Measurement of the $$Z^0 → s\overline{s}$$ Coupling at the SLD [Thesis]
- SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Colorado State Univ., Fort Collins, CO (United States)
This dissertation presents a direct measurement of the parity-violating coupling of the $Z^0$ to strange quarks, As, derived from $e^+e^-$ collision data containing approximately 550,000 hadronic decays of polarized $Z^0$ bosons. Data were recorded with the SLC Large Detector (SLD) at the SLAC Linear Collider (SLC) between 1993 and 1998 with an average electron beam polarization of 73% and 74% during the 1993-5 and 1996-8 run periods, respectively. Making use of several unique features of the SLC and SLD, this measurement relies on a new generation particle identification system, the Cherenkov Ring Imaging Detector, to test the Standard Model prediction of universality in the coupling of the $Z^0$ to down-type quarks. Polarized $$Z^0 →s\overline{s}$$ events are tagged by the presence in each event hemisphere of a high-momentum $$K^±, K^0_s or Λ^0/\overline{Λ}^0$$ identified using particle identification and/or a mass tag. The background from heavy flavor events is suppressed with the CCD-based vertex detector. The event thrust axis is signed with the strangeness of the tagged particle to point in the direction of the initial s quark. The coupling $$A_s$$ is derived from a maximum likelihood fit to the polar angle distributions of the tagged s quark measured with left- and right-handed electron beams. To reduce the model dependence of the measurement, the background from $$u\overline{u}$$ and $$d\overline{d}$$ events as well as the analyzing power of the method for $$s\overline{s}$$ events are constrained from the data. We obtain $$A_s = 0.86 ± 0.08(stat.) ± 0.05(syst.)$$. The result is consistent with both the Standard Model prediction and previous bottom quark coupling, $$A_b$$, measurements performed by SLD and LEP, and therefore supports the predicted universality of the $$Z_0$$ to down-type quark couplings.
- Research Organization:
- SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 1454222
- Report Number(s):
- SLAC-R-549; UC-414
- Country of Publication:
- United States
- Language:
- English
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