Mumbai-Pune Collider Physics Initiative

New Physics in Stacks of Soft Tracks

Interested members

Tuhin S. Roy
Sourabh Dube



The proposal involved training and using the variable ξ, namely, the number of tracks associated with the primary vertex, which are not parts of reconstructed objects such as jets, isolated leptons, etc. It variable was originally proposed in Phys. Rev. D 94, 111703(R) by Amit Chakraborty, Sabyasachi Chakraborty and Tuhin S. Roy from the pheno group at TIFR. It is especially useful for new physics searches with compressed spectrum in the channel monojet+missing transverse momentum (ET). In models such as in compressed supersymmetry, events are often characterized by a rather large number of soft partons from the cascade decays, none of which results in reconstructed objects. We find that ξ, binned in pT, can discriminate these new physics events from events due to Z+jets, that is, the main background in the channel monojet+ET. The information contained in soft tracks is largely uncorrelated with traditional variables such as the effective mass, ET, pT of the jet, etc., and, therefore, can be combined with these to increase the discovery potential by more than 200% (depending on the spectra, of course). In fact, simple cuts on ξ(pT), when combined with cuts on the effective mass, outperforms sophisticated optimized Multivariate Data Analysis using all conventional variables. One can model the background distribution of ξ(pT) in an entirely data-driven way and make these robust against pileup by identifying the primary vertex.

Current Status

A study to investigate the feasibility of implementing the proposal in CMS has been initiated by Sourabh Dube.

Follow-ups and Applications

  1. arXiv:1704.07048 Constraining compressed versions of MUED and MSSM using soft tracks at the LHC by Sabyasachi Chakraborty (TIFR, Mumbai) , Saurabh Niyogi (Delhi U.) , K. Sridhar (TIFR, Mumbai)