Soft Colour Interactions as the Origin of Rapidity Gaps in DIS

Abstract

We introduce soft colour interactions as a novel mechanism to understand the observed events with large rapidity gaps in $ep$ collisions at HERA. Colour exchanges between produced partons and colour-charges in the proton remnant modifies the colour structure for hadronization, such that colour singlet systems may appear well separated in rapidity. Our explicit model show characteristics of diffractive scattering, although no explicit pomeron dynamics have been introduced, and for non-gap events an increased forward energy flow gives agreement with data.

Figures (6)

• Figure 1: The string configuration in a DIS boson-gluon-fusion event: (a) conventional Lund string connection of partons, and (b,c) after reconnection due to soft colour interactions.
• Figure 2: Distribution of maximum pseudorapidity ($\eta_{max}$). Hadron level after colour reconnection with probability parameter $R$ for all events and those satisfying the 'gap' definition (full line).
• Figure 3: Distributions (in arbitrary units) for the selected rapidity gap events, i.e. with no energy in $\eta_{max}<\eta<6.6$ and $\eta_{max}<3.2$: (a) squared momentum transfer $t$ from incoming proton to remnant system $R$, for two widths $\sigma =0.44$ (full) and 1 GeV (dotted) of the gaussian primordial $k_\bot$ distribution compared with exponential slopes $1/\sigma^2$; (b,c) invariant mass of the forward remnant system $M_R$ and the produced central system $M_X$ (cf. Fig. 1)
• Figure 4: Distribution of maximum pseudorapidity $\eta_{max}$. (a) Partons from boson-gluon-fusion matrix element (BGFME) with cut-off $y_{cut}$, and hadrons (HAD) after parton showers and string hadronization without SCI. (b) Parton level (PS) and hadron level (HAD), after SCI, for different initial state parton shower cut-off values $Q_0^2$.
• Figure 5: Ratio of rapidity gap events, i.e. with no energy in $\eta_{max}<\eta<6.6$ and $\eta_{max}<3.2$, to all DIS events as function of $x$ and $Q^2$.