Abstract
The EMC experiment revealed that only a small fraction of the nucleon spin is carried
by quarks. Two decades later, the spin crisis remains an open issue. Quark orbital angular
momentum is now considered to be one of the principal contributions in generating the nucleon
spin, but a precise determination of this critical piece has remained elusive. The leading twist
tensor structure function b1 of spin-1 hadrons can provide new insight into this puzzle, since
it is directly related to effects arising from orbital angular momentum, which differ from the
case in a spin-1/2 target. For this reason, it provides a unique tool to study partonic effects,
while also being sensitive to coherent nuclear properties in the simplest nuclear system.
At low x, shadowing effects are expected to dominate b1, while at larger values, b1 provides a clean probe of exotic QCD effects, such as hidden color due to 6-quark configuration.
Since the deuteron wave function is relatively well known, any novel effects are expected to
be readily observable. All available models predict a small or vanishing value of b1 at moderate x. However, the first pioneer measurement of b1 at HERMES revealed a crossover to
an anomolously large negative value in the region 0.2 < x < 0.5, albeit with relatively large
experimental uncertainty.
We will perform an inclusive measurement of the deuteron polarized cross sections in the
region 0.30 < x < 0.50, for 1.5 < Q2 < 3.6 GeV2
. With 28 days of 11 GeV incident beam,
we can determine b1 with sufficient precision to discriminate between conventional nuclear
models, and the more exotic behaviour which is hinted at by the HERMES data. The UVa solid
polarized ND3 target will be used, along with the Hall C spectrometers, and an unpolarized
115 nA beam. An additional 11.8 days will be needed for overhead. This measurement will
provide access to the tensor quark polarization, and allow a test of the Close-Kumano sum
rule, which vanishes in the absence of tensor polarization in the quark sea. Until now, tensor
structure has been largely unexplored, so the study of these quantities holds the potential of
initiating a new field of spin physics at Jefferson Lab.
by quarks. Two decades later, the spin crisis remains an open issue. Quark orbital angular
momentum is now considered to be one of the principal contributions in generating the nucleon
spin, but a precise determination of this critical piece has remained elusive. The leading twist
tensor structure function b1 of spin-1 hadrons can provide new insight into this puzzle, since
it is directly related to effects arising from orbital angular momentum, which differ from the
case in a spin-1/2 target. For this reason, it provides a unique tool to study partonic effects,
while also being sensitive to coherent nuclear properties in the simplest nuclear system.
At low x, shadowing effects are expected to dominate b1, while at larger values, b1 provides a clean probe of exotic QCD effects, such as hidden color due to 6-quark configuration.
Since the deuteron wave function is relatively well known, any novel effects are expected to
be readily observable. All available models predict a small or vanishing value of b1 at moderate x. However, the first pioneer measurement of b1 at HERMES revealed a crossover to
an anomolously large negative value in the region 0.2 < x < 0.5, albeit with relatively large
experimental uncertainty.
We will perform an inclusive measurement of the deuteron polarized cross sections in the
region 0.30 < x < 0.50, for 1.5 < Q2 < 3.6 GeV2
. With 28 days of 11 GeV incident beam,
we can determine b1 with sufficient precision to discriminate between conventional nuclear
models, and the more exotic behaviour which is hinted at by the HERMES data. The UVa solid
polarized ND3 target will be used, along with the Hall C spectrometers, and an unpolarized
115 nA beam. An additional 11.8 days will be needed for overhead. This measurement will
provide access to the tensor quark polarization, and allow a test of the Close-Kumano sum
rule, which vanishes in the absence of tensor polarization in the quark sea. Until now, tensor
structure has been largely unexplored, so the study of these quantities holds the potential of
initiating a new field of spin physics at Jefferson Lab.
| Original language | American English |
|---|---|
| Type | Proposal |
| Media of output | Jefferson Laboratory |
| Publisher | Jefferson Laboratory |
| Number of pages | 28 |
| Volume | PAC-38 |
| State | Submitted - 2013 |