Search For Isolated Fractionally Charged Particles |
Results
Summary as of January 2007.
Total mass throughput for all experiments- 351.4 milligrams of fluid
Total drops measured all experiments - 105.6 million
No evidence for fractional charge particles was found.
Experimental run utilizing Automated Millikan apparatus number 4 (2004-2007).
- Lateral E field, vertical airflow apparatus
- Active fluid drop charge control using electrically fine tuned, radioactively ionized air
- Drop generation rate 0.833 Hz (limited by drop to drop hydrodynamic cross interactions)
- Fluid - Carbonaceous chondrite meteoric material suspended in mineral oil.
- Number of drops - 42.5 million
- Mass - 262.8 milligrams
- Duration - 36 months
M.L. Perl et al.,"Search for fractional charge particles in meteoric material," Physical Review Letters (to be submitted).
Charge histogram in units of e of the
42.5 million drops measured during
the 36 month experimental run.Each charge measurement to be valid:
- Charge magnitude less than 20e
- Drop trajectory Chi Squared fit > 10-2
- Charge consistency of the positions <0.05e
- Minimum drop to drop separation >2.1 mm
Residual charges in units of e of the 42.5 million drops measured during the 36 month experimental run. This graph represents the superposition of all of the regions between the charge peaks of the charge histogram above.
Measurement accuracy is 1/24e.
No evidence for fractional charged particles in a meteorite mineral oil suspension were found with charges between 0.25e and 0.75e.
Experimental run utilizing Automated Millikan apparatus number 3 (2000-2001).
- Lateral E field, vertical airflow apparatus
- Drop generation rate 1 Hz (limited by drop to drop hydrodynamic cross interactions)
- Fluid - Dow Corning silicon oil
- Number of drops - 17 million
- Mass - 70.1 milligrams
- Duration - 8 months
I. T Lee et al.,"Large bulk matter search for fractional electric charge particles," Physical Review D, v.66(1), 2002.
Charge histogram of the 17 million
drops measured during the 8 month experimental run. Each charge measurement to be valid:
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This graph represents the superposition of all of the regions between the charge peaks of the charge histogram above. Measurement accuracy is 1/50e. No evidence for fractional charged
particles in silicone oil were found with charges between 0.18e and
0.82e. In this residual charge range there were fewer than 1.17 x 10-22
fractionally charged particles per nucleon with 95% confidence level.
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Experimental run utilizing Automated Millikan apparatus number 2 (1999).
- Drop generation rate 4 Hz (limited by drop to drop hydrodynamic cross interactions)
- Fluid - Dow Corning silicon oil
- Number of drops - 40.12 million
- Mass - 17.4 milligrams
- Duration - 5 months
V. Halyo et al.," Search for free fractional electric charge elementary particles using an
automated Millikan oil drop technique," Physical Review Letters, v.84 no.12, pp. 2576-2579, 2000.
Charge histogram of the 40 million drops measured during the 5 month experimental run. Each charge measurement to be valid:
- Charge magnitude less than 4.5e
- 6 or more position measurements
- Charge consistency of the positions <0.2e
- Trajectory modeling residual < 8s
Enough positional measurement to extract multiple independent charge measurements were required to guard against pseudo fractional charge measurements caused by a drop picking up an ion in the middle of a velocity measurement.
Residual charges of the 40 million drops measured during the 5 month experimental run. This graph represents the superposition of all of the regions between the charge peaks of the charge histogram above.
Measurement accuracy is 1/50e.
The single fraction charge event near 0.3e passed all data cuts but as it is a singular event it is unknown whether it is evidence of free fractional electric charge or if it indicates a source of background requiring additional data cuts. In particular this measurement occurred under the conditions of the measured drop being in the same field of measurement as a highly charged drop with a trajectory that brought it cyclically close to the measured drop (which had a much lower charge.) This could in principle produce a fractional charge measurement artifact by hydrodynamic coupling to the measured drop. No other similar events however were observed in the other 40 million measure drops. A subsequent experiment will measure the same type of fluid with increased throughput to attempt to clarify this issue.
Experimental run utilizing Automated Millikan Apparatus number 1 (1995).
- Drop generation rate - 0.7 Hz (limited by the requirement that only one drop be in the camera field of view)
- Fluid - Dow Corning silicon oil
- Number of drops - 5,974,941
- Mass - 1.07 milligrams
- Duration - 9 months
N .M. Mar et al, "Improved search for elementary particles with fractional electric charge,"
Phys Rev D, Vol. 53 No. 11, 1996.
Charge histogram of the 5,974,941 drops measured during the 9 month experimental run. Each drop was required to have three charge measurements consistent to within 0.15e to guard against pseudo fractional charge measurements caused by a drop picking up an ion in the middle of a velocity measurement.
Plot of the region between the charge peaks for all 5,974,941 drops. No fractional charges were detected.
The standard deviation of the charge measurements was 1/40e.
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April 30, 2007
Stanford Linear Accelerator Center
Website maintenance: erlee@SLAC.stanford.edu