Extending the study of the Higgs sector at the LHC by proton tagging

TL;DR

This paper argues that forward proton tagging and central exclusive diffractive production at the LHC can substantially expand Higgs-sector discovery and characterization, especially within the MSSM. By exploiting the $pp\to p+\phi+p$ mechanism, it demonstrates enhanced sensitivity in the intense-coupling regime and continued reach in the decoupling limit, while addressing challenging wedge regions where conventional searches struggle. The authors develop a detailed calculation framework for the $0^+$ and $0^-$ cross sections, quantify key uncertainties, and provide simplified formulae for rapid signal-background estimates. They also discuss how CEDP can help identify CP properties, measure widths, and discriminate between $H$, $h$, and $A$, including strategies for observing the pseudoscalar $A$ through semi-exclusive and inclusive diffractive channels. Overall, forward proton tagging emerges as a powerful, complementary tool that extends the LHC’s Higgs-program reach and enables unique tests of Higgs dynamics and CP structure.

Abstract

We show that forward proton tagging may significantly enlarge the potential of studying the Higgs sector at the LHC. We concentrate on Higgs production via central exclusive diffractive processes (CEDP). Particular attention is paid to regions in the MSSM parameter space where the partial width of the Higgs boson decay into two gluons much exceeds the SM case; here the CEDP are found to have special advantages.

Figures (5)

• Figure 1: The cross sections, times the appropriate ${b\bar{b}}$ and $\tau^+\tau^-$ branching fractions, predicted for central exclusive diffractive production of $h(0^+)$, $H(0^+)$ and $A(0^-)$ MSSM Higgs bosons (for $\tan\beta=30$ and 50) at the LHC, obtained using the MRST99 MRST99 gluon distribution. The dotted curve in the upper plots shows the cross section for the production of a SM Higgs boson. The vertical line separates the mass regime of light $h(0^+)$ and heavy $H(0^+)$ bosons. The curves were computed using version 3.0 of the HDECAY code HDEC, with all other parameters taken from Table 2 of HDEC; the radiative corrections were included according to Ref. HHW.
• Figure 2: The cross sections for the central exclusive diffractive production of $h$ and $H$ bosons, $pp\to p + (h,H) + p$, times the appropriate ${b\bar{b}}$ branching fraction, as a function of their mass, in two regions of MSSM parameter space where observation of the $H$ using non-diffractive processes is difficult. Note that in the first region the curve changes from dotted to continuous when the mass of the $A(0^-)$ bosons reaches 200 GeV; and that the value of $m_h$ is practically unchanged for values of $m_A$ in the region $m_A>200$ GeV.
• Figure 3: The upper plots show the differences $\Delta M = m_A - m_h$ (continuous curve) and $\Delta M = m_H-m_A$ (dashed curve) as a function of $m_A$ for $\tan\beta = 30$ and 50 respectively. The lower plots show the total widths of the MSSM neutral high bosons.
• Figure 4: The mass bands $m_\phi \pm \Gamma$ for neutral MSSM Higgs bosons as a function of $m_A$, for different values of $\tan\beta$. A vertical slice through these plots, at a given value of $m_A$, indicates the position of the MSSM resonance Higgs peaks. The upper right hand plot shows that the $h$ and $H$ bosons are clearly identifiable for $\tan\beta=30$, if $A(0^-)$ production is suppressed. The lower plots show how the sensitivity of the widths, to variations of $\tan\beta$, will change the profile of the peaks. This way of presentation was motivated by Ref. BDN. Note that the widths of the bosons for $\tan\beta$ less than about 15 become barely visible on this type of plot.
• Figure 5: (a) The QCD diagram for double-diffractive exclusive production of a Higgs boson $h$, $pp\to p + h + p$, where the gluons of the hard subprocess $gg\to h$ are colour screened by the second $t$-channel gluon. (b) The rescattering or absorptive corrections to $pp\to p + h + p$, where the shaded region represents the soft $pp$ rescattering corrections, leading to the suppression factor $S^2$.