共查询到20条相似文献,搜索用时 546 毫秒
1.
J. -S. Real 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):463-468
The G0 experiment is dedicated to the determination of the strange quark contribution to the electric and magnetic nucleon
form factors for a large range of momentum transfers between 0.1 to 1(GeV/c)2 . This information is provided by the asymmetries of cross-sections measured with longitudinally polarized electrons in elastic
electron-proton scattering and quasi-elastic electron-deuteron scattering. A set of measurements at two different Q2 will allow the complete separation of the electric and magnetic weak, as well as axial nucleon form factors. This report
summarizes the physics case, gives details about the dedicated set-up used, and shows the results of the combination of the
strange quark contribution in the electric and magnetic form factors of the protons. The experiment was performed at the Jefferson Laboratory, during years 2003 and 2004, and will be completed after backward-angle measurements in 2006, 2007. 相似文献
2.
D. S. Armstrong 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):451-455
The nucleon's strange electric and magnetic form factors G
E
s and G
M
s can be probed via parity-violating electron scattering. The HAPPEX Collaboration has made new measurements of the parity-violating
asymmetry A
PV in elastic scattering of 3GeV electrons off hydrogen and 4He targets with 〈θlab〉 ≈ 6.0° . For 4He the preliminary result is A
PV = (+ 6.43±0.23(stat)±0.22(syst))×10-6 . For hydrogen the preliminary result is A
PV = (- 1.60±0.12(stat)±0.05(syst))×10-6 . From these values we extract G
s
E = 0.004±0.014±0.013 at 〈Q
2〉 = 0.077 GeV/c^2 , and G
s
E +0.09G
s
M = 0.004±0.011±0.005 at 〈Q
2〉 = 0.109 GeV/c^2 , both consistent with zero, providing stringent new limits on the role of strange quarks in the vector
structure of the nucleon. 相似文献
3.
Utilizing the methods of chiral effective field theory we present an analysis of the electromagnetic NΔ-transition current in the framework of the non-relativistic “small scale expansion” (SSE) to leading-one-loop order. We
discuss the momentum dependence of the magnetic dipole, electric quadrupole and Coulomb quadrupole transition form factors
up to a momentum transfer of Q2 < 0.3GeV^2. Particular emphasis is put on the identification of the role of chiral dynamics in this transition. Our analysis
indicates that there is indeed non-trivial momentum dependence in the two quadrupole form factors at small Q2 < 0.15GeV^2 arising from long-distance pion physics, leading, for example, to negative radii in the (real part of the) quadrupole
transition form factors. We compare our results with the EMR(Q2) and CMR(Q2) multipole ratios from pion-electroproduction experiments and find a remarkable agreement up to four-momentum transfer of
Q2 ≈ 0.3GeV^2. Finally, we discuss the chiral extrapolation of the three transition form factors at Q2 = 0, identifying rapid changes in the (real part of the) quark mass dependence of the quadrupole transition moments for pion
masses below 200MeV, which arise again from long-distance pion dynamics. Our findings indicate that dipole extrapolation methods
currently used in lattice QCD analyses of baryon form factors are not applicable for the chiral extrapolation of NΔ quadrupole transition form factors. 相似文献
4.
K. A. Aniol HAPPEX Collaboration 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):597-599
The HAPPEX Collaboration measured parity-violating electron scattering from
4He$(e, e)$and
H(e, e) in 2004 and 2005 for Q
2≤0.11GeV^2. Results for the strange-quark contributions to the electromagnetic form factors of the nucleon from the 2004 data
will be reviewed. Preliminary results from the 2005 data, which have significantly greater statistical precision, are G
E
s = 0.004±0.014stat±0.013syst for Q
2 = 0.0772GeV^2 from the helium data and G
E
s +0.088G
M
s = 0.004±0.011stat±0.005syst±0.004FF for Q
2 = 0.1089GeV^2 from the hydrogen data. 相似文献
5.
S.?Dey S.S.?Dasgupta C.C.?Dey P.?Bhattacharya 《The European Physical Journal A - Hadrons and Nuclei》2003,16(2):193-197
A kinematically complete experiment has been performed to study the α-n final-state interaction (FSI) in the α + d ↦α + p
+ n break-up reaction at 50 MeV incident energy for the alpha-particles. For this, we have chosen four pairs of correlation
angles for the outgoing alpha and protons. These are ( θα = 18°, θp = 42°), ( θα = 20°, θp = 45°), ( θα = 22°, θp = 42°) and ( θα = 22°, θp = 47°), selected kinematically where the allowed phase spaces are in favor of the α-n final-state interaction. Our experimental
data show strong α-n FSI in all the selected configurations. Also, the FSI is found to be stronger at the lower alpha-particle
energy when two FSI peaks appear in the same configuration.
Received: 17 June 2002 / Accepted: 3 October 2002 / Published online: 4 February 2003
RID="a"
ID="a"e-mail: dey_s2001@yahoo.com; Present address: 445 Waupelani Drive, Apt. F3, State College, PA 16801, USA.
Communicated by M. Gar?on 相似文献
6.
S. Dubnička A. Z. Dubničková 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):399-401
A special eight-resonance unitary and analytic model of nucleon electromagnetic structure is used to analyze first the classical
proton form factor data obtained by the Rosenbluth technique, and then also the contradictory JLab proton polarization data
on the ratio μp
G
Ep(Q
2)/G
Mp(Q
2) , with the aim to investigate the implications of the latter for the behavior of strange nucleon form factors. 相似文献
7.
R. Bijker 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):403-407
The strange form factors of the nucleon are studied in a two-component model consisting of a three-quark intrinsic structure
surrounded by a meson cloud. A comparison with the available experimental world data from the SAMPLE, PVA4, HAPPEX and G0
Collaborations shows a good overall agreement. It is shown that the strangeness contribution to the electric and magnetic
form factors is of the order of a few percent. In particular, the strange quark contribution to the charge radius is small
〈r
2
s〉E = 0.005 fm^2 and to the magnetic moment it is positive μs = 0.315 μN . 相似文献
8.
I. K. Bensafa P. Achenbach M. Ases Antelo C. Ayerbe D. Baumann R. Böhm D. Bosnar E. Burtin X. Defaÿ N. D'Hose M. Ding M. O. Distler L. Doria H. Fonvieille J. M. Friedrich J. Friedrich J. García Llongo P. Janssens G. Jover Mañas M. Kohl G. Laveissière M. Lloyd M. Makek J. Marroncle H. Merkel P. Merle U. Müller L. Nungesser B. Pasquini R. Pérez Benito J. Pochodzalla M. Potokar G. Rosner S. Sánchez Majos M. Seimetz S. Širca T. Spitzenberg G. Tamas R. Van de Vyver L. Van Hoorebeke Th. Walcher M. Weis 《The European Physical Journal A - Hadrons and Nuclei》2007,32(1):69-75
The beam-helicity asymmetry has been measured simultaneously for the reactions
p→epγ and
p→epπ
0 in the Δ(1232)-resonance region at Q
2 = 0.35(GeV/c)2. The experiment was performed at MAMI with a longitudinally polarized beam and an out-of-plane detection of the proton. The
results are compared with calculations based on dispersion relations for virtual Compton scattering and with the MAID model
for pion electroproduction. There is an overall good agreement between experiment and theoretical calculations. The remaining
discrepancies may be ascribed to an imperfect parametrization of some γ
(*)
N→πN multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels (γ and π
0) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization. 相似文献
9.
D. I. Glazier M. Seimetz J. R. M. Annand H. Arenhövel M. Ases Antelo C. Ayerbe P. Bartsch D. Baumann J. Bermuth R. Böhm D. Bosnar M. Ding M. O. Distler D. Elsner J. Friedrich S. Hedicke P. Jennewein G. Jover Ma nas F. H. Klein F. Klein M. Kohl K. W. Krygier K. Livingston I. J. D. MacGregor M. Makek H. Merkel P. Merle D. Middleton U. Müller R. Neuhausen L. Nungesser M. Ostrick R. Pérez Benito J. Pochodzalla Th. Pospischil M. Potokar A. Reiter G. Rosner J. Sanner H. Schmieden A. Süle Th. Walcher D. P. Watts M. Weis 《The European Physical Journal A - Hadrons and Nuclei》2005,24(1):101-109
The electric form factor of the neutron, GE,n, has been measured at the Mainz Microtron by recoil polarimetry in the quasielastic D(¯e, e¯n)p reaction. Three data points have been extracted at squared four-momentum transfers Q
2 = 0.3, 0.6 and 0.8 (GeV/c)2. Corrections for nuclear binding effects have been applied.This revised version was published online in March 2005. In the previous version, the email address of one author was inadvertently assigned to multiple authors. 相似文献
10.
L. Capozza 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):497-499
The spin asymmetry in the scattering of transversely polarised electrons on unpolarised hydrogen target has been measured
by the A4 Collaboration at backward-scattering angle. The square of the four-momentum transfer was Q
2 = 0.22 (GeV/c)^2 like in one of the previous measurements of the A4 Collaboration at forward angle. In this kinematical configuration the
spin asymmetry is of the order of 100ppm and presents a very clear azimuthal angle dependency. Some preliminary results are
presented and are in agreement with theoretical predictions. Also some details about the extraction of the asymmetry are given
and the handling of the background is discussed. 相似文献
11.
《The European Physical Journal C - Particles and Fields》2007,51(1):1-23
The production of the neutral strange hadrons K0
S, Λ and Λ̄ has been measured in ep collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative
yields of strange and charged light hadrons, Λ (Λ̄) asymmetry and polarization have been measured in three kinematic regions:
Q2 > 25 GeV2; 5 < Q2 < 25 GeV2; and in photoproduction (Q2≃0). In photoproduction the presence of two hadronic jets, each with at least 5 GeV transverse energy, was required. The measurements
agree in general with Monte Carlo models and are consistent with measurements made at e+e- colliders, except for an enhancement of baryon relative to meson production in photoproduction. 相似文献
12.
We extract the neutron charge form factor G
n
E(Q
2) from the charge form factor of deuteron G
d
C(Q
2) obtained from T
20(Q
2) data at 0≤Q
2≤ 1.717 (GeV/c)2. The extraction is based on the relativistic impulse approximation in the instant form of the relativistic Hamiltonian dynamics.
Our results (12 new points) are compatible with existing values of the neutron charge form factor of other authors. We propose
a fit for the whole set (36 points) taking into account the data for the slope of the form factor at Q
2 = 0.
Received: 26 July 2002 / Accepted: 18 September 2002 / Published online: 4 February 2003
RID="a"
ID="a"e-mail: krutov@ssu.samara.ru
RID="b"
ID="b"e-mail: troitsky@theory.sinp.msu.ru
Communicated by V.V. Anisovich 相似文献
13.
D. Elsner A. Süle P. Barneo P. Bartsch D. Baumann J. Bermuth R. Böhm D. Bosnar M. Ding M. Distler D. Drechsel I. Ewald J. Friedrich J. M. Friedrich S. Grözinger P. Jennewein S. Kamalov F. H. Klein M. Kohl K. W. Krygier H. Merkel P. Merle U. Müller R. Neuhausen Th. Pospischil M. Potokar G. Rosner H. Schmieden M. Seimetz O. Strähle L. Tiator Th. Walcher M. Weis 《The European Physical Journal A - Hadrons and Nuclei》2006,27(1):91-97
The reaction p(e, e'p)π0 has been studied at Q2 = 0.2 (GeV/c)2 in the region of W = 1232MeV. From measurements left and right of
, cross-section asymmetries ρLT have been obtained in forward kinematics ρLT(
= 20°) = (- 11.68±2.36stat±2.36sys) and backward kinematics ρLT(
= 160°) = (12.18±0.27stat±0.82sys) π0. Multipole ratios
{S1+ * M1+}/| M1+|2 and
{S0+ * M1+}/| M1+|2 were determined in the framework of the MAID2003 model. The results are in agreement with older data. The unusally strong
negative
{S0+ * M1+}/| M1+|2 required to bring also the result of Kalleicher et al. in accordance with the rest of the data is almost excluded. 相似文献
14.
M.P. Rekalo E. Tomasi-Gustafsson 《The European Physical Journal A - Hadrons and Nuclei》2003,16(4):563-567
We discuss the applicability of pQCD to the elastic scattering of electrons on protons and deuterons. We analyze the Q2-dependence of the reduced deuteron form factor, taking into account the recent data on the electric proton form factor and
we find that the value of the QCD-scale parameter Λ differs essentially from the value Λ = 0.1 GeV, previously found using
the dipole parametrization of the electromagnetic nucleon form factors GE and GM. Moreover, the predicted scaling behavior of the reduced deuteron form factor cannot be recovered in the Dirac and Pauli
representations for the nucleon electromagnetic form factors.
Received: 14 October 2002 / Accepted: 12 November 2002 / Published online: 11 March 2003
RID="a"
ID="a"Permanent address: National Science Center KFTI, 310108 Kharkov, Ukraine.
RID="b"
ID="b"e-mail: etomasi@cea.fr
Communicated by V.V. Anisovich 相似文献
15.
A. V. Glushkov 《Physics of Atomic Nuclei》2011,74(1):58-66
The results obtained by analyzing arrival directions for primary cosmic particles characterized by energies in the region
E
0 ⩾ 1017 eV and zenith angles in the range θ ⩽ 60° and detected at the Yakutsk array for studying extensive air showers (EASs) over the period spanning 1974 and 2009
are presented. It is shown that these events exhibit different anisotropies in different energy intervals. 相似文献
16.
Bo-Wen Xiao Xin Qian Bo-Qiang Ma 《The European Physical Journal A - Hadrons and Nuclei》2002,15(4):523-527
The electromagnetic form factor of the kaon meson is calculated in the light-cone formalism of the relativistic constituent
quark model. The calculated K+ form factor is consistent with almost all of the available experimental data at low-energy scale, while other properties
of the kaon could also be interrelated in this representation with reasonable parameters. Predictions of the form factors
for the charged and neutral kaons at a higher-energy scale are also given, and we find the non-zero K0 form factor at Q
2≠ 0 due to the mass difference between the strange and down quarks inside K0.
Received: 21 June 2002 / Accepted: 29 July 2002 / Published online: 3 December 2002
RID="a"
ID="a"e-mail: mabq@phy.pku.edu.cn
Communicated by A. Sch?fer 相似文献
17.
M. Weis P. Bartsch D. Baumann J. Bermuth A. M. Bernstein K. Bohinc R. Böhm M. Ding M. O. Distler I. Ewald J. M. Friedrich J. Friedrich M. Kahrau M. Kohl K. W. Krygier A. Liesenfeld H. Merkel P. Merle U. Müller R. Neuhausen M. M. Pavan Th. Pospischil M. Potokar G. Rosner H. Schmieden M. Seimetz S. Širca A. Wagner Th. Walcher 《The European Physical Journal A - Hadrons and Nuclei》2008,38(1):27-33
The differential cross-sections σ0 = σT + εσL , σLT , and σTT of electroproduction from the proton were measured from threshold up to an additional center-of-mass energy of 40MeV, at a value
of the photon four-momentum transfer of Q
2 = 0.05 GeV2/c2 and a center-of-mass angle of θ = 90° . By an additional out-of-plane measurement with polarized electrons σLT' was determined. This showed for the first time the presence of an imaginary part of the s -wave above the threshold, which is usually interpreted as a unitary cusp. The predictions of the Heavy Baryon Chiral Perturbation Theory
(HBChPT) are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological
model and are in good agreement with the dynamical model DMT. 相似文献
18.
We analyze the proton and deutron data on the spin-dependent asymmetry A
1(x, Q
2), supposing that the DIS structure functions g
1(x, Q
2) and F
3(x, Q
2) have a similar Q
2 dependence. As a result, we have found that Λ
1
p
−Λ
1
n
=0.190±0.038 at Q
2=10 GeV2 and Λ
1
p
−Λ
1
n
=0.165±0.026 at Q
2=3 GeV2; these values are in the best agreement with the Bjorken sum rule predictions.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 9–14 (10 January 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
19.
W. Melnitchouk 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):223-234
We explore the relationship between exclusive and inclusive electromagnetic scattering from the pion, focusing on the transition
region at intermediate Q2. Combining Drell-Yan data on the leading twist quark distribution in the pion with a model for the resonance region at large
x, we calculate QCD moments of the pion structure function over a range of Q2, and quantify the role of higher twist corrections. Using a parameterization of the pion elastic form factor and phenomenological
models for the π↦ρ transition form factor, we further test the extent to which local duality may be valid for the pion.
Received: 10 February 2003 / Accepted: 12 March 2003 / Published online: 27 May 2003 相似文献
20.
We study the asymptotic behavior of the ratio of Pauli and Dirac electromagnetic nucleon form factors, F2/F1, in time-like region, for different parametrizations built for the space-like region. We investigate how fast the ratio F2/F1 approaches the asymptotic limits according to the Phragmèn-Lindel?f theorem. We show that the QCD-inspired logarithmic behavior
of this ratio results in very far asymptotics, experimentally unachievable. This is also confirmed by the normal component
of the nucleon polarization, Py, in e+ + e-↦N + ˉ (in collisions of unpolarized leptons), which is a very interesting observable, with respect to this theorem. Finally
we observe that the 1/Q parametrization of F2/F1 contradicts this theorem. 相似文献