Project Description1
C. Project Description
C.1 Introduction
The primary research efforts of the University of Nebraska-Lincoln (UNL) HEP group are the DØ experiment at Fermilab and the CMS experiment at CERN's LHC. Other efforts include its nationally recognized education/outreach initiative, the Cosmic Ray Observatory Project, and related involvements in the Pierre Auger Observatory and early planning and development work for DUSEL and UNO. The Nebraska High Energy Physics group specifically seeks NSF support over the next 3 years for their efforts to:
A. Meet the group's institutional responsibilities in DØ. Group activities include:
(i) Performing physics analysis in the areas of QCD, top physics, Higgs and new particle
searches, and electroweak processes using the high luminosity data set of Run II (all).
(ii) Snow continuing as Luminosity Group convener (Sec.C.3.1)through Run II’sconclusion.
(iii) Overseeing the completion of algorithm upgrades(Claes) to the Level-2 trigger(C.3.1).
(iv) Converting W ratesconsistency check of new luminosityconstants into a tool for long
termluminosity monitoring, and a cross section publication (Bellavance – Sect. C.3.2).
(v)Implementing newly developed improvementsto DØ’s b-tagging(Dominguez – C.3.1).
(vi) Completing tracking improvements in timing and efficiency (Bloom – Sect C.3.1).
B.Meet the group’s responsibilities in the CMS Experiment at CERN’s LHC which include:
(i)Coordinating and implementing the pp luminosity measurement including access to luminosity information for online monitoring and offline physics analysis.
(ii)Performing simulation studies and trigger studies for the group’s primary interests in high-pT, high-mass physics.
(iii) Completing the construction, testing and installation of Forward Pixel Detector and begin the R&D work on its upgrade (anticipated following just 2 years ofoperation).
(iv)Expanding UNL’s Tier-2 site (C.2.4); Bloom serving as US CMS Tier-2 program
manager overseeing the development of all seven Tier-2 computing centers.
(v)Snow serving on the CMS Ph.D. Thesis Award Program committee.
C.(i) Lead the Cosmic Ray Observatory Project, CROP (Sec. C.2.6, C.4.1), a unique outreach
experiment in Nebraska to study extended cosmic-ray air showers using high-school based
detectors (Snow, Claes). CROP’s principal funding comes from anindependent NSF grant.
(ii) Head the Outreach, Education & Public Relations Task for the Pierre Auger Project
(Snow – Sect. C.4.2); explore possible UNL involvement in its proposed northern site.
(iii) Serve on the Physics Committee, and lead the Broader Impact Committee,for HUSEP
(Claes – Sect C.2.4, C.4.3) to complete the TDR for the proposed Henderson DUSEL.
(iv) Serve as E&O Coordinator for UNO, participating in the R&D effort UNO, and
exploring an expanded role for UNL in this future experiment (Claes – Sect. C.4.3).
An electronic Appendix of supporting material has been prepared and is available for review [1].
C.1.1 The UNL HEP group
The faculty size of the HEP group doubled in September 2004 with the additions of Bloom and Dominguez. The approval for these hires demonstrates the University's strong commitment to, and tangible support of, High Energy Physics as well as its high regard for the Department of Physics and Astronomy in general. Bloom and Dominguez bring, respectively, expertise in top quark physics and Higgs searches. Coupled with Snow's expertise in QCD and diffractive physics and Claes' expertise in searches for new phenomena, the UNL group has broad talent in hadron collider physics. With new personnel supported by NSF grants (including new postdoc and graduate student hires by Bloom and Dominguez) the UNL HEP group now exceeds 15 people. Bloom and Dominguez are currently supported on CAREER grants and UNL start-up funds, expiring in August 2007, so no direct support for their contributions is budgeted in this request. Their integration into a coherent UNL HEP group effort is described; the expiration of grants will dovetail perfectly with the round of proposals that follow this one.
Postdoc Angela Bellavance worked full-time on DØ, stationed at Fermilab. After 3 years in the Nebraska group, she was appointed Senior Research Associate. At the beginning of 2005, postdoc Andrei Sobol joined the group's CMS effort as our postdoc based full time at CERN.
Sudhir Malik and Michael Eads, supported by Bloom and Dominguez, each divide their time between DØ (detector shifts and analysis) and CMS Forward Pixel work.
Mikko Voutilainen,a graduate student at the Helsinki University of Technology (HUT) in Finland, joined the Nebraska group in August 2004 as a full time Fermilab residence pursuing his Ph.D. on DØ. HUT will formally grant Mikko his Ph.D. upon completion of his dissertation, though Snow serves as his primary thesis advisor. Mikko's primary financial support comes from Finland, but our grant has provided a workstation at DØ and covered thesis-related travel.
Graduate student Kayle DeVaughan began full-time work May 2006. Kayle, along with fellow UNL students Dale Johnston and Petru Lunca-Popa, working with Bloom and Dominguez and currently supported on their startup funds, were all recruited from Claes’ 2005 Introduction to High Energy Physics course, and now are all stationed at DØ. New graduate students Jason Keller, Tony Kelly, and Emily Petermann are the most recent additions to the group. Together with a dedicated group of 5 undergrad employees (many of them supported in part by the University/PepsiCo UCARE program), this team comprises the current Experimental HEP group at UNL.
C.2 Prior NSF Support
C.2.1 PHY- 0098799 “Experimental High Energy Physics”, 2001-2004, $556,361
PHY-0400369 “Experimental High Energy Physics”, 2004- , $573,000
University of Nebraska: Co-PIs; D. Claes, G. Snow.
C.2.1.1 The DØ Experiment DØhas rapidly turned on followingthe successful extended Tevatron shutdown that began in February 2006. Within two weeks of turning back on (mid-June) 14 pb-1 of physics quality data had been logged. Improved accelerator performance has enabled DØ to date to collect over 1.37 fb-1 integrated luminosity, 10 times the entire Run I data sample, at 1.8 TeV. Operating at a center-of-mass energy of 1.96 TeV with 36-on-36 bunches, peak instantaneous luminosities just prior to shutdown were routinely beginning over 150E30 /cm2/sec (peak initial luminosity to date 157.6E30). Data are now reconstructed and available for physics analysis within a few days. DØ's 36Run II publications (see Sec. D.1) along with the more recent results presented at summer conferences demonstrate the power of its upgraded detector. The top quark has been 'rediscovered', the W and Z cross sections have been shown to increase with center-of-mass energy as expected, and many benchmark physics processes are now accessible with the new inner silicon tracking, outer fiber tracking, and magnetic field (reconstruction of K to two pions, omega to lambda plus K, b-tagging using displaced vertices). QCD/jet distributions and limits from searches for new physics have emerged, and the unique Forward Proton Detectors are measuring diffractively and elastically scattered protons and antiprotons. With the anticipated integrated luminosity of 4-6 fb-1 by late 2008, DØ will pursue its full Run II physics menu which includes single top production, searches for standard-model or supersymmetric Higgs particles, jet production to unprecedented values of ET, and many other processes. During this period when institutions have been transitioning from DØ to the LHC, the UNL group has steadfastly maintained a high level of activity in DØ.
QCD Analyses Snow and graduate student Voutilainen are active in the QCD analysis group; Snow served as QCD analysis group co-convenor during Run I. Mikko's thesis work covers the inclusive jet cross section versus jet transverse momentum and the dijet mass distribution using a large fraction of the full Run II data set. Shortly after arriving, Mikko became a key player in the Jet Energy Scale working group. He solely developed the jet energy scale corrections presently in use for jets entering the inter-cryostat region of the detector and quantified the absolute jet trigger efficiency using muon triggers(internal DØ notes summarizing this work are listed in D.2). These technical results made Mikko a leading player in the first Run II inclusive jet cross section results presented at the 2005 Moriond-QCD conference based on 378 pb-1 integrated luminosity. Mikko followed this up with colloquia at both his home institutions: the University of Nebraska and Helsinki University of Technology. In June 2005, Mikko was named co-convener of the Jet Identification working group, a position normally assumed by postdocs or more senior physicists. The task of this working group has been to optimize DØ's jet-finding cone algorithm for use in all future publications. In April 2006 Mikko presented the “Inclusive Jet Cross Section Measurements” for DØ at DIS 2006, the conference in Deep Inelastic Scattering in Tsukuba, Japan. Mikko was one of 4 Fermilab graduate students selected to present preliminary thesis results at the 2006 Fermilab Annual Users Meeting.
New Phenomena Analyses Carl Lundstedt's thesis work under Claes, a search for supersymmetric scalar top quarks, saw print in 2004 (cite: PRL 93, 162004 (2004)). The limits set by this search (an exclusion contour in the LSP mass versus stop mass plane) proved more stringent than those set by CDF for Run 1 despite higher jet ET and missing transverse energy cuts and DØ's inability then to flavor-tag jets. Claes serves on the DØ Run 2 editorial board (which oversees and approves analysis before public presentation or publication) reviewing all the analyses of new phenomena searches in the jets+MEt final states. Editorial boards approve the earliest draft of any paper, before distribution to the collaboration for review. The boards also mediate and approve all changes recommended by the collaboration or journal referees. Preliminary results have been shown at the Spring and Summer 2005 and Winter 2006 conferences on searches for scalar top squarks, generic squarks, gluinos, 1st generation leptoquarks, and the monojets evidence of extra dimensions. These analyses are constantly being reviewed as the overall luminosity (total amount of data) increases, and the collaboration converges on its Jet Energy Scale (calibration of the calorimeter) and luminosity measurements. The Run 2 editorial board work is now converging rapidly on all jets+MEt analyses. The search results for squarks and gluinos (cite: Phys.Lett.B 639, 119(2006)) and a scalar leptoquark search(cite: Phys.Lett.B 640, 230(2006)) were both published this year,and a PLB draft of DØ’s search for scalar top quarks is now in collaboration review.
Electroweak Analyses Bellavance's analysis interests in precision electroweak measurements led her tothe DØ Electroweak group's W Working Group. The September 2, 2004, Fermilab Result of the Week : 'Rare and Beautiful Decays' (cite: cites Bellavance's triggering contributions in the search for evidence of Bs mesons decaying into a muon/anti-muon pairs (PRL 94, 042001 (2005). Four candidates were observed, while 3.7 +/- 1.1 candidates were predicted to come from background. This observation shows that fewer than 1 in roughly 2.2 million Bs particles decay into muon pairs. Bellavance was chosen to represent the collaboration with talks on W/Z Cross Sections at the 5th Rencontres du Vietnam (August 4, 2004) and Moriond-QCD Winter Conference, La Thuile (March 15, 2005).
Currently Bellavance is analyzing inclusive W rates vs. time and measured luminosity as an independent check of DØ’s luminosity. The expertise she’s developing in the systematic uncertaintieswill prove invaluable when she turns her attention to producing publishable crosssections based on 1 fb-1.
Level-3 Work As upgrade coordinator of DØ's Level-3 (L3) software trigger Claes supervised the work of over three dozen contributors (students and postdocs) to the online data acquisition system for DØ's second run. His leadership role in the Trigger Upgrade provided continuity within the effort for over 7 years (through four successive co-convenors). During Claes’ last 3 years the L3 effort grew with the addition of the Strasbourg group (studying a 3D vertex finder), the University of Mainz (electron filtering studies), Aachen (the newest addition to the Level-3 muon effort), Uppsala (tau), CPPM, France (developing a secondary vertexing tool), and Ho Chi Min Institute (assisting in the development of monitoring code).
The ultimate goal of L3 was to reduce the data coming from the combined hardware triggering systems of Level-1 and Level-2 (delivered at ~1 kHz for instantaneous luminosities of 2x1032 cm-2 sec-1) to a rate manageable by the data storage systems (about 50 Hz). As newly commissioned subdetector systems were brought online, and the DAQ hardware underwent its staged upgrade, the L3 trigger reliably provided the rejection power to both enrich the physics samples and maintain an acceptable throughput to tape. With the exception of the muon and tau tools, there was little feedback from the physics or object ID groups, and most early tool development was directed internally within the L3 group.
Jet and electron filters show sharp turn-ons to ~100% efficiency; rejection factors of 10 were realized even before the track-match or preshower tools were implemented. With a high pT global tracker added, the central di-electron trigger enjoyed a total rejection of 150; a single electron filter requiring Et > 12 GeV plus shower shape cuts together with one track > 12 GeV acheived a rejection of ~300. Together with muons, taus, and a Missing ET filter, DØ has been filtering on all fundamental physics objects since the end of 2002.
Claes pushed early for the monitoring of data quality and certification of code changes. This began with the online monitoring of L3 histograms collected in the control room during regular data-taking where a quick analysis of the event record (debug info and physics results) from randomly sampled online events produced distributions of physics quantities. Plots of electron, jet, tau, muon and global track multiplicity, ET, phi and eta were continuously reviewed by a Global Monitor shift. Next a comparator looked for discrepancies between online quantities and those computed when the data was rerun offline through the trigger simulator. Several variables (ET, , , and candidate number for taus, electrons, jets and tracks) were checked and automatically posted html output files summarized the results. This evolved into a certification tool for comparing new L3 releases against a benchmark set of histograms from the previous release. The utility of this tool (ultimately developed in its final form by the L3 team at Simon Fraser) now has seen widespread use at DØ. It has spawned the physics certification tools that provide rapid feedback, through trigger studies, on all new production (and trigger) releases.
Claes wrote the L3 triggering section and edited the overall triggering sectionsfor the (upgraded) Run II DØ detector Nucl. Instr. and Methods paper (cite: The Upgraded DØ Detector, Nucl. Instr. Meth.).
Triggermeister From August 31, 2004 through December 15, 2005 Bellavance served as the experiment’s Triggermeister, overseeing the experiment's data-acquisition rates and monitoring, controlling and documenting the bandwidth allocation to all triggers. She worked on three major trigger list versions, and was always on-call for online emergencies. Whenever trigger rates grew unreasonable or subdetectors experienced hardware problems, she was called on the produce an emergency list. Bellavance reported at biweekly trigger board meetings. She identified quirks that had been running Level-3 filters out of order, which led to timing studies of the trigger-order dependence, speeding up the triggering process and removing a severe bottleneck at Level-3. Her web-page improvements included a major upgrade in the way prescales were displayed online as well as improvement to the triggermeister web pages themselves. Her software improvements mean trigger rate studies now take into account the overlaps between triggers. She continues to help the new triggermiesters whenever they encounter problems not seen before, need help with database entries.
Luminosity Measurement A new Luminosity Monitor (LM) system installed at the beginning of Run II employs two 24-scintillator hodoscopes located close to the beam pipe on either side of the interaction region. The scintillators are read out with mesh photomultiplier tubes relatively insensitive to the Run II central magnetic field. Snow served as chair of two 6-person Luminosity Editorial Boards (EB) that reviewed the Run II luminosity measurement and, in particular, the determination of the normalization constant that converts measured rates in the luminosity monitors to absolute luminosity. The first EB (late 2003 to mid-2004) certified the normalization constant used in all Run II physics publications. Changes in running conditions call for a re-determination of the normalization constant: a reduced central magnetic field setting in place since the late-2004 shutdown, new read-out electronics commissioned in early 2005, and optimized high voltage settings for the LM photomultipliers. A second EB oversaw the determination of the new constant. Snow then assumed the convenorship of the Luminosity Review Panel evaluating the present luminosity hardware, electronics, and counting technique through the remainder of Run II when instantaneous luminosity values will routinely exceed 100 x 1030 cm-2s-1.