1. Precision Measurement of Singlet mp Capture in a Hydrogen TPC
V.A. Andreev, D.V. Balin, A.A. Fetisov, V.A. Ganzha, V.I. Jatsoura,
A.G. Krivshich, E.M. Maev, O.E. Maev, G.E. Petrov, S. Sadetsky, G.N. Schapkin, G.G. Semenchuk, M. Soroka, A.A. Vorobyov, N.I. Voropaev
Petersburg Nuclear Physics Institute (PNPI), Gatchina,Russia
P.U. Dick, A. Dijksman, J. Egger, W.D. Herold, V. Markushin,
C. Petitjean, R. Schmidt, W. Schoeps
Paul Scherrer Institut, PSI, Villigen, Switzerland
T.A. Case, K.M. Crowe, P. Kammel
University of California, Berkeley, UCB and LBNL, USA
J. Deutsch, J. Govaerts, R. Prieels
Universite Catholique de Louvain Belgium
F.J. Hartmann
Technische Universitaet Muenchen,Garching, Germany
introduction
experimental progress
towards final experiment
outlook

2. rate LS (from mp(F=0) state)
goal
- + p  m+ n
rate LS (from mp(F=0) state)
LS to 1% gp to 7% precision
method
pure protium 10 bar as active target unambiguous interpretation clean m stop definition gas impurity control high statistics
measure -/m+ lifetime in hydrogen to 10 ppm LS = 1/- - 1/ LS ~1.5x10-3 l0
physics
test hadronic symmetries of Standard Model : QCD tests, chiral symmetry breaking, pseudoscalar formfactor gP(q2 = m2m)
electro-weak symmetries of lepton-quark interaction m-e universality, additional interactions at quark-lepton level
J. Govaerts, nucl-th/ (2000). Nucl Phys A, in press

3. theory: LS = 688.4±3.8 s-1 Ja = Va - Aa
nucleon charged current at q2= mm2
Ja = Va - Aa
Va= gV(q2) ga + igM(q2) sab qb/2M
Aa= gA(q2) ga g5 + igP(q2) qa/m g5
gA(0)=1.2670(35) q2 dependence from quasielastic n scattering
CVC: gV(0)=1, gM(0)=mp-mn-1 q2 dependence from e scatt.
nucleon weak CC formfactors
gV(q2) = (5) gA(q2) = 1.245(3)
gM(q2) = (25) gP(q2) = 8.44(23) gP(q2) = 8.21(09)
PCAC heavy baryon chiral perturbation theory:
accurate QCD prediction, precise expt’l test mssing nm n p m-
gpNN Fp

4. main experimental challenges
Physics effects
Interpretation At low density (1% LH2) mostly capture from mp(F=0) atomic state.
Wall stops and diffusion. Stop volume determined by tracking, transfer, diffusion suppressed.
Transfer to impurities. (cZ<10-8, cd<10-7) . TPC monitors nuclear recoils from m+Z  Z’+n+n and transfer to deuterium. Continuous purification/monitoring system system.
mSR effect for m+. Tranverse field ~70G. LT LS m
ppm pm
Lortho
Lpara
F=0
F=1
J=1
J=0
lOP
Time distortions due to detector effects
Self correlation
Two event correlations additional background terms correlated losses (“double kill”)
time dependent efficiency ?
Statistics
1010 statistics. Different analysis methods. Complementary: Tracking of m-e vertices of several m’s to overcome pile-up Pile-up free data sample.
m decay at all stages, l0

5. Experimental progress
Jan 97 proposal R presented at BVR, start phase 1: design, test basic detector system
Aug 97 progress report (systematics, chamber prototypes)
Dec 98 1st test run
prototype TPC+4 MWPCs
new DAQ, analog readout (12 channels)
Mar 99 continuation test run
digital readout, new TDC 400, 100 channels
Dec 99 2nd test run
TPC amd 6 MWPC, m and e internal/ext tracking
full digital readout all channels, 500 channels.
Mar 00 continuation test run
upgraded DAQ, event selection and compression
DAQ with 3 thresholds
Mar 00 gas system development
gas purification and chromatography at 0.01 ppm
protium production
Apr 00 start phase 2: design high purity detector system

6. Prototype Oct 99 Gatchina dimension: 30 x 15 x 10 cm3
gas gain 5000 (e)
drift velocity (cm/s) 2 kV/cm
voltage (kV) cathode cathodes strip anodes material diam(mm) pitch(mm) gap(mm)
cathode stainless/W anode W
Gatchina

7. Digital Readout two thresholds for TPC (electrons, muons)
custom made (Berkeley/PSI) deadtime less TDCs
high bandwidth DAQ to processor farm, VME-64, VX works
readout of contiguous (ms) time regions to provide complete history information

8. muon tracking Dt
Dz=8cm

9. PU free time spectra m - m + 12 ms 12 ms xe+l0t
m stop in fiducial volume
e after m time (bin width 200ns)

10. PU free, external e tracking

11. Impurities effect on lifetime of 0.01 ppm Z>1 1. ppm D
~0.01 ppm required or 0.1 ppm if measured & corrected
detection in TPC
impurity capture m+Z  Z’+n+n

12. Gas system
gas handling and purity analysis system developed ppm purity and sensitivity achieved. 3 LN2 traps, zeolite absorber, compressor production 60L/h gas chromatograph
A) commercial hydrogen, 1L, O2~0.1ppm, N2~0.2ppm B) after cleaning, 30L, O2<0.001ppm, N2~0.02ppm
on site analysis of TPC gas no special materials/ purification of TPC prototype

13. m transfer to deuterium, diffusion
mp+d  md + p  pmd  m(5.3MeV)+3He(0.2KeV)
Ramsauer Townsend minimum in md + p scattering at 1.6 eV mp
md pmd
m+He

14. Concept final experiment
Option 1
i) m tracked with scint, MWPC & TPC ii) e tracked with MWPC/scint. combination external to hydrogen vessel iii) samples of competing background processes recorded with selective trigger (3rd threshold)
Dead-time free data taking of event class I) and ii) Data includes pile-up and pile-up free events for complementary analysis pile-up free m-e (m+,m-) in 2 months
Option 2
Hermetic geometry with all MWPC inside hydrogen vessel. e tracked with MWPC combination inside the hydrogen vessel No windows, very small multiple scattering.
Pad TPC
During next months we will evaluate options based on
analysis of test runs, Monte Carlo
test of materials and procedures, without/with beam to define final set-up.

15. Technical design
all components inside H2 low outgasing, bakeable to 120 C wires W 4.5 ppm/K cathode frame Kovar 4.8 ppm/K anode frame ceramic/Pyrex 6./3. ppm/K
external detectors inner detector: chamber 3 SINDRUM I f =38.4cm, L = 58cm outer detector: chamber or scint. array a’la mLAN
DAQ upgrade with 2-4 VME CPUs CAEN tdc’s for MWPC readout
High vacuum& gas handling integrate present purification system non mechanical circulation system based on zeolite absobers at LN2 temperature (400atmL/h) present (new) protium system <1ppm, level needs careful study

16. study final design by MC

17. Summary and outlook
phase 1: basically finished optimize set-up & detector elements develop subsystems: electronics high speed DAQ gas purification, analysis study physics characteristics
phase 2: started develop ultra-clean techniques (det., recirculation) increase solid angle of external detectors construction final detector system integration
further generation Muon on Request : LS gP present proposal 1% 7% with MORE 0.3% 2%
tentative schedule
technical report within next 6-12 months
commissioning & start of production
collaboration

18. Statistics

19. Gas System

20. diffusion

21. external tracking