2016 Vol. 40, No. 1
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The product of the Λb0(
where the rst uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the branching fraction of the decay 0→J/ψp *(892)0, and the fourth is due to the knowledge of fΛb0/fd. The sum of the asymmetries in the production and decay between Λb0 and b0 is also measured as a function of pT and y. The previously published branching fraction of Λb0→J/ψpπ-, relative to that of Λb0→J/ψpK-, is updated. The branching fractions of Λb0→Pc+(→J/ψp)K- are determined. 0) di erential production cross-section and the branching fraction of the decay Λb0→J/ψpK- ( 0→J/ψp *(892)0) is measured as a function of the beauty hadron transverse momentum, pT, and rapidity, y. The kinematic region of the measurements is pT <20 GeV/c and 2.0< y< 4.5. The measurements use a data sample corresponding to an integrated luminosity of 3fb-1 collected by the LHCb detector in pp collisions at centre-of-mass energies √ = 7 TeV in 2011 and √ = 8 TeV in 2012. Based on previous LHCb results of the fragmentation fraction ratio, fΛb0/fd, the branching fraction of the decay Λb0→J/ψpK- is measured to be
We review the recent BESIII measurement of e+e-→ππhc in which its line shape is studied between the center-of-mass energies of 3.9 to 4.42 GeV and an iso-vector charmonium-like state Zc(4020) is observed in the invariant mass of πhc at the BESIII experiment. The charged Zc(4020)± is the second observed Zc state following Zc(3900), while the Zc(4020)0 is the rst observed neutral Zc state. The line shape of (e+e-→ππhc) is also re-analyzed in view of searching for the Y state and the existence of the Y(4220) state is con rmed and compared with the previous work of the BESIII experiment.
We search for the ψ(4S) state in the B±→ηJ/ψK± and e+e-→ηJ/ψ processes based on the Belle measurements with the assumed mass M =(4230±8) MeV/c2 and width Γ =(38 12) MeV. No signi cant signal is observed in the ηJ/ψ mass spectra. The 90% con dence level upper limit on the product branching fraction B(B±→ ψ(4S)K±)B(ψ(4S)→ηJ/ψ)<6.8×10-6 is obtained in the B±→ηJ/ψK± decays. By assuming the partial width of ψ(4S)→e+e- to be 0.63 keV, a branching fraction limit B(ψ(4S)→ηJ/ψ)<1.3% is obtained at the 90% con dence level in e+e-→ηJ/ψ, which is consistent with the theoretical prediction.
By assuming that the scalar meson KK0*(1430) belongs to the rst excited states or the lowest lying ground states of q ', we study the pure annihilation-type decays B→K0*±(1430)K(*) in the QCD factorization approach. Within the Standard Model, the branching fractions are of the order of 10-8-10-7, which is possible to measure in the ongoing LHCb experiment or forthcoming Belle-II experiment. We also study these decays in the family non-universal Z' model. The results show that if mZ' 600 GeV (ξ =0.02), both the branching fractions and CP asymmetries of 0 →K0*+(1430)K- could be changed remarkably, which provides us with a place for probing the e ect of new physics. These results could be used to constrain the parameters of the Z' model.
The prompt γ-ray spectrum from depleted uranium (DU) spherical shells induced by 14 MeV D-T neutrons is measured. Monte Carlo (MC) simulation gives the largest prompt γ flux with the optimal thickness of the DU spherical shells 3-5 cm and the optimal frequency of neutron pulse 1 MHz. The method of time of flight and pulse shape coincidence with energy (DC-TOF) is proposed, and the subtraction of the background γ-rays discussed in detail. The electron recoil spectrum and time spectrum of the prompt γ-rays are obtained based on a 2"×2" BC501A liquid scintillator detector. The energy spectrum and time spectrum of prompt γ-rays are obtained based on an iterative unfolding method that can remove the influence of γ-rays response matrix and pulsed neutron shape. The measured time spectrum and the calculated results are roughly consistent with each other. Experimental prompt γ-ray spectrum in the 0.4-3 MeV energy region agrees well with MC simulation based on the ENDF/BVI.5 library, and the discrepancies for the integral quantities of γ-rays of energy 0.4-1 MeV and 1-3 MeV are 9.2% and 1.1%, respectively.
The triaxial dynamics of the quadrupole-deformed rotor model of both the rigid and the irrotational type are investigated in detail. The results indicate that level patterns of the two types of model can be matched with each other to the leading order of the deformation parameter β. In particular, it is found that the dynamical structure of the irrotational type with most triaxial deformation (γ=30°) is equivalent to that of the rigid type with oblate deformation (γ=60°), and the associated spectrum can be classified into the standard rotational bands obeying the rotational L(L+1)-law or regrouped into a new ground- and γ-band with odd-even staggering in the new γ-band, commonly recognized as a signature of the triaxiality. The differences between the two types of the model in this case are emphasized, especially in the E2 transitional characteristics.
Within the framework of Ginzburg-Landau theory, the effect of multiplicity correlation between the dynamical multiplicity fluctuations is analyzed for a first-order phase transition from quark-gluon plasma to hadrons. Normalized factorial correlators are used to study the correlated dynamical fluctuations. A scaling behavior is found among the factorial correlators, and an approximate universal exponent, which is weakly dependent on the details of the phase transition, is obtained.
The precise spectra of Cosmic Ray (CR) electrons and positrons have been published by the measurement of AMS-02. It is reasonable to regard the difference between the electron and positron spectra (ΔΦ= Φe--Φe+) as being dominated by primary electrons. The resulting electron spectrum shows no sign of spectral softening above 20 GeV, which is in contrast with the prediction of the standard model of CR propagation. In this work, we generalize the analytic one-dimensional two-halo model of diffusion to a three-dimensional realistic calculation by implementing spatial variant diffusion coefficients in the DRAGON package. As a result, we can reproduce the spectral hardening of protons observed by several experiments, and predict an excess of high energy primary electrons which agrees with the measurement reasonably well. Unlike the break spectrum obtained for protons, the model calculation predicts a smooth electron excess and thus slightly over-predicts the flux from tens of GeV to 100 GeV. To understand this issue, further experimental and theoretical studies are necessary.
As the main tracking detector of BESIII, the drift chamber provides accurate measurements of the position and the momentum of the charged particles produced in e+e- collisions at BEPCII. After six years of operation, the drift chamber is suffering from aging problems due to huge beam-related background. The gains of the cells in the first ten layers show an obvious decrease, reaching a maximum decrease of about 29% for the first layer cells. Two calculation methods for the gain change (Bhabha events and accumulated charges with 0.3% aging ratio for inner chamber cells) give almost the same results. For the Malter effect encountered by the inner drift chamber in January 2012, about 0.2% water vapor was added to the MDC gas mixture to solve this cathode aging problem. These results provide an important reference for MDC operating high voltage settings and the upgrade of the inner drift chamber.
Linear alkyl benzene (LAB) will be used as the solvent in a liquid scintillator mixture for the JUNO antineutrino experiment. Its light absorption properties should therefore be understood prior to its effective use in the experiment. Attenuation length measurements at a light wavelength of 430 nm have been performed on samples of LAB prepared for the JUNO experiment. Inorganic impurities in LAB have also been studied for their possibilities of light absorption in our wavelength of interest. In view of a tentative plan by the JUNO collaboration to utilize neutron capture with hydrogen in the detector, we also present in this work a preliminary study on the carbon-hydrogen ratio and the attenuation length of the samples.
A new method for analyzing the collimation angle of a neutron Soller collimator is described. A Gaussian distribution formula is used to define the angular distribution function of the neutron source and the neutron transmission function of the Soller collimator. A relationship between the FWHM of the collimator rocking curve and the collimation angle is derived. Using this method, some rocking curve experiment results are analyzed. The results show that the new function can be a good theoretical model for fitting the experimental data, especially for the data of two collimators with different collimation angles.
In the readout electronics of the Water Cerenkov Detector Array (WCDA) in the Large High Altitude Air Shower Observatory (LHAASO) experiment, both high-resolution charge and time measurement are required over a dynamic range from 1 photoelectron (P.E.) to 4000 P.E. The Analog Front-end (AFE) circuit is one of the crucial parts in the readout electronics. We designed and optimized a prototype of the AFE through parameter calculation and circuit simulation, and conducted initial electronics tests on this prototype to evaluate its performance. Test results indicate that the charge resolution is better than 1%@4000 P.E. and remains better than 10%@1 P.E., and the time resolution is better than 0.5 ns RMS, which is better than the application requirements.
The Dark Matter Particle Explorer (DAMPE) is a Chinese scientific satellite designed for cosmic ray studies with a primary scientific goal of indirect detection of dark matter particles. As a crucial sub-detector, the BGO calorimeter measures the energy spectrum of cosmic rays in the energy range from 5 GeV to 10 TeV. In order to implement high-density front-end electronics (FEE) with the ability to measure 1848 signals from 616 photomultiplier tubes on the strictly constrained satellite platform, two kinds of 32-channel front-end ASICs, VA160 and VATA160, are customized. However, a space mission period of more than 3 years makes single event effects (SEEs) become threats to reliability. In order to evaluate SEE sensitivities of these chips and verify the effectiveness of mitigation methods, a series of laser-induced and heavy ion-induced SEE tests were performed. Benefiting from the single event latch-up (SEL) protection circuit for power supply, the triple module redundancy (TMR) technology for the configuration registers and the optimized sequential design for the data acquisition process, 52 VA160 chips and 32 VATA160 chips have been applied in the flight model of the BGO calorimeter with radiation hardness assurance.
Considering the effects of aging on the existing Inner Drift Chamber (IDC) of BESIII, a GEM-based inner tracker, the Cylindrical-GEM Inner Tracker (CGEM-IT), is proposed to be designed and constructed as an upgrade candidate for the IDC. This paper introduces a full simulation package for the CGEM-IT with a simplified digitization model, and describes the development of software for cluster reconstruction and track fitting, using a track fitting algorithm based on the Kalman filter method. Preliminary results for the reconstruction algorithms which are obtained using a Monte Carlo sample of single muon events in the CGEM-IT, show that the CGEM-IT has comparable momentum resolution and transverse vertex resolution to the IDC, and a better z-direction resolution than the IDC.
A silicon pixel detector with fine pitch size of 19 μm×19 μm, developed based on SOI (silicon-on-insulator) technology, was tested under the illumination of infrared laser pulses. As an alternative method for particle beam tests, the laser pulses were tuned to very short duration and small transverse profile to simulate the tracks of MIPs (minimum ionization particles) in silicon. Hit cluster sizes were measured with focused laser pulses propagating through the SOI detector perpendicular to its surface and most of the induced charge was found to be collected inside the seed pixel. For the first time, the signal amplitude as a function of the applied bias voltage was measured for this SOI detector, deepening understanding of its depletion characteristics.
In this paper we show a systematic method of appropriate parameter choice for a circular proton-proton collider by using an analytical expression for the beam-beam tune shift limit, starting from a given design goal and technical limitations. A suitable parameter space has been explored. Based on the parameter scan, sets of appropriate parameters designed for a 50 km and 100 km circular proton-proton collider are proposed.
A study of spin dynamics based on simulations with the Polymorphic Tracking Code (PTC) is reported, exploring the dependence of the static polarization limit on various beam parameters and lattice settings for a practical RHIC lattice. It is shown that the behavior of the static polarization limit is dominantly affected by the vertical motion, while the effect of beam-beam interaction is small. In addition, the ''nonresonant beam polarization'' observed and studied in the lattice-independent model is also observed in this lattice-dependent model. Therefore, this simulation study gives insights of polarization evolution at fixed beam energies, that are not available in simple spin tracking.
The time-resolved electron beam envelope parameters, including cross sectional distribution and beam centroid position, are very important for the study of beam transmission characteristics in a magnetic field and for verifying the rationality of the magnetic field parameters employed. One kind of high time-resolved beam envelope measurement system has recently been developed, constituted of a high-speed framing camera and a streak camera. It can obtain three panoramic images of the beam and time continuous information along the given beam profile simultaneously. Recently obtained data has proved that several fast vibrations of the beam envelope along the diameter direction occur during the front and the tail parts of the electron beam. The vibration period is several nanoseconds. The effect of magnetic field on the electron beam is also observed and verified. Beam debugging experiments have proved that the existing beam transmission design is reasonable and viable. This beam envelope measurement system will establish a good foundation for beam physics research.
Photoinjectors are widely used for linear accelerators as electron sources to generate high-brightness electron beams. The drive laser, which determines the timing structure and quality of the electron beam, is a crucial component of a photoinjector. A new drive laser system has been designed and constructed for the upgraded 3.5-cell DC-SRF photoinjector at Peking University. The drive laser system consists of a 1064 nm laser oscillator, a four-stage amplifier, second and fourth harmonic generators, an optical system to transfer the UV pulses to the photocathode, and a synchronization system. The drive laser system has been successfully applied during stable operation of the DC-SRF photoinjector and its performance meets requirements. A 266 nm laser with an average power close to 1 W can be delivered to illuminate the Cs2Te photocathode and the instability is less than 5% for long time operation. The design considerations for improving the UV laser quality, a detailed description of the laser system, and its performance are presented in this paper.
Active power filters (APFs) are widely used for their outstanding performance in current and voltage ripple compensation. As modern high-energy accelerators are demanding much more stringent current ripple guidelines, APFs are used in the magnet power supply (MPS) in accelerator systems. However, conventional APFs have many drawbacks due to the traditional topology, such as complex structure, nonadjustable working voltage, requirement of power supply, and so on. This paper proposes a new APF topology, which works as two types of chopper circuits. This APF does not need extra electricity, but uses the power of the MPS current ripple to realize ripple depression. Experimental results prove its feasibility and effectiveness.
SLAC energy doubler (SLED) type radio-frequency pulse compressors are widely used in large-scale particle accelerators for converting long-duration moderate-power input pulses into short-duration high-power output pulses. Phase shift keying (PSK) is one of the key components in SLED pulse compression systems. Performance of the PSK will influence the output characteristics of the SLED, such as the rise-time of the output pulse, maximal peak power gain, and energy efficiency. In this paper, a high power microwave source based on power combining and pulse compression of conventional klystrons is introduced. The effects of nonideal PSK with slow switching speed and PSK without power output during the switching process are investigated, and the experimental results with nonideal PSK agree well with the analytical results.
Carbon ions have significant advantages in tumor therapy because of their physical and biological properties. In view of the radiation protection, the safety of patients is the most important issue in therapy processes. Therefore, the effects of the secondary particles produced by the carbon ions in the tumor therapy should be carefully considered, especially for the neutrons. In the present work, the neutron radiation field induced by carbon ions was evaluated by using the FLUKA code. The simulated results of neutron energy spectra and neutron dose was found to be in good agreement with the experiment data. In addition, energy deposition of carbon ions and neutrons in tissue-like media was studied, it is found that the secondary neutron energy deposition is not expected to exceed 1% of the carbon ion energy deposition in a typical treatment.
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