分类: 数学 >> 控制和优化 提交时间: 2016-08-30
摘要: In this paper necessary conditions and sufficient conditions are given for a linear operator to be a positive operators of an Extended Lorentz cone. Similarities and differences with the positive operators of Lorentz cones are investigated.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: We report the neutrino mass hierarchy (MH) sensitivity of medium baseline reactor neutrino experiments with multiple detectors. Sensitivity of determining the MH can be significantly improved by adding a near detector and combining both the near and far detectors. The size of the sensitivity improvement is related to accuracy of the individual mass-splitting measurements and requires strict control on the relative energy scale uncertainty of the near and far detectors. We study the impact of both baseline and target mass of the near detector on the combined sensitivity. A figure-of-merit is defined to optimize the baseline and target mass of the near detector and the optimal selections are ∼13~km and ∼4~kton respectively for a far detector with the 20~kton target mass and 52.5~km baseline. As typical examples of future medium baseline reactor neutrino experiments, the optimal location and target mass of the near detector are selected for JUNO and RENO-50. Finally, we discuss distinct effects of the neutrino spectrum uncertainty for setups of a single detector and double detectors, which indicate that the spectrum uncertainty can be well constrained in the presence of the near detector.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: In this article we study restoration of chiral symmetry at finite temperature for quark matter with a chiral chemical potential, μ5, by means of a quark-meson model with vacuum fluctuations included. Vacuum fluctuations give a divergent contribution to the vacuum energy, so the latter has to be renormalized before computing physical quantities. The vacuum term is important for restoration of chiral symmetry at finite temperature and μ5≠0, therefore we present several plausible renormalization schemes for the ultraviolet divergences at μ5≠0. Then we compute the critical temperature as a function of μ5. The main result of our study is that the choice of a renormalization scheme affects the critical temperature; among the three renormalization schemes we investigate, there exists one in which the critical temperature increases with μ5, a result which has not been found before by chiral model studies and which is in qualitative agreement with recent lattice data as well as with studies based on Schwinger-Dyson equations and universality arguments.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: A new tuner control system of spoke superconducting radio frequency (SRF) cavity has been developed and applied to cryomodule I (CM1) of C-ADS injector I at IHEP. We have successfully implemented the tuner controllerfor the first time and achieved a cavity tuning phase error of 0.7degrees (about 4 Hz peak to peak) in the presence of electromechanical coupled resonance. This paper will present the preliminary experimental results based on the new tuner controller under proton beam commissioning.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: A conservative constraint on the Einstein Equivalence Principle (EEP) can be obtained under the assumption that the observed time delay between correlated particles from astronomical sources is dominated by the gravitational fields through which they move. Current limits on the EEP are mainly based on the observed time delays of photons with different energies, and it is highly desirable to develop more accurate tests involving different types of particles. The detection by the advanced LIGO/VIRGO systems of gravitational waves (GWs) will provide attractive candidates for constraining the EEP, which would further extend the tested particle species to the gravitons, with potentially higher accuracy. Considering the capabilities of the advanced LIGO/VIRGO network and the source direction uncertainty, we show that the joint detection of GWs and electromagnetic signals can potentially probe the EEP to an accuracy of 10−11, which is several orders of magnitude tighter than previous limits.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: Quasi-periodic oscillation (QPO) detected in the X-ray radiation of black hole X-ray binaries (BHXBs) is thought to originate from dynamical processes in the close vicinity of the black holes (BHs), and thus carries important physical information therein. Such a feature is extremely rare in active galactic nuclei (AGNs) with supermassive BHs. Here we report on the detection of a possible X-ray QPO signal with a period of 3800\,s at a confidence level >99.99% in the narrow-line Seyfert 1 galaxy (NLS1) 1H~0707-495 in one data set in 0.2-10\,keV taken with {\it XMM-Newton}. The statistical significance is higher than that of most previously reported QPOs in AGNs. The QPO is highly coherent (quality factor Q=ν/Δν⩾15) with a high rms fractional variability (∼15%). A comprehensive analysis of the optical spectra of this AGN is also performed, yielding a central BH mass 5.2×106M⊙ from the broad emission lines based on the scaling relation. The QPO follows closely the known frequency-BH mass relation, which spans from stellar-mass to supermassive BHs. The absence of the QPO in other observations of the object suggests it a transient phenomenon. We suggest that the (high-frequency) QPOs tend to occur in highly accreting BH systems, from BHXBs to supermassive BHs. Future precise estimation of the BH mass may be used to infer the BH spin from the QPO frequency.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: The Circular Electron Positron Collider (CEPC) is a future Higgs factory proposed by the Chinese high energy physics community. Using Monte Carlo samples of 5 ab−1 at 250 GeV center-of-mass energy, the benchmark luminosity of CEPC Higgs runs, model independent (MI) analyses on Higgsstrahlung (ZH) cross section σZH and Higgs mass mH are performed with ZH events where the Z boson decays into a pair of muons. The relative precision of σZH could reach 0.92\% and the mH could be measured to an accuracy of 6.5 MeV. Using information from Higgs decay final states, the backgrounds could be further reduced, leading to a mass precision of 5.4 MeV. The impacts of tracker size are investigated and parameterized for these measurements. Using similar analysis technology, we analyzed the capability of CEPC in measuring the Higgs invisible decay. Using ZH (Z→μ+μ−) events at 5 ab−1, the upper limit of invisible decay cross section beyond the standard model (SM) σBSMZH,H→inv can be determined to be 2.0 fb at 95\% confidence level.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: Flavor SU(3) symmetry is a powerful tool to analyze charmed baryon decays, however its applicability remains to be experimentally validated. Since there is not much data on Ξc decays, various exclusive Λc decays especially the ones into a neutron state are essential for the test of flavor symmetry. These decay modes are also helpful to investigate final state interactions in charmed baryon decays. In this work, we discuss the explicit roles of Λc decays into a neutron in testing the flavor symmetry and exploring final state interactions. The involved decay modes include semileptonic decays, two-body and three-body non-leptonic decays, but all of them have not been experimentally observed to date.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: The liquid scintillator (LS) has been widely utilized in the past, running and future neutrino experiments, and requirement to the LS radio-purity is higher and higher. The water extraction is a powerful method to remove soluble radioactive nuclei, and a mini-extraction station has been constructed. To evaluate the extraction efficiency and optimize the operation parameters, a setup to load radioactivity to LS and a laboratory scale setup to measure radioactivity which use Bi^{212}-Po^{212}-Pb^{208} cascade decay are developed. Experiences from laboratory study will be useful to large scale water extraction plants design and the optimization of working in future.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: The gamma-ray observation of dwarf spheroidal satellites (dSphs) is an ideal approach for probing the dark matter (DM) annihilation signature. The latest Fermi-LAT dSph searches have set stringent constraints on the velocity independent annihilation cross section in the small DM mass range, which gives very strong constraints on the scenario to explain the the AMS-02 positron excess by DM annihilation. However, the dSph constraints would change in the velocity dependent annihilation scenarios, because the velocity dispersion in the dSphs varies from that in the Milky Way. In this work, we use a likelihood map method to set constraints on the velocity dependent annihilation cross section from the Fermi-LAT observation of six dSphs. We consider three typical forms of the annihilation cross section, i.e. p-wave annihilation, Sommerfeld enhancement, and Breit-Wigner resonance. For the p-wave annihilation and Sommerfeld-enhancement, the dSph limits would become much weaker and stronger compared with those for the velocity independent annihilation, respectively. For the Breit-Wigner annihilation, the dSph limits would vary depending on the model parameters. We show that the scenario to explain the AMS-02 positron excess by DM annihilation is still viable in the velocity dependent cases
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: Cosmography is a model-independent de 1. To ensure data in the convergence radius, y=z/(1+z) redshift was defined. However, discussions about the usefulness of y-redshift and the leading cause of the issue are commonly absent. In the present paper, we study the cosmography in both z and y redshift using the supernova and mock redshift drift data. By introducing the bias-variance tradeoff, we reveal that the large bias square between cosmography and Union2.1 supernova data is the "chief culprit" of convergence issue. Moreover, expansion up to higher order and introduction of the y-redshift both are not effective to reconcile this contradiction. Minimizing risk, it suggests that Taylor expansion up to the second term is a better choice for available supernova data. Forecast from future supernova data and redshift drift shows that redshift drift can give much tighter constraints on the cosmography. We also investigate the effect of convergence issue on the deceleration parameter and dark energy. It inspires us that dynamical observations including redshift drift can give more detailed information on cosmic evolution
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: In this letter, we explore the nature of the electroweak phase transition (EWPT) with both particle colliders and gravitational wave (GW) detection. With the observed Higgs mass, the shape of the Higgs potential is fully determined within the standard model (SM) of particle physics. However, it could be changed if there exists new physics beyond the SM. Working with the effective field theory, we show that a modified Higgs potential with a sextic term included can keep the observed 125 GeV Higgs mass but behave different when compared with the SM case. Furthermore, this potential can produce a strong first order phase transition (SFOPT) for the electroweak baryogenesis and interestingly predict new phenomena in the Higgs sector, which can be tested at colliders such as the Large Hadron Collider (LHC) and the planning Circular Electron Positron Collider (CEPC). We point out this SFOPT can lead to detectable signals for the GW interferometers , such as eLISA, DECIGO and BBO. Our present study on the EWPT bridges the particle physics at colliders with the astrophysics and cosmology in the early universe.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: We explore a dark matter model extending the standard model particle content by one fermionic SU(2)L triplet and two fermionic SU(2)L quadruplets, leading to a minimal realistic UV-complete model of electroweakly interacting dark matter which interacts with the Higgs doublet at tree level via two kinds of Yukawa couplings. After electroweak symmetry-breaking, the physical spectrum of the dark sector consists of three Majorana fermions, three singly charged fermions, and one doubly charged fermion, with the lightest neutral fermion χ01 serving as a dark matter candidate. A typical spectrum exhibits a large degree of degeneracy in mass between the neutral and charged fermions, and we examine the one-loop corrections to the mass differences to ensure that the lightest particle is neutral. We identify regions of parameter space for which the dark matter abundance is saturated for a standard cosmology, including coannihilation channels, and find that this is typically achieved for mχ01∼2.4 TeV. Constraints from precision electroweak measurements, searches for dark matter scattering with nuclei, and dark matter annihilation are important, but leave open a viable range for a thermal relic.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: WIMPs are a well-motivated galactic dark matter candidate. Liquid argon (LAr) is an attractive target for the direct detection of WIMPs. The LAr prototype detector is designed to study the technology and property of LAr detector. The prototype detector have an active volume containing 0.65 kg of liquid argon. The liquid nitrogen(LN) cooling system allows the temperature of liquid argon to be maintained at the boiling point (87.8 K) with fluctuations less than 0.1 K. The prototype was calibrated with a Na22 source, with the light yield 1.591�.019 p.e./keV for the 511 keV gamma rays using the domestic-made argon purification system.
分类: 物理学 >> 核物理学 提交时间: 2016-08-30
摘要: We use the Higgs coupling and the muon anomalous magnetic moment measurements to constrain the parameter space of the natural supersymmetry (SUSY) in the Generalized Minimal Supergravity (GmSUGRA) model. We scan the parameter space of the GmSUGRA model with small electroweak fine-tuning measure (ΔEW≤100). The parameter space after applying various sparticle mass bounds, Higgs mass bounds, B-physics bounds, the muon magnetic moment constraint, and the Higgs coupling constraint from measurements at HL-LHC, ILC, and CEPC, is shown in the planes of various interesting model parameters and sparticle masses. Our study indicates that the Higgs coupling and muon anomalous magnetic moment measurements can constrain the parameter space effectively. It is shown that ΔEW∼ 30, consistence with all constraints, and having supersymmetric contributions to the muon anomalous magnetic moment within 1σ can be achieved. The precision of kb and kτ measurements at CEPC can bound mA to be above 1.2 TeV and 1.1 TeV respectively. The combination of the Higgs coupling measurement and muon anomalous magnetic moment measurement constrain e~R mass to be in the range from 0.6 TeV to 2 TeV. The range of both e~L and ν~e masses is 0.4 TeV ∼ 1.2 TeV. In all cases, the χ~01 mass needs to be small (mostly ≤ 400 GeV). The comparison of bounds in the tanβ−mA plane shows that the Higgs coupling measurement is complementary to the direct collider searches for heavy Higgs when constraining the natural SUSY. A few mass spectra in the typical region of parameter space after applying all constraints are shown as well.
分类: 物理学 >> 核物理学 提交时间: 2016-08-29
摘要: A search for the resonant production of high-mass photon pairs is presented. The analysis is based on samples of proton-proton collision data collected by the CMS experiment at center-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and 3.3 inverse femtobarns, respectively. The search focuses on spin-0 and spin-2 resonances with masses between 0.5 and 4 TeV and with widths, relative to the mass, between 1.4E-4 and 5.6E-2. Limits are set on scalar resonances produced through gluon-gluon fusion, and on Randall--Sundrum gravitons. A modest excess of events compatible with a narrow resonance with a mass of about 750 GeV is observed. The local significance of the excess is approximately 3.4 standard deviations. The significance is reduced to 1.6 standard deviations once the effect of searching under multiple signal hypotheses is considered. More data are required to determine the origin of this excess.
分类: 物理学 >> 核物理学 提交时间: 2016-08-29
摘要: The production of W±Z events in proton--proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC. The collected data correspond to an integrated luminosity of 3.2 fb−1. The W±Z candidates are reconstructed using leptonic decays of the gauge bosons into electrons or muons. The measured inclusive cross section in the detector fiducial region for leptonic decay modes is σfid.W±Z→ℓ′νℓℓ=63.2±3.2 (stat.) ±2.6 (sys.) ±1.5 (lumi.) fb. In comparison, the next-to-leading-order Standard Model prediction is 53.4+3.6−2.8 fb. The extrapolation of the measurement from the fiducial to the total phase space yields σtot.W±Z=50.6±2.6 (stat.) ±2.0 (sys.) ±0.9 (th.) ±1.2 (lumi.) pb, in agreement with a recent next-to-next-to-leading-order calculation of 48.2+1.1−1.0 pb. The cross section as a function of jet multiplicity is also measured, together with the charge-dependent W+Z and W−Z cross sections and their ratio.
分类: 物理学 >> 核物理学 提交时间: 2016-08-29
摘要: A search for W′ bosons in events with one lepton (electron or muon) and missing transverse momentum is presented. The search uses 3.2 fb−1 of pp collision data collected at s√=13 TeV by the ATLAS experiment at the LHC in 2015. The transverse mass distribution is examined and no significant excess of events above the level expected from Standard Model processes is observed. Upper limits on the W′boson cross-section times branching ratio to leptons are set as a function of the W′ mass. Assuming a W′ boson as predicted by the Sequential Standard Model, W′ masses below 4.07 TeV are excluded at the 95% confidence level. This extends the limit set using LHC data at s√=8 TeV by around 800 GeV.
分类: 物理学 >> 核物理学 提交时间: 2016-08-29
摘要: The results of a search for the stop, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, jets, and missing transverse momentum are reported. The search uses the 2015 LHC pp collision data at a center-of-mass energy of s√=13 TeV recorded by the ATLAS detector and corresponding to an integrated luminosity of 3.2 fb−1. The analysis targets two types of signal models: gluino-mediated pair production of stops with a nearly mass-degenerate stop and neutralino; and direct pair production of stops, decaying to the top quark and the lightest neutralino. The experimental signature in both signal scenarios is similar to that of a top quark pair produced in association with large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits on gluino and stop masses are set at 95% confidence level. The results extend the LHC Run-1 exclusion limit on the gluino mass up to 1460 GeV in the gluino-mediated scenario in the high gluino and low stop mass region, and add an excluded stop mass region from 745 to 780 GeV for the direct stop model with a massless lightest neutralino. The results are also reinterpreted to set exclusion limits in a model of vector-like top quarks.
分类: 物理学 >> 核物理学 提交时间: 2016-08-29
摘要: Based on a sample of 1.31×109 J/ψ events collected with the BESIII detector, an amplitude analysis of the isospin violating decays η′→π+π−π0 and η′→π0π0π0 is performed. Significant P-wave contribution from η′→ρ±π∓ is observed for the first time in η′→π+π−π0. The branching fraction is determined to be B(η′→ρ±π∓)=(7.44±0.60±1.26±1.84)×10−4, where the first uncertainty is statistical, the second systematic and the third model dependent. In addition to the non-resonant S-wave component, a contribution from the σ meson is also essential. The branching fractions of the S-wave components are determined as B(η′→π+π−π0)S=(37.63±0.77±2.22±4.48)×10−4 and B(η′→π0π0π0)=(35.22±0.82±2.60)×10−4, respectively. The latter one is consistent with previous BESIII measurements.