43 research outputs found
Jets associated with Z^0 boson production in heavy-ion collisions at the LHC
The heavy ion program at the LHC will present unprecedented opportunities to
probe hot QCD matter, that is, the quark gluon plasma (QGP). Among these
exciting new probes are high energy partons associated with the production of a
Z^0 boson, or Z^0 tagged jets. Once produced, Z^0 bosons are essentially
unaffected by the strongly interacting medium produced in heavy-ion collisions,
and therefore provide a powerful signal of the initial partonic energy and
subsequent medium induced partonic energy loss. When compared with theory,
experimental measurements of Z^0 tagged jets will help quantify the jet
quenching properties of the QGP and discriminate between different partonic
energy loss formalisms. In what follows, I discuss the advantages of tagged
jets over leading particles, and present preliminary results of the production
and suppression of Z^0 tagged jets in relativistic heavy-ion collisions at LHC
energies using the Guylassy-Levai-Vitev (GLV) partonic energy loss formalism.Comment: To appear in the proceedings of the 2010 Winter Workshop on Nuclear
Dynamics, which was held in Ocho Rios, Jamaica, mon
The B-L/Electroweak Hierarchy in Heterotic String and M-Theory
E8 x E8 heterotic string and M-theory, when compactified on a Calabi-Yau
threefold admitting an SU(4) vector bundle with Wilson lines, can give rise to
the exact MSSM spectrum with three right-handed neutrino chiral superields, one
per family. Rank preserving Wilson lines require that the standard model group
be augmented by a gauged U(1)_B-L. Since there are no fields in this theory for
which 3(B-L) is an even, non-zero integer, the gauged B-L symmetry must be
spontaneously broken at a low scale, not too far above the electroweak scale.
It is shown that in these heterotic standard models, the B-L symmetry can be
broken, with a phenomenologically viable B-L/electroweak hierarchy, by at least
one right-handed sneutrino acquiring a vacuum expectation value. This is
explicitly demonstrated, in a specific region of parameter space, using a
renormalization group analysis and soft supersymmetry breaking operators. The
vacuum state is shown to be a stable, local minimum of the potential and the
resultant hierarchy is explicitly presented in terms of tan[beta].Comment: 16 pages; typos fixed, analysis generalize
Towards resolution of the scalar meson nonet enigma
By the application of a linear mass spectrum to a composite system of both
the pseudoscalar and scalar meson nonets, we find three mass relations for the
masses of the scalar states which suggest the assignment for the
scalar meson nonet: Comment: 16 pages, LaTe
A Study in Depth of f0(1370)
Claims have been made that f0(1370) does not exist. The five primary sets of
data requiring its existence are refitted. Major dispersive effects due to the
opening of the 4pi threshold are included for the first time; the sigma -> 4pi
amplitude plays a strong role. Crystal Barrel data on pbar-p -> 3pizero at rest
require f0(1370) signals of at least 32 and 33 standard deviations in 1S0 and
3P1 annihilation respectively. Furthermore, they agree within 5 MeV for mass
and width. Data on pbar-p -> eta-eta-pizero agree and require at least a 19
standard deviation contribution. This alone is sufficient to demonstrate the
existence of f0(1370). BES II data for J/Psi -> phi-pi-pi contain a visible
f0(1370) signal > 8 standard devations. In all cases, a resonant phase
variation is required. The possibility of a second pole in the sigma amplitude
due to the opening of the 4pi channel is excluded. Cern-Munich data for pi-pi
elastic scattering are fitted well with the inclusion of some mixing between
sigma, f0(1370) and f0(1500). The pi-pi widths for f2(1565), rho3(1690),
rho3(1990) and f4(2040) are determined.Comment: 25 pages, 22 figures. Typos corrected in Eqs 2 and 7. Introduction
rewritten. Conclusions unchange
Production of -mesons in pp and pn reactions
We investigate the cross section for the reaction near
threshold and at medium energies. An effective Lagrangian approach with
one-pion exchange is applied to analyze different contributions to the cross
section for different isospin channels. The Reggeon exchange mechanism is also
considered. The results are used to calculate the contribution of the
meson to the cross sections and invariant mass distributions of the
reactions and . It is found that the
experimental observation of mesons in the reaction is much more promising than the observation of mesons in the
reaction .Comment: 26 pages, including 11 eps figures, to be bublished in J. Phys.
SU(3) Mixing for Excited Mesons
The SU(3)-flavor symmetry breaking and the quark-antiquark annihilation
mechanism are taken into account for describing the singlet-octet mixing for
several nonets assigned by Particle Data Group(PDG). This task is approached
with the mass matrix formalism
Quark-gluonium content of the scalar-isoscalar states f_0(980), f_0(1300), f_0(1500), f_0(1750), f_0(1420 ^{+150}_{- 70}) from hadronic decays
On the basis of the decay couplings f_0 -> \pi\pi, K\bar K, \eta\eta,
\eta\eta', which had been found before, in the study of analytical
(IJ^{PC}=00^{++})-amplitude in the mass range 450-1900 MeV, we analyse the
quark-gluonium content of resonances f_0(980), f_0(1300), f_0(1500), f_0(1750)
and the broad state f_0(1420 ^{+ 150}_{-70}). The K-matrix technique used in
the analysis makes it possible to evaluate the quark-gluonium content both for
the states with switched-off decay channels (bare states, f^{bare}_0) and the
real resonances. We observe significant change of the quark-gluonium
composition in the evolution from bare states to real resonances, that is due
to the mixing of states in the transitions f_0(m_1)-> real mesons-> f_0(m_2)
responsible for the decay processes as well. For the f_0(980), the analysis
confirmed the dominance of q\bar q component thus proving the n\bar n/s\bar s
composition found in the study of the radiative decays. For the mesons
f_0(1300), f_0(1500) and f_0(1750), the hadronic decays do not allow one to
determine uniquely the n\bar n, s\bar s and gluonium components providing
relative pecentage only. The analysis shows that the broad state f_0(1420 ^{+
150}_{-70}) can mix with the flavour singlet q\bar q component only, that is
consistent with gluonium origin of the broad resonance.Comment: 20 pages, LaTeX, 10 PostScript figures, epsfig.st
Kaon induced Lambda(1405) production on a deuteron target at DAFNE
The K^- induced production of Lambda(1405) in the K^- d to pi Sigma n
reaction is investigated having in mind the conditions of the DAFNE facility at
Frascati where kaons are obtained from the decay of slow moving phi mesons. We
find that the K^- d to Lambda(1405) n process favors the production of
Lambda(1405) initiated by the K^- p channel, which gives largest weight to the
higher mass Lambda(1405) appearing at 1420 MeV in chiral theories. We find that
the fastest kaons from the decay of the phi are well suited to see this
resonance, particularly if one selects forward going neutrons in the center of
mass, which reduce the contribution of single scattering and make the double
scattering dominate where the signal of the resonance appears clearer.Comment: 6pages, 7 figure
The CDF dijet excess from intrinsic quarks
The CDF collaboration reported an excess in the production of two jets in
association with a . We discuss constraints on possible new particle state
interpretations of this excess. The fact of no statistically significant
deviation from the SM expectation for {+dijet} events in CDF data disfavors
the new particle explanation. We show that the nucleon intrinsic strange quarks
provide an important contribution to the boson production in association
with a single top quark production. Such {+t} single top quark production
can contribute to the CDF {+dijet} excess, thus the nucleon intrinsic quarks
can provide a possible explanation to the CDF excess in {+dijet} but not in
{+dijet} events.Comment: 4 latex pages, 1 figure. Version for journal publicatio
Boost operators in Coulomb-gauge QCD: the pion form factor and Fock expansions in phi radiative decays
In this article we rederive the Boost operators in Coulomb-Gauge Yang-Mills
theory employing the path-integral formalism and write down the complete
operators for QCD. We immediately apply them to note that what are usually
called the pion square, quartic... charge radii, defined from derivatives of
the pion form factor at zero squared momentum transfer, are completely blurred
out by relativistic and interaction corrections, so that it is not clear at all
how to interpret these quantities in terms of the pion charge distribution. The
form factor therefore measures matrix elements of powers of the QCD boost and
Moeller operators, weighted by the charge density in the target's rest frame.
In addition we remark that the decomposition of the eta' wavefunction in
quarkonium, gluonium, ... components attempted by the KLOE collaboration
combining data from phi radiative decays, requires corrections due to the
velocity of the final state meson recoiling against a photon. This will be
especially important if such decompositions are to be attempted with data from
J/psi decays.Comment: 14 pages, 4 figure