[Triumf-seminars] TRIUMF Seminar today at 14:00

[postmaster@admin.triumf.ca]

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Date/Time: Thu 2005-12-15 at 14:00

Location:  Auditorium          

Speaker:   Mina Nozar (TRIUMF)

Title:     Partial Wave Analysis (PWA) as a tool to identify states by their characteristics J^{pc} quantum numbers

Abstract: The self-interacting nature of gluons in QCD, by virtue of their color charge, gives justification for existence of states outside the constituent quark model.  In these states, the gluons directly contribute to the state configuration.  Among these hybrid states, the ones with unusual (exotic) J^{PC} = 0^{--}, 0^{+-}, 1^{-+}, 2^{+-}, ... quantum numbers are of particular interest since they can not be formed from a bound state of quark anti-quark alone, and therefore represent a clear and unambiguous signature of hadronic states outside the constituent quark model.  The MIT bag model, the flux-tube model, and lattice-QCD calculations predict the lightest hybrid meson to have J^{PC} = 1^{-+}  with mass in the 1.4-2.1 GeV range.

Various experiments have looked for such states in different production mechanisms: Crystal Barrel at LEAR using proton anti-proton annihilation at rest, VES at IHEP with a 37 GeV pion beam incident on a nuclear target, Brookhaven E852 using an 18 GeV pion beam on a proton target , and most recently, the JLab g6c CLAS experiment, using a 4.8-5.4 GeV photon beam on a proton target.  In all of these experiments, some variation of PWA is employed to extract the J^{PC} quantum numbers of the states contributing to the total observed intensity distribution.

In this talk, an overview of the PWA technique, initially developed for the analysis of the E852 data and later extended and applied to the CLAS g6c data, will be presented.  Although the preferred decay mode of the 1^{-+} state is to an S-wave and a P-wave meson, e.g. b_1(1235)pi and f_1(1285) pi, it has a small but non negligible decay width to rho pi, a much simpler final state.  For this reason, I have chosen the  PWA of the charged 3-pion final state in both hadro- and photo-production as an illustration of the application of the PWA.  



Stimulants available 15 minutes before the talk.

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