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BVR, July 18th 2005, CB + T. Iwamoto PowerPoint PPT Presentation


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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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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


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an internal note

requested by the

INFN MEG Referees

(MEG-TN027)


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MEG internal note and then NIM collaboration paper


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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.....


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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


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attempt to grade the different C&M methods


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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)


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  • 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)


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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


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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


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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 !!


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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)


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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......


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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


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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 !)


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model: “coaxial SINGLETRON”


Precise calibration l.jpg

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)


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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


Nai detector stage design l.jpg

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


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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)


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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 !


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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


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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 %


P p n g 129 mev e e l.jpg

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......).


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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


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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)


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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 !


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reconstruction of the 8 -source positions in gaseous Xe.

Recent measurement with the large-prototype.

(Po-source produced in Genoa)


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RINGS

IN

LIQUID XENON

the ring radius

depends on

the Rayleigh scattering length

in LXe


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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.


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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


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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


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EXTRA SLIDES


Some distributions a l.jpg

Some distributions – a)

Pe+ + Pe- = Eg

129 MeV

Thickness

0.15 X0

Energy loss

and MS


Some distributions b l.jpg

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


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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


Mc ingredients l.jpg

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


1 p p n p 0 some distributions l.jpg

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)


Impact point and g energy release in lxe l.jpg

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%


Efficiency vs converter thickness41 l.jpg

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


Rough estimate of the time needed for the lxe calibration l.jpg

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


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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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