Abstract
A long-standing kinematic challenge in data analysis at hadron colliders is the determination of the masses of invisible particles. This issue is particularly relevant in searches for evidence of dark matter production, which remains one of the prominent targets of future collider experiments. In this paper, we show that the additional information from the precision timing measurements, provided by planned detector upgrades during the high- luminosity run of the LHC (HL-LHC), allows for previously unrealizable measurements of invisible particle kinematics. As a concrete example, we focus on the signal of pair produced long-lived particles (LLP1,2), each decaying with a displaced vertex to visible (V1,2) and invisible (I1,2) final state particles, pp → LLP1 + LLP2→ (V1 + I1) + (V2 + I2). We explicitly show that the complete kinematics of the invisible particles in such events can be determined with the addition of timing information, and evaluate the precision with which the masses of new long-lived and invisible particles can be determined.
Highlights
Timing layer following from the decays of neutral long lived particle (LLP)
We show that the additional information from the precision timing measurements, provided by planned detector upgrades during the highluminosity run of the LHC (HL-LHC), allows for previously unrealizable measurements of invisible particle kinematics
Each LLP decays into visible and invisible particles, with: pp → LLPa + LLPb → (Va + Ia) + (Vb + Ib). This signature appears in many well-motivated beyond the standard model (BSM) theories, such as the second lightest supersymmetric particle decaying to the lightest supersymmetric particle (LSP) and the second lightest Kaluza-Klein particle decaying to the lightest Kaluza-Klein particle (LKP), respectively [6,7,8,9,10,11]
Summary
We begin by reviewing the general properties of the proposed precision timing detectors at the HL-LHC, focusing in particular on the hermetic design of the CMS timing layer [2]. We emphasize that this derivation is completely generic, in that it can be applied to any system with the same event topology As these four-vectors are fully-determined, the masses of LLPs and invisible (dark matter) particles can be calculated; this is one of our main results in this paper. When the pair-produced LLPs are identical, and with identical decay products, the symmetry constraints on the system reduces the effective number of kinematic unknowns, such that the kinematics of the system can be completely determined with 2-fold ambiguities even in the absence of timing information This can be observed by first considering the relations following from 4-momentum conservation in each branch of the decay processes (LLPi → Vi + Ii) for i = a or b, respectively: pIa = pa − pVa ⇒ m2Ia = m2a + m2Va − 2EVa m2a + |pa|2 − 2pVa · pa , pIb = pb − pVb. Knowledge of ∆, combined with eq (2.15), is sufficient for determining the LLP and invisible particle masses, which is one of the results of this paper
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