High Energy Physics Experiment

The precise determination of theBc→τντbranching ratio provides an advantageous opportunity for understanding the electroweak structure of the Standard Model, measuring the CKM matrix element|Vcb|and probing new physics models. In this paper, we discuss the potential of measuring the processes ofBc→τντwithτdecaying leptonically at the proposed Circular Electron Positron Collider (CEPC). We conclude that during theZpole operation, the channel signal can achieve fiveσsignificance with∼109Zdecays, and the signal strength accuracies forBc→τντcan reach around 1% level at the nominal CEPCZpole statistics of one trillionZdecays assuming the totalBc→τντyield is3.6×106. Our theoretical analysis indicates the accuracy could provide a strong constraint on the general effective Hamiltonian for theb→cτνtransition. If the totalBcyield can be determined toO(1%)level of accuracy in the future, these results also imply|Vcb|could be measured up toO(1%)level of accuracy.

In a recent paper [arXiv:2002.00459], Buttazzo et al. show how the annually modulated rate of the DAMA experiments can be possibly interpreted as an artefact due to the interplay between a time-dependent background and the method to account for it. In this work, we compare this hypothesis against the sinusoidal dark matter signal as proposed by the DAMA collaboration. We produce in a Bayesian approach a quantitative comparison of how much the experimental observations are in support of each hypothesis. Our conclusions are that the odds against the hypothesis of a time varying background being responsible for the annual modulation are decreased by a Bayes factor larger than 10^8 after considering the public available data of the DAMA/NaI and DAMA/LIBRA experiments. In this work we also elaborate on general aspects of the analysis procedure. Indeed, in order to optimise the background subtraction procedure, the DAMA collaboration only considers data-taking cycles with a duration of roughly one year. We argue that any data-taking cycle is informative, and we propose a procedure to include this effect, as well as the possibility to include a slowly varying component for the background.

The DAMA collaboration reported an annually modulated rate with a phase compatible with a Dark Matter induced signal. We point out that a slowly varying rate can bias or even simulate an annual modulation if data are analyzed in terms of residuals computed by subtracting approximately yearly averages starting from a fixed date, rather than a background continuous in time. In the most extreme case, the amplitude and phase of the annual modulation reported by DAMA could be alternatively interpreted as a decennial growth of the rate. This possibility appears mildly disfavoured by a detailed study of the available data, but cannot be safely excluded. In general, a decreasing or increasing rate could partially reduce or enhance a true annual modulation, respectively. The issue could be clarified by looking at the full time-dependence of the DAMA total rate, not explicitly published so far.

Thep¯over p multiplicity ratio is measured in deep-inelastic scattering for the first time using (anti-) protons carrying a large fraction of the virtual-photon energy,z>0.5. The data were obtained by the COMPASS Collaboration using a 160 GeV muon beam impinging on an isoscalar6LiD target. The regime of deep-inelastic scattering is ensured by requiringQ2> 1 (GeV/c)2for the photon virtuality andW>5GeV/c2for the invariant mass of the produced hadronic system. The range in Bjorken-xis restricted to0.01<x<0.40. Protons and antiprotons are identified in the momentum range20÷60GeV/c. In the whole studiedz-region, thep¯over p multiplicity ratio is found to be below the lower limit expected from calculations based on leading-order perturbative Quantum Chromodynamics (pQCD). Extending our earlier analysis of the K−over K+multiplicity ratio by including now events with larger virtual-photon energies, this ratio becomes closer to the expectation of next-to-leading order pQCD. The results of both analyses strengthen our earlier conclusion that the phase space available for hadronisation should be taken into account in the pQCD formalism.

A ferromagnetic axion haloscope searches for Dark Matter in the form of axions by exploiting their interaction with electronic spins. It is composed of an axion-to-electromagnetic field transducer coupled to a sensitive rf detector. The former is a photon-magnon hybrid system, and the latter is based on a quantum-limited Josephson parametric amplifier. The hybrid system consists of ten 2.1 mm diameter YIG spheres coupled to a single microwave cavity mode by means of a static magnetic field. Our setup is the most sensitive rf spin-magnetometer ever realized. The minimum detectable field is5.5×10−19T with 9 h integration time, corresponding to a limit on the axion-electron coupling constantgaee≤1.7×10−11at 95% CL. The scientific run of our haloscope resulted in the best limit on DM-axions to electron coupling constant in a frequency span of about 120 MHz, corresponding to the axion mass range42.4-43.1μeV. This is also the first apparatus to perform an axion mass scanning by changing the static magnetic field.

The axion provides a solution for the strong CP problem and is one of the leading candidates for dark matter. This paper proposes an axion detection scheme based on quantum nondemolition detection of magnon, i.e., quanta of collective spin excitations in solid, which is expected to be excited by the axion-electron interaction predicted by the Dine-Fischer-Srednicki-Zhitnitsky (DFSZ) model. The prototype detector is composed of a ferromagnetic sphere as an electronic spin target and a superconducting qubit. Both of these are embedded inside a microwave cavity, which leads to a coherent effective interaction between the uniform magnetostatic mode in the ferromagnetic crystal and the qubit. An upper limit for the coupling constant between an axion and an electron is obtained asgaee<1.6?10??at the 95\% confidence level for the axion mass of33.117μeV<ma<33.130μeV.

A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishingcosϕ−ϕSmodulations provide evidence for a sizable worm-gear (II) distribution,g1T. Most of the other modulations are found to be consistent with zero with the notable exception of largesinϕSmodulations for charged pions and positive kaons.

Studies of the production of light- and heavy-flavor baryons are of prominent importance to characterize the partonic phase created in ultrarelativistic heavy-ion collisions and to investigate hadronization mechanisms at the LHC. Studies performed in p-Pb and pp collisions have revealed unexpected features, qualitatively similar to what is observed in larger collision systems and, in the charm sector, not in line with the expectations frome+e−ande−pinteractions. The ALICE experiment has exploited its excellent tracking and particle identification capabilities down to low transverse momentum to perform an extensive study of protons, hyperons and charmed baryons. In this paper, a discussion of the most recent results on light (protons and hyperons) and heavy-flavor(Λc)baryon production is presented, together with a comparison to phenomenological models.

Any asymmetry in energy of the colliding beams will lead to a longitudinal boost of the center-of-mass frame of colliding particles w.r.t. the laboratory frame and consequently to the counting loss in luminometer due to the loss of colinearity of Bhabha final states. At CEPC running at the Z0 pole, asymmetry in energy of the colliding beams should be known as well as 12.5% of the beam-spread, in order to control the uncertainty of Bhabha count at the level of 0.01%. Here we discuss the method, initially proposed for FCCee, to determine variation of the beam-spread from the measurement of the effective center-of-mass energy ine+e−→μ+μ−collisions.

Some highlights from the 18thinternational conference onBphysics at frontier machines are presented, including first results from the full LHC Run 2 data and from early Belle II data.