e08-008: Exclusive study of deuteron electrodisintegration near threshold

The study of threshold electrodisintegration of and elastic scattering on the only stable two nucleon system, the deuteron, can reveal specific aspects of the N-N interaction. The simplicity of electrodisintegration along with the simplicity of the deuteron makes this study most appropriate for revealing these interactions. By using an incident beam of polarized electrons and by measuring the polarization of the recoiling proton, the ratio of the electric (G _E ) and magnetic (G _M ) form factors for $d\left( {\vec e,e'\vec p} \right)$ (and $p\left( {\vec e,e'\vec p} \right)$ ) reactions may be extracted. This experiment was conducted in Hall A at Jefferson Lab in Newport News, Virginia using a beam of polarized electrons provided by the CEBAF Accelerator incident on a liquid deuterium (and hydrogen) target. The scattered electron and the recoiling (polarized) proton were detected using the High Resolution Spectrometers of Hall A. To determine the polarization of the recoil proton, an analyzing material was placed perpendicular to the protons trajectory through the spectrometer, in front of a set of straw chambers. Due to the spin-orbit interactions involved in the scattering of the proton from the analyzer material, asymmetries seen in the distribution of events detected by these straw chambers reveal the polarization of the recoil proton. By tracking the spin procession of the polarized protons from the straw chambers back to the target, the transferred and induced polarization of the proton may be determined. The (double-spin) asymmetries observed in the straw chambers will first be studied for the well-known elastic $p\left( {\vec e,e'\vec p} \right)$ process and compared to the asymmetries for $d\left( {\vec e,e'\vec p} \right)n\left( {x_B = 1} \right)$ . The analysis will then be repeated to determine how these asymmetries change with increasing x _B (to the kinematic limit for deuteron electrodisintegration).     

Hadronic colliders as probes of the proton spin structure

We perform a systematic analysis of different processes with high energy polarized proton beams: jets, direct photon, lepton pairs (Drell-Yan) andWZ production. Different sets of polarized partonic densities are used that fit EMC and SLAC polarized deep inelastic scattering data with variable amount of quark and gluon components of the proton spin. The case of the future Relativistic Heavy Ion Collider (RHIC) used as a polarized collider at a maximum energy of \(\sqrt s = 500\) GeV is analyzed in detail.     

Magnetic moment of proton halo nucleus 28 P

The magnetic moment of ²⁸P (I _π = 3^?+?, T_1/2 = 270.3 ms) in the ground state has been measured by the $\upbeta $ -nuclear magnetic resonance method for the first time. The measured magnetic moment of $\vert \upmu (^{28}$ P)∣ = 0.309(9)  $\upmu _{{\rm N}}$ is well reproduced by the shell model value of +0.306  $\upmu _{{\rm N} }$ . The shell model calculation also yields a proton density distribution with a long tail. The present results provide a strong confirmation of the configuration of the 2s _1/2 proton which should lead to the proton halo.     

Spin effects in diffractive reactions

Double spin asymmetries in the diffractive \(Q\bar Q\) and J/ψ leptoproduction are discussed. It is shown that the asymmetries for longitudinally polarized lepton and longitudinally or transversely polarized proton can be used to study spin dependent gluon distribution of the proton at small x.     

Beam spin asymmetries of charged and neutral pion production in semi-inclusive DIS

We present a study on the beam single spin asymmetries $A_{LU}^{\sin\phi_{h}}$ of π ⁺, π ^? and π ⁰ production in semi-inclusive deep inelastic scattering process, by considering Collins effect and the g ^⊥ D ₁ term simultaneously. We calculate the twist-3 distributions $e(x, \boldsymbol{k}_{T}^{2})$ and $g^{\perp}(x, \boldsymbol{k}_{T}^{2})$ for the valence quarks inside the proton in a spectator model. We consider two different options for the form of diquark propagator, as well as two different choices for the model parameters in the calculation. Using the model results, we estimate the beam spin asymmetries $A_{LU}^{\sin\phi_{h}}$ for the charged and neutral pions and compare the results with the measurement from the HERMES Collaboration. We also make predictions on the asymmetries at CLAS with a 5.5 GeV beam using the same model results. It is found that different choices for the diquark propagator will not only lead to different expressions for the distribution functions, but also result in different sizes of the asymmetries. Our study also shows that, although the spectator model calculation can describe the asymmetries for certain pion production in some kinematic regions, it seems difficult to explain the asymmetries of pion production for all three pions in a consistent way from the current versions.     

The size of the proton: Closing in on the radius puzzle

We analyze the recent electron-proton scattering data from Mainz using a dispersive framework that respects the constraints from analyticity and unitarity on the nucleon structure. We also perform a continued fraction analysis of these data. We find a small electric proton charge radius, r _E ^p = 0.84 _?0.01 ^+0.01 fm, consistent with the recent determination from muonic hydrogen measurements and earlier dispersive analyses. We also extract the proton magnetic radius, r _M ^p = 0.86 _?0.03 ^+0.02 fm, consistent with earlier determinations based on dispersion relations.     

Physics beyond the Standard Model through b → s μ ?+? μ ? transition

A comprehensive study of the impact of new-physics operators with different Lorentz structures on decays involving the b ?? s ?? ^?+? ?? ^? transition is performed. The effects of new vector?Caxial vector (VA), scalar?Cpseudoscalar (SP) and tensor (T) interactions on the differential branching ratios, forward?Cbackward asymmetries (A _FB??s), and direct CP asymmetries of ${\bar B}_{\rm s}^0 \to \mu^+ \mu^-$ , ${\bar B}_{\rm d}^0 \to$ $ X_{\rm s} \mu^+ \mu^-$ , ${\bar B}_{\rm s}^0 \to \mu^+ \mu^- \gamma$ , ${\bar B}_{\rm d}^0 \to {\bar K} \mu^+ \mu^-$ , and ${\bar B}_{\rm d}^0\to {\bar{K}^*} \mu^+ \mu^-$ are examined. In ${\bar B}_{\rm d}^0\to {\bar{K}^*} \mu^+ \mu^-$ , we also explore the longitudinal polarization fraction f _L and the angular asymmetries $A_{\rm T}^{(2)}$ and A _LT, the direct CP asymmetries in them, as well as the triple-product CP asymmetries $A_{\rm T}^{\rm (im)}$ and $A^{\rm (im)}_{\rm LT}$ . While the new VA operators can significantly enhance most of the observables beyond the Standard Model predictions, the SP and T operators can do this only for A _FB in ${\bar B}_{\rm d}^0 \to {\bar K} \mu^+ \mu^-$ .     

Three-Quark Currents and Baryon Spin

We show that three-quark axial currents as required by broken SU(6) spin-flavor symmetry reduce the quark spin contribution to proton spin from \({{\Sigma}_p = 1}\) (one-quark axial current value) to \({{\Sigma}_p = 0.41(12)}\) consistent with the empirical value \({{\Sigma}_{p, exp} = 0.33(08)}\) . In the case of the \({{\Delta}^+(1232)}\) baryon, we find that three-quark axial currents increase the one-quark axial current value \({{\Sigma}_{{\Delta}^+} = 3}\) to \({{\Sigma}_{{\Delta}^+} = 3.87(22)}\) . We also calculate the quark orbital angular momenta L _u and L _d in the proton and \({{\Delta}^+}\) and interpret our results in terms of the prolate and oblate geometric shapes of these baryons consistent with their intrinsic quadrupole moments.     

Production of charmed hadrons in neutrino proton and antineutrino proton charged current interactions

Usind data from avp and \(\bar v\) p experiment with BEBC at CERN, the rates for inclusive production ofD ^*+,Λ _c ⁺ andD ⁰ invp scattering and ofD ^*? in \(\bar v\) p scattering are measured. Some examples of the exclusive production ofD ^*+,Λ _c ⁺ and∑ _c ⁺⁺ are given. The cross section for the reactionvp→μ ^? _c ⁺⁺ is estimated.     

Role of an acceptor impurity in the proton transfer in proton-conducting oxides

The influence of interaction of protons with defects (acceptor impurities, oxygen vacancies) and with each other on the proton transfer in acceptor-doped proton-conducting oxides A ^II B _1?x ^IV R _x ^III O_{3 ? δ} with the perovskite structure and in oxides A _2?x ^III R _x ^II O_{3 ? δ} with the structure of a distorted fluorite (bixbyite) has been investigated theoretically. The tracer diffusion coefficient D* and proton mobility have been calculated by the Monte Carlo method and analytically. It has been shown that the interaction of protons with defects substantially affects the magnitude and behavior of the transfer coefficients. The interaction with acceptor impurities plays the most important role. The proton mobility significantly decreases even at a low dopant concentration (x ～ 1–3 at %). The dependence of the proton conductivity σ on the impurity concentration can exhibit maxima. For oxides with the bixbyite structure including nonequivalent cation sites, the distribution of the dopant over these sites has a strong influence on the dependence σ(x). The obtained results have been used to interpret the experimental data on the proton conductivity for a number of oxides.     

Azimuthal asymmetries in lepton-pair production at a fixed-target experiment using the LHC beams (AFTER)

A multi-purpose fixed-target experiment using the proton and lead-ion beams of the LHC was recently proposed by Brodsky, Fleuret, Hadjidakis and Lansberg, and here we concentrate our study on some issues related to the spin physics part of this project (referred to as AFTER). We study the nucleon spin structure through pp and pd processes with a fixed-target experiment using the LHC proton beams, for the kinematical region with 7?TeV proton beams at the energy in center-of-mass frame of two nucleons $\sqrt{s}=115~\mathrm{GeV}$ . We calculate and estimate the cos2? azimuthal asymmetries of unpolarized pp and pd dilepton production processes in the Drell?CYan continuum region and at the Z-pole. We also calculate the sin(2??? _S ), sin(2?+? _S ) and sin2? azimuthal asymmetries of pp and pd dilepton production processes with the target proton and deuteron longitudinally or transversally polarized in the Drell?CYan continuum region and around Z resonances region. We conclude that it is feasible to measure these azimuthal asymmetries, consequently the three-dimensional or transverse momentum dependent parton distribution functions (3dPDFs or TMDs), at this new AFTER facility.     

Recent STAR results on W production and asymmetry in polarized \vec p + \vec p collisions at √r = 500 GeV

The production of W± bosons in longitudinally polarized proton + proton collisions at RHIC is a unique way to study the flavor-dependent spin structure of the proton, since at leading order it couples directly and exclusively to specific quark flavor pairings: $u + \bar d \to W^ +$ and $\bar u + d \to W^ -$ . Measurement of the longitudinal single-spin asymmetry of the electron decay daughters in W production is sensitive to the polarizations of the quarks involved. Results from the first proton-proton collisions at √r = 500 GeV in 2009 are presented, along with a discussion of the forward-rapidity tracking upgrade.     

Study of 3He Nuclei by Polarization Observables in Quasi-Elastic Electron Scattering

In a recent set of measurements at Jefferson Laboratory, we have studied the missing-momentum dependence of beam-target asymmetries in exclusive \({\overrightarrow{^3{{\rm He}}}({{\rm e}},{\rm e}'{\rm p}){\rm pn}, \overrightarrow{^3{{\rm He}}}({{\rm e}},{\rm e}'{\rm p}){\rm d} }\) , and \({\overrightarrow{^3{{\rm He}}}({{\rm e}},{\rm e}'{\rm d}){\rm p}}\) channels at a previously unattainable level of precision and unreached range in missing momenta. We have also measured single-spin asymmetries in the processes \({\overrightarrow{^3{{\rm He}}}({\vec{{\rm e}}},{\rm e}')}\) and \({\overrightarrow{^3{{\rm He}}}({{\rm \vec{e}}},{\rm e}'{\rm n})}\) , where the nuclei were polarized vertically. Preliminary results are presented.     

Measurement of \Sigma beam asymmetry in \pi^{0}_{} photoproduction off the neutron in the second and third resonances region⋆

The $ \Sigma$ beam asymmetry in the photoproduction of neutral pions from quasi-free nucleons in a deuteron target was measured for the first time between 0.60 and 1.50GeV, with the GRAAL polarized and tagged photon beam. The asymmetry values from the quasi-free proton were found equal to the ones extracted from a pure proton target. The asymmetries from quasi-free proton and quasi-free neutron were found equal up to 0.82GeV and substantially different at higher energies. The results are compared with recent partial-wave analyses.     

Polarization observablesΣ,P y,T 1 in the reaction\vec \gamma d \to \vec pn at photon energies between 200 and 600 MeV and dibaryon resonances

The polarization observables Σ,P _y ,T ₁,P _y ^⊥ ,P _y ^∥ are derived in proton polarization measurements of the \(\vec \gamma d \to \vec pn\) reaction, using a linearly polarized photon beam of energies between 300 and 600 MeV for c.m.s. proton emission angles of 90° and 120°. A multipole analysis is performed in the framework of the gauge-invariant pole model considering theγN→πN amplitudes and the deuteron structure without dibaryon resonances and with different sets of isovector and isoscalar dibaryon resonances. It is shown that the inclusion of dibaryon resonances substantially improves agreement with experimental data.     

Study of theJ/\Psi \to p\bar p\gamma and\Upsilon /(1S) \to p\bar p\gamma decays as possible tests of the proton wave function

Considering the proton either as a three-quark state with its wave function fulfilling QCD sum rules or as a quark-diquark state with wave function parametrizations that are shown to fitG _M ^P , we study the possibility of discriminating between these two competing pictures by comparing their respective predictions for \(J/\Psi \to p\bar p\gamma \) and \(\Upsilon (1S) \to p\bar p\gamma \) decays. ForJ/Ψ decay, thep \(\bar p\) invariantmass distributions derived from either model are found to be of about the same magnitude, but neither of them is able by itself to reproduce present-day data. Differences between the two pictures may eventually show up in the case of Υ(1S) decay, but the predicted counting rates are small. We also consider some other possible production mechanisms for \(p\bar p\gamma \) final states.     

Spectroscopy of88Y homologous levels

The⁹¹Zr( $z\bar p$ ,α)⁸⁸Y reaction has been studied at incident energy of 22 MeV using a polarized proton source and a Q3D spectrometer. The differential cross sections and asymmetries for transitions to levels of⁸⁸Y homologous to the lowest excitation energy states of⁸⁷Y have been measured and interpreted both in terms of the experimental differential cross sections and asymmetries of the parent⁸⁷Y states and by means of the finite-range distorted wave Born approximation theory using conventional Woods-Saxonα-particle potential. The advantage of the concept of homology consists in having to deal with a uniquel-transfer, that given by the transition to the corresponding parent state. In order to validate the concept of homology as a spectroscopic tool to identify spin, parity and dominant configuration of highly excited states in ( $z\bar p$ ,α) reaction on odd mass target nuclei, shell model calculations have been performed. Several new attributions of spin and parity for⁸⁸Y residual nucleus are proposed.     

Study of TMDs with polarized beam and/or targets

A Fourier analysis of single- and double-spin azimuthal asymmetries measured at HERMES in semi-inclusive deep-inelastic scattering of unpolarized or 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. In particular, the measured double-spin asymmetries are sensitive to the poorly known worm-gear quark distribution g _1T ^⊥      

First measurement of the polarisation transfer on the proton in the reactionsH(\vec e,e'\vec p) andD(\vec e,e'\vec p)

The measurement of the polarisation transfer to the proton in the reactions $H(\vec e,e'\vec p)$ and $D(\vec e,e'\vec p)$ performed with longitudinally polarised electrons in quasi-free kinematics is presented. The coincidence measurement was executed atQ ²≈8fm ^?2 using the 855 MeV, c.w. beam of the Mainz Microtron MAMI. The recoil polarisation was determined by means of a carbon analyser. The experiment shows that the binding of the nucleon does not modify the polarisationP _x of the recoil proton within an error ofΔ P _x/P_x≈10%. The measured polarisation agrees with recent theoretical predictions. Implications for the measurement of the electric form factor of the neutron using the $D(\vec e,e'\vec n)$ reaction are discussed.     

Feasibility studies of the time-like proton electromagnetic form factor measurements with \overline{{P}}ANDA at FAIR

The possibility of measuring the proton electromagnetic form factors in the time-like region at FAIR with the $ \overline{{P}}$ ANDA detector is discussed. Detailed simulations on signal efficiency for the annihilation of $ \bar{{p}}$ + p into a lepton pair as well as for the most important background channels have been performed. It is shown that precise measurements of the differential cross-section of the reaction $ \bar{{p}}$ + p $ \rightarrow$ e ^- + e ⁺ can be obtained in a wide kinematical range. The determination of the ratio R of the moduli of the electric and magnetic proton form factors will be possible up to a value of momentum transfer squared of q ² ? 14 (GeV/c)^2 with absolute precision from 0.01 to 0.5 (for R ～ 1 . The total $ \bar{{p}}$ + p $ \rightarrow$ e ^- + e ⁺ cross-section will be measured up to q ² ? 28 (GeV/c)^2. The results obtained from simulated events are compared to the existing data. Sensitivity to the two-photon exchange mechanism is also investigated.