The neutron is a cornerstone in our depiction of the visible universe. Despite the neutron zero-net electric charge, the asymmetric distribution of the positively- (up) and negatively-charged (down) ...quarks, a result of the complex quark-gluon dynamics, lead to a negative value for its squared charge radius, Formula: see text. The precise measurement of the neutron's charge radius thus emerges as an essential part of unraveling its structure. Here we report on a Formula: see text measurement, based on the extraction of the neutron electric form factor, Formula: see text, at low four-momentum transfer squared (Q
) by exploiting the long known connection between the N → Δ quadrupole transitions and the neutron electric form factor. Our result, Formula: see text, addresses long standing unresolved discrepancies in the Formula: see text determination. The dynamics of the strong nuclear force can be viewed through the precise picture of the neutron's constituent distributions that result into the non-zero Formula: see text value.
We have determined the proton and the neutron charge radii from a global analysis of the proton and the neutron elastic form factors, after first performing a flavor decomposition of these form ...factors under charge symmetry in the light cone frame formulation. We then extracted the transverse mean-square radii of the flavor dependent quark distributions. In turn, these are related in a model-independent way to the proton and neutron charge radii but allow us to take into account motion effects of the recoiling nucleon for data at finite but high momentum transfer. In the proton case we find
⟨
r
p
⟩
=
0.852
±
0
.
002
(
stat
.
)
±
0
.
009
(
syst
.
)
(
fm
)
, consistent with the proton charge radius obtained from muonic hydrogen spectroscopy
1
,
2
. The current method improves on the precision of the
⟨
r
p
⟩
extraction based on the form factor measurements. Furthermore, we find no discrepancy in the
⟨
r
p
⟩
determination among the different electron scattering measurements, all of which, utilizing the current method of extraction, result in a value that is consistent with the smallest
⟨
r
p
⟩
extraction from the electron scattering measurements
3
. Concerning the neutron case, past results relied solely on the neutron-electron scattering length measurements, which suffer from an underestimation of underlying systematic uncertainties inherent to the extraction technique. Utilizing the present method we have performed the first extraction of the neutron charge radius based on nucleon form factor data, and we find
⟨
r
n
2
⟩
=
-
0.122
±
0
.
004
(
stat
.
)
±
0
.
010
(
syst
.
)
(
fm
2
)
.
Superconducting nanowire single photon detectors are capable of single-photon detection across a large spectral range with near unity detection efficiency, picosecond timing jitter, and sub-10 μm ...position resolution, at rates as high as 109 counts/s. In an effort to bring this technology into nuclear physics experiments, we fabricate niobium nitride (NbN) nanowire detectors using ion beam assisted sputtering and test their performance in strong magnetic fields. We demonstrate that these devices are capable of detection of 400 nm wavelength photons with saturated internal quantum efficiency at temperatures of 3 K and in magnetic fields of up to 5 T at high count rates and with nearly zero dark counts.
Enhanced UV light detection using a p-terphenyl wavelength shifter Joosten, S.; Kaczanowicz, E.; Ungaro, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2017, Volume:
870, Issue:
C
Journal Article
Peer reviewed
Open access
UV-glass photomultiplier tubes (PMTs) have poor photon detection efficiency for wavelengths below 300 nm due to the opaqueness of the window material. Costly quartz PMTs could be used to enhance the ...efficiency below 300 nm. A less expensive solution that dramatically improves this efficiency is the application of a thin film of a p-terphenyl (PT) wavelength shifter on UV-glass PMTs. This improvement was quantified for Photonis XP4500B PMTs for wavelengths between 200 nm and 400 nm. The gain factor ranges up to 5.4±0.5 at a wavelength of 215 nm, with a material load of 110±10μg∕cm2 (894 nm). The wavelength shifter was found to be fully transparent for wavelengths greater than 300 nm. The resulting gain in detection efficiency, when used in a typical C̆erenkov counter, was estimated to be of the order of 40%. Consistent coating quality was assured by a rapid gain testing procedure using narrow-band UV LEDs. Based on these results, 200 Photonis XP4500B PMTs were treated with PT for the upgraded low-threshold C̆erenkov counter (LTCC) to be used in the CEBAF Large Acceptance Spectrometer upgraded detector (CLAS12) at the Thomas Jefferson National Accelerator Facility.
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