224 research outputs found
The H-Dibaryon and the Hard Core
The H dibaryon, a single, triply magic bag containing two up, two down and
two strange quarks, has long been sought after in a variety of experiments. Its
creation has been attempted in , proton and most recently in relativistic
heavy ion induced reactions. We concentrate on the latter, but our conclusions
are more generally applicable. The two baryons coalescing to form the single
dibaryon, likely in the case of heavy ions, must penetrate
the short range repulsive barrier which is expected to exist between them. We
find that this barrier can profoundly affect the probability of producing the H
state, should it actually exist.Comment: 9 pages including 4 figure
Comment on Intrinsic and dynamically generated scalar meson states
The scalar-meson assignments of Shakin and Wang in a generalized
Nambu--Jona-Lasinio model are contradicted by recent experimental information.
Also the strict distinction made by these authors between ``intrinsic'' and
``dynamically generated'' states is contested, as well as a number of other
statements.Comment: 7 pages, (v2 cosmetics, v3 corrections in one reference), to be
published in Phys.Rev.
Tau and Charm physics highlights
In tau physics, we are at the frontier between the completion of the LEP
program and the start of analyses from b-factories, which are expected to
produce results in the coming years. Nice results from CLEO are steadily
delivered in the meantime. For charm, impressive progress have been achieved by
fixed target experiments in the search for CP violation and D^0 - \bar D^0
oscillations. First results from b-factories demonstrate the power of these
facilities in such areas. The novel measurement of the D* width by CLEO happens
to be rather different from current expectations. The absence of a charm
factory explains the lack or the very slow progress in the absolute scale
determinations for charm decays.Comment: "Typos corrected and references added
Resonant State in Helium-4 Lambda
In a recent experiment E906 at the BNL-AGS, a search for light S=-2
hypernuclei, strong evidence was found for the nuclide Hydrogen-4 double
Lambda. One of the most striking components of this data was the appearance of
a narrow low-momentum pi- line at k(pi-) = 104-105 MeV/c. This was ascribed to
the decay of Hydrogen-4 double Lambda into a resonant state in Helium-4 Lambda.
The existence of such a state is shown to be plausible and its characteristics
are delineated.Comment: 4 pages, 1 figur
Precision Measurement of the Proton and Deuteron Spin Structure Functions g2 and Asymmetries A2
We have measured the spin structure functions g2p and g2d and the virtual
photon asymmetries A2p and A2d over the kinematic range 0.02 < x < 0.8 and 0.7
< Q^2 < 20 GeV^2 by scattering 29.1 and 32.3 GeV longitudinally polarized
electrons from transversely polarized NH3 and 6LiD targets. Our measured g2
approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3
reduced matrix elements d2p and d2n are less than two standard deviations from
zero. The data are inconsistent with the Burkhardt-Cottingham sum rule if there
is no pathological behavior as x->0. The Efremov-Leader-Teryaev integral is
consistent with zero within our measured kinematic range. The absolute value of
A2 is significantly smaller than the sqrt[R(1+A1)/2] limit.Comment: 12 pages, 4 figures, 2 table
Lifetime Differences, direct CP Violation and Partial Widths in D0 Meson Decays to K+K- and pi+pi-
We describe several measurements using the decays D0->K+K- and pi+pi-. We
find the ratio of partial widths, Gamma(D0->K+K-)/Gamma(D0->pi+pi-), to be
2.96+/-0.16+/-0.15, where the first error is statistical and the second is
systematic. We observe no evidence for direct CP violation, obtaining A_CP(KK)
= (0.0+/-2.2+/-0.8)% and A_CP(pipi = (1.9+/-3.2+/-0.8)%. In the limit of no CP
violation we measure the mixing parameter y_CP = -0.012+/-0.025+/-0.014 by
measuring the lifetime difference between D0->K+ K- or pi+pi- and the CP
neutral state, D0->K-pi+. We see no evidence for mixing.Comment: 14 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLNS, submitted to PRD, Rapid Communicatio
Measurement of the Mass Splittings between the States
We present new measurements of photon energies and branching fractions for
the radiative transitions: Upsilon(2S)->gamma+chi_b(J=0,1,2). The masses of the
chi_b states are determined from the measured radiative photon energies. The
ratio of mass splittings between the chi_b substates,
r==(M[J=2]-M[J=1])/(M[J=1]-M[J=0]) with M the chi_b mass, provides information
on the nature of the bbbar confining potential. We find
r(1P)=0.54+/-0.02+/-0.02. This value is in conflict with the previous world
average, but more consistent with the theoretical expectation that r(1P)<r(2P);
i.e., that this mass splittings ratio is smaller for the chi_b(1P) triplet than
for the chi_b(2P) triplet.Comment: 11 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
A search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
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