3,383 research outputs found
Experimental Studies of Diffractive Processes at the Tevatron
We review the diffractive measurements made by the CDF and D\O\
collaborations during Run I at the Tevatron and summarize the detector upgrades
relevant for the Run II diffractive physics program.Comment: 6 pages, 2 figures (in eps) talk given at XXXI International
Symposium on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL
http://ismd31.ccnu.edu.cn
Reference priors for high energy physics
Bayesian inferences in high energy physics often use uniform prior
distributions for parameters about which little or no information is available
before data are collected. The resulting posterior distributions are therefore
sensitive to the choice of parametrization for the problem and may even be
improper if this choice is not carefully considered. Here we describe an
extensively tested methodology, known as reference analysis, which allows one
to construct parametrization-invariant priors that embody the notion of minimal
informativeness in a mathematically well-defined sense. We apply this
methodology to general cross section measurements and show that it yields
sensible results. A recent measurement of the single top quark cross section
illustrates the relevant techniques in a realistic situation
Trial factors for the look elsewhere effect in high energy physics
When searching for a new resonance somewhere in a possible mass range, the
significance of observing a local excess of events must take into account the
probability of observing such an excess anywhere in the range. This is the so
called "look elsewhere effect". The effect can be quantified in terms of a
trial factor, which is the ratio between the probability of observing the
excess at some fixed mass point, to the probability of observing it anywhere in
the range. We propose a simple and fast procedure for estimating the trial
factor, based on earlier results by Davies. We show that asymptotically, the
trial factor grows linearly with the (fixed mass) significance
Fine-tuning implications for complementary dark matter and LHC SUSY searches
The requirement that SUSY should solve the hierarchy problem without undue
fine-tuning imposes severe constraints on the new supersymmetric states. With
the MSSM spectrum and soft SUSY breaking originating from universal scalar and
gaugino masses at the Grand Unification scale, we show that the low-fine-tuned
regions fall into two classes that will require complementary collider and dark
matter searches to explore in the near future. The first class has relatively
light gluinos or squarks which should be found by the LHC in its first run. We
identify the multijet plus E_T^miss signal as the optimal channel and determine
the discovery potential in the first run. The second class has heavier gluinos
and squarks but the LSP has a significant Higgsino component and should be seen
by the next generation of direct dark matter detection experiments. The
combined information from the 7 TeV LHC run and the next generation of direct
detection experiments can test almost all of the CMSSM parameter space
consistent with dark matter and EW constraints, corresponding to a fine-tuning
not worse than 1:100. To cover the complete low-fine-tuned region by SUSY
searches at the LHC will require running at the full 14 TeV CM energy; in
addition it may be tested indirectly by Higgs searches covering the mass range
below 120 GeV.Comment: References added. Version accepted for publication in JHE
Measurement of Dijet Angular Distributions at CDF
We have used 106 pb^-1 of data collected in proton-antiproton collisions at
sqrt(s)=1.8 TeV by the Collider Detector at Fermilab to measure jet angular
distributions in events with two jets in the final state. The angular
distributions agree with next to leading order (NLO) predictions of Quantum
Chromodynamics (QCD) in all dijet invariant mass regions. The data exclude at
95% confidence level (CL) a model of quark substructure in which only up and
down quarks are composite and the contact interaction scale is Lambda_ud(+) <
1.6 TeV or Lambda_ud(-) < 1.4 TeV. For a model in which all quarks are
composite the excluded regions are Lambda(+) < 1.8 TeV and Lambda(-) < 1. 6
TeV.Comment: 16 pages, 2 figures, 2 tables, LaTex, using epsf.sty. Submitted to
Physical Review Letters on September 17, 1996. Postscript file of full paper
available at http://www-cdf.fnal.gov/physics/pub96/cdf3773_dijet_angle_prl.p
Search for charged Higgs decays of the top quark using hadronic tau decays
We present the result of a search for charged Higgs decays of the top quark,
produced in collisions at 1.8 TeV. When the charged
Higgs is heavy and decays to a tau lepton, which subsequently decays
hadronically, the resulting events have a unique signature: large missing
transverse energy and the low-charged-multiplicity tau. Data collected in the
period 1992-1993 at the Collider Detector at Fermilab, corresponding to
18.70.7~pb, exclude new regions of combined top quark and charged
Higgs mass, in extensions to the standard model with two Higgs doublets.Comment: uuencoded, gzipped tar file of LaTeX and 6 Postscript figures; 11 pp;
submitted to Phys. Rev.
Search for Chargino-Neutralino Associated Production at the Fermilab Tevatron Collider
We have searched in collisions at = 1.8 TeV for events
with three charged leptons and missing transverse energy. In the Minimal
Supersymmetric Standard Model, we expect trilepton events from
chargino-neutralino (\chione \chitwo) pair production, with subsequent decay
into leptons. We observe no candidate , ,
or events in 106 pb integrated
luminosity. We present limits on the sum of the branching ratios times cross
section for the four channels: \sigma_{\chione\chitwo}\cdot
BR(\chione\chitwo\to 3\ell+X) 81.5 \mgev\sp and
M_\chitwo > 82.2 \mgev\sp for , ~\mgev\sp and
M_\squark= M_\gluino.Comment: 9 pages and 3 figure
Inclusive jet cross section in collisions at TeV
The inclusive jet differential cross section has been measured for jet
transverse energies, , from 15 to 440 GeV, in the pseudorapidity region
0.10.7. The results are based on 19.5 pb of data
collected by the CDF collaboration at the Fermilab Tevatron collider. The data
are compared with QCD predictions for various sets of parton distribution
functions. The cross section for jets with GeV is significantly
higher than current predictions based on O() perturbative QCD
calculations. Various possible explanations for the high- excess are
discussed.Comment: 8 pages with 2 eps uu-encoded figures Submitted to Physical Review
Letter
Measurement of the lepton charge asymmetry in W-boson decays produced in p-pbar collisions
We describe a measurement of the charge asymmetry of leptons from W boson
decays in the rapidity range 0 enu, munu events from
110+/-7 pb^{-1}of data collected by the CDF detector during 1992-95. The
asymmetry data constrain the ratio of d and u quark momentum distributions in
the proton over the x range of 0.006 to 0.34 at Q2 \approx M_W^2. The asymmetry
predictions that use parton distribution functions obtained from previously
published CDF data in the central rapidity region (0.0<|y_l|<1.1) do not agree
with the new data in the large rapidity region (|y_l|>1.1).Comment: 13 pages, 3 tables, 1 figur
Search for New Particles Decaying to Dijets at CDF
We have used 106 pb^-1 of data collected with the Collider Detector at
Fermilab to search for new particles decaying to dijets. We exclude at the 95%
confidence level models containing the following new particles: axigluons and
flavor universal colorons with mass between 200 and 980 GeV/c, excited quarks
with mass between 80 and 570 GeV/c^2 and between 580 and 760 GeV/c^2, color
octet technirhos with mass between 260 and 480 GeV/c^2, W' bosons with mass
between 300 and 420 GeV/c^2, and E_6 diquarks with mass between 290 and 420
GeV/c^2.Comment: 18 pages, 4 figures, 1 table. Submitted to Physical Review D Rapid
Communications. Postscript file of paper is also available at
http://www-cdf.fnal.gov/physics/pub97/cdf3276_dijet_search_prd_rc.p
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