A Study of the &Delta I=1/2 Rule
in the Weak Decay of S-Shell Hypernuclei

This experiment seeks to measure the neutron to proton stimulated non-mesonic decay of the hypernucleus, _&Lambda⁴H. Combining this result with similar, existing measurements in other s-shll hypernuclei, a test of the &Delta I=1/2 rule as applied to the non-mesonic decay of the Lambda hyperon (&Lambda), can be made for the first time. The experiment will use the Neutral Meson Spectrometer system to tag the formation of the _&Lambda⁴H hypernucleus in a liquid He target. A set of neutron TOF scintillation detectors and proton range detectors will be installed to observe, in coincidence with the NMS, these decay particles. The experiment will be performed at the C8 beamline of the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL).

My contribution to this experiment is writing the software to process the CMU neutron detector data. Jinghua Liu has already invested a considerable effort in this regard, but much work remains.

Status Reports

8/3/00

Run 1707: bad channels.

7/31/00

Fastbus mapping of Out-of-beam scintillators. Typos in FBUS_MAP.dat. Assumed naming conventions.

7/10/00

Brief preliminary report now that I know roughly what to do.

Other important links

Brief preliminary Report

Jinghua Liu (UM) has mapped the ADC information from all out-of-beam (OOB) elements from the raw data into his event-display software, which visually displays for each event the relative ADC values for the active target, the NMS CsI, and all OOB scintillators. There has been no attempt to incorporate TDC or chamber information, nor to do any tracking.

Robin Barber (UH) has also done significant work on the OOB tracking exclusive of the neutron counters. Many technical notes appear on the UH web page.

Henry Juengst (UM) has completed the mapping of all the ADCs and TDCs from the OOB elements for incorporation into his analysis code using a mapping file from Jinghua and correcting some apparent typos.

The CMU group has worked extensively with these detectors on other experiments.

Goals:

• Verify mapping. Answer lingering questions about what "right", "left", "up", and"down" mean.
• Incorporate TDC information.
• Calibration. How much has Jingua done? Cosmics?
• Tracking. Incorporate Robin's analysis.
• Rudimentary particle identification. Prior to this will need to establish some "typical" event types.
• Identify non-working channels (e.g. TDC but no ADC, no hits for entire run, overflows)

FASTBUS mapping of Out-of-beam scintillators

All out-of-beam scintillator data pass through fastbus crate 2 in the following slots:

0

veto and some "L" NC ADCs

2

some "L" and some "R" NC ADCs

4

some "R" NC ADCs

6

front and back timing scintillator ADCs

11

veto and some "L" NC TDCs

12

some "L" NC TDCs

13

some "L" and some "R" NC TDCs

14

some "R" NC and beamline and target TDCs

15

front and back timing scintillator TDCs

The file FBUS_MAP.dat obtained from Jinghua contains several apparent typos in the sections pertaining to the TDCs for the out-of-beam scintillators:

• LN30A is missing -- should be address (2,12,18)?
• LN30B is missing -- should be address (2,12,16)?
• RN20B is missing -- should be address (2,13,32)?
• RN29A has the identifiier 2,9,1 -- should be 2,10,1. These identifiers are specified in the array IdCHAN in init_fbusmap.f.

• RN12A is amidst left veto TDCs in address (2,11,17) rather than amidst right NC TDCs in address (2,13,18).
• Rn25B instead of RN25B. Not used in init_fbusmap.f anyway.

All out-of-beam scintillator ADCs appear to be self-consistent.

The conventions in the naming in FBUS_MAP.dat are assumed as follows:

• "L" refers to beam right. "R" refers to beam left.
• "V" refers to vetoes. "N" refers to neutron counters.
• Layer 1 in NC stack is nearest the target, layer 5 farthest.
• Row "0" in the name (referred to as row 1 in the IdCHAN(2)) is the first row on the top of the stack, with row numbers increasing as one goes vertically downward.
• The veto layer is referred to as layer 6 in the ADC name, but not in the TDC name (where the layer number is absent).
• "A" refers to beam upstream. "B" refers to beam downstream.

Large number of differences between the FBUS_MAP.dat from Jinghua and the one from Robin's page. All differences, excepting the target scintillators, appear to be in the out-of-beam chambers (as expected) and in the ``local position'' field for other out-of-beam components. All typos and irregularities listed above exist in both versions.

Run 1707: Bad Channels

Using the mapping and conventions assumed above, I have compiled a partial list of obvious problems with the neutron counters for run 1707. At the moment, I don't know whether the mapping, software, or hardware is causing these problems. I list them exclusively for the purpose of documenting the problem.

Neutron counters:

• L layer 1 row 10: A ADC dead.
• L layer 2 row 10: both ADCs dead.
• L layer 3 row 1: both ADCs and TDCs dead.
• L layer 4 row 7: B ADC almost never fires.
• L layer 4 row 9: neither ADC fires with regularity.
• L layer 5 row 5: B ADC dead.
• R layer 1 row 10: B ADC dead.
• R layer 2 row 1: A ADC only fires with A TDC doesn't; B ADC nearly dead; B TDC completely dead.
• R layer 2 row 6: ADCs and TDCs appear to be completely uncorrelated.
• R layer 3 row 1: B ADC dead.
• R layer 4 row 10: B ADC dead.
• R layer 5 row 1: A ADC dead.
• R layer 5 row 5: A ADC dead.

Many of the counters seem to have sorely mismatched gains (lots of TDC action without much in the ADCs) and are suffering from uncalibrated pedestals.

How can I better categorize these things to give me a hint about whether the hardware or the software is messed up?!

Other Important Links

• Experiment E931 maintained by the Medium-Energy Physics Group at the University of Houston
• Henry's Hyper Hall University of Minnesota
• Jinghua Liu University of Minnesota

C. M. Riedel, July 2000

This page is under construction.