18,753 research outputs found
The Electric Dipole Moment and CP Violation in in SUGRA Models with Nonuniversal Gaugino Masses
The constraints of electric dipole moments (EDMs) of electron and neutron on
the parameter space in supergravity (SUGRA) models with nonuniversal gaugino
masses are analyzed. It is shown that with a light sparticle spectrum, the
sufficient cancellations in the calculation of EDMs can happen for all phases
being order of one in the small tan case and all phases but
() order of one in the large tan case. This is
in contrast to the case of mSUGRA in which in the parameter space where
cancellations among various SUSY contributions to EDMs happen
must be less than for small and for
large . Direct CP asymmetries and the T-odd polarization of lepton in
are investigated in the models. In the large tan case,
and for l= () can be enhanced by about a factor of
ten (ten) and ten (three) respectively compared to those of mSUGRA.Comment: 12 pages, latex, 4 figures, a few change
Onset of collective and cohesive motion
We study the onset of collective motion, with and without cohesion, of groups
of noisy self-propelled particles interacting locally. We find that this phase
transition, in two space dimensions, is always discontinuous, including for the
minimal model of Vicsek et al. [Phys. Rev. Lett. {\bf 75},1226 (1995)] for
which a non-trivial critical point was previously advocated. We also show that
cohesion is always lost near onset, as a result of the interplay of density,
velocity, and shape fluctuations.Comment: accepted for publication in Phys. Rev. Let
The meson annihilation to leptons and inclusive light hadrons
The annihilation of the meson to leptons and inclusive light hadrons is
analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find
that the decay mode, which escapes from the helicity suppression, contributes a
sizable fraction width. According to the analysis, the branching ratio due to
the contribution from the color-singlet component of the meson can be of
order (10^{-2}). We also estimate the contributions from the color-octet
components. With the velocity scaling rule of NRQCD, we find that the
color-octet contributions are sizable too, especially, in certain phase space
of the annihilation they are greater than (or comparative to) the color-singlet
component. A few observables relevant to the spectrum of charged lepton are
suggested, that may be used as measurements on the color-octet and
color-singlet components in the future experiments. A typical long
distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.
Quantifying regional biodiversity in the tropics : a case study of freshwater fish in Trinidad and Tobago
Funding: European Research Council (AdG BioTIME 250189 and PoC BioCHANGE 727440) (AEM).Extinction rates are predicted to accelerate during the Anthropocene. Quantifying and mitigating these extinctions demands robust data on distributions of species and the diversity of taxa in regional biotas. However, many assemblages, particularly those in the tropics, are poorly characterized. Targeted surveys and historical museum collections are increasingly being used to meet the urgent need for accurate information, but the extent to which these contrasting data sources support meaningful inferences about biodiversity change in regional assemblages remains unclear. Here, we seek to elucidate uncertainty surrounding regional biodiversity estimates by evaluating the performance of these alternative methods in estimating the species richness and assemblage composition of the freshwater fish of Trinidad & Tobago. We compared estimates of regional species richness derived from two freshwater fish datasets: a targeted two year survey of Trinidad & Tobago rivers and historical museum collection records submitted to The University of the West Indies Zoology Museum. Richness was estimated using rarefaction and extrapolation, and assemblage composition was benchmarked against a recent literature review. Both datasets provided similar estimates of regional freshwater fish species richness (50 and 46 species, respectively), with a large overlap (85%) in species identities. Regional species richness estimates based on survey and museum data are thus comparable, and consistent in the species they include. Our results suggest that museum collection data are a viable option for setting reliable baselines in many tropical systems, thereby widening options for meaningful monitoring and evaluation of temporal trends.PostprintPeer reviewe
Search for Low-Mass Dark-Sector Higgs Bosons
Recent astrophysical and terrestrial experiments have motivated the proposal of a dark sector with GeV-scale gauge boson force carriers and new Higgs bosons. We present a search for a dark Higgs boson using 516 fb^(-1) of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the product of the standard model-dark-sector mixing angle and the dark-sector coupling constant
Precise measurement of the e^+e^- → π^+π^-(γ) cross section with the initial-state radiation method at BABAR
A precise measurement of the cross section of the process e^+e^-→π^+π^-(γ) from threshold to an energy of 3 GeV is obtained with the initial-state radiation (ISR) method using 232 fb^(-1) of data collected with the BABAR detector at e^+e^- center-of-mass energies near 10.6 GeV. The ISR luminosity is determined from a study of the leptonic process e^+e^-→μ^+μ^-(γ)γ_(ISR), which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process e^+e^-→π^+π^-(γ) is obtained with a systematic uncertainty of 0.5% in the dominant ρ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured ππ cross section from threshold to 1.8 GeV is (514.1±2.2(stat)±3.1(syst))×10^(-10)
Study of B → X_uℓv decays in BB events tagged by a fully reconstructed B-meson decay and determination of │V_(ub)│
We report measurements of partial branching fractions for inclusive charmless semileptonic B decays B → X_uℓν and the determination of the Cabibbo–Kobayashi–Maskawa (CKM) matrix element |V_(ub)|. The analysis is based on a sample of 467×10^6 Υ(4S)→BB decays recorded with the BABAR detector at the PEP-II e^+e^- storage rings. We select events in which the decay of one of the B mesons is fully reconstructed and an electron or a muon signals the semileptonic decay of the other B meson. We measure partial branching fractions ΔB in several restricted regions of phase space and determine the CKM element |V_(ub)| based on different QCD predictions. For decays with a charged lepton momentum p_ℓ^*>1.0 GeV in the B meson rest frame, we obtain ΔB=(1.80±0.13_(stat)±0.15_(sys)±0.02_(theo))×10^(-3) from a fit to the two-dimensional M_X-q^2 distribution. Here, M_X refers to the invariant mass of the final state hadron X and q^2 is the invariant mass squared of the charged lepton and neutrino. From this measurement we extract |V_(ub)|=(4.33±0.24_(exp)±0.15_(theo))×10^(-3) as the arithmetic average of four results obtained from four different QCD predictions of the partial rate. We separately determine partial branching fractions for B^0 and B^- decays and derive a limit on the isospin breaking in B → X_uℓν decays
Search for lepton-number violating processes in B^+ → h^-l^+l^+ decays
We have searched for the lepton-number violating processes B^+→h^-ℓ^+ℓ^+ with h^-=K^-/π^- and ℓ^+=e^+/μ^+, using a sample of 471±3 million BB̅ events collected with the BABAR detector at the PEP-II e^+e^- collider at the SLAC National Accelerator Laboratory. We find no evidence for these decays and place 90%-confidence-level upper limits on their branching fractions B(B^+→π^-e^+e^+)<2.3×10^(-8), B(B^+→K^-e^+e^+)<3.0×10^(-8), B(B^+→π^-μ^+μ^+)<10.7×10^(-8), and B(B^+→K^-μ^+μ^+)<6.7×10^(-8)
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