Reclustering in Jet Stop Search - Challenges and Solutions
Explore the challenges of top quark reconstruction in stop pair production and learn about the innovative jet reclustering method. See how reclustered jets enhance stability and agreement in control regions, aiding in top reconstruction efficiency and background rejection.
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Jet Reclustering in 0L Direct Stop Search Published in JHEP: http://link.springer.com/article/10.1007/JHEP09(2014)015. Chaowaroj (Max) Wanotayaroj Walter Hopkins Stephanie Majewski James Brau University of Oregon 3/2/2025 Chaowaroj (Max) Wanotayaroj 1
The Search All Hadronic Decay Stop Search Search for all hadronic decay of the top quarks from stop pair production. Challenges: Top reconstruction is challenging due to the high jet multiplicity. Also, the top daughters span a wide range of R (middle right plot). Top Reconstruction for 6 jets: ???? method. Take the two highest b-tag weight AkT4 jets as seeds then combine the two closest jets from the seed to make a top. To improve the mass reach, we needed a boosted signal region which extends to 4-5 jet bins. But ????method won t work. 3/2/2025 Chaowaroj (Max) Wanotayaroj 2
Using Reclustered Jets Reclustered Jets Recluster jets by running fastjet using calibrated, pileup subtracted AkT4 jets as input. Reclustered jet masses are stable against pileup (left plot). Flexible Uncertainties can be propagated from the constituent jets, thus can use any R parameter. Reclustered jets show good agreement in ? ? control region (right plot). Work in progress 3/2/2025 Chaowaroj (Max) Wanotayaroj 3
Using Reclustered Jets Reclustered Jets AkT12 is chosen as the most efficient for top reconstruction that still retains a reasonable background rejection. AkT8 is also used for W reconstruction to help reject backgrounds. The leading and sub-leading ?? reclustered jet mass distributions, shown below, are as expected. Leading top candidate Sub-leading top candidate Work in progress Work in progress 1 mAkT12 3/2/2025 Chaowaroj (Max) Wanotayaroj 4
Using Reclustered Jets Two Topologies Since only the signal has two tops, the sub-leading top candidate mass can be used but it has a low signal efficiency. To separate the easy topology (two tops well separated in (?,?) plane) from the difficult topology (two tops daughters are overlapping in (?,?) plane, we define the top mass asymmetry variable: ????12 ????12 ?mtop= 0.5 was chosen to be the separating point. Optimized the two signal region separately. 0 1 ????12 +????12 ?mtop= ??? 0 1 Work in progress 3/2/2025 Chaowaroj (Max) Wanotayaroj 5
Using Reclustered Jets The Two Signal Regions Now the sub-leading top candidate mass can be used to reject backgrounds in the easy case with high signal efficiency. Do not cut on the subleading jet mass. Leading top candidate Sub-leading top candidate Work in progress Work in progress Easy Work in progress Work in progress Difficult These plots show 4-5 jets events only (SRB) 3/2/2025 Chaowaroj (Max) Wanotayaroj 6
Results Reclustering technique enables us to extend the search into a higher stop mass region. The top plot: excluded region from the previous analysis (ATLAS-CONF-2013- 024) which does not included boosted signal region (top). Boosted signal region helps extend the stop mass reach by ~50 GeV for the expected limits (bottom plot). In Run-2, this approach is expected to become even more important as we start to probe even higher stop masses. 3/2/2025 Chaowaroj (Max) Wanotayaroj 7
