High Pt Dielectron Mass and Angular Distribution for Z' searches

A Z' Search in High Pt Dielectron Events using the Dielectron Invariant Mass and Angular Distribution

We report results from a search for massive Z' bosons in the dielectron channel using a 448 pb^-1 dataset accumulated with the CDF II detector in ppbar collisions at sqrt(s) = 1.96 TeV at the Fermilab Tevatron. To identify the Z' signal, we use both the dielectron invariant mass M_ee distribution, and the angular distribution cos(θ*) of the electron pair in the Collins-Soper frame. The CDF data is found to be consistent with the null (no Z') hypothesis, with a probability greater than the values obtained in 87% of pseudo-experiments. So we set 95% confidence level upper limits on the Z' mass for many Z' models: the sequential Z'_SM, the canonical superstring-inspired E6 models (Z_χ, Z_ψ, Z_η, Z_I,Z_N), the four general U(1) model-lines advocated in Phys.Rev.D70:093009,2004 , the "littlest" Higgs Z_H model, and contact-interaction searches.

Contacts: C. Ciobanu, G. DeLentdecker, J. Goldstein, S. Harper, T. Junk, J. Lee, K. McFarland, P. Renton and G. Veramendi.
Data: Run II, 448 pb^-1
Documentation: Public Note EPS, Talk at PHENO 2005 PDF, Talk at Fermilab Wine and Cheese PDF
Publication (submitted to PRL): hep-ex/0602045 (pdf)

Plots and Tables:

Highest Mass Event
	M_ee=470 GeV/c² GIF.
Background Distributions
	Dijet Invariant Mass (M_jj) Distribution EPS or GIF.
	Dijet cos(θ^*) Distribution for three mass ranges. EPS or GIF.
Data-Monte Carlo comparisons
	M_ee Distribution EPS or GIF.
	cos(θ^*) Distribution for three mass ranges. EPS or GIF.
	A_FB Distribution EPS or GIF.
	M_ee Distribution for the search region M_ee>200 GeV/c². EPS or GIF.
	cos(θ^*) Distribution for the search region M_ee>200 GeV/c². Note that the yellow band includes only the statistical uncertainty. There is also a 50% uncertainty on the background, which makes the left-most bin less significant. EPS or GIF.
Model Exclusions:
	Z' Exclusion plot for general U(1) model lines. We derive exclusion contours in the (x, M_Z') plane for different g_Z values of the strength of the coupling between the Z' boson and the Standard Model fermions. Current limits are compared with LEP. EPS, JPG or GIF.

*95% C.L. lower limits on sequential and canonical E6 models.*
Z' Model	Z'_SM	Z_χ	Z_ψ	Z_η	Z_I	Z_N	Z_sec
Expected Limit (GeV/c²)	860	735	725	745	650	710	675
Observed Limit (GeV/c²)	850	740	725	745	650	710	680

JPG or GIF.

*95% C.L. lower limits on the littlest Higgs Z' models.*
Z' Model	Z_H^0.3	Z_H^0.5	Z_H^0.7	Z_H^1.0
Expected Limit (GeV/c²)	625	765	835	910
Observed Limit (GeV/c²)	625	760	830	900

JPG or GIF.

*95% C.L. lower limits on contact interaction mass scales.*
Z' Model	LL	LR	RL	RR	VV	AA
Λ_qe⁺(TeV/c²)	3.7	4.7	4.5	3.9	5.6	7.8
Λ_qe^-(TeV/c²)	5.9	5.5	5.8	5.6	8.7	7.8

JPG or GIF.

Page was last updated Feb. 2nd, 2006 by Catalin Ciobanu.
Contact, Legal Notices, and Fermilab Policy on Computing