BaBar Experiment :: Chemistry Science Scientific Essays

BaBar Experiment Abstract I investigated the L = 1 mesons D*2(2460)0 and D1(2420)0 using data gathered by the BaBar detector at Pep-II. The decay process of these particles is interesting because it could serve to confirm or deny certain predictions made by HQET models. Thus far, the data gathered rougly conforms with measurements made by the CLEO and ARGUS collaborations. The data is still preliminary, however, and as such this paper should be considered merely a summary of the work done thus far. 1 Introduction 1.1 The BaBar experiment The BaBar detector at Pep-II was designed to study B mesons produced in asymmetric e+e- collisions. \Asymmetric" refers to the fact that the colliding electrons and positrons have different energies. This gives the resulting particles momentum in the laboratory reference frame, allowing their lifetimes to be measured even if they carry away most of the collision energy. In the current run at Pep-II, electrons are stored in one ring at 9 GeV and positrons in the other at 3.1 GeV. This sets the collision energy right at the T(4S) resonance, a short-lived combination of a bottom quark and its antiquark. This decays preferentially into a pair of mesons B and B|hence the name of the detector. Mesons are short-lived systems made up of a quark and an anti-quark; Bs are mesons in which one quark is a bottom (or an anti-bottom) and the other is a light quark (up, down, strange, or their corresponding antiquarks). The BaBar detector is optimized to measure the decay process of these B's as precisely as possible. It is hoped that differences between the B and the B decay processes will be uncovered and measured, which will lead to a better understanding of CP symmetry violation. \CP violation" describes an event that breaks the so-called Charge{ Parity symmetry. For a time, it was believed that if matter and antimatter were interchanged (hence, Charge) and if right and left were reversed (Parity), systems would behave in an identical manner. This symmetry has since been found to be broken in certain kaon decays, and it is suspected that further violations will be discovered in B decays. Note that if time is reversed as well as charge and parity, then the system will behave in an indentical manner; this is known as CPT symmetry, and is required for Lorentz transformations. It is hoped that learning more about events that violate the \broken" CP symmetry will shed some light on the relative scarcity of antimatter in the universe.