42 research outputs found
The Cross-Section Measurement for the \u3csup\u3e3\u3c/sup\u3eH (e, e\u27, K\u3csup\u3e+\u3c/sup\u3e) nnĪ Reaction
The small binding energy of the hypertriton leads to predictions of the non-existence of bound hypernuclei for isotriplet three-body systems such as nnĪ. However, invariant mass spectroscopy at GSI has reported events that may be interpreted as the bound nnĪ state. The nnĪ state was sought by missing-mass spectroscopy via the (e, eā²K+) reaction at Jefferson Labās experimental Hall A. The present experiment has higher sensitivity to the nnĪ-state investigation in terms of better precision by a factor of about three. The analysis shown in this article focuses on the derivation of the reaction cross-section for the 3H(Ī³*, K+)X reaction. Events that were detected in an acceptance, where a Monte Carlo simulation could reproduce the data well (ā Ęp/pā® \u3c 4%), were analyzed to minimize the systematic uncertainty. No significant structures were observed with the acceptance cuts, and the upper limits of the production cross-section of the nnĪ state were obtained to be 21 and 31nbsr-1 at the 90% confidence level when theoretical predictions of (āBĪ, Ī) = (0.25, 0.8)āMeV and (0.55, 4.7)āMeV, respectively, were assumed. The cross-section result provides valuable information for examining the existence of nnĪ
Spectroscopic Study of a Possible Ī Resonance and a Pair of (e, e\u27Kāŗ) Reaction With a Tritium Target
A mass spectroscopy experiment with a pair of nearly identical high-resolution spectrometers and a tritium target was performed in Hall A at Jefferson Lab. Utilizing the (e,eā²K+) reaction, enhancements, which may correspond to a possible Īnn resonance and a pair of Ī£NN states, were observed with an energy resolution of about 1.21 MeV (Ļ), although greater statistics are needed to make definitive identifications. An experimentally measured Īnn state may provide a unique constraint in determining the Īn interaction, for which no scattering data exist. In addition, although bound A = 3 and 4 Ī£ hypernuclei have been predicted, only an A=4 Ī£ hypernucleus (4Ī£He) was found, utilizing the (Kā,Ļā) reaction on a 4He target. The possible bound Ī£NN state is likely a Ī£ā°nn state, although this has to be confirmed by future experiments
Determination of the Argon Spectral Function From (e, e\u27p) Data
The E12-14-012 experiment, performed in Jefferson Lab Hall A, has measured the (e,eā²p) cross section in parallel kinematics using a natural argon target. Here, we report the full results of the analysis of the data set corresponding to beam energy 2.222 GeV, and spanning the missing momentum and missing energy range 15 ā² pm ā² 300āāMeV /c and 12 ā² Em ā² 80āāMeV. The reduced cross section, determined as a function of pm and Em with ā 4% accuracy, has been fitted using the results of Monte Carlo simulations involving a model spectral function and including the effects of final state interactions. The overall agreement between data and simulations turns out to be quite satisfactory (Ļ2/d. o. f. =1.9). The resulting spectral function will provide valuable new information, needed for the interpretation of neutrino interactions in liquid argon detectors
Measuring Recoiling Nucleons From the Nucleus with the Future Electron Ion Collider
Short range correlated nucleon-nucleon (NN) pairs are an important part of the nuclear ground state. They are typically studied by scattering an electron from one nucleon in the pair and detecting its spectator correlated partner (āspectator-nucleon taggingā). The Electron Ion Collider (EIC) should be able to detect these nucleons, since they are boosted to high momentum in the laboratory frame by the momentum of the ion beam. To determine the feasibility of these studies with the planned EIC detector configuration, we have simulated quasielastic scattering for two electron and ion beam energy configurations: 5 GeV eā and 41 GeV/A ions, and 10 GeV eā and 110 GeV/A ions. We show that the knocked-out and recoiling nucleons can be detected over a wide range of initial nucleon momenta. We also show that these measurements can achieve much larger momentum transfers than current fixed target experiments. By detecting both low and high initial-momentum nucleons, the planned EIC has the potential to provide the data that should allow scientists to definitively show if the European Muon Collaboration effect and short-range correlation are connected, and to improve our understanding of color transparency
Observation of Beam Spin Asymmetries in the Process ep ā e\u27ĻāŗĻā» X with CLAS 12
The observation of beam spin asymmetries in two-pion production in semi-inclusive deep inelastic scattering off an unpolarized proton target is reported. The data presented here were taken in the fall of 2018 with the CLAS12 spectrometer using a 10.6 GeV longitudinally spin-polarized electron beam delivered by CEBAF at JLab. The measured asymmetries provide the first opportunity to extract the parton distribution function e(x), which provides information about the interaction between gluons and quarks, in a collinear framework that offers cleaner access than previous measurements. The asymmetries also constitute the first ever signal sensitive to the helicity-dependent two-pion fragmentation function Gā„1. A clear sign change is observed around the Ļ mass that appears in model calculations and is indicative of the dependence of the produced pions on the helicity of the fragmenting quark
Multidimensional, High Precision Measurements of Beam Single Spin Asymmetries in Semi-Inclusive āŗ Electroproduction off Protons in the Valence Region
High precision measurements of the polarized electron beam-spin asymmetry in semi-inclusive deep inelastic scattering (SIDIS) from the proton have been performed using a 10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. We report here a high precision multidimensional study of single Ļ+ SIDIS data over a large kinematic range in Bjorken x, fractional energy, and transverse momentum of the hadron as well as photon virtualities Q2 ranging from 1ā7āāGeV2. In particular, the structure function ratio FsinĻLU/FUU has been determined, where FsinĻLU is a twist-3 quantity that can reveal novel aspects of emergent hadron mass and quark-gluon correlations within the nucleon. The dataās impact on the evolving understanding of the underlying reaction mechanisms and their kinematic variation is explored using theoretical models for the different contributing transverse momentum dependent parton distribution functions
Deep Exclusive Electroproduction of \u3ci\u3eĻ\u3c/i\u3e\u3csup\u3e0\u3c/sup\u3e at High \u3ci\u3eQ\u3c/i\u3e\u3csup\u3e2\u3c/sup\u3e in the Quark Valence Regime
We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of B (0.36, 0.48, and 0.60) and Q2 (3.1 to 8.4āāGeV2) obtained from Jefferson Lab Hall A experiment E12-06-014. The corresponding structure functions dĻT/dt+ĪµdĻL/dt, dĻTT/dt, dĻLT/dt, and dĻLTā²/dt are extracted as a function of the proton momentum transfer tātmin. The results suggest the amplitude for transversely polarized virtual photons continues to dominate the cross section throughout this kinematic range. The data are well described by calculations based on transversity generalized parton distributions coupled to a helicity flip distribution amplitude of the pion, thus providing a unique way to probe the structure of the nucleon
Measurement of Charged-Pion Production in Deep-Inelastic Scattering Off Nuclei with the CLAS Detector
Background: Energetic quarks in nuclear deep-inelastic scattering propagate through the nuclear medium. Processes that are believed to occur inside nuclei include quark energy loss through medium-stimulated gluon bremsstrahlung and intranuclear interactions of forming hadrons. More data are required to gain a more complete understanding of these effects.
Purpose: To test the theoretical models of parton transport and hadron formation, we compared their predictions for the nuclear and kinematic dependence of pion production in nuclei.
Methods: We have measured charged-pion production in semi-inclusive deep-inelastic scattering off D, C, Fe, and Pb using the CLAS detector and the CEBAF 5.014-GeV electron beam. We report results on the nuclear-to-deuterium multiplicity ratio for Ļ+ and Ļā as a function of energy transfer, four-momentum transfer, and pion energy fraction or transverse momentumāthe first three-dimensional study of its kind.
Results: The Ļ+ multiplicity ratio is found to depend strongly on the pion fractional energy z and reaches minimum values of 0.67 Ā± 0.03, 0.43 Ā± 0.02, and 0.27 Ā± 0.01 for the C, Fe, and Pb targets, respectively. The z dependencies of the multiplicity ratios for Ļ+ and Ļā are equal within uncertainties for C and Fe targets but show differences at the level of 10% for the Pb-target data. The results are qualitatively described by the GiBUU transport model, as well as with a model based on hadron absorption, but are in tension with calculations based on nuclear fragmentation functions.
Conclusions: These precise results will strongly constrain the kinematic and flavor dependence of nuclear effects in hadron production, probing an unexplored kinematic region. They will help to reveal how the nucleus reacts to a fast quark, thereby shedding light on its color structure and transport properties and on the mechanisms of the hadronization process