Probing Hard Color-Singlet Exchange in Proton-Antiproton
           Collisions at sqrt(s) = 630 GeV and 1800 GeV
    
  
  

    
Probing Hard Color-Singlet Exchange in Proton-Antiproton Collisions at sqrt(s) = 630 GeV and 1800 GeV
Contact Person: Andrew Brandt

The exchange of a quark or gluon between interacting partons in hadronic collisions typically results in final-state particle production over several units of rapidity. In contrast, the exchange of a color-singlet is expected to yield a rapidity gap, defined as the absence of particles in a region of rapidity (or pseudorapidity) The observation of rapidity gaps between jets at both Fermilab in proton-antiproton collsions and DESY in proton-electron collisions implies the exchange of a hard color-singlet. The measured fraction of dijet events arising from color-singlet exchange is roughly 1% in proton-antiproton collisions and 10% in positron-proton collisions. These rates are too large to be explained by electroweak boson exchange and indicate a strong-interaction process.

We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at center-of-mass energies of 630 GeV and 1800 GeV using the DØ detector. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, separation in pseudorapidity between the two highest transverse energy jets, and proton-antiproton center-of-mass energy. The results are consistent with a color-singlet fraction that increases with an increasing fraction of quark-initiated processes and inconsistent with two-gluon models for the hard color-singlet.

Paper: Physics Letters B 440 189 (1998) (Download here).
Figures From Paper:

Fig. 1: (top left) Jet characteristics of the 630 GeV opposite-side jet data sample (solid line) and 1800 GeV opposite-side sample (dashed line). The normalized distributions are shown for (a) the average ET, (b) Dh, and (c) average x of the two leading jets. (eps file)
Fig. 2: (top middle) Multiplicity in the region |h|<1 between the two leading jets for the high-ET sample: (a) two-dimensional multiplicity: number of calorimeter towers (ncal) vs. number of tracks (ntrk) (b) ncalonly with Negative Binomial fit. (eps file)
Fig. 3: (top right) Two-dimensional multiplicity ncal vs. ntrk in the region |h|<1 for the (a) 1800-OS and (b) 630-OS samples. (eps file)
Fig. 4: (bottom left) The color-singlet fraction: (a) as a function of the second leading jet ET; as a function of Dh between the two leading jets for (b) the low-ET sample and (c) the high-ET sample; (d) as a function of average x for each Dh bin in (b) and (c). Statistical error bars and relative normalization uncertainties for each sample (hatched bands) are shown. (eps file)
Fig. 5: (bottom middle) Fits of Monte Carlo models to the color-singlet fraction (a) as a function of ET and (b)--(c) Dh for the low-ET sample and the high-ET sample, respectively. Shown are comparisons to BFKL jet level (solid line), BFKL parton level (dashed line), photon (dot-dashed line), and U(1) (dotted line) models. (eps file)
Fig. 6: (bottom right Fits of Monte Carlo models to the color-singlet fraction (a) as a function of ET and (b)--(c) Dh for the low-ET sample and the high-ET sample, respectively. Shown are comparison to free-factor (solid line), soft-color (dashed line), single-gluon (dotted line), and simple two-gluon (dot-dashed line) models. (eps file)

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Last modified: Tue Dec 15 15:18:53 CST 1998