5,028 research outputs found
Suppression of Non-photonic Electrons from Enhancement of Charm Baryons in Heavy Ion Collisions
At intermediate transverse momentum (2 < p_T < 6 GeV/c), baryon production in
Au+Au collisions is enhanced compared to p+p collisions. Since charm baryon
decays produce electrons less frequently than charm meson decays, the
non-photonic electron spectrum is sensitive to the Lambda_c/D ratio. In this
report we study the dependence of the non-photonic electron spectrum on the
baryon-to-meson ratio for charm hadrons. As an example, we take the Lambda_c/D
ratio to have the same form as the Lambda/K^0_S ratio. In this case, even if
the total charm quark yield in Au+Au collisions scales with the number of
binary nucleon-nucleon collisions (N_bin), the electron spectrum at 2 < p_T < 5
GeV/c is suppressed relative to N_bin scaled p+p collisions by as much as 20%.Comment: Added STAR data to figure 1 and made slight text modifications (fixed
figure replacement
Scalar Sector in the Minimal Supersymmetric 3-3-1 model
We consider the minimal supersymmetric extension of the 3-3-1 model and we
study the mass spectra in the scalar sector of this model without the
anti-sextet. We show that all our lighest scalars are in agreement with the
experimental limits.Comment: It was included on the introduction of the article the motivation to
> study the model, and we moved the sections 4.1 and 4.2 to the appendix. It
has 22 pages, 9 figures. It was accepted to be published at International
Journal of Modern Physics
A new approach to calculate the transport matrix in RF cavities
A realistic approach to calculate the transport matrix in RF cavities is
developed. It is based on joint solution of equations of longitudinal and
transverse motion of a charged particle in an electromagnetic field of the
linac. This field is a given by distribution (measured or calculated) of the
component of the longitudinal electric field on the axis of the linac. New
approach is compared with other matrix methods to solve the same problem. The
comparison with code ASTRA has been carried out. Complete agreement for
tracking results for a TESLA-type cavity is achieved. A corresponding algorithm
will be implemented into the MARS15 code.Comment: 4 pp. Particle Accelerator, 24th Conference (PAC'11) 2011. 28 Mar - 1
Apr 2011. New York, US
Gauge invariance, radiative interferences and properties of vector mesons
We state the implications on the properties of vector mesons due to gauge
invariance. In particular, we find that polarized vector mesons exhibit a
property in the radiation distribution of order in the photon
energy, namely it is null when the gyromagnetic ratio becomes . Therefore,
the generalization of the Burnett-Kroll theorem for polarized vector-meson
states is held only if . In addition, radiative interferences between the
electric charge and any gauge invariant term is found to be parametrized by a
common global factor which can be used to extract information of the involved
states by a proper choice of the kinematical region, where they could be
relevant.Comment: 5 pages, 1 figure. To appear in the Proceedings of the IX Mexican
Workshop on Particles and Fields, Colima Mexico. Uses RevTex
Updated Estimate of the Muon Magnetic Moment Using Revised Results from e+e- Annihilation
A new evaluation of the hadronic vacuum polarization contribution to the muon
magnetic moment is presented. We take into account the reanalysis of the
low-energy e+e- annihilation cross section into hadrons by the CMD-2
Collaboration. The agreement between e+e- and tau spectral functions in the pi
pi channel is found to be much improved. Nevertheless, significant
discrepancies remain in the center-of-mass energy range between 0.85 and 1.0
GeV, so that we refrain from averaging the two data sets. The values found for
the lowest-order hadronic vacuum polarization contributions are a_mu[had,LO] =
(696.3 +- 6.2[exp] +- 3.6[rad])e-10 (e+e- -based) and a_mu[had,LO] = (711.0 +-
5.0[exp] +- 0.8[rad] +- 2.8[SU2])e-10 (tau-based), where the errors have been
separated according to their sources: experimental, missing radiative
corrections in e+e- data, and isospin breaking. The corresponding Standard
Model predictions for the muon magnetic anomaly read a_mu = (11,659,180.9 +-
7.2[had] +- 3.5[LBL] +- 0.4[QED+EW])e-10 (e+e- -based) and a_mu = (11,659,195.6
+- 5.8[had] +- 3.5[LBL] +- 0.4[QED+EW])e-10 (tau-based), where the errors
account for the hadronic, light-by-light (LBL) scattering and electroweak
contributions. The deviations from the measurement at BNL are found to be (22.1
+- 7.2 +- 3.5 +- 8.0)e-10 (1.9 sigma) and (7.4 +- 5.8 +- 3.5 +- 8.0)e-10 (0.7
sigma) for the e+e- and tau-based estimates, respectively, where the second
error is from the LBL contribution and the third one from the BNL measurement.Comment: 14 pages, 7 figures (to be submitted to Phys Lett B
Two-Loop Heavy-Flavor Contribution to Bhabha Scattering
We evaluate the two-loop QED corrections to the Bhabha scattering cross
section which involve the vacuum polarization by heavy fermions of arbitrary
mass m_f >> m_e. The results are valid for generic values of the Mandelstam
invariants s,t,u >> m_e^2.Comment: 13 pages, 6 figures. Equations in the appendix generalized to the
heavy-quark cas
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