Universality in the physics of cold atoms with large scattering length

Effective field theories exploit a separation of scales in physical systems in order to perform systematically improvable, model-independent calculations. They are ideally suited to describe universal aspects of a wide range of physical systems. I will discuss recent applications of effective field theory to cold atomic and molecular few-body systems with large scattering length.Comment: Invited talk at Few-Body 17, June 2003, Durham, NC, USA, 5 pages, 3 figures, uses espcrc1.st

Few-Body Effects in Cold Atoms and Limit Cycles

Physical systems with a large scattering length have universal properties independent of the details of the interaction at short distances. Such systems can be realized in experiments with cold atoms close to a Feshbach resonance. They also occur in many other areas of physics such as nuclear and particle physics. The universal properties include a geometric spectrum of three-body bound states (so-called Efimov states) and log-periodic dependence of low-energy observables on the physical parameters of the system. This behavior is characteristic of a renormalization group limit cycle. We discuss universality in the three- and four-body sectors and give an overview of applications in cold atoms.Comment: 7 pages, 3 figures, plenary talk at the 18th International IUPAP Conference on Few-Body Problems in Physics (FB18), Santos, Brazil, August 200

Prompt Upsilon and Psi Production at LEP

Color-octet contributions to quarkonia production at LEP are studied herein. The short distance formation of heavy quark-antiquark pairs in color-octet configurations via gluon fragmentation processes is significantly enhanced relative to the creation of color-singlet pairs via heavy quark fragmentation. But the subsequent long distance hadronization of these colored pairs into physical quarkonium bound states is suppressed compared to the nonperturbative evolution of their colorless counterparts. We find that the overall LEP rates for gluon fragmentation into prompt Upsilon and Psi vector bosons exceed those from heavy quark fragmentation. Inclusion of the dominant color-octet quarkonium production channel eliminates sizable discrepancies between previous predictions and recent measurements of prompt Z \to \Jpsi+X, $Z \to \psi'+X$ and $Z \to \Upsilon+X$ branching fractions.Comment: 15 pages, harvmac, 3 uuencoded figure

Perturbative QCD and Tau Decay

Sufficiently inclusive observables in the decay of the tau lepton can be calculated using the methods of perturbative QCD. These include the asymmetry parameter $A_\tau$ that determines that angular distribution of the total hadron momentum in the decay of a polarized tau. It should be possible to measure $A_\tau$ accurately using existing data from LEP. Reliable estimates of theoretical errors are essential in order to determine whether a given observable is sufficiently inclusive to be calculated using perturbative methods. The theoretical uncertainties due to higher orders in $\alpha_s$ can be estimated using recent calculations to all orders in the large-$(33-2N_f)$ limit. These estimates indicate that tau decay data can be used to determine $\alpha_s(M_Z)$ to a precision of 2% or better.Comment: 9 pages, LaTeX with espcrc2.sty, invited talk presented at the TAU 96 Workshop, Estes Park, Colorado, in September 199

Next-to-leading Order Calculation of the Color-Octet 3S1 Gluon Fragmentation Function for Heavy Quarkonium

The short-distance coefficients for the color-octet 3S1 term in the fragmentation function for a gluon to split into heavy quarkonium states is calculated to order alpha_s^2. The gauge-invariant definition of the fragmentation function by Collins and Soper is employed. Ultraviolet divergences are removed using the MS-bar renormalization procedure. The longitudinal term in the fragmentation function agrees with a previous calculation by Beneke and Rothstein. The next-to-leading order correction to the transverse term disagrees with a previous calculation.Comment: 17 pages, 4 figure

Quarkonium Polarization in the NRQCD Factorization Framework

The NRQCD factorization approach for calculating inclusive production of heavy quarkonium gives unambiguous predictions for the polarization of quarkonium states. The factorization formula for polarized states can be obtained by using the threshold expansion method to calculate the short-distance coefficients and then using symmetries of NRQD to reduce the NRQCD matrix elements. A particularly dramatic prediction of the NRQCD factorization framework is that prompt psi's and psi-primes's produced at the Tevatron should be predominantly transversely polarized at large transverse momentum.Comment: 11 pages, LaTeX, invited talk presented at the Quarkonium Physics Workshop, University of Illinois at Chicago, June 199

Searching for BcB_c mesons in the ATLAS experiment at LHC

We discuss the feasibility of the observation of the signal from $B_c$ mesons in the ATLAS experiment of the LHC collider at a luminosity of ${\approx}\ 10^{33}$cm$^{-2}$s$^{-1}$. In particular we address the decay mode$B_c{\rightarrow}J/\psi \pi$followed by the leptonic decay$J/\psi{\rightarrow}\mu^+\mu^-$, which should permit an accurate measurement of the$B_c$mass. We performed a Monte Carlo study of the signal and background concluding that a precision of$40$MeV for the$B_c$ mass could be achieved after one year of running.Comment: Latex,7 pages including 3 uuencoded Postscript figures appended at the end of the latex fil