Thesis Summary

Started     Sep 2002
Finished    Mar 2007

Abstract

The inclusive production rate of the charged vector meson rho+-(770) in hadronic Z decays is measured with the ALEPH detector at the LEP collider. A total of 3,239,746 hadronic events are selected from data recorded by ALEPH from the 1991 to 1995 running periods. Decays of rho+- --> pi0 pi+- are reconstructed for xE > 0.05 and xp > 0.05 where xE = E(rho)/E(beam) and xp = p(rho)/p(beam). The rho+- multiplicity per hadronic event is evaluated to be:

<N(rho+-)> = 2.59 +- 0.03 +- 0.15 +- 0.04

Key points

• For these studies the ALPHA (ALeph PHysics Analysis) Package, containing 4,923,816 Monte Carlo data and 3,239,746 Real Data, is used.
• Event Reconstruction, Simulation and Selection
  Recorded data containing the raw event information are reconstructed offline by the JULIA program. Event simulation proceeds in two steps: simulation of the physics under investigation (carried out by event generators and the KINGAL program), and simulation of the response of the detector to the KINGAL particles (carried out by the GALEPH program). Event selection covers two main areas: the first is a selection on event quality, the second is the selection of the hadronic signal Z -> q q-bar.
• Charged track cuts and neutral pion selection via the Ranking method has been optimised to increase the signal significance of the rho+- meson.
• Distortions in the invariant mass spectra caused by residual Bose-Einstein Correlations are found to be important in the extraction of rho+- rates from two pion invariant mass spectra. This effect is not included in the Monte Carlo programs. The Söding Model, used to describe background interference effects, appears to work well as a model of these distortions and is used successfully in this analysis.
• The results can be found at: http://www1.gantep.edu.tr/~bingul/hep/phd/results.html