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BVR, July 18th 2005, CB + T. Iwamoto

CALIBRATION AND MONITORING METHODS (C&M) FOR THE LIQUID XENON CALORIMETER AND FOR THE WHOLE MEG DETECTOR........ Xe calorimeter, wire-chamber spectrometer, timing counters an updated discussion on : advantages, disadvantages, open problems, etc. of proposed methods.

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BVR, July 18th 2005, CB + T. Iwamoto

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  1. CALIBRATION AND MONITORING METHODS (C&M) FOR THE LIQUID XENON CALORIMETER AND FOR THE WHOLE MEG DETECTOR........ Xe calorimeter, wire-chamber spectrometer, timing counters an updated discussion on: advantages, disadvantages, open problems, etc. of proposed methods • C&M for the entire MEG: • at any time • during PSI beam-off periods, tuning.... • efficient use of beam-on periods BVR, July 18th 2005, CB + T. Iwamoto

  2. an internal note requested by the INFN MEG Referees (MEG-TN027)

  3. MEG internal note and then NIM collaboration paper

  4. KEEP MEG UNDER CONTROL PARTICULARLY AT HIGH (AND VARIABLE) BEAM INTENSITIES......... BR   eg~ 10-13 Beam Intensity ~ 5 107 /s • frequent checks of calorimeter energy scale, linearity and stability • checks of LXe optical properties • energy resolution, spacial resolution, time resolution • shower properties • at the right  energy ( 53 MeV), but also at other energies.....

  5. TWO MAIN TARGETS: • MAINTAIN THE MEG ENERGY, SPACE AND TIME • RESOLUTIONS OPTIMIZED OVER LONG PERIODS • OF TIME • HAVE RECORDED PROOFS OF MEG PERFORMANCES • (WHATEVER THE FINAL MEG RESULT ON BR   eg) • emphasize the reliability of our experiment ! • GOOD C&M IS THE KEY TO MEG SUCCESS no single calibration method has all the required characteristics use complementary (and redundant) methods, make the best use of their intrinsic properties

  6. attempt to grade the different C&M methods

  7. 500 KV PROTON ACCELERATOR AND LITIUM TARGET FOR A 17.6 MEV GAMMA LINE [P.R. 73, 666 (1948), N.P. 21 1 (1960), Zeitschrift f. Physik A351 229 (1995)] 37Li (p,)48Be • Potentialities : • strongly exothermic nuclear reaction • unique: -emission much favoured over -emission • obtainable: at resonance (E p =440 keV 14 keV) •  106 /s (isotropic) for Ip 50 A • from LiF target at COBRA center; ’s on the whole cal. • entrance face • energy and position calibration; shower properties • rather frequent use • privilege simple, fast, (semi-automatic) mechanical system • for proton beam and LiF target introduction and positioning • (give up the use for the calorimeter monitoring from the back)

  8. further studies: • compatibility with normal beam and target • COBRA field, accelerator (and focusing element) position • project for easiness of target-tube mounting • p-beam divergence and protons on target; p29 MeV/c • post-acceleration to scan the resonance • thin-target, thick-target • H2+ ions, effects on -line, (H2+ elimination by a mag.-triplet)

  9. astrophysics data http://pntpm.ulb.ac.be/nacre.htm E sigma error S-factor error (MeV) (b) (b) (MeV b) (MeV b) 0.1294.55E-062.3E-07 1.37E-037.00E-05 0.375 1.44E-03 8.5E-05 5.10E-02 3.00E-03 0.384 5.86E-03 1.5E-04 2.02E-01 5.00E-03 0.388 4.44E-03 1.8E-04 1.51E-01 6.00E-03 1.0057.59E-05 4.3E-06 1.23E-037.00E-05 at the Tp* 384 keV resonance and compound nucleus formation + non resonant direct reaction elsewhere

  10. E0 = 17.6 MeV E1 = 14.6 6.1 Bpeak 0/(0+ 1)= 0.720.07 37Li (p,)48Be resonant at Ep= 440 keV =14 keV peak = 5 mb 0 1 NaI 12”x12”  spectrum

  11. other interesting possibilities..... : 13H (p,) 24HeE ~ 20 MeV !! used in SNO  in : Hahn et al. PRC 51 1624 (1995) but Tritium....and low rate....... 511B (p,)612C Cecil et al. NP A539 75 (1992) 10x10 cm NaI crystal resonant at Ep= 163 keV = 7 keV E0 = 16.1 MeV peak = 5.5 b E1 = 11.7 + 4.4 peak = 152 b •  7500/s (isotropic) • 20.0001/s for Ip 50 A lower proton energy ! lower rate at 50 A !!

  12. ENERGY, TARGET THICKNESS AND -LINE QUALITY correspondence between resonanceand range intervalR “thin target” R   “thick target” R >>  if Tp = 445 keV and R =  R = 0.120  N=7 x 1017 LiF/cm2 at 80 A Ip Np= 5x1014 p/s N= 1.8x106 /s(up to 1.6x105 in calorimeter) very clean -line (more difficult calibration tuning) if Tp = 445 keV and R = Range (445 keV) >> R = 413  N = 2.5 x 1019 LiF/cm2 at 80 A Ip Np= 5x1014 p/s N= 6x105 /s (+ N=1.8x106 /s) -line with appreciable left shoulder from 17.6 to 17.1 MeV (simple calibration tuning) of the total 5x1014 p/s, 2x106 p/sproduce photons at resonance, some of the residual 2.5x108 p/s produce direct photons of lower energy (if Tp > resonant energy, right tail also.........) H2+ ion effects........(30% of CW-beam)

  13. N= 1.8x106 /s over 4(up to 1.6x105 /sinto the whole calorimeter) (PMT non linearity over Ia = 4 A, therefore at about 2x105 /sin the calorimeter) Very high -intensity (other optional reactions have smaller cross-section) (possibility of using low-efficiency selective triggers) MEG aquisition rate is about 100 Hz The accelerator current can be easily limited, but one can also test the calorimeter and the PMT behaviour as a function of an increasing -rate in the calorimeter......

  14. CHOICE OF THE ACCELERATOR Cockroft-Walton, Van der Graaf, Radio Frequency Quadrupole HV Engineering, NEC, AccSys, Neue Technologien GmbH • overall price, guarantees, delivery time, test, assistance, • spare parts, etc. • energy interval of operation, current, stability, beam phase space, • background radiation, etc. • simplicity of use, reliability, type of computer control • source duration, 1-year without servicing, etc. • fast conditioning and tuning • beam height • possibility of moving the accelerator system • availability and possible use at the beginning of the experiment • The collection of information on all points is a slow, multistep process......: • visits to experiments using similar accelerators • visit to accelerator factories • discussion with national lab. experts

  15. STRONG PREFERENCE FOR A COCKROFT-WALTON • reliable system, in use for several precision experiments, visits to GS • good assistance in mounting and test; “nearby” factory • large energy interval of machine operation • visit to HV in Amersfoort and visit of HV to Pisa (Legnaro lab. expert • present) • adequate current, good beam properties, stability • fast tuning and operation if 1 MV machine in the same tank of the • 0.5 MV machine. (15% increase in price) • very low-background machine • well interfaced, good safety system, interlocks, good software • (and program source available) • compact machine in pressurized (and shielding) container • one year operation without service If one wants to use the machine for the MEG start-up an order must be issued as soon as possible (September !)

  16. model: “coaxial SINGLETRON”

  17. BVR February 2005 FULLY TESTED...... PRECISE CALIBRATION θ • Potentialities : • energy and position calibration • shower properties and reconstruction at • Eg  55 MeV, the proper energy ! • fully tested in “large prototype” runs • Open problems: • definition of -lines by collimators or by • -hit reconstruction (for ~ 180º). • NaI set-up. Several positions. • NaI behind coils. • H2 cryogenics, negative beam, different • target, target introduction in COBRA. • how often it can be performed ? E (MeV)

  18. TWO POSSIBLE WAYS TO PERFORM THE º CALIBRATION IN MEG • EXTRAPOLATION FROM PREVIOUS TESTS FOR MEG • Movable NaI system • Safe solution at the beginning of the experiment. • CONVERSION METHOD • No movable parts. • More comprehensive applications (wire-chambers,timing counters). • It depends on a trigger systems which is presently untested. • Both methods allow Xe calorimeter calibration in 1-2 days

  19. NaI Detector Stage design Anti Counter • NaI detector (~100kg) needs to be moved 2 dimensionally at the opposite side of the xenon detector. • The movable stage and motor need to be magnetic tolerable with reasonable positioning accuracy. • Test under COBRA field  OK No bearing ball Linear slider g up Screw drive Prism guide p0 down g target Linear slider: http://www.tollo.com Motor: http://www.animatics.com Motor Example

  20. an interesting possibility for a  calibration in MEG • abandon NaI detector in coincidence • illuminate the whole calorimeter at the same time with -2 • convert the -1 in a 0.1 X0 converter close to the H2 target • detect conversion and measure conversion point with a • “special counter” • measure e+ branch of the pair in the chambers • use part of the information for selecting -1 by trigger angle between ’s defined by impact points on LXe-Cal and “ special counter” (angles  1800 useful for calibrating at different energies) loss at conversion but huge increase in solid angle MC METHOD SIMULATION RESULTS (F.Cei)

  21. TRIGGER UNDER STUDY • Ingredients: • LXe Cal. and QSUM threshold • “special counter” • good time resolution, pixelization for conversion point reconstruction, • separation of e+ e-- pairs from single particles • positron (from n ) or pair trajectory (from n ) by the wire-chamber trigger • timing-counters • depending on the particular calibration........ A FULL TEST OF THE WIRE-CHAMBERS SPECTROMETER CAN ALSO BE PERFORMED !

  22. WIRE CHAMBER SPECTROMETER AND TIMING COUNTERS TEST (at full COBRA field) by - p  0 n and -1 conversion into an e+ e– pair and also by  - p  n and  conversion into an e+ e– pair (a pair spectrometer and a -line !!) but also the Cockroft-Walton allows a calibration of the LXe Cal and, wire-chamber spectrometer, timing counters • CW use is much simpler than  calibration ! • LXe Cal illuminated by 17.6 MeV ’s at high rate • Use of -converter for testing the wire-chambers spectrometer • maximum COBRA field for LXe Cal test • half COBRA field for wire-chamber spectrometer test

  23. g energy release: increased statistics 0.1 X0, NDC > 4, relative angle > 1750 • Intrinsic width for photons • emitted with relative angle • > 1750: 0.3 %. • Leakage effects: ~ 1 %. • Remaining contributions from natural angular width of e+e- pair production and multiple scattering in the target. FWHM 2.60.3 %

  24. p-p  n g (129 MeV)  e+ e- • Main purpose: calibration of wire-chamber spectrometer and timing counters. • Use e+e- pair production from 129 MeV gamma conversion in Tungsten. • Both e+ and e- must be detected and their tracks reconstructed. Pair spectrometer ! • Interesting thing: it provides a fixed (total) energy calibration point for the wire-chamber spectrometer (normally not easily obtainable......).

  25. Efficiency vs converter thickness 106 events (> 4 chambers) • 4 chambers required for detection Large errors due to small statistics, but promising results; 0.1 X0 looks the best choice. Generated 100000 events in the whole solid angle (4 p). ~ 400 Hz

  26. Total momentum distribution No reconstruction included Thickness 0.1 X0 FWHM ~ 0.7  0.9 % This FWHM must be compared with the value quoted in the Proposal: e+ + e- momentum (MeV)

  27. Am SOURCES ON WIRE AND WALLS BVR February 2005 Sources in production. Soon available for all LXe devices. • Potentialities : • PMT quantum efficiencies • Xenon optical properties • low-energy position and energy • calibration • use in Xe gas and liquid • stability checks ? • a unique method for cryogenic liquid • detectors !! Wire presently mounted in “Large Prototype” • Open problems: • will the method be usable under full intensity beam conditions ? • To be verified by test !

  28. reconstruction of the 8 -source positions in gaseous Xe. Recent measurement with the large-prototype. (Po-source produced in Genoa)

  29. RINGS IN LIQUID XENON the ring radius depends on the Rayleigh scattering length in LXe

  30. Determination of the relative QE for 4 different PMTs by the use of 4 dot-wire-sources in Xe gas of the large-prototype the relative QEs are given by the slope of the linear fits.

  31. C&M by NEUTRONS AND NICKEL-LINE , AT THE BACK OF THE CALORIMETER large-prototype NaI /E=2.5% in the large-prototype the line is worse..... (thermal neutrons in LXe !) the measurement must be repeated, protecting LXe from thermal neutrons by a borated-foil

  32. CONCLUSIONS • Several C&M methods tested with satisfactory results: • wire-sources • p0and  from p–charge exchange • thermal neutrons and nickel -line • Other C&M methods in preparation or being modified • for MEG: • CW accelerator and 37Li (p,)48Be reaction • new methods for p0and  from p–charge exchange

  33. EXTRA SLIDES

  34. Some distributions – a) Pe+ + Pe- = Eg 129 MeV Thickness 0.15 X0 Energy loss and MS

  35. Some distributions – b) Thickness 0.15 X0 Region to be selected (both e+/e- seen) e+/e- momenta At least 4 chambers (7 hits) required Relative angle genergy

  36. RADIO FREQUENCY QUADRUPOLE ACCELERATOR • practically monoenergetic • pulsed operation; frequency 100 Hz 100 ms pulses • average current 50 mA , pulsed current 5 mA • beam energy bin approx. 10 keV • small vessel, pre-accelerator • beam optical properties ? 1mm ; 20 mR • RF radiation ? No • proton source ? Plasma • cost ? acceptable (AccSys), (Neue Tech.) !!!!! • special design....time to produce ? One year • not an out-of-the-shelf machine • Companies: AccSys, Neue Technologien GMBH

  37. MC ingredients • Liquid hydrogen (LH2) target close to the muon stopping target (10 cm length x 5 cm diameter); • Thin tungsten converter adjacent to the LH2 target; thickness between 0.05 X0and 0.3 X0; • p0 decay & n g pair generated in the LH2 target with the correct energy and angular distributions; • Tracking of photons from p0 decay; • Tracking of electron & positron from photon conversion; • Multiple scattering in tungsten included; • Minimum number of chambers (4) in DC system required to define a track; • Energy/momentum reconstructions: work in progress • Increase of MC statistics: under way

  38. 1) p-p  n p0Some distributions Converter thickness 0.15 X0 After converter FWHM ~ 60 Before converter FWHM < 20 1stg–e+relative angle and multiple scattering effect Dq (0) 2nd g–e+relative angle vs energy loss in LXe DE in LXe (MeV) Region to be selected for energy calibration Higher density of points forDE< 60 MeV DE (MeV)

  39. Impact point and g energy release in LXe cos (q) Converter thickness 0.15 X0 Uniform coverage of the whole calorimeter FWHM  6.50 g1-e+ Relative angle g2-e+ Dq > 1750 FWHM(energy)  4 - 5%

  40. Efficiency vs converter thickness 106 events (> 4 chambers) Generated 100000 events in the solid angle covered by the LXe calorimeter (10%) • 4 chambers; relative angle  1750 ~ 23 Hz

  41. Rough estimate of the time needed for the LXe calibration Reconstruction and trigger efficiencies under evaluation Solid angle factor • <e> (20  30)/105/10 = (20  30) x 10-6 • R = Rp0 x <e> = (Rp0/106)x 106 x (20  30) x 10-6 = (20  30) x (Rp0/106) Hz(max.MEG acquisition rate 100 Hz) • Events/day  8.64 x 104 R  2 x 106 x (Rp0/106) • Assuming  50 locations to be calibrated (216 PMTs in groups of 4): (< 1000 events/location would be sufficient) 1000 events/50 s total for 50 locations 2500 s < 1 h

  42. Assuming N0 = 106 129 MeV photons/s: N(e+e- pairs detected)/s = N0 x epair ~ 400/s. Requiring 106 pairs in the wire-chamber spectrometer (at a rate of 100 Hz: Time = 106/(100/s) = 104 s (less than three hours).

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