4,723 research outputs found
Isospin breaking in pion-nucleon scattering at threshold by radiative processes
We investigate the dispersive contribution by radiative processes such as
(pi- proton to neutron gamma) and (pi- proton to Delta gamma) to the
pion-nucleon scattering lengths of charged pions in the heavy baryon limit.
They give a large isospin violating contribution in the corresponding isoscalar
scattering length, but only a small violation in the isovector one. These terms
contribute 6.3(3)% to the 1s level shift of pionic hydrogen and give a chiral
constant F_pi^2f_1=-25.8(8) MeV.Comment: 9 pages with 1 figur
Precision determination of the pi-N scattering lengths and the charged pi-NN coupling constant
We critically evaluate the isovector GMO sumrule for the charged
coupling constant using recent precision data from p and d atoms
and with careful attention to systematic errors. From the d scattering
length we deduce the pion-proton scattering lengths (statistic) (systematic))~ and . From this a direct evaluation gives (statistic)(systematic) or .Comment: 4 pages, 1 figure, latex and postscript; invited talk at PANIC99; to
appear in Nucl. Phys. A; changed notation: g^2 and f^2 replaced by
conventional g^2/4\pi and f^2/4\p
Chiral Dynamics of Deeply Bound Pionic Atoms
We present and discuss a systematic calculation, based on two-loop chiral
perturbation theory, of the pion-nuclear s-wave optical potential. A proper
treatment of the explicit energy dependence of the off-shell pion self-energy
together with (electromagnetic) gauge invariance of the Klein-Gordon equation
turns out to be crucial. Accurate data for the binding energies and widths of
the 1s and 2p levels in pionic ^{205}Pb and ^{207}Pb are well reproduced, and
the notorious "missing repulsion" in the pion-nuclear s-wave optical potential
is accounted for. The connection with the in-medium change of the pion decay
constant is clarified.Comment: preprint ECT*-02-16, 4 pages, 3 figure
Impulse approximation in the n p --> d pi^0 reaction reexamined
The impulse approximation (one-body operator) in the n p --> d pi^0 reaction
is reexamined with emphasis on the issues of reducibility and recoil
corrections. An inconsistency when one pion exchange is included in the
production operator is demonstrated and then resolved via the introduction of
"wave function corrections" which nearly vanish for static nucleon propagators.
Inclusion of the recoil corrections to the nucleon propagators is found to
change the magnitude and sign of the impulse production amplitude, worsening
agreement with the experimental cross section by approximately 30%. A cutoff is
used to account for the phenomenological nature of the external wave functions,
and is found to have a significant impact up to approximately 2.5 GeV.Comment: Published versio
Isospin breaking of the narrow charmonium state of Belle at 3872 MeV as a deuson
The narrow charmonium state near 3872 MeV reported by the Belle collaboration
and confirmedby CDF lies almost exactly at the neutral D anti-D* threshold. As
was predicted many years ago it can be a deuteronlike meson-meson state called
a deuson. If so, it should be an axial, or possibily a pseudoscalar state with
C=0, and isospin predominantly 0. Large isospin breaking is expected because of
the isospin mass splitting between the neutral and charged D (D*) mesons.
Because of this large isospin breaking the decay X(3872) to J/psi rho would be
allowed, while J/psi sigma would be forbidden by C-parity, as indicated by the
present data.Comment: 7 latex pages 5 figures. This report supercedes the unpublished
reminder hep-ph/0308277. Version 2 to appear in Physics Letters B, one
reference added and minor improvement
Ground state energy fluctuations in nuclear matter II
Improvements are performed on a recently proposed statistical theory of the
mean field of a many-fermion system. The dependence of the predictions of the
theory upon its two basic ingredients, namely the Hartree-Fock energy and the
average energy of the two particle-two hole excitations, is explored.Comment: 16 pages, 1 figure, revte
Some Preliminary Observations On The Acoustic Behavior Of Semi-Domestic Reindeer (Rangifer Tarandus Tarandus) With Emphasis On Intraspecific Communication And The Mother-Calf Relationship
Thesis (M.S.) University of Alaska Fairbanks, 197
On the Economic Choice of Experiment Sizes for Decision Regarding Certain Linear Combinations
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146925/1/rssb00712.pd
A Note on the Posterior Mean of a Population Mean
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147084/1/rssb00794.pd
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