Searcharxiv⌕ Search

arXiv subjects

DIRAC Collaboration

Publications and source records attributed to DIRAC Collaboration.

5 recordsLinked to original sources
arXiv2017

Measurement of the $\pi K$ atom lifetime and the $\pi K$ scattering length

After having announced the statistically significant observation (5.6~$\sigma$) of the new exotic $\pi K$ atom, the DIRAC experiment at the CERN proton synchrotron presents the measurement of the corresponding atom lifetime, based on the full $\pi K$ data sample: $\tau = (5.5^{+5.0}_{-2.8}) \cdot 10^{-15}s$. By means of a precise relation ($<1\%$) between atom lifetime and scattering length, the following value for the S-wave isospin-odd $\pi K$ scattering length $a_0^{-}~=~\frac{1}{3}(a_{1/2}-a_{3/2})$ has been derived: $\left|a_0^-\right| = (0.072^{+0.031}_{-0.020}) M_{\pi}^{-1}$.

hep-ex↗
arXiv2016

Observation of $\pi^- K^+$ and $\pi^+ K^-$ atoms

The observation of hydrogen-like $\pi K$ atoms, consisting of $\pi^- K^+$ or $\pi^+ K^-$ mesons, is presented. The atoms have been produced by 24 GeV/$c$ protons from the CERN PS accelerator, interacting with platinum or nickel foil targets. The breakup (ionisation) of $\pi K$ atoms in the same targets yields characteristic $\pi K$ pairs, called "atomic pairs", with small relative momenta in the pair centre-of-mass system. The upgraded DIRAC experiment has observed $349\pm62$ such atomic $\pi K$ pairs, corresponding to a signal of 5.6 standard deviations.

hep-ex↗
arXiv2015

First observation of long-lived $\pi^+ \pi^-$ atoms

After observing and investigating the double-exotic $\pi^+\pi^-$ atom with the ground state lifetime $\tau$ of about $3 \times 10^{-15}$~s, the upgraded DIRAC experiment at the CERN PS accelerator observes for the first time long-lived states of the same atom with lifetimes of about $10^{-11}$~s and more. The number of characteristic pion pairs resulting from the breakup (ionisation) of long-lived $\pi^+\pi^-$ atoms amounts to $436\pm61$, corresponding to a signal-to-error ratio of better than 7 standard deviations. This observation opens a new possibility to measure energy differences between $p$ and $s$ atomic states and so to determine $\pi \pi$ scattering lengths.

hep-ex↗
arXiv2003

DIRAC: A High Resolution Spectrometer for Pionium Detection

The DIRAC spectrometer has been commissioned at CERN with the aim of detecting $π^+ π^-$ atoms produced by a 24 GeV/$c$ high intensity proton beam in thin foil targets. A challenging apparatus is required to cope with the high interaction rates involved, the triggering of pion pairs with very low relative momentum, and the measurement of the latter with resolution around 0.6 MeV/$c$. The general characteristics of the apparatus are explained and each part is described in some detail. The main features of the trigger system, data-acquisition, monitoring and setup performances are also given.

hep-ex↗