High Energy Physics
Particle Physics Research at Penn Overview
The goal of particle physics is to understand what are the most fundamental constituents of matter and how these elementary particles interact. The next few years hold great promise for answering fundamental questions such as
- What is the origin of electroweak symmetry breaking and mass (the Higgs sector)?
- Are there additional fundamental particles (e.g. supersymmetric partners of the known particles)?
- What is the origin of the matter anti-matter asymmetry in the Universe?
- What is dark matter?
- What is dark energy?
Penn has a very active and strong elementary particle physics theory group . The central thread is the unification of all interactions. This includes theoretical efforts in string and brane theory, phenomenological studies of the electroweak interaction, and attempts to connect the fundamental theory with experiment. The puzzles of dark matter, dark energy and the nature of the early universe demand a joint venture between cosmology and particle physics. Penn has a new Center for Particle Cosmology that provides an incubator for such research, fostering the development of new theoretical approaches, grounded in the current epoch of remarkable experimental progress.
Experimentalists in the Penn faculty are working on the following projects:
- The ATLAS experiment at the Large Hadron Collider (LHC) at CERN on the French-Swiss border. The goal of ATLAS is to discover new elementary particles. With data, there are lots of interesting topics for graduate students to work on, please join us! The detector started taking data in 2009 at a center-of-mass energy of 7 TeV, and has rapidly accumulated a large amount of data, with over 5 fb-1 collected by the end of the 2011 run. We have four faculty on ATLAS, working on the search for the origin of electroweak symmetry breaking in terms of the Higgs boson in the standard model, and on several searches for physics beyond the standard model. We are already involved in research and development for several upgrades to ATLAS, which will provide some very interesting hardware projects in the next years. It is expected that ATLAS will continue to take data in 2012, then shutdown for 2013-14 while LHC repairs take place to reach the design energy of 14 TeV, followed by data-taking for several years at 14 TeV.
- The Sudbury Neutrino Observatory in Ontario. The results from this facility have provided
revolutionary insight into the properties of neutrinos and the core of
the sun. The solar neutrinos produced by fusion interactions in
the core of the sun are electron neutrinos. En route from the
sun to the earth, these electron neutrinos change into other types of
neutrinos. The direct evidence for solar neutrino transformation also
indicates that neutrinos have mass. The facilty commenced in 1999 and
data taking was completed in 2006. A new experiment called SNO+ will
reuse the detector to search for neutrinoless double beta decay as
well as measuring the low-energy neutrino flux from the sun. We are involved in commissioning electronic upgrades, with first solar neutrino data expected in the next two years.
- The Long Baseline Neutrino
Experiment (LBNE) is focused on the areas of neutrino mixing that
are least known. The primary physics is aimed at electron neutrino
appearance measurements, with the highest priority being a search for
a Standard Model-like CP-violating asymmetry in the oscillation of a
muon neutrino into an electron neutrino with a beam originating at
Fermi National Accelerator Laboratory. Penn has been involved in the
physics and design for over a decade. The focus of our effort is the
development of a 200 kt Cherenkov far detector. We have three primary
efforts: photomultiplier characterization, simulation and
reconstruction development, and front-end electronics design. This
project is in a research and development phase for the next few years.
- The Penn instrumentation group provides an invaluable resource to the field of experimental particle physics, with expertise in detector design and electronics. We are involved in several research and development projects to upgrade the ATLAS detector and to develop the water Cherenkov detector for LBNE, and design and development of the camera for the Large Synoptic Space Telescope.
We have active seminar programs in Experimental Particle Physics and Theoretical Particle Physics at Penn.
EXPERIMENTAL PARTICLE PHYSICS
ATLAS Experiment at CERN
Faculty: Brig Willliams,Evelyn Thomson, Joe Kroll, Elliot Lipeles
Postdoctoral researchers: James Degenhardt, Sasa Fratina, Tae Min Hong, Rustem Ospanov, Peter Wagner
Staff scientists: Mitch Newcomer, Rick Van Berg, Paul Keener, Godwin Meyers, Mike Reilly, Nandor Dressnandt, Joel Heinrich
Graduate students: John Alison, Dominick Olivito, Ryan Reece, Elizabeth Hines, Josh Kunkle, Brett Jackson, Chris Lester (DOE graduate fellowship), Jon Stahlman, Doug Schaefer (NSF graduate fellowship), Rami Vanguri, Kurt Brendlinger, Jamie Saxon, Alex Tuna
Recent postdoctoral researchers: Mauro Donega (ETH Zurich), Franck Martin, Ole Rohne (Oslo)
Recent graduate students: Mike Hance (LBNL Owen Chamberlain Fellow)
Since 1994, the University of Pennsylvania group has played a large role in the design and construction of ATLAS, one of two large "general purpose" experiments at the LHC. The ATLAS detector stands nearly five stories tall and includes precision tracking systems for observing the trajectories and thus measuring the momenta of particles produced in the interactions, calorimetry for measuring the total energies of all observable particles produced, and muon chambers for observing muons which escape the calorimeter.
We have four faculty on ATLAS and a big group of 5 postdocs and 13 graduate students. Our first ATLAS graduate student graduated in summer 2011 and went on to a prestigious Owen Chamberlain Fellowship at LBNL. We expect many of our current graduate students to finish in 2012 and 2013 and are actively recruiting new graduate students. We are currently active in the search for the Higgs boson (decay channels two-photon, two tau-leptons, two W bosons->lvlv) as well as searches for new exotic massive gauge bosons (W', Z') and supersymmetry (direct gaugino, gluino-mediated stop production, compressed spectra). We have expertise in alignment of charged particle tracking, electron identification, and tau lepton identification. Our research has contributed significantly to the following recent papers
- Search for the standard model Higgs boson in the two photon channel and WW->lvlv channel
- Search for an exotic Z' gauge boson and W' gauge boson
- Measurement of the isolated prompt photon cross section, W and Z cross sections , and Z to tau tau cross section
We have an outstanding electronics and instrumentation group, which designed most of the front-end electronics for the TRT, and are involved in several hardware upgrade projects for ATLAS. We are working on the optimization of resources for the ATLAS trigger, and on the operation and understanding of the performance of the ATLAS Transition Radiation Tracker. Elliot Lipeles leads the ATLAS trigger rate group. James Degenhardt was deputy run coordinator of the TRT and Sasa Fratina was offline software coordinator for the TRT during the first collisions in 2009-2010. Peter Wagner, Dominick Olivito, Jon Stahlman are all DAQ experts for the TRT. Our detector research has contributed significantly to the following papers and conference notes
Left: ATLAS underground cavern (November 2005) with all of the muon toroidal magnets.
Right: Installation of the barrel TRT in the center of ATLAS (August 2006).
Sudbury Neutrino Observatory, SNO+, DEAP/CLEAN
To be updated
Faculty: Gene Beier, Josh Klein
Postdoctoral researchers: Gabriel Orebi Gann, Stan Seibert
Graduate Students: Tim Shokair, Richie Bonventre
Former postdoctoral researchers: Jeff Secrest, Huaizhang Deng
Former graduate students: Monica Dunford, Chris Kyba, Mark Neubauer, Vadim
Rusu, Peter Wittich
The Sudbury Neutrino Observatory (SNO detector). Shown in the figure are Penn graduate student Doug McDonald, Professor Josh Klein and graduate student Peter Wittich (from left) and others with the acrylic vessel underground in Sudbury.
The Sudbury Neutrino Observatory project (SNO) has solved one of the great puzzles of twentieth-century physics and astrophysics---the anomalously low flux of neutrinos coming from the sun. Since the late 1960's when Ray Davis first announced that he detected about one-third the number of neutrinos predicted by models of stellar evolution, scientists were in a quandary regarding the source of the discrepancy. Was his experiment wrong? Was our understanding of stars wrong? Or was there something else, perhaps an inadequate understanding of the properties of neutrinos?
SNO has shown that Davis's experiment was correct, and that the model of the sun is also correct. The puzzle was solved when SNO showed that some of the Boron-8 electron-neutrinos that are produced in nuclear fusion reactions that power the sun transform to another type of neutrino which does not produce a signal in Davis's detector.
Unlike previous solar neutrino experiments, the SNO detector is sensitive to three different neutrino reactions. One of the reactions is, like Davis's experiment, only sensitive to the electron-neutrinos that the sun produces. The other two reactions are sensitive to electron-neutrinos, and, in different proportions, to mu-neutrinos and tau-neutrinos --- types that are not produced in the solar fusion reactions. The three reaction types can be separated using the position, angle, and energy information of the events observed.
By comparing measurements of the flux of solar Boron-8 electron neutrinos (nu_e) to the total flux of all neutrino types (nu_x) coming from the Sun, SNO has shown that Davis's original measurement was correct---the nu_e flux is suppressed---but that the flux of all types of neutrinos is in agreement with the predictions of the model. The conclusion is that some of the electron-neutrinos that were produced in the sun transform into the other types of neutrinos before they are detected on earth. The most likely mechanism for producing this transformation requires that neutrinos have small, but non-zero mass. This is an indication of exciting new physics beyond the Standard Model of elementary particle physics. Although the mass of the neutrinos is tiny, the total mass of all the neutrinos in the universe is comparable to that of all the visible stars.
The unique feature of SNO is the use of a kiloton of heavy water, D2O, as a neutrino target. The valuable D2O is securely contained in a spherical acrylic vessel which is twelve meters in diameter. The vessel is surrounded by light water, H2O, and is viewed by 9500 photomultiplier tubes. To limit backgrounds introduced by cosmic radiation at the earth's surface, the entire laboratory and detector are located two kilometers underground in a cavity in one of the world's most productive nickel mines. The SNO cavity, which is the size of a ten story apartment building, is maintained as a "clean room" to exclude trace contamination from mine dust.
The SNO experiment began taking calibration and neutrino data in May 1999. The program of calibrations determines the optical parameters, the spatial, angular, and energy responses of the detector, the response to signals from neutrinos and processes that produce background, and systematic effects which might bias interpretations. The calibrations are taken routinely to track the time dependence of the detector response.
Neutrino data will be acquired in at least three configurations of the detector. The initial configuration was the simplest, with only heavy water inside the acrylic vessel. In June, 2001, the detector configuration was altered to the first of two configurations that will enhance the detection capability for nu_x. Measurements in these two configurations will produce independent measures of the flux of nu_x and serve as checks on each other and on the result from the initial phase. The additional data will also permit accurate measurements of possible distortions in the electron energy spectrum and day-night spectral differences for nu_e induced events. These measurements will lead to precise evaluation of the physics parameters responsible for neutrino flavor transformation in the solar sector. Additional topics of study include atmospheric neutrinos and a search for anti-neutrino interactions. SNO's neutron detection capability is a unique asset for this work. A program of data acquisition and analysis lasting at least through 2005 is envisioned, in order to obtain the highest precision results possible.
The University of Pennsylvania group constructed and is responsible for maintaining all the front-end signal processing electronics for the detector. This includes PMT signal detection and digitization, triggering, and GPS timing electronics. The effort has required three custom designed integrated circuits and fourteen custom designed printed circuit boards. Graduate students contributed to or were solely responsible for nine of the circuit boards. This represents one of the many substantial and crucial contributions to the SNO experiment by students.
Penn researchers were deeply involved in commissioning the detector and are now active in operations and data analysis at all levels. The opportunities for learning a wide range of physics and experimental techniques---from hardware design to data acquisition software to data analysis---are great; Penn graduate students working on SNO get a broad exposure to both the hardware and analysis skills required to do effective research and an opportunity to work on one of the most exciting experiments in the particle physics.
Long Baseline Neutrino Experiment
To be updated
Electronics Instrumentation
To be updated
More information on electronics at PENN
Staff Scientists: Rick Van Berg Mitch Newcomer (Instrumentation
Group Leader), Paul Keener, Godwin Meyers, Walter
Kononenko, Ben LeGeyt, Mike Reilly, Nandor Dressnandt
We have built up a sophisticated capability at Penn to design and test custom integrated circuits. We have developed two bipolar integrated circuits for SNO, have completed a custom bipolar circuit for ATLAS in two separate radiation hard technologies, have played a critical role assisting Queen's University in the development of the CMOS chip for SNO, have completed a custom bipolar circuit for CDF, and have recently played a major role (along with CERN and Lund University) in completing the design of a CMOS circuit for ATLAS. We have also helped dozens of other institutions around the world utilize the ASD8 chip or one of its variants for high rate wire tracking systems. Penn front end chips are in use at major experiments at Fermilab, Brookhaven, CERN, DESY, TRIUMF, and elsewhere around the world.
With the combination of the IMS Integrated Circuit tester purchased via an NSF University Infrastructure Grant and the automatic wafer probe system, Penn has a very sophisticated capability for testing integrated circuits. Production testing of IC's for SNO processed over 10,000 chips, there were also almost 10,000 ASDQ chips tested for CDF, and we are looking forward to testing almost 70,000 chips for ATLAS. We have also done testing of custom circuits designed by other groups and some detailed characterization of commercial circuits required for some special needs. The integrated circuit design and test capabilities are the outgrowth of a tradition of building novel and elegant electronics systems for particle physics experiments. Clearly the integrated circuits are only one facet, albeit the single most sophisticated portion, of such systems. At the more conventional level of system architecture and printed board design the Penn group has covered a wide gamut of projects recently from the full system of fifteen different printed circuits that make up the SNO electronics to the single boards used in the the CDF 30,000 wire Central Outer Tracker readout and Central Electromagnetic Calorimeter calibration systems and the very high density, high rate, low noise TRT readout card assemblies for ATLAS.