Patrizia an update on the search for gluino decays to bottom + sbottom. SUSY breaking due to Yukawa couplings would push all the third generation sparticles to (relatively) low mass. If the bottom squark were lighter than the gluino then the decay gluino -> sbottom bottom would dominate since the decay gluino -> stop top would be shut off by the large top mass even though the stop would be lighter than the sbottom. The sbottom would then decay to b LSP so that gluino pair production would lead to 4 b jets plus missing ET. The sensitivity of the search is very dependent on two mass differences:
delta_m = mgluino - msbottom
and
delta_m0 = msbottom - mLSP
If either is small then some of the b jets will be soft and will likely be lost.
They use 1B data from the Sum ET trigger. As a first selection they require:
In this sample, they are still completely background dominated, so they can use the data as a background sample to compare to signal MC in order to optimize a cut on MET. The optimal MET cut ranges from about 60 at large delta_m to about 100 at small delta_m. So, they require MET>60 for large delta_m and MET>100 for small delta_m. Next they look at delta_phi between the MET and the two leading jets. In the data the MET is, of course, dominantly back to back with the leading jet and aligned with the second jet (or vice versa). However, this is also common in the signal, especially at large delta_m. They cut events with delta_phi within 0.8 of jet1 or jet2 and within 0.8 of back to back with jet2 or jet1.
Next they select events with at least one SECVTX tag and no isolated leptons (to reduce top backgrounds). 55 events are found with MET>60 and 10 have MET>100.
They estimate the top background from MC with xsec=5pb to be 10.1 +- 0.5 for the MET>60 cut and 3.9 +- 0.3 for MET>100. The QCD background is estimated from the tag rate matrix to be 44+-4 for MET>60 and 5.6+-0.6 for MET>100 although Nicola said that they need to do more work to check on the tag rate predictions. The data is consistent with the sum of these two backgrounds.
The signal efficiency varies from about 10% to 20% depending on delta_m and the gluino mass. The number of expected events is large enough to exclude gluino masses up to roughly 240 GeV, although they have not yet calculated the limits.
Search for charged Higgs
in the e tau and mu tau channels
Michele Gallinaro, U.
of Pennsylvania
*** Blessing ***
Marcus Hohlmann and Michele Gallinaro have used the top tau dilepton
results to exclude charged Higgs for some regions of parameter space. For
large tan(beta) and mH < mt, top would decay to
Hb with H decaying to tau nu.
This search is motivated by arecent recent theoretical paper ( hep-ph/9610514
) that claims a larger sensitivity for CDF in the use of the pure
leptonic decays (both for the W and/or the H+) wrt the inclusive search
already published.
Marcus and Michele have then reinterpreted the top tau dilepton (e tau
and mu tau) results as limits for the charged Higgs production. 4 events
are observed with 1.1+-0.4 expected from SM top and 2.5+-0.4 expected from
background. This search has to be compared to :
The acceptance as a function of tan(beta) is evaluated as a function
of mH first and then is multiplied by the op branching ratio
and H->tau branching ratio which is calculated as a function of tan(beta).The
acceptance is ~1% for HH and ~0.75% for WH with mH=120 and drops
rapidly for mH>140.
From the 4 observed events and background estimates, they exclude values
of mH and tan(beta) predicting more than 7.1 events. The top
cross-section used is not fixed but is derived from the data (see Brendan) as
the one which keeps constant the observed lepton+jets events (minus background).
See CDF4295.
The result is to exclude charged Higgs for tan(beta) greater than about
80 and mH less than about 160. If they use the track based tau
id instead of calorimeter based, the limit degrades to tan(beta) > 200.
---> plot of the limit as a function of branching Ratio
---> plot of the limit as a function of tanbeta
To compare with the charged Higgs search which used hadronic tau
decays, they calculate a limit assuming a top cross section of 6.8/BR(top->WbWb)
and find that their excluded region is completely contained within the
previous limit. (N.B. This method of extracting a limit does not incorporate
the effect of the contamination from non-WW events (e.g. WH) on
the ttbar cross section and so is an optimistic limit. They used it just
to make an apples to apples comparison to the inclusive tau limit)
---> plot of the comparison of the two limits
They intend to write a PRD rapid communication on this analysis.
Discussion & Comments: it was pointed out that it
would be nice to have a single combined result from this check.
The facts are:
- it is a measurement in a complementary channel that stands by itself
..but...
- it is overall not competitive with the one already published
- the authors do not think combining is worth the effort
The result was blessed!
Search for new particles
in diphotons+X and the eeggMET event
Dave Toback, U. of
Chicago
*** PRE-Blessing ***
Dave Toback summarized the analysis for the search of new physics in
events with di-photons+X
The interest in exotic final states is not new to theorist and experimentalist,
but it surely received a new boost from the appearance of the eeggMET
event. This analysis and the limits obtained on some popular SUSY models,
a detailed description of the event and of its possible interpretation
have been written up in a PRL ---> NOTE: 2nd
draft out to the collaboration!!!!
All the documentation about this analysis can be found also at this link
Brief summary of the analysis: the idea is to select a diphoton sample defined keeping in mind that for our goal we are more interested in the efficiency than in the purity (15+/- 4%) . The selection requires 2 central (|eta|<1), isolated, ET>12 GeV photons (where the photons are identified with the cuts of the "photon treaty"). ID and Isolation efficiencies come from Z-->ee events
At this point we look for other "objects" in these events:
The MET resolution from the Z-->ee events describes well the observed spectrum, and the N(jet) distribution is well modeled by a exponential extrapolation ---> plots in the PRL format
Limits on SUSY models with gammagammaMET:
- model where the LSP is mostly Higgsino so that the favored decay
is : N2--->N1 gamma (use SPYTHIA for the acceptance, choose the model
parameters inspired by the eeggMET event kinematic)
This model predicts 2.4 events with two photons with ET(gamma)>12 GeV
and MET>35 GeV .
In the data we observe one event. No esclusion of this model is possible.
We have evaluated (for reference) a upper limit on the production
cross section for N2N2 of sigma (95%)=1.1pb.
- light gravitino scenario: the gravitino is the LSP so that
we always have at the end of the decay chain N1---> ~G gamma
The production of gammagamma events in this model are dominated by C1N2
and C1C1 production. The acceptances/cuts have been optimized for the scenario
of Babu et al. , so limits are set using ET(gamma)> 12 GeV and MET>35
GeV
--->
contour plot of the 95%CL limit in the M2 versus tanbeta plane
---> plot
of the 95%CL limit of the cross section versus C1 mass (PRL!): the
black line represents the results obatined for a specific "central"
value of tanbeta=5 and mu>0. The green area comes from the spread of
the 95%CL obtained spanning the parameter space between 1.01<tanbeta<25
and M2<200GeV/c^2 (for both signs of mu).
eegammagammaMET event (link to the OFFICIAL lego plot)