分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
摘要：By analyzing the large-angle Bhabha scattering events e+e− → (γ)e+e and diphoton events e e → γγ for the data sets collected at center-of-mass (c.m.) energies between 2.2324 and 4.5900 GeV (131 energy points in total) with the upgraded Beijing Spectrometer (BESIII) at the Beijing Electron-Positron Collider (BEPCII), the integrated luminosities have been measured at the different c.m. energies, individually. The results are the important inputs for R value and J/ψ resonance parameter measurements.
分类： 物理学 >> 核物理学 提交时间： 2016-09-22
摘要：Recently, an excess of events in diphoton channel with invariant mass of about 750 GeV has been reported by the ATLAS and CMS Collaborations. Considering it as a tantalizing hint for new physics beyond the Standard Model (SM), we propose a simple extension of the SM with an additional doublet Higgs H′ and a singlet s. We consider the neutral component H′0 of H′ as the 750 GeV resonance, and assume that s is lighter than 2.6 GeV. In particular, H′0 can be produced at tree level via qq¯ production, and decay into a pair of s at tree level. And then s can decay into a pair of collimated photons, which cannot be distinguished at the LHC. We show that the diphoton production cross section can be from 3 to 13 fb, the decay width of H′0 can be from 30 to 60 GeV, and all the current experimental constraints including dijet constraint can be satisfied.
分类： 物理学 >> 核物理学 提交时间： 2016-09-20
摘要：Recently, both ATLAS and CMS collaborations at the CERN Large Hadron Collider (LHC) have announced their observations of an excess of diphoton events around the invariant mass of 750 GeV with a local significance of 3.6σ and 2.6σ, respectively. In this paper, we interpret the diphoton excess as the on-shell production of a real singlet scalar in the pp→S→γγ channel. To accommodate the observed production rate, we further introduce a vector-like fermion F, which is carrying both color and electric charges. The viable regions of model parameters are explored for this simple extension of the Standard Model (SM). Moreover, we revisit the problem of electroweak vacuum stability in the same scenario, and find that the requirement for the electroweak vacuum stability up to high energy scales imposes serious constraints on the Yukawa coupling of the vector-like fermion and the quartic couplings of the SM Higgs boson and the new singlet scalar. Consequently, a successful explanation for the diphoton excess and the absolute stability of electroweak vacuum cannot be achieved simultaneously in this economical setup.
分类： 物理学 >> 核物理学 提交时间： 2016-09-09
摘要：This article describes a search for high-mass resonances decaying to a pair of photons using a sample of 20.3 fb−1of pp collisions at s√=8 TeV recorded with the ATLAS detector at the Large Hadron Collider. The data are found to be in agreement with the Standard Model prediction, and limits are reported in the framework of the Randall-Sundrum model. This theory leads to the prediction of graviton states, the lightest of which could be observed at the Large Hadron Collider. A lower limit of 2.66 (1.41) TeV at 95% confidence level is set on the mass of the lightest graviton for couplings of k/M¯¯¯¯¯Pl=0.1 (0.01).
分类： 物理学 >> 核物理学 提交时间： 2016-09-05
摘要：The latest LHC data suggest an intriguing excess at mγγ=750 GeV which apparently requires an explanation from the beyond standard model physics. In this note we explore the possibility for this signal to arise from a top-pion in the Top Triangle Moose model which can be viewed as a dimensional-deconstruction version of the top-color assisted technicolor model. We demonstrate that the observed excess can be accommodated by and has important implications for this interesting model.
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