Physics Commons^™

Measurement Of Spin-Density Matrix Elements In P(770) Production With A Linearly Polarized Photon Beam At E𝛾 = 8.2-8.8 Gev, S. Adhikari, F. Afzal, C. S. Akondi, M. Albrecht, M. Amaryan, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, T. D. Beattie, V. V. Berdnikov, T. Black, W. Boeglin, W. J. Briscoe, T. Britton, B. Zihlmann, Et Al., Gluex Collaboration

Physics Faculty Publications

The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized 8.5 GeV photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson ρ(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of s-channel helicity conservation at small squared four-momentum transfer t and are able to extract the t dependence of natural- and unnatural-parity exchange contributions to …

Measurement Of Spin Density Matrix Elements In Λ(1520) Photoproduction At 8.2-8.8 Gev, Shankar Adhikari, C. S. Akondi, M. Albrecht, Moskov Amaryan, Tyler Viducic, B. Zihlmann, Et Al., Gluex Collaboration, D. I. Glazier, V. Mathieu

Physics Faculty Publications

We report on the measurement of spin density matrix elements of the Λ(1520) in the photoproduction reaction γp→Λ(1520)K⁺, via its subsequent decay to K⁻p. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Laboratory using a linearly polarized photon beam with E_γ = 8.2 GeV–8.8 GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, − (t − t₀). We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are …

Polarized Structure Function ΣLt' From 𝜋⁰P Electroproduction Data In The Resonance Region At 0.2 Gev² < Q² < 1.0 Gev², E. L. Isupov, V. D. Burkert, A. A. Golubenko, K. Joo, N. S. Markov, V. I. Mokeev, L. C. Smith, N. Zachariou, W. R. Armstrong, H. Atac, Et Al

Physics Faculty Publications

The first results on the σ_LT′ structure function in exclusive π⁰p electroproduction at invariant masses of the final state of 1.5GeV < W < 1.8 GeV and in the range of photon virtualities 0.4 GeV² < Q² < 1.0 GeV² were obtained from data on beam spin asymmetries and differential cross sections measured with the CLAS detector at Jefferson Lab. The Legendre moments determined from the σ_LT′ structure function have demonstrated sensitivity to the contributions from the nucleon resonances in the second and third resonance regions. These new data on the beam spin asymmetries in π⁰p electroproduction extend the opportunities for the extraction of the nucleon resonance electro-excitation amplitudes in …

Measuring The Weizsäcker-Williams Distribution Of Linearly Polarized Gluons At An Electron-Ion Collider Through Dijet Azimuthal Asymmetries, Adrian Dumitru, Vladimir Skokov, Thomas Ullrich

Publications and Research

The production of a hard dijet with small transverse momentum imbalance in semi-inclusive DIS probes the conventional and linearly polarized Weizsäcker-Williams (WW) transverse momentum dependent (TMD) gluon distributions. The latter, in particular, gives rise to an azimuthal dependence of the dijet cross section. In this paper we analyze the feasibility of a measurement of these TMDs through dijet production in DIS on a nucleus at an electron-ion collider. We introduce the MCDIJET Monte Carlo generator to sample quark-antiquark dijet configurations based on leading-order parton level cross sections with WW gluon distributions that solve the nonlinear small-x QCD evolution equations. …

Compton Scattering From The Deuteron Above Pion-Production Threshold, B. Strandberg, J. R. M. Annand, W. Briscoe, J. Brudvik, F. Cividini, L. Clark, E. J. Downie, K. England, G. Feldman, K. G. Fissum, D. I. Glazier, K. Hamilton, K. Hansen, L. Isaksson, R. Al Jebali, Michael A. Kovash, S. Lipschutz, M. Lundin, M. Meshkian, D. G. Middleton, L. S. Myers, D. O'Donnell, G. O'Rielly, B. Oussena, M. F. Preston, B. Schröder, B. Seitz, I. Strakovsky, M. Taragin

Physics and Astronomy Faculty Publications

The electromagnetic polarizabilities of the nucleon are fundamental nucleon-structure observables that characterize its response to external electromagnetic fields. The neutron polarizabilities can be accessed from Compton-scattering data on light nuclear targets. Recent measurements of the differential cross section for Compton scattering on the deuteron below the pion-production threshold have decreased the uncertainties in the neutron polarizabilities, yet the proton polarizabilities remain known substantially more accurately. As the sensitivity of the cross section to the polarizabilities increases with incident photon energy, measurements above the pion threshold may offer a way for an improved determination of the neutron polarizabilities. In this Rapid …

Measurement Of The Beam Asymmetry Σ And The Target Asymmetry T In The Photoproduction Of Ω Mesons Off The Proton Using Clas At Jefferson Laboratory, P. Roy, Z. Akbar, S. Park, V. Crede, A. V. Anisovich, I. Denisenko, E. Klempt, V. A. Nikonov, A. V. Sarantsev, K. P. Adhikari, S. Adhikari, S. Anefalos Pereira, J. Ball, I. Balossino, M. Bashkanov, M. Battaglieri, V. Batourine, I. Bedlinskiy, A. S. Biselli, S. Boiarinov, W. J. Briscoe, J. Brock, W. K. Brooks, V. D. Burkert, C. Carlin, D. S. Carman, A. Celentano, G. Charles, T. Chetry, G. Ciullo, Wesley P. Gohn

Physics and Astronomy Faculty Publications

The photoproduction of ω mesons off the proton has been studied in the reaction γp → pω using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the target asymmetry T has been measured in photoproduction from the decay ω → π⁺π⁻π⁰, using a transversely polarized target with energies ranging from just above the reaction threshold up to 2.8 GeV. Significant nonzero values are observed for these asymmetries, reaching about 30–40% in the third-resonance region. New measurements for the …

New Result For The Neutron Β-Asymmetry Parameter A0 From Ucna, M. A.-P. Brown, E. B. Dees, E. Adamek, B. Allgeier, M. Blatnik, T. J. Bowles, L. J. Broussard, R. Carr, S. Clayton, C. Cude-Woods, S. Currie, X. Ding, B. W. Filippone, A. García, P. Geltenbort, S. Hasan, K. P. Hickerson, J. Hoagland, R. Hong, G. E. Hogan, A. T. Holley, T. M. Ito, A. Knecht, C. -Y. Liu, J. Liu, M. Makela, J. W. Martin, D. Melconian, M. P. Mendenhall, S. D. Moore, Subash C. Nepal, N. Nouri, Bradley R. Plaster

Physics and Astronomy Faculty Publications

Background: The neutron β-decay asymmetry parameter A₀ defines the angular correlation between the spin of the neutron and the momentum of the emitted electron. Values for A₀ permit an extraction of the ratio of the weak axial-vector to vector coupling constants, λ ≡ g_A/g_V, which under assumption of the conserved vector current hypothesis (g_V = 1) determines g_A. Precise values for g_A are important as a benchmark for lattice QCD calculations and as a test of the standard model.

Purpose: The UCNA experiment, carried out at the …

Measurement Of The Q² Dependence Of The Deuteron Spin Structure Function G1 And Its Moments At Low Q² With Clas, Clas Collaboration, K. P. Adhikari, L. El Fassi, S E. Kuhn, M. J. Amaryan, S. Bültmann, G. Charles, Gail Dodge, N. Guler, C. E. Hyde, A. Klein, D. Payette, J. Poudel, Y. Prok, L. B. Weinstein, J. Zhang, Z. W. Zhao

Physics Faculty Publications

We measured the g₁ spin structure function of the deuteron at low Q², where QCD can be approximated with chiral perturbation theory (χPT). The data cover the resonance region, up to an invariant mass of W ≈ 1.9  GeV. The generalized Gerasimov-Drell-Hearn sum, the moment Γ^d₁ and the spin polarizability γ^d₀ are precisely determined down to a minimum Q² of 0.02  GeV² for the first time, about 2.5 times lower than that of previous data. We compare them to several χPT calculations and models. These results are the first in a …

Measurement Of The Helicity Asymmetry E In Ω → Π+Π−Π0 Photoproduction, Z. Akbar, P. Roy, S. Park, V. Crede, A. V. Anisovich, I. Denisenko, E. Klempt, V. A. Nikonov, A. V. Sarantsev, K. P. Adhikari, S. Adhikari, M. J. Amaryan, S. Anefalos Pereira, H. Avakian, J. Ball, M. Battaglieri, V. Batourine, I. Bedlinskiy, S. Boiarinov, W. J. Briscoe, J. Brock, W. K. Brooks, V. D. Burkert, F. T. Cao, C. Carlin, D. S. Carman, A. Celentano, G. Charles, T. Chetry, G. Ciullo, Wesley P. Gohn

Physics and Astronomy Faculty Publications

The double-polarization observable E was studied for the reaction γp → pω using the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at the Thomas Jefferson National Accelerator Facility and the longitudinally polarized frozen-spin target (FROST). The observable was measured from the charged decay mode of the meson, ω → π⁺π⁻π⁰, using a circularly polarized tagged-photon beam with energies ranging from the ω threshold at 1.1 to 2.3 GeV. A partial-wave analysis within the Bonn-Gatchina framework found dominant contributions from the 3/2⁺ partial wave near threshold, which is identified with the subthreshold N …

Compton Scattering From 4He At 61 Mev, M. H. Sikora, M. W. Ahmed, A. Banu, C. Bartram, B. Crowe, E. J. Downie, G. Feldman, H. Gao, H. W. Grießhammer, H. Hao, C. R. Howell, H. J. Karwowski, D. P. Kendellen, Michael A. Kovash, X. Li, D. M. Markoff, S. Mikhailov, V. Popov, R. E. Pywell, J. A. Silano, M. C. Spraker, P. Wallace, H. R. Weller, C. S. Whisnant, Y. K. Wu, W. Xiong, X. Yan, Z. W. Zhao

Physics and Astronomy Faculty Publications

The Compton scattering cross section from ⁴He has been measured with high statistical accuracy over a scattering angle range of 40^∘−159^∘ using a quasimonoenergetic 61-MeV photon beam at the High Intensity Gamma-Ray Source. The data are interpreted using a phenomenological model sensitive to the dipole isoscalar electromagnetic polarizabilities (α_s and β_s) of the nucleon. These data can be fit with the model using values of α_s and β_s that are consistent with the currently accepted values. These data will serve as benchmarks of future calculations from effective field theories and …

Target And Beam-Target Spin Asymmetries In Exclusive Pion Electroproduction For Q2 > 1 Gev2. Ii. Ep → Eπ0P, P. E. Bosted, A. Kim, K. P. Adhikari, D. Adikaram, Z. Akbar, M. J. Amaryan, S. Anefalos Pereira, H. Avakian, R. A. Badui, J. Ball, I. Balossino, M. Battaglieri, I. Bedlinskiy, A. S. Biselli, S. Boiarinov, W. J. Briscoe, W. K. Brooks, S. Bültmann, V. D. Burkert, T. Cao, D. S. Carman, A. Celentano, S. Chandavar, G. Charles, T. Chetry, G. Ciullo, L. Clark, L. Colaneri, P. L. Cole, M. Contalbrigo, Wesley P. Gohn

Physics and Astronomy Faculty Publications

Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive π⁰ electroproduction reaction γ^∗p → pπ⁰, expanding an analysis of the γ^∗p → nπ⁺ reaction from the same experiment. The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic ranges covered are 1.1 < W < 3 GeV and 1 < Q² < 6 GeV². Results were obtained for about 5700 bins in W, Q², cos(θ^∗), and ϕ^∗. The beam-target asymmetries were found …

Determination Of The Proton Spin Structure Functions For 0.05 < Q2 <5gev2 Using Clas, R. G. Fersch, N. Guler, P. Bosted, A. Deur, K. Griffioen, C. Keith, S E. Kuhn, R. Minehart, Y. Prok, K. P. Adhikari, S. Bültmann, S. Careccia, Gail Dodge, V. G. Lagerquist, L. B. Weinstein

Physics Faculty Publications

We present the results of our final analysis of the full data set of g^p₁ Q², the spin structure function of the proton, collected using CLAS at Jefferson Laboratory in 2000-2001. Polarized electrons with energies of 1.6, 2.5, 4.2, and 5.7 GeV were scattered from proton targets ¹⁵NH₃ dynamically polarized along the beam direction) and detected with CLAS. From the measured double spin asymmetries, we extracted virtual photon asymmetries A^p₁ and A^p₂ and spin structure functions g ^p₁ and g^p₂ over a wide kinematic range (0.05 GeV …

Target And Beam-Target Spin Asymmetries In Exclusive Pion Electroproduction For Q² > 1 Gev² . Ii. Ep→ Eπºp, Clas Collaboration, K. P. Adhikari, D. Adikaram, M. J. Amaryan, S. Bültmann, N. Guler, S E. Kuhn, A. Klein, S. Koirala, B. Torayev, J. Zhang, Z. W. Zhao

Physics Faculty Publications

Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive π⁰ electroproduction reaction γ^∗p→pπ⁰, expanding an analysis of the γ^∗p→nπ⁺ reaction from the same experiment. The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic ranges covered are 1.1 < W < 3 GeV and 1 < Q²< 6 GeV² . Results were obtained for about 5700 bins in W, Q², cos(θ^∗) , and ϕ^∗. The beam-target asymmetries were found to generally be greater than zero, with …

Measurement Of The Helicity Asymmetry E In Ω→Π+ΠˉΠᵒ Photoproduction, Z. Akbar, P. Roy, S. Park, V. Crede, A. V. Anisovich, I. Denisenko, E. Klempt, V. A. Nikonov, A. V. Sarantsev, K. P. Adhikari, M. J. Amaryan, G. Charles, A. Klein, Y. Prok, J. Zhang, Z. W. Zhao

Physics Faculty Publications

The double-polarization observable E was studied for the reaction γp→pω using the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at the Thomas Jefferson National Accelerator Facility and the longitudinally polarized frozen-spin target (FROST). The observable was measured from the charged decay mode of the meson, ω→π⁺π^-π⁰, using a circularly polarized tagged-photon beam with energies ranging from the ω threshold at 1.1 to 2.3 GeV. A partial-wave analysis within the Bonn-Gatchina framework found dominant contributions from the 3/2⁺ partial wave near threshold, which is identified with the subthreshold N(1720)3/2⁺ nucleon …

Target And Beam-Target Spin Asymmetries In Exclusive Π+ And Π− Electroproduction With 1.6- To 5.7-Gev Electrons, P. E. Bosted, A. S. Biselli, S. Careccia, G. Dodge, R. Fersch, N. Guler, S. E. Kuhn, J. Pierce, Y. Prok, X. Zheng, K. P. Adhikari, D. Adikaram, Z. Akbar, M. J. Amaryan, S. Anefalos Pereira, G. Asryan, H. Avakian, R. A. Badui, J. Ball, N. A. Baltzell, M. Battaglieri, V. Batourine, I. Bedlinskiy, S. Boiarinov, W. J. Briscoe, S. Bültmann, V. D. Burkert, T. Cao, D. S. Carman, A. Celentano, Wesley P. Gohn

Physics and Astronomy Faculty Publications

Beam-target double-spin asymmetries and target single-spin asymmetries in exclusive π+ and quasiexclusive π− electroproduction were obtained from scattering of 1.6- to 5.7-GeV longitudinally polarized electrons from longitudinally polarized protons (for π+) and deuterons (for π−) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic range covered is 1.1 < W < 2.6 GeV and 0.05 < Q² < 5 GeV², with good angular coverage in the forward hemisphere. The asymmetry results were divided into approximately 40 000 kinematic bins for π+ from free protons and 15 000 bins for π− production from bound nucleons in the deuteron. The …

Measurement Of Target And Double-Spin Asymmetries For The Ep → Eπ+(N) Reaction In The Nucleon Resonance Region At Low Q², Clas Collaboration, K. P. Adhikari, S E. Kuhn, D. Adikaram, M. J. Amaryan, S. Bültmann, Gail Dodge, N. Guler, L. B. Weinstein

Physics Faculty Publications

We report measurements of target- and double-spin asymmetries for the exclusive channel ^→e^→p → eπ⁺(n) in the nucleon resonance region at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). These asymmetries were extracted from data obtained using a longitudinally polarized NH₃ target and a longitudinally polarized electron beam with energies 1.1, 1.3, 2.0, 2.3, and 3.0 GeV. The new results are consistent with previous CLAS publications but are extended to a low Q² range from 0.0065 to 0.35(GeV/c)². The Q² access was made possible by a custom-built Cherenkov detector …