Sudakov logarithms at small values of the jet resolution variable with the full next-to-leading order (NLO) matrix-element corrections at large values. As a by-product this combination naturally leads to a smooth connection of the NLO calculations for different jet multiplicities. I…
We study the single hadron inclusive production in the forward rapidity region in proton-nucleus collisions. We find the long-standing negative cross section at next-to-leading-order (NLO) is driven by the large negative threshold logarithmic contributions. We established a factorization theorem for resumming these logarithms with systematically improvable accuracy within the color glass condensate formalism. We demonstrate how the threshold leading logarithmic accuracy can be realized by a suitable scale choice in the NLO results. The NLO spectrums with the threshold logarithms resummed remai…
We present a determination of the parton distribution functions of the proton in which NLO and NNLO fixed-order calculations are supplemented by NLLx small-x resummation. Deep inelastic structure functions are computed consistently at NLO+NLLx or NNLO+NLLx, while for hadronic processes small-x resummation is included only in the PDF evolution, with kinematic cuts introduced to ensure the fitted data lie in a region where the fixed-order calculation of the hard cross-sections is reliable. In all other respects, the fits use the same methodology and are based on the same global dataset as the re…
We include resummation of large transverse logarithms into the next-to-leading order Balitsky-Kovchegov equation. The resummed NLO evolution equation is shown to be stable, the evolution speed being significantly reduced by higher order corrections. The contributions from $α_s^2$ terms that are not enhanced by large logarithms are found to be numerically important close to phenomenologically relevant initial conditions.
QCD resummation predictions for the production of charged (W') and neutral (Z') heavy gauge bosons decaying leptonically are presented. The results of our resummation code at next-to-leading order and next-to-leading logarithmic (NLO+NLL) accuracy are compared to Monte Carlo predictions obtained with PYTHIA at leading order (LO) supplemented with parton showers (PS) and FEWZ at NLO and next-to-next-to-leading order (NNLO) for the $p_T$-differential and total cross sections in the Sequential Standard Model (SSM) and general SU(2)xSU(2)xU(1) models. The LO+PS Monte Carlo and NNLO fixed-order pre…
We derive precision predictions for the production of dark-matter particles recoiling against a jet with large transverse momentum at the LHC. The dark-matter fermions are described within a simplified model and couple to the Standard Model via a vector mediator. Our predictions for the mono-jet signature include the resummation of the leading and next-to-leading threshold logarithms. The corresponding matching coefficient is evaluated at NLO. The resummed result is matched to the fixed-order NLO cross section obtained from the MadGraph framework. We discuss numerical results for several bench…
We are interested in the transverse-momentum ($q_T$) distribution of a diphoton pair produced in hadron collisions. We resum the logarithmically-enhanced perturbative QCD contributions at small values of $q_T$ up to next-to-next-to-leading logarithmic accuracy. We consistently combine resummation with the known next-to-leading order perturbative result at intermediate and large values of $q_T$ . We include all perturbative terms up to order $α_S^2$ in our computation which, after integration over $q_T$ , reproduces the known next-to-next-to-leading order result for the diphoton pair production…
We calculate the soft-gluon corrections for $tW$ production to all orders. The soft limit is defined in the pair invariant mass or one particle inclusive kinematic schemes. We find that at NLO the contribution of the soft-gluon effect dominates in the total cross section or the differential distributions. After resumming the soft-gluon effect to all orders using the renormalization group equation, we find that the NLO+NNLL results increase the NLO cross sections by $12\%\sim 17\%$ depending on the scheme and the collider energy. Our results are in agreement with the measurements at the 8 and 1…
We investigate the QCD effects in the production of neutral Higgs bosons via bottom quark fusion in both the standard model and the minimal supersymmetric standard model at the CERN Large Hadron Collider. We include the next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) and the threshold resummation effects. We use the soft-collinear effective theory to resum the large logarithms near threshold from soft gluon emission. Our results show that the resummation effects can enhance the total cross sections by about 5% compared with the NLO results.
We investigate threshold resummation effects in the production of a color sextet (antitriplet) scalar at next-to-next-to-leading logarithmic (NNLL) order at the LHC in the frame of soft-collinear effective theory. We show the total cross section and the rapidity distribution with NLO+NNLL accuracy, and we compare them with the NLO results. Besides, we use recent dijet data at the LHC to give the constraints on the couplings between the colored scalars and quarks.
We study QCD effects in single graviton production at the CERN Large Hadron Collider (LHC) in the Randall-Sundrum (RS) Model. We present in detail the complete next-to-leading order (NLO) QCD corrections to the inclusive total cross sections. The NLO QCD corrections enhance significantly the total cross sections and decrease efficiently the dependence of the total cross sections on the factorization and renormalization scales. We also examine the uncertainty of the total cross sections due to the parton distribution function (PDF) uncertainties. For the differential cross sections on the trans…
We develop threshold resummation for single-particle inclusive cross sections in hadron-hadron collisions to the level of next-to-next-to-leading logarithm, up to full matching with two-loop hard functions. We define and calculate all one-loop soft functions for all partonic channels. This enables us to separate the hard and soft functions at one loop. Along with these results, the one-loop finite parts of jet functions are used to check that the full soft, collinear and virtual corrections are reproduced to one loop for all partonic reactions. We exhibit these NLO results explicitly. NLO expa…
We solve the Balitsky-Kovchegov evolution equation at next-to-leading order accuracy including a resummation of large single and double transverse momentum logarithms to all orders. We numerically determine an optimal value for the constant under the large transverse momentum logarithm that enables including a maximal amount of the full NLO result in the resummation. When this value is used the contribution from the $α_s^2$ terms without large logarithms is found to be small at large saturation scales and at small dipoles. Close to initial conditions relevant for phenomenological applications …
We perform the all orders resummation of threshold enhanced contributions for the Higgs boson pair production cross section via gluon fusion, including finite top quark mass ($M_t$) effects. We present results for the total cross section and Higgs pair invariant mass ($M_{hh}$) distribution. We obtain results at next-to-leading logarithmic accuracy (NLL) which retain the full $M_t$ dependence, and are matched to the full next-to-leading order (NLO) prediction. Our NLL+NLO results represent the most advanced prediction with full $M_t$ dependence for this process, and produce an increase of abou…
We introduce a new version of the FONLL code, now capable of calculating differential distributions for top quark production with next-to-leading-log resummation of log(p_t/m) terms. Numerical results for LHC and FCC kinematics are presented. In the transverse momentum region presently explored by ATLAS and CMS, no significant difference with respect to available fixed order predictions is predicted by FONLL. The large transverse momentum resummation of FONLL may instead become relevant if top is ever measured at transverse momentum scales of several TeV.
A novel computation of the fully-differential cross section for neutral Higgs-boson production through gluon fusion in the CP-conserving NMSSM is presented. Based on the calculation of NLO corrections to the total cross section [1], we implemented the NMSSM amplitudes in three codes, applying different resummation techniques: analytic transverse-momentum resummation at NLO+NLL, and two fully-differential NLO+PS Monte-Carlo approaches using the MC@NLO and POWHEG matching procedures, respectively. We study phenomenological predictions for distributions in the NMSSM with a special emphasis on the…
We present the joint threshold and recoil resummed transverse momentum distributions for heavy quark hadroproduction, at next-to-leading logarithmic accuracy. We exhibit their dependence on the production channel and the color configurations, and compare these distributions to eachother and to NLO.
We present a study of threshold resummation effects for slepton pair production at the Large Hadron Collider (LHC). After confirming the known NLO QCD corrections and generalizing the NLO SUSY-QCD corrections to the case of mixing squarks in the virtual loop contributions, we employ the Mellin N-space resummation formalism to compute logarithmically enhanced soft-gluon terms to all perturbative orders.
We present the status of the automation of NLO processes within the event generator WHIZARD. The program provides an automated FKS subtraction and phase space integration over the FKS regions, while the (QCD) NLO matrix element is accessed via the Binoth Les Houches Interface from an externally linked one-loop program. Massless and massive test cases and validation are shown for several e+e- processes. Furthermore, we discuss work in progress and future plans. The second part covers the matching of the NRQCD prediction with NLL threshold resummation to the NLO continuum top pair production at …
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.
Theoretical predictions show that at low values of Bjorken $x$ the spin structure function, $g_1$ is influenced by large logarithmic corrections, $ln^2(1/x)$, which may be predominant in this region. These corrections are also partially contained in the NLO part of the standard DGLAP evolution. Here we calculate the non-singlet component of the nucleon structure function, $g_1^{NS}=g_1^p-g_1^n$, and its first moment, using a unified evolution equation. This equation incorporates the terms describing the NLO DGLAP evolution and the terms contributing to the $ln^2(1/x)$ resummation. In order to …
We calculate DIS-scheme splitting and coefficient functions for electromagnetic deep inelastic scattering with small x resummations, as given by the NLL BFKL equation with running coupling and approximate NLL resummed impact factors. The resummations are combined with a NLO fixed order expansion, and the improved quantities thus obtained are stable at small x and significantly suppressed with respect to LL results. These results are implemented in a global fit to DIS and related data, and the results compared to a NLO fixed order DIS-scheme fit and with a previous LL resummed fit. The NLL resu…
We investigate the effect of large-x resummation on parton distributions by performing a fit of Deep Inelastic Scattering data from the NuTeV, BCDMS and NMC collaborations, using NLO and NLL soft-resummed coefficient functions. Our results show that soft resummation has a visible impact on quark densities at large x. Resummed parton fits would therefore be needed whenever high precision is required for cross sections evaluated near partonic threshold.
The production of high-mass, color-singlet particles in hadron colliders is universally accompanied by initial state QCD radiation that is predominantly soft with respect to the hard process scale $Q$ and/or collinear with respect to the beam axis. At TeV-scale colliders, this is in contrast to top quark and multijet processes, which, by definition, are hard and central. Consequently, vetoing events with jets possessing transverse momenta above $p_T^{\rm Veto}$ in searches for new color-singlet states can efficiently reduce non-singlet backgrounds, thereby increasing experimental sensitivity. …
We present an extension of the Monte Carlo Event Generator Whizard which includes chargino production at the ILC at NLO. We include photons using both a fixed order and a resummation approach. In the latter, leading higher order corrections are automatically included. We present results for cross sections and event generation for both methods.
The leading and next-to-leading threshold logarithms of the QCD corrections to electroproduction of heavy quarks in single-particle inclusive kinematics are resummed to all orders in perturbation theory. The resummed cross-section is used to derive the NLO and NNLO results near threshold and their numerical impact on the charm structure function is studied.
Exclusive vector-quarkonium photoproduction at NLO in alpha_s in collinear factorisation with evolution of the generalised parton distributions and high-energy resummation
We examine the ratio of the decay rate of the eta_c into light hadrons to the decay rate into photons and find that most of the large next-to-leading-order (NLO) correction is associated with running of the strong coupling alpha_s. We resum such contributions by analyzing final-state chains of vacuum-polarization bubbles. We show that the nonperturbative parts of the bubble chains can be absorbed into a color-octet matrix element, once one has used contour deformations of the phase-space integrals to cancel certain contributions. We argue that these contributions are incompatible with the unce…
We present results for the complete NNLL+NLO (~ α_s) 1-jettiness (τ_1) event shape distribution for single jet (J) production in electron-nucleus (N_A) collisions e^- + N_A \to e^- + 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 τ_1-spectrum including the resummation (τ_1<<P_{J_T}) and fixed-order (τ_1~ P_{J_T}) perturbative QCD regions. They incorporate non-perturbative soft radiation effects, the anti-k_T jet algorithm in the fixed-order calculation, and a smooth matching between the res…
We compute the resummed hadronic transverse-energy ($E_T$) distribution due to initial-state QCD radiation in the production of a Standard Model Higgs boson of mass 126 GeV by gluon fusion at the Large Hadron Collider, with matching to next-to-leading order calculations at large $E_T$. Effects of hadronization, underlying event and limited detector acceptance are estimated using aMC@NLO with the Herwig++ and Pythia 8 event generators.
We consider the impact of the resummation of large logarithms, which appear in the QCD evolution of the heavy-quark distributions, on the phenomenology of deep-inelastic heavy-quark production. The heavy-quark PDFs are derived using the fixed-order matching conditions as a boundary for the QCD evolution and the result obtained is compared to the distributions defined by the matching conditions at all scales. With such an approach, the effect of heavy-quark PDF evolution is found to be sizable at LO and dramatically reduces at NLO. The NNLO evolved distributions are not very different from the …
We discuss exclusive vector meson electroproduction within the QCD collinear factorization framework. In Bjorken kinematics the amplitude factorizes in a convolution of the nonperturbative meson distribution amplitude and the generalized parton densities with the perturbatively calculable hard-scattering amplitudes, which are presently known to next-to-leading order (NLO). At small $x_{\rm B}$ NLO corrections are very large. It is related to appearance of BFKL type logarithms in the hard-scattering amplitudes, that calls for a resummation of these effects at higher orders. Here we report the f…
We improve the theoretical predictions for the production of extra neutral gauge bosons at hadron colliders by implementing the Z' bosons in the MC@NLO generator and by computing their differential and total cross sections in joint p_T and threshold resummation. The two improved predictions are found to be in excellent agreement with each other for mass spectra, p_T spectra, and total cross sections, while the PYTHIA parton and ``power'' shower predictions usually employed for experimental analyses show significant shortcomings both in normalization and shape. The theoretical uncertainties fro…
