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1.
Antiproton proton annihilation reactions allow unique access to the moduli and phases of nucleon electromagnetic form factors
in the time-like region. We present the helicity amplitudes for the unequal-mass single-photon reaction pˉ → l
+
l
- in the s channel including the lepton mass. The relative signs of these amplitudes are determined using simple invariance properties.
Helicity amplitudes for one-photon exchange annihilation reaction pˉ → Bˉ are also given, where B is any spin-one-half particle with structure. Crossing relations between the ep → ep scattering and the pˉ → l
+
l
- annihilation channels are discussed and the crossing matrix for the helicity amplitudes is given. This matrix may be used
to verify known expressions for the space-like helicity amplitudes due to one-photon exchange. 相似文献
2.
C. Bini 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):446-450
The KLOE experiment at the Frascati e
+
e
- collider DAFNE has completed this year its data taking. An integrated luminosity of 2.7fb^-1 has been collected mostly at
the φ-resonance peak. A wide experimental program is in progress. The detection of φ radiative decays allows to study the properties of the lowest-mass scalar and pseudoscalar mesons and to obtain information
on their structure. The main results are reviewed together with the prospects for low-energy e
+
e
- physics at Frascati. 相似文献
3.
General expressions, including the lepton mass, for the spin-averaged differential cross-section for the annihilation reaction
lepton-antilepton to proton-antiproton are given, as well as general formulae for the single- and double-spin asymmetries
in the centre-of-mass frame. In particular, we discuss the single-spin asymmetry, normal to the scattering plane, which measures
the relative phase difference between nucleon electromagnetic form factors GE and GM. Recent experimental investigations of these form factors in the space- and time-like region are reviewed. It is thought
that measurements of the phase of these form factors will provide fundamental information on the internal nucleon structure.
The phases between GE and GM are accessible through polarisation observables measured in the antiproton-proton-to-lepton-antilepton reaction, or in its
time-reversed process. 相似文献
4.
5.
L. S. Geng E. Oset M. Döring 《The European Physical Journal A - Hadrons and Nuclei》2007,32(2):201-211
We evaluate theoretically the radiative decay widths into γΛ and γΣ
0 of the two poles of the Λ(1405) found in chiral unitary theories and we find quite different results for each of the two poles. We show that, depending
on which reaction is used to measure the Λ(1405) radiative decays, one gives more weight to one or the other pole, resulting in quite different shapes in the γΛ(Σ
0) invariant-mass distributions. Our results for the high-energy pole agree with those of the empirical determination of the
γΛ and γΣ
0 radiative widths (based on an isobar model fitting of the K-p atom data), which are sometimes referred to as “experimental data”. We have made a detailed study of the K
-
p→π
0
γΛ(Σ
0) and π
-
p→K
0
γΛ(Σ
0) reactions and have shown that they, indeed, lead to different shapes for the γΛ(Σ
0) invariant-mass distributions. 相似文献
6.
R. Schumacher 《The European Physical Journal A - Hadrons and Nuclei》2008,35(3):299-305
Multiple polarization observables must be measured to access the amplitude structure of pseudoscalar meson photoproduction
off the proton. The hyperon-producing reactions are especially attractive to study, since the weak decays allow straightforward
measurement of the induced and recoil polarization observables. In this paper we emphasize γ + p → K
+ + Λ , discussing recent measurements of Cx, Cz, and P for this reaction. An empirical constraint on the helicity amplitudes is obtained. A simplified model involving spin-flip
and spin-non-flip amplitudes is presented. Finally, a semi-classical model of how the polarization may arise is presented. 相似文献
7.
O. Bartalini V. Bellini J. P. Bocquet M. Capogni L. Casano M. Castoldi P. Calvat A. D'Angelo R. Di Salvo A. Fantini C. Gaulard G. Gervino F. Ghio B. Girolami A. Giusa V. Kouznetsov A. Lapik P. Levi Sandri A. Lleres D. Moricciani A. N. Mushkarenkov V. Nedorezov L. Nicoletti C. Perrin D. Rebreyend F. Renard N. Rudnev T. Russew G. Russo C. Schaerf M. -L. Sperduto M. -C. Sutera A. Turinge 《The European Physical Journal A - Hadrons and Nuclei》2005,26(3):399-419
Neutral pion photoproduction has been measured from 550 to 1500 MeV with the GRAAL facility, located at the ESRF in Grenoble.
Differential cross-section and beam asymmetry have been measured over a wide angular range. These high-precision data improve
significantly the database for the beam asymmetry in the second and third resonance regions covering for the first time the
energy domain 1100-1500 MeV. New partial-wave analyses including these data are presented for which the beam asymmetry brings
crucial constraints. 相似文献
8.
A. Lleres O. Bartalini V. Bellini J. P. Bocquet P. Calvat M. Capogni L. Casano M. Castoldi A. D'Angelo J. -P. Didelez R. Di Salvo A. Fantini C. Gaulard G. Gervino F. Ghio B. Girolami A. Giusa M. Guidal E. Hourany V. Kouznetsov R. Kunne A. Lapik P. Levi Sandri D. Moricciani A. N. Mushkarenkov V. Nedorezov L. Nicoletti C. Perrin C. Randieri D. Rebreyend F. Renard N. Rudnev T. Russew G. Russo C. Schaerf M. -L. Sperduto M. -C. Sutera A. Turinge 《The European Physical Journal A - Hadrons and Nuclei》2007,31(1):79-93
Beam asymmetries and hyperon recoil polarizations for the reactions γp → K
+Λ and γp → K
+Σ0 have been measured from the threshold production to 1500MeV with the GRAAL facility located at the ESRF in Grenoble. These
results complement the database for the beam asymmetry, covering for the first time the production threshold region. Recent
theoretical analyses are presented for which the beam asymmetry data bring interesting new information and allow to better
determine some resonance parameters. Most importantly, these results strengthen the need of a new D13 state around 1900MeV. 相似文献
9.
B. Pasquini D. Drechsel L. Tiator 《The European Physical Journal A - Hadrons and Nuclei》2006,27(2):231-242
The relativistic amplitudes of pion photoproduction are evaluated by dispersion relations at t = const. The imaginary parts of the amplitudes are taken from the MAID model covering the absorption spectrum up to center-of-mass
energies W = 2.2GeV. For sub-threshold kinematics the amplitudes are expanded in powers of the two independent variables ν and t related to energy and momentum transfer. Subtracting the loop corrections from this power series allows one to determine
the counter terms of covariant baryon chiral perturbation theory. The proposed continuation of the amplitudes into the unphysical
region provides a unique framework to derive the low-energy constants to any given order as well as an estimate of the higher-order
terms by global properties of the absorption spectrum. 相似文献
10.
O. Bartalini V. Bellini J. P. Bocquet P. Calvat M. Capogni L. Casano M. Castoldi A. D'Angelo J. -P. Didelez R. Di Salvo A. Fantini D. Franco C. Gaulard G. Gervino F. Ghio G. Giardina B. Girolami A. Giusa M. Guidal E. Hourany R. Kunne A. Lapik P. Levi Sandri A. Lleres F. Mammoliti G. Mandaglio D. Moricciani A. N. Mushkarenkov V. Nedorezov L. Nicoletti C. Perrin C. Randieri D. Rebreyend F. Renard N. Rudnev T. Russew G. Russo C. Schaerf M. -L. Sperduto M. -C. Sutera A. Turinge V. Vegna 《The European Physical Journal A - Hadrons and Nuclei》2007,33(2):169-184
Beam asymmetry and differential cross-section for the reaction γp → ηp were measured from production threshold to 1500MeV photon laboratory energy. The two dominant neutral decay modes of the
η -meson, η → 2γ and η → 3π0 , were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared
with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different.
The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found. 相似文献
11.
A. D'Angelo O. Bartalini V. Bellini J. P. Bocquet P. Calvat M. Capogni L. Casano M. Castoldi J. -P. Didelez R. Di Salvo A. Fantini D. Franco G. Gervino F. Ghio G. Giardina B. Girolami A. Giusa M. Guidal E. Hourani V. Kouznetsov R. Kunne A. Lapik P. Levi Sandri A. Lleres F. Mammoliti G. Mandaglio D. Moricciani A. N. Mushkarenkov V. Nedorezov L. Nicoletti C. Randieri D. Rebreyend F. Renard N. Rudnev T. Russew G. Russo C. Schaerf M. -L. Sperduto M. -C. Sutera A. Turinge V. Vegna 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):441-445
Meson photoproduction with polarized photons has proved to be a powerful tool to identify contributions of baryon resonances
that are not evident in the differential cross-sections. It provides information that are complementary to those extracted
using pion-nucleon scattering data. Extensive results have been produced in the past on beam asymmetries by the Graal collaboration
for η and π
0 on the proton. New results are now available for the same reactions on the quasi-free neutron and for the K+ photoproduction on the proton. Contributions from hitherto undetected baryon resonances may be important to understand the
results. 相似文献
12.
S. Tosi 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):695-697
The high integrated luminosity collected by the BABAR detector at the SLAC PEP-II e
+
e
-
B-Factory offers an excellent opportunity for the study of heavy-quark spectroscopy. A selection of the most recent results
reported by BABAR will be presented, focussing on recently observed states with both open- and hidden-charm content. 相似文献
13.
C. Fernández-Ramırez E. Moya de Guerra J. M. Udıas 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):572-574
We present an extraction of the E2/M1 ratio of the Δ(1232) from experimental data applying an effective Lagrangian model. We compare the result obtained with different nucleonic
models and we reconcile the experimental results with the lattice QCD calculations. 相似文献
14.
J. Ahrens S. Altieri J. R. M. Annand H. -J. Arends R. Beck M. A. Blackston C. Bradtke A. Braghieri N. d'Hose H. Dutz A. Fix S. Goertz P. Grabmayr S. Hasegawa E. Heid H. Holvoet N. Horikawa T. Iwata O. Jahn P. Jennewein F. Klein R. Kondratiev M. Lang B. Lannoy V. Lisin M. Martinez-Fabregate J. C. McGeorge W. Meyer A. Panzeri P. Pedroni T. Pinelli I. Preobrajenski G. Reicherz Ch. Rohlof G. Rosner M. Rost T. Rostomyan D. Ryckbosch M. Schumacher B. Seitz G. Tamas A. Thomas R. Van de Vyver H. R. Weller F. Zapadtka 《The European Physical Journal A - Hadrons and Nuclei》2007,34(1):11-21
The helicity dependence of the total cross-section and the invariant-mass distributions in the (pπ±) and (π+π-) final states for the γp → pπ+π- reaction have been measured for the first time at incident photon energies from 400 to 800MeV. The measurement was performed
with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Although this
channel is found to be predominantly excited by the intermediate production of a Δπ state, both the measured unpolarized and
the helicity-dependent observables are generally not well described by the existing theoretical models. 相似文献
15.
J. Ahrens S. Altieri J. R. M. Annand H. -J. Arends R. Beck A. Braghieri N. d'Hose H. Dutz S. Goertz P. Grabmayr S. Hasegawa E. Heid H. Holvoet L. Van Hoorebeke N. Horikawa T. Iwata O. Jahn P. Jennewein R. Kondratiev J. Krimmer M. Lang B. Lannoy K. Livingston J. C. McGeorge W. Meyer A. Panzeri P. Pedroni T. Pinelli I. Preobrajenski G. Reicherz G. Rosner M. Rost T. Rostomyan D. Ryckbosch M. Schumacher B. Seitz G. Tamas A. Thomas R. van de Vyver Th. Walcher F. Zapadtka 《The European Physical Journal A - Hadrons and Nuclei》2005,26(1):135-140
The G asymmetry of the γp↦Nπ reaction has been measured for the first time for Eγ = 340±14 MeV. This observable, for which very scarce published data exist, plays an important role to disentangle the contributions
of the various nucleon resonances. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector system, a linearly
polarized, tagged photon beam, and a longitudinally polarized proton target. 相似文献
16.
We analyze two recent reactions of Belle, producing Dˉ and Dˉ* states that have an enhancement of the invariant Dˉ , Dˉ* mass distribution above threshold, from the point of view that they might be indicative of the existence of a hidden charm
scalar and an axial vector meson state below Dˉ or Dˉ* thresholds, respectively. We conclude that the data is compatible with the existing prediction of a hidden charm scalar meson
with mass around 3700MeV, though other possibilities cannot be discarded. The peak seen in the Dˉ* spectrum above threshold is, however, unlikely to be due to a threshold enhancement produced by the presence, below threshold,
of the hidden charm axial vector meson X(3872) . 相似文献
17.
Sayipjamal Dulat Bing-Song Zou 《The European Physical Journal A - Hadrons and Nuclei》2005,26(1):125-134
With accumulation of high statistics data at BES and CLEO-c, many new interesting channels can get enough statistics for partial-wave
analysis (PWA). Among them, ψ↦γpˉ,γΛˉ,γΣˉ,γΞˉ channels provide a good place for studying baryon-antibaryon interactions; the double radiative decays ψ↦γγV with V ≡ ρ,ω,φ have a potential to provide information on the flavor content of any meson resonances (R) with positive charge parity
(C = +) and mass above 1 GeV through ψ↦γR↦γγV; ψ(2s)↦γχc0,1,2 with χc0,1,2↦Kˉπ+π- and 2π+2π- decays are good processes to study χcJ charmonium decays. Using the covariant tensor formalism, here we provide theoretical PWA formulae for these channels. 相似文献
18.
A. Sibirtsev J. Haidenbauer S. Krewald T. -S. H. Lee U. -G. Meißner A. W. Thomas 《The European Physical Journal A - Hadrons and Nuclei》2007,34(1):49-68
A Regge model with absorptive corrections is employed in a global analysis of the world data on positive and negative pion
photoproduction for photon energies from 3 to 8GeV. In this region resonance contributions are expected to be negligible so
that the available experimental information on differential cross-sections and single polarization observables at - t ⩽ 2 GeV^2 allows us to determine the non-resonant part of the reaction amplitude reliably. The model amplitude is then used
to predict observables for photon energies below 3GeV. Differences between our predictions and data in this energy region
are systematically examined as possible signals for the presence of excited baryons. We find that the data available for the
polarized photon asymmetry show promising resonance signatures at invariant energies around 2GeV. With regard to differential
cross-sections the analysis of negative pion photoproduction data, obtained recently at JLab, indicates likewise the presence
of resonance structures around 2GeV. 相似文献
19.
Ya. Azimov V. Kuznetsov M. V. Polyakov I. Strakovsky 《The European Physical Journal A - Hadrons and Nuclei》2005,25(3):325-327
Using the results of the GRAAL Collaboration on the η photoproduction from the neutron target, we attempt to extract the partial
radiative width of the possible new nucleon resonance N
*(1675). The obtained estimates support this resonance to be a very attractive candidate for the non-strange member of the
exotic antidecuplet of baryons --a partner of the Θ+ pentaquark. Our phenomenological value for the transition magnetic moment μ(n
*
n), appears to be in good agreement with the predictions of the Chiral Quark Soliton Model. 相似文献
20.
A.?Sibirtsev J.?Haidenbauer F.?Huang S.?Krewald U.?-G.?Mei?ner 《The European Physical Journal A - Hadrons and Nuclei》2009,40(1):65-75
We present a systematic analysis of backward pion photoproduction for the reactions
p
p and
p
n . Regge phenomenology is applied at invariant collision energies above 3GeV in order to fix the reaction amplitude. A comparision
with older data on - and -photoproduction at = 180° indicates that the high-energy limit as given by the Regge calculation could be reached possibly at energies of around ≃ 3 GeV. In the energy region of
2.5 GeV, covered by the new measurements of
p
p differential cross-sections at large angles at ELSA, JLab, and LEPS, we see no clear signal for a convergence towards the
Regge results. The baryon trajectories obtained in our analysis are in good agreement with those given by the spectrum of
excited baryons. 相似文献