54921013
Design and study of a TCF lattice with negative momentum compaction factor
The feasibility of designing a negative momentum compaction factor (alpha(p) < 0) lattice for a circular e(-)e(+) collider is investigated. The modular method for an alpha(p) < 0 lattice is introduced. As a practical example, an alpha(p) < 0 lattice for a Tau-charm factory (TCF) is proposed and studied. (C) 1999 Elsevier Science B.V. All rights reserved.
16640761
Recent studies on beam-photoelectron instability in BEPC
An experiment investigating the photoelectron instability has been performed in BEPC at IHEP, China. The betatron oscillation of each bunch was observed and recorded by a single pass beam position monitor system which has a capability to measure the transverse position of every bunch over 16000 turns. The effect of an octupole magnet on the instability was also studied. This paper describes results of those observations and analyses.
17279318
THE PROPOSED EXPERIMENTAL STUDY ON BEAM-PHOTOELECTRON INTERACTIONS IN BEPC
A vertical collective effect suspected as photoelectron instability (PEI) has been observed at Photon Factory (PF) of KEK in recent years. This phenomena may impose a limitation on the performance of the proposed B-Factories or T-c Factories. An experiment has been planned to test it using positron beam at Beijing Electron Positron Collider (BEPC) in 1996 under the cooperation between IHEP and KEK. Preliminary simulation results have shown that the PEI may occur in BEPC on the total beam current level of 40 mA over more than 20 bunches. The instrumentation for observation of PEI is jointly prepared by both sides of IHEP and KEK. The machine study has been scheduled and the experiment will progress under the conditions of the best machine performance.
119741336
Electron cloud instability studies in the Beijing Electron Positron Collider
The electron cloud instability (ECI) in the Beijing Electron Positron Collider (BEPC) was studied systematically with experiments and simulations in recent years. Several electron cloud detectors have been installed into the BEPC storage ring to measure the electron yield. The effects of solenoid, the clearing electrode, the chromaticity, and the octupole on ECI have been investigated in BEPC experimentally. To evaluate the ECI in BEPCII, the upgrade project of BEPC, a computer code has been developed to simulate the electron density in the antechamber under different conditions, as well as the progress of the single bunch and coupled-bunch instabilities caused by the electron cloud. The experimental and simulation results, as well as the activities, are reported in this paper.
53366099
Microwave instabilities in electron rings with negative momentum compaction factor
Bunch lengthening (or shortening) caused by the potential well distortion and the microwave instability in electron rings with negative momentum compaction factor is discussed in detail based on the resonator impedance model; further, a comparison with rings of positive momentum compaction factor is given. It was found that the bunch shape is less deformed and the current threshold of the microwave instability is higher in the rings with negative momentum compaction factor over a very wide range of the impedance parameters. The results also show that even within the range where the threshold for positive momentum compaction is higher than that for negative momentum compaction, the bunch lengthening is still less serious in most cases. Finally, an example of bunch lengthening in the case that /spl alpha/<0 with a real wake field of the SLC damping ring (old vacuum chamber) is given in contrast to the case in which /spl alpha/>0.
121523785
Electron cloud instability experiments on the BEPC
The electron cloud instability (ECI), which takes place in positively charged particle circular accelerators, is studied both experimentally and theoretically in the recent years. Many ECI-related experiments, including electron cloud (EC) measurement, beam parameter dependences, instability cure, etc., have been carried out on the Beijing Electron Positron Collider (BEPC) since 1996. A great number of fruitful results are obtained from these experiments, which also influence the simulation studies in the meantime. Ways to control the ECI are also studied in the experiments. Some achievements are beneficial for the BEPCII, the upgraded project of BEPC in the near future.
125447590
The design study of the BTCF lattice
124472455
Search for diphoton events with large missing transverse momentum in 7 TeV proton-proton collision data with the ATLAS detector
A search for diphoton events with large missing transverse momentum has been performed using proton-proton collision data at is root s = 7 TeV recorded with the ATLAS detector, corresponding to an integrated luminosity of 4.8 fb(-1). No excess of events was observed above the Standard Model prediction and model-dependent 95% confidence level exclusion limits are set. In the context of a generalised model of gauge-mediated supersymmetry breaking with a bino-like lightest neutralino of mass above 50 GeV, gluinos (squarks) below 1.07 TeV (0.87 TeV) are excluded, while a breaking scale Lambda below 196 TeV is excluded for a minimal model of gauge-mediated supersymmetry breaking. For a specific model with one universal extra dimension, compactification scales 1/R < 1.40 TeV are excluded. These limits provide the most stringent tests of these models to date. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
16148475
Cosmological Evolution of the Duty Cycle of Quasars
Quasars are powered by accretion onto supermassive black holes, but the problem of the duty cycle related to the episodic activity of the black holes remains one of the major questions of the cosmological evolution of quasars. In this Letter, we obtain quasar duty cycles based on analyses of a large sample composed of 10,979 quasars with redshifts z ≤ 2.1 from the Sloan Digital Sky Survey (SDSS) Data Release 3 (DR3). We estimate the masses of the quasar black holes and obtain their mass function (MF) in the present sample. We then get the duty cycle (z) = 10-3 ~ 1 based on Soltan's argument, implying that black holes are undergoing multiple episodic activity. We find that the duty cycle has a strong evolution. By comparison, we show that the evolution of the duty cycle follows the history of the cosmic star formation rate (SFR) density in the universe, providing intriguing evidence of a natural connection between star formation and the triggering of black hole activity. Feedback on star formation from black hole activity is briefly discussed.
118454726
Search for light resonances decaying into pairs of muons as a signal of new physics
A search for groups of collimated muons is performed using a data sample collected by the CMS experiment at the LHC, at a centre-of-mass energy of 7TeV, and corresponding to an integrated luminosity of 35 pb−1. The analysis searches for production of new low-mass states decaying into pairs of muons and is designed to achieve high sensitivity to a broad range of models predicting leptonic jet signatures. With no excess observed over the background expectation, upper limits on the production cross section times branching fraction times acceptance areset, ranging from 0.1 to 0.5 pb at the 95% CL depending on event topology. In addition, the results are interpreted in several benchmark models in the context of supersymmetry with a new light dark sector exploring previously inaccessible parameter space.
14896531
Strong Ca II Absorption Lines in the Reddened Quasar SDSS J2339–0912: Evidence of the Collision/Merger in the Host Galaxy?
We report the detection of strong Ca II/Mg II absorption lines at the quasar redshift in the narrow-line quasar SDSS J2339-0912 (z = 0.6604). The quasar exhibits strong Fe II, a small Balmer emission line width, and a very red B - Ks color. Both the optical continuum and broad emission lines are reddened by SMC-like dust of E(B - V) 1.0 mag, while its near-infrared color (J - Ks = 1.60) shows little reddening. The Ca II absorption lines are saturated and resolved with an FWHM of 362 km s-1 and an equivalent width of W = 4.2 A (in the source rest frame). Mg II absorption lines are also saturated and have a similar line width. The line profile and the fact that there is no evidence of starlight from the host galaxy suggest that these absorption lines are not of a stellar origin. The ratio of column density of Ca II to that of dust is consistent with that of the interstellar medium (ISM) in our Galaxy. We suggest that both the heavy reddening and the large absorption line width are due to the highly disturbed ISM on the line of sight toward the quasar and that the disturbance is caused by a galaxy collision or even merger in the quasar host galaxy.