Probing Hard Color-Singlet Exchange in ppbar Collisions at root-s=630 GeV and 1800 GeV

Abstract

We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at root-s = 630 GeV and 1800 GeV using the DZero 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.

Figures (6)

• Figure 1: Jet characteristics of the 630-OS (solid line) and 1800-OS (dashed line) data samples. The normalized distributions are shown for (a) the average $E_T$, (b) $\Delta\eta$, and (c) $\bar{x}$ of the two leading jets.
• Figure 2: Multiplicity in the region $|\eta|\!<\!1$ between the two leading jets for the high-$E_T$ sample: (a) two-dimensional multiplicity, $n_{\rm{cal}}$ vs. $n_{\rm{trk}}$; (b) $n_{\rm{cal}}$ only with NBD fit.
• Figure 3: Two-dimensional multiplicity ($n_{\rm{cal}}$ vs. $n_{\rm{trk}}$) in the region $|\eta|\!<\!1$ for the (a) 1800-OS and (b) 630-OS samples.
• Figure 4: The color-singlet fraction $f_S^{(2D)}$: (a) as a function of the second leading jet $E_T$; as a function of $\Delta\eta$ between the two leading jets for (b) the low-$E_T$ sample and (c) the high-$E_T$ sample; (d) as a function of $\bar{x}$ for each $\Delta\eta$ bin in (b) and (c). The horizontal error bar on the first $\bar{x}$ bin shows the $1\sigma$ spread in $\bar{x}$ values entering that (representative) bin. Statistical error bars and relative normalization uncertainties for each sample (hatched bands) are shown.
• Figure 5: Fits of Monte Carlo models to the color-singlet fraction (a) $f_S^{(2D)}(E_T)$ and (b)--(c) $f_S^{(2D)}(\Delta\eta)$ for the low-$E_T$ sample and the high-$E_T$ sample, respectively. Shown are comparisons to BFKL jet level (solid line), BFKL $2\!\rightarrow\!2$ parton level (dashed line), photon (dot-dashed line), and U(1) (dotted line) models.