Triggering long-lived particles in HL-LHC and the challenges in the first stage of the trigger system

Abstract

Triggering long-lived particles (LLPs) at the first stage of the trigger system is very crucial in LLP searches to ensure that we do not miss them at the very beginning. The future High Luminosity runs of the Large Hadron Collider will have increased number of pileup events per bunch crossing. There will be major upgrades in hardware, firmware and software sides, like tracking at level-1 (L1). The L1 trigger menu will also be modified to cope with pileup and maintain the sensitivity to physics processes. In our study we found that the usual level-1 triggers, mostly meant for triggering prompt particles, will not be very efficient for LLP searches in the 140 pileup environment of HL-LHC, thus pointing to the need to include dedicated L1 triggers in the menu for LLPs. We consider the decay of the LLP into jets and develop dedicated jet triggers using the track information at L1 to select LLP events. We show in our work that these triggers give promising results in identifying LLP events with moderate trigger rates.

Collider searches for scalar singlets across lifetimes

“…On top of that, TeraZ can exlude relaxions of m φ 3 GeV. 11 We obtain the approximate 95% CL bound on sin 2 θ from the provided 68% CL bound on δκ with κ = 1 + δκ by sin 2 θ (95) 1 − (1 + r δκ (68) ) 2 where r = q…”

Determining the lifetime of long-lived particles at the HL-LHC

“…This opens up the possibility to use the L1 tracking for designing dedicated LLP triggers. Several attempts have been made to develop dedicated triggers for LLPs, both by experimental collaborations [90,91] and phenomenological studies [92,93]. The Phase-II upgrade of the CMS L1 trigger [94] also has some discussions on how specific triggers can be developed for triggering events with displaced objects.…”

“…Then, in processes with LLPs which are not accompanied by many high-energy prompt particles, and in the presence of ∼ 140 other such vertices, the chances of misidentifying any PU vertex as being the PV will be higher (for a quantitative discussion cf Ref. [92]). In such a scenario, the d z of the secondary vertex calculated from the reconstructed PV will not be the same as that calculated from the vertex where the LLP is actually produced, which will affect the overall measured LLLP decay length (d) in the lab frame.…”

“…Considering narrow jets reduces the PU contribution and therefore, proves useful for identifying the LLP jets, since the latter deposits energy in smaller physical region, as has been discussed in Ref. [92]. Also, the proposal to include the timing layer in the Phase-II upgrade of CMS (MTD) with a timing resolution of 30 ps, would help in bringing down the PU amount to the current PU amount, around 30-50 vertices per bunch crossing [74].…”

Extraction of neutrino Yukawa parameters from displaced vertices of sneutrinos

“…For such cases any leptons would be soft and triggering the event would be more difficult. For interested readers, we refer [29,30] for the recent proposals on these issues.…”