Date: 7 March, 1978
To: SP26, SP28 Physicists
From: G. Hanson
Subject: Does tau pi + nu(tau)?

The Data Sample

I have been looking at SP17 two-prong data with a high-momentum leading particle. The basic cuts are the following:

  1. 2 prongs in the IR vertex with p > 300 MeV/c and P > 150 MeV/c (relative to the beam direction);
  2. copl < 170°; 10° < coll < 170°;
  3. No post hits;
  4. (pmiss + p1 + p2)/Ecm < 0.92 (to remove radiative QED events);
  5. Total charge = 0.
  6. In addition, I require at least one prong to have either 0.5 < x < 0.92 (x = 2p/Ecm) or 0.5 < x < 0.92 (x = , M = 1.820 GeV/c2), depending on the study.
The main data sample is all data with Ecm > 6.0 GeV.

It is clear that there is an excess of such 2-prong events with low NXSHW (0, 1, and 2) over what would be expected from "old" physics. The NXSHW distribution is shown in Figure 1 and compared with a jet model Monte Carlo which is normalized to give the correct number of 3-prong hadron events. The Monte Carlo predicts about the right number of events for NXSHW 3. Charm production contributes very little to the 2-prong, NXSHW = 0 sample because (1) it is difficult to produce both low charged and low neutral multiplicity with charm and (2) charm production does not include many events with x > 0.5. (I have done some Monte Carlo studies of high energy charm production.) These low NXSHW 2-prong events, then, are almost certainly due to +- production, unless there is a third type of "new" physics. Such events are, of course, expected assuming the usual models of decay. I therefore concentrate on the 2-prong, NXSHW = 0 sample as a source of events which are mainly due to +- production and decay.

Figure 3