The origin of thermal component in the transverse momentum spectra in high energy hadronic processes

TL;DR

This paper proposes that the thermal component in high energy hadronic transverse momentum spectra originates from an event horizon linked to confinement, explaining its dependence on event structure and correlating its slope with saturation momentum.

Contribution

It introduces a novel interpretation of the thermal component as an effect of confinement-related horizons, connecting it to the saturation momentum and event topology in high energy collisions.

Findings

Thermal component absent in diffractive events with rapidity gaps.

Slope of the thermal spectrum correlates with saturation momentum.

Data supports the link between thermal slope and saturation momentum.

Abstract

The transverse momentum spectra of hadrons produced in high energy collisions can be decomposed into two components: the exponential ("thermal") and the power ("hard") ones. Recently, the H1 Collaboration has discovered that the relative strength of these two components in Deep Inelastic Scattering depends drastically upon the global structure of the event - namely, the exponential component is absent in the diffractive events characterized by a rapidity gap. We discuss the possible origin of this effect, and speculate that it is linked to confinement. Specifically, we argue that the thermal component is due to the effective event horizon introduced by the confining string, in analogy to the Hawking-Unruh effect. In diffractive events, the $t$-channel exchange is color-singlet and there is no fragmenting string -- so the thermal component is absent. The slope of the soft component of the hadron spectrum in this picture is determined by the saturation momentum that drives the deceleration in the color field, and thus the Hawking-Unruh temperature. We analyze the data on non-diffractive $pp$ collisions and find that the slope of the thermal component of the hadron spectrum is indeed proportional to the saturation momentum.