The study of hadronic scattering amplitudes and in particular the spectroscopy of light mesons provide a unique tool to investigate the strong interaction. One complication for the analysis of the meson spectrum at high masses are multi-body final states into which heavy resonances can decay. In this thesis a method for the amplitude analysis of the pi-pi+pi-pi+pi- system is being developed and applied to diffractive pion dissoziation data recorded with the COMPASS experiment at CERN.

A partial wave decomposition of the 5-pion system is presented here, which for the first time allows to search for mesonic 5-body resonances. A novel technique based on an evolutionary algorithm is developed to solve the problem of finding a reliable truncation of the partial wave expansion of the hadronic amplitude. 
The well known pi2(1670) and pi(1800) states are found with good agreement to measurements in other channels. In addition there is evidence for several other resonant contributions, among them the controversial pi2(1880) which is being discussed as a hybrid-meson candidate. In the course of the analysis a new software-framework for amplitude analysis has been developed, which is now being used by the COMPASS collaboration for the analysis of several hadronic channels.

Future experiments in particle physics will have to collect large amounts of data in order to search for the subtle effects that would indicate new physics beyond the standard model or to be able to apply sophisticated analysis methods like the amplitude analysis presented in the first part of this thesis. Therefore, modern detectors have to operate at extremely high signal rates. A high-rate capable Time Projection Chamber (TPC) would be an ideal, large-volume charged-particle tracking detector. In order to investigate the possibilities to construct such a device a detailed simulation of a TPC has been implemented. With these tools it is demonstrated that the key challenges of event mixing and space-charge accumulation can indeed be solved.

First Amplitude Analysis of Resonant Structures in the 5-Pion Continuum at COMPASS

The FDIRC (Focusing Detector of Internally Reflected Cherenkov light) is a new concept of PID (Particle IDentification) detector aimed at separating kaons from pions up to a few GeV/c. It is the successor of the BABAR DIRC and benefits from the knowledge accumulated with a first FDIRC prototype built and operated at SLAC. The FDIRC is intended to be used in an environment with a luminosity 100 times higher than for BABAR and Belle. Backgrounds will be higher as well; yet, the FDIRC has been designed to perform at least as well as the BABAR DIRC. The main improvement is a complete redesign of the photon camera, moving from a huge tank of ultra-pure water to much smaller focusing cameras with solid fusedsilica optics. Furthermore, the detection chain will be 10 times faster than in BABAR to reject more background and to measure more accurately Cherenkov angles. This is achieved using H-8500 MaPMTs and a new front-end electronics (FEE) with significantly improved timing precision, higher hit rate capability, and small dead time. A full-scale FDIRC prototype covering 1/12th of the barrel azimuth is installed at SLAC and has just started recording cosmic-ray data. In this paper, we summarize the FDIRC design, present the status of the prototype test at SLAC and review the ongoing work to analyse the data.

The focusing DIRC: An innovative PID detector

A review of the particle identification scheme of the BaBar detector; its design and performance and the R&D program for future upgrades.

/pdf/dirc-the-particle-identification-system-for-babar-2cmq91o8nr.pdf

DIRC: The Particle identification system for BABAR

The BaBar magnet is a thin, 1.5 T superconducting solenoid with a hexagonal flux return. This chapter discusses the physics requirements and performance goals for the magnet, describes key interfaces, and summarizes the projected magnet performance. It also presents the design of the superconducting solenoid, including magnetic design, cold mass design, quench protection and stability, cold mass cooling, cryostat design, and coil assembly and transportation. The cryogenic supply system and instrumentation are described briefly, and the flux return is described.

/pdf/babar-technical-design-report-chapter-9-magnet-coil-and-flux-3jntd04khr.pdf

BaBar technical design report: Chapter 9, Magnet coil and flux return

L'experience BaBar a pour objectif de rechercher et de mesurer la violation de $CP$ dans le secteur des mesons $B$ et de contraindre les parametres du modele standard. Une des originalites de son dispositif experimental est le DIRC, le detecteur a effet Cherenkov utilise pour distinguer les pions des kaons charges. Une table de correction est mise en place pour corriger ses defauts d'alignement, et permet au DIRC d'atteindre ses performances nominales, c'est a dire une separation entre kaon et pion de $4\sigma$ pour une quantite de mouvement de $3\gevc$. La recherche de violation de $CP$ dans le canal de desintegration du $B^0$ en $\rho\pi$ devrait permettre de contraindre l'angle $\alpha$ du triangle d'unitarite, un des parametres du modele standard. L'objectif de cette analyse est de mesurer les parametres de violation de $CP$ ainsi que les autres parametres entrant dans la description de la distribution de probabilite du temps de desintegration. Une methode de maximum de vraisemblance combine l'information temporelle et des variables discriminantes du bruit de fond du continuum $\e^+\e^-\to q\bar(q)$, dont certaines sont resumees dans un reseau de neurones. L'autre bruit de fond, constitue des autres modes de desintegration du $B$, est pris en compte par des termes correctifs dans l'ajustement. Cette analyse presente a ce jour les meilleures mesures pour ce canal, et semble donner une indication de la violation directe de $CP$. Pour interpreter ces mesures en termes de contraintes sur les parametres du modele standard, il est necessaire d'utiliser un modele pour predire la contribution a longue distance des amplitudes de desintegration. Pour un exemple de tel modele, la ``factorisation QCD'', un test de validation compare les predictions aux donnees experimentales sur les desintegrations non charmees du meson $B$. Ce test semble indiquer un desaccord, qui pourrait etre reduit dans l'avenir par une meilleure connaissance experimentale et theorique des desintegrations du $B$.

https://tel.archives-ouvertes.fr/tel-00003154/document

Etude de modes de désintegration non charmée du méson B et recherche de la violation de la symétrie CP

The DIRC is a new type of Cherenkov imaging device that will be used for the first time in the BABAR detector at the asymmetric B-factory, PEP-II. It is based on total internal reflection and uses long, rectangular bars made from synthetic fused silica as Cherenkov radiator and light guide. The principles of the DIRC ring imaging Cherenkov technique are explained and results from the prototype program are presented. Its choice for the BABAR detector particle identification system is motivated, followed by a discussion of the quartz radiator properties and the detector design.

/pdf/dirc-the-internally-reflecting-ring-imaging-cherenkov-ziqcql1h90.pdf

DIRC, the internally reflecting ring imaging Cherenkov detector for BABAR

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DIRC, the internally reflecting ring imaging Cherenkov detector for BABAR