Vector Boson Production Research Articles

Measurements of vector boson production in lead–lead and proton–lead collisions with the ATLAS detector

Abstract Photons and weak bosons do not interact strongly and, thus, their production yields provide direct tests of scaling with a number of binary nucleon–nucleon collisions in the heavy-ion environment. In addition, they should be sensitive to the nuclear modification of parton distribution functions (nPDF). Proton-lead collisions also provide an excellent opportunity to test nPDF in a less dense environment than lead–lead via looking at forward–backward production of weak bosons. The ATLAS detector has proven to be an excellent apparatus in measurements involving photons, electrons and muons, the latter being products of weak boson decays, in the high occupancy environment produced in heavy-ion collisions. The experiment has recorded 30 nb − 1 of proton–lead data and 140 μb − 1 of lead–lead data, both of which have similar integrated partonic luminosities. We present the prompt photon, Z and W boson yields as a function of centrality, and also differentially in transverse momentum and rapidity, in lead–lead and proton–lead collisions from the ATLAS experiment. For W ± bosons, a lepton charge asymmetry has also been studied, which may also shed light on nPDF.

Search forWWγandWZγproduction and constraints on anomalous quartic gauge couplings inppcollisions ats=8 TeV

A search for WV gamma triple vector boson production is presented based on events containing a W boson decaying to a muon or an electron and a neutrino, a second V (W or Z) boson, and a photon. The data correspond to an integrated luminosity of 19.3 inverse femtobarns collected in 2012 with the CMS detector at the LHC in pp collisions at sqrt(s) = 8 TeV. An upper limit of 311 fb on the fiducial cross section for the WV gamma production process is obtained at 95% confidence level for photons with a transverse energy above 30 GeV and with an absolute value of pseudorapidity of less than 1.44. This limit is approximately a factor of 3.4 larger than the standard model predictions that are based on next-to-leading order QCD calculations. Since no evidence of anomalous WW gamma gamma or WWZ gamma quartic gauge boson couplings is found, this paper presents the first experimental limits on the dimension-8 parameter f[T,0] and the CP-conserving WWZ gamma parameters kappa[0,W] and kappa[C,W]. Limits are also obtained for the WW gamma gamma parameters a[0,W] and a[C,W].

Search for light vector boson production in [formula omitted] interactions with the KLOE experiment

We have searched for a light vector boson U, the possible carrier of a “dark force”, with the KLOE detector at the DAΦNE e+e− collider, motivated by astrophysical evidence for the presence of dark matter in the Universe. Using e+e− collisions collected with an integrated luminosity of 239.3 pb−1, we look for a dimuon mass peak in the reaction e+e−→μ+μ−γ, corresponding to the decay U→μ+μ−. We find no evidence for a U vector boson signal. We set a 90% CL upper limit for the mixing parameter squared between the photon and the U boson of 1.6×10−5 to 8.6×10−7 for the mass region 520<mU<980 MeV.

Nonperturbative contributions to a resummed leptonic angular distribution in inclusive neutral vector boson production

We present an analysis of nonperturbative contributions to the transverse momentum distribution of $Z/\gamma^*$ bosons produced at hadron colliders. The new data on the angular distribution $\phi^*_\eta$ of Drell-Yan pairs measured at the Tevatron is shown to be in excellent agreement with a perturbative QCD prediction based on the Collins-Soper-Sterman (CSS) resummation formalism at NNLL accuracy. Using these data, we determine the nonperturbative component of the CSS resummed cross section and estimate its dependence on arbitrary resummation scales and other factors. With the scale dependence included at the NNLL level, a significant nonperturbative component is needed to describe the angular data.

Review of single vector boson production in pp collisions at $$\sqrt{s} = 7$$ s = 7 TeV

This review summarises the main results on the production of single vector bosons in the Standard Model, both inclusively and in association with light and heavy flavour jets, at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of 7 TeV. The general purpose detectors at this collider, ATLAS and CMS, each recorded an integrated luminosity of $\approx 40\,{\rm pb^{-1}}$ and $5\,{\rm fb^{-1}}$ in the years 2010 and 2011, respectively. The corresponding data offer the unique possibility to precisely study the properties of the production of heavy vector bosons in a new energy regime. The accurate understanding of the Standard Model is not only crucial for searches of unknown particles and phenomena but also to test predictions of perturbative Quantum-Chromo-Dynamics calculations and for precision measurements of observables in the electroweak sector. Results from a variety of measurements in which single W or Z bosons are identified are reviewed. Special emphasis in this review is given to interpretations of the experimental results in the context of state-of-the-art predictions.

Complete Higgs sector constraints on dimension-6 operators

Constraints on the full set of Standard Model dimension-6 operators have previously used triple-gauge couplings to complement the constraints obtainable from Higgs signal strengths. Here we extend previous analyses of the Higgs sector constraints by including information from the associated production of Higgs and massive vector bosons (H+V production), which excludes a direction of limited sensitivity allowed by partial cancellations in the triple-gauge sector measured at LEP. Kinematic distributions in H+V production provide improved sensitivity to dimension-6 operators, as we illustrate here with simulations of the invariant mass and $p_T$ distributions measured by D0 and ATLAS, respectively. We provide bounds from a global fit to a complete set of CP-conserving operators affecting Higgs physics.

Disentangling flavor violation in the top-Higgs sector at the LHC

We study the LHC phenomenology of flavor changing Yukawa couplings between top quark, Higgs boson, and either an up or charm quark. Such $tuh$ or $tch$ couplings arise for instance in models in which Higgs sector is extended by the existence of additional Higgs bosons or by higher dimensional operators. We emphasize the importance of anomalous single top plus Higgs production in these scenarios, in addition to the more widely studied $t \to h j$ decays. By recasting existing CMS searches in multilepton and diphoton plus lepton final states, we show that bounds on $tuh$ couplings are improved by a factor of 1.5 when single top plus Higgs production is accounted for. We also recast the CMS search for vector boson plus Higgs production into new, competitive constraints on $tuh$ and $tch$ couplings, setting the limits of $BR(t\to hu) < 0.7%$ and $BR(t\to hc) <1.2%$. We then investigate the sensitivity of future searches in multilepton channel and in fully hadronic channel. In multilepton searches, studying the lepton rapidity distributions and charge assignments can be used to discriminate between $tuh$ couplings, for which anomalous single top production is relevant, and $tch$ couplings, for which it is suppressed by the parton distribution function of the charm quark. An analysis of fully hadronic $t+h$ production and $t\to h j$ decay can be competitive with the multilepton search at 100 fb$^{-1}$ of 13 TeV data if jet substructure techniques are employed to reconstruct boosted top quarks and Higgs bosons. To show this we develop a modified version of the HEPTopTagger algorithm, optimized for tagging $t \to h j$ decays. Our sensitivity estimates on $BR(t\to hu)$ ($BR(t\to hc)$) at 100 fb$^{-1}$ of 13 TeV data for multilepton searches, vector boson plus Higgs search and fully hadronic search are $0.22%$ ($0.33%$), $0.15%$ ($0.19%$) and $0.36%$ ($0.48%$), respectively.

Triple vector boson production through Higgs-strahlung with NLO multijet merging

Triple gauge boson hadroproduction, in particular the production of three $W$-bosons at the LHC, is considered at next-to leading order accuracy in QCD. The NLO matrix elements are combined with parton showers. Multijet merging is invoked such that NLO matrix elements with one additional jet are also included. The studies here incorporate both the signal and all relevant backgrounds for $VH$ production with the subsequent decay of the Higgs boson into $W$-- or $\tau$--\-pairs. They have been performed using \SherpaOpenLoops in combination with Collier.

Two-loop planar master integrals for the production of off-shell vector bosons in hadron collisions

We describe the calculation of all planar master integrals that are needed for the computation of NNLO QCD corrections to the production of two off-shell vector bosons in hadron collisions. The most complicated representatives of integrals in this class are the two-loop four-point functions where two external lines are on the light-cone and two other external lines have different invariant masses. We compute these and other relevant integrals analytically using differential equations in external kinematic variables and express our results in terms of Goncharov polylogarithms. The case of two equal off-shellnesses, recently considered in ref. [1], appears as a particular case of our general solution.

Two-loop planar master integrals for the production of off-shell vector bosons in hadron collisions

We describe the calculation of all planar master integrals that are needed for the computation of NNLO QCD corrections to the production of two off-shell vector bosons in hadron collisions. The most complicated representatives of integrals in this class are the two-loop four-point functions where two external lines are on the light-cone and two other external lines have different invariant masses. We compute these and other relevant integrals analytically using differential equations in external kinematic variables and express our results in terms of Goncharov polylogarithms. The case of two equal off-shellnesses, recently considered in Ref. [1], appears as a particular case of our general solution.

Recent Results from the CMS Experiment at the LHC

Numerous studies on Jet Production, Vector Boson Production, V+Jets Production and Multi-Boson Production have been carried out by the Compact Muon Solenoid (CMS) Collaboration to test perturbative quantum chromodynamics (QCD) pre- dictions, and to put more stringent constraints on PDFs (Parton Distribution Functions). In this paper, some of these experimental results will be presented, and their possible impacts on Higgs physics and new physics searches will be discussed.

ATLAS QCD measurements for Higgs studies and New Physics searches

Our understanding of the modelling of Standard Model processes plays an important role for Higgs physics and searches beyond the Standard Model. Measurements such as vector boson plus jet production are essential for the understanding of backgrounds, modelling of double parton interactions, heavy flavour production from gluon splitting and modelling of the underlying event. Precision QCD measurements can also be used to constrain parton density functions, which are important for the understanding of the Higgs boson production cross section and the Standard Model backgrounds at the LHC kinematic limits. A review of recent ATLAS measurements is presented.

V+jets production at the CMS

Measurements of Vector Boson production in association with jets are presented, using p-p collision data at sqrt{s} = 7 TeV. The measurements presented include Z + jets azimuthal correlations, event shapes, vector boson + jets differential cross section measurements, hard double-parton scattering using W + jets events and electroweak Z + forward - backward jet production.

Standard Model and QCD results from ATLAS and CMS

This talk presents several Standard Model and QCD results from the ATLAS and CMS collaborations based on proton-proton collision data collected at 7 TeV, 2.76 TeV and 8 TeV centre-of-mass energy. Namely, differential cross sections of jet and dijet production, isolated photon production, and vector boson production in association with jets are discussed.

Nucleon structure and hard p–p processes at high energies

The production of heavy flavour hadrons in pp collisions at large values of their transverse momenta can be a new unique source for estimation of intrinsic heavy quark contribution to the proton. We analyze the inclusive production of the open strangeness and the semi-inclusive hard processes of the photon and vector boson production accompanied by the c- or b-jets in pp collisions. We show that one should select the parton-level (sub)processes (and final-state signatures) that are the most sensitive to the intrinsic heavy quark contributions. We present some predictions for these processes made within the perturbative QCD including the intrinsic strangeness and intrinsic charm in the proton that can be verified in the NA61 experiment and at LHC.

Search for the Higgs boson in lepton, tau, and jets final states

We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with two or more jets using 9.7 fb−1 of Run II Fermilab Tevatron Collider data collected with the D0 detector. The analysis is sensitive to Higgs boson production via gluon fusion, associated vector boson production, and vector boson fusion, followed by the Higgs boson decay to tau lepton pairs or to W boson pairs. The ratios of 95% C.L. upper limits on the cross section times branching ratio to those predicted by the standard model are obtained for orthogonal subsamples that are enriched in either H→ττ decays or H→WW decays, and for the combination of these subsample limits. The observed and expected limit ratios for the combined subsamples at a Higgs boson mass of 125 GeV are 11.3 and 9.0, respectively.Received 30 November 2012DOI:https://doi.org/10.1103/PhysRevD.88.052005© 2013 American Physical Society

Parton densities from LHC vector boson production at small and large transverse momenta

The parton densities of the proton are of fundamental importance not only for our description of hadronic and nuclear structure, but also for reliable predictions for new heavy-particle searches at colliders. At the large partonic momentum fractions required for the production of these particles, the parton distribution functions\char22{}in particular, that of the gluon\char22{}are unfortunately still badly constrained. In this paper, we investigate the possibility to improve on their determination with new data coming from electroweak vector boson production at large transverse momenta at the LHC with center-of-mass energies of 7, 8, or 14 TeV. We demonstrate that this process is dominated by quark-gluon scattering, that theoretical predictions can be reliably made on the basis of next-to-leading order perturbation theory and its resummation, and that these data should thus be used in global fits. We also point out that the nonperturbative parameters determined from Tevatron Run 1 $Z$-boson data at low ${p}_{T}$ describe very well the new LHC data at $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$.

Vector boson+jets as background to top-quark physics at Tevatron and LHC

I review here the latest measurements related to vector boson production in association with light or heavy flavor jets at the Tevatron and at the LHC. The methods to estimate the W+jets and Z+jets background in top-quark analyses are also presented.

Hadron collider production of massive color-octet vector bosons at next-to-leading order

This paper completes the study of the next-to-leading order (NLO) QCD corrections to massive color-octet vector boson production at the LHC and Tevatron. The massive color-octet vector bosons are generically referred to as colorons. Building on our previous calculation of quark-initiated coloron production at NLO, we use the pinch technique to investigate coloron production via gluon fusion. We demonstrate that this one-loop production amplitude is finite, and find that its numerical contribution to coloron production is typically four orders of magnitude smaller than the contribution from quark annihilation. Coloron production via gluon fusion is therefore only relevant if the colorons are (nearly) fermiophobic. We then present extensive plots and tables of our full results for NLO coloron production at the Tevatron and the LHC.

Effective field theory: A modern approach to anomalous couplings

We advocate an effective field theory approach to anomalous couplings. The effective field theory approach is the natural way to extend the standard model such that the gauge symmetries are respected. It is general enough to capture any physics beyond the standard model, yet also provides guidance as to the most likely place to see the effects of new physics. The effective field theory approach also clarifies that one need not be concerned with the violation of unitarity in scattering processes at high energy. We apply these ideas to pair production of electroweak vector bosons.