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Register a new userStudying Short-Range Correlations with Real Photon Beams at GlueX
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The past few years has seen tremendous progress in our understanding of short-range correlated (SRC) pairing of nucleons within nuclei, much of it coming from electron scattering experiments leading to the break-up of an SRC pair. The interpretation of these experiments rests on assumptions about the mechanism of the reaction. These assumptions can be directly tested by studying SRC pairs using alternate probes, such as real photons. We propose a 30-day experiment using the Hall D photon beam, nuclear targets, and the GlueX detector in its standard configuration to study short-range correlations with photon-induced reactions. Several different reaction channels are possible, and we project sensitivity in most channels to equal or exceed the 6 GeV-era SRC experiments from Halls A and B. The proposed experiment will therefore decisively test the phenomena of np dominance, the short-distance NN interaction, and reaction theory, while also providing new insight into bound nucleon structure and the onset of color transparency.
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The experiment, E08-014, in Hall-A at Jefferson Lab aims to study the short-range correlations (SRC) which are necessary to explain the nuclear strength absent in the mean field theory. The cross sections for $mathrm{^{2}H}$, $mathrm{^{3}He}$, $mathrm{^{4}He}$, $mathrm{^{12}C}$, $mathrm{^{40}Ca}$ and $mathrm{^{48}Ca}$, were measured via inclusive quasielastic electron scattering from these nuclei in a $mathrm{Q^{2}}$ range between 0.8 and $mathrm{2.8~(GeV/c)^{2}}$ for $x_{bj}>1$. The cross section ratios of heavy nuclei to $mathrm{^{2}H}$ were extracted to study two-nucleon SRC for $1<x_{bj}<2$, while the study of three-nucleon SRC was carried out from the cross section ratios of heavy nuclei to $mathrm{^{3}He}$ for $x_{bj}ge 2$. Meanwhile, the isospin dependence in SRCs has also been examined through the cross section ratio of $mathrm{^{48}Ca}$ and $mathrm{^{40}Ca}$.
A future Electron-Ion Collider (EIC) will deliver luminosities of $10^{33} - 10^{34}$ cm$^{-2}$s$^{-1}$ for collisions of polarized electrons and protons and heavy ions over a wide range of center-of-mass energies (40 $mathrm{GeV}$ to 145 $mathrm{GeV}$). One of its promising physics programs is to study the partonic structure of quasi-real photons. Measuring di-jet in photoproduction events, one can effectively access the underlying parton dynamics of the photons through the selection of the resolved photon processes. In this paper, we discuss the feasibility of tagging resolved photon processes and measuring the di-jet cross section as a function of jet transverse momentum in ranges of $x_{gamma}^{rec}$ at an EIC. These studies show that parton distributions in the photon can be extracted at an EIC.
We present new data probing short-range correlations (SRCs) in nuclei through the measurement of electron scattering off high-momentum nucleons in nuclei. The inclusive 4He/3He cross section ratio is observed to be both x and Q2 independent for 1.5 < x < 2, confirming the dominance of two- nucleon (2N) short-range correlations (SRCs). For x > 2, our data do not support a previous claim of three-nucleon (3N) correlation dominance. While contributions beyond those from stationary 2N- SRCs are observed, our data show that isolating 3N-SRCs is more complicated than for 2N-SRCs.
We present an overview of Short-Range Correlations (SRC) studies using the inclusive measurement of the electron scattering off nuclei. A brief introduction of the origin of the SRC is given, followed by the survey of the two-nucleon SRC (2N-SRC) study and its interesting connection to the EMC effect. A discussion of the three-nucleon SRC study (3N-SRC) measured by the Jefferson Labs Hall B and Hall C experiments which showed contradictory results is given and, most importantly, we report a new result from the Hall A E08-014 experiment which was dedicated on studying 3N-SRC. Our high precision 4He/3He cross section ratios at the x > 2 region do not show a 3N-SRC plateau as predicted by the naive SRC model. To further investigate the 3N-SRC as well as the Isospin effect of the SRC, we have designed several approved experiments in Hall A and in Hall C, including the Tritium experiments using the mirror nuclei (3H and 3He) which are currently running in Hall A.
We studied the $^{12}$C(p,2p+n) reaction at beam momenta of 5.9, 8.0 and 9.0 GeV/c. For quasielastic (p,2p) events we reconstructed {bf p_f} the momentum of the knocked-out proton before the reaction; {bf p_f} was then compared (event-by-event) with {bf p_n}, the measured, coincident neutron momentum. For $|p_n|$ > k$_F$ = 0.220 GeV/c (the Fermi momentum) a strong back-to-back directional correlation between {bf p_f} and {bf p_n} was observed, indicative of short-range n-p correlations. From {bf p_n} and {bf p_f} we constructed the distributions of c.m. and relative motion in the longitudinal direction for correlated pairs. After correcting for detection efficiency, flux attenuation and solid angle, we determined that 49 $pm$ 13 % of events with $|p_f|$ > k_F had directionally correlated neutrons with $|p_n|$ > k$_F$. Thus short-range 2N correlations are a major source of high-momentum nucleons in nuclei.
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