Enhanced Pauli blocking of light scattering in a trapped Fermi gas

Pauli blocking of spontaneous emission by a single excited-state atom has been predicted to be dramatic at low temperature when the Fermi energy $E_\mathrm{F}$ exceeds the recoil energy $E_\mathrm{R}$. The photon scattering rate of a ground-state Fermi gas can also be suppressed by occupation of the final states accessible to a recoiling atom, however suppression is diminished by scattering events near the Fermi edge. We analyze two new approaches to improve the visibility of Pauli blocking in a trapped Fermi gas. Focusing the incident light to excite preferentially the high-density region of the cloud can increase the blocking signature by 14%, and is most effective at intermediate temperature. Spontaneous Raman scattering between imbalanced internal states can be strongly suppressed at low temperature, and is completely blocked for a final-state $E_\mathrm{F} > 4 E_\mathrm{R}$ in the high imbalance limit.Comment: 12 pages, 8 figures. v4: to appear in Journal of Physics B: Atomic, Molecular, and Optical Physic

ULYSSES, universal LeptogeneSiS equation solver: Version 2

ULYSSES is a Python package that calculates the baryon asymmetry produced from leptogenesis in the context of a type-I seesaw mechanism. In this release, the new features include code which solves the Boltzmann equations for low-scale leptogenesis; the complete Boltzmann equations for thermal leptogenesis applying proper quantum statistics without assuming kinetic equilibrium of the right-handed neutrinos; and, primordial black hole-induced leptogenesis. ULYSSES version 2 has the added functionality of a pre-provided script for a two-dimensional grid scan of the parameter space. As before, the emphasis of the code is on user flexibility, rapid evaluation and is publicly available at https://github.com/earlyuniverse/ulysses

The CLIC Potential for New Physics

The Compact Linear Collider (CLIC) is a mature option for the future of high energy physics. It combines the benefits of the clean environment of $e^+e^-$ colliders with operation at high centre-of-mass energies, allowing to probe scales beyond the reach of the Large Hadron Collider (LHC) for many scenarios of new physics. This places the CLIC project at a privileged spot in between the precision and energy frontiers, with capabilities that will significantly extend knowledge on both fronts at the end of the LHC era. In this report we review and revisit the potential of CLIC to search, directly and indirectly, for physics beyond the Standard Model

Emergent Dark Matter, Baryon, and Lepton Numbers

We present a new mechanism for transferring a pre-existing lepton or baryon asymmetry to a dark matter asymmetry that relies on mass mixing which is dynamically induced in the early universe. Such mixing can succeed with only generic scales and operators and can give rise to distinctive relationships between the asymmetries in the two sectors. The mixing eliminates the need for the type of additional higher-dimensional operators that are inherent to many current asymmetric dark matter models. We consider several implementations of this idea. In one model, mass mixing is temporarily induced during a two-stage electroweak phase transition in a two Higgs doublet model. In the other class of models, mass mixing is induced by large field vacuum expectation values at high temperatures - either moduli fields or even more generic kinetic terms. Mass mixing models of this type can readily accommodate asymmetric dark matter masses ranging from 1 GeV to 100 TeV and expand the scope of possible relationships between the dark and visible sectors in such models.Comment: 36 pages, 5 figure

Light meson spectroscopy from Dalitz plot analyses ηc decays to η0K + K − , η0π + π − , and ηπ + π − produced in two-photon interactions

We study the processes γγ → ηc → η0KþK−, η0πþπ−, and ηπþπ− using a data sample of 519 fb−1 recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy e+e− collider at center-of-mass energies at and near the Υ(nS) (n = 2, 3, 4) resonances. This is the first observation of the decay ηc → η0KþK− and we measure the branching fraction Γðηc → η0KþK−Þ=ðΓðηc → η0πþπ−Þ 1⁄4 0.644 0.039stat 0.032sys. Significant interference is observed between γγ → ηc → ηπþπ− and the nonresonant two-photon process γγ → ηπþπ−. A Dalitz plot analysis is performed of ηc decays to η0KþK−, η0πþπ−, and ηπþπ−. Combined with our previous analysis of ηc → KK ̄ π, we measure the K 0ð1430Þ parameters and the ratio between its η0K and πK couplings. The decay ηc → η0πþπ− is dominated by the f0ð2100Þ resonance, also observed in J=ψ radiative decays. A new a0(1700)→ ηπ resonance is observed in the ηc → ηπþπ− channel. We also compare ηc decays to η and η0 final states in association with scalar mesons as they relate to the identification of the scalar glueball

Measurements of the Absolute Branching Fractions of B±→K±X_(cc)

A study of the two-body decays B±→X_(cc)K±, where X_(cc) refers to one charmonium state, is reported by the BABAR Collaboration using a data sample of 424  fb⁻¹. The absolute determination of branching fractions for these decays are significantly improved compared to previous BABAR measurements. Evidence is found for the decay B⁺→X(3872)K⁺ at the 3σ level. The absolute branching fraction B[B⁺→X(3872)K⁺]=[2.1±0.6(stat)±0.3(syst)]×10⁻⁴ is measured for the first time. It follows that B[X(3872)→J/ψπ⁺π⁻]=(4.1±1.3)%, supporting the hypothesis of a molecular component for this resonance

Precision Measurement of the Ratio B(Υ(3S) → τ⁺τ⁻)/B(Υ(3S) → μ⁺μ⁻)

We report on a precision measurement of the ratio R^(Υ(3S))_(τμ) = B(Υ(3S) → τ⁺τ⁻)/B(Υ(3S) → μ⁺μ⁻) using data collected with the BABAR detector at the SLAC PEP-II e⁺e⁻ collider. The measurement is based on a 28  fb⁻¹ data sample collected at a center-of-mass energy of 10.355 GeV corresponding to a sample of 122 million Υ(3S) mesons. The ratio is measured to be R^(Υ(3S))_(τμ) = 0.966±0.008_(stat)±0.014_(syst) and is in agreement with the standard model prediction of 0.9948 within 2 standard deviations. The uncertainty in R^(Υ(3S))_(τμ) is almost an order of magnitude smaller than the only previous measurement

Search for lepton-flavor-violating decays D⁰ → X⁰e±μ∓

We present a search for seven lepton-flavor-violating neutral charm meson decays of the type D⁰ → X⁰e±μ∓, where X⁰ represents a π⁰, K⁰_S, K*⁰, ρ⁰, ϕ, ω, or η meson. The analysis is based on 468  fb⁻¹ of e⁺e⁻ annihilation data collected at or close to the Υ(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signals are observed, and we establish 90% confidence level upper limits on the branching fractions in the range (5.0−22.5) × 10⁻⁷. The limits are between 1 and 2 orders of magnitude more stringent than previous measurements