Drell-Yan Production Cross Sections Research Articles

Single-soft emissions for amplitudes with two colored particles at three loops

We compute the three-loop correction to the universal single-soft emission current for the case of scattering amplitudes with two additional color-charged partons. We present results valid for QCD and N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 4 super-symmetric Yang-Mills theory. To achieve our results we develop a new integrand expansion technique for scattering amplitudes in the presence of soft emissions. Furthermore, we obtain contributions from single final-state parton matrix elements to the Higgs boson and Drell-Yan production cross section at next-to-next-to-next-to-next-to leading order (N4LO) in perturbative QCD in the threshold limit.

Soft integrals and soft anomalous dimensions at N3LO and beyond

We calculate soft phase-space and loop master integrals for the computation of color-singlet cross sections through N3LO in perturbative QCD. Our results are functions of homogeneous transcendental weight and include the first nine terms in the expansion in the dimensional regulator ϵ. We discuss the application of our results to the computation of deeply-inelastic scattering and e+e− annihilation processes. We use these results to compute the perturbative coefficient functions for the Drell-Yan and gluon-fusion Higgs boson production cross sections to higher orders in ϵ through N3LO in QCD in the limit where only soft partons are produced on top of the colorless final state. Furthermore, we extract the anomalous dimension of the inclusive threshold soft function and of the N-Jettiness beam and jet functions to N4LO in perturbative QCD.

TMD fragmentation functions at N3LO

We compute the unpolarized quark and gluon transverse-momentum dependent fragmentation functions (TMDFFs) at next-to-next-to-next-to-leading order (N3LO) in perturbative QCD. The calculation is based on a relation between the TMDFF and the limit of the semi-inclusive deep inelastic scattering cross section where all final-state radiation becomes collinear to the detected hadron. The required cross section is obtained by analytically continuing our recent computation of the Drell-Yan and Higgs boson production cross section at N3LO expanded around the limit of all final-state radiation becoming collinear to one of the initial states. Our results agree with a recent independent calculation by Luo et al.

Benchmark for LHC searches for low-mass custodial fiveplet scalars in the Georgi-Machacek model

The Georgi-Machacek (GM) model is used to motivate and interpret LHC searches for doubly charged scalars decaying to vector bosons pairs. The doubly charged scalars are part of a degenerate fermiophobic custodial fiveplet with states $H_5^{\pm\pm}$, $H_5^\pm$, and $H_5^0$ and common mass $m_5$. The GM model has been extensively studied at the LHC for $m_5 > 200$ GeV but there is a largely unprobed region of parameter space from $120$ GeV $< m_5 < 200$ GeV where light doubly-charged scalars could exist. This region has been neglected by experimental searches due in part to the lack of a benchmark for $m_5 < 200$ GeV. In this paper we propose a new "low-$m_5$" benchmark for the GM model, defined for $m_5 \in (50, 550)$ GeV, and characterize its properties. We apply all existing experimental constraints and summarize the phenomenology of the surviving parameter space. We show that the benchmark populates almost the entirety of the relevant allowed parameter plane for $m_5$ below 200 GeV and satisfies the constraints from the 125 GeV Higgs boson signal strengths. We compute the 125 GeV Higgs boson's couplings to fermion and vector boson pairs and show that they are always enhanced in the benchmark relative to those in the Standard Model. We also compute the most relevant production cross sections for $H_5$ at the LHC, including Drell-Yan production of $H_5$ pairs. The process $pp \to H \to H_5 H_5$ contributes in a small region of parameter space, but is small compared to the Drell-Yan production cross section. Finally we compute the branching ratios of $H_5^0 \to \gamma\gamma$ and $H_5^{\pm} \to W^{\pm} \gamma$. The width-to-mass ratio of each of the $H_5$ states is below 1\% over the entire benchmark, so that the narrow-width approximation is well justified.

N-jettiness beam functions at N3LO

We present the first complete calculation for the quark and gluon N-jettiness ( {mathcal{T}}_N ) beam functions at next-to-next-to-next-to-leading order (N3LO) in perturbative QCD. Our calculation is based on an expansion of the differential Higgs boson and Drell-Yan production cross sections about their collinear limit. This method allows us to employ cutting edge techniques for the computation of cross sections to extract the universal building blocks in question. The class of functions appearing in the matching coefficents for all channels includes iterated integrals with non-rational kernels, thus going beyond the one of harmonic polylogarithms. Our results are a key step in extending the {mathcal{T}}_N subtraction methods to N3LO, and to resum {mathcal{T}}_N distributions at N3LL′ accuracy both for quark as well as for gluon initiated processes.

Transverse momentum dependent PDFs at N3LO

We compute the quark and gluon transverse momentum dependent parton distribution functions at next-to-next-to-next-to-leading order (N3LO) in perturbative QCD. Our calculation is based on an expansion of the differential Drell-Yan and gluon fusion Higgs production cross sections about their collinear limit. This method allows us to employ cutting edge multiloop techniques for the computation of cross sections to extract these universal building blocks of the collinear limit of QCD. The corresponding perturbative matching kernels for all channels are expressed in terms of simple harmonic polylogarithms up to weight five. As a byproduct, we confirm a previous computation of the soft function for transverse momentum factorization at N3LO. Our results are the last missing ingredient to extend the qT subtraction methods to N3LO and to obtain resummed qT spectra at N3LL′ accuracy both for gluon as well as for quark initiated processes.

On next-to-leading power threshold corrections in Drell-Yan production at N3LO

The cross-section for Drell-Yan production of a vector boson has been previously calculated at next-to-next-to-leading order, supplemented by enhanced logarithmic terms associated with the threshold region. In this paper, we calculate a large set of enhanced terms associated with the colour structure CF3 at N3LO, for the double real emission contribution in the quark-antiquark channel, as an expansion around the threshold region up to and including the first subleading power. We perform our calculation using the method of regions, which systematically characterises all contributions according to whether the virtual gluon is (next-to) soft, collinear or hard in nature. Our results will prove useful for developing general formalisms for classifying next-to-leading power (NLP) threshold effects. They are also interesting in their own right, given that they constitute a previously unknown contribution to the Drell-Yan cross-section at mathcal{O}left({alpha}_s^3right) .

The method of regions and next-to-soft corrections in Drell–Yan production

We perform a case study of the behaviour of gluon radiation beyond the soft approximation, using as an example the Drell–Yan production cross section at NNLO. We draw a careful distinction between the eikonal expansion, which is in powers of the soft gluon energies, and the expansion in powers of the threshold variable 1−z, which involves important hard-collinear effects. Focusing on the contribution to the NNLO Drell–Yan K-factor arising from real–virtual interference, we use the method of regions to classify all relevant contributions up to next-to-leading power in the threshold expansion. With this method, we reproduce the exact two-loop result to the required accuracy, including z-independent non-logarithmic contributions, and we precisely identify the origin of the soft-collinear interference which breaks simple soft-gluon factorisation at next-to-eikonal level. Our results pave the way for the development of a general factorisation formula for next-to-leading-power threshold logarithms, and clarify the nature of loop corrections to a set of recently proposed next-to-soft theorems.

Uncertainties of Drell-Yan production cross section in pp collisions at the LHC

The results of calculations of uncertainties of the Drell-Yan production cross section at the energy √s = 13 TeV are presented. Systematic errors related to uncertainties in the quark and gluon distribution functions, the choice of the QCD factorization scale, and the QCD running coupling constant are considered.

ATLAS measurements of Drell-Yan lepton-pair production as probes of the Standard Model

Measurements of Drell-Yan lepton-pair production cross sections and associated angular correlations can provide unique insight into perturbative Quantum Chromodynamics in the absence of colour flow between initial and final states, the V-A nature of electroweak interactions, as well as enhance the knowledge of parton distribution functions in the proton. Drell-Yan production is also an important source of background for other Standard-Model processes such as Higgs-boson production as well as for new phenomena, particularly at high dilepton invariant mass, and so must be evaluated precisely at the Large Hadron Collider. The measurements presented in this note are based on approximately 5 fb-1 of data collected at a centre-of-mass energy of 7 TeV in 2011 with the ATLAS detector based at the CERN Laboratory.

Top quark effects in composite vector pair production at the LHC

In the context of strongly coupled Electroweak Symmetry Breaking, composite light scalar singlet and composite triplet of heavy vectors may arise from an unspecified strong dynamics and the interactions among themselves and with the Standard Model gauge bosons and fermions can be described by a SU(2) L ×SU(2) R /SU(2) L+R effective chiral Lagrangian. In this framework, the production of the V + V − and V 0 V 0 final states at the LHC by gluon fusion mechanism is studied in the region of parameter space consistent with the unitarity constraints in the elastic channel of longitudinal gauge boson scattering and in the inelastic scattering of two longitudinal Standard Model gauge bosons into Standard Model fermions pairs. The expected rates of same-sign di-lepton and tri-lepton events from the decay of the V 0 V 0 final state are computed and their corresponding backgrounds are estimated. It is of remarkable relevance that the V 0 V 0 final state can only be produced at the LHC via a gluon fusion mechanism since this state is absent in the Drell–Yan process. It is also found that the V + V − final-state production cross section via gluon fusion mechanism is comparable with the V + V − Drell–Yan production cross section. The comparison of the V 0 V 0 and V + V − total cross sections will be crucial for distinguishing the different models since the vector pair production is sensitive to many couplings. This will also be useful to determine if the heavy vectors are only composite vectors or are gauge vectors of a spontaneously broken gauge symmetry.

A possible determination of the quark radiation length in cold nuclear matter

We calculate the differential Drell–Yan production cross section in proton–nucleus collisions by including both next-to-leading order perturbative effects and effects of the nuclear medium. We demonstrate that dilepton production in fixed target experiments is an excellent tool to study initial-state parton energy loss in large nuclei and to accurately determine the stopping power of cold nuclear matter. We provide theoretical predictions for the attenuation of the Drell–Yan cross section at large values of Feynman xF and show that for low proton beam energies experimental measurements at Fermilabʼs E906 can clearly distinguish between nuclear shadowing and energy loss effects. If confirmed by data, our results may help determine the quark radiation length in cold nuclear matter X0∼10−13 m.

Production of the Exotic1--Hadronsϕ(2170),X(4260), andYb(10890)at the LHC and Tevatron via the Drell-Yan Mechanism

We calculate the Drell-Yan production cross sections and differential distributions in the transverse momentum and rapidity of the J(PC) = 1(--) exotic hadrons ϕ(2170), X(4260), and Y(b)(10890) at the LHC and the Tevatron. These hadrons are tetraquark (four-quark) candidates, with a hidden ss, cc, and bb quark pair, respectively. In deriving the distributions, we include the order α(s) QCD corrections, resum the large logarithms in the small transverse momentum region in the impact-parameter formalism, and use the state of the art parton distribution functions. Production rates for the processes pp(p) → ϕ(2170)× (→ ϕ(1020)π+ π- → K+ K- π+ π-) +…, pp(p) → X(4260)(→J/ψπ+ π- → μ+ μ- π+ π-)+…, and pp(p) → Y(b)(10890)(→ Υ(1S,2S,3S)π+ π- → μ+ μ- π+ π-) +… are presented. Their measurements will help in understanding the dynamics of these exotic hadrons.

Initial-state quark energy loss from Drell–Yan production in proton-proton and proton-nucleus collisions

Drell-Yan production cross sections were measured by the NA3 and E866 experiments, in p-Pt and pp collisions, as a function of the dimuon mass and x F . We compare these measurements to next-to-leading order Drell-Yan calculations, made with the CTEQ6M parton densities modified (or not) by nuclear effects, using the EPS09 parameterization. The analysis of the data allows us to evaluate the initial-state quark energy loss. Drell-Yan measurements are ideally suited to isolate the initial-state parton energy loss, given the absence of final-state effects on the produced dimuon. Our study shows that these data indicate negligible quark energy loss and allow us to derive rather strict upper limits. For completeness, our study has been repeated using the less accurate measurements of Drell-Yan cross section ratios between heavy and light nuclear targets, provided by the E772 and E866 experiments. Our results provide an additional constraint on the models trying to explain quarkonium production in proton-nucleus collisions, as a function of quarkonium rapidity and collision energy, where initial- and final-state energy loss has frequently been assumed to play an important role, convoluted with several other complex mechanisms, including final-state quarkonium breakup, formation time effects, etc.

Beam Thrust Cross Section for Drell-Yan Production at Next-to-Next-to-Leading-Logarithmic Order

At the LHC and Tevatron strong initial-state radiation (ISR) plays an important role. It can significantly affect the partonic luminosity available to the hard interaction or contaminate a signal with additional jets and soft radiation. An ideal process to study ISR is isolated Drell-Yan production, pp → Xℓ+ ℓ- without central jets, where the jet veto is provided by the hadronic event shape beam thrust τB. Most hadron collider event shapes are designed to study central jets. In contrast, requiring τ B << 1 provides an inclusive veto of central jets and measures the spectrum of ISR. For τ B << 1 we carry out a resummation of α s(n)ln(m)τ B corrections at next-to-next-to-leading-logarithmic order. This is the first resummation at this order for a hadron-hadron collider event shape. Measurements of τ B at the Tevatron and LHC can provide crucial tests of our understanding of ISR and of τ B's utility as a central jet veto.

Inverse seesaw mechanism, leptogenesis, observable proton decay, andΔR±±in supersymmetricSO(10)with heavyWR

We explore low-scale leptogenesis in a class of supersymmetric SO(10) models using extra singlet neutrinos and the Higgs representations {126}_H\oplus {\ovl{126}}_H as well as {16}_H \oplus {\bar {16}}_H. A singlet neutrino, which can be as light as 10^5-10^6 GeV, decays through its small mixings with right-handed neutrinos creating a lepton asymmetry which is shown to be flavor dependent. While the doublet vacuum expectation value in {\ovl{16}}_H triggers the generation of desired mixings, it also induces a large RH triplet vev that breaks the LR intermediate gauge symmetry and gives large RH neutrino masses. Manifest unification of gauge couplings and generation of heavy RH neutrino masses are achieved by renormalizable interactions. The canonical (Type-I) see-saw contributions to the light neutrino mass matrix cancel out while the Type-II see-saw contribution is negligible. Determining the parameters of the dominant inverse see-saw formula using the underlying quark-lepton symmetry and neutrino oscillation data, we show how leptogenesis under the gravitino constraint is successfully implemented. New formulas for the decay rate and the asymmetry parameter are derived leading to baryon asymmetry within the observed range. The model is found to work for hierarchical as well as inverted hierarchical light neutrino masses. Testable predictions of the model are RH doubly charged Higgs bosons which may be leptophilic and accessible to the Tevatron, LHC or a linear collider. In a model-independent manner, the Drell-Yan pair production cross section is shown to be bounded between 59%-79% of their left-handed counterparts with same mass. In contrast to single-step breaking SUSY GUTs, which predict a long proton lifetime for p\to e^+\pi^0, here this lifetime is substantially reduced, bringing it within one order of the current experimental limit.

Drell-Yan production and Lam-Tung relation in the color glass condensate formalism

We study the Drell-Yan production cross section and structure functions in proton (deuteron)-nucleus collisions using the color glass condensate formalism. The nucleus is treated in the color glass condensate framework which includes both higher twist effects due to the inclusion of multiple scatterings and leading twist pQCD shadowing due to the small $x$ resummation, while the proton (or deuteron) is treated within the DGLAP improved parton model. In particular, the Drell-Yan structure functions are used in order to investigate the Lam-Tung relation at small $x$, which is known to be identically zero at leading twist up to next-to-leading order, and is thus a good playground for studying higher twist effects. In agreement with this, we find that violations of this relation are more important for low momentum and invariant mass of the Drell-Yan pair, and also in the region of rapidity that corresponds to smaller values of $x$ in the nucleus.

High-energy Drell–Yan dimuon process in a Glauber model

In the framework of the Glauber model, taking into account the K′-factor, we analyse the Drell–Yan dimuon production cross sections for an absolute measurement of continuum dimuon (Drell–Yan) cross section in 800 GeV/c pp collisions. The calculated results of the leading order agree only poorly with the new experimental data, but there is a general agreement between the next-to-leading-order QCD correction results and the experimental data. It is shown that the QCD corrections to the Drell–Yan process cannot be omitted. Then, by means of the nuclear parton distribution obtained from the DGLAP equation, taking into account the energy loss of the beam proton through the nucleus, we analyse the QCD corrections to the measured Drell–Yan production cross sections for an 800 GeV proton beam incident on Be, Fe and W nuclear targets in the Glauber model. It is shown that the theoretical results are in good agreement with the FNAL E866. Finally, we compare the calculated results from the DGLAP equation with those from the latest nuclear effect models.

Quark Energy Loss and Shadowing in Nuclear Drell–Yan Process**Theproject partially supported by National NaturalScience Foundation of China under Grant Nos. 90103020, 10075057, and 10175074, CAS Knowledge Innovation Project under Grant No. KJCX2-SW-N02, the StateKey Basic Research Development Program under Grant No. G20000774,and the Natural ScienceFoundation of Hebei Province of China under Grant No. 103143

The energy loss effect in nuclear matter is another nucleareffect apart from the nuclear effects on the parton distributionas in deep inelastic scattering process. The quark energy loss canbe measured best by the nuclear dependence of the high energynuclear Drell–Yan process. By means of three kinds of quarkenergy loss parameterizations given in literature and thenuclear parton distribution extracted only with lepton-nucleusdeep inelastic scattering experimental data, measured Drell–Yanproduction cross sections are analyzed for 800 GeV proton incidenton a variety of nuclear targets from FNAL E866. It is shown thatour results with considering the energy loss effect are muchdifferent from those of the FNAL E866, who analyzes theexperimental data with the nuclear parton distribution functionsobtained by using the deep inelastic lA collisions and pA nuclearDrell–Yan data. Considering the existence of energy loss effect inDrell–Yan lepton pairs production, we suggest that the extractionof nuclear parton distribution functions should notinclude Drell–Yan experimental data.

NNLO coefficient functions of Higgs and Drell–Yan cross sections in Mellin space

We calculate the Mellin moments of next-to-next-to-leading order coefficient functions of the Drell-Yan and Higgs production cross sections. The results can be expressed in term of finite harmonic sums which are maximally threefold up to weight four. Various algebraic relations among these finite sums reduce the complexity of the results suitable for fast numerical evaluations. It is shown that only five non--trivial functions occur besides Euler's $\psi$--function in the representation of these Wilson coefficients.