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Preparations for the Spin-Filtering\ud Experiments at COSY/Jülich

By Christian Weidemann

Abstract

Polarized antiprotons allow unique access to a number of fundamental physics observables.\ud One example is the transversity distribution which is the last missing piece to complete\ud the knowledge of the nucleon partonic structure at leading twist in the QCD-based parton\ud model. The transversity is directly measurable via Drell-Yan production in double polarized\ud antiproton-proton collisions. This and a multitude of other findings, which are accessible\ud via ppbar scattering experiments, led the Polarized Antiproton eXperiments (PAX) collaboration\ud to propose such investigations at the High Energy Storage Ring (HESR) of the Facility for\ud Antiproton and Ion Research (FAIR).\ud Already the production of intense polarized antiproton beams is still an unsolved problem.\ud The PAX anticipated time plan to experiments at HESR mainly consists of three phases.\ud PAX@COSY, as first step, is aiming for an optimization of the polarization build-up in\ud proton beams at the Cooler Synchrotron COSY Jülich. The spin-filtering method, where\ud the originally unpolarized beam becomes polarized due to the spin-dependent part of the\ud hadronic interaction with a Polarized Internal Target (PIT), will be applied. The feasibility of\ud this method was shown to work for protons by the Filter Experiment (FILTEX) at the Test\ud Storage Ring (TSR) in Heidelberg. PAX@CERN will determine the spin-dependent cross\ud sections in ppbar scattering at beam energies of 50 - 450 MeV using the antiproton beam of\ud the Antiproton Decelerator (AD) at CERN. PAX@FAIR constitutes the third phase where the\ud antiproton beam will be polarized in a dedicated Antiproton Polarizer Ring (APR) at the\ud HESR, converted into a double-polarized proton-antiproton collider, in order to study the\ud transverse spin structure of nucleons.\ud The present thesis discusses the preparations for the spin-filtering experiments at COSY. This\ud includes the successful installation and commissioning of the experimental equipment such\ud as a low-β section, a dedicated pumping system, an Atomic Beam Source (ABS), a Breit-\ud Rabi Polarimeter (BRP), and a target chamber with an openable storage cell. In addition,\ud the accomplished investigations of the beam lifetime dependencies, resulting in significantly\ud improved beam lifetimes, and relevant machine parameters, e.g., the machine acceptance, are\ud described. The results are utilized to calculate the expected polarization build-up in a cooled\ud and stored proton beam with a kinetic energy of 49.3MeV using a target with an areal density\ud of 5*10¹³ atoms/cm². Simulations of the determination of the beam polarization using elastic\ud proton-deuteron scattering and a polarimeter, that consists of silicon micro-strip detectors,\ud allows one to estimate the achievable precision of the measurement of the spin-dependent\ud total hadronic cross section. The presented results constitute the basis of a beam time request\ud for transverse spin-filtering to the COSY Program Advisory Committee (PAC), which was\ud approved in spring 2011.\u

Topics: ddc:530, ddc:600
Year: 2011
OAI identifier: oai:USBKOELN.ub.uni-koeln.de:4513

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