Thursday, December
4th 2003 - h. 15:00 

Auditorium B. Touschek


P. Giromini


  Heavy  flavor properties of jets produced
at sqrt(s)=1.8 TeV


The study is motivated by the evidence, previously reported by CDF, for a class of jets, produced in association with a W boson, that contain long-lived objects consistent with b or c quark decays, identified by the presence of secondary vertices (SECVTX tags) or tracks with large impact parameters (JPB tags), but which also have an anomalously large content of soft leptons (SLT tags).

This anomaly, as well as other well known discrepancies between the NLO prediction and the measurements of the single b cross section and of the b bar-b cross sections based upon detection of one or two leptons from b decays, could be explained by postulating the existence of light sbottom quarks with 100 %
semileptonic branching ratio.

The present analysis probes this hypothesis by studying a large sample of events with two or more central jets with E_T > 15 GeV, one of which (lepton-jet) is consistent with a semileptonic bottom or charmed decay
to a lepton with E_T > 8 GeV.
The measurement is a comparison between the data and a HERWIG-based simulation of the semileptonic decay rate for the additional jets (away-jets), which have no lepton trigger requirement.

We first measure rates of lepton- and away-jets with SECVTX and JPB       tags in order to determine the heavy flavor content of the data; we  tune the heavy-flavor simulation within the experimental and theoretical
uncertainties to match the observed rates of tags. The tuned parton-level prediction of HERWIG sheds new light on the origin of the discrepancy between the NLO prediction and the measurement of the single b and  b bar-b cross sections at the Tevatron.

We then measure yields of soft leptons due to heavy-flavor decays in the away-jets, and compare them to the prediction of the tuned simulation. We find that away-jets have a 50 % excess of soft lepton tags as compared with the simulation.
An excess of this size was expected if light scalar quarks with a 100 % semileptonic branching ratio were pair produced at the Tevatro


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MCD, 27/11/2003