1,785 research outputs found
More loosely bound hadron molecules at CDF?
In a recent paper we have proposed a method to estimate the prompt production
cross section of X(3872) at the Tevatron assuming that this particle is a
loosely bound molecule of a D and a D*bar meson. Under this hypothesis we find
that it is impossible to explain the high prompt production cross section found
by CDF at sigma(X(3872)) \sim 30-70 nb as our theoretical prediction is about
300 times smaller than the measured one. Following our work, Artoisenet and
Braaten, have suggested that final state interactions in the DD*bar system
might be so strong to push the result we obtained for the cross section up to
the experimental value. Relying on their conclusions we show that the
production of another very narrow loosely bound molecule, the X_s=D_s D_s*bar,
could be similarly enhanced. X_s should then be detectable at CDF with a mass
of 4080 MeV and a prompt production cross section of sigma(X_s) \sim 1-3 nb.Comment: Minor revisions made. To appear in Phys Lett
J/Ψ and Z production in Pb-Pb collisions at LHC with the ATLAS experiment
Using the ATLAS detector, a centrality-dependent suppression has been observed in the yield of J/ψ mesons produced in Pb-Pb collisions at the LHC at a nucleon-nucleon center-of-mass energy √sNN = 2.76TeV. Moreover the first observation of Z bosons in heavy ion collisions has been performed. J/ψ mesons and Z bosons are reconstructed via their decays to μ+μ− pairs
On lattice chiral gauge theories
The Smit-Swift-Aoki formulation of a lattice chiral gauge theory is presented. In this formulation the Wilson and other non invariant terms in the action are made gauge invariant by the coupling with a nonlinear auxilary scalar field, omega. It is shown that omega decouples from the physical states only if appropriate parameters are tuned so as to satisfy a set of BRST identities. In addition, explicit ghost fields are necessary to ensure decoupling. These theories can give rise to the correct continuum limit. Similar considerations apply to schemes with mirror fermions. Simpler cases with a global chiral symmetry are discussed and it is shown that the theory becomes free at decoupling. Recent numerical simulations agree with those considerations
Update on Counting Valence Quarks at RHIC
We update our former analysis of the Nuclear Modification Factors (NMF) for
different hadron species at RHIC and LHC. This update is motivated by the new
experimental data from STAR which presents differences with the preliminary
data used to fix some of the parameters in our model. The main change is the
use of AKK fragmentation functions for the hard part of the spectrum and minor
adjustments of the coalescence (soft) contribution. We confirm that observation
of the NMF for the f_0 meson can shed light on its quark composition.Comment: 4 pages, 4 figure
Le partage des responsabilités dans l'espace Dublin, entre confiance mutuelle et sécurité des demandeurs d'asile
On 21 January 2011, the Grand Chamber of the European Court of Human Rights delivered its judgment in the case of MSS v. Belgium and Greece. This judgment puts into question the practices followed by many national authorities in the implementation of the Dublin system. Particularly noteworthy are the effects on the "safety presumption" that Member States accord to each other in the field of asylum.
The authors explore the implications of the MSS decision, first, in regard of the evidentiary requirements imposed on asylum seekers to rebut the safety presumption. They come to the conclusion that through the decision, a real paradigm-shift has taken place - from the theoretical to the actual supremacy of the non-refoulement principle in Dublin matters. This is also true in light of the increased requirements imposed by the Court as regards the scope and depth of judicial review on transfer decisions.
Moreover, the MSS judgment could give new impetus to the stalled reform process concerning the Dublin Regulation. Indeed, the Court's decision seems to enshrine in positive ECHR law the most progressive elements of the Commission's proposal, including procedural guarantees and, de facto, the mechanism for the temporary suspension of transfers to member states not offering adequate protection
Non-Perturbative Renormalisation using Domain Wall Fermions
The viability of the Non-Perturbative Renormalisation (NPR) method of the
Rome/Southampton group is studied, for the first time, in the context of domain
wall fermions. The procedure is used to extract the renormalisation
coefficients of the various quark bilinears, as well as the four-fermion
operators relevant to the effective Hamiltonian. The
renormalisation of the Hamiltonian is also discussed.Comment: LATTICE99(Improvement and Renormalization),3 pages, LaTeX2e; minor
typos correcte
Commissioning of the ATLAS Muon Trigger System with early data
An overview of the early results on commissioning and performance of the ATLAS Muon Trigger System is shown. The ATLAS Muon Trigger has been designed to cope with the high interaction rate expected at the LHC. The presented
performance studies have been obtained using both cosmic-ray and 900GeV collision data
Results from a Non-Perturbative Renormalization of Lattice Operators
We propose a general renormalization method, which avoids completely the use
of lattice perturbation theory. We present the results from its numerical
applications to two-fermion operators on a lattice, at
.Comment: 3 pages postscript file. Contribution to Lattice '9
Chiral behaviour of the lattice -parameter with the Wilson and Clover Actions at
We present results for the kaon -parameter from a sample of
configurations using the Wilson action and configurations using the
SW-Clover action, on a lattice at . We compare
results obtained by renormalizing the relevant operator with different
``boosted" values of the strong coupling constant . In the case of
the SW-Clover action, we also use the operator renormalized non-perturbatively.
In the Wilson case, we observe a strong dependence of on the prescription
adopted for , contrary to the results of the Clover case which are
almost unaffected by the choice of the coupling. We also find that the matrix
element of the operator renormalized non-perturbatively has a better chiral
behaviour. This gives us our best estimate of the renormalization group
invariant -parameter, .Comment: LaTeX, 17 pages, 3 postscript figures uuencode
Search for tetraquark decays in 4 muons, , and channels at LHC
We perform a quantitative analysis of the tetraquark
decays into hidden- and open-bottom mesons and calculate, for the first time,
the tetraquark total decay width. On the basis of our
results, we propose the decays as the most suitable
channels to observe the tetraquark states, since the
calculated two-lepton cross section upper limit, fb, is so large
as to be potentially detectable with the 2018 LHCb sensitivity,
paving the way to the observation of the tetraquark in the
future LHCb upgrade. The signal for the ground state, ,
is likely to be too small even for the upgraded LHCb, but it may not be
hopeless for the fully-bottom state.Comment: 11 pages, 1 figur
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