Triggering on Hard Probes in Heavy-Ion Collisions with the CMS Experiment at the LHC

TL;DR

This paper discusses the development of a specialized trigger system for the CMS experiment at the LHC to efficiently select high-interest heavy-ion collision events with rare probes like jets and heavy flavors.

Contribution

It introduces a novel two-layer trigger strategy combining custom electronics and commodity computing to handle the high collision rate and select key events.

Findings

Effective trigger system for heavy-ion collisions implemented

Significant reduction in data volume while retaining interesting events

Enhanced capability to study rare probes like jets and heavy flavors

Abstract

Studies of heavy-ion collisions at the LHC will benefit from an array of qualitatively new probes not readily available at lower collision energies. These include fully formed jets at ET > 50 GeV, Z0's and abundantly produced heavy flavors. For Pb+Pb running at LHC design luminosity, the collision rate in the CMS interaction region will exceed the available bandwidth to store data by several orders of magnitude. Therefore an efficient trigger strategy is needed to select the few percent of the incoming events containing the most interesting signatures. In this report, we will present the heavy-ion trigger strategy developed for the unique two-layer trigger system of the CMS experiment which consists of a ``Level-1'' trigger based on custom electronics and a High Level Trigger (HLT) implemented using a large cluster of commodity computers.