Abstract
Extensive studies of high-energy deuteron photodisintegration over the past two decades
have probed the limits of meson-baryon descriptions of nuclei and reactions. At high energies, photodisintegration cross sections have been shown to follow the constituent counting
rules, which suggests that quarks are the relevant degrees of freedom.
In an attempt to more clearly identify the underlying dynamics at play in high-energy
nuclear photodisintegration, E03-101 measured, in 2007, the hard photodisintegration of
two protons, using 3He. The basic idea is that theoretical models should be able to predict
the relative size of pp versus pn disintegrations. The results from E03-101 clearly indicate
the onset of scaling; but due to the cross section being smaller than expected, the statistics
were insufficient to determine the underlying mechanism that produces high transverse
momentum proton pairs. Preliminary data on a two body hard breakup of 3He to p-d
pairs are also available from that experiment over a small s-range.
We propose here a second generation measurement of hard photodisintegration of 3He
into np, pp, and pd pairs. The experiment is aimed at addressing issues the previous
measurements and current theory are insufficient to resolve:
1. A measurement of both γ
3He → pp(n) and γ
3He → pn(p) will address the issue
of the small ratio of γ
3He → pp(n) to γ d → pn.
2. High quality data over a large s-range on the two body break-up of γ
3He → pd will
confirm the scaling of the invariant cross section as a function of s and determine
the power with a small uncertainty.
3. Higher statistics for γ
3He → pp(n) will provide a conclusive check to determine if
hard re-scattering is the correct dynamical treatment to explain the production of
high PT nucleons as proposed.
The experimental hall beam time request is for 19 days. No new equipment and no
special setup or development time are required. This measurement does not need the 12
GeV upgrade but JLab is the only facility world wide at which such a measurement can
be done.
have probed the limits of meson-baryon descriptions of nuclei and reactions. At high energies, photodisintegration cross sections have been shown to follow the constituent counting
rules, which suggests that quarks are the relevant degrees of freedom.
In an attempt to more clearly identify the underlying dynamics at play in high-energy
nuclear photodisintegration, E03-101 measured, in 2007, the hard photodisintegration of
two protons, using 3He. The basic idea is that theoretical models should be able to predict
the relative size of pp versus pn disintegrations. The results from E03-101 clearly indicate
the onset of scaling; but due to the cross section being smaller than expected, the statistics
were insufficient to determine the underlying mechanism that produces high transverse
momentum proton pairs. Preliminary data on a two body hard breakup of 3He to p-d
pairs are also available from that experiment over a small s-range.
We propose here a second generation measurement of hard photodisintegration of 3He
into np, pp, and pd pairs. The experiment is aimed at addressing issues the previous
measurements and current theory are insufficient to resolve:
1. A measurement of both γ
3He → pp(n) and γ
3He → pn(p) will address the issue
of the small ratio of γ
3He → pp(n) to γ d → pn.
2. High quality data over a large s-range on the two body break-up of γ
3He → pd will
confirm the scaling of the invariant cross section as a function of s and determine
the power with a small uncertainty.
3. Higher statistics for γ
3He → pp(n) will provide a conclusive check to determine if
hard re-scattering is the correct dynamical treatment to explain the production of
high PT nucleons as proposed.
The experimental hall beam time request is for 19 days. No new equipment and no
special setup or development time are required. This measurement does not need the 12
GeV upgrade but JLab is the only facility world wide at which such a measurement can
be done.
| Original language | American English |
|---|---|
| Type | Proposal |
| Media of output | Jefferson Laboratory |
| Publisher | Jefferson Laboratory |
| Number of pages | 22 |
| Volume | PR12-11-004 |
| State | Published - 2009 |