232 research outputs found
Model-independent Study of Magnetic Dipole Transitions in Quarkonium
We study magnetic dipole (M1) transitions between two quarkonia in the
framework of non-relativistic effective field theories of QCD. Relativistic
corrections of relative order v^2 are investigated in a systematic fashion.
Non-perturbative corrections due to color-octet effects are considered for the
first time and shown to vanish at leading order. Exact, all order expressions
for the relevant 1/m and 1/m^2 operators are derived. The results allow us to
scrutinize several potential model claims. In particular, we show that QCD
excludes both contributions to the anomalous magnetic moment of the quarkonium
induced by low-energy fluctuations and contributions to the magnetic dipole
operators of the type induced by a scalar potential. Finally, we apply our
results to the transitions J/psi -> eta_c gamma, Upsilon(1S) -> eta_b gamma,
Upsilon(2S) -> eta_b(2S) gamma, Upsilon(2S) -> eta_b gamma, eta_b(2S) ->
Upsilon(1S) gamma, h_b(1P) -> chi_{b0,1}(1P) gamma and chi_{b2}(1P) -> h_b(1P)
gamma by assuming these quarkonium states in the weak-coupling regime. Our
analysis shows that the J/psi -> eta_c gamma width is consistent with a
weak-coupling treatment of the charmonium ground state, while such a treatment
for the hindered transition Upsilon(2S) -> eta_b gamma appears difficult to
accommodate within the CLEO III upper limit.Comment: 44 pages, 8 figures; typos corrected, one reference added; to appear
in Physical Review
A Bayesian belief network for local air quality forecasting
This study is focused on the development of a Bayesian network for air quality assessment and aims at offering a pragmatic and scientifically credible approach to modelling complex systems where substantial uncertainties exist. In particular, the main object is the prediction of the occurrence of suitable conditions for the stagnation of pollutants in a given area. The analytical modeling of the network provides a set of independent nodes, represented by the outputs of a forecasting meteorological Limited Area Model, from which descend the conditions for the stagnation of pollutants in different areas of the city (through measurements of the heuristic pollutant from monitoring stations) and finally the global conditions. The urban area of Genoa (Italy) was selected in order to test the actual capability of the model prototype. Network training was performed by means of historical data resulting from significant statistical series of the past years by the air quality-monitoring network. The system used for data assimilation, construction and network learning is completely based on an open source statistical processing software
Make Bow-tie Dynamic by Rethinking it as a Hierarchical Bayesian Network. Dynamic Risk Assessment of an LNG Bunkering Operation
In the present era, the spread of cyber-physical systems in the framework of the so-called Industry 4.0, is leading towards a complete automation of industrial processes, which are increasingly decentralized, smart, and require fewer and fewer frontline personnel. The risk assessment process is certainly not excluded from the revolution, and in perspective needs to be automatic, dynamic and linked with the conditions that emerge, moment by moment, in the life of a complex system. Analytical techniques can help in converting data in information and hence system knowledge to spot trends in operational performance, thus improving risk assessment quality. Even though the bow-tie approach is widely used within the context of complex systems, it still evidences several limitations, mainly connected to the actual assessment of likelihood and interdependencies in the fault and event trees. This paper shows how a bow tie analysis can be reframed as a Hierarchical Bayesian Network, where the probability distributions of the network nodes are updated with real time predictions during the operations. The proposed model was then applied to the risk assessment of a shore-to-ship LNG bunkering operation
The infrared behaviour of the static potential in perturbative QCD
The definition of the quark-antiquark static potential is given within an
effective field theory framework. The leading infrared divergences of the
static singlet potential in perturbation theory are explicitly calculated.Comment: 4 pages, 2 postscript figures, uses revtex.st
Heavy Hadron Spectroscopy
I review recent theoretical advances in heavy hadron spectroscopy.Comment: Plenary talk at the XXXIII International Conference on High Energy
Physics (ICHEP 06), Moscow, Russia, July 26 - August 2, 2006; 11 page
A New Tool for the Lamb Shift Calculation
We solve the Bethe-Salpeter equation for hydrogenic bound states by choosing
an appropriate interaction kernel . We want to use our solution to
calculate up to a higher order the hydrogen Lamb-shift, and as a first
application we present up to order \left(\aa / \pi\right)(\za)^7 the
contribution of the lowest order self-energy graph, calculated {\it exactly}.
The basic formalism is a natural extension to the hydrogenic bound states of
the one previously presented by R. Barbieri and E. Remiddi and used in the case
of positronium.Comment: 21 pages, Latex, Preprint DFUB-94-0
Effective field theories for heavy quarkonium
We review recent theoretical developments in heavy quarkonium physics from
the point of view of Effective Field Theories of QCD. We discuss
Non-Relativistic QCD and concentrate on potential Non-Relativistic QCD. Our
main goal will be to derive QCD Schr\"odinger-like equations that govern the
heavy quarkonium physics in the weak and strong coupling regime. We also
discuss a selected set of applications, which include spectroscopy, inclusive
decays and electromagnetic threshold production.Comment: 162 pages, 30 figures, revised version, references added. Accepted
for publication in Reviews of Modern Physic
Thermal width and gluo-dissociation of quarkonium in pNRQCD
The thermal width of heavy-quarkonium bound states in a quark-gluon plasma
has been recently derived in an effective field theory approach. Two phenomena
contribute to the width: the Landau damping phenomenon and the break-up of a
colour-singlet bound state into a colour-octet heavy quark-antiquark pair by
absorption of a thermal gluon. In the paper, we investigate the relation
between the singlet-to-octet thermal break-up and the so-called
gluo-dissociation, a mechanism for quarkonium dissociation widely used in
phenomenological approaches. The gluo-dissociation thermal width is obtained by
convoluting the gluon thermal distribution with the cross section of a gluon
and a 1S quarkonium state to a colour octet quark-antiquark state in vacuum, a
cross section that at leading order, but neglecting colour-octet effects, was
computed long ago by Bhanot and Peskin. We will, first, show that the effective
field theory framework provides a natural derivation of the gluo-dissociation
factorization formula at leading order, which is, indeed, the singlet-to-octet
thermal break-up expression. Second, the singlet-to-octet thermal break-up
expression will allow us to improve the Bhanot--Peskin cross section by
including the contribution of the octet potential, which amounts to include
final-state interactions between the heavy quark and antiquark. Finally, we
will quantify the effects due to final-state interactions on the
gluo-dissociation cross section and on the quarkonium thermal width.Comment: 17 pages, 6 figure
Heavy Quarkonium in a weakly-coupled quark-gluon plasma below the melting temperature
We calculate the heavy quarkonium energy levels and decay widths in a
quark-gluon plasma, whose temperature T and screening mass m_D satisfy the
hierarchy m alpha_s >> T >> m alpha_s^2 >> m_D (m being the heavy-quark mass),
at order m alpha_s^5. We first sequentially integrate out the scales m, m
alpha_s and T, and, next, we carry out the calculations in the resulting
effective theory using techniques of integration by regions. A collinear region
is identified, which contributes at this order. We also discuss the
implications of our results concerning heavy quarkonium suppression in heavy
ion collisions.Comment: 25 pages, 2 figure
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