-
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
[show abstract]
[hide abstract]
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;
-
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
[show abstract]
[hide abstract]
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;
-
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
[show abstract]
[hide abstract]
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;
-
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
[show abstract]
[hide abstract]
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
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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
[show abstract]
[hide abstract]
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;
-
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
[show abstract]
[hide abstract]
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).
-
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
[show abstract]
[hide abstract]
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;
-
[show abstract]
[hide abstract]
ABSTRACT: CLARA (CLAS12 Reconstruction and Analysis framework) is CLAS12 physics data processing (PDP) application development framework based on a service oriented architecture (SOA). This framework allows users to design and deploy data processing services as well as dynamically compose PDP applications using available services. Services can be written in Java, C++, and Python languages. The PDP service bus provides a layer on top of a distributed pub-sub middleware implementation. This allows complex service composition and integration without writing a code. We believe that by deviating from the traditional self contained, monolithic PDP application models we can improve maintenance, scalability and quality of physics data analysis. The SOA approach also helps us to separate a specific service programmer from a PDP application designer. Examples of service creation and deployment, along with the CLAS12 track reconstruction application design are presented.
Journal of Physics Conference Series 12/2011; 331(3):032013.
-
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
[show abstract]
[hide abstract]
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;
-
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
[show abstract]
[hide abstract]
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).
-
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
[show abstract]
[hide abstract]
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
-
R. Nasseripour,
B. L. Berman,
N. Benmouna,
Y. Ilieva,
J. M. Laget,
K. P. Adhikari,
M. J. Amaryan,
P. Ambrozewicz,
M. Anghinolfi,
H. Baghdasaryan, [......],
M. F. Vineyard,
D. P. Watts,
L. B. Weinstein,
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: The two-body photodisintegration of 4He into a proton and a triton has been studied using the CEBAF Large-Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Real photons produced with the Hall-B bremsstrahlung-tagging system in the energy range from 0.35 to 1.55 GeV were incident on a liquid 4He target. This is the first measurement of the photodisintegration of 4He above 0.4 GeV. The differential cross sections for the γ4He→pt reaction were measured as a function of photon-beam energy and proton-scattering angle and are compared with the latest model calculations by J.-M. Laget. At 0.6-1.2 GeV, our data are in good agreement only with the calculations that include three-body mechanisms, thus confirming their importance. These results reinforce the conclusion of our previous study of the three-body breakup of 3He that demonstrated the great importance of three-body mechanisms in the energy region 0.5-0.8 GeV.
Phys. Rev. C. 10/2009; 80(4).
-
W Chen,
T Mibe,
D Dutta,
H Gao,
J M Laget,
M Mirazita,
P Rossi,
S Stepanyan,
I I Strakovsky,
M J Amaryan, [......],
S Tkachenko,
M Ungaro,
M F Vineyard,
D P Watts,
L B Weinstein,
D P Weygand,
M H Wood,
A Yegneswaran,
J Zhang,
B Zhao
[show abstract]
[hide abstract]
ABSTRACT: We report a measurement of the differential cross section for the gamman-->pi- p process from the CLAS detector at Jefferson Laboratory in Hall B for photon energies between 1.0 and 3.5 GeV and pion center-of-mass (c.m.) angles (thetac.m.) between 50 degrees and 115 degrees. We confirm a previous indication of a broad enhancement around a c.m. energy ([sqrt]s) of 2.1 GeV at thetac.m.=90 degrees in the scaled differential cross section s7dsigma/dt and a rapid falloff in a center-of-mass energy region of about 400 MeV following the enhancement. Our data show an angular dependence of this enhancement as the suggested scaling region is approached for thetac.m. from 70 degrees to 105 degrees.
Physical Review Letters 07/2009; 103(1):012301. · 7.37 Impact Factor
-
J Lachniet,
A Afanasev,
H Arenhövel,
W K Brooks,
G P Gilfoyle,
D Higinbotham,
S Jeschonnek,
B Quinn,
M F Vineyard,
G Adams, [......],
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
J Yun,
M Yurov,
L Zana,
J Zhang,
B Zhao,
Z W Zhao
[show abstract]
[hide abstract]
ABSTRACT: The neutron elastic magnetic form factor was extracted from quasielastic electron scattering on deuterium over the range Q;{2}=1.0-4.8 GeV2 with the CLAS detector at Jefferson Lab. High precision was achieved with a ratio technique and a simultaneous in situ calibration of the neutron detection efficiency. Neutrons were detected with electromagnetic calorimeters and time-of-flight scintillators at two beam energies. The dipole parametrization gives a good description of the data.
Physical Review Letters 06/2009; 102(19):192001. · 7.37 Impact Factor
-
M Battaglieri,
R De Vita,
A P Szczepaniak,
K P Adhikari,
M Aghasyan,
M J Amaryan,
P Ambrozewicz,
M Anghinolfi,
G Asryan,
H Avakian, [......],
D P Weygand,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
M Yurov,
L Zana,
J Zhang,
B Zhao,
Z W Zhao
[show abstract]
[hide abstract]
ABSTRACT: We report on the results of the first measurement of exclusive f_{0}(980) meson photoproduction on protons for E_{gamma}=3.0-3.8 GeV and -t=0.4-1.0 GeV2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The resonance was detected via its decay in the pi;{+}pi;{-} channel by performing a partial wave analysis of the reaction gammap-->ppi;{+}pi;{-}. Clear evidence of the f_{0}(980) meson was found in the interference between P and S waves at M_{pi;{+}pi;{-}} approximately 1 GeV. The S-wave differential cross section integrated in the mass range of the f_{0}(980) was found to be a factor of about 50 smaller than the cross section for the rho meson. This is the first time the f_{0}(980) meson has been measured in a photoproduction experiment.
Physical Review Letters 04/2009; 102(10):102001. · 7.37 Impact Factor
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M Nozar,
C Salgado,
D P Weygand,
L Guo,
G Adams,
Ji Li,
P Eugenio,
M J Amaryan,
M Anghinolfi,
G Asryan, [......],
D P Watts,
L B Weinstein,
M Williams,
E Wolin,
M H Wood,
A Yegneswaran,
L Zana,
J Zhang,
B Zhao,
Z W Zhao
[show abstract]
[hide abstract]
ABSTRACT: A search for exotic mesons in the pi;{+}pi;{+}pi;{-} system photoproduced by the charge exchange reaction gammap-->pi;{+}pi;{+}pi;{-}(n) was carried out by the CLAS Collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A partial wave analysis was performed on a sample of 83 000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the photoproduction of an exotic J;{PC}=1;{-+} resonant state in the 1 to 2 GeV mass range. Our partial wave analysis shows production of the a_{2}(1320) and the pi_{2}(1670) mesons, but no evidence for the a_{1}(1260), nor the pi_{1}(1600) exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic pi_{1}(1600) cross section, less than 2% of the a_{2}(1320) production.
Physical Review Letters 04/2009; 102(10):102002. · 7.37 Impact Factor
-
The CLAS Collaboration,
S. A. Morrow,
M. Guidal,
M. Garçon,
J. M. Laget,
E. S. Smith,
G. Adams,
K. P. Adhikari,
M. Aghasyan,
M. J. Amaryan, [......],
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
M. Yurov,
L. Zana,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: The ep → e
′
pρ0 reaction has been measured using the 5.754GeV electron beam of Jefferson Lab and the CLAS detector. This represents the largest
ever set of data for this reaction in the valence region. Integrated and differential cross-sections are presented. The W , Q2 and t dependences of the cross-section are compared to theoretical calculations based on the t -channel meson-exchange Regge theory, on the one hand, and on quark handbag diagrams related to Generalized Parton Distributions
(GPDs) on the other hand. The Regge approach can describe at the » \approx 30% level most of the features of the present data while the two GPD calculations that are presented in this article which
succesfully reproduce the high-energy data strongly underestimate the present data. The question is then raised whether this
discrepancy originates from an incomplete or inexact way of modelling the GPDs or the associated hard scattering amplitude
or whether the GPD formalism is simply inapplicable in this region due to higher-twists contributions, incalculable at present.
European Physical Journal A 12/2008; 39(1):5-31. · 2.19 Impact Factor
-
R. Nasseripour,
B. A. Raue,
D. S. Carman,
P. Ambrozewicz,
M. J. Amaryan,
E. Anciant,
M. Anghinolfi,
B. Asavapibhop,
G. Asryan,
G. Audit, [......],
D. P. Weygand,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
L. Zana,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: The first measurements of the polarized structure function σLT' for the reaction 1H(e⃗,e'K+)Λ in the nucleon resonance region are reported. Measurements are included from threshold up to W=2.05 GeV for central values of Q2 of 0.65 and 1.00 GeV2, and nearly the entire kaon center-of-mass angular range. σLT' is the imaginary part of the longitudinal-transverse response and is expected to be sensitive to interferences between competing intermediate s-channel resonances, as well as resonant and nonresonant processes. The results for σLT' are comparable in magnitude to previously reported results from CLAS for σLT, the real part of the same response. An intriguing sign change in σLT' is observed in the high Q2 data at W≈1.9 GeV. Comparisons to several existing model predictions are shown.
Phys. Rev. C. 06/2008; 77(6).
-
K. Park,
V. D. Burkert,
W. Kim,
I. G. Aznauryan,
R. Minehart,
L. C. Smith,
K. Joo,
L. Elouadrhiri,
G. Adams,
M. J. Amaryan, [......],
E. Wolin,
M. H. Wood,
A. Yegneswaran,
J. Yun,
M. Yurov,
L. Zana,
B. Zhang,
J. Zhang,
B. Zhao,
Z. W. Zhao
[show abstract]
[hide abstract]
ABSTRACT: The exclusive electroproduction process e⃗p→e'nπ+ was measured in the range of the photon virtuality Q2=1.7-4.5 GeV2, and the invariant mass range for the nπ+ system of W=1.15-1.7 GeV using the CEBAF Large Acceptance Spectrometer. For the first time, these kinematics are probed in exclusive π+ production from protons with nearly full coverage in the azimuthal and polar angles of the nπ+ center-of-mass system. The nπ+ channel has particular sensitivity to the isospin ½ excited nucleon states, and together with the pπ0 final state will serve to determine the transition form factors of a large number of resonances. The largest discrepancy between these results and present modes was seen in the σLT' structure function. In this experiment, 31,295 cross section and 4,184 asymmetry data points were measured. Because of the large volume of data, only a reduced set of structure functions and Legendre polynomial moments can be presented that are obtained in model-independent fits to the differential cross sections.
Phys. Rev. C. 01/2008; 77(1).
-
I. Hleiqawi,
K. Hicks,
D. S. Carman,
T. Mibe,
G. Niculescu,
A. Tkabladze,
M. Amarian,
P. Ambrozewicz,
M. Anghinolfi,
G. Asryan, [......],
D. P. Weygand,
S. Whisnant,
M. Williams,
E. Wolin,
M. H. Wood,
A. Yegneswaran,
L. Zana,
J. Zhang,
B. Zhao,
Z. Zhao
Physical Review C 08/2007; 76(3):39905. · 3.31 Impact Factor
