Short-range correlated (SRC) nucleon pairs are a vital part of the nucleus, accounting for almost all nucleons with momentum greater than the Fermi momentum (k_{F}). A fundamental characteristic of ...SRC pairs is having large relative momenta as compared to k_{F}, and smaller center of mass (c.m.) which indicates a small separation distance between the nucleons in the pair. Determining the c.m. momentum distribution of SRC pairs is essential for understanding their formation process. We report here on the extraction of the c.m. motion of proton-proton (pp) SRC pairs in carbon and, for the first time in heavier and ansymetric nuclei: aluminum, iron, and lead, from measurements of the A(e,e^{'}pp) reaction. We find that the pair c.m. motion for these nuclei can be described by a three-dimensional Gaussian with a narrow width ranging from 140 to 170 MeV/c, approximately consistent with the sum of two mean-field nucleon momenta. Comparison with calculations appears to show that the SRC pairs are formed from mean-field nucleons in specific quantum states.
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The Heavy Photon Search experiment took its first data in a 2015 engineering run using a 1.056 GeV, 50 nA electron beam provided by CEBAF at the Thomas Jefferson National Accelerator Facility, ...searching for a prompt, electroproduced dark photon with a mass between 19 and 81 MeV/c2. A search for a resonance in the e+e− invariant mass distribution, using 1.7 days (1170 nb−1) of data, showed no evidence of dark photon decays above the large QED background, confirming earlier searches and demonstrating the full functionality of the experiment. Upper limits on the square of the coupling of the dark photon to the standard model photon are set at the level of 6×10−6. Future runs with higher luminosity will explore new territory.
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A determination of the spin and parity of the $\Lambda(1405)$ is presented using photoproduction data from the CLAS detector at Jefferson Lab. The reaction $\gamma + p \to K^+ + \Lambda(1405)$ is ...analyzed in the decay channel $\Lambda(1405) \to \Sigma^+ + \pi^-$, where the decay distribution to $\Sigma^+ \pi^-$ and the variation of the $\Sigma^+$ polarization with respect to the $\Lambda(1405)$ polarization direction determines the parity. The $\Lambda(1405)$ is produced, in the energy range $2.55 < W < 2.85$ GeV and for $0.6 < \cos \theta_{K^+} < 0.9$, with polarization $P = 0.45 \pm 0.02 (\text{stat}) \pm 0.07 (\text{syst})$. The analysis shows that the decays are in $S$ wave, with the $\Sigma^+$ polarized such that the $\Lambda(1405)$ has spin-parity $J^P = 1/2^-$, as expected by most theories.
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A new radial time projection chamber based on Gas Electron Multiplier amplification layers was developed for the BONuS12 experiment in Hall B at Jefferson Lab. This device represents a significant ...evolutionary development over similar devices constructed for previous experiments, including cylindrical amplification layers constructed from single continuous GEM foils with less than 1% dead area. Particular attention had been paid to producing excellent geometric uniformity of all electrodes, including the very thin metalized polyester film of the cylindrical cathode. This manuscript describes the design, construction, and performance of this new detector.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The heavy photon search experiment (HPS) at the Thomas Jefferson National Accelerator Facility searches for electroproduced dark photons. We report results from the 2016 engineering run consisting of ...10 608 nb–1 of data for both the prompt and displaced vertex searches. A search for a prompt resonance in the e+e– invariant mass distribution between 39 and 179 MeV showed no evidence of dark photons above the large QED background, limiting the coupling of ε2≳10–5, in agreement with previous searches. The search for displaced vertices showed no evidence of excess signal over background in the masses between 60 and 150 MeV, but had insufficient luminosity to limit canonical heavy photon production. This is the first displaced vertex search result published by HPS. HPS has taken high-luminosity data runs in 2019 and 2021 that will explore new dark photon phase space.
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Radiative corrections to elastic scattering represent an important part of the interpretation of electron-induced nuclear reactions at small energy transfers, where they represent a dominant part of ...the background. Here we present and validate a new event generator for simulating QED radiative processes in electron-carbon scattering that exactly calculates the coherent sum of the Bethe-Heitler amplitudes for the leading diagrams. We demonstrate that the generator describes the shape of the radiative tail of an elastic peak with a precision better than
10
%
over the whole energy range of the scattered electrons and can thus be reliably employed in the analyses of electron scattering experiments for more precise extraction of inelastic cross-sections.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The exclusive reaction γp→pK+K− was studied in the photon energy range 3.0–3.8 GeV and momentum transfer range 0.6<−t<1.3 GeV2. Data were collected with the CLAS detector at the Thomas Jefferson ...National Accelerator Facility. In this kinematic range the integrated luminosity was approximately 20 pb−1. The reaction was isolated by detecting the K+ and the proton in CLAS, and reconstructing the K− via the missing-mass technique. Moments of the dikaon decay angular distributions were extracted from the experimental data. Besides the dominant contribution of the ϕ meson in the P wave, evidence for S−P interference was found. The differential production cross sections dσ/dt for individual waves in the mass range of the ϕ resonance were extracted and compared to predictions of a Regge-inspired model. This is the first time the t-dependent cross section of the S-wave contribution to the elastic K+K− photoproduction has been measured.
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Department of Pharmacology and Physiology, The George Washington University, Washington, DC
Submitted 20 April 2007;
accepted in final form 13 August 2007
Prenatal nicotine exposure alters the ...cardiorespiratory network responses to hypoxia/hypercapnia; however the mechanism(s) responsible for these cardiorespiratory network responses and their alteration by prenatal nicotine exposure are unknown. We used an in vitro medullary slice that allows simultaneous examination of rhythmic respiratory-related activity and excitatory synaptic neurotransmission to cardioinhibitory vagal neurons (CVNs). Respiratory related increases in glutamatergic neurotransmission only occurred on recovery from hypoxia/hypercapnia in unexposed animals. These responses were not altered by nicotinic antagonists but were mediated in part by activation of P2 purinergic receptors. Prenatal nicotine exposure transformed central cardiorespiratory responses to hypoxia/hypercapnia; CVNs received a respiratory related glutamatergic neurotransmission during periods of hypoxia and hypercapnia, whereas increases in glutamatergic neurotransmission during recovery were absent. The excitatory neurotransmission to CVNs during hypoxia/hypercapnia in prenatal nicotine-exposed animals were wholly dependent on nicotinic receptor activation. In the presence of nicotinic antagonists, the responses in prenatal nicotine animals reverted to the pattern of responses in unexposed animals in which an increase in glutamatergic neurotransmission occurred not during but only on recovery from hypoxia/hypercapnia, and this recruited excitatory pathway was blocked by P2 receptor antagonists. These data identify a new functional role for purinergic receptors in the cardiorespiratory responses to hypoxia/hypercapnia and their role in occluding nicotinic receptor activation with prenatal nicotine exposure.
Address for reprint requests and other correspondence: D. Mendelowitz, Dept. of Pharmacology and Physiology, The George Washington University, 2300 Eye St. NW, Washington, DC 20037 (E-mail: dmendel{at}gwu.edu )
We report on a new experimental method based on initial-state radiation (ISR) in e–p scattering, which exploits the radiative tail of the elastic peak to study the properties of electromagnetic ...processes and to extract the proton charge form factor (GEp) at extremely small Q2. The ISR technique was implemented in an experiment at the three-spectrometer facility of the Mainz Microtron (MAMI). This led to a precise validation of radiative corrections far away from elastic line and provided first measurements of GEp for 0.001≤Q2≤0.004(GeV/c)2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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