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:

- 2 prongs in the IR vertex with p > 300 MeV/c and P
_{}> 150 MeV/c (relative to the beam direction); _{copl}< 170°; 10° <_{coll}< 170°;- No post hits;
- (p
_{miss}+ p_{1}+ p_{2})/E_{cm}< 0.92 (to remove radiative QED events); - Total charge = 0.
- In addition, I require at least one prong to have either 0.5 < x < 0.92
(x = 2p/E
_{cm}) or 0.5 < x_{}< 0.92 (x_{}= , M_{}= 1.820 GeV/c^{2}), depending on the study.

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.