Session EF: Mini-Symposium on Hadron Structure and QCD in High Energy Processes II

Studies of spin-averaged SIDIS at Jefferson Lab

Cross sections for semi-inclusive deep-inelastic electroproduction of positive and negative charged pions have been measured at Jefferson Lab from both proton and deuteron targets. The kinematic range spans $0.2 [Preview Abstract]

Quark helicity distributions from DIS and SIDIS at COMPASS

The COMPASS collaboration at CERN is measuring the spin structures of nucleon. At this meeting we will present the inclusive asymmetry A$_{1,d }$and the semi-inclusive asymmetries A$_{1,d}^{pi+}$, A$_{1,d}^{pi-}$ ,A$_{1,d}^{K+}$, A$_{1,d}^{K-}$measured in the polarized deep inelastic muon-deuteron scattering. The data cover the range Q$^{2}>$1GeV$^{2}$ and 0.004 $<$x$<$0.3. These results were obtained from the data collected in years 2002-2004 and 2006. We will also present the valence, non-strange sea and strange quark helicity distributions extracted from the LO analysis using these results. The strange quark distribution is compatible with zero in the whole measured range.   

Access quark information through SIDIS measurements at JLab-12 GeV

At JLab-12 GeV, one hopes to access quark information such as helicity and transverse spin distributions, Sivers functions and momentum distributions through semi-inclusive deep-inelastic scattering experiments (SIDIS). But, how can we know that the hard probe really hit a quark? How can we know that the quark information is still preserved through the fragmentation process? What will be the experimental evidences? A plan of measurements of SIDIS cross section ratios will be outlined, the goal of these measurements is to to firmly establish the kinematic region over which SIDIS reactions can be reliably interpreted to the next-to-leading-order QCD in terms of parton distributions and fragmentation functions.   

Measurement of Single Target-Spin Asymmetry in Semi-Inclusive DIS using Transversely Polarized $^3$He Target

We recently measured the neutron target single spin asymmetry in the semi-inclusive deep inelastic $^{3}He^{\uparrow}(e,e'\pi^{+/-})X$ reactions with a transversely polarized $^3$He target. The experiment was performed at Jefferson Lab Hall A from October 2008 to February 2009. The pions were detected in the high-resolution spectrometer in coincidence with the scattered electrons detected by the BigBite spectrometer. The kinematic coverage focuses on the valence quark region, $x = 0.13$ to $0.41$, at $Q^2=1.31$ to $ 3.10~(\mathrm{GeV}/c)^2$. Good particle identification was achieved using a RICH detector, an aerogel Cherenkov counter and Time-of-Flight detectors, which allowed for clean $\pi^{\pm}$ and $K^{\pm}$ detection. The data from this experiment, when combined with the world data, will provide constraints on the transversity and Sivers distributions on both $u$-quark and $d$-quark in the valence region. An update on the on-going analysis will be presented in this talk.   

Measurement of Double Spin Asymmetry $A_{LT}$ in Semi-Inclusive Pion Electroproduction on a Transversely Polarized $^3$He Target

We recently measured the neutron double spin asymmetry $A_{LT}$ in the semi-inclusive deep inelastic $^{3}He^{\uparrow}(\overrightarrow{e},e'\pi^{+/-})X$ reactions with polarized electron beam and a transversely polarized $^3$He target. The measurement was performed in Jefferson Lab Hall A, using a 6 GeV polarized electron beam scattered from a 40 cm polarized 3He target. The produced pions were detected by the left high-resolution spectrometer in coincidence with the scattered electrons detected by the BigBite spectrometer. The kinematic coverage focused on the valence quark region, $x \sim 0.13$-$0.41$, at $Q^2 \sim 1.31$-$3.10(\mathrm{GeV}/c)^2$. When combined with the world data, the new data will provide constraints on the $g^{q}_{1T}$ distribution functions. These distribution functions describe the longitudinal polarization of up and down quarks in the valence region for a transversely polarized nucleon. Current data analysis progress will be presented in this talk.   

Target Single-Spin Asymmetry Measurements in Quasi-Elastic $^{3}$He$\uparrow$(e, e$'$)

The target single-spin asymmetry for the neutron, $A_{y}$, was measured using the inclusive quasi-elastic $^{3}$He$\uparrow$(e, e$'$) reaction in Hall A at Jefferson Lab with a vertically polarized $^{3}$He target for $Q^{2}$ = 0.13, 0.46 and 0.97 GeV$^{2}$. Since the target single-spin asymmetry is expected to be zero in the one-photon exchange approximation, the non-zero results from this experiment clearly demonstrate the effects due to two-photon exchange. They establish the two-photon exchange process as a powerful tool to probe hadron structure, such as information on Generalized Parton Distributions. The ongoing analysis of this experiment will be presented.   

Recent DVCS Results from HERMES

This talk presents recently released HERMES results on DVCS beam spin, beam charge and target spin asymmetries for polarised and unpolarised hydrogen and deuterium targets. A new analysis technique has been used to extract the relevant asymmetries simultaneously: beam charge and beam spin asymmetry for unpolarised target data and the longitudinal target spin asymmetry and beam spin asymmetry for longitudinally polarised target data. The extracted asymmetries and their dependences on $t$ $x_B$ and $Q^2$ are presented over the entire kinematic acceptance of HERMES. The results are compared with asymmetries calculated based on a phenomenological GPD model based on double distributions from Vanderhaeghen, Guidal and Guichon.   

Timelike Compton Scattering with CLAS

Deeply Virtual Compton Scattering (DVCS), $\backslash$Epg, has been under intense theoretical and experimental studies in recent years as a new tool to access Generalized Parton Distributions (GPDs) of the nucleon. The simplest observables in DVCS for studying GPDs are spin dependent cross section differences. These asymmetries measure the imaginary part of Compton Form-Factors (CFFs), where GPDs enter at specific kinematical point, $\xi=x$. Here $\xi$ is the generalized Bjorken variable and $x$ is the light-cone momentum fraction of the struck quark. The real part of CFF is proportional to the integral of GPDs over $x$ and can only be accessed in the measurements of the DVCS cross section or the beam charge asymmetry. Studying the real part is important for modeling GPDs. It is sensitive to the so-called $D$-term, introduced in the modeling of GPDs to ensure the polynomiality of their Mellin moments. Photoproduction of lepton pairs, or so-called Time-like Compton Scattering (TCS), is an inverse process to DVCS and offers additional constraints on GPDs. In particular, TCS can be used as an effective tool to study the real part of the Compton amplitude using the azimuthal angular asymmetry arising from exchange of $l^+$ and $l^-$ momenta. In this report, first analysis of the Time-like Compton Scattering using the CLAS electroproduction data will be presented. Details of the extraction of quasi-real photoproduction of lepton pairs will be discussed.   

Deeply Virtual Exclusive Reactions with CLAS

Deeply virtual exclusive reactions offer a unique opportunity to study the structure of the nucleon at the parton level as one varies both the size of the probe, i.e. the photon virtuality $Q^2$, and the momentum transfer to the nucleon {\it t}. Such processes can reveal much more information about the structure of the nucleon than either inclusive electroproduction ($Q^2$ only) or elastic form factors ($t=-Q^2$). A dedicated experiment to study Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP) has been carried out in Hall B at Jefferson Lab. DVCS helicity--dependent and helicity--independent cross sections, as well as beam spin asymmetry, and cross sections and asymmetries for the $\pi^0$ and $\eta$ exclusive electroproduction in a wide kinematic range of $Q^2$, $x_B$ and {\it t} have been measured with CLAS. The preliminary data will be presented for the kinematic range in $Q^2$=1-4.5 GeV$^2$, $x_B$=0.1-0.5 and t up to 2 GeV$^2$. We view the work presented in this report as leading into the program of the Jefferson Lab 12 GeV upgrade. The increased energy and luminosity will allow us to make the analysis at much higher $Q^2$ and $x_B$ and perform Rosenbluth L/T separations of the cross sections.   

First results of the helicity asymetry measurements for pi0 photoproduction with FROST at Jlab

One of the longstanding unsolved problems in the nuclear physics is that of the nucleon resonances $N^\star$ and $\Delta^\star$. The lifetime of these intermediate states is very short since they decay strongly. Their parameters, mass, width, and coupling constants to various decay modes are not well known. To solve this problem, double polarization experiments are considered to be a very effective tool. I will present the result of a single pion photoproduction from the first double polarization experiment at Jefferson Lab and compare this result with the prediction of theoretical models.   

Exclusive $\pi^{0}$ electroproduction in the resonance region at low $Q^{2}$.

We report the analysis of single $\pi^{0}$ electroproduction in the resonance region to study the electromagnetic excitation of the nucleon resonances. The study is aimed at understanding of the internal structure and dynamics of the nucleon. The experiment was performed using an unpolarized cryogenic hydrogen target and 2.0 GeV polarized electron beam during the e1e run period with CLAS at Jefferson Lab. The new measurements will produce a data base with high statistics and large kinematic coverage for the hadronic invariant mass W up to 1.8 GeV in the momentum transfer $Q^{2}$ range of 0.3 - 1.0 (GeV/c)$^{2}$. Preliminary results will be presented and compared with the various model calculations.   

${\pi^0}$ electroproduction in semi-inclusive deep inelastic scattering off D, C, Fe, Pb

Measurement of neutral pion electroproduction is being performed in semi-inclusive deep inelastic scattering off deuterium, carbon, iron, and lead targets. The data were taken with the CLAS detector in Jefferson Lab using a 5.014 GeV electron beam. The two targets, liquid deuterium plus a solid foil, were positioned in the beam simultaneously. Hadronic multiplicity ratios $R^{\pi^0}_{\mathrm{A}}$ and transverse momentum broadening distributions ${\Delta}p_{T}^{2}$ were measured as a function of $\mathit{\left(z_{h},{\nu},Q^2,p_T\right)}$ kinematic bins. These results provide new insights into the phenomena of hadron formation through the access to the average lifetime of the quasi-free quark and time required to form full hadronic wave function. The status of data analysis as well as preliminary results of multiplicity ratios will be presented.