379 research outputs found
Toy Model for Pion Production II: The role of three-particle singularities
The influence of three-particle breakup singularities on s-wave meson
production in nucleon-nucleon collisions is studied within the distorted wave
Born approximation. This study is based on a simple scalar model for the
two-nucleon interaction and the production mechanism. An algorithm for the
exact numerical treatment of the inherent three-body cuts, together with its
straightforward implementation is presented. It is also shown that two
often-used approximations to avoid the calculation of the three-body breakup
are not justified. The possible impact on pion production observables is
discussed.Comment: 14 pages, 6 figure
Plasmon-graviton conversion in a magnetic field in TeV-scale gravity
Kaluza-Klein (KK) gravitons emission rates due to plasmon-graviton conversion
in magnetic field are computed within the ADD model of TeV-scale gravity.
Plasma is described in the kinetic approach as the system of charged particles
and Maxwell field both confined on the brane. Interaction with multidimensional
gravity living in the bulk with compact extra dimensions is introduced
within the linearized theory. Plasma collective effects enter through the
two-point correlation function of the fluctuations of the energy-momentum
tensor. The estimate for magnetic stars is presented leading to the lower limit
of the D-dimensional Plank mass.Comment: Submitted to Proceedings of "RusGrav-14" International Conference,
27.06-02.07 2011, Ulyanovks, Russi
Photocouplings at the Pole from Pion Photoproduction
The reactions and are analyzed in a
semi-phenomenological approach up to GeV. Fits to differential cross
section and single and double polarization observables are performed. A good
overall reproduction of the available photoproduction data is achieved. The
J\"ulich2012 dynamical coupled-channel model -which describes elastic
scattering and the world data base of the reactions ,
, and at the same time - is employed as the hadronic
interaction in the final state. The framework guarantees analyticity and, thus,
allows for a reliable extraction of resonance parameters in terms of poles and
residues. In particular, the photocouplings at the pole can be extracted and
are presented.Comment: 37 pages, 31 figures. Angles of the photocouplings at the pole
adapted to the convention of Phys. Rev. C 87, 068201 (2013
Coupled-channel dynamics in the reactions piN --> piN, etaN, KLambda, KSigma
Elastic piN scattering and the world data of the family of reactions pi^- p
--> eta n, K^0 Lambda$, K^0 Sigma^0, K^+ Sigma^-, and pi^+ p --> K^+ Sigma^+
are described simultaneously in an analytic, unitary, coupled-channel approach.
SU(3) flavor symmetry is used to relate both the t- and the u- channel
exchanges that drive the meson-baryon interaction in the different channels.
Angular distributions, polarizations, and spin-rotation parameters are compared
with available experimental data. Partial-wave amplitudes are determined and
the resonance content is extracted from the analytic continuation, including
resonance positions and branching ratios, and possible sources of uncertainties
are discussed. The results provide the final-state interactions for the ongoing
analysis of photo- and electroproduction data.Comment: 53 pages, 48 figures; results updated to published versio
Black hole evaporation with separated fermions
In models with a low quantum gravity scale, a well-motivated reason to expect
quark and lepton fields are localized but physically separated is to avoid
proton decay. This could happen in a ``fat-brane'' or in an additional,
orthogonal 1/TeV sized dimension in which the gauge and Higgs fields live
throughout. Black holes with masses of order the quantum gravity scale are
therefore expected to evaporate non-universally, preferentially radiating
directly into quarks or leptons but not both. Should black holes be copiously
produced at a future hadron collider, we find the ratio of final state jets to
charged leptons to photons is 113:8:1, which differs from previous analyses
that assumed all standard model fields live at the same point in the extra
dimensional space.Comment: 5 pages, REVTe
Spin correlations in pion production near threshold
A first measurement of longitudinal as well as transverse spin correlation
coefficients for the reaction was made using a
polarized proton target and a polarized proton beam. We report kinematically
complete measurements for this reaction at 325, 350, 375 and 400 MeV beam
energy. The spin correlation coefficients and the analyzing power as well as angular
distributions for and the polarization observables
were extracted. Partial wave cross sections for dominant
transition channels were obtained from a partial wave analysis that included
the transitions with final state angular momenta of . The measurements
of the polarization observables are compared
with the predictions from the J\"ulich meson exchange model. The agreement is
very good at 325 MeV, but it deteriorates increasingly for the higher energies.
At all energies agreement with the model is better than for the reaction
.Comment: Preprint, 21 pp, submitted to Phys. Rev. C. Keywords: Mesons,
Polarization, Spin Correlations, Few body system
Light meson mass dependence of the positive parity heavy-strange mesons
We calculate the masses of the resonances D_{s0}^*(2317) and D_{s1}(2460) as
well as their bottom partners as bound states of a kaon and a D^*- and
B^*-meson, respectively, in unitarized chiral perturbation theory at
next-to-leading order. After fixing the parameters in the D_{s0}^*(2317)
channel, the calculated mass for the D_{s1}(2460) is found in excellent
agreement with experiment. The masses for the analogous states with a bottom
quark are predicted to be M_{B^*_{s0}}=(5696\pm 40) MeV and M_{B_{s1}}=(5742\pm
40) MeV in reasonable agreement with previous analyses. In particular, we
predict M_{B_{s1}}-M_{B_{s0}^*}=46\pm 1 MeV. We also explore the dependence of
the states on the pion and kaon masses. We argue that the kaon mass dependence
of a kaonic bound state should be almost linear with slope about unity. Such a
dependence is specific to the assumed molecular nature of the states. We
suggest to extract the kaon mass dependence of these states from lattice QCD
calculations.Comment: 10 page
A diquark model for baryons containing one heavy quark
We present a phenomenological ansatz for coupling a heavy quark with two
light quarks to form a heavy baryon. The heavy quark is treated in the heavy
mass limit, and the light quark dynamics is approximated by propagating scalar
and axial vector 'diquarks'. The resulting effective lagrangian, which
incorporates heavy quark and chiral symmetry, describes interactions of heavy
baryons with Goldstone bosons in the low energy region. As an application, the
Isgur--Wise form factors are estimated.Comment: 9 pages + 8 figures, both as uuencoded PS, discussion of Bjorken
limit (1 par + 1 fig) added, to appear in Z.Phys.
Stringent neutron-star limits on large extra dimensions
Supernovae (SNe) are copious sources for Kaluza-Klein gravitons which are
generic for theories with large extra dimensions. These massive particles are
produced with average velocities ~0.5 c so that many of them are
gravitationally retained by the SN core. Every neutron star thus has a halo of
KK gravitons which decay into nu bar-nu, e^+e^- and gamma gamma on time scales
\~10^9 years. The EGRET gamma-flux limits (E_gamma ~ 100 MeV) for nearby
neutron stars constrain the fundamental scale for n=2 extra dimensions to M
>500 TeV, and M>30 TeV for n=3. The upcoming GLAST satellite is a factor ~30
more sensitive and thus may detect KK decays, for example at the nearby neutron
star RX J185635--3754. The requirement that neutron stars are not excessively
heated by KK decays implies M>1700 TeV for n=2, and M>60 TeV for n=3.Comment: Minor changes, matches version to appear in PR
Near threshold eta meson production in the d+d->alpha+eta reaction
The d+d->alpha+eta reaction has been investigated near threshold using the
ANKE facility at COSY-Juelich. Both total and differential cross sections have
been measured at two excess energies, Q=2.6 MeV and 7.7 MeV, with a
subthreshold measurement being undertaken at Q=-2.6 MeV to study the physical
background. While consistent with isotropy at the lower energy, the angular
distribution reveals a pronounced anisotropy at the higher one, indicating the
presence of higher partial waves. Options for the decomposition into partial
amplitudes and their consequences for determination of the s-wave eta-alpha
scattering length are discussed.Comment: 8pp, fig.3 added, normalisation in eq.4.1 correcte
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