arXiv subjects

S. Fleming

Publications and source records attributed to S. Fleming.

10 recordsLinked to original sources

arXiv2020

Nonrelativistic Effective Field Theory with a Resonance Field

We discuss shallow resonances in the nonrelativistic scattering of two particles using an effective field theory (EFT) that includes an auxiliary field with the quantum numbers of the resonance. We construct the manifestly renormalized scattering amplitude up to next-to-leading order in a systematic expansion. For a narrow resonance, the amplitude is perturbative except in the immediate vicinity of the resonance poles. It naturally has a zero in the low-energy region, analogous to the Ramsauer-Townsend effect. For a broad resonance, the leading-order amplitude is nonperturbative almost everywhere in the regime of validity of the EFT. We regain the results of an EFT without the auxiliary field, which is equivalent to the effective-range expansion with large scattering length and effective range. We also consider an additional fine tuning leading to a low-energy amplitude zero even for a broad resonance. We show that in all cases the requirement of renormalizability when the auxiliary field is not a ghost ensures the resonance poles are in the lower half of the complex momentum plane, as expected by other arguments. The systematic character of the EFT expansion is exemplified with a toy model serving as underlying theory.

hep-ph↗

arXiv2020

Effective Field Theory for Two-Body Systems with Shallow S-Wave Resonances

Resonances are of particular importance to the scattering of composite particles in quantum mechanics. We build an effective field theory for two-body scattering which includes a low-energy $S$-wave resonance. Our starting point is the most general Lagrangian with short-range interactions. We demonstrate that these interactions can be organized into various orders so as to generate a systematic expansion for an $S$ matrix with two low-energy poles. The pole positions are restricted by renormalization at leading order, where the common feature is a non-positive effective range. We carry out the expansion explicitly to next-to-leading order and illustrate how it systematically accounts for the results of a toy model -- a spherical well with a delta shell at its border.

nucl-th↗

arXiv2016

Abundance analysis of SDSS J134338.67+484426.6; an extremely metal-poor star from the MARVELS pre-survey

We present an elemental-abundance analysis of an extremely metal-poor (EMP; [Fe/H] < -3.0) star, SDSS J134338.67+484426.6, identified during the course of the MARVELS spectroscopic pre-survey of some 20000 stars to identify suitable candidates for exoplanet searches. This star, with an apparent magnitude V = 12.14, is the lowest metallicity star found in the pre-survey, and is one of only ~20 known EMP stars that are this bright or brighter. Our high-resolution spectroscopic analysis shows that this star is a subgiant with [Fe/H] = -3.42, having "normal" carbon and no enhancement of neutron-capture abundances. Strontium is under-abundant, [Sr/Fe] =-0.47, but the derived lower limit on [Sr/Ba] indicates that Sr is likely enhanced relative to Ba. This star belongs to the sparsely populated class of alpha-poor EMP stars that exhibit low ratios of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar metallicity. The observed variations in radial velocity from several epochs of (low- and high-resolution) spectroscopic follow-up indicate that SDSS J134338.67+484426.6 is a possible long-period binary. We also discuss the abundance trends in EMP stars for r-process elements, and compare with other magnesium-poor stars.

astro-ph.SR↗

arXiv2009

X(3872) in Effective Field Theory

If the X(3872) resonance is a shallow boundstate of a the charm mesons $D^{0} \bar D^{*0}$ and $D^{*0} \bar D^{0}$, it can be described by an effective theory of nonrelativistic D mesons coupled to nonrelativistic pions (X-EFT). In this talk, I give a brief overview of the X(3872), followed by a short review of X-EFT. I end my talk with results from calculations of the next-to-leading-order correction to the partial decay width $Γ[X\to D^0 \bar D^{0} π^0]$, and the decay of X(3872) to P-wave quarkonia.

hep-ph↗

arXiv2007

Pion Interactions in the X(3872)

We consider pion interactions in an effective field theory of the narrow resonance X(3872), assuming it is a weakly bound molecule of the charm mesons D^{0} \bar D^{*0} and D^{*0} \bar D^{0}. Since the hyperfine splitting of the D^{0} and D^{*0} is only 7 MeV greater than the neutral pion mass, pions can be produced near threshold and are non-relativistic. We show that pion exchange can be treated in perturbation theory and calculate the next-to-leading-order correction to the partial decay width Γ[X \to D^0 \bar D^{0} π^0].

hep-ph↗

arXiv2002

B Physics at the Tevatron: Run II and Beyond

This report provides a comprehensive overview of the prospects for B physics at the Tevatron. The work was carried out during a series of workshops starting in September 1999. There were four working groups: 1) CP Violation, 2) Rare and Semileptonic Decays, 3) Mixing and Lifetimes, 4) Production, Fragmentation and Spectroscopy. The report also includes introductory chapters on theoretical and experimental tools emphasizing aspects of B physics specific to hadron colliders, as well as overviews of the CDF, D0, and BTeV detectors, and a Summary.

hep-ph↗

arXiv2000

Summing Sudakov logarithms in B -> X_s + gamma in effective field theory

We construct an effective field theory valid for processes in which highly energetic light-like particles interact with collinear and soft degrees of freedom, using the decay B -> X_s + gamma near the endpoint of the photon spectrum, x = 2 E_gamma / m_b -> 1, as an example. Below the scale mu=m_b both soft and collinear degrees of freedom are included in the effective theory, while below the scale mu=m_b sqrt{x-y}, where 1-y is the lightcone momentum fraction of the b quark in the B meson, we match onto a theory of bilocal operators. We show that at one loop large logarithms cancel in the matching conditions, and that we recover the well known renormalization group equations that sum leading Sudakov logarithms.

hep-ph↗

arXiv1996

Production of Heavy Quarkonium in High Energy Colliders

Recent data from the Tevatron has revealed that the production rate of prompt charmonium at large transverse momentum is orders of magnitude larger than the best theoretical predictions of a few years ago. These surprising results can be understood by taking into account two recent developments that have revolutionized the theoretical description of heavy quarkonium production. The first is the realization that fragmentation must dominate at large transverse momentum, which implies that most charmonium in this kinematic region is produced by the hadronization of individual high-$p_T$ partons. The second is the development of a factorization formalism for quarkonium production based on nonrelativistic QCD that allows the formation of charmonium from color-octet $c \bar c$ pairs to be treated systematically. This review summarizes these theoretical developments and their implications for quarkonium production in high energy colliders.

hep-ph↗

arXiv1995

Double gluon fragmentation to $J/ψ$ pairs at the Tevatron

It has been proposed that the large cross sections for prompt $ψ$, $ψ'$, and $χ_c$ production at the Fermilab Tevatron $p\bar p$ collider can be explained by a dominant color-octet term in the fragmentation function for a gluon to split into quarkonium. We show that this mechanism makes testable predictions for double-quarkonium $ψψ$, $ψψ'$, $ψχ_c$, $ψΥ$ and $ψχ_b$ production, as well as for $W ψ$ production, using color-octet matrix elements previously determined from charmonium production data. The $ψψ$ signal would already be measurable at the Tevatron, while the $ψχ_c$ and $Wψ$ signals would be on the edge of present detectability.

hep-ph↗

arXiv1994

Perturbative QCD Fragmentation Functions as a Model for Heavy-Quark Fragmentation

The perturbative QCD fragmentation functions for a heavy quark to fragment into heavy-light mesons are studied in the heavy-quark limit. The fragmentation functions for S-wave pseudoscalar and vector mesons are calculated to next-to-leading order in the heavy-quark mass expansion using the methods of heavy-quark effective theory. The results agree with the $m_b\to \infty$ limit of the perturbative QCD fragmentation functions for $\bar b$ into $B_c$ and $B_c^*$. We discuss the application of the perturbative QCD fragmentation functions as a model for the fragmentation of heavy quarks into heavy-light mesons. Using this model, we predict the fraction $P_{V}$ of heavy-light mesons that are produced in the vector meson state as functions of the longitudinal momentum fraction $z$ and the transverse momentum relative to the jet axis. The fraction $P_V$ is predicted to vary from about 1/2 at small $z$ to almost 3/4 near $z=1$.

hep-ph↗