The OLYMPUS experiment Milner, R.; Hasell, D.K.; Kohl, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2014, Letnik:
741
Journal Article
Recenzirano
The OLYMPUS experiment was designed to measure the ratio between the positron–proton and electron–proton elastic scattering cross-sections, with the goal of determining the contribution of two-photon ...exchange to the elastic cross-section. Two-photon exchange might resolve the discrepancy between measurements of the proton form factor ratio, μpGEp/GMp, made using polarization techniques and those made in unpolarized experiments. OLYMPUS operated on the DORIS storage ring at DESY, alternating between 2.01GeV electron and positron beams incident on an internal hydrogen gas target. The experiment used a toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight detectors to measure rates for elastic scattering over the polar angular range of approximately 25°–75°. Symmetric Møller/Bhabha calorimeters at 1.29° and telescopes of GEM and MWPC detectors at 12° served as luminosity monitors. A total luminosity of approximately 4.5fb−1 was collected over two running periods in 2012. This paper provides details on the accelerator, target, detectors, and operation of the experiment.
Nab: Measurement principles, apparatus and uncertainties Počanić, Dinko; Alarcon, R.; Alonzi, L.P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2009, Letnik:
611, Številka:
2
Journal Article
Recenzirano
The Nab collaboration will perform a precise measurement of
a, the electron–neutrino correlation parameter, and
b, the Fierz interference term in neutron beta decay, in the Fundamental Neutron ...Physics Beamline at the SNS, using a novel electric/magnetic field spectrometer and detector design. The experiment is aiming at the
10
-
3
accuracy level in
Δ
a
/
a
, and will provide an independent measurement of
λ
=
G
A
/
G
V
, the ratio of axial-vector to vector coupling constants of the nucleon. Nab also plans to perform the first ever measurement of
b in neutron decay, which will provide an independent limit on the tensor weak coupling.
Synthetic photocontrolled proteins could be powerful tools for probing cellular chemistry. Several previous attempts to produce such systems by incorporating photoisomerizable chromophores into ...biomolecules have led to photocontrol but with incomplete reversibility, where the chromophore becomes trapped in one photoisomeric state. We report here the design of a modified GCN4-bZIP DNA-binding protein with an azobenzene chromophore introduced between Cys residues at positions 262 and 269 (S262C, N269C) within the zipper domain. As predicted, the trans form of the chromophore destabilizes the helical structure of the coiled-coil region of GCN4-bZIP, leading to diminished DNA binding relative to wild type. Trans-to-cis photoisomerization of the chromophore increases helical content and substantially enhances DNA binding. The system is observed to be readily reversible; thermal relaxation of the chromophore to the trans state and concomitant dissociation of the protein-DNA complex occurs with tau(1/2) approximately 10 min at 37 degrees C. It appears that conformational dynamics in the zipper domain make the transition state for isomerization readily available so that retention of reversible switching is observed.
The Nab experiment will measure the correlation a between the momenta of the beta particle and antineutrino in neutron decay as well as the Fierz term b which distorts the beta spectrum.
Status of the NPDGamma experiment Fry, J.; Alarcon, R.; Allen, R. ...
Hyperfine interactions,
11/2017, Letnik:
238, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The NPDGamma experiment measures the parity-violating (PV) gamma asymmetry from polarized cold neutrons captured on protons at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory ...(ORNL). The (PV) neutron spin asymmetry
A
γ
of photons from polarized cold neutron capture on protons is proportional to the Δ
I
=1 long range weak meson coupling
h
π
1
between nucleons in the hadronic weak interaction (HWI). Liquid para-hydrogen production data taking concluded in April 2014 and once the background aluminum asymmetry measurements are complete, the PV asymmetry
A
γ
can be extracted. Preliminary results of the analysis of
A
γ
are presented.
Femto-second pump-probe and micro-Raman spectroscopy (RS) measurements have been made to identify optical phonons in Ge2Sb2Te5/InAs(111) and an InAs(111) substrate. A theory of transient stimulated ...Raman scattering (TSRS) incorporating the Raman tensor predicts which phonon modes may be observed in transient reflectance (R) and anisotropic reflectance (AR) pump-probe measurements, and how their amplitudes depend upon angles φ and θ that describe the orientation of the pump and probe beam electric fields within the sample plane. AR measurements of an InAs(111) substrate revealed the 6.5 THz T2 transverse optical phonon with amplitude proportional to sin(2(θ−φ)), as expected for both TSRS and the specular optical Kerr effect (SOKE), confirming that TSRS and SOKE are equivalent descriptions of the same phenomenon. The AR responses of Ge2Sb2Te5/InAs(111) revealed a single coherent optical phonon (COP) mode at about 3.4 THz with sin(2(θ−φ)) amplitude variation that confirms the T2-like character of the mode and hence the underlying cubic structure of the epilayer. This mode was also observed in the R measurement for one sample, with amplitude independent of φ and θ as predicted by TSRS theory. Both R and AR signals were heavily damped, which is attributed to dephasing of T2x, T2y and T2z modes that become non-degenerate due to structural distortions. RS measurements revealed three modes for Ge2Sb2Te5/InAs(111) and three modes for InAs(111). Taken together the TSRS and RS measurements provide rich information about optical phonons in the phase change material Ge2Sb2Te5 and the InAs(111) surface.
•Coherent optical phonons are observed in Ge2Sb2Te5/InAs(111) thin films.•Coherent optical phonons are excited by transient stimulated Raman scattering.•Optical polarisation dependence of coherent phonons confirms cubic crystal structure.•Damping of phonon oscillations is due to dephasing of 3 nearly degenerate modes.
PDF
