Vector Boson Production Research Articles

Recent Standard Model measurements at CMS

Recent results of Standard Model physics using 7 and 8 TeV data recorded by the CMS detector are reviewed. This overview includes studies of vector boson production, results on V+jets production with light and heavy flavours, multiboson measurements and anomalous couplings searches and also the latest results on jet production and properties. The most recent 13 TeV results are presented as well. The outlined results are compared to the prediction of the Standard Model.

Neutral triple vector boson production in Randall-Sundrum model at the LHC

In this paper, triple neutral electroweak gauge boson production processes, viz. \gamma\gamma\gamma, \gamma\gamma Z, \gamma ZZ and ZZZ productions merged to 1-jet have been studied at the leading order in QCD in the context of Randall-Sundrum model at the LHC with center of mass energy \sqrt{S}=13 TeV. Decay of Z bosons into lepton-pairs has been considered. We present a selection of kinematical distributions matched to parton shower and show their deviation from the SM results as a result of the RS model. The uncertainties as a result of the factorization and renormalization scales are also presented.

Limit on the production of a low-mass vector boson in [formula omitted], [formula omitted] with the KLOE experiment

The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the light vector mediator of this dark force, the U boson, with the KLOE detector at the DAΦNE e+e− collider. Using an integrated luminosity of 1.54 fb−1, we studied the process e+e−→Uγ, with U→e+e−, using radiative return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find evidence for a signal, and set a 90% CL upper limit on the mixing strength between the Standard Model photon and the dark photon, ε2, at 10−6–10−4 in the 5–520 MeV/c2 mass range.

NLO QCD + NLO EW corrections to WZZ productions with leptonic decays at the LHC

Precision tests of the Standard Model (SM) require not only accurate experiments, but also precise and reliable theoretical predictions. Triple vector boson production provides a unique opportunity to investigate the quartic gauge couplings and check the validity of the gauge principle in the SM. Since the tree-level predictions alone are inadequate to meet this demand, the next-to-leading order (NLO) calculation becomes compulsory. In this paper, we calculate the NLO QCD + NLO electroweak (EW) corrections to the $W^{\pm}ZZ$ productions with subsequent leptonic decays at the $14~{\rm TeV}$ LHC by adopting an improved narrow width approximation which takes into account the off-shell contributions and spin correlations from the $W^{\pm}$- and $Z$-boson leptonic decays. The NLO QCD+EW corrected integrated cross sections for the $W^{\pm}ZZ$ productions and some kinematic distributions of final products are provided. The results show that both the NLO QCD and NLO EW corrections are significant. In the jet-veto event selection scheme with $p_{T,jet}^{cut} = 50~ {\rm GeV}$, the NLO QCD+EW relative corrections to the integrated cross section are $20.5\%$ and $31.1\%$, while the genuine NLO EW relative corrections are $-5.42\%$ and $-4.58\%$, for the $W^+ZZ$ and $W^-ZZ$ productions, respectively. We also investigate the theoretical dependence of the integrated cross section on the factorization/renormalization scale, and find that the scale uncertainty is underestimated at the LO due to the fact that the strong coupling $\alpha_s$ is not involved in the LO matrix elements.

Probing shadowed nuclear sea with massive gauge bosons in the future heavy-ion collisions

The production of the massive bosons $Z^0$ and $W^{\pm}$ could provide an excellent tool to study cold nuclear matter effects and the modifications of nuclear parton distribution functions (nPDFs) relative to parton distribution functions (PDFs) of a free proton in high energy nuclear reactions at the LHC as well as in heavy-ion collisions (HIC) with much higher center-of mass energies available in the future colliders. In this paper we calculate the rapidity and transverse momentum distributions of the vector boson and their nuclear modification factors in p+Pb collisions at $\sqrt{s_{NN}}=63$TeV and in Pb+Pb collisions at $\sqrt{s_{NN}}=39$TeV in the framework of perturbative QCD by utilizing three parametrization sets of nPDFs: EPS09, DSSZ and nCTEQ. It is found that in heavy-ion collisions at such high colliding energies, both the rapidity distribution and the transverse momentum spectrum of vector bosons are considerably suppressed in wide kinematic regions with respect to p+p reactions due to large nuclear shadowing effect. We demonstrate that in the massive vector boson productions processes with sea quarks in the initial-state may give more contributions than those with valence quarks in the initial-state, therefore in future heavy-ion collisions the isospin effect is less pronounced and the charge asymmetry of W boson will be reduced significantly as compared to that at the LHC. Large difference between results with nCTEQ and results with EPS09 and DSSZ is observed in nuclear modifications of both rapidity and $p_T$ distributions of $Z^0$ and $W$ in the future HIC.

Search for intrinsic charm in vector boson production accompanied by heavy-flavor jets

Up to now, the existence of intrinsic (or valence-like) heavy quark component of the proton distribution functions has not yet been confirmed or rejected. The LHC with pp-collisions at $\sqrt{s}$ = 7-13 TeV can supply us with extra unique information concerning this hypothesis. On the basis of our theoretical studies, it is demonstrated that investigations of the intrinsic heavy quark contributions look very promising in processes like $pp \rightarrow Z/W + c(b) + X$. A ratio of $Z+$ heavy jets over $W+$ heavy jets differential cross section as a function of the leading jet transverse momentum is proposed to maximize the sensitivity to the intrinsic charm component of the proton.

ExtrapolatingW-associated jet-production ratios at the LHC

Electroweak vector-boson production, accompanied by multiple jets, is an important background to searches for physics beyond the Standard Model. A precise and quantitative understanding of this process is helpful in constraining deviations from known physics. We study four key ratios in $W + n$-jet production at the LHC. We compute the ratio of cross sections for $W + n$- to $W + (n-1)$-jet production as a function of the minimum jet transverse momentum. We also study the ratio differentially, as a function of the $W$-boson transverse momentum; as a function of the scalar sum of the jet transverse energy, $H_T^{\rm jets}$; and as a function of certain jet transverse momenta. We show how to use such ratios to extrapolate differential cross sections to $W+6$-jet production at next-to-leading order, and we cross-check the method against a direct calculation at leading order. We predict the differential distribution in $H_T^{\rm jets}$ for $W+6$ jets at next-to-leading order using such an extrapolation. We use the BlackHat software library together with SHERPA to perform the computations.

Recent Standard Model results from CMS

The data recorded by the Compact Muon Solenoid experiment during the first LHC run (2010-2012) has allowed to refine our knowledge on the production of jets and vector boson using the proton-proton collisions at √s = 7 or 8 TeV. Representative studies concerning the PDF and as extractions, the study of inclusive vector boson production, of production vector bosons in association with jets, and some recent results on anomalous gauge couplings evaluation are discussed.

Search for pair-produced resonances decaying to jet pairs in proton–proton collisions at [formula omitted

Results are reported of a general search for pair production of heavy resonances decaying to pairs of hadronic jets in events with at least four jets. The study is based on up to 19.4 fb−1 of integrated luminosity from proton–proton collisions at a center-of-mass energy of 8 TeV, recorded with the CMS detector at the LHC. Limits are determined on the production of scalar top quarks (top squarks) in the framework of R-parity violating supersymmetry and on the production of color-octet vector bosons (colorons). First limits at the LHC are placed on top squark production for two scenarios. The first assumes decay to a bottom quark and a light-flavor quark and is excluded for masses between 200 and 385 GeV, and the second assumes decay to a pair of light-flavor quarks and is excluded for masses between 200 and 350 GeV at 95% confidence level. Previous limits on colorons decaying to light-flavor quarks are extended to exclude masses from 200 to 835 GeV.

Parton density constraints from massive vector boson production at the LHC

We demonstrate that not only the production of virtual photons decaying into low- mass lepton pairs, but also the one of weak bosons at large transverse momenta is dominated by quark-gluon scattering. Measurements of these processes at the LHC can therefore provide useful constraints on the parton densities in the proton, in particular the one of the gluon, and their nuclear modifications.

ATLAS measurements of vector boson production, inclusive and with associated jets

The most recent measurements of inclusive vector boson production and vector boson production in association with jets and heavy flavours with the ATLAS experiment are summarised. The presented analyses use proton–proton collision data, collected at center of mass energy s=7 TeV at the Large Hadron Collider, corresponding to an integrated luminosity up to 4.6 fb−1. The measured cross sections, unfolded for detector effects, are compared to the state–of–the–art Standard Model predictions.

Measurements of vector boson plus jets from ATLAS

Measurements of single W, Z boson production in association with jets probe QCD in multi-scale environment. Measurements of W + jet and Z + jet production and their ratio, extending to high jet multiplicities, and a large set of kinematic distributions are presented for 7 TeV data. The results are compared to the predictions of modern Monte Carlo generators. The production of vector bosons plus heavy flavors is sensitive to the c and b quark parton distribution functions (PDFs) and gluon splitting effects. Measurements of W + c and Z + b (b ) are reported and compared to predictions based on various PDFs in 4 and 5 flavour schemes. An overview of the results is given.

Measurements of vector boson plus jets from ATLAS

Measurements of single W, Z boson production in association with jets probe QCD in multi-scale environment. Measurements of W + jet and Z + jet production and their ratio, extending to high jet multiplicities, and a large set of kinematic distributions are presented for 7 TeV data. The results are compared to the predictions of modern Monte Carlo generators. The production of vector bosons plus heavy flavors is sensitive to the c and b quark parton distribution functions (PDFs) and gluon splitting effects. Measurements of W + c and Z + b(b) are reported and compared to predictions based on various PDFs in 4 and 5 flavour schemes. An overview of the results is given.

Measurements of inclusive vector boson production from ATLAS

The measurements of single W, Z boson production in association with jets probes QCD in a multi-scale environment. In this paper, we summarize the latest measurements of W +jet and Z +jet production and their ratio, extending to high jet multiplicities over a large set of kinematic distributions for proton-proton collisions at a center of mass energy of 7 TeV data at the LHC. The results are compared to the latest theoretical predictions of modern Monte Carlo generators. In addition, the measurement of production of vector bosons in association with heavy flavours allows to study c and b-quark parton distribution functions (PDFs) and gluon splitting effects. Also the corresponding measurements of W + c and Z + b (b ) are reported and compared to predictions based on various PDFs in four and five-flavour schemes.

RareBdecays and processes with the ATLAS detector

We present rare B decays and processes measured with the ATLAS detector. First, the associated production of vector boson + prompt J/ψ that is a key process for understanding of quarkonium production mechanisms, and second, the rare B0s → µ+µ− decay, that due to its small branching fraction, is an excellent probe for physics beyond the standard model.

Recent results on associated vector boson production with the ATLAS and CMS experiments

Several aspects of the associated vector boson production in pp collisions at √s = 7 TeV and √s = 8 TeV at the LHC have been recently investigated by the ATLAS and CMS collaborations. The production cross sections of the W and Z bosons in association with jets, as well as their ratio and the double differential cross section in the Z + jets final state are presented. Measurements of the cross sections of a vector boson (W or Z) in association with heavy flavour jets (b, c) and a top quark pair are also described. The measured cross sections are compared to expectations based on next-to-leading order QCD calculations as well as on Monte Carlo simulations.

Measurements of inclusive vector boson production from ATLAS

Measurements of inclusive vector boson production from ATLAS

Gluon fusion contribution to VHj production at hadron colliders

We study the associated production of an electroweak vector boson and the Higgs boson with a jet via gluon–gluon fusion. At the leading order, these processes occur at one-loop level. The amplitudes of these one-loop processes are gauge invariant and finite. Therefore, their contributions towards the corresponding hadronic cross sections and kinematic distributions can be calculated separately. We present results for the Large Hadron Collider and its discussed upgrades. We find that the gluon–gluon one-loop process gives dominant contribution to the γHj production. We observe a destructive interference effect in the gg→ZHj amplitude. We also find that in the high transverse momentum and central rapidity region, the ZHj production cross section via gluon–gluon fusion becomes comparable to the cross section contributions coming from quark–quark and quark–gluon channels.

Measurements of vector bosons with charm and beauty at ATLAS

Several recent results from the ATLAS experiment at the Large Hadron Collider are presented, using proton-proton collisions = 7 TeV. Measurements of W bosons in association with b-jets and single c-quark jets are presented, in addition to a new measurement of the production of b-jets in association with Z bosons. These measurements allow QCD predictions to be tested and also probe the parton density of the proton. The associated production of quarkonia and vector bosons is observed in the J/Ψ + W channel, and compared to colour singlet and colour octet production models.

Non-perturbative QCD effects in q T spectra of Drell-Yan and Z-boson production

The factorization theorems for transverse momentum distributions of dilepton/boson production, recently formulated by Collins and Echevarria-Idilbi-Scimemi in terms of well-defined transverse momentum dependent distributions (TMDs), allows for a systematic and quantitative analysis of non-perturbative QCD effects of the cross sections involving these quantities. In this paper we perform a global fit using all current available data for Drell-Yan and Z-boson production at hadron colliders within this framework. The perturbative calculable pieces of our estimates are included using a complete resummation at next-to-next-to-leading-logarithmic accuracy. Performing the matching of transverse momentum distributions onto the standard collinear parton distribution functions and recalling that the corresponding matching coefficient can be partially exponentiated, we find that this exponentiated part is spin-independent and resummable. We argue that the inclusion of higher order perturbative pieces is necessary when data from lower energy scales are analyzed. We consider non-perturbative corrections both to the intrinsic nucleon structure and to the evolution kernel and find that the non-perturbative part of the TMDs could be parametrized in terms of a minimal set of parameters (namely 2-3). When all corrections are included the global fit so performed gives a χ 2 /d.o.f. ≲ 1 and a very precise prediction for vector boson production at the Large Hadron Collider (LHC).