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N. Brambilla

Publications and source records attributed to N. Brambilla.

At least 37 records · Page 2Linked to original sources
arXiv2007

Prospects for e+e- physics at Frascati between the phi and the psi

We present a detailed study, done in the framework of the INFN 2006 Roadmap, of the prospects for e+e- physics at the Frascati National Laboratories. The physics case for an e+e- collider running at high luminosity at the phi resonance energy and also reaching a maximum center of mass energy of 2.5 GeV is discussed, together with the specific aspects of a very high luminosity tau-charm factory. Subjects connected to Kaon decay physics are not discussed here, being part of another INFN Roadmap working group. The significance of the project and the impact on INFN are also discussed. All the documentation related to the activities of the working group can be found in http://www.roma1.infn.it/people/bini/roadmap.html.

hep-ex↗
arXiv2005

QCD Effective Field Theories for Heavy Quarkonium

QCD nonrelativistic effective field theories (NREFT) are the modern and most suitable frame to describe heavy quarkonium properties. Here I summarize few relevant concepts and some of the interesting physical applications (spectrum, decays, production) of NREFT.

hep-ph↗
arXiv2005

Heavy Quarkonium Physics

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

hep-ph↗
arXiv2003

The $\sqrt{mΛ_{QCD}$ scale in heavy quarkonium

We investigate the effects produced by the three-momentum scale $\sqrt{mΛ_{QCD}}$ in the strong coupling regime of heavy quarkonium. We compute the leading non-vanishing contributions due to this scale to the masses and inclusive decay widths. We find that they may provide leading corrections to the S-wave decay widths but only subleading corrections to the masses.

hep-ph↗
arXiv2002

Perturbative evaluation of the eigenvalues of the Herbst Hamiltonian

We reconsider the well-known and long-debated problem of the calculation of the eigenvalues of the Herbst Hamiltonian 2\sqrt{p^2 +m^2} - κ/r. We give a formulation of the problem that allows, for the first time, a perturbative evaluation of the eigenvalues for any n and l, and in principle up to any order in κvia standard Kato perturbation theory. We present the evaluation of the energy of the n=1 and n=2 states up to κ^6, confirming the result previously obtained by Le Yaouanc et al. with a completely different technique. Moreover we give the n=2, l=1 level, which is new. Discussion of the results and comparison with previous findings are given at the end.

hep-ph↗
arXiv2001

Quarkonium spectroscopy and perturbative QCD: massive quark-loop effects

We study the spectra of the bottomonium and B_c states within perturbative QCD up to order alpha_s^4. The O(Lambda_QCD) renormalon cancellation between the static potential and the pole mass is performed in the epsilon-expansion scheme. We extend our previous analysis by including the (dominant) effects of non-zero charm-quark mass in loops up to the next-to-leading non-vanishing order epsilon^3. We fix the b-quark MSbar mass $\bar{m}_b \equiv m_b^{\bar{\rm MS}}(m_b^{\bar{\rm MS}})$ on Upsilon(1S) and compute the higher levels. The effect of the charm mass decreases $\bar{m}_b$ by about 11 MeV and increases the n=2 and n=3 levels by about 70--100 MeV and 240--280 MeV, respectively. We provide an extensive quantitative analysis. The size of non-perturbative and higher order contributions is discussed by comparing the obtained predictions with the experimental data. An agreement of the perturbative predictions and the experimental data depends crucially on the precise value (inside the present error) of alpha_s(M_Z). We obtain $m_b^{\bar{\rm MS}}(m_b^{\bar{\rm MS}}) = 4190 \pm 20 \pm 25 \pm 3 ~ {\rm MeV}$.

hep-ph↗
arXiv2001

New predictions for inclusive heavy-quarkonium P-wave decays

We show that some NRQCD colour-octet matrix elements can be written in terms of (derivatives of) wave functions at the origin and non-perturbative universal constants once the factorization between the soft and ultrasoft scale is achieved by using an effective field theory where only ultrasoft degrees of freedom are kept as dynamical entities. This allows us to derive a new set of relations between inclusive heavy-quarkonium P-wave decays into light hadrons with different principal quantum number and with different heavy flavour. In particular, we can estimate the branching ratios of bottomonium P-wave states by using charmonium data.

hep-ph↗
arXiv2001

Quarkonium Spectroscopy and Perturbative QCD: A New Perspective

We study the energy spectrum of bottomonium in perturbative QCD, taking alpha_s(Mz)=0.1181 +/- 0.0020 as input and fixing m_b^{MSbar}(m_b^{MSbar}) on the Upsilon(1S) mass. Contrary to wide beliefs, perturbative QCD reproduces reasonably well the gross structure of the spectrum as long as the coupling constant remains smaller than one. We perform a detailed analysis and discuss the size of non-perturbative effects. A new qualitative picture on the structure of the bottomonium spectrum is provided. The lowest-lying (c,cbar) and (b,cbar) states are also examined.

hep-ph↗
arXiv2000

The QCD Potential at $O(1/m)$

Within an effective field theory framework, we obtain an expression for the next-to-leading term in the $1/m$ expansion of the singlet $Q{\bar Q}$ QCD potential in terms of Wilson loops, which holds beyond perturbation theory. The ambiguities in the definition of the QCD potential beyond leading order in $1/m$ are discussed and a specific expression for the $1/m$ potential is given. We explicitly evaluate this expression at one loop and compare the outcome with the existing perturbative results. On general grounds we show that for quenched QED and fully Abelian-like models this expression exactly vanishes.

hep-ph↗
arXiv2000

The Role of the QCD Vacuum in the Heavy-Quark Bound State Dynamics

The effective field theory approach allows a rigorous disentangling of high and low energy effects in the heavy quarkonium dynamics. Focusing in particular on the spectrum, we describe the nature of the non-perturbative effects and discuss our present knowledge of them.

hep-ph↗
arXiv1999

The Heavy Quarkonium Spectrum at Order $mα_s^5 \ln α_s$

We compute the complete leading-log terms of the next-to-next-to-next-to-leading-order corrections to potential NRQCD. As a by-product we obtain the leading logs at $O(mα_s^5)$ in the heavy quarkonium spectrum. These leading logs, when $Λ_{QCD} \ll mα_s^2$, give the complete $O(mα_s^5 \ln α_s)$ corrections to the heavy quarkonium spectrum.

hep-ph↗
arXiv1999

Potential NRQCD: an effective theory for heavy quarkonium

Within an effective field theory framework we study heavy-quark--antiquark systems with a typical distance between the heavy quark and the antiquark smaller than $1/Λ_{\rm QCD}$. A suitable definition of the potential is given within this framework, while non-potential (retardation) effects are taken into account in a systematic way. We explore different physical systems. Model-independent results on the short distance behavior of the energies of the gluonic excitations between static quarks are obtained. Finally, we show how infrared renormalons affecting the static potential get cancelled in the effective theory.

hep-ph↗
arXiv1998

Confinement and chiral symmetry breaking in heavy-light quark systems

Assuming a Gaussian approximation for the QCD gluodynamics, all the nonperturbative physics can be encoded into two parameters: the gluon correlation length $T_g$ and the gluon condensate $G_2$. These parameters are sufficient in order to describe the heavy-heavy quark nonperturbative interaction. In this work we adopt the same framework in order to study heavy-light bound states in the non-recoil limit. Spontaneous chiral symmetry breaking and a confining chiral non-invariant interaction emerge quite naturally. The gap equation is solved and discussed. In particular a relation between the light quark condensate and $T_g$ is derived. The energy spectrum for the bound state equation is evaluated and commented.

hep-ph↗
arXiv1998

Field Strength Correlators and Dual Effective Dynamics in QCD

We establish a relation between the two-point field strength correlator in QCD and the dual field propagator of an effective dual Abelian Higgs model describing the infrared behaviour of QCD. We find an analytic approximation to the dual field propagator without sources and in presence of quark sources. In the latter situation we also obtain an expression for the static $q \bar{q}$ potential. Our derivation sheds some light on the dominance and phenomenological relevance of the two-point field strength correlator.

hep-ph↗
arXiv1996

Heavy Quarkonia: Wilson Area Law, Stochastic Vacuum Model and Dual QCD

The $Q \bar{Q}$ semirelativistic interaction in QCD can be simply expressed in terms of the Wilson loop and its functional derivatives. In this approach we present the $Q \bar{Q}$ potential up to order $1/m^2$ using the expressions for the Wilson loop given by the Wilson Minimal Area Law (MAL), the Stochastic Vacuum Model (SVM) and Dual QCD (DQCD). We confirm the original results given in the different frameworks and obtain new contributions. In particular we calculate up to order $1/m^2$ the complete velocity dependent potential in the SVM. This allows us to show that the MAL model is entirely contained in the SVM. We compare and discuss also the SVM and the DQCD potentials. It turns out that in these two very different models the spin-orbit potentials show up the same leading non-perturbative contributions and 1/r corrections in the long-range limit.

hep-ph↗