119 research outputs found
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
exceeds the recoil energy . 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 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
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
Measurement of additional radiation in the initial-state-radiation processes e+e- →μ+μ-γ and e+e- →π+π-γ at BABAR
A dedicated measurement of additional radiation in e+e-→μ+μ-γ and e+e-→π+π-γ initial-state-radiation events is presented using the full BABAR data sample. For the first time results are presented at next-to- and next-to-next-to-leading order, with one and two additional photons, respectively, for radiation from the initial and final states. Comparison with predictions from phokhara and afkqed Monte Carlo generators is performed, revealing discrepancies in the one-photon rates and angular distributions for the former. This disagreement has a negligible effect on the BABAR measurement of the e+e-→π+π-(γ) cross section, but could affect other measurements significantly. This study sheds a new light on the longstanding discrepancy in this channel that affects the theoretical prediction of hadronic vacuum polarization contributions to the muon magnetic moment anomaly
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
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
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
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