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Register a new userA direct measurement of short range NN correlations in nuclei via the reaction C(p,2p+n)
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The reaction 12C(p,2p+n) was measured at beam momenta of 5.9 and 7.5 GeV/c.. We established the quasi-elastic character of the reaction C(p,2p) at $theta_{cm}simeq 90^o$, in a kinematically complete measurement. The neutron momentum was measured in triple coincidence with the two emerging high momentum protons. We present the correlation between the momenta of the struck target proton and the neutron. The events are associated with the high momentum components of the nuclear wave function. We conclude that two-nucleon short range correlations have been seen experimentally. The conclusion is based on kinematical correlations and is not based on specific theoretical models.
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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.
Recently, a new technique for measuring short-range NN correlations in nuclei (NN SRCs) was reported by the E850 collaboration, using data from the EVA spectrometer at the AGS at Brookhaven Nat. Lab. In this talk, we will report on a larger set of data from new measurement by the collaboration, utilizing the same technique. This technique is based on a very simple kinematic approach. For quasi-elastic knockout of protons from a nucleus ($^{12}$C(p,2p) was used for the current work), we can reconstruct the momentum {bf p$_f$} of the struck proton in the nucleus before the reaction, from the three momenta of the two detected protons, {bf p$_1$} and {bf p$_2$} and the three momentum of the incident proton, {bf p$_0$} : {bf p$_f$} = {bf p$_1$} + {bf p$_2$} - {bf p$_0$} If there are significant n-p SRCs, then we would expect to find a neutron with momentum -{bf p$_f$} in coincidence with the two protons, provided {bf p$_f$} is larger than the Fermi momentum $k_F$ for the nucleus (${sim}$220 MeV/c for $^{12}$C). Our results reported here confirm the earlier results from the E850 collaboration.
The $^{11}$C($alpha$, p) reaction is an important $alpha$-induced reaction competing with $beta$-limited hydrogen-burning processes in high-temperature explosive stars. We directly measured its reaction cross sections both for the ground-state transition ($alpha$, $p_{0}$) and the excited-state transitions ($alpha$, $p_{1}$) and ($alpha$, $p_{2}$) at relevant stellar energies 1.3 - 4.5 MeV by an extended thick-target method featuring time of flight for the first time. We revised the reaction rate by numerical integration including the ($alpha$, $p_{1}$) and ($alpha$, $p_{2}$) contributions and also low-lying resonances of ($alpha$, $p_{0}$) using both the present and the previous experimental data which were totally neglected in the previous compilation works. The present total reaction rate lies between the previous ($alpha$, $p_{0}$) rate and the total rate of the Hauser-Feshbach statistical model calculation, which is consistent with the relevant explosive hydrogen-burning scenarios such as the $ u p$-process.
The $^{6}$Be continuum states were populated in the charge-exchange reaction $^1$H($^{6}$Li,$^{6}$Be)$n$ collecting very high statistics data ($sim 5 times 10^6$ events) on the three-body $alpha$+$p$+$p$ correlations. The $^{6}$Be excitation energy region below $sim 3$ MeV is considered, where the data are dominated by contributions from the $0^+$ and $2^+$ states. It is demonstrated how the high-statistics few-body correlation data can be used to extract detailed information on the reaction mechanism. Such a derivation is based on the fact that highly spin-aligned states are typically populated in the direct reactions.
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.
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