From:	FNALD::ALBROW       12-JAN-1998 09:36:41.21
To:	ALBROW TOBACK FRISCH
CC:	
Subj:	gamma gamma paper

 Dear Dave and Henry,
        I finally get to read the very nice gamma gamma paper. 

** Thank you

I just have the following little questions/comments:
(excuse me if answers are in notes, but readers will not have access to them)
1) p5 para 3. The fraction of events...two prompt photons... is measured to be
   15 +- 4%. How is that known, and what is the breakdown of the other 85%?

** A good question. We did not have space in the PRL to address this issue. This
   is discussed  in detail in  CDF Note 4183  (section 5) and  in the CDF photon
   literature. It is measured using the standard CES/CPR method developed by the
   photon group (see the references in  4183). The method estimates that ~52% of
   the events are such that both photon candidates are fakes (pizeros, etas etc)
   ~33%  which have  one real  photon,  the  rest (~15  percent)  are two photon
   events. 

2) next line: "We search the diphoton CANDIDATE events" as 85 % are not really.

** Fair enough. We think  that given the preceeding  lines this is fairly clear.
   For literary reasons we have left it as is.

3) p.6 you say "0 events with 3 or more jets, with 1.7 +- 1.5 expected.
  Something wrong here? (a) only 0.5 events are expected with 2 or more jets
so how can we have 1.7 with 3 or more? (b) table shows 0.1 +- 0.1 expected,
apparently for the same condition.

** There are the main  counting experiments with uses  all photons above 12 GeV.
   We also present results  for both photons above  25 GeV. For all photons with
   Et>12 GeV, we expect 1.6 events expected with 4 or more jets; 2 are observed.
   For two photons with Et>25 we expect 1.7 events with three or more jets, with
   zero observed. The table only discusses the full sample. 

4) Although we do not remark on it, the condition in Table 1 with 3 Obs
and 0.3 +- 0.1 expected is also rather unlikely. I did not convolute the
poisson with the gaussian on 0.3, but the poisson for 0.3 --> >= 3 is a
0.36% probability. 0.4 --> >= 3 is 0.79%.

** You are  correct that it  is a small  probability  for 0.3 to  fluctuate to 3
   events.  However, we do  comments  on this  rather  explicitly by telling the
   reader   that  these  are  very  clearly   Standard  Model   backgrounds. The
   backgrounds  are Wgamma  and Zgamma  (mostly  Zgamma),  there appears to be 2
   Zgamma events in our data. 0.3 fluctuating to 2 is not so bad. Futhermore, as
   pointed  out in the  CDF Notes,  when we  push the ET  threshold  to 25GeV we
   expect  0.2  event  (dominated  by  Zgamma  fakes) and  we  observe no Zgamma
   candidates  which look like  Zgamma (i.e,  only the eeggmet  event passes the
   lgammagamma cuts). So we have a fluctuation up and a fluctuation down. 

5) middle p.8 ...jets which fake electronS and/or ...

** Ooops. You are correct. Done.

6) p.8 last full para (my ignorance?) is the gravitino not considered to be a  
   neutralino?

** That is  correct.  The  neutralinos are  the  supersymmetric  partners on the
   neutral bosons (Z,gamma and neutral Higgs's).

7) All the credit for SPYTHIA is given in refs to Mrena. Is this right?

** The updated SPYTHIA reference contains only his name. It has the appropriate
   PYTHIA references within it.

                       Cheers, Mike