CDF Search based on ``Yet Another Extension of the Standard Model: Oases in the Desert?', (authors: J.D. Bjorken, S. Pakvasa, and S.F. Tuan)'


Sasha Paramonov, Collin Wolfe, Jason Tsui, Drew Fustin, Steve Levy, Carla Pilcher, Henry Frisch, with lots of help from Arjun Menon


Source: hep-ph/0206116


Brief General Introduction


This model has new heavy particles in the down sector: right-handed ewk-singlet down (D,S,B; generically called Q) quarks, and ewk-doublet heavy charged and neutral leptons (\nu_E, E, \nu_M, M, \nu_T, T; generically called N and L). The heavy down particles mix with the respective SM down sector. We have implemented this model within a copy of the program MadGraph.

MadGraph V3.0 outputs the helicities along with 4-vectors, an essential ingredient as the couplings depend strongly on the helicities. The Q (heavy quark) decays into W:Z,H (Higgs) in the approximate ratios of 2:1:1. We use Fabio Maltoni's Decay program to decay the W,Z, and Higgs to make the matrix element final files of partons. These are then run through the CDF reconstruction and simulation.

Nitty Gritty of the Model: Couplings of the Q, N, and L to A,W,Z, and H


Arjun Menon has translated the paper into currents so that we can read off the couplings for the MadGraph code. We've made a table of the couplings with the MadGraph conventions from Arjun's currents:

Couplings (Page 3 is the table; pp1,2 are the MadGraph conventions. Substance by Arjun Menon) .
.Tex file of Couplings .

Production


The following plots show the cross-sections for quark-pair and lepton pair production versus mass. The masses are unknown, but the paper suggests that the new down quarks may be two or three times more massive than the new leptons. Two other plots have been produced that scale the quark mass down by a factor of two or three in order to be able to directly compare the lepton cross-section with the quark cross-sections of quarks that are this factor more massive.

Plot of the cross-sections at pbar-p collisions at root-s=1.96 TeV for pair-production of leptons and quarks over a range of masses.

. Same plot, but with the quark masses scaled by one-half to allow comparison between the cross-sections of leptons with quarks that are twice as massive.

Same plot, but with the quark masses scaled by one-third to allow comparison between the cross-sections of leptons with quarks that are three times as massive.

Final State Sigma times BR's and Kinematics


The Decay package in MadGraph decays the secondary particles tracking the (all-important) helicities. This is still all at LO and parton level; the output files are the ones fed to Pythia, CDFSIM, CDF production, and ntupling. Pt, eta, and helicity distributions for the u-quark and the W- in QQ~ -> u u~ W- W+ production. For M_Q = 300 GeV, the total QQ crossection is 0.412 pb. The sigma times (BR)**2 for n QQ~ -> u u~ W- W+ is 0.103 pb.
Note that the longitudinal W's completely dominate at this mass (was much more evenly distributed at M_Q= 175 GeV). Note also the high-Pt W's.

Plots of Pt, eta, and helicity distributions for the quarks and W's in QQ~ -> u u~ W- W for M_Q=300 GeV.

Plots of Pt, eta, and helicity distributions for the secondaries from the W decays in QQ~ -> u u~ W- W for M_Q=300 GeV.

The two scatter plots correspond to plots of the Pt of the e+ from W+ decay vs the Pt of the e- from W- decay (first plot), or the pt's of the nu vs nubar, but summed over all decay modes of the two W's for statistics. One can see that the I=+1/2 plot seems to have softer Pt spectra.

Last updated Feb 6, 2005; HJF