Hello.
I'm David Sperka, a Ph.D. student in physics at Boston University. My research is with the CMS Collaboration, one of the all purpose detectors at the brand new Large Hadron Collider at CERN in Geneva, Switzerland. My work involves developing algorithms for the CMS High Level Trigger (HLT), as well as monitoring the CPU performance of the HLT menu. I have been stationed at CERN since July 2011 serving as an on-call expert for the HLT during data taking. I am also currently a trigger contact for the Beyond Two Generations (B2G) analysis group, which focuses on new physics searches invovling top quarks.
With the discovery by the CMS and ATLAS experiments of a boson with mass about 125 GeV, it is likely that there are other undiscovered particles which cancel the contributions of the known particles of nature (like the W) to this boson's mass allowing it to remain so light. I am involved in the search for new charged vector bosons, generically referred to as W'. These particles exist in many new physics scenarios, such as Extra Dimensions or Little Higgs models. In 2010, the CMS collaboration performed a search for such particles, assuming that they are heavier copies of the Standard Model W. With this assumption, the new particle will often decay to a lepton and neutrino. For the analysis I contributed a determination of the muon trigger efficiency and corresponding systematic uncertainty. When the muon and electron searches were combined, W' bosons with mass below 1.58 TeV were excluded. At the time this was the world's most stringent limit on W' masses.
Search for a W' boson decaying to a muon and a neutrino in pp collisions at sqrt(s) = 7 TeV
My study of the muon trigger efficiency was included in an extensive review article describing the performance of the CMS muon system during the 2010 data run:
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
With a much larger dataset in 2011, and with high confidence in the understanding of the detector, CMS was able to search for W' particles in different decay channels. For example, a heavy W' boson can decay to a top and bottom quark pair, a channel which is not allowed for the Standard Model W boson. This channel is complementary to the search in the leptonic channel since in some models of new physics, there is a W' which couples more strongly to the third generation of fermions. In some models with purely right-handed fermionic couplings and with a right handed neutrino which has a mass larger than the W' mass, the leptonic decay mode is even forbidden. For this analysis I performed the data analysis of the electron+jets channel, and also to the statistical combination with the muon+jets channel. Assuming pure right-handed couplings, and by using a multi-variate analysis with a Boosted Decision Tree, CMS was able to exclude W' bosons with mass below 1.85 TeV, which is currently the most stringent limit in this channel
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Additionally, I've been an author of all CMS publications since November, 2010
As an undergraduate I did research with the CDF detector at Fermi National Accelerator Laboratory in Batavia, Illinois. I was involved in the search for rare decays of B mesons. B mesons are particles composed of a b quark, and either a strange or down type anti-quark. The Standard Model predicts that the probability for these particles to decay to a pair of muons is only about one in 10 billion. However in some new physics models, such as Supersymmetry, the probability can be much higher. The results of that search can be found here:
Search for FCNC Rare Decay Bs,d → μ+ μ-
mail to: dsperka [at] bu [dot] edu
Boston:
office: PRB 368
phone: 617-353-6045
CERN:
office: 42-1-017
phone: +41-22-76-62378