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.
We report the first observation of the parity-violating gamma-ray asymmetry A_{γ}^{np} in neutron-proton capture using polarized cold neutrons incident on a liquid parahydrogen target at the ...Spallation Neutron Source at Oak Ridge National Laboratory. A_{γ}^{np} isolates the ΔI=1, ^{3}S_{1}→^{3}P_{1} component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to a single coupling constant in either the DDH meson exchange model or pionless effective field theory. We measured A_{γ}^{np}=-3.0±1.4(stat)±0.2(syst)×10^{-8}, which implies a DDH weak πNN coupling of h_{π}^{1}=2.6±1.2(stat)±0.2(syst)×10^{-7} and a pionless EFT constant of C^{^{3}S_{1}→^{3}P_{1}}/C_{0}=-7.4±3.5(stat)±0.5(syst)×10^{-11} MeV^{-1}. We describe the experiment, data analysis, systematic uncertainties, and implications of the result.
We present azimuthal angular correlations between charged hadrons and energy deposited in calorimeter towers in central d+Au and minimum bias p+p collisions at sqrts_{NN}=200 GeV. The charged hadron ...is measured at midrapidity |η|<0.35, and the energy is measured at large rapidity (-3.7<η<-3.1, Au-going direction). An enhanced near-side angular correlation across |Δη|>2.75 is observed in d+Au collisions. Using the event plane method applied to the Au-going energy distribution, we extract the anisotropy strength v_{2} for inclusive charged hadrons at midrapidity up to p_{T}=4.5 GeV/c. We also present the measurement of v_{2} for identified π^{±} and (anti)protons in central d+Au collisions, and observe a mass-ordering pattern similar to that seen in heavy-ion collisions. These results are compared with viscous hydrodynamic calculations and measurements from p+Pb at sqrts_{NN}=5.02 TeV. The magnitude of the mass ordering in d+Au is found to be smaller than that in p+Pb collisions, which may indicate smaller radial flow in lower energy d+Au collisions.
Performance of prototypes for the ALICE electromagnetic calorimeter Allen, J.; Awes, T.; Badalá, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2010, Letnik:
615, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The performance of prototypes for the ALICE electromagnetic sampling calorimeter has been studied in test beam measurements at FNAL and CERN. A
4
×
4
array of final design modules showed an energy ...resolution of about
11
%
/
E
(
GeV
)
⊕
1.7
%
with a uniformity of the response to electrons of 1% and a good linearity in the energy range from 10 to 100
GeV. The electromagnetic shower position resolution was found to be described by
1.5
mm
⊕
5.3
mm
/
E
(
GeV
)
. For an electron identification efficiency of 90% a hadron rejection factor of
>
600
was obtained.
Charged-pion-interferometry measurements were made with respect to the second- and third-order event plane for Au+Au collisions at sqrts_{NN}=200 GeV. A strong azimuthal-angle dependence of the ...extracted Gaussian-source radii was observed with respect to both the second- and third-order event planes. The results for the second-order dependence indicate that the initial eccentricity is reduced during the medium evolution, which is consistent with previous results. In contrast, the results for the third-order dependence indicate that the initial triangular shape is significantly reduced and potentially reversed by the end of the medium evolution, and that the third-order oscillations are largely dominated by the dynamical effects from triangular flow.
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