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| HyperCP | |
|---|---|
| Name | HyperCP |
| Other names | Fermilab E871 |
| Location | Fermilab |
| Operation | 1996–1999 |
| Facility | Meson Laboratory |
| Spokesperson | Don Summers |
| Experiment number | E871 |
HyperCP
HyperCP was a fixed-target high-energy physics experiment at Fermilab designed to study rare decays of hyperons and kaons. The apparatus aimed to probe charge-parity violation, search for flavor-changing neutral currents, and test predictions of the Standard Model through precision measurements involving strange baryons and mesons. The collaboration involved institutions across the United States, Japan, Russia, and Europe, producing results that influenced subsequent experiments at facilities such as CERN and J-PARC.
HyperCP was proposed following measurements at the Tevatron, intending to exploit the high-intensity charged secondary beam from the Meson Center beamline at Fermilab. The collaboration included physicists from University of Illinois, University of California, Irvine, Massachusetts Institute of Technology, University of Oxford, Nagoya University, and Moscow State University. The experiment targeted rare processes exemplified by searches similar in motivation to those at the NA48 experiment, KTeV experiment, and later LHCb experiment. HyperCP operated in the era contemporaneous with the LEP collider shutdown activities and took advantage of advances in tracking and data acquisition pioneered at experiments like CDF and D0.
HyperCP used a high-rate charged secondary beam produced when 800 GeV protons from the Tevatron struck a target, creating copious strange particles including Ξ and Ω hyperons, and neutral kaons like K_S and K_L. The beamline incorporated magnetic elements similar to those used on the Meson Test Beam Facility and followed designs informed by experiences at BNL and CERN SPS. The setup emphasized vertex resolution and momentum measurement to distinguish decay topologies relevant to searches analogous to those performed at KEK and SLAC. Triggering strategies drew on techniques used in the E871 predecessor experiments and contemporaneous rare-decay searches at FNAL.
The detector suite combined multiwire proportional chambers, drift chambers, and scintillation hodoscopes for precise tracking and timing, paralleling instrumentation developments from ARGUS and CLEO. Two large analyzing magnets provided momentum analysis in a manner comparable to magnets at PSI and TRIUMF. A hadronic calorimeter and muon identification systems borrowed concepts from the NuTeV experiment and E871-era detector R&D. Data acquisition used custom electronics and trigger processors akin to systems developed for CDF Run I and BTeV proposals, while alignment and calibration procedures benefited from techniques established at SLAC National Accelerator Laboratory and DESY.
HyperCP collected O(10^9) hyperon decays and O(10^7) kaon decays, relying on high-throughput readout and online filtering inspired by the MARK II detector and ALEPH data flows. Analysis pipelines employed reconstruction algorithms similar to those used by BaBar, Belle, and KLOE collaborations, with Monte Carlo simulations implemented in toolkits derived from GEANT frameworks used at CERN and Brookhaven National Laboratory. Statistical methods included likelihood fits and blind analysis approaches reflecting practices from the B-factory experiments and the Muon g-2 analyses. Systematic error evaluation used cross-checks against control channels studied also by Hyperon experiments at Brookhaven and CERN ISR.
HyperCP produced precise measurements of decay asymmetries in charged hyperon channels, contributing to constraints on CP violation beyond those from NA48 and KTeV. A notable outcome was the report of three events in the decay Σ+ → p μ+ μ− consistent with a narrow dimuon mass, prompting theoretical interest from groups working on supersymmetry, dark photon models, and light pseudoscalar searches relevant to axion-like particle phenomenology. The collaboration published limits on flavor-changing neutral current processes comparable to bounds set by LHCb and Belle II in later years, and provided inputs used in global fits alongside results from PDG compilations and fits from the CKM matrix program. HyperCP’s measurements of hyperon polarization and decay parameters informed models developed at JLab and guided analyses at COMPASS.
HyperCP’s dataset and methodology influenced detector design and rare-decay search strategies in subsequent experiments at CERN, J-PARC, and Fermilab’s later programs including proposals for upgraded fixed-target studies. The collaboration’s anomalous dimuon finding stimulated theoretical and experimental follow-up at institutions such as MIT, University of Chicago, Harvard University, Princeton University, and research groups at SLAC and LBL. Techniques in high-rate tracking, trigger logic, and blind analysis from HyperCP were adopted by successor projects like Mu2e, NA62, and ORKA proposals. Alumni of the collaboration continued careers at national labs and universities, contributing expertise to projects at CERN LHC, FNAL Intensity Frontier, and J-PARC Hadron Experimental Facility.