Research

Supersymmetry


I am currently concentrating on Supersymmetry (SUSY) and generic new-physics searches using the trilepton data of CDF. This is the golden channel for the discovery of SUSY at the Tevatron and a flagship CDF analysis. If we produce chargino and neutralino pairs (these are the supersymmetric partners of the gauge bosons), their leptonic decay would result to three leptons and missing energy. We are hunting for this signature. Because of our large luminosity, inclusion of low pT leptons, extended detector coverage (forward leptons) and the inclusion of new objects (like hadronically decaying taus and isolated tracks), our analysis is the most sensitive SUSY search at the Tevatron ! This is currently an exclusive New Mexico analysis performed by myself, graduate student Marcelo Vogel and Professor Michael Gold.

My previous 1 fb-1 analysis of mu+mu+X CDF data also includes low-pT leptons and introduces an innovative technique for estimating the heavy-quark background in trilepton analyses. It is the first search of new physics with pT as low as 5 GeV for all three leptons . This work was recently publshed in Phys. Rev. D.

My 1 fb-1 analysis was combined with the work of other groups and resulted to the strongest chargino-neutralino limit at the time. The work was published in Phys. Rev. Letters.

In summer 2011, I completed the 5.8 fb-1 analysis, just in time for the SUSY-11 conference. We achieved the highest yield of trileptons ever detected in the signal region, and we observed a surplus of events at low dilepton mass. At the same time, we set the most stringent limit on chargino mass at the time of release. For more information about this exiting work, please visit my supersymmetry page.

Gravitons


My CDF analysis achieved the world-best limit on the RS-graviton mass (>1111 GeV/c2) when released. More details on the public G→γγ/ee/μμ and G→γγ/ee analyses pages. The UNM group contributed with the dielectron and dimuon channels that improved the graviton-mass lower limits by ~150 GeV/c2. The search for new high-mass dielectron resonances along with the search for RS-gravitons decaying to diphotons and dielectrons is published in PRL (Phys. Rev. Lett. 107, 191806 (2011)).

Top Physics


Tevatron regularly produces top quarks and CDF analyzes their properties. Actually the top quark was discovered here in 1995! According to the Standard Model (SM) of particle physics, the top quark would decay to bottom quarks 99.9% of the times. This is a property that is worth testing: any discrepancy with expectation would mean either the presence of non-SM top quark (like a supersymmetric scalar top) or non-SM background to the top quark production or a fourth generation of quarks.

I performed the first measurement of the ratio of Branching Fractions R=B(top->b)/B(top->q) at CDF II using an artificial neural network technique. The result is consistent with the Standard Model expectation and was the most precise to date (part of the Particle Data Group summary of particle properties). This analysis was published in Phys. Rev. Letters. To learn more, please visit my
top quark page.

Electroweak Physics with QCD effects


I have performed the world's first and only measurement of A2 and A3 two of the four leading-order angular coefficients of the W boson production in a hadron collider, as a function of the W's transverse momentum. These angular coefficients are ratio of the corresponding helicity cross section of the W and the total unpolarized cross section. Before my work, only A0 was known (measured by D0 and later by CDF).


These angular coefficients are sensitive to polarization effects and QCD activity, so they offer an excellent environment for confirming our current understanding of electroweak and strong interactions. At the same time, these coefficients are not consistent with expectation, if the W is produced in association with a new particle, such as the Higgs. My results (published in Phys. Rev. D) are consistent with the Standard Model, with a ~1 sigma deviation for W pT above 75 GeV. For more information, please visit my electroweak+QCD page.

Phenomenology


I published the first complete set of helicity cross sections of the W produced in hadron collisions, as a function of its pT. Because of the correlation of the helicity cross sections with polarization properties, QCD effects and presence of new particles, this literature is important for understanding of the Standard Model prediction and facilitating future discoveries. This work has been already used by two CDF publications and sited by leaders of the field (e.g., Prof. Hagiwara). To find out more about this work, please visit my W Helicity page.


Another phenomenological endeavor is the Apollo generator (named it based on the fact that it has to eventually talk to Pythia for fragmentation). It is the first adaptive Monte Carlo simulator specifically designed for new-physics event generation. The current event generators are inefficient for new-physics generation, simply because they use fixed values of the new-physics parameters. The user has to manually change these parameters and re-run, without knowing how the change will affect the generation. Apollo generates only 1 sample, where not only the kinematics but also the theory-parameters are sampled, based on cross-section importance. This is essential for methodically studying the Tevatron and LHC new-physics sensitivities, optimizing event selection, correlating theoretical parameters with experimental observables, and setting multi-dimensional model-parameter limits. This method will increase the discovery potential and its proper interpretation. For more information, please visit my Apollo generation page and the corresponding new-physics generation page.

Hardware and Software Projects


I am working on very interesting hardware projects, that include muon chambers, CDF trigger, and laser diodes. As part of my formal training, I have completed advanced electrical and computer engineering projects, as well as an original project in accelerator simulations. My software endeavors include Monte Carlo coordination for the exotic group of CDF, offline muon reconstruction code and the design of a new-physics event generator. I have also served as CDF operations manager.