QCD MEETING
                        May  6, 1999 at 3 PM
                        Black Hole
 
Note that the video was cut off for most of the meeting so only a few of
the presentations scheduled were made. The ones with XXX's next to them
were not presented.
 
 
NEWS/ANNOUNCEMENTS
 
1.      General news and announcements/Run II news
 
        1.1     Run II
        -report from photon and weak boson working group        10  min
        -Run II jet clustering meeting to be held Friday May 7
        from 10 AM to 2 PM in the Snakepit
 
UPDATES
 
XXX2.      DPE dijets   Koji Terashi                            30 min
        Koji Terashi
 
 
3.      What have we been doing with the inclusive jets? Brenna Flaugher
                                                                20 min
 
 
PREBLESSING
 
4.      Central rapidity gaps in minimum bias events
        Mary Convery                                                             
30 min
        (see CDF note 4947)
 
XXX5.     Some differential dijet plots                          20 min
        Frank Chlebana
 
UPDATES(revisited)
 
XXX6.      Diffractive dijets at 1800 GeV                          30 min
        Kerstin Borras (note the time of presentation may depend
        on when the DESY videoconf room is available)
 
1. News/announcements
 
1.1 13 EPS abstracts submitted; see http://www.pa.msu.edu/~huston/eps_abstracts
 
1.2 Change of QCD meeting schedule
 
To emphasize the growing concentration of the
collaboration on Run II preparations, there is a proposal to have Thursdays
devoted to these topics with the physics meetings on Fridays.
The QCD meeting would be from 1-4 PM on Friday. This would take
place starting at the beginning of June.
 
Note that there is probably going to be a conflict for our first
meeting of this new schedule on June 4. That's also the time
of the Run 2 workshop meeting. We will probably be rescheduling the QCD
meeting, either to an off-week or to Wed of that week.
 
There may also be some restructuring of the physics groups with the QCD
group taking on more responsibility.
 
 
1.3     QCD Baby of the Week
 
hep-ex/8 lbs 0 ounces; Ali Ahmad Anwar Bhatti; authors: Shabnamad and
Anwar Bhatti
 
1.4     Run II news
 
As onset of blessings is mostly over and physics analyses are winding down,
we will be trying over the course of the rest of the year to step up
reviews of Run II triggers/software during the QCD meetings.
 
In 2 weeks John Mayer will be at the QCD meeting discussing the work in
Run 2 calorimeter reconstruction and jet algorithms.
 
If you have a student who can work on Run II QCD related issues (for example
on the Run II physics analysis debugging),  please contact Anwar and Joey.
 
If you could use  an Italian summer student for the same, please contact
Anwar and Joey.
 
 
Updates
 
3.      What have we been doing with the inclusive jets?        Brenna
 
        Brenna described the Inclusive Jet godparents decision about the
statistical comparison  between data and various PDF's. Godparents
have been meeting every two weeks since January and various variations
of the best fit technique have been tried.
 
     It was decided that
 
    a) analysis will use best-fit technique
    b) chi-sqr definition  is a slight variation on
       inclusive jet analysis has been using before.
 
    c) The statistical errors on the data will be used. GP had
       asked to use uncertainty on the theory prediction. Both give
       essentially same results.
 
    d) Evaluate total probability based on total chi-sqr and 33 DOF
       relative to standard curve (chi-sqr=43.68).
 
     Using these rules, the
     MRST1   (chisqr=47.61) is best, followed by
     CTEQ4HJ (       50.57)
     MRST3   (       52.64),
     MRST2   (       54.92).
 
     CTEQ3M and CTEQ4M are less likely.
 
    e) Quote statistical  chi-sqr separately.
 
    Godparents of three jet analysis (+interested parties) will meet
on Thursday June 3, to find a common technique for all three analysis.
 
 
Preblessing
 
4       Central rapidity gaps in minimum bias events    Mary.
 
        Mary Convery described the work she has done with Dino Goulianos
on extracting a soft double diffraction signal.
In Regge theory/phenomenology, in single diffraction in p-bar(p)
interactions, one of the interaction particles emits a "pomeron" and
dissociates. There is a rapidity gap between this cluster and p (p-bar).
In double diffraction, p and p-bar exchange a pomeron and both  dissociate,
resulting in two clusters of particles with a rapidity-gap in between.
Note that the same topology is observed in the jet-gap-jet events where
these clusters have a jet each. Soft-double diffraction study may also
help us understand the survival probability of in the jet-gap-jet events.
Gap generation in both (with or without jet) classes of events may have
the same physical origin.
 
        Mary used run 1A and 630 GeV minimum bias data with 0,1 vertex.
After all quality cuts she has 1021k events at 1800 GeV and
1670k events at 630 GeV.  Using a 2D plot of eta-max left and
eta-max right, the DD signal is clearly visible.
 
        To extract the DD cross section, she defines a gap to be a region
without any a track or a tower above threshold. The gap is required to
transverse the \eta=0 point. The analysis is done for
different gap size requirements and results are compared with
Regge predictions.  The measured rate is about factor of 10 lower
than the Regge prediction using standard pomeron flux and are
in reasonable agreement if renormalized flux is used. For example,
requiring gap>1.6 both on +/- eta side, the measured rate is
0.975\pm0.033 compared to 9.7^+2.5_-2.0 using standard flux and
0.72^+0.18_-0.15 using re-normalized flux.
 
         The main effort in the data analysis went into understanding the
detector response to low energy particles. Using Suren's low-energy
tower calibration (obtained using underlying event in Pythia ND events
for his diffractive W analysis) did not give a very good agreement in
eta-max distribution.  The data is
biased to lower eta values. This bias is attributed to inadequate simulation
of the shower-spreading and loss of particles in the cracks. Mary moved
the eta-max associated with a MC particle by +/-15 cm randomly to simulate
the shower-spreading in transverse direction. The eta-max selection will
always pick a tower close to \eta=0. The new distribution shows a better
agreement but it is still not perfect. A new set of eta-dependent
calibration constants were determined for the data already shifted in eta.
Using new constants, the data and the MC improved. The systematic
uncertainty of +/- 50% on the calibration constants used to evaluate
the change in the DD cross section.
 
  The analysis is described in detail in CDF-4947 and will
be presented for blessing in the next QCD meeting.