Unveiling the High-Rate Frontier: ATLAS' Bold Adventure
Nature, with its inherent symmetry, presents a fascinating challenge at the Large Hadron Collider (LHC). The majority of proton-proton collisions result in a unique pattern: two jets of hadrons emerging back-to-back with almost equal momentum. This 'dijet' phenomenon is a treasure trove for physicists seeking to go beyond the Standard Model.
But here's where it gets controversial: the abundance of dijet events creates a bottleneck. The ATLAS experiment, with its 'trigger' system, must select the most intriguing collisions from a billion happening every second. The first-level trigger reduces the rate to a manageable 100,000 events per second, and then the high-level trigger further narrows it down to just 1,200 events per second.
And this is the part most people miss: the ATLAS Collaboration has developed an innovative solution called Trigger-Level Analysis (TLA). Instead of recording all collision data, TLA saves only the essential information, reducing the size of each event from a massive 1 megabyte to a mere 6.5 kilobytes. This allows ATLAS to capture far more events, especially those with low dijet masses.
ATLAS researchers are now exploring an extraordinary dataset - 60 billion trigger-level events from LHC Run 2 - in their quest for new particles. In a recent paper, the ATLAS Collaboration presents a search for new particles decaying into dijets, based on this vast dataset. Using TLA, physicists were able to record data at an incredible rate, over 20 times faster than the standard high-level trigger.
Dijet searches focus on finding small excesses in the reconstructed dijet mass spectrum, which could indicate a new particle beyond the Standard Model. While traditional searches look at masses above 1 TeV, this trigger-level analysis pushes the boundaries, extending sensitivity down to 375 GeV. This is the lowest inclusive dijet mass ever studied at the LHC, without relying on additional constraints.
The data analysis revealed a compatibility with the smoothly falling Standard Model background. The most significant excess observed was for a Z' signal with a mass of 650 GeV, with a global significance of 2.2σ. Through meticulous work on background estimation and jet calibration, physicists set new limits on the mass and interaction strength of potential new particles.
Looking forward, trigger-level analyses of Run 3 data hold even greater promise. An upgraded TLA system has enabled ATLAS to record more complex collision signatures, further enhancing its sensitivity to new physics in the high-rate frontier.
The journey continues, and the ATLAS Collaboration invites you to explore these fascinating findings and join the discussion. What do you think about this innovative approach to data analysis? Could it lead to groundbreaking discoveries? Share your thoughts in the comments!
