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First measurement of target and double spin asymmetries for polarized e- polarized p --> e p pi0 in the nucleon resonance region above the Delta(1232)  [PDF]
CLAS Collaboration,A. S. Biselli
Physics , 2008, DOI: 10.1103/PhysRevC.78.045204
Abstract: The exclusive channel polarized proton(polarized e,e prime p)pi0 was studied in the first and second nucleon resonance regions in the Q2 range from 0.187 to 0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). Longitudinal target and beam-target asymmetries were extracted over a large range of center-of-mass angles of the pi0 and compared to the unitary isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model DMT. A strong sensitivity to individual models was observed, in particular for the target asymmetry and in the higher invariant mass region. This data set, once included in the global fits of the above models, is expected to place strong constraints on the electrocoupling amplitudes A_{1/2} and S_{1/2} for the Roper resonance N(1400)P11, and the N(1535)S11 and N(1520)D13 states.
Transverse Single Spin Asymmetries and Cross-Sections for Forward pi0 and eta Mesons at Large Feynman-x in sqrt(s)=200 GeV polarized p+p Collisions at STAR  [PDF]
Len K. Eun
Physics , 2012,
Abstract: The STAR collaboration has previously reported a large transverse single spin asymmetry, A_N, for forward pi0 meson production. The cross-section in this region was measured up to Feynman-x (xF) of 0.55, and found to be consistent with perturbative Quantum Chromo-Dynamics predictions. During RHIC running in the year 2006 (6.8 inverse-pb, 56 % average polarization), an even larger A_N was observed for the eta meson at forward rapidity for xF > 0.5. All data were collected by the STAR Forward Pion Detector during sqrt(s) = 200 GeV polarized p+p collisions at RHIC. Understanding these large spin asymmetries requires information on the production cross-section. In this thesis, we present the results of the cross-section as well as the A_N measurements for both pi0 and eta mesons at average pseudo-rapidity of 3.7, for 0.4 < xF < 0.75. The details of the calibration, and the analysis methods are also discussed. Finally, we present selected aspects of the high voltage system for the STAR Forward Meson Spectrometer inner calorimeter, which was designed primarily by the author and his thesis advisor.
Measurement of the Polarized Structure Function $σ_{LT^\prime}$ for $p(\vec{e},e'p)π^o$ in the $Δ(1232)$ Resonance Region  [PDF]
CLAS Collaboration,K. Joo,L. C. Smith
Physics , 2003, DOI: 10.1103/PhysRevC.68.032201
Abstract: The polarized longitudinal-transverse structure function $\sigma_{LT^\prime}$ has been measured in the $\Delta(1232)$ resonance region at $Q^2=0.40$ and 0.65 GeV$^2$. Data for the $p(\vec e,e'p)\pi^o$ reaction were taken at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) using longitudinally polarized electrons at an energy of 1.515 GeV. For the first time a complete angular distribution was measured, permitting the separation of different non-resonant amplitudes using a partial wave analysis. Comparison with previous beam asymmetry measurements at MAMI indicate a deviation from the predicted $Q^2$ dependence of $\sigma_{LT^{\prime}}$ using recent phenomenological models.
Measurement of the Polarized Structure Function $σ_{LT^\prime}$ for $p(\vec{e},e'π^+)n$ in the $Δ(1232)$ Resonance Region  [PDF]
CLAS Collaboration,K. Joo,L. C. Smith
Physics , 2004, DOI: 10.1103/PhysRevC.70.042201
Abstract: The polarized longitudinal-transverse structure function $\sigma_{LT^\prime}$ has been measured using the $p(\vec e,e'\pi^+)n$ reaction in the $\Delta(1232)$ resonance region at $Q^2=0.40$ and 0.65 GeV$^2$. No previous $\sigma_{LT^\prime}$ data exist for this reaction channel. The kinematically complete experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) using longitudinally polarized electrons at an energy of 1.515 GeV. A partial wave analysis of the data shows generally better agreement with recent phenomenological models of pion electroproduction compared to the previously measured $\pi^0 p$ channel. A fit to both $\pi^0 p$ and $\pi^+ n$ channels using a unitary isobar model suggests the unitarized Born terms provide a consistent description of the non-resonant background. The $t$-channel pion pole term is important in the $\pi^0 p$ channel through a rescattering correction, which could be model-dependent.
Spin asymmetries for vector boson production in polarized p+p collisions  [PDF]
Jin Huang,Zhong-Bo Kang,Ivan Vitev,Hongxi Xing
Physics , 2015,
Abstract: We study the cross section for vector boson ($W^{\pm}/Z^0/\gamma^*$) production in polarized nucleon-nucleon collisions for low transverse momentum of the observed vector boson. For the case where one measures the transverse momentum and azimuthal angle of the vector bosons, we present the cross sections and the associated spin asymmetries in terms of transverse momentum dependent parton distribution functions (TMDs) at tree level within the TMD factorization formalism. To assess the feasibility of experimental measurements, we estimate the spin asymmetries for $W^{\pm}/Z^0$ boson production in polarized proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC) by using current knowledge of the relevant TMDs. We find that some of these asymmetries can be sizable if the suppression effect from TMD evolution is not too strong. The $W$ program at RHIC can, thus, test and constrain spin theory by providing unique information on the universality properties of TMDs, TMD evolution, and the nucleon structure. For example, the single transverse spin asymmetries could be used to probe the well-known Sivers function $f_{1T}^{\perp q}$, as well as the transversal helicity distribution $g_{1T}^{q}$ via the parity-violating nature of $W$ production.
Phenomenology of single spin asymmetries in p(transv. polarized)-p -> pion + X  [PDF]
Mauro Anselmino,Maria Boglione,Francesco Murgia
Physics , 1999, DOI: 10.1103/PhysRevD.60.054027
Abstract: A phenomenological description of single transverse spin effects in hadron-hadron inclusive processes is proposed, assuming a generalized factorization scheme and pQCD hard interactions. The transverse momentum, k_T, of the quarks inside the hadrons and of the hadrons relatively to the fragmenting quark, is taken into account in distribution and fragmentation functions, and leads to possible non zero single spin asymmetries. The role of k_T and spin dependent quark fragmentations -- the so-called Collins effect -- is investigated in details in p(transv. polarized)-p -> pion + X processes: it is shown how the experimental data could be described, obtaining an explicit expression for the spin asymmetry of a polarized fragmenting quark, on which some comments are made. Predictions for other processes, possible further applications and experimental tests are discussed.
Measurements of Double-Polarized Compton Scattering Asymmetries and Extraction of the Proton Spin Polarizabilities  [PDF]
P. P. Martel,R. Miskimen,P. Aguar-Bartolome,J. Ahrens,C. S. Akondi,J. R. M. Annand,H. J. Arends,W. Barnes,R. Beck,A. Bernstein,N. Borisov,A. Braghieri,W. J. Briscoe,S. Cherepnya,C. Collicott,S. Costanza,A. Denig,M. Dieterle,E. J. Downie,L. V. Fil'kov,S. Garni,D. I. Glazier,W. Gradl,G. Gurevich,P. Hall Barrientos,D. Hamilton,D. Hornidge,D. Howdle,G. M. Huber,T. C. Jude,A. Kaeser,V. L. Kashevarov,I. Keshelashvili,R. Kondratiev,M. Korolija,B. Krusche,A. Lazarev,V. Lisin,K. Livingston,I. J. D. MacGregor,J. Mancell,D. M. Manley,W. Meyer,D. G. Middleton,A. Mushkarenkov,B. M. K. Nefkens,A. Neganov,A. Nikolaev,M. Oberle,H. Ortega Spina,M. Ostrick,P. Ott,P. B. Otte,B. Oussena,P. Pedroni,A. Polonski,V. Polyansky,S. Prakhov,A. Rajabi,G. Reicherz,T. Rostomyan,A. Sarty,S. Schrauf,S. Schumann,M. H. Sikora,A. Starostin,O. Steffen,I. I. Strakovsky,T. Strub,I. Supek,M. Thiel,L. Tiator,A. Thomas,M. Unverzagt,Y. Usov,D. P. Watts,L. Witthauer,D. Werthmüller,M. Wolfes
Physics , 2014, DOI: 10.1103/PhysRevLett.114.112501
Abstract: The spin polarizabilities of the nucleon describe how the spin of the nucleon responds to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is through polarized Compton scattering. Double-polarized Compton scattering asymmetries on the proton were measured in the $\Delta(1232)$ region using circularly polarized incident photons and a transversely polarized proton target at the Mainz Microtron. Fits to asymmetry data were performed using a dispersion model calculation and a baryon chiral perturbation theory calculation, and a separation of all four proton spin polarizabilities in the multipole basis was achieved. The analysis based on a dispersion model calculation yields $\gamma_{E1E1} = -3.5 \pm 1.2$, $\gamma_{M1M1}= 3.16 \pm 0.85$, $\gamma_{E1M2} = -0.7 \pm 1.2$, and $\gamma_{M1E2} = 1.99 \pm 0.29$, in units of $10^{-4}$ fm$^4$.
Longitudinal Spin Asymmetry and Cross Section of Inclusive pi0 Production in Polarized p+p Collisions at RHIC  [PDF]
Frank Simon,for the STAR Collaboration
Physics , 2006, DOI: 10.1063/1.2750792
Abstract: We present the first measurement of the cross section and the double longitudinal spin asymmetry of inclusive pi0 production in polarized p+p collisions at Sqrt(s) = 200 GeV at mid-rapidity with the STAR detector, using the barrel electromagnetic calorimeter. The measured cross section is compared to NLO pQCD calculations and can provide constraints on the pion fragmentation functions. Fragmentation is studied directly by measuring the momentum fraction of pi0 in jets, a quantity that is affected by the fragmentation process and jet reconstruction effects. The double longitudinal spin asymmetry is compared to NLO pQCD calculations based on different assumptions for the gluon polarization in the nucleon to provide constraints on delta g/g. At the present level of statistics the measured asymmetry disfavors a large positive gluon polarization, but can not yet distinguish between other scenarios.
Predictions for single spin asymmetries in lepton + p(transv. polarized) -> pion + X and gamma^* + p(transv. polarized) -> pion + X  [PDF]
M. Anselmino,M. Boglione,J. Hansson,F. Murgia
Physics , 1999, DOI: 10.1007/s100520050714
Abstract: Predictions for the single transverse spin asymmetry A_N in semi-inclusive DIS processes are given; non negligible values of A_N may arise from spin effects in the fragmentation of a polarized quark into a final hadron with a transverse momentum k_T with respect to the jet axis, the so-called Collins effect. The elementary single spin asymmetry of the fragmenting quark has been fixed in a previous paper, by fitting data on p(transv. polarized) + P -> pion + X, and the predictions given here are uniquely based on the assumption that the Collins effect is the only cause of the observed single spin asymmetries in p(transv. polarized) + p -> pion + X. Eventual spin and k_T dependences in quark distribution functions, the so-called Sivers effect, are also discussed.
Polarized Moller Scattering Asymmetries  [PDF]
Andrzej Czarnecki,William J. Marciano
Physics , 2000, DOI: 10.1142/S0217751X00002433
Abstract: The utility of polarized electron beams for precision electroweak studies is described. Parity violating Moller scattering asymmetries in e-e- --> e-e- are discussed. Effects of electroweak radiative corrections and the running sin^2(theta_W(Q^2)) are reviewed. The sensitivity of E158 (a fixed target e-e- experiment at SLAC) and future e-e- collider studies to ``new physics'' is briefly outlined.
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