-
W Luo,
E J Brash,
R Gilman,
M K Jones,
M Meziane,
L Pentchev,
C F Perdrisat,
A J R Puckett,
V Punjabi,
F R Wesselmann, [......],
E Tomasi-Gustafsson,
A Vasiliev,
M Veilleux,
S Wood,
Z Ye,
Y Zanevsky,
X Zhang,
Y Zhang,
X Zheng,
L Zhu
[show abstract]
[hide abstract]
ABSTRACT: We present new data for the polarization observables of the final state proton in the (1)H(γ,p)π(0) reaction. These data can be used to test predictions based on hadron helicity conservation and perturbative QCD. These data have both small statistical and systematic uncertainties and were obtained with beam energies between 1.8 and 5.6 GeV and for π(0) scattering angles larger than 75° in the center-of-mass frame. The data extend the polarization measurements database for neutral pion photoproduction up to E(γ)=5.6 GeV. The results show a nonzero induced polarization above the resonance region. The polarization transfer components vary rapidly with the photon energy and π(0) scattering angle in the center-of-mass frame. This indicates that hadron helicity conservation does not hold and that the perturbative QCD limit is still not reached in the energy regime of this experiment.
Physical Review Letters 06/2012; 108(22):222004. · 7.37 Impact Factor
-
I. Ciepał,
St. Kistryn,
E. Stephan,
A. Biegun,
K. Bodek,
A. Deltuva,
E. Epelbaum,
M. Eslami-Kalantari,
A. Fonseca,
J. Golak, [......],
H. Sakai,
K. Sekiguchi, I. Sitnik,
R. Siudak,
R. Skibiński,
R. Sworst,
J. Urban,
H. Witała,
A. Wrońska,
J. Zejma
[show abstract]
[hide abstract]
ABSTRACT: Set of vector analyzing power data of the d⃗p elastic scattering and 1H(d⃗, pp)n breakup reactions at 130-MeV deuteron beam energy has been measured in the domain of very forward polar angles. The results are compared with theoretical predictions originating from various approaches: realistic nucleon-nucleon (NN) potentials and the NN potentials combined with a three-nucleon force (3NF) model and with predictions based on the ChPT framework. In case of the breakup process, none of the theoretical calculations reveal sensitivity to any of the dynamical effects such as 3NF or Coulomb interaction and they describe the experimental data equally well. For the elastic scattering, the Coulomb correction appears not negligible at very small θdc.m.. The effect seems to be confirmed by the data.
Phys. Rev. C. 01/2012; 85(1).
-
W. Luo,
E. J. Brash,
R. Gilman,
M. K. Jones,
M. Meziane,
L. Pentchev,
C. F. Perdrisat,
A. J. R. Puckett,
V. Punjabi,
F. R. Wesselmann, [......],
E. Tomasi-Gustafsson,
A. Vasiliev,
M. Veilleux,
S. Wood,
Z. Ye,
Y. Zanevsky,
X. Zhang,
Y. Zhang,
X. Zheng,
L. Zhu
[show abstract]
[hide abstract]
ABSTRACT: We present new data for the polarization observables of the final state
proton in the $^{1}H(\vec{\gamma},\vec{p})\pi^{0}$ reaction. These data can be
used to test predictions based on hadron helicity conservation (HHC) and
perturbative QCD (pQCD). These data have both small statistical and systematic
uncertainties, and were obtained with beam energies between 1.8 and 5.6 GeV and
for $\pi^{0}$ scattering angles larger than 75$^{\circ}$ in center-of-mass
(c.m.) frame. The data extend the polarization measurements data base for
neutral pion photoproduction up to $E_{\gamma}=5.6 GeV$. The results show
non-zero induced polarization above the resonance region. The polarization
transfer components vary rapidly with the photon energy and $\pi^{0}$
scattering angle in c.m. frame. This indicates that HHC does not hold and that
the pQCD limit is still not reached in the energy regime of this experiment.
09/2011;
-
A. Budzanowski,
A. Chatterjee,
H. Clement,
P. Hawranek,
F. Hinterberger,
R Jahn,
R Joosten,
K. Kilian,
Da. Kirillov,
Di. Kirillov, [......],
J. Ritman,
P. von Rossen,
J. Roy,
A. Sibirtsev, I. Sitnik,
R. Siudak,
R. Tsenov,
K. Ulbrich,
J. Urban,
G. J. Wagner
[show abstract]
[hide abstract]
ABSTRACT: The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and
\Theta = 0 deg with a high missing mass resolution in order to study the Lambda
p final state interaction. Narrow S = -1 resonances predicted by bag model
calculations are not visible in the missing mass spectrum. Small structures
observed in a previous experiment are not confirmed. Upper limits for the
production cross section of a narrow resonance are deduced for missing masses
between 2058 and 2105 MeV/c^2.
05/2011;
-
M Meziane,
E J Brash,
R Gilman,
M K Jones,
W Luo,
L Pentchev,
C F Perdrisat,
A J R Puckett,
V Punjabi,
F R Wesselmann, [......],
M Vanderhaeghen,
M Veilleux,
B B Wojtsekhowski,
S Wood,
Z Ye,
Y Zanevsky,
X Zhang,
Y Zhang,
X Zheng,
L Zhu
[show abstract]
[hide abstract]
ABSTRACT: Intensive theoretical and experimental efforts over the past decade have aimed at explaining the discrepancy between data for the proton electric to magnetic form factor ratio, G(E)/G(M), obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange contribution. In an effort to search for effects beyond the one-photon-exchange or Born approximation, we report measurements of polarization transfer observables in the elastic H(e[over →],e(')p[over →]) reaction for three different beam energies at a Q(2)=2.5 GeV(2), spanning a wide range of the kinematic parameter ε. The ratio R, which equals μ(p)G(E)/G(M) in the Born approximation, is found to be independent of ε at the 1.5% level. The ε dependence of the longitudinal polarization transfer component P(ℓ) shows an enhancement of (2.3±0.6)% relative to the Born approximation at large ε.
Physical Review Letters 04/2011; 106(13):132501. · 7.37 Impact Factor
-
A. J. R. Puckett,
E. J. Brash,
O. Gayou,
M. K. Jones,
L. Pentchev,
C. F. Perdrisat,
V. Punjabi,
K. A. Aniol,
T. Averett,
F. Benmokhtar, [......], I. Sitnik,
S. Strauch,
L. Todor,
E. Tomasi-Gustafsson,
G. M. Urciuoli,
H. Voskanyan,
K. Wijesooriya,
B. B. Wojtsekhowski,
X. Zheng,
L. Zhu
[show abstract]
[hide abstract]
ABSTRACT: Precise measurements of the proton electromagnetic form factor ratio $R =
\mu_p G_E^p/G_M^p$ using the polarization transfer method at Jefferson Lab have
revolutionized the understanding of nucleon structure by revealing the strong
decrease of $R$ with momentum transfer $Q^2$ for $Q^2 \gtrsim 1$ GeV$^2$, in
strong disagreement with previous extractions of $R$ from cross section
measurements. In particular, the polarization transfer results have exposed the
limits of applicability of the one-photon-exchange approximation and
highlighted the role of quark orbital angular momentum in the nucleon
structure. The GEp-II experiment in Jefferson Lab's Hall A measured $R$ at four
$Q^2$ values in the range 3.5 GeV$^2 \le Q^2 \le 5.6$ GeV$^2$. A possible
discrepancy between the originally published GEp-II results and more recent
measurements at higher $Q^2$ motivated a new analysis of the GEp-II data. This
article presents the final results of the GEp-II experiment, including details
of the new analysis, an expanded description of the apparatus and an overview
of theoretical progress since the original publication. The key result of the
final analysis is a systematic increase in the results for $R$, improving the
consistency of the polarization transfer data in the high-$Q^2$ region. This
increase is the result of an improved selection of elastic events which largely
removes the systematic effect of the inelastic contamination, underestimated by
the original analysis.
02/2011;
-
M. Meziane,
E. J. Brash,
R Gilman,
M K Jones,
W Luo,
L. Pentchev,
C. F. Perdrisat,
A. J. R. Puckett,
V. Punjabi,
F. R. Wesselmann, [......],
M. Vanderhaeghen,
M. Veilleux,
B. B. Wojtsekhowski,
S. Wood,
Z Ye,
Y. Zanevsky,
X Zhang,
Y Zhang,
X Zheng,
L Zhu
[show abstract]
[hide abstract]
ABSTRACT: Intensive theoretical and experimental efforts over the past decade have
aimed at explaining the discrepancy between data for the proton electric to
magnetic form factor ratio, $G_{E}/G_{M}$, obtained separately from cross
section and polarization transfer measurements. One possible explanation for
this difference is a two-photon-exchange (TPEX) contribution. In an effort to
search for effects beyond the one-photon-exchange or Born approximation, we
report measurements of polarization transfer observables in the elastic
$H(\vec{e},e'\vec{p})$ reaction for three different beam energies at a fixed
squared momentum transfer $Q^2 = 2.5$ GeV$^2$, spanning a wide range of the
virtual photon polarization parameter, $\epsilon$. From these measured
polarization observables, we have obtained separately the ratio $R$, which
equals $\mu_p G_{E}/G_{M}$ in the Born approximation, and the longitudinal
polarization transfer component $P_\ell$, with statistical and systematic
uncertainties of $\Delta R \approx \pm 0.01 \mbox{(stat)} \pm 0.013
\mbox{(syst)}$ and $\Delta P_\ell/P^{Born}_{\ell} \approx \pm 0.006
\mbox{(stat)}\pm 0.01 \mbox{(syst)}$. The ratio $R$ is found to be independent
of $\epsilon$ at the 1.5% level, while the $\epsilon$ dependence of $P_\ell$
shows an enhancement of $(2.3 \pm 0.6) %$ relative to the Born approximation at
large $\epsilon$.
12/2010;
-
A. Budzanowski,
A. Chatterjee,
P. Hawranek,
R. Jahn,
V. Jha,
K. Kilian,
S. Kliczewski,
Da. Kirillov,
Di. Kirillov,
D. Kolev, [......],
N. Piskunov,
D. Protić,
J. Ritman,
P. von Rossen,
B. J. Roy, I. Sitnik,
R. Siudak,
R. Tsenov,
J. Urban,
G. Vankova
[show abstract]
[hide abstract]
ABSTRACT: The cross section for the reaction $p+^6\text{Li}\to\eta+^7\text{Be}$ was
measured at an excess energy of 11.28 MeV above threshold by detecting the
recoiling $^7$Be nuclei. A dedicated set of focal plane detectors was built for
the magnetic spectrograph Big Karl and was used for identification and four
momentum measurement of the $^7$Be. A differential cross section of
$\frac{d\sigma}{d\Omega}=(0.69\pm{0.20}\text{(stat.)}\pm
0.20\text{(syst.)})\text{nb/sr}$ for the ground state plus the 1/2$^-$ was
measured. The result is compared to model calculations.
10/2010;
-
A. Budzanowski,
A. Chatterjee,
H. Clement,
E. Dorochkevitch,
P. Hawranek,
F. Hinterberger,
R Jahn,
R Joosten,
K. Kilian,
S. Kliczewski, [......],
D. Protic,
J. Ritman,
P. von Rossen,
A. Sibirtsev, I. Sitnik,
R. Siudak,
R. Tsenov,
K. Ulbrich,
J. Urban,
G. J. Wagner
[show abstract]
[hide abstract]
ABSTRACT: We have measured inclusive data on $K^+$-meson production in $pp$ collisions at COSY J\"ulich close to the hyperon production threshold and determined the hyperon-nucleon invariant mass spectra. The spectra were decomposed into three parts: $\Lambda p$, $\Sigma^0p$ and $\Sigma^+n$. The cross section for the $\Sigma^+n$ channel was found to be much smaller than a previous measurement in that excess energy region. The data together with previous results at higher energies are compatible with a phase space dependence. Comment: accepted by Phys. lett. B some typos corrected
07/2010;
-
A J R Puckett,
E J Brash,
M K Jones,
W Luo,
M Meziane,
L Pentchev,
C F Perdrisat,
V Punjabi,
F R Wesselmann,
A Ahmidouch, [......],
A Vasiliev,
M Veilleux,
B B Wojtsekhowski,
S Wood,
Z Ye,
Y Zanevsky,
X Zhang,
Y Zhang,
X Zheng,
L Zhu
[show abstract]
[hide abstract]
ABSTRACT: Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon's quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this Letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil polarization method, at momentum transfers Q2=5.2, 6.7, and 8.5 GeV2. By extending the range of Q2 for which G(E)(p) is accurately determined by more than 50%, these measurements will provide significant constraints on models of nucleon structure in the nonperturbative regime.
Physical Review Letters 06/2010; 104(24):242301. · 7.37 Impact Factor
-
A. J. R. Puckett,
E. J. Brash,
M K Jones,
W Luo,
M. Meziane,
L. Pentchev,
C. F. Perdrisat,
V. Punjabi,
F. R. Wesselmann,
A. Ahmidouch, [......],
A. Vasiliev,
M. Veilleux,
B. B. Wojtsekhowski,
S. Wood,
Z Ye,
Y. Zanevsky,
X Zhang,
Y Zhang,
X Zheng,
L Zhu
[show abstract]
[hide abstract]
ABSTRACT: Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon's quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil polarization method, at momentum transfers Q2=5.2, 6.7, and 8.5 GeV2. By extending the range of Q2 for which GEp is accurately determined by more than 50%, these measurements will provide significant constraints on models of nucleon structure in the non-perturbative regime.
05/2010;
-
A. Budzanowski,
A. Chatterjee,
H. Clement,
E. Dorochkevitch,
P. Hawranek,
F. Hinterberger,
R Jahn,
R Joosten,
K. Kilian,
S. Kliczewski, [......],
J. Ritman,
P. von Rossen,
B. J. Roy,
A. Sibirtsev, I. Sitnik,
R. Siudak,
R. Tsenov,
K. Ulbrich,
J. Urban,
G. J. Wagner
[show abstract]
[hide abstract]
ABSTRACT: The reaction pp -> K+ + (Lambda p) was measured at Tp=1.953 GeV and Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. The large final state enhancement near the Lambda p threshold can be described using the standard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously the Lambda p invariant mass spectrum and the total cross section data of the free Lambda p scattering. Comment: submitted to Physics Letters B, 10 pages, 3 figures
03/2010;
-
The HIRES Collaboration,
A. Budzanowski,
A. Chatterjee,
H. Clement,
E. Dorochkevitch,
P. Hawranek,
F. Hinterberger,
R Jahn,
R Joosten,
K. Kilian, [......],
J. Ritman,
P. von Rossen,
B. J. Roy,
A. Sibirtsev, I. Sitnik,
R. Siudak,
R. Tsenov,
K. Ulbrich,
J. Urban,
G. J. Wagner
11/2009;
-
A. Budzanowski,
A. Chatterjee,
P. Hawranek,
R Jahn,
V. Jha,
K. Kilian,
Da. Kirillov,
Di. Kirillov,
S. Kliczewski,
D Kolev, [......],
J. Ritman,
P. von Rossen,
B. J. Roy, I. Sitnik,
R. Siudak,
H. J. Stein,
R. Tsenov,
J. Urban,
G. Vankova,
C. Wilkin
[show abstract]
[hide abstract]
ABSTRACT: Inclusive measurements of pion production in proton--proton collisions in the forward direction were undertaken at 400 and 600 MeV at COSY using the Big Karl spectrograph. The high resolution in the $\pi^+$ momentum ensured that there was an unambiguous separation of the $pp\to {\pi}^+d/\pi^+pn$ channels. Using these and earlier data, the ratio of the production cross sections could be followed through the $\Delta$ region and compared with the predictions of final state interaction theory. Deviations are strongly influenced by long-range terms in the production operator and the tensor force in the final $pn$ system. These have been investigated in a realistic $pp\to\pi^+d/\pi^+pn$ calculation that includes $S \rightleftharpoons D$ channel coupling between the final nucleons. A semi-quantitative understanding of the observed effects is achieved. Comment: 10 pages, 3 figures
04/2009;
-
V Jha,
A Budzanowski,
A Chatterjee,
P Hawranek,
R Jahn,
B K Jain,
S Kailas,
K Kilian,
S Kliczewski,
Da Kirillov, [......],
D Proti,
J Ritman,
P Von Rossen,
B J Roy,
P Shukla, I Sitnik,
R Siudak,
R Tsenov,
J Urban,
G Vankova
[show abstract]
[hide abstract]
ABSTRACT: We have performed an experiment to search for the bound state of η meson in nuclei. We have measured the reaction p + 27 Al → 3 He + p + π − + X at recoil-free kinematics. An η meson possibly produced in this reaction would be thus almost at rest in the laboratory system and could therefore be bound with high probability, if bound nuclear η states exist. The decay of such a state through the N * (1535) resonance would lead to a proton-π − pair emitted in opposite directions. For these conditions we find some indication of such a bound state. An upper limit of ≈ 0.5 nb for the formation cross section is found.
International Journal of Modern Physics E. 01/2009; 18(6):1378-1382.
-
A Budzanowski,
A Chatterjee,
P Hawranek,
R Jahn,
B K Jain,
V Jha,
S Kailas,
K Kilian,
S Kliczewski,
Da Kirillov, [......],
D Proti,
J Ritman,
P Von Rossen,
B J Roy,
P Shukla, I Sitnik,
R Siudak,
R Tsenov,
J Urban,
G Vankova
[show abstract]
[hide abstract]
ABSTRACT: We have studied the reaction p + 27 Al → 3 He + p + π − + X at recoil-free kinematics. An η meson possibly produced in this reaction would be thus almost at rest in the laboratory system and could therefore be bound with high probability, if nuclear η states exist. The decay of such a state through the N * (1535) resonance would lead to a proton-π − pair emitted in opposite directions. For these conditions we find some indication of such a bound state. An upper limit of ≈0.5 nb is found.
RAPID COMMUNICATIONS PHYSICAL REVIEW C. 01/2009; 79.
-
Gem Collaboration,
P. K. Biswas,
A. Budzanowski,
A. Chatterjee,
R. Jahn,
S. Guha,
P. Hawranek,
B. K. Jain,
S. B. Jawale,
V. Jha, [......],
J. Ritman,
P. von Rossen,
B. J. Roy,
P. Shukla, I. Sitnik,
R. Siudak,
R. Tsenov,
M. Ulicny,
J. Urban,
G. Vankova
[show abstract]
[hide abstract]
ABSTRACT: A large acceptance scintillator detector with wavelength shifting
optical fibre readout has been designed and built to detect the decay
particles of η-nucleus bound system (the so-called η-mesic
nuclei), namely, protons and pions. The detector, named as ENSTAR
detector, consists of 122 pieces of plastic scintillator of various
shapes and sizes, which are arranged in a cylindrical geometry to
provide particle identification, energy loss and coarse position
information for these particles. A solid angle coverage of ˜95% of
total 4π is obtained in the present design of the detector. Monte
Carlo phase space calculations performed to simulate the formation and
decay of η-mesic nuclei suggest that its decay particles, the
protons and pions are emitted with an opening angle of
150±20, and with energies in the range of 25 300 and
225 450 MeV, respectively. The detailed GEANT simulations show that
˜80 % of the decay particles (protons and pions) can be detected
within ENSTAR. Several test measurements using alpha source, cosmic-ray
muons, etc. have been carried out to study the response of ENSTAR
scintillator pieces. The in-beam tests of fully assembled detector with
proton beam of momentum 870MeV/c from the Cooler synchrotron COSY have
been performed. The test results show that the scintillator fibre design
chosen for the detector has performed satisfactorily well. The present
article describes the detector design, simulation studies, construction
details and test results.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2007; 578:198-206. · 1.21 Impact Factor
-
K. Kilian,
S. Kliczewski,
Da. Kirillov,
Di. Kirillov,
D Kolev,
M. Kravcikova,
T. Kutsarova,
M. Lesiak,
J. Lieb,
H. Machner, [......],
J. Ritman,
P. von Rossen,
B. J. Roy,
P. Shukla, I. Sitnik,
R. Siudak,
R. Tsenov,
M. Ulicny,
J. Urban,
G. Vankova
[show abstract]
[hide abstract]
ABSTRACT: A large acceptance scintillator detector with wavelength shifting optical fibre readout has been designed and built to detect the decay particles of $\eta$-nucleus bound system (the so-called $\eta$-mesic nuclei), namely, protons and pions. The detector, named as ENSTAR detector, consists of 122 pieces of plastic scintillator of various shapes and sizes, which are arranged in a cylindrical geometry to provide particle identification, energy loss and coarse position information for these particles. A solid angle coverage of $\sim$95% of total 4$\pi$ is obtained in the present design of the detector. Monte Carlo phase space calculations performed to simulate the formation and decay of $\eta$-mesic nuclei suggest that its decay particles, the protons and pions are emitted with an opening angle of 150$^\circ \pm 20^\circ$, and with energies in the range of 25 to 300 MeV and 225 to 450 MeV respectively. The detailed GEANT simulations show that $\sim$ 80 % of the decay particles (protons and pions) can be detected within ENSTAR. Several test measurements using alpha source, cosmic-ray muons etc. have been carried out to study the response of ENSTAR scintillator pieces. The in-beam tests of fully assembled detector with proton beam of momentum 870 MeV/c from the Cooler synchrotron COSY have been performed. The test results show that the scintillator fiber design chosen for the detector has performed satisfactorily well. The present article describes the detector design, simulation studies, construction details and test results.
06/2007;
-
V Jha,
A Budzanowski,
A Chatterjee,
J Ernst,
P Hawranek,
K Kilian,
S Kliczewski,
Da Kirillov,
Di Kirillov,
D Kolev, [......],
D Proti,
P Von Rossen,
B J Roy,
P Shukla, I Sitnik,
R Siudak,
R Tsenov,
M Ulicny,
J Urban,
G Vankova
[show abstract]
[hide abstract]
ABSTRACT: An experiment to search for the bound state of η meson in nuclei has been performed at COSY, Juelich using the ENSTAR detector and Big Karl magnetic spectrometer. Reaction (p, 3 He) on 27 Al target has been used to search for the η-mesic nucleus 25 Mgη in the missing mass distribution from the measured 3 He particles. A preliminary figure of 1.5 nb for the upper limit of the formation cross section of η-nucleus bound state has been determined.
International Journal of Modern Physics A. 01/2007; 22(3):596-599.
-
M Abdel-Bary,
A Budzanowski,
A Chatterjee,
J Ernst,
R Gebel,
P Hawranek,
R Jahn,
V Jha,
K Kilian,
S Kliczewski, [......],
D Proti,
P Von Rossen,
B J Roy, I Sitnik,
R Siudak,
R Tsenov,
M Ulicny,
J Urban,
G Vankova,
C Wilkin
[show abstract]
[hide abstract]
ABSTRACT: Measurement of the d + d → 4 He + η reaction using vector and tensor polarised beam has been performed at COSY using Big Karl magnetic spectrograph. The beam polarisation necessary for obtaining the vector and tensor analysing power for this reaction was measured. The method and the results of the tensor polarisation measurement of the deuteron beam are presented.
01/2006;
