Combined Statistical Uncertainty Research Articles

Measurement of the branching fraction of the decay J/ψ→pp¯η

A high-precision measurement of the branching fraction of the decay J/ψ→pp¯η is performed using (10 087±44)×106 J/ψ events recorded by the BESIII detector at the BEPCII storage ring. The branching fractions of the two decays J/ψ→pp¯η(η→γγ) and J/ψ→pp¯η(η→π+π−π0) are measured individually to be B(J/ψ→pp¯η(η→γγ))=(1.480±0.001±0.024)×10−3 and B(J/ψ→pp¯η(η→π+π−π0))=(1.557±0.003±0.038)×10−3, where the first uncertainties are statistical and the second systematic. Both results are compatible within their uncorrelated systematic uncertainties. The combined result is B(J/ψ→pp¯η)=(1.495±0.001±0.023)×10−3, where the first uncertainty is the combined statistical uncertainty and the second one the combined systematic uncertainty of both analyses, incorporating correlations between them. In addition, the pp¯ threshold region is investigated for a potential threshold enhancement, and no evidence for one is observed. Published by the American Physical Society 2024

The Young Massive Star Cluster Westerlund 2 Observed with MUSE. II. MUSEpack—A Python Package to Analyze the Kinematics of Young Star Clusters

Abstract We mapped the Galactic young massive star cluster Westerlund 2 with the integral field spectrograph MUSE (spatial resolution: 0.2 arcsec px−1, spectral resolution: Δλ = 1.25 Å, wavelength range: 4600–9350 Å) mounted on the Very Large Telescope. We present the fully reduced data set and introduce our new Python package “MUSEpack,” which we developed to measure stellar radial velocities (RVs) with an absolute precision of 1–2 km s−1 without the necessity of a spectral template library. This novel method uses the two-dimensional spectra and an atomic transition line library to create templates around strong absorption lines for each individual star. Automatic, multi-core processing makes it possible to efficiently determine stellar RVs of a large number of stars with the necessary precision to measure the velocity dispersion of young star clusters. MUSEpack also provides an enhanced method for removing telluric lines in crowded fields without sky exposures, and a Python wrapper for ESO’s data reduction pipeline. We observed Westerlund 2 with a total of 11 short and 5 long exposures (survey area: ∼11 arcmin2 or 15.8 pc2) to cover the bright nebular emission and OB stars, as well as the fainter pre-main-sequence stars (≥1 M ⊙). We extracted 1725 stellar spectra with a mean signal-to-noise ratio of S/N > 5 per pixel. Typical RV uncertainties of 4.78 km s−1, 2.92 km s−1, and 1.1 km s−1 are reached for stars with a mean S/N > 10, S/N > 20, and S/N > 50 per pixel, respectively. It is possible to reach RV accuracies of 0.9 km s−1, 1.3 km s−1, and 2.2 km s−1 with ≥5, 3–4, and 1–2 spectral lines used to measure the RVs, respectively. The combined statistical uncertainty on the RV measurements is 1.10 km s−1.

Monte carlo determination of correction factors for dosimetric measurements in gamma knife perfexion small fields

Introduction In the formalism proposed by Alfonso et al. (2008) for the dosimetry of small and non-standard photon fields, Monte Carlo (MC) simulation is indicated as a proper means for determining machine-specific reference field ( k Q msr , Q f msr , f ref ) and clinical radiation fields ( k Q clin , Q msr f clin , f msr ) correction factors (CFs) assigned to calibration and relative dosimetry measurements, respectively. Purpose To determine CFs for the Gamma Knife Perfexion (PFX) radiosurgery unit for a variety of commercially available detectors utilizing MC simulations. Materials and methods A recently introduced EGSnrc comprehensive simulation model for the PFX irradiation unit was used. A set of 13 ionization chambers, 6 diodes detectors, TLD microcubes and alanine pellets were simulated based on blueprints provided by the vendors. CFs calculations were performed using the egs_chamber user code. Intermediate Phase Space Scoring and photon cross section enhancement variance reduction techniques were implemented in order to increase time efficiency. MC calculations were performed by a super-computer consisting of 8520 computational threads achieving a combined statistical uncertainty of 0.3%. Results Calculated k Q msr , Q f msr , f ref for ionization chambers commonly used for reference dosimetry in PFX were up to 1.02 (IBA-CC01). Calculations for k Q clin , Q msr f clin , f msr revealed an overestimation of diode detectors up to 6% for the 4mm-collimator, while CFs for ionization chambers (active volume ⩽0.04cm3) reached 1.48 (PTW-31015). Conclusion A set of CFs were determined for the PFX unit allowing for more accurate dosimetry measurements. Disclosure This work was supported by computational time granted from the Greek Research & Technology Network (GRNET) in the National HPC facility -ARIS- under project ID pr001027.