18727634
Mott transition in an anyon gas.
We introduce and analyze a lattice model of anyons in a periodic potential and an external magnetic field, which exhibits a transition from a Mott insulator to a quantum Hall fluid. The transition is characterized by the anyon statistics [alpha], which can vary between fermions, [alpha]=0, and bosons, [alpha]=1. For bosons the transition is in the universality class of the classical three-dimensional [ital XY] model. Near the fermion limit, the transition is described by a massless 2+1 Dirac theory coupled to a Chern-Simons gauge field. Analytic calculations perturbative in [alpha], and also a large-[ital N] expansion, show that due to gauge fluctuations, the critical properties of the transition are dependent on the anyon statistics. Comparison with previous calculations at and near the boson limit, strongly suggest that our lattice model exhibits a fixed line of critical points, with universal critical properties that vary continuously and monotonically as one passes from fermions to bosons. Possible relevance to experiments on the transitions between plateaus in the fractional quantum Hall effect and the magnetic-field-tuned superconductor-insulator transition are briefly discussed.
119850463
Charged Pion Photoproduction
We extracted the differential cross section for the γn→π−p process from a deuterium target using the CLAS detector at Jefferson Lab in Hall B for photon energies between 1.0 and 3.5 GeV and pion center‐of‐mass (c.m.) angles (θc.m.) between 50° and 115°. We confirm a previous indication of a broad enhancement around a c.m. energy (s) of 2.1 GeV at θc.m. = 90° in the scaled differential cross section, s7dσdt and a rapid fall‐off in a center‐of‐mass energy region of about 400 MeV following the enhancement. Our data show an angular dependence of this enhancement as the suggested scaling region is approached for θc.m. from 70° to 105°.
16855657
Critical statistical charge for anyonic superconductivity.
We examine a criterion for the anyonic superconductivity at zero temperature in Abelian matter-coupled Chern-Simons gauge-field theories in three dimensions. By solving the Dyson-Schwinger equations, we obtain a critical value of the statistical charge for the superconducting phase in a massless fermion-Chern-Simons model. {copyright} {ital 1996 The American Physical Society.}
119207670
PHASE-RESOLVED SPECTRAL ANALYSIS OF 4U 1901+03 DURING ITS OUTBURST
The high-mass X-ray binary 4U 1901+03 is reported to have a pulse profile evolving with the X-ray luminosity and energy during its outburst in 2003 February-July: the pulse peak changed from double to single along with the decreasing luminosity. We have carried out a detailed analysis on the contemporary phase-resolved energy spectrum of 4U 1901+03 as observed by the Rossi X-ray Timing Explorer. We find that the spectra are phase dependent. At the beginning of the outburst, the maximum of the optical depth for Compton scattering is near the major phase peak. During the decay of the outburst, the optical depth has the maximum away from the main peak of the pulse profile. For each observation, Fe Kα emission line is detected in the phase-resolved spectra, and its flux is constant across the pulse phases. This suggests that the origin of the Fe emission is from the accretion disk, not the surface of the neutron star.
28535306
Implications of a cosmological constant varying as R-2.
We advocate the possibility that the (effective) cosmological constant {Lambda} varies in time as {ital R}{sup {minus}2}, {ital R} being the scale factor of our expanding Universe. This behavior can be obtained under some simple and general assumptions in conformity with quantum cosmology. After pointing out several advantages worth noticing, we show that such a time-varying {Lambda} leads to no conflict with existing observations. However, it does change the predictions of the standard cosmology in the matter-dominated epoch and alleviates some problems in reconciling observations with the inflationary scenario. In particular, this medium'' time variation of {Lambda} leads to creation of matter with a rate at present which is comparable to that in the steady-state cosmology.
44727684
BRST quantization of topological field theory.
The canonical quantization of the topological field-theory model {Sigma}, proposed by Horowitz, is examined through the Becchi-Rouet-Stora-Tyutin approach. With this approach we have a manifestly covariant description of a certain class of topological quantum field theories. However, if {ital M} in the present model is any orientable four-dimensional manifold, one would end up with different theories when different polarizations are chosen. Therefore a restriction {ital M}={ital R}{sup 1}{times}{Sigma}, as pointed out by Horowitz, is required for consistency.
43756291
Top quark search with the D0 1992-1993 data sample.
We present results on the search for the top quark in {ital p{bar p}} collisions at {radical}{ital s} =1.8 TeV with an integrated luminosity of 13.5{plus_minus}1.6 pb{sup {minus}1}. We have considered {ital t{bar t}} production in the standard model using electron and muon dilepton decay channels ({ital t{bar t}}{r_arrow}{ital e}{mu}+jets, {ital ee}+jets, and {mu}{mu}+jets) and single-lepton decay channels ({ital t{bar t}}{r_arrow}{ital e}+jets and {mu}+jets) with and without tagging of {ital b} quark jets. An analysis of these data optimized for top quark masses below 140 GeV/{ital c}{sup 2} gives a lower top quark mass limit of 128 GeV/{ital c}{sup 2}. An analysis optimized for higher top quark masses yields 9 events with an expected background of 3.8{plus_minus}0.9. If we assume that the excess is due to {ital t{bar t}} production, and assuming a top quark mass of 180 GeV/{ital c}{sup 2}, we obtain a cross section of 8.2{plus_minus}5.1 pb.
2423491
Comparative study of the hadronic production of Bc mesons.
A comparative study of the full {alpha}{sup 4}{sub {ital s}} perturbative QCD calculation of the hadronic production of the {ital B}{sub {ital c}} and {ital B}{sub {ital c}}{sup {asterisk}} mesons and the fragmentation approximation is presented. We examined the various subprocesses in detail and the distribution {ital C}({ital z}), where {ital z} is twice the fraction of the {ital B}{sub {ital c}} or {ital B}{sub {ital c}}{sup {asterisk}} meson energy in the center of mass of the subprocess, which proved insightful and revealed the importance of certain nonfragmentation contributions. We concluded that the condition for the applicability of the fragmentation approximation in hadronic collisions is that the transverse momentum {ital P}{sub {ital T}} of the produced {ital B}{sub {ital c}} and {ital B}{sub {ital c}}{sup {asterisk}} be much larger than the mass of the {ital B}{sub {ital c}} meson: i.e., {ital P}{sub {ital T}}{gt}{ital M}{sub {ital B}{sub {ital c}}}. Numerical results for the cross sections at the Fermilab Tevatron are also presented using updated parton distribution functions with various kinematic cuts. {copyright} {ital 1996 The American Physical Society.}
42826202
Observation of the Top Quark.
The D0 collaboration reports on a search for the Standard Model top quark in p{bar p} collisions at {radical}s = 1.8 TeV at the Fermilab Tevatron, with an integrated luminosity of approximately 50 pb{sup {minus}1}. We have searched for t{bar t} production in the dilepton and single lepton decay channels, with and without tagging of b quark jets. We observe 17 events with an expected background of 3.8 {plus_minus} 0.6 events. The probability for an upward fluctuation of the background to produce the observed signal is 2 {times} 10{sup {minus}6} (equivalent to 4.6 standard deviations). The kinematic properties of the excess events are consistent with top quark decay. We conclude that we have observed the top quark and measure its mass to be 199{sub {minus}21}{sup +19} (stat.) {plus_minus}22 (syst.) GeV/c{sup 2} and its production cross section to be 6.4 {plus_minus} 2.2 pb.
64414878
IN-VACUUM UNDULATOR CONTROLLER DESIGN FOR SSRF
Two 25mm period in-vacuum undulators (IVU25) have been installed in SSRF 3.5 GeV storage ring. The controller for IVU25 based on Siemens S7-300 PLC is used to control two stepper motors for the gap and tapper of magnetic pole array. The controller monitors cooling water’s temperature and flux, monitor the array’s temperature, too. And configure Ethernet access for remote control as well as MPS and PPS interlock. A simple user interface supports routine operation and detail information is showed at cascading windows. With real time feedback of the linear absolute encoders (LAEs) the tracking precision of gap and taper are less than 1 micron. This paper describes the design of controller hardware and software.
30514138
Search for a vector glueball by a scan of the J/ psi resonance.
The cross section for {ital e}{sup +}{ital e}{sup {minus}}{r_arrow}{rho}{pi} has been measured by the BES detector at BEPC at center-of-mass energies covering a 40 MeV interval spanning the {ital J}/{psi} resonance. The data are used to search for the vector gluonium state hypothesized by Brodsky, Lepage, and Tuan as an explanation of the {rho}{pi} puzzle in charmonium physics. The shape of the {rho}{pi} cross section is compatible with that of the total hadronic cross section. No distortions indicating the presence of a vector glueball are seen. {copyright} {ital 1996 The American Physical Society.}