The proton is one of the main building blocks of all visible matter in the Universe
. Among its intrinsic properties are its electric charge, mass and spin
. These properties emerge from the complex ...dynamics of its fundamental constituents-quarks and gluons-described by the theory of quantum chromodynamics
. The electric charge and spin of protons, which are shared among the quarks, have been investigated previously using electron scattering
. An example is the highly precise measurement of the electric charge radius of the proton
. By contrast, little is known about the inner mass density of the proton, which is dominated by the energy carried by gluons. Gluons are hard to access using electron scattering because they do not carry an electromagnetic charge. Here we investigated the gravitational density of gluons using a small colour dipole, through the threshold photoproduction of the J/ψ particle. We determined the gluonic gravitational form factors of the proton
from our measurement. We used a variety of models
and determined, in all cases, a mass radius that is notably smaller than the electric charge radius. In some, but not all cases, depending on the model, the determined radius agrees well with first-principle predictions from lattice quantum chromodynamics
. This work paves the way for a deeper understanding of the salient role of gluons in providing gravitational mass to visible matter.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Incom Inc. Large Area Picosecond Photodetector (LAPPD) 38 has been tested at Jefferson Lab to identify single-photoelectron signals to assess the potential of this type of device for future ...applications in Cherenkov light detection. Single-photoelectron signals were clearly detected if a tight masking of photons impinging on the photocathode was used compared to the pixelation of the charge collection signal board.
In this work, inclusive electron scattering from nuclear targets has been measured to extract the nuclear dependence of the inelastic cross section in Hall C at the Thomas Jefferson National ...Accelerator facility. Results are presented for 2H, 3He, 4He, 9B, 12C, 63Cu and 197Au at an incident electron beam energy of 5.77 GeV for a range of momentum transfer from Q2 = 2 to 7 (GeV/c)2. These data improve the precision of the existing measurements of the EMC effect in the nuclear targets at large x, and allow for more detailed examinations of the A dependence of the EMC effect.
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The visible world is founded on the proton, the only composite building block of matter that is stable in nature. Consequently, understanding the formation of matter relies on explaining the dynamics ...and the properties of the proton's bound state. A fundamental property of the proton involves the response of the system to an external electromagnetic field. It is characterized by the electromagnetic polarizabilities
that describe how easily the charge and magnetization distributions inside the system are distorted by the electromagnetic field. Moreover, the generalized polarizabilities
map out the resulting deformation of the densities in a proton subject to an electromagnetic field. They disclose essential information about the underlying system dynamics and provide a key for decoding the proton structure in terms of the theory of the strong interaction that binds its elementary quark and gluon constituents. Of particular interest is a puzzle in the electric generalized polarizability of the proton that remains unresolved for two decades
. Here we report measurements of the proton's electromagnetic generalized polarizabilities at low four-momentum transfer squared. We show evidence of an anomaly to the behaviour of the proton's electric generalized polarizability that contradicts the predictions of nuclear theory and derive its signature in the spatial distribution of the induced polarization in the proton. The reported measurements suggest the presence of a new, not-yet-understood dynamical mechanism in the proton and present notable challenges to the nuclear theory.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
We measure ^{2}H(e,e^{'}p)n cross sections at 4-momentum transfers of Q^{2}=4.5±0.5 (GeV/c)^{2} over a range of neutron recoil momenta p_{r}, reaching up to ∼1.0 GeV/c. We obtain data at fixed ...neutron recoil angles θ_{nq}=35°, 45°, and 75° with respect to the 3-momentum transfer qover →. The new data agree well with previous data, which reached p_{r}∼500 MeV/c. At θ_{nq}=35° and 45°, final state interactions, meson exchange currents, and isobar currents are suppressed and the plane wave impulse approximation provides the dominant cross section contribution. We compare the new data to recent theoretical calculations, where we observe a significant discrepancy for recoil momenta p_{r}>700 MeV/c.
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Abstract
The PICOSEC Micromegas (MM) detector is a precise timing gaseous detector consisting of
a Cherenkov radiator combined with a photocathode and a MM amplifying structure. A 100-channel
PICOSEC ...MM prototype with 10 × 10 cm
2
active area equipped with a Cesium Iodide (CsI)
photocathode demonstrated a time resolution below
σ
= 18 ps. The objective of this work
is to improve the PICOSEC MM detector robustness aspects, i.e. integration of resistive MM and
carbon-based photocathodes, while maintaining good time resolution. The PICOSEC MM prototypes
have been tested in laboratory conditions and successfully characterised with 150 GeV/c muon
beams at the CERN SPS H4 beam line. The excellent timing performance below
σ
= 20 ps for
an individual pad obtained with the 10 × 10 cm
2
area resistive PICOSEC MM of
20 MΩ/□ showed no significant time resolution degradation as a result of adding a
resistive layer. A single-pad prototype equipped with a 12 nm thick Boron Carbide (B
4
C)
photocathode presented a time resolution below
σ
= 35 ps, opening up new possibilities for
detectors with robust photocathodes. The results made the concept more suitable for the
experiments in need of robust detectors with good time resolution.
We apply a recently developed technique to extract for the first time the neutron F(2)(n) structure function from inclusive proton and deuteron data in the nucleon resonance region, and test the ...validity of quark-hadron duality in the neutron. We establish the accuracy of duality in the low-lying neutron resonance regions over a range of Q(2), and compare with the corresponding results on the proton and with theoretical expectations. The confirmation of duality in both the neutron and proton opens the possibility of using resonance region data to constrain parton distributions at large x.
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We have measured the nuclear transparency of the A(e,e'pi+) process in 2H, 12C, 27Al, 63Cu, and 197Au targets. These measurements were performed at the Jefferson Laboratory over a four momentum ...transfer squared range Q2=1.1 to 4.7 (GeV/c)2. The nuclear transparency was extracted as the super-ratio of (sigmaA/sigmaH) from data to a model of pion-electroproduction from nuclei without pi-N final-state interactions. The Q2 and atomic number dependence of the nuclear transparency both show deviations from traditional nuclear physics expectations and are consistent with calculations that include the quantum chromodynamical phenomenon of color transparency.
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We studied the single-photoelectron detection capabilities of a multianode photomultiplier tube H8500C-03 and its performance in high magnetic field. Our results show that the device can readily ...resolve signals at the single photoelectron level making it suitable for photon detection in both threshold and ring imaging Cherenkov detectors. We also found that a large longitudinal magnetic field, up to 300 Gauss, induces a change in the relative output of at most 55% for an edge pixel, and of at most 15% for a central pixel. The H8500C-03 signal loss in transverse magnetic fields it is significantly more pronounced than for the longitudinal case. Our studies of single photoelectron reduction in magnetic fields point to the field induced misfocusing of the photoelectron extracted from the photocathode as primary cause of signal loss. With appropriate shielding this PMT could function in high magnetic held environments.
We present new data on electron scattering from a range of nuclei taken in Hall C at Jefferson Lab. For heavy nuclei, we observe a rapid falloff in the cross section for $x>1$, which is sensitive to ...short range contributions to the nuclear wave-function, and in deep inelastic scattering corresponds to probing extremely high momentum quarks. This result agrees with higher energy muon scattering measurements, but is in sharp contrast to neutrino scattering measurements which suggested a dramatic enhancement in the distribution of the `super-fast' quarks probed at x>1. The falloff at x>1 is noticeably stronger in ^2H and ^3He, but nearly identical for all heavier nuclei.
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