The KATRIN experiment: calibration & monitoring

Transcription

1 The KATRIN experiment: calibration & monitoring NPI Rez near Prague

2 content KATRIN overview < Am/Co measurements at Mainz < first Rb/Kr measurements at Mainz < multiple background events <

3 the KATRIN experiment > next generation tritium experiment > beta decay experiment > to measure neutrino mass > model independent way > compl. to double β decay & cosm. > sensitivity 0.2 ev (90%c.l.) (no signal) > discovery potential 0.35 ev (5 σ) > design report, 2005

4 calibration & monitoring interested in energy < voltage measured < matching each other calibration < no physical motivation < bias of 10 ev -> mass of 1e 6 ev < diff. of tritium & helium mass 1.7 ev < > stability of calibration monitoring > strong physical motivation > time change of bias of 0.03 ev > implies fictitious mass of 0.02 ev

5 Am/Co measurements at Mainz

6 Am/Co source > 241 Am gammas ± 0.2 ev > width better than 0.03 ev > half-life of 432 y > 1.11 GBq by Amersham > photoeffect on a Co foil > K-shell bind. eng ± 0.02 ev > with respect to Fermi level > width 1.3 ev > el. kin. eng about ± 0.2 ev > chemical shifts 2.0 ev

7 Am/Co measurements history count rate [Hz] > autumn 2003, ESA 12 Rez/Prague > induced by X-rays 0.5 > MC by A. Spalek > spring 2004, Mainz > reassembled source part > autumn 2004, Mainz > understanding background > spring 2005, Mainz > final feasibility study ESA 12 measurement & MC sim. ^ energy [ev]

8 Mainz setup > source part reassembled > Am/Co source in the magnet B > pumped to about 2e 9 mbar > if baked up to 250 C > pumping speed 1500 l/s > a full electrode, two grids > air coils > Earth field compensation coils > tank pumped to 1e 10 mbar > segmented detector > 1.5 kev resolution

9 spectrometer performance > Rb/Kr K-32 line > energy of about ev > natural width of 2.8 ev > theoretical res kev > el. inhomog. 0.5 V (rough) > HV ripple 0.8 V Energy [ev] > spec res. 1.5 ev > fitted position ± 0.03 ev > fitted width 3.16 ± 0.12 ev > chi^2/d.o.f. 0.94

10 the first scan Energy [ev] > vanishing effect > background of 3.2 khz

11 gamma background count rate [Hz] > Am 26.3 & 59.6 kev gammas > Np X-rays > Am self-absorption > factor of 2.2 for 26.3 gammas > Am X-rays > all these emit electrons energy [kev] the thinner Co foil the better < 0.1 µm on mylar foil, hard to sputter < 3.0 µm Co foil picked up < the thinnest, self-supported <

12 tilted source position > monel shielding 58 deg. > source tilted 65 deg. > 26.3 kev shielded completely > 59.6 kev suppressed significantly > transmission checked by 57 Co > lower by factor of the tilted source holder ^ 57 Co K-14.4 line, the tilted way < Energy [ev]

13 adiabatic way Energy [ev] > energy res kev > 300 el./s > as expected

14 turning nonadiabatic > energy res kev > 3.6 T mag. A&B, 5.2 G an. plane > worse adiabacity > lower background > bck. component from the source > Np & Am X-rays > photoeffect on Co L-shells Energy [ev]

15 sputtering the foil > well defined surface > reproducibility > get rid of Co oxides > in favor of metal component > Ar ions of about 100 ev > about 16 nm of Co sputtered reference sputtered the setup during the sputtering ^ black before, and magenta after < Energy [ev]

16 turning even more nonadiabatic > fixing magnetic flux > 2.4 T mag. A&B, 0.56 T cm 2 > varying energy resolution > starting 3.9 ev (5.0 G) (black) > reaching the adiabatic edge > 2.4 ev (3.1 G) (magenta) > loosing the ability to guide el. > finishing 1.5 ev (1.9 G) > signal to background ration Energy [ev]

17 turning even more nonadiabatic > fixing energy resolution > (mag. field at the an. plane) > zooming the det. image > (varying detector field) > improving signal to bckg. ratio > paying the effect > getting space at the an. plane Energy [ev]

18 nonadiabatic way > energy res kev > 2.4 T mag. A&B, 1.8 G an. plane > mag. flux 0.17 T cm 2 > effect of about 2 Hz > background of about 16 Hz > our best Energy [ev]

19 Am/Co conclusion good & stable source < to monitor & calibrate < > J. Bonn for sharing his experience, assistance & hospitality > E. Otten for valuable discussions, financial support > F. Glück for his code to calculate el. & mag. fields, and to track el. > B. Flatt for spec. introduction

20 first Rb/Kr measurements at Mainz, A. Kovalik INP Rez near Prague, ЛЯП ОИЯИ Дубна

21 Rb/Kr source > a convenient solid source > to monitor > June, 2005, Mainz > 29 kbq source (83Rb, 86 d) > evaporated at Rez/Prague > memo to be published

22 spectrometer setup > spectrometer magnets 45 A > mag. fields of 5.4 T > pumped to 5e-10 mbar > Rb/Kr in the magnet > pumped to 8e-9 mbar > no bake up > detector charged up 40 V > the inner segment only > moderate conditions

23 the first scan > Iair = 0 A > Ic = 60 A (1.7 T) full field > Ban. = 11.5 G, res. 3.8 ev > beam diameter of 43 cm > source diameter of 6.7 mm Energy [ev] Energy [ev] > a wide scan at the top > a zoom on the left

24 optimized position > keeping the setup constant > moving the source > 4.5 mm down, 1 mm left > signal to background ratio Energy [ev] Energy [ev] > a wide scan at the top > a zoom on the left

25 improved resolution > Iair = -7.5 A > Ic = 35 A (1.0 T) > Ban. = 4.9 G, res. 1.6 ev > worse adiabaticity Energy [ev] Energy [ev] > a wide scan at the top > a zoom on the left > background component coming from the source

26 optimized mapped area Ic = 55 A Ic = 45 A Ic = 35 A Ic = 25 A Energy [ev] > Iair = -7.5 A > Ic = 55, 45, 35, 25 A > Ban. 5.6, 5.3, 4.9, 4.6 G > res. 1.8, 1.7, 1.6, 1.5 ev

27 the K-32 line > Ic = 25 A, Iair = -7.5 A > analyz. plane field of 4.6 G > resolution of 1.5 ev > 29 % of the source mapped Energy [ev] Energy [ev] > the K-32 line at the top > low energy tail on the left

28 the K-32 line fitted > position about ev > width 2.8 ev > theoretical res. 1.5 ev > el. inhomog. 0.5 V (rough) > HV ripple 0.8 V > spec. res. of 1.5 ev > position ± 0.03 ev > width 3.16 ± 0.12 ev > chi^2/d.o.f = Energy [ev] > spec. res. of 2.0 ev > position ± 0.03 ev > width 2.96 ± 0.12 ev > chi^2/d.o.f = 0.94 > 83mKr activity est. 1.9 kbq > gamma spec. 29 kbq > e.i. 6.6 % of 83mKr kept

29 L-9.4 lines > keeping the setup constant > resolution of 0.6 ev > detector eff. 3 times lower > both 83Rb & 83mKr decays Energy [ev] Energy [ev] > L-9.4 lines at the top > the L1-9.4 line on the left

30 L-32 lines > keeping the setup constant > resolution of 2.6 ev Energy [ev] Energy [ev] > L-32 lines region at the top > the L3-32 line on the left

31 Rb/Kr conclusion & outlook all lines clearly observed < no disturbing backgrnd. < source quality superior < activity to be enhanced < Kr escape to be avoided < long term stability < > J. Bonn for assistance, ideas, experience shared, and financial support > F. Glück for his elmag. code > A. Spalek & D. Venos who prepared the source

32 multiple background events at Mainz, J. Bonn NPI Rez near Prague, Universität Mainz

33 experimental evidence > B. Flatt: background, X-ray gun > N. Titov: background > the tritium runs & sweeping electrodes with HV > no evidence in the tritium data Energy [kev] several electrons < with the retarded energy < at the same moment <

34 not an electronic effect Energy [kev] > gammas not multiplied

35 a scope look

36 a scope look

37 independence of count rate > 1.11 GBq Am/Co vs. > pure spectrometer background > 25 kv vs kv (no reason) > the same behavior Am/Co induced, U 0 = 25.0 kv pure background, U 0 = 18.2 kv Am/Co induced, U 0 = 25.0 kv pure background, U 0 = 18.2 kv Energy [kev] the first segment data on the top ^ the third segment data on the left < Energy [kev]

38 mirrors and traps > spectrometer a magnetic trap > analyzing plane & magnets > canceled by I_B = 0 A & > strong counter-field I_air = 10 A. > electrodes directly mapped I B = 50 A I B = 0 A I B = 50 A I B = 0 A Energy [kev] the first segment data on the top ^ the third segment data on the left < Energy [kev]

39 shaping time > 3 µs vs. 1 µs > too slow to separate the events µs 1 µs µs 1 µs Energy [kev] the first segment data on the top ^ the third segment data on the left < Energy [kev]

40 energy resolution > 1.5 G, 1.3 G, and 1.1 G > 1.2 ev, 1.0 ev, kev > diam. of 47, 50, 55 cm first seg. > diam. of 80, 87, 94 cm third seg. > full electrode of 100 cm in diam. > grids with diam. of 89, 80 cm Ban = 1.5 G Ban = 1.3 G Ban = 1.1 G Ban = 1.5 G Ban = 1.3 G Ban = 1.1 G Energy [kev] the first segment data on the top ^ the third segment data on the left < Energy [kev]

41 beam diameter > diam. of 47 (80) cm 1 st (3 rd ) seg. > 1.2 ev ( T cm 2 > 2.4 ev ( T cm 2 > T cm 2, 47 -> 50 cm > neither resolution nor beam diam. > adiabacity driven Φ = 0.26 T.cm 2, d an = 47 cm, res. 1.2 ev 18.6 kev Φ = 0.51 T.cm 2, d an = 47 cm, res. 2.4 ev 18.6 kev Φ = 0.51 T.cm 2, d an = 50 cm, res. 2.0 ev 18.6 kev Φ = 0.26 T.cm 2, d an = 47 cm, res. 1.2 ev 18.6 kev Φ = 0.51 T.cm 2, d an = 47 cm, res. 2.4 ev 18.6 kev Φ = 0.51 T.cm 2, d an = 50 cm, res. 2.0 ev 18.6 kev Energy [kev] the first segment data on the top ^ the third segment data on the left < Energy [kev]

42 adiabacity > 2.6 G, 3.8 G, 4.9 G, and 6.1 G > 1.9, 2.8, 3.6, kev > narrowing the beam flux > suppressing the effect > Am/Co spec. to be subtracted res. 1.9 ev 18.6 kev, d an = 50 cm res. 2.8 ev 18.6 kev, d an = 41 cm res. 3.6 ev 18.6 kev, d an = 36 cm res. 4.5 ev 18.6 kev, d an = 33 cm res. 1.9 ev 18.6 kev, d an = 86 cm res. 2.8 ev 18.6 kev, d an = 72 cm res. 3.6 ev 18.6 kev, d an = 63 cm res. 4.5 ev 18.6 kev, d an = 57 cm Energy [kev] the first segment data on the top ^ the third segment data on the left < Energy [kev]

43 screening voltage > 1.8 G, kev > +5 V, +10 V, +15 V screening > both the intermed. & dipole el. > can cure the effect U = +0 V U = +5 V U = +10 V U = +15 V U = +0 V U = +5 V U = +10 V U = +15 V Energy [kev] the first segment data on the top ^ the third segment data on the left < Energy [kev]

44 true secondary electrons Probability Energy [ev] > secondary electron emission > elastical reflection > redifussion > true secondary electrons phenomenological prob. model < by M.A. Furman & M.T.F. Pivi < LBNL (2003) <

45 probability of the process rad π/8 rad π/4 rad 3π/8 rad Probability E 0 = 10 ev E 0 = 50 ev E 0 = 70 ev E 0 = 100 ev E 0 = 200 ev Incident energy [ev] Probability incident energy dependence - top ^ incident angle dependence - left < π/8 π/4 Incident angle [rad] 3π/8 π/2

46 yield per incident electron rad π/8 rad π/4 rad 3π/8 rad True secondary electrons yield True secondary electrons yield E 0 = 10 ev E 0 = 50 ev E 0 = 70 ev E 0 = 100 ev E 0 = 200 ev Incident energy [ev] incident energy dependence - top ^ incident angle dependence - left < π/8 π/4 Incident angle [rad] 3π/8 π/2

47 yield per penetrated electron rad π/8 rad π/4 rad 3π/8 rad True secondary electrons yield True secondary electrons yield E 0 = 10 ev E 0 = 50 ev E 0 = 70 ev E 0 = 100 ev E 0 = 200 ev Incident energy [ev] incident energy dependence - top ^ incident angle dependence - left < π/8 π/4 Incident angle [rad] 3π/8 π/2

48 a simulation mockup > few tens of electrons produced > to be guided to the detector > have to be bound on a field-line > a nonadiabatic process > driven by plasmons (problably) > as for the reflected ones > they may hit the electrode again > to leave & bind on a field-line > they hit the detector ~1 µs later > repeatedly some reflected by the mag. field< not many of them < energy < resolution accepted < energy > resolution high prob. <

49 multiple events conclusion & outlook multiple background events < driven by lack of adiabacity < true secondary el. suggested < simulation offered < unknown nonadiabatic process < a threshold energy study? contribution to tritium background? > F. Glück for his code to calculate el. & mag. fields, and to track el. > E. Otten for valuable discussions

50 acknowledgment O. Dragoun < A. Kovalik, ЛЯП ОИЯИ Дубна < M. Rysavy, A. Spalek, D. Venos < J. Bonn, E. Otten, Universität Mainz < F. Glück, FZK Karlsruhe < B. Flatt, Universität Mainz <