DIRAC Experiment and Test of Low-Energy QCD

The low-energy QCD predictions to be tested by the DIRAC experiment are revised. The experimental method, the setup characteristics and capabilities, along with first experimental results are reported. Preliminary analysis shows good detector performance: alignment error via $\Lambda$ mass measurement $m_\Lambda = 1115.6 MeV/c^2$ with $\sigma = 0.92 MeV/c^2$, $p \pi^-$ relative momentum resolution $\sigma_Q \approx 2.7 MeV/c$, and evidence for $\pi^

DIRAC: A High Resolution Spectrometer for Pionium Detection

The DIRAC spectrometer has been commissioned at CERN with the aim of detecting $\pi^+ \pi^-$ 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.Comment: 49 pages, 37 figures. Figures 1, 2, 5 and 28 are removed because of size limitations imposed by hep-ex. They don't offer essential information. Latex class file 'elsart.cls' also provide

Performances of the optical readout system for the large angle electromagnetic shower calorimeter for CLAS

none18We present the study of a lucite light guide system developed for the modules of the electromagnetic calorimeter that will be installed in CLAS at CEBAF to detect showering particles emitted at angles larger than 45°. We show that it is possible to produce lucite guides with length up to 120 cm and to adapt them to the module geometry with low costs, time and efforts. The performances are comparable or even better than that of equivalent systems realized with optic fibres. The guides showed high homogeneity and light transmission efficiency.M. Taiuti;M. Anghinolfi;N. Bianchi;G.P. Capitani;P. Corvisiero;E. DeSanctis;P. LeviSandri;V.I. Mokeev;V. Muccifora;M. Olcese;E. Polli;G. Ricco;A.R. Reolon;M. Ripani;P. Rossi;A. Rottura;M. Sanzone;A. ZucchiattiTaiuti, MAURO GINO; M., Anghinolfi; N., Bianchi; G. P., Capitani; Corvisiero, Pietro; E., Desanctis; P., Levisandri; V. I., Mokeev; V., Muccifora; M., Olcese; E., Polli; Ricco, Giovanni; A. R., Reolon; M., Ripani; P., Rossi; A., Rottura; Sanzone, Marcella; A., Zucchiatt

The response of a BGO scintillation detector to 100\u2013500 MeV kinetic energy pions, protons and deuterons

The light response of pions, protons and deuterons with respect to electrons of the same energy is measured in a BGO calorimeter using the inclusive 16O(e, e\u2032), 16O(e, \u3c0), 16O(e, p) and 16O(e, d) reactions. An average 5% quenching is found in the 100\u2013500 MeV energy range of this experiment

Stochastic description of internal target effects on electron rings

The effects of internal targets on the beam accumulated in electron storage rings are studied with a linear stochastic model which describes the beam emittance and the beam phase-space growth and provides simple formulae for the longitudinal and transverse beam emittance. The description of facilities with and without beam damping is carried out in a consistent way. The obtained results are comparable to those obtained with other models and numerical simulations

Measurement of the response of long plastic scintillator bars for the large angle electromagnetic shower calorimeter for CLAS

The behaviour of plastic scintillator bars with length up to 450 cm, designed for the CLAS large angle electromagnetic shower calorimeter, is considered in relation to the overall calorimeter response function. In particular methods adopted to measure the light emission yield and transmission efficiency are described and the influence of the scintillator bar properties on the calorimeter energy read-out and timing is discussed. We found that the new scintillator NE110A manufactured by NE Technology Ltd. showed the best agreement with our demands. The effect of wrapping materials on the scintillator bar properties has been studied considering also the temperature variations expected in Hall B at CEBAF

“Performance of silicon-drift detectors in kaonic atom X-ray measurements”

Large-area silicon drift detectors (SDDs) were used for the first time in the background condition of a collider for precision spectroscopy of the kaonic atom X-rays in the SIDDHARTA experiment for the study of the strong interaction in a low-energy regime. The measurements were performed at the DAΦNE electron–positron collider (LNF, Italy), using gas targets of hydrogen, deuterium, helium-3, and helium-4. A test measurement using the kaonic 4He X-rays showed an excellent performance of the SDD devices under the beam conditions, and a good background suppression capability using the time correlation between the kaonic atom X-rays and the back-to-back correlated K+K− pairs produced by φ decays

Test of chiral perturbation theory with DIRAC at CERN

The DIRAC experiment at CERN aims to form pi /sup +/ pi /sup -/ atomic states and to measure their lifetime with 10% accuracy. This will give a precision of 5% in the determination of pi pi S-wave scattering lengths, of the same level of Chiral Perturbation Theory calculations. In this way a crucial test on the theory validity would be performed. (13 refs)

Dirac experiment

The main objective of DIRAC experiment is the measurement of the lifetime tau of the exotic hadronic atom consisting of pi /sup +/ and pi /sup -/ mesons. The lifetime of this atom is determined by the decay mode pi /sup +/ pi /sup -/ to pi /sup 0/ pi /sup 0/ due to the strong interaction. Through the precise relationship between the lifetime and the S-wave pion-pion scattering length difference a/sub 0/-a/sub 2/ for isospin 0 and 2 (respectively), a measurement of tau with an accuracy of 10% will allow a determination of a/sub 0/-a/sub 2/at a 5% precision level. Pion-pion scattering lengths have been calculated in the framework of chiral perturbation theory with an accuracy below 5%. In this way DIRAC experiment will provide a crucial test of the chiral symmetry breaking scheme in QCD effective theories at low energies. (19 refs)