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

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 TPC @ 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 = - 0.88 m2m) electro-weak symmetries of lepton-quark interaction m-e universality, additional interactions at quark-lepton level J. Govaerts, nucl-th/0004056 (2000). Nucl Phys A, in press

theory: LS = 688.4±3.8 s-1 Ja = Va - Aa nucleon charged current at q2= - 0.88 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) = 0.9755(5) gA(q2) = 1.245(3) gM(q2) = 3.5821(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

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

Experimental progress Jan 97 proposal R-97-05 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

Prototype Oct 99 Gatchina dimension: 30 x 15 x 10 cm3 gas gain 5000 (e) drift velocity (cm/s) 0.6 @ 2 kV/cm voltage (kV) cathode -30 cathodes strip - 6.5 anodes 0 material diam(mm) pitch(mm) gap(mm) cathode stainless/W 50 1 3.5 anode W 25 4 3.5 Gatchina

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

muon tracking Dt Dz=8cm

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

PU free, external e tracking

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

Gas system gas handling and purity analysis system developed. 0.01 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

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

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. 1010 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.

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, 0.1 level needs careful study

study final design by MC

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 2001-2002 collaboration

Statistics

Gas System

diffusion

external tracking