Diffraction in CDF: Run I results and plans for Run II Page: 3 of 6
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3 Hard diffraction using rapidity gaps
Using forward rapidy gaps to tag diffractive events, CDF measured the ratio
of SD to non-diffractve (ND) rates for W-boson 3, dijet 4, b-quark 5 and J/ 6
production at Vi = 1800 GeV, and using central gaps determined the frac-
tion of jet-gap-jet events as a function of Ejet and of rapidity gap separation
between the two jets (Atyet) at 'i= 630 and 1800 GeV.
Forward gaps were defined as no hits in one of the beam-beam counters,
BBC (3.2 < 171 < 5.9), and no towers with energy E > 1.5 GeV in the forward
calorimeters, FCAL (2.4 < 174 < 4.2). Using the POMPYT Monte Carlo (MC)
simulation with a flat gluon/quark Pomeron structure, the measured SD/ND
ratios were corrected for 'gap acceptance', defined as the ratio of diffractive
events with a gap to all diffractive events generated with - x=j < 0.1 in the
selected kinematical range of the hard scattering products.
For jet-gap-jet events, the gap was defined as no tracks or towers with
energy above ~ 300 MeV in the region 4qJ < 1. The ND background was
estimated using events with both jets at positive or negative q.
Table 1: Ratios of diffractive ( < 0.1) to non-diffractive rates.
Hard process v/s R = A (%) Kinematical region
W(-> ev)+G 1800 1.15 0.55 ET, $T > 20 GeV
Jet+Jet+G 1800 0.75 0.1 ETCt > 20 GeV, y1ct > 1.8
b(- e + X)+G 1800 0.62 0.25 flcI < 1.1, pT > 9.5 GeV
J/4(-> ILIL)+G 1800 1.45 0.25 ?7lI < 0.6, pT > 2 GeV
Jet-G-Jet 1800 1.13 0.16 ETCt > 20 GeV, y1t > 1.8
Jet-G-Jet 630 2.7 0.9 Et > 8 GeV, yet > 1.8
The results are summarized in Table 1. At yi=1800 GeV the DIFF/ALL
ratios are approximately equal. Since the processes under study have different
sensitivities to the quark and gluon content of the Pomeron, these results
indicate that the value of the gluon fraction in the Pomeron, f9, is not very
different from that in the proton. From the W, dijet and b-quark ratios,
f9 was determined to be 5 0.54+164. In addition, a suppression of a factor
D = 0.19 + 0.04 was found in these ratios relative to POMPYT predictions
using the standard Pomeron flux. This discrepancy indicates a breakdown of
factorization 5. The value of D is approximately the same as that in soft SD
(see Fig. 2), as predicted in Ref. 1.
The ratio of jet-gap-jet fractions at 's = 630 to 1800 GeV is 2.4 + 0.8.
The AOyet, E et and x-Bjorken distributions are consistent with being flat 9.
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Goulianos, K. Diffraction in CDF: Run I results and plans for Run II, article, July 20, 2001; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc720389/m1/3/: accessed September 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.