Search for super symmetry at the Tevatron using the trilepton signature

Abstract

This dissertation describes a search for the associated production of the supersymmetric particles, the chargino and the neutralino, through their R-parity conserving decays to three leptons and missing energy. This search is carried out using the data collected at the CDF experiment at the Tevatron √ s = 1.96 TeV pp collider at Fermilab. The results are obtained by combining five independent channels with varying signal to background ratio. Overall, a total of 6.4 ± 1.1 background events from standard model processes and 11.4 ± 1.1 signal events for a particular choice of mSUGRA model parameters are expected. The observation of 7 events in data is consistent with the standard model background expectation, and the mSUGRA model is constrained. Limits are set on the cross section of Chargino-Neutralino pair production, and a limit on the mass of the chargino is extracted. A method of obtaining model-independent results is also discussed.ii Acknowledgements I feel the deepest respect for my advisor Sunil Somalwar. I want to thank him for being a friend, a philosopher, and a guide in the truest sense of those words. Without him, I would not love particle physics; it is as simple as that. and Bob Stone who made sure that the computers work, the CAF runs smoothly and helped me with the day-to-day questions to which I wouldn't know where to find answers. Thanks to Nancy DeHaan for shielding me from the administrative quicksands.The trilepton analysis would not be any fun without Anadi, Else, Giulia, John, and Vadim.Working with them ensured that even the most annoying tasks were enjoyable. I want to thank them for all their guidance, scripts, code, and conversations. The convenors at CDF also deserve a special mention; Ben, Chris, Dave and Monica. They taught me to think carefully, do a good analysis, give a good talk and much more.iii Tim Koeth and Rouven Essig helped to make Batavia and Piscataway as much of a home as Pune is; for that I'm grateful. Between them, I'm sure they will cover the best of experiment and theory and it is a privilege to know them.The last two years have been made special by Aditya and Sarika, Amit and Diptee, Mandar and Shreya, Pankaj and Prajakta, Shreedhar and Meenal, and Salil. The good times we have had together has made sure that the evenings I had for my own were well spent. They have been a sounding board for my wildest ideas, and they have been patient with me.

Slepton co-NLSPs at the Tevatron

“…This is populated mainly by Drell-Yan production, and its acceptance should be dominated by the per-lepton acceptance. (10) The CDF analysis includes two types of electrons and two types of muons, referred to separately as tight and loose to represent more and less stringent ID requirements, respectively [36]. We find that PGS leptons are not refined enough to make this differentiation.…”

“…For a full description of the analysis, we refer the reader to Refs. [16,17] and especially the thesis [36]. The CDF trilepton search selects events from two categories: three leptons, lll, or two leptons and one isolated track llT (7) .…”

“…(10) After including these modifications, the agreement with CDF is better, but still not good enough. To understand better the per-lepton acceptances, we have examined using PGS the dilepton control sample used in the CDF trilepton search [36]. This is populated mainly by Drell-Yan production, and its acceptance should be dominated by the per-lepton acceptance.…”

Search for hadronic resonance in multijet final states with the CDF detector

“…This happens with an efficiency of 1 antiproton per 10000 protons [19]. This production mechanism leads to a particle beam with a wide range of momentum.…”

“…At the Tevatron the time between two bunch crossings and therefore theoretically two events is 392 ns, or a frequency of 2.5 MHz [19]. To store every single one of these events would not just be a huge challenge for the electronics but also would not be useful for analyses since only a fraction of the events are physically interesting.…”