HyperCP Group at University of Virginia
Goals of HyperCP
The goal of HyperCP is to search for new sources of matter-antimatter
differences, or CP violation,
in particular in the decays of Λ and Ξ hyperons,
which are sensitive to sources of CP violation that kaon
decays, for example, are not.
The signature for the CP asymmetry is a difference between
the angular distributions (α parameters) of the Ξ-
and anti-Ξ- decay products, where the Λ and
anti-Λ have been produced from Ξ- and
Our expected sensitivity in the asymmetry is about 2 x 10-4,
of magnitude better than the present experimental limit.
Standard Model predictions are 10-5 and less,
but predictions from New Physics, such as supersymmetry can be much
larger, up to several times 10-3.
Note that we are doing much more physics than hyperon CP violation.
Click here for a complete
list of physics topics.
HyperCP Takes World's Largest Data Set
The HyperCP sensitivity goals demand a large number of events, and hence
an extremely high-rate spectrometer was built in the short space
of two years --- one capable of recording up to 100,000 events
The spectrometer accumulated the largest data set ever taken
--- 231 billion events --- in two runs: 1997 and 1999.
After careful work in precisely calibrating the spectrometer
and tuning up the code,
the primary event reconstruction (of almost 30,000 tapes)
was done on the Fermilab computer
farms and completed in the summer of 2001.
This work, which involved reconstructing a data set twenty-five times
larger than the total amount of data on all of the Web sites in the
was reported at the International Conference on Computing
in High Energy and Nuclear Physics in Beijing, China, in
September, the conference summary speaker having highlighted
the effort as a "tour de force."
UVa's Role in HyperCP
The Antimatter Asymmetry Group at the University of Virginia
has played a salient role in HyperCP from its inception, by
Craig Dukes and Kam-Biu Luk (of Berkeley) in 1993.
Craig serves as scientific spokesperson of the experiment
(with Kam-Biu Luk), which was the first major new
experimental effort initiated by the newly formed Experimental High
Energy Physics group at the University of Virginia.
The UVa group had a leading role in the construction of the spectrometer,
with the following responsibilities:
- The design and construction of the hadronic calorimeter.
- The design and fabrication of the front wire chambers.
- The design and construction of the OS Hodoscope.
- The design and fabrication of all 20,000 preamplifier channels.
- The design and implementation of the triggers.
Status of the Analysis
The analysis of the HyperCP dataset has reached a mature stage with 13
Highlights of the physics analyses include:
For copies of our publications click
- A factor of 20 improvement over the best previous limit in the
search for CP violation in charged-Xi and Lambda hyperon decays.
- Evidence for the rarest baryon decay ever observed:
Sigma-plus -> proton + mu-plus + mu-minus.
- A high-statistics null search for the Theta-plus(1.54) pentaquark.
- Precision measurements of the parameters in the Xi-minus ->
Lambda + pi-minus decay.
- First observation of the flavor-changing neutral-current (FCNC) decay
K-minus -> pi-minus + mu-plus + mu-minus, as well as the charge
conjugate decay, a measurement that resolved a discrepancy between two
- Searches for strangeness-changing two decays and lepton-number
violating decays to are orders of magnitude more sensistive than
Back to main page