35 research outputs found
Impact Shocking of a Zircon-Sanidine Mixture and Investigations of Pb Mobility
The purpose of this project is to explore the mobility, mixing, and possible clumping of Pb isotopes during laboratory impact shock experiments. Impact events are a common planetary occurrence and their effect on istotope systematics and subsequent geochronology is not fully understood. By artificially shocking mixtures of zircon and sanidine and investigating the sample products, it may be possible to understand if and how Pb is mobilized during impact shock. Isotopes of Pb are the final daughter products of the decay chains of 238U, 235U and 232Th and therefore understanding how mobile the daughter product is during impact events could have consequences for dating impact events. These investigations will also reveal if Pb isotopes can be mixed between mineral
Impact Shocking of a Zircon-Sanidine Mixture and Investigations of Pb Mobility
The purpose of this project is to explore the mobility, mixing, and possible clumping of Pb isotopes during laboratory impact shock experiments. Impact events are a common planetary occurrence and their effect on istotope systematics and subsequent geochronology is not fully understood. By artificially shocking mixtures of zircon and sanidine and investigating the sample products, it may be possible to understand if and how Pb is mobilized during impact shock. Isotopes of Pb are the final daughter products of the decay chains of 238U, 235U and 232Th and therefore understanding how mobile the daughter product is during impact events could have consequences for dating impact events. These investigations will also reveal if Pb isotopes can be mixed between minerals
The HPS electromagnetic calorimeter
The Heavy Photon Search experiment (HPS) is searching for a new gauge boson, the so-called “heavy photon.” Through its kinetic mixing with the Standard Model photon, this particle could decay into an electron-positron pair. It would then be detectable as a narrow peak in the invariant mass spectrum of such pairs, or, depending on its lifetime, by a decay downstream of the production target. The HPS experiment is installed in Hall-B of Jefferson Lab. This article presents the design and performance of one of the two detectors of the experiment, the electromagnetic calorimeter, during the runs performed in 2015–2016. The calorimeter's main purpose is to provide a fast trigger and reduce the copious background from electromagnetic processes through matching with a tracking detector. The detector is a homogeneous calorimeter, made of 442 lead-tungstate (PbWO4) scintillating crystals, each read out by an avalanche photodiode coupled to a custom trans-impedance amplifier
A Direct Measurement of Hard Two-Photon Exchange with Electrons and Positrons at CLAS12
One of the most surprising discoveries made at Jefferson Lab has been the
discrepancy in the determinations of the proton's form factor ratio between unpolarized cross section measurements and the
polarization transfer technique. Over two decades later, the discrepancy not
only persists but has been confirmed at higher momentum transfers now
accessible in the 12-GeV era. The leading hypothesis for the cause of this
discrepancy, a non-negligible contribution from hard two-photon exchange, has
neither been conclusively proven or disproven. This state of uncertainty not
only clouds our knowledge of one-dimensional nucleon structure but also poses a
major concern for our field's efforts to map out the three-dimensional nuclear
structure. A better understanding of multi-photon exchange over a wide phase
space is needed. We propose making comprehensive measurements of two-photon
exchange over a wide range in momentum transfer and scattering angle using the
CLAS12 detector. Specifically, we will measure the ratio of positron-proton to
electron-proton elastic scattering cross sections, using the proposed positron
beam upgrade for CEBAF. The experiment will use 2.2, 4.4, and 6.6 GeV lepton
beams incident on the standard CLAS12 unpolarized hydrogen target. Data will be
collected by the CLAS12 detector in its standard configuration, except for a
modified trigger to allow the recording of events with beam leptons scattered
into the CLAS12 central detector. The sign of the beam charge, as well as the
polarity of the CLAS12 solenoid and toroid, will be reversed several times in
order to suppress systematics associated with local detector efficiency and
time-dependent detector performance. The proposed high-precision determination
of two-photon effects will be...Comment: Experimental Proposal E12+23-008 submitted to Jefferson Lab PAC 51,
34 pages, 18 figure
Search for axion-like particles through nuclear Primakoff production using the GlueX detector
We report on the results of the first search for the production of axion-like
particles (ALP) via Primakoff production on nuclear targets using the GlueX
detector. This search uses an integrated luminosity of 100
pbnucleon on a C target, and explores the mass region of 200
< < 450 MeV via the decay . This mass range is
between the and masses, which enables the use of the measured
production rate to obtain absolute bounds on the ALP production with
reduced sensitivity to experimental luminosity and detection efficiency. We
find no evidence for an ALP, consistent with previous searches in the quoted
mass range, and present limits on the coupling on the scale of (1 TeV). We
further find that the ALP production limit we obtain is hindered by the peaking
structure of the non-target-related dominant background in GlueX, which we
treat by using data on He to estimate and subtract these backgrounds. We
comment on how this search can be improved in a future higher-statistics
dedicated measurement
First Measurement of the EMC Effect in B and B
The nuclear dependence of the inclusive inelastic electron scattering cross
section (the EMC effect) has been measured for the first time in B and
B. Previous measurements of the EMC effect in nuclei showed
an unexpected nuclear dependence; B and B were measured to
explore the EMC effect in this region in more detail. Results are presented for
Be, B, B, and C at an incident beam energy of
10.6~GeV. The EMC effect in the boron isotopes was found to be similar to that
for Be and C, yielding almost no nuclear dependence in the EMC
effect in the range . This represents important, new data supporting
the hypothesis that the EMC effect depends primarily on the local nuclear
environment due to the cluster structure of these nuclei.Comment: Submitted to PR
Revealing the short-range structure of the "mirror nuclei" H and He
When protons and neutrons (nucleons) are bound into atomic nuclei, they are
close enough together to feel significant attraction, or repulsion, from the
strong, short-distance part of the nucleon-nucleon interaction. These strong
interactions lead to hard collisions between nucleons, generating pairs of
highly-energetic nucleons referred to as short-range correlations (SRCs). SRCs
are an important but relatively poorly understood part of nuclear structure and
mapping out the strength and isospin structure (neutron-proton vs proton-proton
pairs) of these virtual excitations is thus critical input for modeling a range
of nuclear, particle, and astrophysics measurements. Hitherto measurements used
two-nucleon knockout or ``triple-coincidence'' reactions to measure the
relative contribution of np- and pp-SRCs by knocking out a proton from the SRC
and detecting its partner nucleon (proton or neutron). These measurementsshow
that SRCs are almost exclusively np pairs, but had limited statistics and
required large model-dependent final-state interaction (FSI) corrections. We
report on the first measurement using inclusive scattering from the mirror
nuclei H and He to extract the np/pp ratio of SRCs in the A=3 system.
We obtain a measure of the np/pp SRC ratio that is an order of magnitude more
precise than previous experiments, and find a dramatic deviation from the
near-total np dominance observed in heavy nuclei. This result implies an
unexpected structure in the high-momentum wavefunction for He and H.
Understanding these results will improve our understanding of the short-range
part of the N-N interaction
Strong Interaction Physics at the Luminosity Frontier with 22 GeV Electrons at Jefferson Lab
This document presents the initial scientific case for upgrading the
Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab)
to 22 GeV. It is the result of a community effort, incorporating insights from
a series of workshops conducted between March 2022 and April 2023. With a track
record of over 25 years in delivering the world's most intense and precise
multi-GeV electron beams, CEBAF's potential for a higher energy upgrade
presents a unique opportunity for an innovative nuclear physics program, which
seamlessly integrates a rich historical background with a promising future. The
proposed physics program encompass a diverse range of investigations centered
around the nonperturbative dynamics inherent in hadron structure and the
exploration of strongly interacting systems. It builds upon the exceptional
capabilities of CEBAF in high-luminosity operations, the availability of
existing or planned Hall equipment, and recent advancements in accelerator
technology. The proposed program cover various scientific topics, including
Hadron Spectroscopy, Partonic Structure and Spin, Hadronization and Transverse
Momentum, Spatial Structure, Mechanical Properties, Form Factors and Emergent
Hadron Mass, Hadron-Quark Transition, and Nuclear Dynamics at Extreme
Conditions, as well as QCD Confinement and Fundamental Symmetries. Each topic
highlights the key measurements achievable at a 22 GeV CEBAF accelerator.
Furthermore, this document outlines the significant physics outcomes and unique
aspects of these programs that distinguish them from other existing or planned
facilities. In summary, this document provides an exciting rationale for the
energy upgrade of CEBAF to 22 GeV, outlining the transformative scientific
potential that lies within reach, and the remarkable opportunities it offers
for advancing our understanding of hadron physics and related fundamental
phenomena.Comment: Updates to the list of authors; Preprint number changed from theory
to experiment; Updates to sections 4 and 6, including additional figure