A new way to find the top

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As we learned on Dec. 13, finding the Higgs boson is proving to be more of a challenge every day. CDF scientists are using the top quark to try to pin down the preferred mass of the Higgs indirectly. In the Standard Model, the mass of the top quark, W boson and Higgs boson are all inter-related. If you know any two of the three exactly, you can predict the mass of the third. That’s one of the motivations for scientists to measure the top quark mass with high precision—to get further insight into the mass of the long-hypothesized, but still undetected, Higgs boson.

Since the discovery of the top quark at the Tevatron by CDF and DZero in 1995, scientists have made dozens of top quark mass measurements using various decay modes of the top and anti-top quark pair. Recently, CDF physicists made a measurement of the top quark mass with an entirely new set of data. This measurement will add unique information into the overall picture of the top quark mass and improve the precision of its mass measurement.

Scientists collected a data set consisting of events with a specific signature. These types of events occur when a top or antitop quark decays into a tau lepton or when an electron or muon from the same type of decay is not observed.

The measurement under discussion is performed using a template method. Physicists first build several physical observables with samples whose top quark masses are already known. The shape of those samples is compared to the same observables built using the collected data set. Scientists extract a most-likely top quark mass for the data by deciding which known sample the unknown sample looks the most like.

Using approximately 60 percent of the overall dataset collected at CDF, physicists identified 1,432 candidate events that can be used to measure the top mass. With this unique data sample, CDF physicists measured the top quark mass to be 173.2 ± 2.6 GeV/c2. The measurement is in excellent agreement with the other CDF measurements. This result will soon be incorporated into overall CDF top quark mass combination, helping scientists locate where the Higgs might be hiding.

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—Edited by Andy Beretvas

These CDF physicist contributed to this data analysis. From left: Hyun Su Lee and Jian Tang, both from the University of Chicago; Fermilab Deputy Director Young-Kee Kim and Gabriele Compostella, INFN-CNAF.

These CDF physicist contributed to this data analysis. From left: Hyun Su Lee and Jian Tang, both from the University of Chicago; Fermilab Deputy Director Young-Kee Kim and Gabriele Compostella, INFN-CNAF.