|
|
Phone:Fax:Office:Purdue Address:Fermilab address: |
| My primary area of research is in High Energy Physics. I am currently a member of the CDF collaboration which has built and operates one of the two detectors at the Tevatron - the World's highest energy proton-antiproton collider, located at the Fermi National Accelerator Lab. |
|
These high energy collisions also give rise to very large cross sections for the production of bottom and charm quarks. The decays of hadrons containing bottom quarks are studied at a number of experiments around the world, including Belle, BaBar and CLEO, but these facilities can only produce the B0 and B+/B- mesons. At the Tevatron, all types of hadrons containing bottom quarks are produced, which makes it the only facility currently operating at which one can study the decays of B0s, Λb and Bc hadrons.
One of the mysteries in modern particle physics is the origin of the complete asymmetry between matter and anti-matter in the universe. Although not large enough to explain this observation, one of the only known mechanisms that can produce a matter anti-matter asymmetry is the process of CP violation in the Standard Model. The parameters that give rise to this effect (the elements of the CKM matrix) are difficult to measure reliably and it is only recently that a consistent view of this part of the Standard Model has begun to emerge. Studying the decays of hadrons containing bottom quarks makes possible a number of new measurements and tests of the CP sector of the Standard Model. For this reason, the decays of the B0s mesons are extremely interesting and at this time, they can only be studied at the Tevatron.
CDF has now made the first unambiguous
|
Over the past six years, I have played a lead role in the design, constriction and commissioning of a Time-of-Flight detector that was a new addition to CDF for Run-II. This detector measures the times at which charged particles arrive at a set of scintillation counters, located just outside the CDF tracking volume, with a precision of ~100 ps. This new capability makes it possible to distinguish between charged kaons and pions in the momentum range p<1.5 GeV/c and between protons and pions in the momentum range p<3 GeV/c. The CDF-II TOF system required building and testing about 450 photomultiplier tube assemblies and preamplifiers, as well as 432 channels of custom electronics to digitize the time and amplitude of the PMT pulses. |
| Data from the TOF detector makes it possible to statistically identify pure samples of kaons, pions and protons that are used as input to calibrate the ionization energy loss (dE/dx) of CDF's tracking chamber. The combination of TOF and dE/dx can provide unambiguous particle identification at low momenta, and gives at least 1 sigma statistical separation between kaons and pions above 2 GeV/c. This is an essential part of several of the analyses described above. |
|
|
I am currently involved with studies of the TOF calibration and reconstruction. Part of this effort includes building an electronics module to send clock signals to both the TOF electronics and to the electronics that reads out the CDF-II luminosity monitor. The luminosity monitor provides additional information about the time at which the proton anti-proton interaction occurred. A study of the correllations between the times measured with the TOF detector and the luminosity monitor can help understand systematic effects that are present in TOF event reconstruction and can improve the precision with which we perform particle identification. |
|
One of the unique capabilities of the CDF-II detector is the ability to
identify and trigger on events that are consistent with the production
of bottom or charm hadrons. This is possible because these particles
have lifetimes that are of the order of 1 ps and can travel of order
0.5 mm before they decay. Because of this, the tracks that their decay
products leave in the detector do not point back to the point at which
proton and anti-proton collision took place. The identification of these
displaced tracks is the basis for the Level 2 Secondary Vertex Trigger.
The Secondary Vertex Trigger requires the identification of the high momentum tracks in an event every 396 ns. This is done using the eXtremely Fast Track processor that is part of the CDF-II Level 1 trigger. The XFT processor identifies tracks by the patterns of hits that they leave on the wires in CDF's central tracking chamber. A limitation of the current XFT design is that at high luminosities, the trigger rate is dominated by fake tracks that are incorrectly identified because of the large number of overlapping low momentum tracks produced in inelastic proton anti-proton collisions. |
| The original specification for the XFT system had it producing a trigger decision every 132 ns and it was only possible to classify the times at which wires were hit as either being "prompt" or "delayed". Because we now know that a trigger decision is required only every 396 ns, it is possible to tripple the amount of information used in the trigger decision. The use of this additional information is one upgrade path that will reduce the rate of fake triggers. The current XFT system also identifies tracks using only the wires in the 4 axial superlayers of the tracking chamber but additional information is available from the outer two stereo superlayers as well. Along with Ohio State University, the University of Illinois and others, the CDF group at Purdue will develop electronics hardware to make use of this additional information. This project, that will continue throughout 2004-05, can extend the B-physics capabilities of CDF-II as the Tevatron luminosity increases over the next several years. |
|