B McKinnon

Publications (135)167.96 Total impact

• Article: Demonstration of a novel technique to measure two-photon exchange effects in elastic $e^\pm p$ scattering

  M. Moteabbed, M. Niroula, B. A. Raue, L. B. Weinstein, D. Adikaram, J. Arrington, W. K. Brooks, J. Lachniet, Dipak Rimal, M. Ungaro, [......], S. Tkachenko, H. Voskanyan, E. Voutier, N. K. Walford, M. H. Wood, N. Zachariou, L. Zana, J. Zhang, Z. W. Zhao, I. Zonta
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  ABSTRACT: The discrepancy between proton electromagnetic form factors extracted using unpolarized and polarized scattering data is believed to be a consequence of two-photon exchange (TPE) effects. However, the calculations of TPE corrections have significant model dependence, and there is limited direct experimental evidence for such corrections. We present the results of a new experimental technique for making direct $e^\pm p$ comparisons, which has the potential to make precise measurements over a broad range in $Q^2$ and scattering angles. We use the Jefferson Lab electron beam and the Hall B photon tagger to generate a clean but untagged photon beam. The photon beam impinges on a converter foil to generate a mixed beam of electrons, positrons, and photons. A chicane is used to separate and recombine the electron and positron beams while the photon beam is stopped by a photon blocker. This provides a combined electron and positron beam, with energies from 0.5 to 3.2 GeV, which impinges on a liquid hydrogen target. The large acceptance CLAS detector is used to identify and reconstruct elastic scattering events, determining both the initial lepton energy and the sign of the scattered lepton. The data were collected in two days with a primary electron beam energy of only 3.3 GeV, limiting the data from this run to smaller values of $Q^2$ and scattering angle. Nonetheless, this measurement yields a data sample for $e^\pm p$ with statistics comparable to those of the best previous measurements. We have shown that we can cleanly identify elastic scattering events and correct for the difference in acceptance for electron and positron scattering. The final ratio of positron to electron scattering: $R=1.027\pm0.005\pm0.05$ for $<Q^2>=0.206$ GeV$^2$ and $0.830\leq \epsilon\leq 0.943$.
  06/2013;
• Article: Hard Two-body Photodisintegration of 3He

  I. Pomerantz, Y. Ilieva, R. Gilman, D. W. Higinbotham, E. Piasetzky, S. Strauch, K. P. Adhikari, M. Aghasyan, K. Allada, M. J. Amaryan, [......], B. Wojtsekhowski, M. H. Wood, X. Yan, H. Yao, N. Zachariou, X. Zhan, J. Zhang, Z. W. Zhao, X. Zheng, I. Zonta
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  ABSTRACT: We have measured cross sections for the gamma+3He->p+d reaction at photon energies of 0.4 - 1.4 GeV and a center-of-mass angle of 90 deg. We observe dimensional scaling above 0.7 GeV at this center-of-mass angle. This is the first observation of dimensional scaling in the photodisintegration of a nucleus heavier than the deuteron.
  03/2013;
• Article: Transverse Polarization of $\Sigma^{+}(1189)$ in Photoproduction on a Hydrogen Target in CLAS

  C. S. Nepali, M. Amaryan, K. P. Adhikari, M. Aghasyan, S. Anefalos Pereira, H. Baghdasaryan, J. Ball, M. Battaglieri, V. Batourine, I. Bedlinskiy, [......], E. Voutier, N. K. Walford, D. P. Watts, L. B. Weinstein, D. P. Weygand, N. Zachariou, L. Zana, J. Zhang, Z. W. Zhao, I. Zonta
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  ABSTRACT: Experimental results on the $\Sigma^+(1189)$ hyperon transverse polarization in photoproduction on a hydrogen target using the CLAS detector at Jefferson laboratory are presented. The $\Sigma^+(1189)$ was reconstructed in the exclusive reaction $\gamma+p\rightarrow K^{0}_{S} + \Sigma^+(1189)$ via the $\Sigma^{+} \to p \pi^{0}$ decay mode. The $K^{0}_S$ was reconstructed in the invariant mass of two oppositely charged pions with the $\pi^0$ identified in the missing mass of the detected $p\pi^+\pi^-$ final state. Experimental data were collected in the photon energy range $E_{\gamma}$ = 1.0-3.5 GeV ($\sqrt{s}$ range 1.66-2.73 GeV). We observe a large negative polarization of up to 95%. As the mechanism of transverse polarization of hyperons produced in unpolarized photoproduction experiments is still not well understood, these results will help to distinguish between different theoretical models on hyperon production and provide valuable information for the searches of missing baryon resonances.
  02/2013;
• Article: Near Threshold Neutral Pion Electroproduction at High Momentum Transfers and Generalized Form Factors

  P. Khetarpal, P. Stoler, I. G. Aznauryan, V. Kubarovsky, K. P. Adhikari, D. Adikaram, M. Aghasyan, M. J. Amaryan, M. D. Anderson, S. Anefalos Pereira, [......], H. Voskanyan, E. Voutier, N. K. Walford, L. B. Weinstein, D. P. Weygand, M. H. Wood, N. Zachariou, J. Zhang, Z. W. Zhao, I. Zonta
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  ABSTRACT: We report the measurement of near threshold neutral pion electroproduction cross sections and the extraction of the associated structure functions on the proton in the kinematic range $Q^2$ from 2 to 4.5 GeV$^2$ and $W$ from 1.08 to 1.16 GeV. These measurements allow us to access the dominant pion-nucleon s-wave multipoles $E_{0+}$ and $S_{0+}$ in the near-threshold region. In the light-cone sum-rule framework (LCSR), these multipoles are related to the generalized form factors $G_1^{\pi^0 p}(Q^2)$ and $G_2^{\pi^0 p}(Q^2)$. The data are compared to these generalized form factors and the results for $G_1^{\pi^0 p}(Q^2)$ are found to be in good agreement with the LCSR predictions, but the level of agreement with $G_2^{\pi^0 p}(Q^2)$ is poor.
  11/2012;
• Article: Technical Design Report for the: PANDA Micro Vertex Detector

  PANDA Collaboration, W. Erni, I. Keshelashvili, B. Krusche, M. Steinacher, Y. Heng, Z. Liu, H. Liu, X. Shen, Q. Wang, [......], M. Plominski, J. Szewinski, K. Traczyk, B. Zwieglinski, P. Bühler, A. Gruber, P. Kienle, J. Marton, E. Widmann, J. Zmeskal
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  ABSTRACT: This document illustrates the technical layout and the expected performance of the Micro Vertex Detector (MVD) of the PANDA experiment. The MVD will detect charged particles as close as possible to the interaction zone. Design criteria and the optimisation process as well as the technical solutions chosen are discussed and the results of this process are subjected to extensive Monte Carlo physics studies. The route towards realisation of the detector is outlined.
  07/2012;
• Article: Measurement of Exclusive $\pi^0$ Electroproduction Structure Functions and their Relationship to Transversity GPDs

  CLAS Collaboration, I. Bedlinskiy, V. Kubarovsky, S. Niccolai, P. Stoler, K. P. Adhikari, M. Aghasyan, M. J. Amaryan, M. Anghinolfi, H. Avakian, [......], E. Voutier, N. K. Walford, D. P. Watts, L. B. Weinstein, D. P. Weygand, M. H. Wood, N. Zachariou, J. Zhang, Z. W. Zhao, I. Zonta
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  ABSTRACT: Exclusive $\pi^0$ electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in $Q^2$, $x_B$, $t$, and $\phi_\pi$, in the $Q^2$ range from 1.0 to 4.6 GeV$^2$,\ $-t$ up to 2 GeV$^2$, and $x_B$ from 0.1 to 0.58. Structure functions $\sigma_T +\epsilon \sigma_L, \sigma_{TT}$ and $\sigma_{LT}$ were extracted as functions of $t$ for each of 17 combinations of $Q^2$ and $x_B$. The data were compared directly with two handbag-based calculations including both longitudinal and transversity GPDs. Inclusion of only longitudinal GPDs very strongly underestimates $\sigma_T +\epsilon \sigma_L$ and fails to account for $\sigma_{TT}$ and $\sigma_{LT}$, while inclusion of transversity GPDs brings the calculations into substantially better agreement with the data. There is very strong sensitivity to the relative contributions of nucleon helicity flip and helicity non-flip processes. The results confirm that exclusive $\pi^0$ electroproduction offers direct experimental access to the transversity GPDs.
  06/2012;
• Article: Comparison of forward and backward pp pair knockout in 3He(e, e′pp)n

  H. Baghdasaryan, L. B. Weinstein, J. M. Laget, K. P. Adhikari, M. Aghasyan, M. J. Amaryan, M. Anghinolfi, J. Ball, M. Battaglieri, A. S. Biselli, [......], S. Stepanyan, S. Strauch, M. Taiuti, W. Tang, S. Tkachenko, H. Voskanyan, E. Voutier, M. H. Wood, L. Zana, B. Zhao
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  ABSTRACT: Measuring nucleon-nucleon short range correlations (SRCs) has been a goal of the nuclear physics community for many years. They are an important part of the nuclear wave function, accounting for almost all of the high-momentum strength. They are closely related to the EMC effect. While their overall probability has been measured, measuring their momentum distributions is more difficult. In order to determine the best configuration for studying SRC momentum distributions, we measured the 3He(e, e′pp)n reaction, looking at events with high-momentum protons (pp>0.35 GeV/c) and a low-momentum neutron (pn<0.2 GeV/c). We examined two angular configurations: either both protons emitted forward or one proton emitted forward and one backward (with respect to the momentum transfer, q⃗). The measured relative momentum distribution of the events with one forward and one backward proton was much closer to the calculated initial-state pp relative momentum distribution, indicating that this is the preferred configuration for measuring SRC.
  Phys. Rev. C. 06/2012; 85(6).
• Article: Deep exclusive $\pi^+$ electroproduction off the proton at CLAS

  K. Park, M. Guidal, R. W. Gothe, J. M. Laget, M. Garçon, K. P. Adhikari, M. Aghasyan, M. J. Amaryan, M. Anghinolfi, H. Avakian, [......], E. Voutier, N. K. Walford, D. P. Watts, L. B. Weinstein, D. P. Weygand, M. H. Wood, N. Zachariou, J. Zhang, Z. W. Zhao, I. Zonta
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  ABSTRACT: The exclusive electroproduction of $\pi^+$ above the resonance region was studied using the $\rm{CEBAF}$ Large Acceptance Spectrometer ($\rm{CLAS}$) at Jefferson Laboratory by scattering a 6 GeV continuous electron beam off a hydrogen target. The large acceptance and good resolution of $\rm{CLAS}$, together with the high luminosity, allowed us to measure the cross section for the $\gamma^* p \to n \pi^+$ process in 140 ($Q^2$, $x_B$, $t$) bins: $0.16<x_B<0.58$, 1.6 GeV$^2<$$Q^2$$<4.5$ GeV$^2$ and 0.1 GeV$^2<$$-t$$<5.3$ GeV$^2$. For most bins, the statistical accuracy is on the order of a few percent. Differential cross sections are compared to two theoretical models, based either on hadronic (Regge phenomenology) or on partonic (handbag diagram) degrees of freedom. Both can describe the gross features of the data reasonably well, but differ strongly in their ingredients. If the handbag approach can be validated in this kinematical region, our data contain the interesting potential to experimentally access transversity Generalized Parton Distributions.
  06/2012;
• Source

  Available from: W. J. Briscoe

  Article: Evidence for a backward peak in the γd → π0d cross section near the η threshold

  The CLAS Collaboration, Y. Ilieva, B. L. Berman, A. E. Kudryavtsev, I. I. Strakovsky, V. E. Tarasov, M. Amarian, P. Ambrozewicz, M. Anghinolfi, G. Asryan, [......], L. B. Weinstein, D. P. Weygand, M. Williams, E. Wolin, M. H. Wood, A. Yegneswaran, L. Zana, J. Zhang, B. Zhao, Z. Zhao
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  ABSTRACT: High-quality cross sections for the reaction γd → π0 d have been measured using the CLAS at Jefferson Lab over a wide energy range near and above the η-meson photoproduction threshold. At backward c.m. angles for the outgoing pions, we observe a resonance-like structure near E γ = 700 MeV. Our model analysis shows that it can be explained by η excitation in the intermediate state. The effect is the result of the contribution of the N(1535)S 11-resonance to the amplitudes of the subprocesses occurring between the two nucleons and of a two-step process in which the excitation of an intermediate η-meson dominates.
  European Physical Journal A 04/2012; 43(3):261-267. · 2.19 Impact Factor
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  Available from: John Robert Arrington

  Article: Measurement of the neutron F2 structure function via spectator tagging with CLAS.

  N Baillie, S Tkachenko, J Zhang, P Bosted, S Bültmann, M E Christy, H Fenker, K A Griffioen, C E Keppel, S E Kuhn, [......], W Tang, M Ungaro, M F Vineyard, E Voutier, D P Watts, L B Weinstein, D P Weygand, M H Wood, L Zana, B Zhao
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  ABSTRACT: We report on the first measurement of the F(2) structure function of the neutron from the semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to ≲100 MeV/c and their angles to ≳100° relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The F(2)(n) data collected cover the nucleon-resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65<Q(2)<4.52 GeV(2), with uncertainties from nuclear corrections estimated to be less than a few percent. These measurements provide the first determination of the neutron to proton structure function ratio F(2)(n)/F(2)(p) at 0.2≲x≲0.8 with little uncertainty due to nuclear effects.
  Physical Review Letters 04/2012; 108(14):142001. · 7.37 Impact Factor
• Article: Comment on the narrow structure reported by Amaryan et al

  M. Anghinolfi, J. Ball, N. A. Baltzell, M. Battaglieri, I. Bedlinskiy, M. Bellis, A. S. Biselli, C. Bookwalter, S. Boiarinov, P. Bosted, [......], S. S. Stepanyan, P. Stoler, W. Tang, M. Ungaro, B. Vernarsky, M. F. Vineyard, D. P. Weygand, M. H. Wood, N. Zachariou, B. Zhao
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  ABSTRACT: The CLAS Collaboration provides a comment on the physics interpretation of the results presented in a paper published by M. Amaryan et al. regarding the possible observation of a narrow structure in the mass spectrum of a photoproduction experiment.
  04/2012;
• Article: Upper limits for the photoproduction cross section for the Φ−−(1860) pentaquark state off the deuteron

  H. Egiyan, J. Langheinrich, R. W. Gothe, L. Graham, M. Holtrop, H. Lu, P. Mattione, G. Mutchler, K. Park, E. S. Smith, [......], D. J. Tedeschi, M. Ungaro, E. Voutier, D. P. Watts, L. B. Weinstein, D. P. Weygand, M. H. Wood, N. Zachariou, L. Zana, B. Zhao
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  ABSTRACT: We searched for the Φ−−(1860) pentaquark in the photoproduction process off the deuteron in the Ξ−π−-decay channel using CLAS. The invariant-mass spectrum of the Ξ−π− system does not indicate any statistically significant enhancement near the reported mass M=1.860 GeV. The statistical analysis of the sideband-subtracted mass spectrum yields a 90%-confidence-level upper limit of 0.7 nb for the photoproduction cross section of Φ−−(1860) with a consecutive decay into Ξ−π− in the photon-energy range 4.5 GeV<Eγ<5.5 GeV.
  Phys. Rev. C. 01/2012; 85(1).
• Source

  Available from: John Robert Arrington

  Article: Evidence for the Onset of Color Transparency in $\rho^0$ Electroproduction off Nuclei

  L. El Fassi, L. Zana, K. Hafidi, M. Holtrop, B. Mustapha, W. K. Brooks, H. Hakobyan, X. Zheng, K. P. Adhikari, D. Adikaram, [......], M. F. Vineyard, H. Voskanyan, E. Voutier, D. Watts, L. B. Weinstein, D. P. Weygand, M. H. Wood, N. Zachariou, B. Zhao, Z. W. Zhao
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  ABSTRACT: We have measured the nuclear transparency of the incoherent diffractive $A(e,e'\rho^0)$ process in $^{12}$C and $^{56}$Fe targets relative to $^2$H using a 5 GeV electron beam. The nuclear transparency, the ratio of the produced $\rho^0$'s on a nucleus relative to deuterium, which is sensitive to $\rho A$ interaction, was studied as function of the coherence length ($l_c$), a lifetime of the hadronic fluctuation of the virtual photon, and the four-momentum transfer squared ($Q^2$). While the transparency for both $^{12}$C and $^{56}$Fe showed no $l_c$ dependence, a significant $Q^2$ dependence was measured, which is consistent with calculations that included the color transparency effects.
  01/2012;
• Source

  Available from: John Robert Arrington

  Article: Measurement of the neutron F2 structure function via spectator tagging with CLAS

  N. Baillie, S. Tkachenko, J. Zhang, P. Bosted, S. Bultmann, M. E. Christy, H. Fenker, K. A. Griffioen, C. E. Keppel, S. E. Kuhn, [......], W. Tang, M. Ungaro, M. F. Vineyard, E. Voutier, D. P. Watts, L. B. Weinstein, D. P. Weygand, M. H. Wood, L. Zana, B. Zhao
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  ABSTRACT: We report on the first measurement of the F2 structure function of the neutron from semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to < 100 MeV and their angles to < 100 degrees relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The F2n data collected cover the nucleon resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65 < Q2 < 4.52 GeV2, with uncertainties from nuclear corrections estimated to be less than a few percent. These measurements provide the first determination of the neutron to proton structure function ratio F2n/F2p at 0.2 < x < 0.8 with little uncertainty due to nuclear effects.
  10/2011;
• Article: Erratum: Experimental study of the γp→ηp reaction with the Crystal Ball detector at the Mainz Microtron (MAMI-C) [Phys. Rev. C 82, 035208 (2010)]

  E. F. McNicoll, S. Prakhov, I. I. Strakovsky, P. Aguar-Bartolomé, L. K. Akasoy, J. R. M. Annand, H. J. Arends, R. A. Arndt, Ya. I. Azimov, K. Bantawa, [......], I. Supek, M. Thiel, A. Thomas, L. Tiator, M. Unverzagt, D. P. Watts, D. Werthmüller, R. L. Workman, I. Zamboni, F. Zehr
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  ABSTRACT: Here we correct a factor of 2 missed in one of figures and the corresponding sentence in the text. It does not change any conclusions.
  Physical Review C 07/2011; 84(2):29901. · 3.31 Impact Factor
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  Available from: W. J. Briscoe

  Article: Precise Measurements of Beam Spin Asymmetries in Semi-Inclusive $\pi^0$ production

  M. Aghasyan, H Avakian, P Rossi, E De Sanctis, D. Hasch, M Mirazita, D. Adikaram, M J Amaryan, M Anghinolfi, H Baghdasaryan, [......], H. Voskanyan, E. Voutier, D. Watts, L B Weinstein, D P Weygand, M H Wood, L Zana, J Zhang, B Zhao, Z W Zhao
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  ABSTRACT: We present studies of single-spin asymmetries for neutral pion electroproduction in semi-inclusive deep-inelastic scattering of 5.776 GeV polarized electrons from an unpolarized hydrogen target, using the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. A substantial $\sin \phi_h$ amplitude has been measured in the distribution of the cross section asymmetry as a function of the azimuthal angle $\phi_h$ of the produced neutral pion. The dependence of this amplitude on Bjorken $x$ and on the pion transverse momentum is extracted with significantly higher precision than previous data and is compared to model calculations.
  06/2011;
• Article: Coherent photoproduction of π+ from 3He

  R. Nasseripour, B.L. Berman, K.P. Adhikari, D. Adikaram, M. Anghinolfi, J. Ball, M. Battaglieri, V. Batourine, I. Bedlinskiy, A.S. Biselli, [......], M. Ungaro, B. Vernarsky, M.F. Vineyard, E. Voutier, D.P. Watts, L.B. Weinstein, D.P. Weygand, M.H. Wood, B. Zhao, Z.W. Zhao
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  ABSTRACT: We have measured the differential cross section for the γ3He→π+t reaction. This reaction was studied using the Continuous Electron Beam Accelerator Facility (CEBAF) Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Real photons produced with the Hall-B bremsstrahlung tagging system in the energy range from 0.50 to 1.55 GeV were incident on a cryogenic liquid 3He target. The differential cross sections for the γ3He→π+t reaction were measured as a function of photon-beam energy and pion-scattering angle. Theoretical predictions to date cannot explain the large cross sections except at backward angles, showing that additional components must be added to the model.
  Phys. Rev. C. 03/2011; 83(3).
• Source

  Available from: W. J. Briscoe

  Article: Measurement of single- and double-spin asymmetries in deep inelastic pion electroproduction with a longitudinally polarized target.

  H Avakian, P Bosted, V D Burkert, L Elouadrhiri, K P Adhikari, M Aghasyan, M Amaryan, M Anghinolfi, H Baghdasaryan, J Ball, [......], B Vernarsky, M F Vineyard, E Voutier, D P Watts, L B Weinstein, D P Weygand, M H Wood, J Zhang, B Zhao, Z W Zhao
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  ABSTRACT: We report the first measurement of the transverse momentum dependence of double-spin asymmetries in semi-inclusive production of pions in deep-inelastic scattering off the longitudinally polarized proton. Data have been obtained using a polarized electron beam of 5.7 GeV with the CLAS detector at the Jefferson Lab (JLab). Modulations of single spin asymmetries over the azimuthal angle between lepton scattering and hadron production planes ϕ have been measured over a wide kinematic range in Bjorken x and virtual photon squared four-momentum Q2. A significant nonzero sin2ϕ single spin asymmetry was observed for the first time indicating strong spin-orbit correlations for transversely polarized quarks in the longitudinally polarized proton.
  Physical Review Letters 12/2010; 105(26):262002. · 7.37 Impact Factor
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  Available from: W. J. Briscoe

  Article: Near-threshold Photoproduction of Phi Mesons from Deuterium

  X Qian, W Chen, H Gao, K Hicks, K Kramer, J M Laget, T Mibe, Y. Qiang, S Stepanyan, D J Tedeschi, [......], M F Vineyard, E. Voutier, L B Weinstein, D P Weygand, M H Wood, N. Zachariou, L Zana, J Zhang, B Zhao, Z W Zhao
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  ABSTRACT: We report the first measurement of the differential cross section on $\phi$-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement was carried out by a triple coincidence detection of a proton, $K^+$ and $K^-$ near the theoretical production threshold of 1.57 GeV. The extracted differential cross sections $\frac{d\sigma}{dt}$ for the initial photon energy from 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. This experiment establishes a baseline for a future experimental search for an exotic $\phi$-N bound state from heavier nuclear targets utilizing subthreshold/near-threshold production of $\phi$ mesons.
  11/2010;
• Article: Tensor correlations measured in 3He(e,e' pp)n.

  H Baghdasaryan, L B Weinstein, J M Laget, K P Adhikari, M Aghasyan, M Amarian, M Anghinolfi, H Avakian, J Ball, M Battaglieri, [......], C E Taylor, D J Tedeschi, M Ungaro, M F Vineyard, E Voutier, D P Watts, D P Weygand, M H Wood, B Zhao, Z W Zhao
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  ABSTRACT: We have measured the 3He(e,e' pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum p(tot). For pair relative momenta between 0.3 and 0.5  GeV/c, the ratio is very small at low p(tot) and rises to approximately 0.5 at large p(tot). This shows the dominance of tensor over central correlations at this relative momentum.
  Physical Review Letters 11/2010; 105(22):222501. · 7.37 Impact Factor