Introduction
The Experimental High Energy Physics (HEP) group at Baylor is engaged in experimental elementary particle physics research at the European Center for Nuclear Research (CERN) in Geneva, Switzerland and Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, USA.
Research at the CMS experiment
Search for Supersymmetry in the Missing ET + Multi-Jet Channels
Supersymmetry is a theoretically well-motivated model which may shed light on important questions in current particle physics such as the nature of the dark matter. The supersymmetry search in the missing ET + jets channel is attractive due to the expected high signal rate, and the search is being performed in a way that is sensitive to many other new physics scenarios that share common signatures, such as large extra dimensions. This search is quite complex, and we are collaborating with people from University of California Santa Barbara, Rockefeller University, Fermilab, University of Hamburg, CERN etc. This search using the 2010 data is underway. We expect that about 35/pb of the 2010 data already gives sensitivities beyond the Tevatron experiments.
Jet Internal Structure Measurements
The measurement of jet internal structure gives insights into the transition between partons produced in the hard process a nd jets of hadrons, and is sensitive to the effects of the underlying event. This measurement is critical for tuning the phenomenological models so that they provide a good description of jet fragmentation properties at the LHC energies. We are collaborating with people from Rockefeller University, Vanderbilt University, and Fermilab for this measurement. Preliminary results are available at here, and now improved measurement is in progress.
Hadron Calorimeter
The hadron calorimeter is one of the key components of the CMS detector, especially for the physics analyses we are interest ed in at CMS. More details about the CMS hadron calorimeter may be found at this link. The Baylor CMS group is currently working on the data validation and anoma lous signal removal for the hadron calorimeter. For data validation, when a new CMS software version is released and the data are ``re-processed'', we examine the hadron calorimeter data, find unexpected problems or validate it. When problems are found, we work with the calibration team or reconstruction software team to resolve the issues. The CMS hadron calorimeter is known to yield anomalous signals which are not from hadronic showers initiated by real particles produced in pp collisions, but from particles hitting the transducers or rare random discharges. We are contributing to the effort on characterizing anomalous signals and developing algorithms to remove such anomalous signals.
Data Quality Monitoring
The Baylor CMS group has been leading the data quality monitoring (DQM) and validation for jets and missing ET. As CMS take new data, they need to be monitored in quasi real-time. When we spot unexpected behavior in data, immediate feedback is sent to the detector operation, otherwise we certify the data for offline analyses. We developed the DQM system for jets and missing ET. This work is critical for the physics projects our group has been pursuing or is going to pursue in CMS, including a search for supersymmetry signatures, precise measurement of jet production properties, and searches for the Higgs boson and other physics phenomena beyond the Standard Model of particle physics.
Research at the CDF experiment
The contributions of the BU CDF group to the CDF experiment are very diverse. Besides providing manpower for data taking shifts, the group is responsible for L1 tracking trigger. The L1 tracking trigger at CDF is known as XFT for eXtremely Fast Tracking. Moreover, the CDF group is involved in many interesting physics analyses by studying particles in the SM as well as searches for new physics beyond the SM.
Higgs Searches
The origin of mass is still a mysterious question in the SM. Our current understanding suggests that the mass is generated by the Higgs boson via a mechanism of spontaneously broken symmetry. The Higgs searches at the Tevatron are gaining more and more significance with the amount of accumulated data. With an anticipated 16/fb of data collected in an extention of the current Tevatron run, CDF and DØ together will be sensitive to a SM Higgs boson at the level of at least 3% over the full mass region favored by precision electroweak measurements (mH = 115–158 GeV). This would significantly add to the worldwide knowledge of the electroweak symmetry breaking sector. The Baylor group is involved in two searches for the SM Higgs boson and one search for a non SM Higgs.
Associated production of a Higgs with a W boson
The Baylor group is involved in the Higgs search in its decay into two b jets with the associated production of the W boson. This channel is the most promising channel at Tevatron for the Higgs searches at low masses.
SM Higgs to diphoton
Although the branching ratio of a Higgs boson decaying into two photons is rather small in the SM (~0.2% for 110 < MH < 140 GeV,), it is still considered to be an attractive channels at hadron colliders due to its clean signature of a narrow resonance in the diphoton mass spectru m over a steeply falling background. The Baylor group is pursuing a search in this channel, which will make valuable contributions to the Tevatron Higgscom bination.
Fermiphobic Higgs search
The implementation of the Higgs mechanism in the SM may not the one that nature has chosen. Therefore, the group is searching for evidence of a Higgs boson in alternative models such as the one known as "fermiphobic" Higgs. In such models, the Higgs coupling to fermions are forbiden. Thus, the branching ratio of the Higgs decay to diphon is substantially higher than the SM.
Single Top
The production of single top quarks at the Tevatron was first observed by the CDF and DØ experiments in 2009. The reasons for studying single top production are compelling: the production cross section is directly proportional to the square of the CKM matrix element |Vtb|, and thus a measurement of the rate constrains fourth-generation models, models with flavor-changing neutral currents, and other new phenomena. Furthermore, since the top quark decays before hadronizing, its polarization can be directly observed in the angular correlations of its decay products.
Model independent Search
The description of electroweak symmetry breaking in the Standard Model, in terms of a fundamental scalar Higgs field, is almost certainly incomplete. The quadratically divergent radiative corrections to the Higgs mass suggest the existence of new physics at TeV energies that stabilizes the weak scale. Many new physics models, including supersymmetry (SUSY), predict mechanisms that could produce a photon + jets + missing ET signature. The group is involved in a model-independent signature-based search for anomalous events in this channel by scanning kinematic distributions including missing ET , invariant mass of the photon + leading jets, total transverse energy (HT ), etc., for an excess of events over SM predictions. An excess could indicate the existence of a new heavy particle decaying into photon + jets or a new physics mechanism such as gauge-mediated SUSY breaking.
eXtremely Fast Traking (XFT)
The huge amount of ppbar collision data produced at the Fermilab Tevatron pose a big challenge for data processing and storage. The Tevatron delivers ppbar collisions at 1.7MHz, however CDF can keep only about 100Hz of data in storage media for offline analysis. While the background rejection is important, a high and unbiased efficiency for signals is a necessity. The CDF trigger and data acqusition has three levels of event selections. The Baylor HEP group has played a significant role in the design, installation, commissioning, operation, and maintenance of the eXtremely Fast Tracker (XFT), the Level 1 tracking trigger at the CDF experiment.