Azimuthal Asymmetries in Hadronic Final States at HERA

The distribution of hadrons produced in deeply inelastic electron-proton collisions depends on the azimuthal angle between lepton scattering plane and hadron production plane in the photon-proton centre-of-mass frame. In addition to the well known up-down asymmetry induced by the azimuthal dependence of the Born level subprocess, there is also a non-vanishing left-right asymmetry, provided the incoming electron is polarized. This asymmetry is time-reversal-odd and induced by absorptive corrections to the Born level process. We investigate the numerical magnitude of azimuthal asymmetries in semi-inclusive hadron production at HERA with particular emphasis on a possible determination of the time-reversal-odd asymmetry.Comment: 9 pages, LaTeX, 7 figures included, The complete paper, including figures, is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ttp99/ttp99-29/ or via www at http://www-ttp.physik.uni-karlsruhe.de/Preprints

Compatibility of various approaches to heavy-quark fragmentation

We find that the definition of the heavy-quark fragmentation function given by Jaffe and Randall differs by a factor of the longitudinal-momentum fraction z from the standard Collins-Soper definition. Once this factor is taken into account, the explicit calculation of Braaten et al. is found to be in agreement with the general analysis of Jaffe and Randall. We also examine the model of Peterson et al. for heavy-quark fragmentation and find that the quoted values of the width and of the value of $z$ at the maximum are in error. The corrected values are in agreement with the analysis of Jaffe and Randall.Comment: 4 pages late

Efficient magneto-optical trapping of Yb atoms with a violet laser diode

We report the first efficient trapping of rare-earth Yb atoms with a high-power violet laser diode (LD). An injection-locked violet LD with a 25 mW frequency-stabilized output was used for the magneto-optical trapping (MOT) of fermionic as well as bosonic Yb isotopes. A typical number of $4\times 10^6$ atoms for $^{174}$Yb with a trap density of $\sim 1\times10^8/$cm$^3$ was obtained. A 10 mW violet external-cavity LD (ECLD) was used for the one-dimensional (1D) slowing of an effusive Yb atomic beam without a Zeeman slower resulting in a 35-fold increase in the number of trapped atoms. The overall characteristics of our compact violet MOT, e.g., the loss time of 1 s, the loading time of 400 ms, and the cloud temperature of 0.7 mK, are comparable to those in previously reported violet Yb MOTs, yet with a greatly reduced cost and complexity of the experiment.Comment: 5 pages, 3 figures, 1 table, Phys. Rev. A (to be published

Inclusive J/psi and psi(2S) Production from B Decay in p p-bar Collisions

Using information on B-meson fragmentation functions from CERN LEP 1 and adopting the nonrelativistic QCD factorization formalism proposed by Bodwin, Braaten, and Lepage, we predict the transverse-momentum distribution of J/psi mesons originating from the inclusive decays of b hadrons produced in p p-bar collisions at the Fermilab Tevatron. We determine the relevant colour-octet charmonium matrix elements from fits to CDF data on prompt charmonium hadroproduction and to CLEO data on charmonium production from B-meson decay. Our predictions are found to agree well with recent CDF and D0 data.Comment: 27 pages (Latex), 9 figures (Postscript

Strong Coupling Constant from Scaling Violations in Fragmentation Functions

We present a new determination of the strong coupling constant alpha_s through the scaling violations in the fragmentation functions for charged pions, charged kaons, and protons. In our fit we include the latest e+e- annihilation data from CERN LEP1 and SLAC SLC on the Z-boson resonance and older, yet very precise data from SLAC PEP at center-of-mass energy sqrt(s)=29 GeV. A new world average of alpha_s is given.Comment: 10 pages, 3 eps figue

Quenched Narrow-Line Laser Cooling of 40Ca to Near the Photon Recoil Limit

We present a cooling method that should be generally applicable to atoms with narrow optical transitions. This technique uses velocity-selective pulses to drive atoms towards a zero-velocity dark state and then quenches the excited state to increase the cooling rate. We demonstrate this technique of quenched narrow-line cooling by reducing the 1-D temperature of a sample of neutral 40Ca atoms. We velocity select and cool with the 1S0(4s2) to 3P1(4s4p) 657 nm intercombination line and quench with the 3P1(4s4p) to 1S0(4s5s) intercombination line at 553 nm, which increases the cooling rate eight-fold. Limited only by available quenching laser power, we have transferred 18 % of the atoms from our initial 2 mK velocity distribution and achieved temperatures as low as 4 microK, corresponding to a vrms of 2.8 cm/s or 2 recoils at 657 nm. This cooling technique, which is closely related to Raman cooling, can be extended to three dimensions.Comment: 5 pages, 4 figures; Submitted to PRA Rapid Communication

Two-Photon Doppler cooling of alkaline-earth-metal and ytterbium atoms

A new possibility of laser cooling of alkaline-earth-metal and Ytterbium atoms using a two-photon transition is analyzed. We consider a $^{1}S_{0}$ - $^{1}S_{0}$ transition, with excitation in near resonance with the $^{1}P_{1}$ level. This greatly increases the two-photon transition rate, allowing an effective transfer of momentum. The experimental implementation of this technique is discussed and we show that for Calcium, for example, two-photon cooling can be used to achieve a Doppler limit of 123 microKelvin. The efficiency of this cooling scheme and the main loss mechanisms are analyzed.Comment: 7 pages, 5 figure

Doppler cooling and trapping on forbidden transitions

Ultracold atoms at temperatures close to the recoil limit have been achieved by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms has been cooled and trapped to a temperature as low as 6 \mu K by operating a magneto-optical trap on the spin-forbidden intercombination transition. Quenching the long-lived excited state with an additional laser enhanced the scattering rate by a factor of 15, while a high selectivity in velocity was preserved. With this method more than 10% of pre-cooled atoms from a standard magneto-optical trap have been transferred to the ultracold trap. Monte-Carlo simulations of the cooling process are in good agreement with the experiments

On The Injection Spectrum of Ultrahigh Energy Cosmic Rays in the Top-Down Scenario

We analyze the uncertainties involved in obtaining the injection spectra of UHECR particles in the top-down scenario of their origin. We show that the DGLAP $Q^2$ evolution of fragmentation functions (FF) to $Q=M_X$ (mass of the X particle) from their initial values at low $Q$ is subject to considerable uncertainties. We therefore argue that, for x\lsim 0.1 (the $x$ region of interest for most large $M_X$ values of interest, $x\equiv 2E/M_X$ being the scaled energy variable), the FF obtained from DGLAP evolution is no more reliable than that provided, for example, by a simple Gaussian form (in the variable $\ln(1/x)$) obtained under the Modified Leading Log Approximation (MLLA). Additionally, we find that for x\gsim0.1, the evolution in $Q^2$ of the singlet FF, which determines the injection spectrum, is ``minimal'' -- the singlet FF changes by barely a factor of 2 after evolving it over $\sim$ 14 orders of magnitude in $Q\sim M_X$. We, therefore, argue that as long as the measurement of the UHECR spectrum above \sim10^{20}\ev is going to remain uncertain by a factor of 2 or larger, it is good enough for most practical purposes to directly use any one of the available initial parametrisations of the FFs in the $x$ region x\gsim0.1 based on low energy data even without evolving them to the requisite $Q^2$ value.Comment: Minor changes, added a reference, version to appear in Phys. Rev.