We are happy to announce the public release of the first dedicated search for soft unclustered energy patterns (SUEPs) at the LHC. The search uses the 13 TeV pp collision data collected by the CMS detector in 2016-2018. This effort was led by the PPC group including Professor Christoph Paus, Chad Freer, Luca Lavezzo and Pietro Lugato and was presented at the LHC seminar “Search for exotic signatures of new physics at CMS” and described in a CMS briefing.
SUEPs are predicted by Hidden Valley models that include a new, confining force and are characterized by a large multiplicity of low-momentum, diffuse, charged particles in the final state. In “Hidden Valley” models, these dark worlds cannot be seen directly – as a valley is hidden from view – but would interact with our own via a “portal” or “mediator” particle that can act as a tunnel into the hidden region. This portal can allow some of the effects of the dark world to leak into ours.
Because of their low energies, SUEPs can be challenging to measure in a detector optimized for the study of high energy phenomena. However, sometimes new mediator particles such as the one in this search can recoil against traditional particles causing the mediator to be produced with huge momenta. Subsequently, all of the particles produced from the mediator are pushed to higher energies, which are better suited for measurement by CMS. At higher energies, these SUEPs will due to the boost appear as a cluster of particles, but the spherically symmetric decay can be recovered by boosting into the frame of the mediator as shown below.
The search utilizes a novel approach to predicting the background by estimating the contribution from traditional processes directly from data, using an “extended ABCD” method. The traditional ABCD method makes use four regions, defined by two uncorrelated variables, while the extended ABCD method further splits the control regions to obtain a total of eight control regions (A-H) and one signal region (SR). This extended ABCD method allows us to correct for linear correlations between the discriminating variables to accurately predict a region of interest.
for all control regions (A–H) and the SR.
So far, the first search for soft unclustered energy patterns has not revealed evidence of a Hidden Valley. The PPC group currently has several ongoing efforts to continue and expand the sensitivity of this search. These efforts include utilizing the “scouting” data, where events are reconstructed in the trigger system allowing a lower energy threshold, as well as investigating different production mechanisms. The valley of darkness remains hidden for now but there are still many paths yet to explore. The search for Hidden Valleys and SUEPs continues.
