Diagnostic de Faisceau par "Laser-Wire" et Mesure Rapide du Spectre de Luminosite au Collisionneur Lineaire International

• Main Author: Poirier, Freddy
• Language: ENG
• Published: 2005
• Subjects: [PHYS:PHYS:PHYS_ATOM-PH] Physics/Physics/Atomic Physics; [PHYS:HEXP] Physics/High Energy Physics - Experiment; ILC; luminosite; collisionneur; lineaire; bhabha; bremsstrahlung; beamstrahlung; spectre; deconvolution; modele standard; diagnostique; laser-wire; detecteur; tungstene de plomb; PbWO4; crystal; matrice; calorimetrie; PETRA; DESY; faisceau; dimension; electron; positron; precision
• Online Access: http://tel.archives-ouvertes.fr/tel-00010215; http://tel.archives-ouvertes.fr/docs/00/04/84/45/PDF/tel-00010215.pdf

The International Linear Collider (ILC), a high precision electron-positron machine with centre of mass energy extending up to the TeV scale, is curently being proposed and designed. With unprecedented small beam size and high intensity the ILC aims at luminosities of the order of $10^(34)$~cm$^(-2)$s$^(-1)$. Careful monitoring of the beam parameters that affect the luminosity will be mandatory if these ambitious goals are to be achieved.<br /><br />One of the key parameters is beam emittance, the optimisation of which requires beam size monitors with micron resolution.<br />With this aim, a non-invasive laser-wire monitor prototype was designed, installed and run at the PETRA ring. Prior to its installation, background simulations and measurements were performed to verify that they would be low enough to allow<br /> the laser-wire programme to proceed. A lead-tungstate crystal calorimeter for the laser-wire was commissioned, including a study of temperature dependance, geometrical acceptance and energy response. The first laser-wire measurements of the PETRA positron beam size were then performed. The system, calibration and results are reported here.<br /><br />At the ILC, beam energy spread and beamstrahlung effects modify the luminosity spectrum. Determination of these effects is crucial in order to extract precision physics from threshold scans. In order to provide a run-time diagnostic scheme to address this, a fast luminosity spectrum measurement technique employing forward calorimetry and statistical unfolding was devised, using the Bhabha process at low angles. The scheme is described and first results are presented.