111135169
Studies of bunch lengthening at the BEPC
The Beijing Electron-Positron Collider (BEPC) has been operating for more than ten years. In addition to providing colliding beams for high energy physics and a single beam for synchrotron radiation study, we carried out many machine related beam experiments for understanding better the beam physics and for improving performance. Among them, measurements of bunch length and its lengthening, and the impedance implied thereby, play crucial roles in the future plans for luminosity upgrades. This paper reviews the measurement of the bunch length in the BEPC storage ring, concluding with the scaling law for the bunch lengthening above the microwave instability threshold. The low frequency impedance of the storage ring is also obtained from the bunch lengthening due to the potential well distortion in low bunch current. (C) 2001 Elsevier Science B.V. All rights reserved.
124075894
General conditions for self-cancellation of geometric aberrations in a lattice structure
In this paper we will discuss the general conditions for self-cancellation of geometric aberrations in an uncoupled or even coupled lattice structure. The self-cancellation conditions show that - I transformer even noninterleaved multipoles is not necessary. We will also give two examples for sextupole case to specify the application.
123594822
Transfer matrices of dipoles with bending radius variation
With the increasing demand of high brightness in light source, the uniform dipole can not meet the needs of low emittance, and thus the dipole with bending radius variation is introduced in this paper. The transfer matrix of a non-uniform dipole whose bending radius is linearly changed is chosen as an example and a very simple calculation formula of non-uniform dipole transfer matrices is given. The transfer matrices of some common profile non-uniform dipoles are also listed. The comparison of these transfer matrices and the matrices calculated with slices method verifies the numerical accuracy of this formula. This method can make the non-uniform beam dynamic problem simpler, very helpful for emittance research and lattice design with non-uniform dipoles.
56470793
DESIGN OF BEAM TRANSPORT LINE FROM RCS TO TARGET FOR CSNS
China Spallation Neutron Source (CSNS) uses the high energy proton beam to strike the Tungsten target to generate neutrons through spallation reaction. The proton beam is extracted from the Rapid Cycling Synchrotron (RCS), whose beam power reaches 100 kW. For the sake of target lifetime, beam distribution at the target surface is required as uniform as possible. Nonlinear beam density redistribution method with two octupole magnets has been studied. Also some simulation and theoretical calculation have been done. According to the simulation result, the beam density at the target is optimized and the beam loss is under control.
55843797
LATTICE DESIGN FOR THE BEPCII STORAGE RING
BEPCII, the upgrading project of the BEPC, has been being designed with a luminosity of 10 33 cm -2 s -1 at the J/ψ energy. It still keeps the potential to provide beams as a synchrotron radiation (SR) facility. The storage rings for collision contain a positron and an electron ring and the ring for dedicated SR uses the outer parts of the two rings. To fit all the conditions either on beam or on space limit, lattices are carefully designed for both high energy physics and SR experiments with sufficient dynamic apertures and high efficiencies for injection. The features of the lattices are also discussed in the paper. 1 DESIGN REQUIREMENTS BEPCII is an upgrade project of the Beijing ElectronPositron Collider (BEPC), in which a new inner ring will be installed inside the old one. It will provide colliding beams with the center-of-mass energy from 1.0GeV×2 to 2.0GeV×2 and also the dedicated synchrotron radiation beam with 2.5 GeV. For the colliding beams the luminosity is optimized at 1.89 GeV with 1×10 33 cm -2 s -1 . For the dedicated synchrotron radiation beam, the current is 250 mA with an emittance as low as possible. There have been several beam-lines in the BEPC for the synchrotron radiation experiments, so the current bending magnets and insertion devices in the southern region have to be fixed at their present positions. In order to increase the average luminosity, the “topoff” injection scheme up to 1.89 GeV is adopted. This requires that the injection and collision optics must be the same. The main parameters are shown in Tables 1 and 2.
60626146
ILC Reference Design Report: ILC Global Design Effort and World Wide Study
122833143
E917 at the AGS: High Density Baryon Matter
Nuclear matter of high density is created during the collisions of Au+Au nuclei using the Alternating Gradient Synchrotron (AGS) located at Brookhaven National Laboratory.1, 2 Whether the formation of a quark-gluon plasma (QGP) occurs during these heavy-ion collisions, or even if it is possible to extract an unambiguous signal of its existence from the background of hadronic debris, remains highly speculative. Regardless of whether a QGP is created, the potential exists to do a great deal of interesting and exciting physics with the high density baryonic matter created during the Au+Au collisions at the AGS.
121660884
Limiting Fragmentation, Scaling and Substructual Dependence of Multiparticle Production in High Energy Heavy Ion Reactions
We report on recent results obtained by the EMUO1 collaboration from studies of 16O + emulsion, at 14.6, 60 and 200 A GeV, and 32S + emulsion and 32S + Au interactions at 200 A GeV. Shower-particle production in oxygen-induced interactions are studied over the energy range 2.1-200 A GeV. Scaling and limiting fragmentation are observed. Multiplicity and angular distributions of low energy target-associated particles are presented and compared with distributions obtained using the Ranft and the Fritiof simulation codes.
209834712
Search for anomalous production of prompt like-sign muon pairs and constraints on physics beyond the standard model with the ATLAS detector
An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6 fb(-1) of integr ...
122909812
Precision measurements of B[ψ(3686)→π+π-J/ψ] and B[J/ψ→l+l-]
Based on (106.41 +/- 0.86) x 10(6) psi(3686) events collected with the BESIII detector at the BEPCII collider, the branching fractions of psi(3686) -> pi(+)pi(-)J/psi, J/psi -> e(+)e(-), and J/psi -> mu(+)mu(-) are measured. We obtain B[psi(3686) -> pi(+)pi(-)J/psi] = (34.98 +/- 0.02 +/- 0.45)%, B[J/psi -> e(+)e(-)] = (5.983 +/- 0.007 +/- 0.037)%, and B[J/psi -> mu(+)mu(-)] = (5.973 +/- 0.0007 +/- 0.038)%. The measurement of B[psi(3686) -> pi(+)pi(-)J/psi] confirms the CLEO-c measurement, and is apparently larger than the others. The measured J/psi leptonic decay branching fractions agree with previous experiments within one standard deviation. These results lead to B[J/psi -> l(+)l(-)] = (5.978 +/- 0.005 +/- 0.040)% by averaging over the e(+)e(-) and mu(+)mu(-) channels and a ratio of B[J/psi -> e(+)e(-)]/B[J/psi -> mu(+)mu(-)] = 1.0017 +/- 0.0017 +/- 0.0033, which tests e- mu universality at the four tenths of a percent level. All the measurements presented in this paper are the most precise in the world to date.
12149444
Observation of a Near-Threshold Enhancement in the p-anti-p Mass Spectrum from Radiative J/psi --> gamma-p-anti-p Decays
We observe a narrow enhancement near 2m{sub p} in the invariant mass spectrum of p{bar p} pairs from radiative J/{psi} {yields} {gamma}p{bar p} decays. No similar structure is seen in J/{psi} {yields} {pi}{sup 0} p{bar p} decays. The results are based on an analysis of a 58 million event sample of J/{psi} decays accumulated with the BESII detector at the Beijing electron-positron collider. The enhancement can be fit with either an S- or P-wave Breit Wigner resonance function. In the case of the S-wave fit, the peak mass is below 2m{sup p} at M = 1859{sub -10}{sup +3} (stat){sub -25}{sup +5} (sys) MeV/c{sup 2} and the total width is {Lambda} < 30 MeV/c{sup 2} at the 90 percent confidence level. These mass and width values are not consistent with the properties of any known particle.