Yet Another Extension of the Standard Model: Oases in the Desert?


J.D. Bjorken, S. Pakvasa, and S.F. Tuan


Source: hep-ph/0206116


Some of us here in the CDF collaboration at the University of Chicago have started looking for particles created in the model described by the above paper in Tevatron data. In doing so, we are initially attempting to implement this model within the program MadGraph.

Using MadGraph to simulate the production and decay of the new particles predicted in this model, we found the cross-sections listed in the tables below. In each case, there are approximately 10,000 unweighted events. In these tables, d4 is the new heavy down quark proposed by the model, while u is the Standard Model up quark, d is the Standard Model down quark, W is the W boson, Z is the Z boson, h is the higgs, and a ~ following a particles indicated that it is an anti-particle. Processes are denoted in the following way: the final state particles are written to the right of the last carat. Their parents are written before this carat, and so on.

For a d4 mass of 200 GeV, it was found that its width was 1.0495 GeV. The couplings of the d4 to the W, Z, and h were set so to ensure that the decay of the d4 into these particles was in the proportion 2:1:T, respectively. To compute T, take the ratio of Higgs mass to heavy quark mass, and square it. Subtract this from one and square the result to get T. In these calculations, the higgs mass was set to 160 GeV. If you have an account on the HEP computers here at Chicago, you can find the Madgraph folders for these processes at /cdf/data47c/dafustin/.

ProcessCross-Section
p p~ > d4 d4~3264.916 +/- 9.676 fb
p p~ > d4 d4~ > u W- u~ W+1298.630 +/- 4.817 fb
p p~ > d4 d4~ > d Z d~ Z326.508 +/- 1.107 fb
p p~ > d4 d4~ > u W- d~ Z647.126 +/- 2.371 fb
p p~ > d4 d4~ > d Z u~ W+649.834 +/- 2.406 fb
p p~ > d4 d4~ > u W- d~ h82.351 +/- 0.256 fb
p p~ > d4 d4~ > d h u~ W+83.384 +/- 0.274 fb


For a d4 mass of 320 GeV, it was found that its width was 5.359 GeV. The couplings were also set to ensure a W:Z:h ratio of 2:1:T.

ProcessCross-Section
p p~ > d4 d4~210.427 +/- 0.695 fb
p p~ > d4 d4~ > u W- u~ W+64.270 +/- 0.415 fb
p p~ > d4 d4~ > d Z d~ Z17.445 +/- 0.107 fb
p p~ > d4 d4~ > u W- d~ Z33.517 +/- 0.227 fb
p p~ > d4 d4~ > d Z u~ W+33.691 +/- 0.306 fb
p p~ > d4 d4~ > u W- d~ h18.562 +/- 0.086 fb
p p~ > d4 d4~ > d h u~ W+18.583 +/- 0.081 fb


Also, in being curious as to which particles would be the most suitable to look for, we have created a plot that compares the cross-section of lepton pair-production versus mass with the cross-section of quark pair-production versus mass. Since the model suggests that the new down quarks would be perhaps 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.

Here is the plot of the cross-sections for pair-production of leptons and quarks over a range of masses.

Here is the 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.

Here is the 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.