A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is ...presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing \(\cos{\phi-\phi_S}\) modulations provide evidence for a sizable worm-gear (II) distribution, \(g_{1T}\). Most of the other modulations are found to be consistent with zero with the notable exception of large \(\sin{\phi_S}\) modulations for charged pions and positive kaons.
Quasi-elastic scattering on \(^{12}\)C\((e,e'p)\) was measured in Hall C at Jefferson Lab for space-like 4-momentum transfer squared \(Q^2\) in the range of 8--14.2\,(GeV/\(c\))\(^2\) with proton ...momenta up to 8.3\,GeV/\(c\). The experiment was carried out in the upgraded Hall C at Jefferson Lab. It used the existing high momentum spectrometer and the new super high momentum spectrometer to detect the scattered electrons and protons in coincidence. The nuclear transparency was extracted as the ratio of the measured yield to the yield calculated in the plane wave impulse approximation. Additionally, the transparency of the \(1s_{1/2}\) and \(1p_{3/2}\) shell protons in \(^{12}\)C was extracted, and the asymmetry of the missing momentum distribution was examined for hints of the quantum chromodynamics prediction of Color Transparency. All of these results were found to be consistent with traditional nuclear physics and inconsistent with the onset of Color Transparency.
For the field of high energy physics to continue to have a bright future, priority within the field must be given to investments in the development of both evolutionary and transformational detector ...development that is coordinated across the national laboratories and with the university community, international partners and other disciplines. While the fundamental science questions addressed by high energy physics have never been more compelling, there is acute awareness of the challenging budgetary and technical constraints when scaling current technologies. Furthermore, many technologies are reaching their sensitivity limit and new approaches need to be developed to overcome the currently irreducible technological challenges. This situation is unfolding against a backdrop of declining funding for instrumentation, both at the national laboratories and in particular at the universities. This trend has to be reversed for the country to continue to play a leadership role in particle physics, especially in this most promising era of imminent new discoveries that could finally break the hugely successful, but limited, Standard Model of fundamental particle interactions. In this challenging environment it is essential that the community invest anew in instrumentation and optimize the use of the available resources to develop new innovative, cost-effective instrumentation, as this is our best hope to successfully accomplish the mission of high energy physics. This report summarizes the current status of instrumentation for high energy physics, the challenges and needs of future experiments and indicates high priority research areas.
Evidence for a flavor asymmetry between the \(\bar u\) and \(\bar d\) quark distributions in the proton has been found in deep-inelastic scattering and Drell-Yan experiments. The pronounced ...dependence of this flavor asymmetry on \(x\) (fraction of nucleon momentum carried by partons) observed in the Fermilab E866 Drell-Yan experiment suggested a drop of the \(\bar d\left(x\right) / \bar u\left(x\right)\) ratio in the \(x > 0.15\) region. We report results from the SeaQuest Fermilab E906 experiment with improved statistical precision for \(\bar d\left(x\right) / \bar u\left(x\right)\) in the large \(x\) region up to \(x=0.45\) using the 120 GeV proton beam. Two different methods for extracting the Drell-Yan cross section ratios, \(\sigma^{pd} /2 \sigma^{pp}\), from the SeaQuest data give consistent results. The \(\bar{d}\left(x\right) / \bar{u}\left(x\right)\) ratios and the \(\bar d\left(x\right) - \bar u\left(x\right)\) differences are deduced from these cross section ratios for \(0.13 < x < 0.45\). The SeaQuest and E866/NuSea \(\bar{d}\left(x\right) / \bar{u}\left(x\right)\) ratios are in good agreement for the \(x\lesssim 0.25\) region. The new SeaQuest data, however, show that \(\bar d\left(x\right)\) continues to be greater than \(\bar u\left(x\right)\) up to the highest \(x\) value (\(x = 0.45\)). The new results on \(\bar{d}\left(x\right) / \bar{u}\left(x\right)\) and \(\bar{d}\left(x\right) - \bar{u}\left(x\right)\) are compared with various parton distribution functions and theoretical calculations.
A comprehensive collection of results on longitudinal double-spin asymmetries is presented for charged pions and kaons produced in semi-inclusive deep-inelastic scattering of electrons and positrons ...on the proton and deuteron, based on the full HERMES data set. The dependence of the asymmetries on hadron transverse momentum and azimuthal angle extends the sensitivity to the flavor structure of the nucleon beyond the distribution functions accessible in the collinear framework. No strong dependence on those variables is observed. In addition, the hadron charge-difference asymmetry is presented, which under certain model assumptions provides access to the helicity distributions of valence quarks.
Quasielastic \(^{12}\)C\((e,e'p)\) scattering was measured at space-like 4-momentum transfer squared \(Q^2\)~=~8, 9.4, 11.4, and 14.2 (GeV/c)\(^2\), the highest ever achieved to date. Nuclear ...transparency for this reaction was extracted by comparing the measured yield to that expected from a plane-wave impulse approximation calculation without any final state interactions. The measured transparency was consistent with no \(Q^2\) dependence, up to proton momenta of 8.5~GeV/c, ruling out the quantum chromodynamics effect of color transparency at the measured \(Q^2\) scales in exclusive \((e,e'p)\) reactions. These results impose strict constraints on models of color transparency for protons.
A Fourier analysis of double-spin azimuthal asymmetries measured at HERMES in semi-inclusive deep-inelastic scattering of longitudinally polarized leptons off tranversely polarized protons is ...presented for pions and charged kaons. The extracted amplitudes can be interpreted as convolutions of transverse momentum-dependent distribution and fragmentation functions and provide sensitivity to, e.g., the poorly known worm-gear quark distribution.
We propose to measure the photo-production cross section of $J/{\psi}$ near
threshold, in search of the recently observed LHCb hidden-charm resonances
$P_c$(4380) and $P_c$(4450) consistent with ...'pentaquarks'. The observation of
these resonances in photo-production will provide strong evidence of the true
resonance nature of the LHCb states, distinguishing them from kinematic
enhancements. A bremsstrahlung photon beam produced with an 11 GeV electron
beam at CEBAF covers the energy range of $J/{\psi}$ production from the
threshold photo-production energy of 8.2 GeV, to an energy beyond the presumed
$P_c$(4450) resonance. The experiment will be carried out in Hall C at
Jefferson Lab using a 50{\mu}A electron beam incident on a 9% copper radiator.
The resulting photon beam passes through a 15 cm liquid hydrogen target,
producing $J/{\psi}$ mesons through a diffractive process in the $t$-channel,
or through a resonant process in the $s$- and $u$-channel. The decay $e^+e^-$
pair of the $J/{\psi}$ will be detected in coincidence using the two
high-momentum spectrometers of Hall C. The spectrometer settings have been
optimized to distinguish the resonant $s$- and $u$-channel production from the
diffractive $t$-channel $J/{\psi}$ production. The $s$- and $u$-channel
production of the charmed 5-quark resonance dominates the $t$-distribution at
large $t$. The momentum and angular resolution of the spectrometers is
sufficient to observe a clear resonance enhancement in the total cross section
and $t$-distribution. We request a total of 11 days of beam time with 9 days to
carry the main experiment and 2 days to acquire the needed $t$-channel elastic
$J/{\psi}$ production data for a calibration measurement. This calibration
measurement in itself will greatly enhance our knowledge of $t$-channel elastic
$J/{\psi}$ production near threshold.
Hard exclusive electroproduction of $\omega$ mesons is studied with the
HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and
electron beams off a transversely polarized ...hydrogen target. The amplitudes of
five azimuthal modulations of the single-spin asymmetry of the cross section
with respect to the transverse proton polarization are measured. They are
determined in the entire kinematic region as well as for two bins in photon
virtuality and momentum transfer to the nucleon. Also, a separation of
asymmetry amplitudes into longitudinal and transverse components is done. These
results are compared to a phenomenological model that includes the pion pole
contribution. Within this model, the data favor a positive $\pi\omega$
transition form factor.
A measurement of beam-helicity asymmetries for single-hadron production in deep-inelastic scattering is presented. Data from the scattering of 27.6 GeV electrons and positrons off gaseous hydrogen ...and deuterium targets were collected by the HERMES experiment. The asymmetries are presented separately as a function of the Bjorken scaling variable, the hadron transverse momentum, and the fractional energy for charged pions and kaons as well as for protons and anti-protons. These asymmetries are also presented as a function of the three aforementioned kinematic variables simultaneously.
