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ABSTRACT: By means of effective field theory techniques, we study the modifications of
some properties of weakly coupled heavy quarkonium states propagating through a
quark-gluon plasma at temperatures much smaller than the heavy quark mass, m_Q.
Two different cases are considered, corresponding to two different hierarchies
between the typical size of the bound state, r, the binding energy, E, the
temperature, T, and the screening mass, m_D. The first case corresponds to the
hierarchy m_Q >> 1/r >> T >> E >> m_D, relevant for moderate temperatures, and
the second one to the hierarchy m_Q >> T >> 1/r, m_D >> E, relevant for
studying the dissociation mechanism. In the first case we determine the
perturbative correction to the binding energy and to the decay width of states
with arbitrary angular momentum, finding that the width is a decreasing
function of the velocity. A different behavior characterizes the second
kinematical case, being the width of s-wave states a non-monotonic function of
the velocity, increasing at moderate velocities and decreasing in the
ultra-relativistic limit. We obtain a simple analytical expression of the decay
width for T >> 1/r >> m_D >> E at moderate velocities, and we derive the s-wave
spectral function for the more general case T >> 1/r, m_D >> E. A brief
discussion of the possible experimental signatures as well as a comparison with
the relevant lattice data are also presented.
04/2013;
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ABSTRACT: We compare lattice data for the short-distance part of the static energy in
2+1 flavor quantum chromodynamics (QCD) with perturbative calculations, up to
next-to-next-to-next-to leading-logarithmic accuracy. We show that perturbation
theory describes very well the lattice data at short distances, and exploit
this fact to obtain a determination of the product of the lattice scale r_0
with the QCD scale Lambda_{MS}. With the input of the value of r_0, this
provides a determination of the strong coupling alpha_s at the typical distance
scale of the lattice data. We obtain alpha_s(1.5 GeV)=0.326\pm0.019, which
provides a novel determination of alpha_s at low energy and with three-loop
accuracy (including resummation of the leading ultrasoft logarithms). When this
value is evolved to the Z-mass scale M_Z, it corresponds to
alpha_s(M_Z)=0.1156^{+0.0021}_{-0.0022}.
05/2012;
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ABSTRACT: We study the propagation of non-relativistic bound states moving at constant
velocity across a homogeneous thermal bath and we develop the effective field
theory which is relevant in various dynamical regimes. We consider values of
the velocity of the bound state ranging from moderate to highly relativistic
and temperatures at all relevant scales smaller than the mass of the particles
that form the bound state. In particular, we consider two distinct temperature
regimes, corresponding to temperatures smaller or higher than the typical
momentum transfer in the bound state. For temperatures smaller or of the order
of the typical momentum transfer, we restrict our analysis to the simplest
system, a hydrogen-like atom. We build the effective theory for this system
first considering moderate values of the velocity and then the relativistic
case. For large values of the velocity of the bound state, the separation of
scales is such that the corresponding effective theory resembles the soft
collinear effective theory (SCET). For temperatures larger than the typical
momentum transfer we also consider muonic hydrogen propagating in a plasma
which contains photons and massless electrons and positrons, so that the system
resembles very much heavy quarkonium in a thermal medium of deconfined quarks
and gluons. We study the behavior of the real and imaginary part of the static
two-body potential, for various velocities of the bound state, in the hard
thermal loop approximation. We find that Landau damping ceases to be the
relevant mechanism for dissociation from a certain "critical" velocity on in
favor of screening. Our results are relevant for understanding how the
properties of heavy quarkonia states produced in the initial fusion of partons
in the relativistic collision of heavy ions are affected by the presence of an
equilibrated quark-gluon plasma.
05/2011;
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ABSTRACT: We use the recently obtained theoretical expression for the complete QCD static energy at next-to-next-to-next-to leading-logarithmic accuracy to determine r₀ΛMS by comparison with available lattice data, where r₀ is the lattice scale and ΛMS is the QCD scale. We obtain r₀ΛMS=0.622(-0.015)(+0.019) for the zero-flavor case. The procedure we describe can be directly used to obtain r₀ΛMS in the unquenched case, when unquenched lattice data for the static energy at short distances becomes available. Using the value of the strong coupling α(s) as an input, the unquenched result would provide a determination of the lattice scale r₀.
Physical Review Letters 11/2010; 105(21):212001. · 7.37 Impact Factor
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ABSTRACT: We illustrate how to apply modern effective field theory techniques and dimensional regularization to factorise the various scales which appear in QED bound states at finite temperature. We focus here on the muonic hydrogen atom. Vacuum polarization effects make the physics of this atom at finite temperature very close to that of heavy quarkonium states. We comment on the implications of our results for these states in the quark gluon plasma. In particular, we estimate the effects of a finite charm quark mass in the dissociation temperature of bottomonium. Comment: 22 pages, 8 figures
08/2010;
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ABSTRACT: 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 figures
07/2010;
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ABSTRACT: We use the recently obtained theoretical expression for the complete QCD
static energy at next-to-next-to-next-to leading-logarithmic accuracy to
determine r_0Lambda_MS by comparison with available lattice data, where r_0 is
the lattice scale and Lambda_MS is the QCD scale. We obtain
r_0Lambda_MS=0.637^{+0.032}_{-0.030} for the zero-flavor case. The procedure we
describe can be directly used to obtain r_0Lambda_MS in the unquenched case,
when unquenched lattice data for the static energy at short distances becomes
available. Using the value of the strong coupling alpha_s as an input, the
unquenched result would provide a determination of the lattice scale r_0.
06/2010;
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ABSTRACT: We compute the static energy of QCD at short distances at next-to-next-to-next-to leading-logarithmic accuracy in terms of the three-loop singlet potential. By comparing our results with lattice data we extract the value of the unknown piece of the three-loop singlet potential. Comment: 25 pages, 16 figures. v2: Incorrect files for figure 7 replaced by the correct ones. One reference added
06/2009;
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ABSTRACT: We illustrate how to apply modern effective field theory techniques and dimensional regularization to factorize the various scales which appear in non-relativistic bound states at finite temperature. We focus here on the simplest case: the hydrogen atom. We discuss in detail the interplay of the hard, soft and ultrasoft scales of the non-relativistic system at zero temperature with the additional scales induced at finite temperature. We also comment on the implications of our results for heavy quarkonium bound states in the quark gluon plasma. Comment: 28 pages, 1 table. Numerical factors in formulas (23), (25), (26) and (28), as well as a few misprints elswhere corrected. Supersedes journal version
04/2008;
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ABSTRACT: We improve on a recent determination of alpha_s from Gamma(Upsilon(1S)-->X gamma)/Gamma(Upsilon(1S)-->X) with CLEO data by taking into account color octet contributions and avoiding any model dependence in the extraction. We obtain alpha_s(M_Upsilon(1S))= 0.184+0.015-0.014, which corresponds to alpha_s(M_Z)=0.119+0.006-0.005.
03/2007;
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ABSTRACT: We discuss the theoretical status of inclusive radiative decays of charmonium, with a particular emphasis on the QCD description of the photon spectrum, where progress has occurred in recent years. We also comment on the possible extraction of alpha_s (M_J/psi) and on the possibility to gain important information on the nature of J/psi and psi (2S).
02/2007;
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ABSTRACT: Using pNRQCD and known results for the field strength correlator, we calculate the ultrasoft contribution to the QCD static energy of a quark-antiquark pair at short distances at NNNNLO in alpha_s. At the same order, this provides the logarithmic terms of the singlet static potential in pNRQCD and the log alpha_s terms of the static energy.
11/2006;
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ABSTRACT: We argue that the photon spectra in radiative decays of various heavy quarkonium states provide important information on their nature. If two of these states are in the strong coupling regime, we are able to produce a parameter-free model-independent formula, which holds at next-to-leading order and includes both direct and fragmentation contributions. When the formula is checked against recent CLEO data it favors Y(2S) and Y(3S) in the strong coupling regime and disfavors Y(1S) in it.
Physical Review Letters 04/2006; 96(11):111801. · 7.37 Impact Factor
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ABSTRACT: We analyze the end-point region of the photon spectrum in semi-inclusive radiative decays of very heavy quarkonium (m alpha_s^2 >> Lambda_QCD). We discuss the interplay of the scales arising in the Soft-Collinear Effective Theory, m, m(1-z)^{1/2} and m(1-z) for z close to 1, with the scales of heavy quarkonium systems in the weak coupling regime, m, m alpha_s and m alpha_s^2. For 1-z \sim alpha_s^2 only collinear and (ultra)soft modes are seen to be relevant, but the recently discovered soft-collinear modes show up for 1-z << alpha_s^2. The S- and P-wave octet shape functions are calculated. When they are included in the analysis of the photon spectrum of the Upsilon (1S) system, the agreement with data in the end-point region becomes excellent. The NRQCD matrix elements <1^3S_1| O_8(^1S_0) | 1^3S_1> and <1^3S_1| O_8(^3P_J) | 1^3S_1> are also obtained. Comment: Revtex, 11 pages, 6 figures. Minor improvements and references added. Journal version
01/2004;
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ABSTRACT: We derive the imaginary part of the potential NRQCD Hamiltonian up to order 1/m^4, when the typical momentum transfer between the heavy quarks is of the order of Lambda_{QCD} or greater, and the binding energy E much smaller than Lambda_{QCD}. We use this result to calculate the inclusive decay widths into light hadrons, photons and lepton pairs, up to O(mv^3 x (Lambda_{QCD}^2/m^2,E/m)) and O(mv^5) times a short-distance coefficient, for S- and P-wave heavy quarkonium states, respectively. We achieve a large reduction in the number of unknown non-perturbative parameters and, therefore, we obtain new model-independent QCD predictions. All the NRQCD matrix elements relevant to that order are expressed in terms of the wave functions at the origin and six universal non-perturbative parameters. The wave-function dependence factorizes and drops out in the ratio of hadronic and electromagnetic decay widths. The universal non-perturbative parameters are expressed in terms of gluonic field-strength correlators, which may be fixed by experimental data or, alternatively, by lattice simulations. Our expressions are expected to hold for most of the charmonium and bottomonium states below threshold. The calculations and methodology are explained in detail so that the evaluation of higher order NRQCD matrix elements in this framework should be straightforward. An example is provided. Comment: 61 pages, 9 figures. Minor changes
08/2002;
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ABSTRACT: We show that some nonrelativistic quantum chromodynamics color-octet matrix elements can be written in terms of (derivatives of) wave functions at the origin and of nonperturbative universal constants once the factorization between the soft and ultrasoft scales 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 numbers and with different heavy flavors. In particular, we can estimate the ratios of the decay widths of bottomonium P-wave states from charmonium data.
Physical Review Letters 02/2002; 88(1):012003. · 7.37 Impact Factor
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ABSTRACT: Within an effective field theory framework, we obtain an expression for the next-to-leading term in the 1/m expansion of the singlet QQ̅ 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.
Phys. Rev. D. 12/2000; 63(1).
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ABSTRACT: Using pNRQCD and known results for the field strength correlator, we calculate the ultrasoft contribution to the QCD static energy of a quark–antiquark pair at short distances at N4LO in αs. At the same order, this provides the logarithmic terms of the singlet static potential in pNRQCD and the logαs terms of the static energy.
Physics Letters B.
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ABSTRACT: We present analytic expressions for the vacuum polarization effects due to a light fermion with finite mass in the binding energy and in the wave function at the origin of QED and (weak coupling) QCD non-relativistic bound states. Applications to exotic atoms, ϒ(1s) and production near threshold are briefly discussed.
Physics Letters B.
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International Journal of Modern Physics A 24:379-391. · 1.05 Impact Factor
