Collider Detector At Fermilab Research Articles

Changing patterns in electroweak precision fits with new color-charged states: Oblique corrections and the W -boson mass

The recent measurement by the CDF Collaboration of the $W$ boson mass is in significant tension with the Standard Model expectation, showing a discrepancy of seven standard deviations. A larger value of $m_W$ affects the global electroweak fit, particularly the best-fit values of the Peskin-Takeuchi parameters $S$, $T$ (and perhaps $U$) that measure oblique corrections from new physics. To meet this challenge, we propose some simple models capable of generating non-negative $S$ and $T$, the latter of which faces the greatest upward pressure from the CDF measurement in scenarios with $U=0$. Our models feature weak multiplets of scalars charged under $\mathrm{SU}(3)_{\text{c}} \times \mathrm{U}(1)_Y$, which cannot attain nonzero vacuum expectation values but nevertheless produce e.g. $T \neq 0$ given some other mechanism to split the electrically charged and neutral scalars. We compute the oblique corrections in these models and identify ample parameter space supporting the CDF value of $m_W$.

Electroweak dark matter model accounting for the CDF W -mass anomaly

Recently, the CDF collaboration reported a new measurement of the $W$ boson mass ${M}_{W}=\phantom{\rule{0ex}{0ex}}80.4335\ifmmode\pm\else\textpm\fi{}0.0094\text{ }\text{ }\mathrm{GeV}$, which shows a $\ensuremath{\sim}7\ensuremath{\sigma}$ deviation from the standard model prediction $80.3545\ifmmode\pm\else\textpm\fi{}0.0057\text{ }\text{ }\mathrm{GeV}$ obtained by the electroweak (EW) global fit. This deviation can be explained by new physics generating moderate EW oblique parameters $S$, $T$, and $U$. In this work, we use the loop corrections induced by some extra EW multiplets to explain the CDF ${M}_{W}$ anomaly. The lightest neutral particle in the multiplets can also serve as a candidate of cold dark matter (DM). We consider two such models, namely singlet-triplet scalar DM and singlet-doublet fermionic DM models, and perform numerical scans to find the parameter points accounting for the ${M}_{W}$ anomaly. The constraints from the correct DM thermal relic density and direct detection are also taken into account. We find the parameter points simultaneously interpreting the ${M}_{W}$ anomaly and satisfying the DM requirements in the former model, but do not find such parameter points in the latter model.

Electroweak precision fit and new physics in light of the W boson mass

The $W$ boson mass is one of the most important electroweak precision observables for testing the Standard Model (SM) or its extensions. The very recent measured $W$ boson mass at the Collider Detector at Fermilab (CDF) shows about $7\ensuremath{\sigma}$ 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: $S=0.06\ifmmode\pm\else\textpm\fi{}0.10$, $T=0.11\ifmmode\pm\else\textpm\fi{}0.12$, $U=0.13\ifmmode\pm\else\textpm\fi{}0.09$, or $S=0.14\ifmmode\pm\else\textpm\fi{}0.08$, $T=0.26\ifmmode\pm\else\textpm\fi{}0.06$ with $U=0$ and the corresponding correlation matrices, which strongly indicates the need for the nondegenerate 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. The collider search for these non-SM Higgs bosons will provide a complementary way to test the new physics for $W$ boson mass anomaly.

Jets separated by a large pseudorapidity gap at the Tevatron and at the LHC

We present a phenomenological analysis of events with two high transverse momentum (pT) jets separated by a large (pseudo-)rapidity interval void of particle activity, also known as jet-gap-jet events. In the limit where the collision energy sqrt{s} is much larger than any other momentum scale, the jet-gap-jet process is described in terms of perturbative pomeron exchange between partons within the Balitsky-Fadin-Kuraev-Lipatov (BFKL) limit of perturbative quantum chromodynamics (QCD). The BFKL pomeron exchange amplitudes, with resummation at the next-to-leading logarithmic approximation, have been embedded in the PYTHIA8 Monte Carlo event generator. Standard QCD dijet events are simulated at next-to-leading order in αs matched to parton showers with POWHEG+PYTHIA8. We compare our calculations to measurements by the CDF, D0, and CMS experiments at center-of-mass energies of 1.8, 7 and 13 TeV. The impact of the theoretical scales, the parton densities, final- and initial-state radiation effects, multiple parton interactions, and pT thresholds and multiplicities of the particles in the rapidity gap on the jet-gap-jet signature is studied in detail. With a strict gap definition (no particle allowed in the gap), the shapes of most distributions are well described except for the CMS azimuthal-angle distribution at 13 TeV. The survival probability is surprisingly well modelled by multiparton interactions in PYTHIA8. Without multiparton interactions, theoretical predictions based on two-channel eikonal models agree qualitatively with fits to the experimental data.

Interpreting electroweak precision data including the W-mass CDF anomaly

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†DμH|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).

W boson mass shift and muon magnetic moment in the Zee model

The CDF Collaboration at Fermilab has recently reported a new precision measurement of the $W$ boson mass showing a substantial $7\ensuremath{\sigma}$ deviation from the Standard Model prediction. Moreover, Fermilab has recently confirmed the longstanding tension in the $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ measurement. We propose a unified solution to these deviations within the simplest radiative neutrino mass model; the Zee model. Our analysis establishes nontrivial links between the origin of neutrino mass, the $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ anomaly, and the $W$ boson mass shift while being consistent with lepton flavor violation and all other experimental constraints. We find that the mass spectrum of the physical scalars must be hierarchical to be consistent with the $W$ boson mass shift; remarkably, this is also the key to resolving the $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ tension. Furthermore, this mass splitting offers a unique same-sign dimuon signal through which our model can be tested at the LHC.

CDF W -boson mass and muon g−2 in a type-X two-Higgs-doublet model with a Higgs-phobic light pseudoscalar

The recent measurement of the $W$ boson mass by the CDF collaboration adds an anomaly to the longstanding discrepancy in the muon anomalous magnetic moment, $\mathrm{\ensuremath{\Delta}}{a}_{\ensuremath{\mu}}$. Although type-X in the two-Higgs-doublet model provides an attractive solution to $\mathrm{\ensuremath{\Delta}}{a}_{\ensuremath{\mu}}$ through a light pseudoscalar $A$, the model confronts the exotic Higgs decays of $h\ensuremath{\rightarrow}AA$ and the lepton flavor universality data in the $\ensuremath{\tau}$ and $Z$ decays. To save the model, we propose that the light pseudoscalar be Higgs-phobic. Through the random scanning over the entire parameter space, we perform a comparative study of the Higgs-phobic type-X with and without the CDF ${m}_{W}$ measurement, called the CDF and PDG cases, respectively. Both cases can explain the two anomalies as well as all the other constraints, but have significant differences in the finally allowed parameter space. For example, a small region with almost degenerate masses of new Higgs bosons around 100 GeV is allowed only in the PDG case. The cutoff scale of the model is also studied via the analysis of renormalization group equations, which reaches up to ${10}^{5}\text{ }\text{ }\mathrm{GeV}$ (${10}^{7}\text{ }\text{ }\mathrm{GeV}$) in the CDF (PDG) case. Since the dominant decay modes are $A\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{\tau}$, $H\ensuremath{\rightarrow}ZA$, and ${H}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{W}^{\ifmmode\pm\else\textpm\fi{}}A$ in most of the viable parameter space, we propose the $4\ensuremath{\tau}+V{V}^{\ensuremath{'}}$ states as the golden discovery channel at the LHC.

Violation of custodial symmetry from W -boson mass measurements

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.

Singlet extensions and W boson mass in light of the CDF II result

Recently, the CDF collaboration has reported the precise measurement of the W boson mass, MW=80433.5±9.4MeV, based on 8.8 fb−1 of s=1.96 TeV pp¯ collision data from the CDF II detector at the Fermilab Tevatron. This is about 7σ away from the Standard Model prediction, MWSM=80357±6MeV. Such a large discrepancy may be partially due to exotic particles that radiatively alter the relation between the W and Z boson masses. In this Letter, we study singlet extensions of the Standard Model focusing on the shift of the W boson mass since they are accidentally flavor and CP safe without changing the Standard Model structure. In the minimal extension with a real singlet field, using the bounds from the electroweak oblique parameters, B meson decays, LEP, and LHC, we find that the W boson mass shift is at most a few MeV, and therefore it does not alleviate the tension between the CDF II result and the SM prediction. We then examine how much various bounds are relaxed when the singlet is allowed to decay invisibly, and find that the increase of the W boson mass does not exceed 5MeV due to the bound from the Higgs signal strength. We also discuss phenomenological and cosmological implications of the singlet extensions such as the muon g−2 anomaly, axion/hidden photon dark matter, and self-interacting dark radiation as a possible alleviation of the Hubble tension.

Type II Dirac seesaw with observable ΔNeff in the light of W-mass anomaly

We propose a type II seesaw model for light Dirac neutrinos to provide an explanation for the recently reported anomaly in W boson mass by the CDF collaboration with 7σ statistical significance. In the minimal model, the required enhancement in W boson mass is obtained at tree level due to the vacuum expectation value of a real scalar triplet, which also plays a role in generating light Dirac neutrino mass. Depending upon the couplings and masses of newly introduced particles, we can have thermally or non-thermally generated relativistic degrees of freedom ΔNeff in the form of right handed neutrinos which can be observed at future cosmology experiments. Extending the model to a radiative Dirac seesaw scenario can also accommodate dark matter and lepton anomalous magnetic moment.

New physics effects on the W-boson mass from a doublet extension of the SM Higgs sector

Recently, the CDF collaboration has reported a new precision measurement of the W-boson mass, MW, showing a large deviation from the value predicted by the Standard Model (SM). In this paper, we analyse possible new physics contributions to MW from extended Higgs sectors. We focus on the Two-Higgs-Doublet Model (2HDM) as a concrete example. Employing predictions for the electroweak precision observables in the 2HDM at the two-loop level and taking into account further theoretical and experimental constraints, we identify parameter regions of the 2HDM in which the prediction for MW is close to the new CDF value. We assess the compatibility of these regions with precision measurements of the effective weak mixing angle and the total width of the Z boson.

W boson mass and muon g−2 in a lepton portal dark matter model

We study a lepton portal dark matter model, motivated by the deviation of the $W$ boson mass reported by the CDF collaboration. We introduce vectorlike leptons and a scalar dark matter (DM) that exclusively couples to the extra leptons and muon. The one-loop corrections induced by the new particles can shift the $W$ boson mass. Besides, the discrepancy in the muon anomalous magnetic moment and the DM density can simultaneously be explained by this setup, if the vectorlike lepton is lighter than 200 GeV and nearly degenerate with the DM particle. We also see that the constraints on such a light extra lepton from the collider experiments can be evaded due to the existence of the DM particle.

W -boson mass in the triplet seesaw model

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.

Correlating gravitational waves with W-boson mass, FIMP dark matter, and Majorana seesaw mechanism

We study a minimal extension of the standard model by introducing three right-handed neutrinos and a new scotogenic scalar doublet, in which the mass splittings between neutral and charged components are responsible for the W-boson mass newly measured by the CDF Collaboration. This model can not only generate non-vanishing Majorana neutrino masses via the interaction of right-handed neutrinos and scotogenic scalars, but also explain the Universe’s missing matter in the form of FIMP dark matter. We also study the influence of the mass splitting on the first order electroweak phase transition, and find that it can further enhance the transition strength and thus induce gravitational waves during the phase transition, which may be detected in the forthcoming detectors such as U-DECIGO.

Higgs physics confronts the MW anomaly

The recent high-precision measurement of the W mass by the CDF collaboration is in sharp tension with the Standard Model prediction as obtained by the electroweak fit. If confirmed, this finding can only be explained in terms of new physics effects. In this work, we point out a generic connection between the MW anomaly and Higgs physics observables such as h→γγ,Zγ and the ratio h→ZZ/WW. Moreover, we systematically classify new physics scenarios which can address the MW anomaly via a tree-level contribution to the Tˆ parameter. These include a real scalar triplet, a scalar quadruplet with the same hypercharge of the Higgs doublet, a Z′ boson, a vector triplet with unit hypercharge and a vector boson with the gauge quantum numbers of the Higgs doublet. These solutions to the MW anomaly are characterized by new physics states which are typically too heavy to be discovered in direct searches, but which might leave their imprints in Higgs physics.

The W boson mass weighs in on the non-standard Higgs

We consider the implications of the CDF collaboration high-precision measurement of the W boson mass on models with a non-standard Higgs. We show that this requires an enhancement of more than 5% in the non-standard Higgs coupling to the gauge bosons. This is naturally accommodated in dynamical models such as the dilaton Higgs, the Technicolor and glueball Higgs. The needed composite scale between 2 and 3 TeV can also explain the muon g-2 anomaly, as well as possible violations of lepton flavour universality.

Understanding J/ψ and ψ′ production using a modified version of Non-Relativistic Quantum Chromodynamics

There is serious disagreement between the predictions of Non-Relativistic Quantum Chromodynamics (NRQCD) and the data on J/ψ polarisation which has persisted for almost a quarter of a century. We find that if we account for the effect of perturbative soft gluons on the intermediate charm-anticharm octet states in NRQCD then the polarisation problem can be resolved. In addition, this model, when used to fit the Run 1 data on J/ψ and ψ′ production from the CDF experiment at Tevatron, gives good fits and yields values of (energy-independent) non-perturbative parameters. These, in turn, can be used to make parameter-free predictions for J/ψ and ψ′ data from the CMS experiment at the Large Hadron Collider and the predictions are in excellent agreement with the CMS data.

Singlet-doublet fermion origin of dark matter, neutrino mass and W-mass anomaly

Motivated by the recently reported anomaly in W boson mass by the CDF collaboration with 7σ statistical significance, we consider a singlet-doublet (SD) Majorana fermion dark matter (DM) model where the required correction to W boson mass arises from radiative corrections induced by SD fermions. While a single generation of SD fermions, odd under an unbroken Z2 symmetry, can not explain the W boson mass anomaly while being consistent with DM phenomenology, two generations of SD fermions can do so with the heavier generation playing the dominant role in W-mass correction and lighter generation playing the role in DM phenomenology. Additionally, such multiple generations of SD fermions can also generate light neutrino masses radiatively if a Z2-odd singlet scalar is included.

On the implications of positive W mass shift

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 σ 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.

Study of B(s)0→ϕϕ→(K+K−)(K+K−) decays in the perturbative QCD approach

In this work, we make a detailed analysis on the penguin-dominant processes $B_{(s)}^0 \to \phi\phi \to (K^+K^-)(K^+K^-)$ in the perturbative QCD (PQCD) approach. In addition to the dominant $P$-wave resonance, the scalar background $f_0(980) \to K^+K^-$ is also accounted for. We improve the Gegenbauer moments in $KK$ two-meson distribution amplitudes by fitting the PQCD factorization formulas to measured branching ratios of three-body and four-body $B$ decays. We extract the branching ratios of two-body $B_{(s)}^0 \to \phi\phi$ decays from the corresponding four-body decay modes and calculate the relevant polarization fractions together with two relative phases $\phi_{\parallel,\perp}$, which are consistent with the previous theoretical predictions. The PQCD predictions for the "true" triple product asymmetries (TPAs) are zero which are expected in the standard model due to the vanishing weak phase difference, and support the current data reported by the CDF and LHCb Collaborations. A large "fake" TPA $\mathcal{A}_\text{T-fake}^1=30.4\%$ of the decay $B^0_s \to \phi\phi \to (K^+K^-)(K^+K^-)$ is predicted for the first time, which indicates the presence of the significant final-state interactions. The TPAs of the rare decay channel $B^0 \to \phi\phi\to (K^+K^-)(K^+K^-)$ are also predicted and can be tested in the near future.