37 research outputs found
Measurement of the Neutral Weak Form Factors of the Proton
We have measured the parity-violating electroweak asymmetry in the elastic
scattering of polarized electrons from the proton. The kinematic point
(theta_lab = 12.3 degrees and Q^2=0.48 (GeV/c)^2) is chosen to provide
sensitivity, at a level that is of theoretical interest, to the strange
electric form factor G_E^s. The result, A=-14.5 +- 2.2 ppm, is consistent with
the electroweak Standard Model and no additional contributions from strange
quarks. In particular, the measurement implies G_E^s + 0.39G_M^s = 0.023 +-
0.034 (stat) +- 0.022 (syst) +- 0.026 (delta G_E^n), where the last uncertainty
arises from the estimated uncertainty in the neutron electric form factor.Comment: 10 pages, 4 figures, submitted to Phys. Rev. Let
Overcoming High Energy Backgrounds at Pulsed Spallation Sources
Instrument backgrounds at neutron scattering facilities directly affect the
quality and the efficiency of the scientific measurements that users perform.
Part of the background at pulsed spallation neutron sources is caused by, and
time-correlated with, the emission of high energy particles when the proton
beam strikes the spallation target. This prompt pulse ultimately produces a
signal, which can be highly problematic for a subset of instruments and
measurements due to the time-correlated properties, and different to that from
reactor sources. Measurements of this background have been made at both SNS
(ORNL, Oak Ridge, TN, USA) and SINQ (PSI, Villigen, Switzerland). The
background levels were generally found to be low compared to natural
background. However, very low intensities of high-energy particles have been
found to be detrimental to instrument performance in some conditions. Given
that instrument performance is typically characterised by S/N, improvements in
backgrounds can both improve instrument performance whilst at the same time
delivering significant cost savings. A systematic holistic approach is
suggested in this contribution to increase the effectiveness of this.
Instrument performance should subsequently benefit.Comment: 12 pages, 8 figures. Proceedings of ICANS XXI (International
Collaboration on Advanced Neutron Sources), Mito, Japan. 201
Neutron Position Sensitive Detectors for the ESS
The European Spallation Source (ESS) in Lund, Sweden will become the world's
leading neutron source for the study of materials. The instruments are being
selected from conceptual proposals submitted by groups from around Europe.
These instruments present numerous challenges for detector technology in the
absence of the availability of Helium-3, which is the default choice for
detectors for instruments built until today and due to the extreme rates
expected across the ESS instrument suite. Additionally a new generation of
source requires a new generation of detector technologies to fully exploit the
opportunities that this source provides. The detectors will be sourced from
partners across Europe through numerous in-kind arrangements; a process that is
somewhat novel for the neutron scattering community. This contribution presents
briefly the current status of detectors for the ESS, and outlines the timeline
to completion. For a conjectured instrument suite based upon instruments
recommended for construction, a recently updated snapshot of the current
expected detector requirements is presented. A strategy outline as to how these
requirements might be tackled by novel detector developments is shown. In terms
of future developments for the neutron community, synergies should be sought
with other disciples, as recognized by various recent initiatives in Europe, in
the context of the fundamentally multi-disciplinary nature of detectors. This
strategy has at its basis the in-kind and collaborative partnerships necessary
to be able to produce optimally performant detectors that allow the ESS
instruments to be world-leading. This foresees and encourages a high level of
collaboration and interdependence at its core, and rather than each group being
all-rounders in every technology, the further development of centres of
excellence across Europe for particular technologies and niches.Comment: 8 pages, 1 figure. Proceedings from the 23rd International Workshop
on Vertex Detectors, 15-19 September 2014, Macha Lake, The Czech Republic.
PoS(Vertex2014)02
Measurement of GEp/GMp in ep -> ep to Q2 = 5.6 GeV2
The ratio of the electric and magnetic form factors of the proton, GEp/GMp,
was measured at the Thomas Jefferson National Accelerator Facility (JLab) using
the recoil polarization technique. The ratio of the form factors is directly
proportional to the ratio of the transverse to longitudinal components of the
polarization of the recoil proton in the elastic
reaction. The new data presented in this article span the range 3.5 < Q2 < 5.6
GeV2 and are well described by a linear Q2 fit. Also, the ratio QF2p/F1p
reaches a constant value above Q2=2 GeV2.Comment: 6 pages, 4 figures Added two names to the main author lis
Recent Results and Future Plans at MAX-lab
Recent results obtained for the 4He(γ,n) reaction prior to the facility upgrade are presented. Future plans for measuring Compton scattering from the deuteron at the upgraded facility are discussed
Proton elastic form factor ratios to Q^2 = 1.5 GeV^2 by polarization transfer
This paper was published online on 20 May 2005 without several of the authors’ corrections incorporated. Equation (13) has been replaced. The captions of Figs. 16–18 have also been replaced. Typographical errors on pages 4, 6, 14, 15, 18, 19, 22, and 24 have all been corrected. The paper has been corrected as of 8 June 2005. The text is correct in the printed version of the journal
Proton elastic form factor ratios to Q = 3.5 GeV2 by polarization transfer
The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring Pt and P, the transverse and longitudinal recoil proton polarization components, respectively, for the elastic epepreaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV2. In the single-photon exchange approximation, GEp/GMp is directly proportional to Pt/P. The simultaneous measurement of Pt and P in a polarimeter reduces systematic uncertainties. The results for GEp/GMp show a systematic decrease with increasing Q2, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been reanalyzed and their systematic uncertainties have become significantly smaller than those reported previously