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A new window at the LHC: BSM signals using tagged protons

V. A. Khoze, A. D. Martin, M. G. Ryskin, A. G. Shuvaev

TL;DR

This work proposes using forward-proton tagging to convert LHC collisions into a semi-inclusive Pomeron-Pomeron (or $\gamma\gamma$) collider, enabling the measurement of missing 4-momentum $\not{P}$ and rapidity gaps to suppress backgrounds for BSM signals. It argues that semi-inclusive processes can outperform central exclusive production by allowing softer radiation while maintaining hermetic central detection, and it develops cross sections for semi-inclusive production of pseudoscalars and MSSM neutral Higgses. The paper provides concrete examples: an invisible Higgs scenario with sizeable cross sections and manageable backgrounds, accessible pseudoscalar production in MSSM, and the possibility of discovering light pseudo-Goldstone bosons via distinctive jet-structure signatures. These results suggest forward-proton detectors could offer a practical new window for BSM searches at the LHC, complementing inclusive strategies.

Abstract

The signature at the LHC of many Beyond the Standard Model (BSM) scenarios is events with large missing energy. If the forward outgoing protons are measured, we show that the production and decay of BSM particles in the central rapidity interval, with gaps in rapidity either side, offers certain advantages over inclusive production, to search for signals (a) with missing longitudinal 4-momentum (typical of invisible Higgs production), and (b) for new light pseudoscalar bosons.

A new window at the LHC: BSM signals using tagged protons

TL;DR

This work proposes using forward-proton tagging to convert LHC collisions into a semi-inclusive Pomeron-Pomeron (or ) collider, enabling the measurement of missing 4-momentum and rapidity gaps to suppress backgrounds for BSM signals. It argues that semi-inclusive processes can outperform central exclusive production by allowing softer radiation while maintaining hermetic central detection, and it develops cross sections for semi-inclusive production of pseudoscalars and MSSM neutral Higgses. The paper provides concrete examples: an invisible Higgs scenario with sizeable cross sections and manageable backgrounds, accessible pseudoscalar production in MSSM, and the possibility of discovering light pseudo-Goldstone bosons via distinctive jet-structure signatures. These results suggest forward-proton detectors could offer a practical new window for BSM searches at the LHC, complementing inclusive strategies.

Abstract

The signature at the LHC of many Beyond the Standard Model (BSM) scenarios is events with large missing energy. If the forward outgoing protons are measured, we show that the production and decay of BSM particles in the central rapidity interval, with gaps in rapidity either side, offers certain advantages over inclusive production, to search for signals (a) with missing longitudinal 4-momentum (typical of invisible Higgs production), and (b) for new light pseudoscalar bosons.

Paper Structure

This paper contains 7 sections, 17 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Advantages of semi-inclusive processes
  3. Signal for invisible Higgs bosons
  4. Semi-inclusive pseudoscalar production
  5. $A$ and $h,~H$ production in semi-inclusive processes
  6. Identification of low mass Goldstone bosons
  7. Conclusions

Figures (3)

  • Figure 1: The inclusive and semi-inclusive production of a BSM particle which subsequently decays with large missing transverse energy $E /_T$ or missing 4-momentum, $P /$. The figure shows decays of the BSM object where some of the decay products are visible in the central detector. The method applies equally to totally invisible decays, as discussed in our illustrative example.
  • Figure 2: Schematic diagram for pseudoscalar ($\phi_-$) and scalar ($\phi_+$) boson production by the semi-inclusive process $pp \to p+g\phi g+p$. The gluons of the $gg^{PP} \to g\phi g$ subprocess are indicated by their 4-momenta $k_i$.
  • Figure 3: The three terms contained in the upper triple-gluon vertex, $\Gamma_{\mu\rho\tau}$, of Fig.\ref{['fig:a3']} where $\mu,\rho,\tau$ denote the gluon polarisations. There is a similar structure for the lower triple-gluon vertex.