Narrow Results

By the end of an excellent data taking in 1999, we collected ≈ 1 billion decay positrons with energy greater than 2 GeV and 30 μs after injection. The analysis of the 1999 data set were performed in parallel by various teams in the collaboration and each team provides a different approach to the analysis. The projected errors are expected to be of order 1.3 ppm statistical and below 0.5 ppm systematic. The data obtained in the 2000 run contains ≈ 4 times more decay positrons compared to 1999.

The measurement of the so far unknown chiral-odd quark transverse spin distribution in either semi-inclusive DIS(SIDIS) or inclusive measurements in pp collisions at RHIC has an additional chiral-odd fragmentation function appearing in the cross section. This chiral-odd fragmentation functions (FF) can for example be the so-called Collins FF or the Interference FF. HERMES has given a first hint that these FFs are nonzero, however in order to measure transversity one needs these FFs to be precisely known. At the BELLE e⁺e⁻ collider at the KEK-B factory a data set of about 30fb⁻¹ can be used to obtain these functions.

The measurement of the so far unknown chiral-odd quark transverse spin distribution in either semi-inclusive DIS (SIDIS) or inclusive measurements in pp collisions at RHIC has an additional chiral-odd fragmentation function appearing in the cross section. This chiral-odd fragmentation functions (FF) can for example be the socalled Collins FF ¹ or the Interference FF. HERMES ² has given a first hint that these FFs are nonzero, however in order to measure the transversity one needs these FFs to be precisely known. We have used 29.0 fb⁻¹ of data collected by the Belle experiment at the KEKB e⁺e⁻ collider to measure azimuthal asymmetries for different charge combinations of pion pairs and thus access the Collins FF.

This article discusses tests of CPT and Lorentz invariance with data from the muon g - 2 experiment at Brookhaven National Laboratory. According to an extension of the Standard Model by Kostelecký et al., CPT/Lorentz violating terms in the Lagrangian induce a shift of the anomaly frequency ω_a of muons in a magnetic field. This shift is predicted to be different for positive and negative muons and to oscillate with the Earth's sidereal frequency. We discuss the sensitivity of the g - 2 experiment to different parameters of this Standard Model extension and propose an analysis method to search for sidereal variations of ω_a.

The Muon (g-2) Experiment (E821) at Brookhaven National Laboratory (BNL) started data taking in 1997. The latest result a_μ+ = 11659202(14)(6) × 10⁻¹⁰, based on statistics collected in 1999, is in good agreement with the previous measurement. With the precision of 1.3 ppm, the result shows the discrepancy with the Standard Model prediction a_μ(exp) − a_μ(SM) = 43(16) × 10⁻¹⁰.

Two signals of CPT/Lorentz violation have been searched for in data collected in the muon (g-2) experiment E821 at the Brookhaven Lab AGS. Muons of 3.1 GeV/c were stored in a magnetic storage ring, and their spin precession frequency ω_a relative to their momentum was measured. The difference in the average precession frequencies for μ⁺ and μ^- restricts the Standard-Model Extension parameter b_z. The non-observation of a sidereal variation in the muon frequencies over a several-month data collection period restricts the parameters .

A precise measurement of the magnetic anomaly, a = (g - 2)/2, of the positive muon has been made using the Alternating Gradient Synchrotron at Brookhaven Lab. A brief review of the experiment is given, and an analysis of data collected during the 1999 run is detailed. The result a_μ+ = 11 659 202(14)(6) × 10^-10 (1.3 ppm) is in good agreement with the previous world average a_μ = 11 659 205(46) × 10^-10 (3.9 ppm), and the new world average differs by 2.6σ from the standard model prediction a_μ(SM) = 11 659 160(7) × 10^-10 (0.6 ppm), [a_μ(exp) - a_μ(SM)] = 42(16) × 10^-10.