Showing papers on "Electroweak interaction published in 2022"
TL;DR: In this paper , the authors present evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton-proton collision data collected with the LHCb detector at CERN's Large Hadron Collider.
Abstract: The Standard Model of particle physics currently provides our best description of fundamental particles and their interactions. The theory predicts that the different charged leptons, the electron, muon and tau, have identical electroweak interaction strengths. Previous measurements have shown a wide range of particle decays are consistent with this principle of lepton universality. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton-proton collision data collected with the LHCb detector at CERN's Large Hadron Collider. The measurements are of processes in which a beauty meson transforms into a strange meson with the emission of either an electron and a positron, or a muon and an antimuon. If confirmed by future measurements, this violation of lepton universality would imply physics beyond the Standard Model, such as a new fundamental interaction between quarks and leptons.
97 citations
TL;DR: In this article , the authors analyse possible new physics contributions to MW from extended Higgs sectors, focusing on the Two-Higgs-Doublet Model (2HDM) as a concrete example, and identify parameter regions of the 2HDM in which the prediction for MW is close to the new CDF value.
80 citations
TL;DR: In this article , a new report for the measurement of the W boson mass has been provided by the CDF II experiment, which shows 7σ deviation from the standard model prediction, while the other groups of high energy experiments, e.g., ATLAS and D0 II, show consistent results with the latter.
78 citations
TL;DR: In this article , the authors point out a connection between the $M_W$ anomaly and Higgs physics observables such as the ratio $h to ZZ/WW, and systematically classify new physics scenarios which can address the anomaly via a tree-level contribution to the $\hat T$ parameter.
75 citations
TL;DR: In this article , the authors study singlet extensions of the Standard Model focusing on the shift of the W boson mass, and they find that the increase in the W and Z boson masses is at most a few MeV and therefore does not alleviate the tension between the CDF II result and the SM prediction.
68 citations
TL;DR: In this article , an electroweak triplet scalar field with a non-zero vacuum expectation value (vev) vΔ is introduced to facilitate the generation of small neutrino masses.
60 citations
TL;DR: In this paper , the authors consider an F-theory GUT in which the visible sector is realized on intersecting 7-branes, and extra sector states arise from a probe D3-brane near an E-type Yukawa point.
53 citations
TL;DR: In this paper , the global electroweak fit with the new $W$-boson was performed, and the new values of the oblique parameters were presented: $S = 0.06 \pm 0.10, $T= 0.11 \pm0.12, $U=0.13 \pm
Abstract: The $W$ boson mass is one of the most important electroweak precision observables for testing the Standard Model or its extensions. The very recent measured $W$ boson mass at CDF shows about $7\sigma$ deviations from the SM prediction, which may challenge the internal consistency of the SM. By performing the global electroweak fit with the new $W$-boson, we present the new values of the oblique parameters: $S = 0.06 \pm 0.10$, $T= 0.11 \pm 0.12$, $U=0.13 \pm 0.09$, or $S=0.14 \pm 0.08$, $T= 0.26 \pm 0.06$ with $U =0$ and the corresponding correlation matrices, which strongly indicates the need for the non-degenerate multiplets beyond the SM. As a proof-of-concept, we show that the new results can be accommodated in the two-Higgs doublet model, where the charged Higgs boson has to be either heavier or lighter than both two heavy neutral Higgs bosons. Therefore, searching for these non-SM Higgs bosons will provide a complementary way to test the new physics for the $W$ boson mass anomaly.
44 citations
TL;DR: In this article , the authors presented an updated combination of global PDF fits, PDF4LHC21, based on the Monte Carlo combination of the CT18, MSHT20, and NNPDF3.1 sets followed by either Hessian reduction or its replica compression.
Abstract:
A precise knowledge of the quark and gluon structure of the proton, encoded by the parton distribution functions (PDFs), is of paramount importance for the interpretation of high-energy processes at present and future lepton–hadron and hadron–hadron colliders. Motivated by recent progress in the PDF determinations carried out by the CT, MSHT, and NNPDF groups, we present an updated combination of global PDF fits: PDF4LHC21. It is based on the Monte Carlo combination of the CT18, MSHT20, and NNPDF3.1 sets followed by either its Hessian reduction or its replica compression. Extensive benchmark studies are carried out in order to disentangle the origin of the differences between the three global PDF sets. In particular, dedicated fits based on almost identical theory settings and input datasets are performed by the three groups, highlighting the role played by the respective fitting methodologies. We compare the new PDF4LHC21 combination with its predecessor, PDF4LHC15, demonstrating their good overall consistency and a modest reduction of PDF uncertainties for key LHC processes such as electroweak gauge boson production and Higgs boson production in gluon fusion. We study the phenomenological implications of PDF4LHC21 for a representative selection of inclusive, fiducial, and differential cross sections at the LHC. The PDF4LHC21 combination is made available via the LHAPDF library and provides a robust, user-friendly, and efficient method to estimate the PDF uncertainties associated to theoretical calculations for the upcoming Run III of the LHC and beyond.
44 citations
TL;DR: In this paper , a global fit of electroweak data was performed and it was shown that the anomaly in the $W$ mass claimed by the CDF collaboration can be reproduced as a universal new-physics correction to the $T$ parameter or $| H^\dagger D_\mu H|^2$ operator.
Abstract: We perform a global fit of electroweak data, finding that the anomaly in the $W$ mass claimed by the CDF collaboration can be reproduced as a universal new-physics correction to the $T$ parameter or $| H^\dagger D_\mu H|^2$ operator. Contributions at tree-level from multi-TeV new physics can fit the anomaly compatibly with collider bounds: we explore which scalar vacuum expectation values (such as a triplet with zero hypercharge), $Z'$ vectors (such as a $Z'$ coupled to the Higgs only), little-Higgs models or higher-dimensional geometries provide good global fits. On the other hand, new physics that contributes at loop-level must be around the weak scale to fit the anomaly. Thereby it generically conflicts with collider bounds, that can be bypassed assuming special kinematics like quasi-degenerate particles that decay into Dark Matter (such as an inert Higgs doublet or appropriate supersymmetric particles).
40 citations
TL;DR: In this article , a minimal extension of the Standard Model by introducing three right-handed neutrinos and a new scotogenic scalar doublet was studied, in which the mass splittings between neutral and charged components are responsible for the $W$-boson mass newly measured by the CDF collaboration.
TL;DR: In this article , three types of electroweak global fits in the effective field theory framework are considered: the $S$-$T, the$S$$T$-$\delta G_F, and the eight-parameter flavor-universal one.
Abstract:
The W Mass determination at the Tevatron CDF experiment reported a deviation from the SM expectation at 7$\sigma$ level. We discuss a few possible interpretations and their collider implications. We perform electroweak global fits under various frameworks and assumptions. We consider three types of electroweak global fits in the effective-field-theory framework: the $S$-$T$, the $S$-$T$-$\delta G_F$, and the eight-parameter flavor-universal one. We discuss the amounts of tensions between different $m_W$ measurements reflected in these fits and the corresponding shifts in central values of these parameters. With these electroweak fit pictures in hand, we present a few different classes of models and discuss their compatibility with these results. We find that while explaining the $m_W$ discrepancy, the single gauge boson extensions face strong LHC direct search constraints unless the $Z'$ is fermiophobic (leptophobic) which can be realized if extra vector fermions (leptons) mix with the SM fermions (leptons). Vector-like top partners can partially generate the needed shift to the electroweak observables. The compatibility with top squark is also studied in detail. We find non-degenerate top squark soft masses enhance the needed operator coefficients, enabling an allowed explanation compatible with current LHC measurements. Overall, more theory and experimental developments are highly in demand to reveal the physics behind this discrepancy.Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.
TL;DR: In this paper , the mass of the W boson was measured using proton-proton collision data at 13$ TeV corresponding to an integrated luminosity of 1.7 fb$^{-1}$ recorded by the LHCb experiment.
Abstract: The $W$ boson mass is measured using proton-proton collision data at $\sqrt{s}=13$ TeV corresponding to an integrated luminosity of 1.7 fb$^{-1}$ recorded during 2016 by the LHCb experiment. With a simultaneous fit of the muon $q/p_T$ distribution of a sample of $W \to \mu
u$ decays and the $\phi^*$ distribution of a sample of $Z\to\mu\mu$ decays the $W$ boson mass is determined to be \begin{equation*} m_{W} = 80354 \pm 23_{\rm stat} \pm 10_{\rm exp} \pm 17_{\rm theory} \pm 9_{\rm PDF}~\mathrm{MeV}, \end{equation*} where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. This is an average of results based on three recent global parton distribution function sets. The measurement agrees well with the prediction of the global electroweak fit and with previous measurements.
TL;DR: In this paper , the authors show that the B-meson anomalies arise as the low energy limit of a complete theory of flavor, based on a warped fifth dimension where each Standard Model family is quasi-localized in a different brane.
CERN1
TL;DR: In this paper , the authors investigate the phenomenological implications of the recent $W$ mass measurement by the CDF collaboration, which exhibits tension with the standard model (SM) electroweak fit, and find that the new physics that contributes either to the determination of the electroweak vacuum expectation value, or to the oblique parameters, can improve the agreement with data.
Abstract: We investigate the phenomenological implications of the recent $W$ mass measurement by the CDF collaboration, which exhibits tension with the standard model (SM) electroweak fit. Performing the fit to the electroweak observables within the SM effective field theory, we find that the new physics that contributes either to the determination of the electroweak vacuum expectation value, or to the oblique parameters, can improve the agreement with data. The best description is obtained from a fit where flavor universality is not required in the new physics operators, with 2 to 3 $\sigma$ indications for several nonzero Wilson coefficients. We point out that top partners with order TeV masses could lead to the observed shift in the $W$ mass.
TL;DR: In this article , the authors find evidence for a nonzero value of the $T$ parameter, i.e. for a novel source of violation of custodial symmetry, pointing to physics beyond the Standard Model at the 4.5$\sigma$ level.
Abstract: The new measurement of the $W$-boson mass from the CDF collaboration shows a significant tension with the Standard Model prediction. We quantify this discrepancy within a state-of-the-art analysis of electroweak precision data and scrutinize the leading deformations of the Standard Model Effective Field Theory arising at dimension six. We find evidence for a non-zero value of the $T$ parameter, i.e. for a novel source of violation of custodial symmetry, pointing to physics beyond the Standard Model at the 4.5$\sigma$ level. We contextualize the implications of our findings in light of other present anomalies in Particle Physics.
TL;DR: In this paper , the mixed QCD-electroweak (EW) corrections to the neutral-current Drell-Yan process were computed using semianalytical techniques, overcoming the technical problems in the evaluation of relevant master integrals.
Abstract: We report on the first complete computation of the mixed QCD-electroweak (EW) corrections to the neutral-current Drell-Yan process. Superseding previously applied approximations, our calculation provides the first result at this order that is valid in the entire range of dilepton invariant masses. The two-loop virtual contribution is computed by using semianalytical techniques, overcoming the technical problems in the evaluation of the relevant master integrals. The cancellation of soft and collinear singularities is achieved by a formulation of the q_{T} subtraction formalism valid in the presence of charged massive particles in the final state. We present numerical results for the fiducial cross section and selected kinematical distributions. At large values of the lepton p_{T} the mixed QCD-EW corrections are negative and increase in size, to about -15% with respect to the next-to-leading-order QCD result at p_{T}=500 GeV. Up to dilepton invariant masses of 1 TeV the computed corrections amount to about -1.5% with respect to the next-to-leading-order QCD result.
01 Jan 2022
TL;DR: In this article , the authors considered real SU(2) representations with zero hypercharge, that automatically avoid direct detection constraints from tree-level Z -exchange. And they derived the calculable thermal masses for scalar and fermionic WIMPs, including Sommerfeld enhancement and bound states formation in gauge boson exchange and emission.
Abstract: Abstract We study scenarios where Dark Matter is a weakly interacting particle (WIMP) embedded in an ElectroWeak multiplet. In particular, we consider real SU(2) representations with zero hypercharge, that automatically avoid direct detection constraints from tree-level Z -exchange. We compute for the first time all the calculable thermal masses for scalar and fermionic WIMPs, including Sommerfeld enhancement and bound states formation at leading order in gauge boson exchange and emission. WIMP masses of few hundred TeV are shown to be compatible both with s -wave unitarity of the annihilation cross-section, and perturbativity. We also provide theory uncertainties on the masses for all multiplets, which are shown to be significant for large SU(2) multiplets. We then outline a strategy to probe these scenarios at future experiments. Electroweak 3-plets and 5-plets have masses up to about 16 TeV and can efficiently be probed at a high energy muon collider. We study various experimental signatures, such as single and double gauge boson emission with missing energy, and disappearing tracks, and determine the collider energy and luminosity required to probe the thermal Dark Matter masses. Larger multiplets are out of reach of any realistic future collider, but can be tested in future $$\gamma $$ γ -ray telescopes and possibly in large-exposure liquid Xenon experiments.
TL;DR: In this paper , three physics cases producing long-lived signatures at FCC-ee are highlighted and studied: heavy neutral leptons (HNLs), axion-like particles (ALPs), and exotic decays of the Higgs boson.
Abstract: The electron-positron stage of the Future Circular Collider, FCC-ee, is a frontier factory for Higgs, top, electroweak, and flavour physics. It is designed to operate in a 100 km circular tunnel built at CERN, and will serve as the first step towards ≥100 TeV proton-proton collisions. In addition to an essential and unique Higgs program, it offers powerful opportunities to discover direct or indirect evidence of physics beyond the Standard Model. Direct searches for long-lived particles at FCC-ee could be particularly fertile in the high-luminosity Z run, where 5 × 1012 Z bosons are anticipated to be produced for the configuration with two interaction points. The high statistics of Higgs bosons, W bosons and top quarks in very clean experimental conditions could offer additional opportunities at other collision energies. Three physics cases producing long-lived signatures at FCC-ee are highlighted and studied in this paper: heavy neutral leptons (HNLs), axion-like particles (ALPs), and exotic decays of the Higgs boson. These searches motivate out-of-the-box optimization of experimental conditions and analysis techniques, which could lead to improvements in other physics searches.
TL;DR: In this paper , a Dirac neutrino mass model is presented in the view of the new result on W boson mass of mWCDF−II=80.4335±0.0094 GeV, recently reported by the CDF-II experimental collaboration.
TL;DR: In this paper , the Stueckelberg Extended Standard Model (ESM) was used to solve the CDF W mass anomaly, which is consistent with the various observables at the Z pole and the ATLAS dilepton limits.
06 Jul 2022
TL;DR: In this article , the CDF collaboration has recently published a precision measurement of the W-boson mass that differs from the Standard Model prediction by seven standard deviations, which can be explained with additional electroweak multiplets that either break the custodial symmetry or contribute to oblique parameters at loop level.
Abstract: The CDF collaboration has recently published a precision measurement of the W-boson mass that differs from the Standard Model prediction by seven standard deviations. This result can be explained with additional electroweak multiplets that either break the custodial symmetry or contribute to oblique parameters at loop level. Here, we study one of the best-motivated scenarios involving new multiplets: the type-II seesaw model, which involves a scalar triplet that generates Majorana neutrino masses and can furthermore resolve the W-boson mass discrepancy. This favors a doubly-charged scalar with mass between 100 and 200 GeV as well as other scalars with a fixed mass splitting. The entire preferred parameter space is testable at the LHC.
TL;DR: In this article , the authors lay out a comprehensive physics case for a future high-energy muon collider, exploring a range of collision energies (from 1 to 100 TeV) and luminosities.
Abstract: We lay out a comprehensive physics case for a future high-energy muon collider, exploring a range of collision energies (from 1 to 100 TeV) and luminosities. We highlight the advantages of such a collider over proposed alternatives. We show how one can leverage both the point-like nature of the muons themselves as well as the cloud of electroweak radiation that surrounds the beam to blur the dichotomy between energy and precision in the search for new physics. The physics case is buttressed by a range of studies with applications to electroweak symmetry breaking, dark matter, and the naturalness of the weak scale. Furthermore, we make sharp connections with complementary experiments that are probing new physics effects using electric dipole moments, flavor violation, and gravitational waves. An extensive appendix provides cross section predictions as a function of the center-of-mass energy for many canonical simplified models.
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CERN1
TL;DR: In this paper , the authors used the Fitmaker tool to incorporate the recent CDF measurement of $m_W$ in a global fit to electroweak, Higgs, and diboson data in the Standard Model Effective Field Theory (SMEFT) including dimension-6 operators at linear order.
Abstract: We use the Fitmaker tool to incorporate the recent CDF measurement of $m_W$ in a global fit to electroweak, Higgs, and diboson data in the Standard Model Effective Field Theory (SMEFT) including dimension-6 operators at linear order. We find that including any one of the SMEFT operators ${\cal O}_{HWB}$, ${\cal O}_{HD}$, ${\cal O}_{\ell \ell}$ or ${\cal O}_{H \ell}^{(3)}$ with a non-zero coefficient could provide a better fit than the Standard Model, with the strongest pull for ${\cal O}_{HD}$ and no tension with other electroweak precision data. We then analyse which tree-level single-field extensions of the Standard Model could generate such operator coefficients with the appropriate sign, and discuss the masses and couplings of these fields that best fit the CDF measurement and other data. In particular, the global fit favours either a singlet $Z^\prime$ vector boson, a scalar electroweak triplet with zero hypercharge, or a vector electroweak triplet with unit hypercharge, followed by a singlet heavy neutral lepton, all with masses in the multi-TeV range for unit coupling.
TL;DR: In this paper , the velocity and thickness of the bubble wall of a cosmological first order phase transition at electroweak scale are calculated using a scalar singlet extension of the SM with a parity symmetry and the SM effective field theory supplemented by a dimension six operator.
Abstract: A bstract Computing the properties of the bubble wall of a cosmological first order phase transition at electroweak scale is of paramount importance for the correct prediction of the baryon asymmetry of the universe and the spectrum of gravitational waves. By means of the semiclassical formalism we calculate the velocity and thickness of the wall using as theoretical framework the scalar singlet extension of the SM with a parity symmetry and the SM effective field theory supplemented by a dimension six operator. We use these solutions to carefully predict the baryon asymmetry and the gravitational wave signals. The singlet scenario can easily accommodate the observed asymmetry but these solutions do not lead to observable effects at future gravity wave experiments. In contrast the effective field theory fails at explaining the baryon abundance due to the strict constraints from electric dipole moment experiments, however, the strongest solutions we found fall within the sensitivity of the LISA experiment. We provide a simple analytical approximation for the wall velocity which only requires calculation of the strength and temperature of the transition and works reasonably well in all models tested. We find that generically the weak transitions where the fluid approximation can be used to calculate the wall velocity and verify baryogenesis produce signals too weak to be observed in future gravitational wave experiments. Thus, we infer that GW signals produced by simple SM extensions visible in future experiments are likely to only result from strong transitions described by detonations with highly relativistic wall velocities.
12 Jan 2022
TL;DR: In this paper , a comprehensive study of the electroweak interactions using the available Higgs and electroweak diboson production results from LHC runs 1 and 2 as well as electroweak precision data in terms of the dimension-six operators is presented under the assumption that no new tree level sources of flavor violation or violation of the universality of the weak current are introduced.
Abstract: We present a comprehensive study of the electroweak interactions using the available Higgs and electroweak diboson production results from LHC runs 1 and 2 as well as the electroweak precision data in terms of the dimension-six operators. Under the assumption that no new tree-level sources of flavor violation or violation of the universality of the weak current are introduced, the analysis involves 21 operators. We assess the impact of the data on kinematic distributions for the Higgs production at the LHC by comparing the results obtained by including the simplified template cross-section data with those in which only total Higgs signal strengths are considered. We also compare the results obtained when including the dimension-six anomalous contributions to order $1/{\mathrm{\ensuremath{\Lambda}}}^{2}$ and to order $1/{\mathrm{\ensuremath{\Lambda}}}^{4}$. As an illustration of the LHC potential to indirectly learn about specific forms of new physics, we adapt the analysis to constrain the parameter space for a few simple extensions of the standard model which generate a subset of the dimension-six operators at tree level.
TL;DR: In this paper , an extension of the Standard Model of particle physics that incorporates an additional scalar, a triplet coupled to the Higgs boson, is proposed to explain the recent CDF II measurement of the $W$ boson mass and predicting first-order phase transitions (FOPT) testable in future GW experiments.
Abstract: We suggest an appealing strategy to probe a large class of scenarios beyond the Standard Model simultaneously explaining the recent CDF II measurement of the $W$ boson mass and predicting first-order phase transitions (FOPT) testable in future gravitational-wave (GW) experiments. Our analysis deploys measurements from the GW channels and high energy particle colliders. We discuss this methodology focusing on the specific example provided by an extension of the Standard Model of particle physics that incorporates an additional scalar $\mathrm{SU}(2)_{\rm L}$ triplet coupled to the Higgs boson. We show that within this scenario a strong electroweak FOPT is naturally realised consistently with the measured $W$ boson mass-shift. Potentially observable GW signatures imply the triplet mass scale to be TeV-ish, consistently with the value preferred by the $W$ mass anomaly. This model can be tested in future space-based interferometers such as LISA, DECIGO, BBO, TianQin, TAIJI projects and in future colliders such as FCC, ILC, CEPC.
TL;DR: In this article , the existence of strong first order electroweak phase transition (SFOEWPT) and recent m W precision measurement in the Type-I and Type-II 2HDMs were revisited.
Abstract: A bstract In this work we revisit the existence of a strong first order electroweak phase transition (SFOEWPT) and recent m W precision measurement in the Type-I and Type-II 2HDMs. The $$ \mathcal{O} $$ O (100) GeV new scalars in 2HDMs are favored by SFOEWPT, which is necessary for electroweak baryogenesis, and observed m W shift as well. We find that under current constraints, both Type-I and Type-II 2HDM can explain the SFOEWPT, Z-pole, Higgs precision measurements and m W precision measurement of CDF-II at same time, and all these precision measurements are sensitive to heavy Higgs mass splitting in 2HDM. The allowed regions are ∆ m A/C ∈ (−400 , 400) GeV, tan β ∈ (1 , 50), and ∆ m A/C ∈ (−200 , 300) GeV, tan β ∈ (1 , 10) for Type-I and Type-II 2HDM respectively. Furthermore future lepton collider measurements on Higgs and Z boson properties can explore this scenario in more detail or even rule out it.
TL;DR: In this article , the authors compute all the calculable WIMP masses up to the largest multiplet allowed by perturbative unitarity and show how a future muon collider can fully explore the parameter space of the complex doublet combining missing mass, displaced track and long-lived track searches.
Abstract: We continue the study of weakly interacting massive particles (WIMP) started in [arXiv:2107.09688], focusing on a single complex electroweak $n$-plet with non-zero hypercharge added to the Standard Model. The minimal splitting between the Dark Matter and its electroweak neutral partner required to circumvent direct detection constraints allows only multiplets with hypercharge smaller or equal to 1. We compute for the first time all the calculable WIMP masses up to the largest multiplet allowed by perturbative unitarity. For the minimal allowed splitting, most of these multiplets can be fully probed at future large-exposure direct detection experiments, with the notable exception of the doublet with hypercharge 1/2. We show how a future muon collider can fully explore the parameter space of the complex doublet combining missing mass, displaced track and long-lived track searches. In the same spirit, we study how a future muon collider can probe the parameter space of complex WIMPs in regions where the direct detection cross section drops below the neutrino floor. Finally, we comment on how precision observables can provide additional constraints on complex WIMPs.
TL;DR: In this paper , a global fit of electroweak data within the Standard Model was performed using state-of-the-art experimental and theoretical results, including a determination of the electromagnetic coupling at the electroweak scale based on recent lattice calculations.
Abstract: We perform a global fit of electroweak data within the Standard Model, using state-of-the art experimental and theoretical results, including a determination of the electromagnetic coupling at the electroweak scale based on recent lattice calculations. In addition to the posteriors for all parameters and observables obtained from the global fit, we present indirect determinations for all parameters and predictions for all observables. Furthermore, we present full predictions, obtained using only the experimental information on Standard Model parameters, and a fully indirect determination of Standard Model parameters using only experimental information on electroweak data. Finally, we discuss in detail the compatibility of experimental data with the Standard Model and find a global p-value of 0.5.