M. Williams

Multivariate side-band subtraction using probabilistic event weights

A common situation in experimental physics is to have a signal which can not be separated from a non-interfering background through the use of any selection criteria. In this paper, we describe a procedure for determining, on an event-by-event basis, a quality factor (Q-factor) that a given signal candidate originated from the signal sample. This procedure generalizes the ``side-band subtraction method to higher dimensions without requiring the data to be divided into bins. The Q-factors can then be used as event weights in subsequent analysis procedures, allowing one to more directly access the true spectrum of the signal.

Current status of a coupled-channel partial wave analysis using data from CLAS at Jefferson Lab

The non-strange baryon spectrum has been mapped out predominantly by studying N π elastic scattering with phase-shift analysis as the tool of choice. While there has been much success with these experimental techniques, the results have fueled debates in the community, most notably regarding the missing baryons problem. Theoretical solutions to this discrepancy appeal to a diquark-system within the baryons or a coupling to states other than N π. The CLAS detector at Jefferson Lab has turned out high-statistics, photoproduction datasets which are optimal for resolving these issues. However, new analytical techniques may be required to deal with this rich physics sector. The baryon resonances are photoproduced off liquid hydrogen and the CLAS detector allows us to measure a variety of final states. We will have access to nπ +, pπ 0, pπ + π −, pω,pη, pη′, ΛK + and ΣK + final states. A robust software package has been developed that allows for the fitting of these states individually and in a coupled-channel mode. We make use of flexible C++ based tools that allow fast and general calculations of amplitudes based on a covariant tensor formalism. New techniques have been applied to background subtraction which brings an added level of consistency to the analysis. Polarization information from other experiments is incorporated at fit time to help distinguish potentially ambiguous physics processes by using information outside of the CLAS datasets. Some of these channels have more mature analysis (pω,ΛK +) and the preliminary measuremen will be shown as well as an overview of the analysis tools.