We study the electroweak phase transition in three scalar extension models beyond the Standard Model.Assuming new scalars are decoupled at some heavy scale, we use the covariant derivative expansion method to derive all of the dimension-6 effective operators, whose coefficients are highly correlated in a specific model. We provide bounds to the complete set of dimension-6 operators by including the electroweak precision test and recent Higgs measurements. We find that the parameter space of strong first-order phase transitions(induced by the |H|~6 operator)can be probed extensively in Zh production at future electron-positron colliders.
Recently, many new dwarf spheroidal satellites(dSphs) have been discovered by the Dark Energy Survey(DES). These dSphs are ideal candidates for probing for gamma-ray emissions from dark matter(DM) annihilation.However, no significant signature has been found by the Fermi-LAT dSph observations. In this work, we reanalyze the Fermi-LAT Pass 8 data from the direction of Reticulum II, where a slight excess has been reported by some previous studies. We treat Reticulum II(DES J0335.6-5403) as a spatially extended source, and find that no significant gamma-ray signature is observed. Based on this result, we set upper-limits on the DM annihilation cross section.
A pattern matching based tracking algorithm, named MdcPatRec, is used for the reconstruction of charged tracks in the drift chamber of the BES detector. This paper addresses the shortage of segment finding in the MdcPatRec algorithm. An extended segment construction scheme and the corresponding pattern dictionary are presented. Evaluation with Monte-Carlo and experimental data show that the new method can achieve higher efficiency for low transverse momentum
Gravitational waves(GW),which were predicted by Einstein in 1916 based on the classical theory of General Relativity(GR),were recently detected by LIGO[1].This breakthrough is expected to initiate a novel probe of cosmology,the nature of gravity as well as fundamental physics.In general,signals of GWs can be classified into two categories。
Using data samples collected at center-of-mass energies of √s=4.009, 4.230, 4.260, and 4.360 Ge V with the BES detector operating at the BEPC collider, we perform a search for the process e+e-→γχc J(J =0, 1, 2)and find evidence for e+e-→γχc1 and e+e-→γχc2 with statistical significances of 3.0σ and 3.4σ, respectively. The Born cross sections σB(e+e-→γχc J), as well as their upper limits at the 90% confidence level(C.L.) are determined at each center-of-mass energy.
Recently,a novel idea[1]has been proposed to relax the electroweak hierarchy problem through the cosmological inflation and the axion periotic potential.Here,we further assume that,only the attractive inflation is needed to explain the light mass of the Higgs boson,where we do not need a specified periodic potential of the axion field.Attractive inflation during the early universe drives the Higgs boson mass from the large value in the early universe to the small value at present,where the Higgs mass is an evolving parameter of the Universe.Thus,the small Higgs mass can technically originate from the cosmological evolution rather than dynamical symmetry or anthropics.Further,we study the possible collider signals or constraints at a future lepton collier and the possible constraints from the muon anomalous magnetic moment.A concrete attractive relaxion model is also discussed,which is consistent with the data of Planck 2015.
Offline calibration plays an important role in BES offline data processing. In order to achieve good spatial and momentum resolution, it is necessary to implement high precision offline calibration for the BES drift chamber. This paper studies the time-to-distance relations, which are important calibration constants for track reconstruction. The parameterization of the time-to-distance relation, studies of left-right asymmetry and studies of variation with entrance angle are performed. The impact of dead channels on the time-to-distance relation is given special attention in order to reduce the shift in measured momentum for tracks passing near dead cells. Finally we present the resolutions for barrel Bhabha events(|cos θ|< 0.8) from a J/ψ data set taken in 2012. The average spatial resolution is 123 μm and the momentum resolution for 1.548 Ge V/c Bhabha tracks is 11.9 Me V/c.
Using experimental data, Monte Carlo tuning is implemented for performance parameters associated with the scintillation counters and readout electronics of the BESⅢ time-of-flight(TOF) system, as part of the full simulation model. The implementation of the tuning is described for simulations designed to reproduce the performance of a number of TOF system parameters, including pulse height, hit efficiency, time resolution, dead channels and background. In addition, comparisons with experimental data are presented.
