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1.
We investigate the QED Compton process (QEDCS) in
and
, together with the major background coming from virtual Compton scattering (VCS), where the photon is emitted from the hadronic vertex. We suggest new kinematical constraints which suppress the VCS background and are furthermore suitable for the extraction of the equivalent photon content of the proton at the HERA collider. We show that the cross section, commonly expressed in terms of the proton structure functions, is reasonably well described by the equivalent photon approximation of the proton, also in the inelastic channel in the proposed kinematical region.Received: 5 February 2004, Revised: 8 March 2004, Published online: 9 June 2004 相似文献
2.
A high-quality double-polarization data set for the helicity dependence of the total and differential cross-sections for both
channels in the
region has been obtained in the framework of the GDH experiment. The experiment, performed at the Mainz microtron MAMI, used a 4
detection system, a circularly polarized photon beam, and a longitudinally polarized frozen-spin target. These data are included in the database to perform a multipole analysis to determine the properties of the
-resonance. For the resonant
(1232) multipoles we find a very good agreement with previous analyses, while the nonresonant ones show significant deviations.Received: 11 July 2003, Revised: 16 January 2004, Published online: 17 August 2004PACS:
13.60.Le Meson production - 14.20.Gk Baryon resonances with S = 0 - 25.20.Lj Photoproduction reactions 相似文献
3.
A. Bartl H. Fraas O. Kittel W. Majerotto 《The European Physical Journal C - Particles and Fields》2004,36(2):233-243
We study CP-sensitive observables in the neutralino production
and the subsequent two-body decays of the neutralino
and of the Z boson
. We identify the CP-odd elements of the Z boson density matrix and propose CP-sensitive triple-product asymmetries. We calculate these observables and the cross sections in the minimal supersymmetric standard model with complex parameters and M
1 for an e
+
e
- linear collider with
GeV and longitudinally polarized beams. We show that the asymmetries can reach
for
and
for
and discuss the feasibility of measuring these asymmetries.Received: 4 February 2004, Revised: 17 May 2004, Published online: 2 July 2004 相似文献
4.
Measurements of the time-dependent CP-asymmetry in the decay
and its charge conjugate by the BELLE and BABAR collaborations currently yield
and
, characterizing the direct and mixing-induced CP-asymmetries, respectively. We study the implication of these measurements on the CKM phenomenology taking into account the available information in the quark mixing sector. Our analysis leads to the results that the ratio |P
c
/T
c
| involving the QCD-penguin and tree amplitudes and the related strong phase difference
in the
decays are quite substantial. Using the isospin symmetry to constrain |P
c
/T
c
| and
, where
parameterizes the penguin-induced contribution, we present a fit of the current data including the measurements of
and
. Our best-fits yield
,
,
,
, and
. At 68% C.L., the ranges are
,
,
,
and
. Currently en vogue dynamical approaches to estimate the hadronic matrix elements in
decays do not provide a good fit of the current data.Received: 5 April 2004, Published online: 14 July 2004A.Ya. Parkhomenko: On leave of absence from Department of Theoretical Physics, Yaroslavl State University, Sovietskaya 14, 150000 Yaroslavl, Russia. 相似文献
5.
We analyze the pion electromagnetic, charged-current, and
transition form factors at timelike momentum transfers q,
GeV2, using a dispersion approach. We discuss in detail the propagator matrix of the photon-vector meson system and define certain reduced amplitudes, or vertex functions, describing the coupling of this system to final states. We then apply the derived analytic expressions to the analysis of the recent
,
, and
data. We find the reduced amplitudes for the coupling of the photon and vector mesons to two pseudoscalars to be constant, independent of s, in the range considered, indicating a freezing of the amplitudes for
GeV. The fit to the form factor data leads to the following values of the Breit-Wigner resonance masses
MeV,
MeV and
MeV, where the errors are only statistical.Received: 8 December 2003, Published online: 23 March 2004T. Paulus: Now at Philips 相似文献
6.
A. Bredenstein S. Dittmaier M. Roth 《The European Physical Journal C - Particles and Fields》2004,36(3):341-363
We have constructed a Monte Carlo generator (the corresponding FORTRAN code can be obtained from the authors upon request) for lowest-order predictions for the processes
and
in the standard model and extensions thereof by an effective
coupling as well as anomalous triple and quartic gauge-boson couplings. Polarization is fully supported, and a realistic photon beam spectrum can be taken into account. For the processes
all helicity amplitudes are explicitly given in a compact form. The presented numerical results contain, in particular, a survey of cross sections for representative final states and their comparison to results obtained with the program package Whizard/Madgraph. The impact of a realistic beam spectrum on cross sections and distributions is illustrated. Moreover, the size of various contributions to cross sections, such as from weak charged- or neutral-current, or from strong interactions, is analyzed. Particular attention is paid to W-pair production channels
where we investigate the impact of background diagrams, possible definitions of the W-pair signal, and the issue of gauge-invariance violation caused by finite gauge-boson widths. Finally, the effects of triple and quartic anomalous gauge-boson couplings on cross sections as well as the possibility to constrain these anomalous couplings at future
colliders are discussed.Received: 19 May 2004, Published online: 16 July 2004 相似文献
7.
D. V. Bugg 《The European Physical Journal C - Particles and Fields》2004,36(2):161-168
A partial wave analysis of PS185 data for
is presented. A 3
S
1 cusp is identified in the inverse process
at threshold, using detailed balance to deduce cross sections from
. Partial wave amplitudes for
3
P
0, 3
F
3, 3
D
3 and 3
G
3 exhibit a behaviour very similar to resonances observed in Crystal Barrel data. With this identification, the
data then provide evidence for a new I = 0, J
PC
= 1- resonance with mass
MeV,
MeV, coupling to both 3
S
1 and 3
D
1.Received: 4 June 2004, Published online: 9 July 2004 相似文献
8.
We compute the one-loop
-functions describing the renormalisation of the coupling constant
and the frequency parameter
for the real four-dimensional duality-covariant non-commutative
-model, which is renormalisable to all orders. The contribution from the one-loop four-point function is reduced by the one-loop wavefunction renormalisation, but the
-function remains non-negative. Both
and
vanish at the one-loop level for the duality-invariant model characterised by
. Moreover,
also vanishes in the limit
, which defines the standard non-commutative
-quantum field theory. Thus, the limit
exists at least at the one-loop level.Received: 19 March 2004, Published online: 5 May 2004 相似文献
9.
S. M. Lietti C. A. de S. Pires 《The European Physical Journal C - Particles and Fields》2004,35(1):137-143
In this work, we investigate the sensitivity of the process
at LHC for the photonic 3- and 4-point functions that appear in non-commutative QED. We show that this process serves to study the behavior of the space-space as well as of the space-time non-commutativity. We also show that this process can probe the non-commutative scale
in the range of a few TeV.Received: 9 February 2004, Revised: 27 February 2004, Published online: 8 April 2004 相似文献
10.
We describe the spectra and decays of
and
atoms within a non-relativistic effective field theory. The evaluations of the energy shifts and widths are performed at next-to-leading order in isospin symmetry breaking. We provide general formulae for all S-states, and discuss the states with angular momentum one in some detail. The prediction for the lifetime of the
atom in its ground state yields
s.Received: 9 May 2004, Published online: 23 July 2004 相似文献
11.
The CP asymmetries of the decay
, which originates from
flavor-changing neutral-current processes, and its CP-averaged branching ratio BR
offer interesting avenues to explore flavor physics. We show that we may characterize this channel, within the standard model, in a theoretically clean manner through a surface in observable space. In order to extract the relevant information from BR
, further information is required, which is provided by the
system and the SU(3) flavor symmetry, where we include the leading factorizable SU(3)-breaking corrections and discuss how experimental insights into non-factorizable effects can be obtained. We point out that the standard model implies a lower bound for BR
, which is very close to its current experimental upper bound, thereby suggesting that this decay should soon be observed. Moreover, we explore the implications for color suppression in the
system, and convert the data for these modes in a peculiar standard-model pattern for the CP-violating
observables.Received: 3 August 2004, Published online: 15 November 2004 相似文献
12.
We compute the cross section for exclusive double-diffractive
production at the Tevatron,
, and the LHC. We evaluate both the gg and
-channel exchange contributions to the process. The observation of exclusive
production at the Tevatron will provide a check on the model predictions and offer an opportunity to confirm the expectations for exclusive double-diffractive Higgs production at the LHC.Received: 10 September 2004, Revised: 8 October 2004, Published online: 1 December 2004 相似文献
13.
We perform a global parton analysis of deep inelastic and related hard-scattering data, including
corrections to the parton evolution. Although the quality of the fit is essentially unchanged, there are two important physical consequences. First, the different DGLAP evolution of u and d type quarks introduces isospin violation, i.e.
, which is found to be unambiguously in the direction to reduce the NuTeV
anomaly. A second consequence is the appearance of photon parton distributions
of the proton and the neutron. In principle these can be measured at HERA via the deep inelastic scattering processes
; our predictions are in agreement with the present data.Received: 3 November 2004, Published online: 11 January 2005R.S. Thorne: Royal Society University Research Fellow. 相似文献
14.
By employing the QCD factorization approach, we calculated the next-to-leading order new physics contributions to the branching ratios, CP asymmetries, isospin and U-spin symmetry breaking of the exclusive decays
(
), induced by the charged Higgs penguins in general two-Higgs-doublet models. Within the considered parameter space, we found that (a) the new physics corrections to the observables are generally small in model I and model III-A, moderate in model II, but large in model III-B; (b) from the well measured branching ratios and upper limits, a lower bound of MH > 200 GeV in model II was obtained, while the allowed range of MH in model III-B is
GeV; these bounds are comparable with those from the inclusive
decay; (c) the NLO Wilson coefficient C7(mb) in model III-B is positive and disfavored by the measured value of isospin symmetry breaking
, but it still cannot be excluded if we take the large errors into account; (d) the CP asymmetry
in model III-B has an opposite sign to the one in the standard model (SM), which may be used as a good observable to distinguish the SM from model III-B; (e) the isospin symmetry breaking
is less than
in the region of
preferred by the global fit result, but it can be as large as 20 to
in the regions of
and
. The SM and model III-B predictions for
are opposite in sign for small or large values of the CKM angles; (f) the U-spin symmetry breaking
in the SM and the general two-Higgs-doublet models is generally small in size:
.Received: 9 October 2003, Revised: 11 November 2003, Published online: 18 February 2004 相似文献
15.
V. Yu. Grishina L. A. Kondratyuk M. Büscher W. Cassing 《The European Physical Journal A - Hadrons and Nuclei》2004,21(3):507-520
Using an effective Lagrangian approach as well as the Quark-Gluon Strings Model, we analyze near-threshold production of a
0(980)-mesons in the reaction
as well as the background of non-resonant
-pair production. We argue that the reaction
at an energy release
MeV is dominated by the intermediate production of the a
0(980)-resonance. At larger energies the non-resonant
-pair production --where the kaons are produced in a relative P-wave-- becomes important. The effects of final-state interactions are evaluated in a unitarized scattering length approach and found to be in the order of a 20% suppression close to threshold. Thus, in present experiments at the Cooler Synchrotron COSY-Jülich for
MeV the a
0
+ signal can reliably be separated from the non-resonant
background.Received: 26 February 2004, Published online: 21 September 2004PACS:
25.10. + s Nuclear reactions involving few-nucleon systems - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy
GeV) 相似文献
16.
K. Kossert M. Camen F. Wissmann J. Ahrens J. R. M. Annand H.-J. Arends R. Beck G. Caselotti P. Grabmayr O. Jahn P. Jennewein M. I. Levchuk A. I. L’vov J. C. McGeorge A. Natter V. Olmos de León V. A. Petrun’kin G. Rosner M. Schumacher B. Seitz F. Smend A. Thomas W. Weihofen F. Zapadtka 《The European Physical Journal A - Hadrons and Nuclei》2004,19(3):391-399
Differential cross-sections for quasi-free
photoproduction from the proton and neutron bound in the deuteron have been measured for
MeV at
using the Glasgow photon tagger at MAMI, the Mainz 48 cm
cm NaI(Tl) photon detector and the Göttingen SENECA recoil detector. For the proton measurements made with both liquid-deuterium and liquid-hydrogen targets allow direct comparison of free
photoproduction cross-sections as extracted from the bound-proton data with experimental free cross-sections which are found to be in reasonable agreement below 320 MeV. At higher energies the free cross-sections extracted from quasi-free data are significantly smaller than the experimental free cross-sections and theoretical predictions based on multipole analysis. For the first time, free neutron cross-section have been extracted in the
-region. They are also in agreement with the predictions from multipole analysis up to 320 MeV and significantly smaller at higher photon energies.Received: 28 May 2003, Published online: 27 January 2004PACS:
13.60.Le Meson production - 14.20.Dh Protons and neutrons - 25.20.Lj Photoproduction reactionsK. Kossert: Part of the Doctoral Thesis.,Present address: Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany.Present address F. Wissmann: Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany. Present address B. Seitz: II. Physikalisches Institut der Universität Gießen, Germany. 相似文献
17.
The H Collaboration 《The European Physical Journal C - Particles and Fields》2004,36(4):441-452
Deep-inelastic positron-proton interactions at low values of Bjorken-x down to
which give rise to high transverse momentum
-mesons are studied with the H1 experiment at HERA. The inclusive cross section for
-mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the
and of the four-momentum transfer Q
2 and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward
-meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Received: 8 April 2004, Revised: 7 July 2004, Published online: 30 July 2004Dedicated to the memory of Krzysztof Rybicki 相似文献
18.
In the framework of QCD factorization, we study
decays. In order to more reliably determine the phenomenological parameters X
H and X
A arising from end-point divergences in the hard spectator scattering and weak annihilation contributions, we use the global analysis for twelve
and VP decay modes, such as
,
,
,
, et cetera, but excluding the modes whose (dominant) internal quark-level process is
. Based on the global analysis, we critically investigate possible magnitudes of X
H,A and find that both large and small X
H,A terms are allowed by the global fit. In the case of the large X
H,A effects, the standard model (SM) prediction of the branching ratios (BRs) for
is large and well consistent with the experimental results. In contrast, in the case of the small X
H,A effects, the SM prediction for these BRs is smaller than the experimental data. Motivated by the recent Belle measurement of
through
, if we take into account possible new physics effects on the quark-level process
, we can explicitly show that these large BRs can be understood even in the small X
H,A case. Specifically, we present two new physics scenarios: R-parity violating SUSY and R-parity conserving SUSY.Received: 28 April 2004, Revised: 12 July 2004, Published online: 7 September 2004 相似文献
19.
A model describing the leptoproduction of
mesons is considered. For the amplitude of the photon dissociation into a
pair, the light-cone wave function is used. Scattering of the colorless
pair off the nucleon is computed within reggeon exchange phenomenology. The transition of the scattered quark and antiquark into the final
meson is treated with the aid of the parton-hadron duality concept. Numerical calculations of
and r0400 describe the world data at Q2 < 4 GeV2 rather reasonably. The calculations of the
meson spin density matrix show that the computed matrix elements except r0400 are in good agreement with the available experimental data at Q2 up to 8 GeV2 and the total mass of the
system greater than 4 GeV. The Regge phenomenology predictions at the highest experimentally available energies agree with both the HERA data and calculations performed within the perturbative QCD approach even for very high Q2 (
-20 GeV2). The predicted scale of the S-channel helicity non-conservation is in reasonable agreement with the experimental data.Received: 18 September 2003, Revised: 17 December 2003, Published online: 13 February 2004 相似文献
20.
We investigate the physics potential of the annihilation decays
in the standard model and beyond. In a naive factorization approach, the branching ratios are estimated to be
and
. In the framework of QCD factorization, we compute the non-factorizable corrections and get
,
. Future measurements of these decays would be useful for testing the factorization frameworks. The smallness of these decays in the SM makes them sensitive probes of new physics. As an example, we will consider the possible admixture of the (V + A) charge current to the standard (V-A) current. This admixture will give a significant contribution to the decays.Received: 29 August 2003, Revised: 17 January 2004, Published online: 19 March 2004Corresponding author: Y.D. Yang 相似文献