2017 Vol. 41, No. 2
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The sensitivity of the D0-D0 mixing parameters x and y is estimated in the wrong-sign decay D0→K+π-π0 by time-dependent amplitude analysis. The resolution of the D0 lifetime is essential in time-dependent Dalitz analyses. The Belle Ⅱ detector, which aims to collect a total integrated luminosity of 50 ab-1 of data, has σ=140 fs in Monte Carlo studies, a factor of two improvement over that of Belle and BaBar, so the produced Dalitz signal Monte Carlo samples are smeared with this resolution. Then a time-dependent Dalitz plot fitting is performed on these smeared samples, and the sensitivity of D0-D0 mixing parameters are σx=0.057% and σy=0.049%. These are about an order of magnitude improvement on current experimental results, without considering background effects.
The China Jinping Underground Laboratory (CJPL), which has the lowest cosmic-ray muon flux and the lowest reactor neutrino flux of any laboratory, is ideal to carry out low-energy neutrino experiments. With two detectors and a total fiducial mass of 2000 tons for solar neutrino physics (equivalently, 3000 tons for geo-neutrino and supernova neutrino physics), the Jinping neutrino experiment will have the potential to identify the neutrinos from the CNO fusion cycles of the Sun, to cover the transition phase for the solar neutrino oscillation from vacuum to matter mixing, and to measure the geo-neutrino flux, including the Th/U ratio. These goals can be fulfilled with mature existing techniques. Efforts on increasing the target mass with multi-modular neutrino detectors and on developing the slow liquid scintillator will increase the Jinping discovery potential in the study of solar neutrinos, geo-neutrinos, supernova neutrinos, and dark matter.
The Circular Electron Positron Collider (CEPC) is a future Higgs factory proposed by the Chinese high energy physics community. It will operate at a center-of-mass energy of 240-250 GeV. The CEPC will accumulate an integrated luminosity of 5 ab-1 over ten years of operation, producing one million Higgs bosons via the Higgsstrahlung and vector boson fusion processes. This sample allows a percent or even sub-percent level determination of the Higgs boson couplings. With GEANT4-based full simulation and a dedicated fast simulation tool, we have evaluated the statistical precisions of the Higgstrahlung cross section σZH and the Higgs mass mH measurement at the CEPC in the Z→μ+μ- channel. The statistical precision of σZH (mH) measurement could reach 0.97% (6.9 MeV) in the model-independent analysis which uses only the information from Z boson decays. For the standard model Higgs boson, the mH precision could be improved to 5.4 MeV by including the information from Higgs decays. The impact of the TPC size on these measurements is investigated. In addition, we studied the prospect of measuring the Higgs boson decaying into invisible final states at the CEPC. With the Standard Model ZH production rate, the upper limit of ß(H→inv.) could reach 1.2% at 95% confidence level.
The recent measurement of the differential γ+c-jet cross section, performed at the Tevatron collider in Run II by the D0 collaboration, is studied in a next-to-leading order (NLO) global QCD analysis to assess its impact on the proton parton distribution functions (PDFs). We show that these data lead to a significant change in the gluon and charm quark distributions. We demonstrate also that there is an inconsistency between the new high precision HERA I+II combined data and Tevatron measurement. Moreover, in this study we investigate the impact of older EMC measurements of charm structure function Fc2 on the PDFs and compare the results with those from the analysis of Tevatron data. We show that both of them have the same impact on the PDFs, and thus can be recognized as the same evidence for the inefficiency of perturbative QCD in dealing with charm production in some kinematic regions.
The energy loss effect of incoming gluons from J/ψ production in p-A (or d-A) collisions is investigated by means of the E866, RHIC and LHC experimental data. The gluon mean energy loss per unit path length dE/dL=2.18±0.14 GeV/fm is extracted by fitting the E866 experimental data for J/ψ production cross section ratios RW(Fe)/Be(xF). The obtained result indicates that the incoming gluons lose more energy than the incident quarks. By comparing the theoretical results with E866, RHIC, and LHC experimental data, it is found that the nuclear suppression due to the incident gluon (quark) energy loss reduces (increases) with the increase of the kinematic variable xF (or y). The energy loss effect of incoming gluons plays an important role in the suppression of J/ψ production in a wide energy range from √ =38.7 GeV to √ =5.0 TeV, and the influence of incident quark energy loss can be ignored for high energies (such as at RHIC and LHC energy).
Inspired by the recent measurements of the ηc meson production at LHC experiments, we investigate the relativistic correction effect for the fragmentation functions of gluon/charm quark fragmenting into ηc, which constitute the crucial nonperturbative element for the ηc production at high pT. Employing three distinct methods, we calculate the next-to-leading-order (NLO) relativistic correction to g→ηc fragmentation function in the NRQCD factorization framework, as well as verifying the existing NLO result for the c→ηc fragmentation function. We also study the evolution behavior of these fragmentation functions with the aid of the DGLAP equation.
We construct charged black hole solutions with hyperscaling violation in the infrared (IR) region in Einstein-Maxwell-Dilaton-Axion theory and investigate the temperature behavior of the ratio of holographic shear viscosity to the entropy density. When translational symmetry breaking is relevant in the IR, the power law of the ratio is verified numerically at low temperature T, namely, η/s~Tκ, where the values of exponent κ coincide with the analytical results. We also find that the exponent κ is not affected by irrelevant current, but is reduced by the relevant current.
We explore the discovery potential of Higgs pair production at a 100 TeV collider via full leptonic mode. The same mode can be explored at the LHC when Higgs pair production is enhanced by new physics. We examine two types of fully leptonic final states and propose a partial reconstruction method, which can reconstruct some useful kinematic observables. It is found that the mT2 variable determined by this reconstruction method and the reconstructed visible Higgs mass are crucial to discriminate the signal and background events. It is also noticed that a new variable, denoted as Δm, which is defined as the mass difference of two possible combinations, is very useful as a discriminant. To examine the detector effects, we consider seven detector setups for a 100 TeV collider and investigate the changes in the sensitivity, and we find that lepton isolation and the minimal lepton Pt cut are crucial in order to reduce the integrated luminosity.
We propose to measure the decay asymmetry parameters in the hadronic weak decays of singly charmed baryons, such as Λc+→Λπ+,Σ0π+,pK0, Ξc0→Ξ-π+ and Ωc0→Ω-π+. The joint angular formulae for these processes are presented, and are used to extract the asymmetry parameters in e+e- annihilation data. Base on the current Λc+ data set collected at BESIII, we estimate the experimental sensitivities to measure the parameters αΛπ+ for Λc+→Λπ+, αΣ+π0 for Λc+→Σ+π0 and αΣ0π+ for Λc+→Σ0π+.
Anisotropic flow is an important observable in the study of the quark-gluon plasma that is expected to be formed in heavy-ion collisions. With a multiphase transport (AMPT) model we investigate the elliptic (v2), triangular (v3), and quadrangular (v4) flow of charged particles in Pb+Pb collisions at √ =5.02 TeV. We then compare our flow results with the published ALICE flow results. We find our AMPT simulated results are consistent with ALICE experimental data.
The φ-charmonium dissociation reactions in hadronic matter are studied. Unpolarised cross sections for φJ/ψ→Ds- Ds+, φJ/ψ→Ds*- Ds+ or Ds- Ds*+, φJ/ψ→Ds*- Ds*+, φψ'→Ds- Ds+, φψ'→Ds*- Ds+ or Ds- Ds*+, φψ'→Ds*- Ds*+, φχc→Ds- Ds+, φχc→Ds*- Ds+ or Ds- Ds*+ and φχc→Ds*- Ds*+ are calculated in the Born approximation, in the quark-interchange mechanism and with a temperature-dependent quark potential. The potential leads to remarkable temperature dependence of the cross sections. With the cross sections and the φ distribution function we calculate the dissociation rates of the charmonia in interactions with the φ meson in hadronic matter. The dependence of the rates on temperature and charmonium momentum is relevant to the influence of φ mesons on charmonium suppression.
A development of the optical model for the description of hadron-nucleus scattering is proposed. When describing the behaviour of observables for elastic proton scattering from 40Ca nuclei at the energy of 200 MeV the second Born approximation is used. Analytical expressions for the scattering amplitudes as well as for the differential cross section and polarization observables were obtained. The observables calculated in this approach are in reasonable agreement with the available experimental data.
The recently observed two high-spin rotational bands in the proton emitter 113Cs are investigated using the cranked shell model with pairing correlations treated by a particle-number conserving method, in which the Pauli blocking effects are taken into account exactly. By using the configuration assignments of band 1[π3/2+(g7/2), α=-1/2] and band 2[π1/2+(d5/2), α=1/2], the experimental moments of inertia and quasiparticle alignments can be reproduced much better by the present calculations than those using the configuration assginment of π1/2-(h11/2), which in turn may support these configuration assignments. Furthermore, by analyzing the occupation probability nμ of each cranked Nilsson level near the Fermi surface and the contribution of each orbital to the angular momentum alignments, the backbending mechanism of these two bands is also investigated.
We applied the four dimensional Langevin dynamical model to investigate the average spin of fission fragments. Elongation, neck thickness, asymmetry parameter, and the orientation degree of freedom (K coordinate) are the four dimensions of the dynamical model. We assume that the collective modes depend on the emission angle of the fragments, then different parameters related to the average spin of fission fragments are calculated dynamically. The angle dependence of average spin of fission fragments is investigated by calculating the spin at angles 90° and 165°. Also, the obtained results based on the transition state model at scission point are presented. One can obtain better agreement between the results of the dynamical model and experimental data in comparison with the results of the transition state model.
Recently, the LIGO Scientific Collaboration and Virgo Collaboration published the second observation of a gravitational wave, GW151226[Phys. Rev. Lett. 116, 241103 (2016)], from a binary black hole coalescence with initial masses about 14 M⊙ and 8 M⊙. They claimed that the peak gravitational strain was reached at about 450 Hz, the inverse of which is longer than the average time a photon stays in the Fabry-Perot cavities in the two arms. In this case, the phase-difference of a photon in the two arms due to the propagation of a gravitational wave does not always increase as the photon stays in the cavities. It might even be cancelled to zero in extreme cases. When the propagation effect is taken into account, we find that the claimed signal GW151226 almost disappears.
Fast neutron spectrometers will play an important role in the future of the nuclear industry and nuclear physics experiments, in tasks such as fast neutron reactor monitoring, thermo-nuclear fusion plasma diagnostics, nuclear reaction cross-section measurement, and special nuclear material detection. Recently, a new fast neutron spectrometer based on a GEM (Gas Electron Multiplier amplification)-TPC (Time Projection Chamber), named the neutron-TPC, has been under development at Tsinghua University. It is designed to have a high energy resolution, high detection efficiency, easy access to the medium material, an outstanding n/γ suppression ratio, and a wide range of applications. This paper presents the design, test, and experimental study of the neutron-TPC. Based on the experimental results, the energy resolution (FWHM) of the neutron-TPC can reach 15.7%, 10.3% and 7.0% with detection efficiency higher than 10-5 for 1.2 MeV, 1.81 MeV and 2.5 MeV neutrons respectively.
The Large High Altitude Air Shower Observatory (LHAASO) is to be built at Daocheng, Sichuan Province, China. As one of the major components of the LHAASO project, a Water Cherenkov Detector Array (WCDA), with an area of 78000 m2, contains 350000 tons of purified water. The water transparency and its stability are critical for successful long-term operation of this project. To gain full knowledge of the water Cherenkov technique and investigate the engineering issues, a 9-cell detector array has been built at the Yangbajing site, Tibet, China. With the help of the distribution of single cosmic muon signals, the monitoring and measurement of water transparency are studied. The results show that a precision of several percent can be obtained for the attenuation length measurement, which satisfies the requirements of the experiment. In the near future, this method could be applied to the LHAASO-WCDA project.
ATLAS LAr calorimeter will undergo its Phase-I upgrade during the long shutdown (LS2) in 2018, and a new LAr Trigger Digitizer Board (LTDB) will be designed and installed. Several commercial-off-the-shelf (COTS) multi-channel high-speed ADCs have been selected as possible backups of the radiation tolerant ADC ASICs for the LTDB. To evaluate the radiation tolerance of these backup commercial ADCs, we developed an ADC radiation tolerance characterization system, which includes the ADC boards, data acquisition (DAQ) board, signal generator, external power supplies and a host computer. The ADC board is custom designed for different ADCs, with ADC drivers and clock distribution circuits integrated on board. The Xilinx ZC706 FPGA development board is used as a DAQ board. The data from the ADC are routed to the FPGA through the FMC (FPGA Mezzanine Card) connector, de-serialized and monitored by the FPGA, and then transmitted to the host computer through the Gigabit Ethernet. A software program has been developed with Python, and all the commands are sent to the DAQ board through Gigabit Ethernet by this program. Two ADC boards have been designed for the ADC, ADS52J90 from Texas Instruments and AD9249 from Analog Devices respectively. TID tests for both ADCs have been performed at BNL, and an SEE test for the ADS52J90 has been performed at Massachusetts General Hospital (MGH). Test results have been analyzed and presented. The test results demonstrate that this test system is very versatile, and works well for the radiation tolerance characterization of commercial multi-channel high-speed ADCs for the upgrade of the ATLAS LAr calorimeter. It is applicable to other collider physics experiments where radiation tolerance is required as well.
The BaF2 (barium fluoride) spectrometer is one of the experiment facilities at the CSNS-WNS (White Neutron Source at China Spallation Neutron Source), currently under construction. It is designed to precisely measure the (n, γ) cross section, with 92 crystal elements and complete 4π steradian coverage. In order to improve the precision of measurement, in this paper, a new precise digitization and readout method is proposed. Waveform digitizing with 1 GSps sampling rate and 12-bit resolution is used to precisely capture the detector signal. To solve the problem of massive data readout and processing, the readout electronics is designed as a distributed architecture with 4 PXIe crates. The digitized signal is concentrated to the PXIe crate controller through a PCIe bus on the backplane and transmitted to the data acquisition system over gigabit Ethernet in parallel. Besides, the clock and trigger can be fanned out synchronously to every electronic channel over a high-precision distribution network. Test results show that the prototype of the readout electronics can achieve good performance and meet the requirements of the CSNS-WNS BaF2 spectrometer.
In the lattice design of a diffraction-limited storage ring (DLSR) consisting of compact multi-bend achromats (MBAs), it is challenging to simultaneously achieve an ultralow emittance and a satisfactory nonlinear performance, due to extremely large nonlinearities and limited tuning ranges of the element parameters. Nevertheless, in this paper we show that the potential of a DLSR design can be explored with a successive and iterative implementation of the multi-objective particle swarm optimization (MOPSO) and multi-objective genetic algorithm (MOGA). For the High Energy Photon Source, a planned kilometer-scale DLSR, optimizations indicate that it is feasible to attain a natural emittance of about 50 pm·rad, and simultaneously realize a sufficient ring acceptance for on-axis longitudinal injection, by using a hybrid MBA lattice. In particular, this study demonstrates that a rational combination of the MOPSO and MOGA is more effective than either of them alone, in approaching the true global optima of an explorative multi-objective problem with many optimizing variables and local optima.
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