The HERMES Back Drift Chambers

The tracking system of the HERMES spectrometer behind the bending magnet consists of two pairs of large planar 6-plane drift chambers. The design and performance of these chambers is described. This description comprises details on the mechanical and electronical design, information about the gas mixture used and its properties, results on alignment, calibration, resolution, and efficiencies, and a discussion of the experience gained through the first three years of operation.Comment: 21 pages, LaTex, 16 figures include

Examining the Role of Narrative Performance Appraisal Comments on Performance

Despite their prevalence in performance appraisal systems and purported importance in theory, narrative performance appraisal comments have been rarely examined. This study aimed to contribute to the literature by developing and testing a theory of quality narrative feedback. The author argues that managerial feedback that is both directive (i.e., lengthy, specific, and includes goals) and motivational (i.e., positive and high in interactional justice) would be related to year-lagged performance. Negative and positive emotions are also proposed as mediators of this relationship. Performance appraisal comments were coded for a sample of 1,019 clinical nurses. The structural equations modeling results provided preliminary evidence that feedback favorability and interactional justice demonstrated significant direct and indirect (through positive and negative emotion) effects on year-lagged employee performance. © 2013 Copyright Taylor and Francis Group, LLC

Direct Detection of Dark Matter in the MSSM with Non-Universal Higgs Masses

We calculate dark matter scattering rates in the minimal supersymmetric extension of the Standard Model (MSSM), allowing the soft supersymmetry-breaking masses of the Higgs multiplets, m_{1,2}, to be non-universal (NUHM). Compared with the constrained MSSM (CMSSM) in which m_{1,2} are required to be equal to the soft supersymmetry-breaking masses m_0 of the squark and slepton masses, we find that the elastic scattering cross sections may be up to two orders of magnitude larger than values in the CMSSM for similar LSP masses. We find the following preferred ranges for the spin-independent cross section: 10^{-6} pb \ga \sigma_{SI} \ga 10^{-10} pb, and for the spin-dependent cross section: 10^{-3} pb \ga \sigma_{SD}, with the lower bound on \sigma_{SI} dependent on using the putative constraint from the muon anomalous magnetic moment. We stress the importance of incorporating accelerator and dark matter constraints in restricting the NUHM parameter space, and also of requiring that no undesirable vacuum appear below the GUT scale. In particular, values of the spin-independent cross section another order of magnitude larger would appear to be allowed, for small \tan \beta, if the GUT vacuum stability requirement were relaxed, and much lower cross-section values would be permitted if the muon anomalous magnetic moment constraint were dropped.Comment: 30 pages LaTeX, 40 eps figure

Fermi-liquid instabilities at magnetic quantum phase transitions

This review discusses instabilities of the Fermi-liquid state of conduction electrons in metals with particular emphasis on magnetic quantum critical points. Both the existing theoretical concepts and experimental data on selected materials are presented; with the aim of assessing the validity of presently available theory. After briefly recalling the fundamentals of Fermi-liquid theory, the local Fermi-liquid state in quantum impurity models and their lattice versions is described. Next, the scaling concepts applicable to quantum phase transitions are presented. The Hertz-Millis-Moriya theory of quantum phase transitions is described in detail. The breakdown of the latter is analyzed in several examples. In the final part experimental data on heavy-fermion materials and transition-metal alloys are reviewed and confronted with existing theory.Comment: 62 pages, 29 figs, review article for Rev. Mod. Phys; (v2) discussion extended, refs added; (v3) shortened; final version as publishe

Target dark matter detection rates in models with a well-tempered neutralino

In the post-LEP2 era, and in light of recent measurements of the cosmic abundance of cold dark matter (CDM) in the universe from WMAP, many supersymmetric models tend to predict 1. an overabundance of CDM and 2. pessimistically low rates for direct detection of neutralino dark matter. However, in models with a ``well-tempered neutralino'', where the neutralino composition is adjusted to give the measured abundance of CDM, the neutralino is typically of the mixed bino-wino or mixed bino-higgsino state. Along with the necessary enhancement to neutralino annihilation rates, these models tend to give elevated direct detection scattering rates compared to predictions from SUSY models with universal soft breaking terms. We present neutralino direct detection cross sections from a variety of models containing a well-tempered neutralino, and find cross section asymptotes with detectable scattering rates. These asymptotic rates provide targets that various direct CDM detection experiments should aim for. In contrast, in models where the neutralino mass rather than its composition is varied to give the WMAP relic density via either resonance annihilation or co-annihilation, the neutralino remains essentially bino-like, and direct detection rates may be below the projected reaches of all proposed experiments.Comment: 13 pages including 1 EPS figur

Measurement of Angular Distributions and R= sigma_L/sigma_T in Diffractive Electroproduction of rho^0 Mesons

Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the rho^0(770) meson over a range in the virtual photon negative four-momentum squared 0.5< Q^2 <4 GeV^2 and the photon-nucleon invariant mass range 3.8< W <6.5 GeV. The experiment was performed with the HERMES spectrometer, using a longitudinally polarized positron beam and a ^3He gas target internal to the HERA e^{+-} storage ring. The event sample combines rho^0 mesons produced incoherently off individual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the rho^0 -> pi+ pi- decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent with the dominance of helicity-conserving amplitudes and natural parity exchange. The improved precision achieved at 47 GeV, reveals evidence for an energy dependence in the ratio R of the longitudinal to transverse cross sections at constant Q^2.Comment: 15 pages, 15 embedded figures, LaTeX for SVJour(epj) document class Revision: Fig. 15 corrected, recent data added to Figs. 10,12,14,15; minor changes to tex

Beam-Induced Nuclear Depolarisation in a Gaseous Polarised Hydrogen Target

Spin-polarised atomic hydrogen is used as a gaseous polarised proton target in high energy and nuclear physics experiments operating with internal beams in storage rings. When such beams are intense and bunched, this type of target can be depolarised by a resonant interaction with the transient magnetic field generated by the beam bunches. This effect has been studied with the HERA positron beam in the HERMES experiment at DESY. Resonances have been observed and a simple analytic model has been used to explain their shape and position. Operating conditions for the experiment have been found where there is no significant target depolarisation due to this effect.Comment: REVTEX, 6 pages, 5 figure

The Flavor Asymmetry of the Light Quark Sea from Semi-inclusive Deep-inelastic Scattering

The flavor asymmetry of the light quark sea of the nucleon is determined in the kinematic range 0.02<x<0.3 and 1 GeV^2<Q^2<10 GeV^2, for the first time from semi-inclusive deep-inelastic scattering. The quantity (dbar(x)-ubar(x))/(u(x)-d(x)) is derived from a relationship between the yields of positive and negative pions from unpolarized hydrogen and deuterium targets. The flavor asymmetry dbar-ubar is found to be non-zero and x dependent, showing an excess of dbar over ubar quarks in the proton.Comment: 7 Pages, 2 figures, RevTeX format; slight revision in text, small change in extraction of dbar-ubar and comparison with a high q2 parameterizatio

Measurement of the Proton Spin Structure Function g1p with a Pure Hydrogen Target

A measurement of the proton spin structure function g1p(x,Q^2) in deep-inelastic scattering is presented. The data were taken with the 27.6 GeV longitudinally polarised positron beam at HERA incident on a longitudinally polarised pure hydrogen gas target internal to the storage ring. The kinematic range is 0.021<x<0.85 and 0.8 GeV^2<Q^2<20 GeV^2. The integral Int_{0.021}^{0.85} g1p(x)dx evaluated at Q0^2 of 2.5 GeV^2 is 0.122+/-0.003(stat.)+/-0.010(syst.).Comment: 7 pages, 3 figures, 1 table, RevTeX late