Gaps between jets at hadron colliders in the next-to-leading BFKL framework

TL;DR

Addressing hard diffractive jet-gap-jet events, the paper tests BFKL dynamics at next-to-leading logarithmic accuracy in hadron collisions. It implements the Mueller-Tang prescription to couple the BFKL Pomeron to colored partons and uses renormalization-group improved NLL kernels to compute the gg→gg amplitude, comparing to Tevatron data and providing LHC predictions. The NLL-BFKL framework describes the data without requiring extra normalization, whereas LL needs fixed coupling to fit; non-zero conformal spins contribute non-negligibly in certain kinematic regions. The results support the relevance of BFKL dynamics in jet-gap-jet production and offer concrete, testable measurements at the LHC.

Abstract

We investigate diffractive events in hadron-hadron collisions, in which two jets are produced and separated by a large rapidity gap. In perturbative QCD, the hard color-singlet object exchanged in the t-channel, and responsible for the rapidity gap, is the Balitsky-Fadin-Kuraev-Lipatov (BFKL) Pomeron. We perform a phenomenological study including the corrections due to next-to-leading logarithms (NLL). Using a renormalisation-group improved NLL kernel, we show that the BFKL predictions are in good agreement with the Tevatron data, and present predictions which could be tested at the LHC.

Figures (9)

• Figure 1: Production of two jets separated by a large rapidity gap in a hadron-hadron collision. The kinematic variables of the problem are displayed. $s$ is the total energy squared of the collision, $p_T$ ($\eta_1$) and $-p_T$ ($\eta_2$) are the transverse momenta (rapidities) of the jets and $x_1$ and $x_2$ are their longitudinal momentum fraction with respect to the incident hadrons. $\Delta\eta$ is the size of rapidity gap between the jets.
• Figure 2: Ratio between the conformal-spin components $p=0$, 1, 2, 3 and 4, and the total BFKL cross section at LL and NLL accuracy. Left plot: as a function of $E_T$ for $\Delta \eta >4;$ center plot: as a function $\Delta\eta$ for the second leading jet with $15<E_T<25\ \hbox{GeV};$ right plot: as a function $\Delta\eta$ for the second leading jet with $E_T > 30\ \hbox{GeV}.$
• Figure 3: Left plots: LL- and NLL-BFKL cross sections as a function of the momentum transfer $E_T$ (upper plot) and the rapidity gap $\Delta\eta$ (lower plots, $15<E_T<25\ \hbox{GeV}$ and $E_T>30 \ \hbox{GeV}$); we also give the cross sections when only the conformal spin component $p=0$ is included. Right plots: ratio of the NLL- and LL-BFKL calculations. Since both normalizations have been adjusted to reproduce the data, the ratios are close to 1.
• Figure 4: Scale dependence uncertainty of the BFKL NLL calculations. The scale uncertainty is evaluated by modifying the $E_T^2$ scale used by default to $E_T^2/2$ or $2 E_T^2$. The effect of the scale uncertainty is of the order of 10-15%.
• Figure 5: Comparison between the D0 measurement of the jet-gap-jet event ratio with the NLL- and LL-BFKL calculations. The NLL calculation is in good agreement with the data, without the need to adjust the normalization. The LL calculation gives also a good description of the data after its normalization has been adjusted, although the fit shows that the NLL description is better.