Search

A novel observable, the double nuclear modification factor, is proposed to probe simultaneously the initial and final state effects in nucleus–nucleus collisions. An interesting competition between the combinatorial enhancement in the double parton scattering and the suppression due to parton energy loss can be observed in the production rate of two hard particles. In particular, the production of mesons in association with a W boson is not suppressed but is enhanced in the region of moderate transverse momenta, unlike the case of unassociated (inclusive) production. At the same time, in the region of high enough transverse momenta the nuclear modification factor for associated production converges to that of unassociated . [ABSTRACT FROM AUTHOR]

"Resummed-Range Effective Field Theory" is a consistent nonrelativistic Effective Field Theory of contact interactions with large scattering length a and an effective range r 0 large in magnitude but negative. Its leading order is non-perturbative, and its observables are universal in the sense that they depend only on the dimensionless ratio ξ : = 2 r 0 / a once the overall distance scale is set by | r 0 | . In the two-body sector, the relative position of the two shallow S-wave poles in the complex plane is determined by ξ . We investigate three identical bosons at leading order for a two-body system with one bound and one virtual state ( ξ ≤ 0 ), or with two virtual states ( 0 ≤ ξ < 1 ). Such conditions might, for example, be found in systems of heavy mesons. We find that no three-body interaction is needed to renormalise (and stabilise) the leading order. A well-defined ground state exists for 0.366 ... ≥ ξ ≥ - 8.72 ... . Three-body excitations appear for even smaller ranges of ξ around the "quasi-unitarity point" ξ = 0 ( | r 0 | ≪ | a | → ∞ ) and obey discrete scaling relations. We explore in detail the ground state and the lowest three excitations. We parametrise their trajectories as function of ξ and of the binding momentum κ 2 - of the shallowest 2 B state. These stretch from the point where three- and two-body binding energies are identical to the point of zero three-body binding. As | r 0 | ≪ | a | becomes perturbative, this version turns into the "Short-Range EFT" which needs a stabilising three-body interaction and exhibits Efimov's Discrete Scale Invariance. By interpreting that EFT as a low-energy version of Resummed-Range EFT, we match spectra to determine Efimov's scale-breaking parameter Λ ∗ in a renormalisation scheme with a "hard" cutoff. Finally, we compare phase shifts for scattering a boson on the two-boson bound state with that of the equivalent Efimov system. [ABSTRACT FROM AUTHOR]

The flavor-changing neutral current (FCNC) decays of charmed hadrons with missing energy (Ɇ) can serve as potentially promising hunting grounds for hints of new physics, as the standard-model backgrounds are very suppressed. A few of such processes have been searched for in recent experiments, specifically D0→ Ɇ by Belle and D0→ π0Ɇ and Λ c + → pɆ by BESIII, resulting in upper bounds on their branching fractions. We consider them to illuminate the possible contributions of the quark transition c → uɆ with a couple of invisible spinless bosons carrying away the missing energy, assuming that they are not charge conjugates of each other and hence can have unequal masses. We find that these data are complementary in that they constrain different sets of the underlying operators and do not cover the same ranges of the bosons' masses, but there are regions not yet accessible. From the allowed parameter space, we show that other D-meson decays, such as D → ρɆ, and the charmed-baryon ones Ξc → (Σ, Λ)Ɇ can have sizable branching fractions and therefore may offer further probes of the new-physics interactions. We point out the importance of D0 → γɆ which are not yet searched for but could access parts of the parameter space beyond the reach of the other modes. In addition, we look at a scenario where the invisibles are instead fermionic, namely sterile neutrinos, and a scalar leptoquark mediates c → uɆ. We discuss the implications of the aforesaid bounds for this model. The predictions we make for the various charmed-hadron decays in the different scenarios may be testable in the near future by BESIII and Belle II. [ABSTRACT FROM AUTHOR]

The hadroproduction of a W boson in association with a charm quark at the Large Hadron Collider is at the centre of current investigations due to its potential to probe the strangeness content of the proton. In this paper we present an implementation of the W + c production process in the PowHel event generator matched to the PYTHIA8 parton shower approach, allowing to obtain predictions for differential cross-sections with NLO QCD accuracy matched to the accuracy of the Shower Monte Carlo event generator. Effects of non-diagonal CKM matrix elements, finite charm quark mass and off-shell W decays including spin correlations are taken into account. We investigate the production of a leptonically decaying W boson in association with either a charmed meson (W± + D∗∓) or a charmed jet (W± + jc) and compare our predictions with particle-level measurements by the ATLAS and CMS collaborations at s = 7 and 13 TeV. The role of the so-called "opposite sign" and "same sign" contributions to the theoretical cross-sections is presented and discussed, pointing out the importance of including parton shower effects for a reliable estimate of the latter and a faithful comparison with experimental data. [ABSTRACT FROM AUTHOR]

An anomaly observed in the 8Be nuclear transition by the Atomki collaboration hints at a light, neutral boson decaying into an e + e − pair with a mass of about 17 MeV. In this paper, we study the Atomki anomaly in the framework of axial (ABJ) anomaly. Some theoretical results indicate that the X17 particle is the color singlet pseudoscalar. We take the X17 particle as a pseudoscalar meson (u ū) system which has the axial (ABJ) anomaly, where u denotes the up quark. Besides this, we also give an interpretation for E38 particle with a mass of about 38 MeV as a pseudoscalar meson (d d ̄) system. We obtain the correct masses of the two pseudoscalars by a non-perturbative mass formula. [ABSTRACT FROM AUTHOR]

The rare leptonic decays Bs, d → l+l− (l = e, μ, τ) present an important base to analyse the flavour structure of the standard model (SM) and also become a potential source to dig out possible signatures of new physics (NP) beyond the SM. The muonic decay Bs, d → μ+μ− has been observed at the LHC as well as the upper limits of branching ratios for other Bs, d → l+l− decays have been updated recently. In this paper, using the χ2 fitting method we have studied all these decay channels considering the effect of a Z′ boson. Our analysing method reproduces the result of the muonic channel of Bs meson, hence we have used the same strategy for the other Bs, d → l+l− decays. [ABSTRACT FROM AUTHOR]

Experimental measurements collected by the BABAR, Belle, and LHCb experiments on different observables associated with the semileptonic transition , indicate the existence of disagreement respect with the Standard Model predictions. We analyze the charged scalar boson contributions to these charged-current B meson anomalies within the framework of two Higgs doublet model (2HDM) with the most general Yukawa couplings to quarks and leptons from the third generation, involving left-handed and right-handed (sterile) neutrinos. We perform a phenomenological study of the Yukawa couplings parameter space that accommodates these anomalies. We consider the most recent data from HFLAV world-average and Belle combination, and the upper limits and 10%. In addition, we include in our study the prospect measurements on R(D(*)) that the Belle II experiment could achieve and explore, for the first time, the future implications for the corresponding charged scalar Yukawa couplings. This analysis updates the existing literature and includes new important observables. Our results show that current experimental data and Belle II projection favor the interpretation of a charged scalar boson interacting with right-handed neutrinos. Furthermore, as a side analysis regarding the charged scalar boson interpretation, we revisit the relation between R(D*) and by investigating whether the claim that pseudoscalar new physics interpretations of R(D*) are implausible due to the Bc lifetime is still valid, to the light of the recent data and Belle II prospects on R(D*). Lastly, we reexamine addressing the R(D(*)) anomalies in the context of the 2HDM of type II. We show that with the current Belle combined data is possible to obtain an available parameter space on the plane for a simultaneous explanation of the anomalies, in consistency with and bounds from inclusive radiative B decays. Moreover, projections at the Belle II experiment suggest that the 2HDM of type II would be no longer disfavored. [ABSTRACT FROM AUTHOR]