Twenty years of diffraction at the Tevatron Page: 2 of 6
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1 Run-I Results
In addition to measuring pp elastic, single diffraction (SD), and total cross sections at Vs- = 540
and 1800 GeV, CDF studied several soft and hard diffraction processes at \Fs = 1800 GeV, and
in some cases at V- = 630 GeV 4. Soft processes studied include:
DD Double Diffraction pp - X + gap + Y
DPE Double Pomeron Exchange pp p p + gap + X + gap + p
SDD Single e Double Diffraction pp -3 p + gap + X + gap + Y
In the area of hard diffraction, CDF measured SD dijet, W, b-quark and J/, production,
DD dijet production, and DPE dijet production. Schematic diagrams and event topologies for
representative diffractive processes studied in Run-I are shown in Fig. 1.
N S In I ID I D I I I D
ND SD DD DPE SDD
9 Gap t t
$ Jet Gap et
$ Gap Jet+Jet Gap
Figure 1: Schematic diagrams and 17-0 topologies of representative diffractive processes studied by CDF in Run-I.
The shaded areas represent regions of pseudorapidity in which there is particle production.
Two types of hard diffraction results were obtained in Run-I: diffractive to non-diffractive
cross section ratios, using the rapidity gap signature to select diffractive events, and diffractive
to non-diffractive structure function ratios, using a Roman Pot Spectrometer (RPS) to trigger
on leading antiprotons (see Fig. 2, left).
DIPOLE MAGNETS p CDFJ
at 57 m
x<0.97 Scintillator fiber xy-tracker
270 p pitch, 2 m lever arm
X=1 ( Acceptance: 0 < It < 1, 0.03<4 < 0.1
D P MINIPLUG
ROMAN A-48 U
POTS [D[POLE UFS QU[U
I I I
I I I
z - 56.40 m 31.63 m 23.23 m
BSC-4 BSC-3 BSC-2
Figure 2: Layout of the CDF detector in Run-I (left) and in Run-II (right), showing the special forward detectors
used in the diffractive program.
The Run-I diffractive production results exhibit regularities in normalization and factor-
ization properties pointing to the QCD character of diffraction. The result that has attracted
the most attention is the breakdown of QCD factorization, indicated by an ~ 0(10) suppres-
sion in normalization of the diffractive structure function (DSF) measured from diffractive dijet
production at the Tevatron relative to that measured from diffractive deep inelastic scattering
(DDIS) at HERA. However, less attention has been paid to the remarkable s-independence of
the do.SD/dM2 diffractive differential cross section, a scaling property that seems to regulate the
magnitude of the breakdown of factorization. This "M2-scaling" behavior has profound impli-
cations about the mechanism of diffraction, favoring a composite over a particle-like Pomeron,
as discussed in Ref. 4 and in original references therein.
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Goulianos, K. & U., /Rockefeller. Twenty years of diffraction at the Tevatron, article, October 1, 2005; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc874143/m1/2/: accessed October 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.