Model Independent Search for New Physics on a background of associated boson production

1
Model Independent Search for New Physics (on a
background of associated boson production)
Tim Cox, Abrar Shaukat, Aron Soha, Mani
Tripathi University of California,
Davis SUSY/BSM Review September 20, 2004
2
Associated Boson Production
Associated production of gauge bosons in the SM
is facilitated by t-channel processes as shown
here for an arbitrary pairing of bosons. For
allowed tri-boson couplings, s-channel processes
also exist. Studying precise production rates
for bosons is in itself an exercise of checking
the SM. However, in the SUSY context, it is
difficult to imagine gaugino pair production that
will not influence at least one gauge boson pair
production. Gravitino LSP models make
it necessary to consider photons as well. When
dealing with leptonic decay modes of W and Z
bosons, the contribution from final state
radiation (or, internal bremstrahung) becomes
important.
3
Example D0 Results from Run I data
Based on Z e-e channel and Z nn
invisible channel, D0 Run I data did not show
any significant excess in Zg final
state. There was one event at very high value
of transverse momentum that turned out to be
consistent with the expected background,
resulting in stricter limits on anomalous Zgg and
ZZg couplings.
4
CDF Run I excess in lgMET
In the first 86 pb-1 of data, CDF did a
comprehensive study of lepton gamma MET final
states. An excess in the muon gamma MET (11
events observed when 4.2-0.5 were expected)
raised the possibility of BSM physics. One
explanation consisted of R-parity violating
SUSY in a gravitino LSP scenario.
5
SUSY explanation for the excess
The explanation focuses on the coupling l211 and
resonant production of the smuon. The authors
arrive at this plot
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Preliminary Run 2 results from CDF

• From Fermi News a few weeks ago
• Inclusive lng and llg samples have no surprises.
• Any news on sub-samples with large MET is not yet
  available.

7
Lucs questions

• what is the topology under study
• which signal generator is used (any problems?)
• what are the specific problems of this analysis
  related to OSCAR, FAMOS, ORCA and which
  developments of this software will you contribute
  to
• which experimental results do you intend to
  provide, e.g. (E_T,eta) plot of efficiency,
  calibration, etc.
• A clear description of the "final results" of the
  analysis will be most useful.
• which are your most relevant background
  contributions, both from Standard Model processes
  and from new physics.
• Are these available and at the right order of
  radiative corrections (K-factors?)
• for which parameter values do you need (or will
  you make) full detector simulation
• which test statistic do you use for evidence of a
  discovery
• which systematics will be included
• will you (also) study the CMS reach (with FAMOS?)
• will you reconstruct new particle masses
• which are the Institutes and who are the people
  involved in this analysis (a rough estimate of
  the effort would be helpful)
• is this manpower sufficient to meet the schedule
  of the Physics TDR
• any other problems you have or are expected to
  encounter

8
Topology

• what is the topology under study
• which signal generator is used (any problems?)

The basic topology is lgMET. Additional leptons
may be included. The processes (backgrounds)
are mainly Wg and Zg. WZ, WW and ZZ will be
considered later. As a starting point, we are
using Pythia for mmg event generation. At the
moment this is achieved by turning on FSR in
inclusive Z events. We have some questions about
t-channel processes for other final states, but
no serious problems.
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Pythia Event Generation
10
Pythia Event Generation
Are these available and at the right order of
radiative corrections (K-factors?) The integral
above 10 GeV/c is about 64 pb. Compared to CDF
measurement of 2.5 pb for PT above 7 GeV/c,
this is reasonable. We have to be able to get
good estimates for cross section
after including the t-channel and other higher
order processes.
which experimental results do you intend to
provide, e.g. (E_T,eta) plot of efficiency,
calibration, etc. A clear description of the
"final results" of the analysis will be most
useful. Various efficiencies/acceptances. List
to be developed. The hard work will be on the
backgrounds which have a large overlap
with other studies.
11
Full ORCA reconstruction
We are using the Fermilab facilities for
simulation and reconstruction. This sample of
100K events took nearly one month of real-time
computing. Clearly, at this rate, we can not
study all the backgrounds required for this
process Sharing/overlap is essential.
12
Physics Effort at UCD

• Tim Cox has been involved with ORCA and PRS-MU
  for a long time and will continue in that mode.
  He is a valuable source of help for graduate
  students.
• John Smith and Richard Breedon have had a
  long-term association with CMSIM Detector
  geometry and MC sample generation.
• Mike Case has been involved with XML code and
  DDD. He also supports hardware issues with the
  local cluster at Davis.
• Max Chertok (previous talk) and his postdoc, Aron
  Soha are splitting time between CDF and CMS.
• John Conway and Robin Erbacher have joined the
  faculty this year. John will be involved with
  the Higgs effort fot the TDR while Robin will
  transition to CMS a couple of years later.
• We have recruited out first (expecting a CMS
  thesis) graduate student, Abrar Shaukat. This
  number should ramp up to 5 in the next year or
  two.
• In the past, we have involved several undergrads
  in the past to generate MC samples. A small army
  can be raised as the need arises.

13
Conclusions

• We need a large set of backgrounds with the
  lgMET topology. At the minimum
• Wg, Zg, WW, WZ, ZZ
• t-tbar
• Wb, Zb (with b-gte,m)
• Fakes Jet-gte,m and e-gtg (coupled with Wjet
  and Zjet)
• The goal for the TDR is to isolate the samples
  that are not being generated by some other group
  and then compile a full set of background
  estimates.