Pairs Of Electroweak Gauge Bosons Research Articles

Improved Constraints on the Heavy Gauge Bosons Decaying to Pairs of Electroweak Bosons by Using the Expected Run 3 Data and HL-LHC Options

The expected ATLAS Run 3 data set with time-integrated luminosity of 300 fb−1 and HL–LHC options at the LHC in the diboson channels are used to probe a simple benchmark model with an extended gauge sector, proposed by Altarelli et al. This model accommodates new charged W' and neutral Z' vector bosons with modified trilinear Standard Model gauge couplings, decaying into electroweak gauge boson pairs W Z or W W, where W / Z decay semileptonically. Also presented, from a similar analysis of W' and Z' bosons arising in the EGM, which can decay through W' → lν and Z' → ll , are limits on the W–W' and Z–Z' mixing parameters and the W' and Z' vector boson masses. We present upper limits on the mixing parameters, Z–Z' and W–W', by using the expected Run 3 data and HL–LHC options.

New physics in triboson event topologies

We present a study of the sensitivity to models of new physics of proton collisions resulting in three electroweak bosons. As a benchmark, we analyze models in which an exotic scalar field $\ensuremath{\phi}$ is produced in association with a gauge boson ($V=\ensuremath{\gamma}$ or $Z$). The scalar then decays to a pair of bosons, giving the process $pp\ensuremath{\rightarrow}\ensuremath{\phi}V\ensuremath{\rightarrow}{V}^{\ensuremath{'}}{V}^{\ensuremath{'}\ensuremath{'}}V$. We interpret our results in a set of effective field theories where the exotic scalar fields couple to the Standard Model through pairs of electroweak gauge bosons. We estimate the sensitivity of the LHC and HL-LHC datasets and find sensitivity to cross sections in the 10 fb--0.5 fb range, corresponding to scalar masses of 500 GeV to 2 TeV and effective operator coefficients up to 35 TeV.

UPDATED CONSTRAINTS ON HEAVY RESONANCES USING THE RUN 2 DATA AT LHC

The full ATLAS and CMS Run 2 data set at the Large Hadron Collider (LHC) with time- integrated luminosity of 139 fb −1 and 137 fb −1 , re- spectively, in the diboson channel is used to probe benchmark models with extended gauge sectors: theE 6 -motivated Grand Unification models, the left-right symmetric LR and the sequential standard model. These all predict neutral Z' and charged W' vector bosons, decaying into lepton or electroweak gauge boson pairs. We present constraints on the parameter space of the Z' and W' and compare them to those obtained from the previous analyses performed withLHC data collected at 7 and 8 TeV in Run 1 as well as at 13 TeV in Run 2 at time-integrated luminosity of 36.1 fb −1 . We show that proton-proton collision data at √ s = 13 TeV collected by the ATLAS and the CMS experiments allow to set the most stringent bounds to date on Z-Z' and W-W' mixing.

New heavy gauge bosons decaying to pair of electroweak bosons: prospect studies at Run 3 and HL-LHC with ATLAS

The expected ATLAS Run 3 data set with time-integrated luminosity of 300 fb-1 and HL-LHC option of the LHC with L = 3000 fb-1 in the diboson channels in semileptonic final states are used to probe a simple benchmark model with an extended gauge sector, proposed by Altarelli et al. This model accommodates new charged W' and neutral Z' vector bosons with modified trilinear Standard Model gauge couplings, decaying into electroweak gauge boson pairs WZ or WW , where W / Z decay semileptonically. We present upper limits on the mixing parameters, W - W' and Z- Z ' , by using the expected Run 3 data and HL-LHC options of the LHC.

Updated constraints on Z′ and W′ bosons decaying into bosonic and leptonic final states using the run 2 ATLAS data

The full ATLAS Run 2 data set with time-integrated luminosity of 139 fb$^{-1}$ in the diboson and dilepton channels is used to probe benchmark models with extended gauge sectors: the $E_6$-motivated Grand Unification models, the left-right symmetric $LR$ and the sequential standard model (EGM). These all predict neutral $Z'$ vector bosons, decaying into lepton pairs, $\ell\ell$, or into electroweak gauge boson pairs $WW$, where one $W$ in turn decays semileptonically. 95% C.L. exclusion limits on the $Z'$ resonance production cross section times branching ratio to electroweak gauge boson pairs and to lepton pairs in the mass range of $\sim$ 1 - 6 TeV are converted to constraints on the $Z$-$Z'$ mixing parameter and the heavy resonance mass. We present exclusion regions on the parameter space of the $Z'$ which are significantly extended compared to those obtained from the previous analyses performed with LHC data collected at 7 and 8 TeV in Run 1 as well as at 13 TeV in Run 2 at time-integrated luminosity of 36.1 fb$^{-1}$ and are the most stringent bounds to date. Also presented, from a similar analysis of electrically charged $W'$ bosons arising in the EGM, which can decay through $W'\to WZ$ and $W'\to \ell\nu$, are limits on the $W$-$W'$ mixing parameter and the charged $W'$ vector boson mass.

High-precision limits on W\u2013W' and Z\u2013Z' mixing from diboson production using the full LHC Run 2 ATLAS data set

The full ATLAS Run 2 data set with time-integrated luminosity of 139 , {text {fb}}^{-1} in the diboson channels in hadronic final states is used to probe a simple model with an extended gauge sector (EGM), proposed by Altarelli et al., and often taken as a convenient benchmark by experimentalists. This model accommodates new charged W' and neutral Z' vector bosons with modified trilinear Standard Model gauge couplings, decaying into electroweak gauge boson pairs WZ or WW, where W/Z decay hadronically. Exclusion limits at the 95% CL on the Z' and W' resonance production cross section times branching ratio to electroweak gauge boson pairs in the mass range of sim 1–5 TeV are here converted to constraints on W–W' and Z–Z' mixing parameters and masses for the EGM. We present exclusion regions on the parameter space of the W' and Z' by using the full Run 2 data set comprised of pp collisions at sqrt{s}=13 , hbox {TeV} and recorded by the ATLAS detector at the CERN LHC. The obtained exclusion regions are significantly extended compared to those obtained from the previous analysis performed with Tevatron data as well as with LHC data collected at 7 and 8 TeV in Run 1 and are the most stringent bounds to date.

Universality of next-to-leading power threshold effects for colourless final states in hadronic collisions

We consider the production of an arbitrary number of colour-singlet particles near partonic threshold, and show that next-to-leading order cross sections for this class of processes have a simple universal form at next-to-leading power (NLP) in the energy of the emitted gluon radiation. Our analysis relies on a recently derived factorisation formula for NLP threshold effects at amplitude level, and therefore applies both if the leading-order process is tree-level and if it is loop-induced. It holds for differential distributions as well. The results can furthermore be seen as applications of recently derived next-to-soft theorems for gauge theory amplitudes. We use our universal expression to re-derive known results for the production of up to three Higgs bosons at NLO in the large top mass limit, and for the hadro-production of a pair of electroweak gauge bosons. Finally, we present new analytic results for Higgs boson pair production at NLO and NLP, with exact top-mass dependence.

A model for the LHC diboson excess

The first run of the LHC showed hints of a new resonance with mass near 1.9 TeV decaying into electroweak gauge boson pairs as well as into dijets. While Run 2 has neither confirmed nor ruled out such a resonance, it has yielded new constraints on models attempting to explain these decays. Additionally in W′ models where this new resonance is a charged vector boson that is a weak isospin singlet there is the potential for conflict with the electroweak precision T parameter. We construct variants of a W′ resonance model that provide an excellent fit to both Run 1 and Run 2 data, as well as electroweak precision measurements. The model also predicts a neutral vector boson, a Z′, with mass close to 3 TeV. This Z′ is compatible with the intriguing Run 2 observation of a dielectron pair with invariant mass of 2.9 TeV at CMS.

Cancellation of Glauber Gluon Exchange in the Double Drell–Yan Process

For any factorisation proof, a crucial step is a demonstration of the cancellation of so-called Glauber gluons. We summarise a recent paper in which we demonstrated this cancellation for double Drell–Yan production (the double parton scattering process in which a pair of electroweak gauge bosons is produced), both for the integrated cross section and for the cross section differential in the boson transverse momenta.

Cancellation of Glauber gluon exchange in the double Drell-Yan process

An essential part of any factorisation proof is the demonstration that the exchange of Glauber gluons cancels for the considered observable. We show this cancellation at all orders for double Drell-Yan production (the double parton scattering process in which a pair of electroweak gauge bosons is produced) both for the integrated cross section and for the cross section differential in the transverse boson momenta. In the process of constructing this proof, we also revisit and clarify some issues regarding the Glauber cancellation argument and its relation to the rest of the factorisation proof for the single Drell-Yan process.

WIMPs at the galactic center

Simple models of weakly interacting massive particles (WIMPs) predict dark matter annihilations into pairs of electroweak gauge bosons, Higgses or tops, which through their subsequent cascade decays produce a spectrum of gamma rays. Intriguingly, an excess in gamma rays coming from near the Galactic center has been consistently observed in Fermi data. A recent analysis by the Fermi collaboration confirms these earlier results. Taking into account the systematic uncertainties in the modelling of the gamma ray backgrounds, we show for the first time that this excess can be well fit by these final states. In particular, for annihilations to (WW, ZZ, hh, tt̄), dark matter with mass between threshold and approximately (165, 190, 280, 310) GeV gives an acceptable fit. The fit range for bb̄ is also enlarged to 35 GeV ≲ mχ ≲ 165 GeV. These are to be compared to previous fits that concluded only much lighter dark matter annihilating into b, τ, and light quark final states could describe the excess. We demonstrate that simple, well-motivated models of WIMP dark matter including a thermal-relic neutralino of the MSSM, Higgs portal models, as well as other simplified models can explain the excess.

Higher dimensional operators and the LHC Higgs data: The role of modified kinematics

The inclusion of higher-dimensional gauge invariant operators induces new Lorentz structures in Higgs couplings with electroweak gauge boson pairs. This in principle affects the kinematics of Higgs production and decay, thereby modifying the efficiencies of the experimental cuts compared to what simulations based on the standard model interactions yield. Taking some sample cases, we perform a rigorous analysis of how the efficiencies differ for various strengths of the additional operator vis-a-vis the standard model interactions, scanning over the values of both of them. While the response to cuts can be markedly different in some regions, we find that the sensitivity to new operator structures is relatively limited, so long as we remain confined to the 2-sigma regions around the best fit signal strengths measured at the Large Hadron Collider. We also show modifications to certain kinematical distributions including the new operators in the diphoton final state.

Diboson Production at Colliders

This article is devoted to the physics of pairs of electroweak gauge bosons (dibosons) produced at high-energy particle colliders. Particular emphasis is placed on published results on diboson production from the CDF and DØ experiments at the Fermilab Tevatron and the CMS and ATLAS experiments at the CERN Large Hadron Collider (LHC). The study of diboson production at colliders plays an important role in tests of electroweak theory and searches for new phenomena at the TeV-energy scale and beyond. The diboson physics program has been a highlight of Run II at the Fermilab Tevatron. The progress made on analysis methods through the study of Standard Model diboson signals has had a direct and positive impact on the sensitivity of Higgs boson and New Physics searches in the Tevatron experiments. It is anticipated that diboson physics will play an even bigger role in the TeV-scale exploration now under way at the LHC.

Effective Yukawa couplings and flavor-changing Higgs boson decays at linear colliders

We analyze the advantages of a linear-collider program for testing a recent theoretical proposal where the Higgs-boson Yukawa couplings are radiatively generated, keeping unchanged the standard-model mechanism for electroweak-gauge-symmetry breaking. Fermion masses arise at a large energy scale through an unknown mechanism, and the standard model at the electroweak scale is regarded as an effective field theory. In this scenario, Higgs boson decays into photons and electroweak gauge-boson pairs are considerably enhanced for a light Higgs boson, which makes a signal observation at the LHC straightforward. On the other hand, the clean environment of a linear collider is required to directly probe the radiative fermionic sector of the Higgs boson couplings. Also, we show that the flavor-changing Higgs-boson decays are dramatically enhanced with respect to the standard model. In particular, we find a measurable branching ratio in the range (10^{-4}-10^{-3}) for the decay H\to bs for a Higgs boson lighter than 140 GeV, depending on the high-energy scale where Yukawa couplings vanish. We present a detailed analysis of the Higgs boson production cross sections at linear colliders for interesting decay signatures, as well as branching-ratio correlations for different flavor-conserving/nonconserving fermionic decays.