MICE

1MICE Vittorio Palladino, RAL, 17 February 2003

MICE

International Muon Ionization Cooling Experiment

This talk:Measurements & measuring technique Next talk (Rob Edgecock):MICE – the UK PerspectiveMICE – the UK Perspective.


A detector physicist view of MICE

given a ~ 10 % cooling engine ..... a mysterious black blox ....

build for it an unequivocal ~ 1% “diagnostics” tool

two complete (almost) identical detectors

(two spectrometers equipped with timing & PID)

one in front of and one in the back

of the box

each providing a complete measurement of all six parameters

of each particle

to measure the beam emittance both in & out of the box

i.e. the ~10% emittance reduction

with ~ 1% uncertainty

i.e. with an absolute error equal to 0.1%


Quantities to be measured in a cooling experiment

equilibrium emittance

cooling effect at nominal inputemittance ~10%

curves for 21 MV, 3 full absorbers, particles on crest

both output emittance & transmission decreases ...better FOM needed


Quantities to be measured in a cooling experiment (ctd)

number of particles inside acceptance of subsequent accelerator(for nominal NuFact, 15 mm rad, 30%)

Need to count muons coming in within an acceptance box and muons coming out. must not only measure emittances, but also count particles

It is difficult to count very precisely particles of a given type in a bunch

and to measure emittance very precisely. => single particle experiment


Emittance measurement

Each spectrometer measures 6 parameters per particle x y t x’ = dx/dz = Px/Pz y’ = dy/dz = Py/Pz t’ = dt/dz =E/Pz

Normalized emittance n

by using (x, y, t, p/mc.dx/dz, p/mc.dy/dz, p/m.dt/dz)

Determines, for an ensemble (sample) of N particles, the moments:Averages <x> <y> etc… Second moments: variance(x) x

2 = < x2 - <x>2 > etc… covariance(x,y) xy = < x.y - <x><y> >

Covariance matrix

M = M =

2't

't'y2

'y

't'x2

'x

'tt2t

'yt2y

'xt'xy'xxxtxy2x

...............

............

............

............

............

2'y'xyx

D4

't'y'xytxD6

)Mdet(

)Mdet(

Evaluate emittance with: Compare Compare in in with with outout

Getting at e.g. Getting at e.g. x’t’x’t’ is essentially impossibleis essentially impossible with multiparticle bunch with multiparticle bunch measurements measurements


Single particle experiment => truely thorough analysis •Correlations between phase space parameters can be easily measured.

•The detailed understanding of the role of each beam parameter energy transverse momentum RF phase (=time) ............can easily be studied by making selection cuts in the ensemble. A wide range of parameters being sampled, any desired input beam conditions can be reconstructed by appropriate slicing and/or reweighting of the population of particles observed.


requirements on detector system:

1. tag each particle considered: select muon, in & out !

in …… reject e, p, => TOF 2 stations 10 m flight with 70 ps resolution

& up-Cerenkov, if life were tough out …… reject e => down-Cerenkov + em Calorimeter 2. measure all 6 particle parameters i.e. x,y,t, px/pz , py/pz , E/pz

3. each with resolution 10% ( 1% in quadrature) of width around equilibrium emittance

… … ie adequate to preserve unsmeared

estimates of variances & covariances .. emittance

!!!

4. stand possibly severe noise level from RF cavities


Incoming muon beam

Diffusers 1&2

Beam PIDTOF 0

CherenkovTOF 1

Trackers 1 & 2 measurement of emittance in and out

Liquid Hydrogen absorbers 1,2,3

Downstreamparticle ID:

TOF 2 Cherenkov

Calorimeter

RF cavities 1 RF cavities 2

Spectrometer solenoid 1

Matching coils 1&2

Focus coils 1 Spectrometer solenoid 2

Coupling Coils 1&2

Focus coils 2 Focus coils 3Matching coils 1&2

10% cooling of 200 MeV muons requires ~ 20 MV of RF single particle measurements =>

measurement precision can be as good as out/ in ) = 10-3

never done before either….


two “timing helicometers”Each measures, very precisely, & time stamps

the helicoidal trajectory of each individual muon

Difference is in the PID systems

emphasis on separation in front of the front detector

fighting beam contamination

on e separation in the back of the back detector fighting muon decay

need of simply matching with the cooling section and of keeping a large-emittance beam in a small physical volume

=> solenoidal spectrometer coaxial to cooling channel Blondel, Janot 01

Each a precise tracker device inside a 4 T solenoidal magnetic field

matching the transverse diameter of the muon beam being cooled (30 cm)

capable also of precise (70 ns) timing


Tracking & timing the helices

need of simply matching with the cooling section keeping a large-emittance beam in a small physical volume

=> chose solenoid magnets coaxial to the cooling channel Blondel, Janot 01

(x,y) measurements at 3 different z values in principle sufficient length such that average makes about (2/3 of) a turn ie about 1 m for 200 MeV/c in a 4 T solenoid

70 ps TOF measures phase of to 5° wrt the 201 MHz RF

B Field


Pz resolution degrades at low pt :

Performance

Pt/Pz

E/Pz

TRANSVERSE MOMENTUM RESOLUTION pt = 110 keV

resolution in E/Pz is much better behaved

measurement rms is 4% of beam rms… also ≈100 m spatial resolution real small

resolution

resolution


MICE simulations & general sofware effort A fast simulation (DWARF4), including dE/dx & MS, was used for the basic design ….. emittance generation tracking particle identification ................ since the time of the LOI

A more complete GEANT4 simulation (G4MICE) long term foundation of the MICE sofwtare, including everything true end-to-end simulation of BOTH cooling AND detectors complete description of the detectors, down to digitization first repository of reconstruction algorithms now already providing first results


solenoidal geometry... one major drawback for trackers

exposed almost directly to a large dark current

and x-ray background

however i) background moderate at RF gradient of 8.3 MV/m baseline due to limited availability of RF power ii) LiH absorbers do absorb dark current e- completely, only x-rays only through iii) the detectors are built of low-Z material x-rays Compton hits are less frequent & distinguishable from triplets

it appears that the performance of the detectors will not be affected

studies of this background continue .... with high priority ! did we ever have the RF power ...

background from the nearby high-gradient RF cavities


measure 4 x 104 Hz/cm2 e rate at 8 MV/m in lab G 805 MHz pillbox cavity scaling to 201 Mhz by the volume ratio of cavities

(emitter area proportional to surface, energy to length)

gives total e rate of 30 MHz for detector radius 15 cm (an area of 700 cm2)

converted to photons by absorber (efficiency = Re/X0 ~ 0.07) Re e range, X0 rad length 0.26% Compton scatters in the detector per plane 6 fibre ribbons 0.035 cm thick X0 45 cm

rate about 0.5 MHz/plane (admittedly large

uncertainty)

about 2-3 orders of magnitude below levels found tolerable by G4MICE studies

... while materials & surface treatments also being investigated

Estimating the background


measured dark currents

real background reduced by factorL/X0(H2) . L/X0(det)0.07 0.0026

Backgrounds

Dark current backgrounds measured on a 805 MHz cavity in magnetic fieldwith a 1mm scintillating fiber at d=O(1m)

Extrapolation to MICE (201 MHz):scale rates as (area.energy) X 100and apply above reduction factor 2 10-4

4 104 Hz/cm2 @ 8 MV/m @805 MHz0.8 kHz/cm2 per sci-fi 500 kHz/plane ! within one order of magnitude !


.43 X 4 cells = 1.7 m 11.5 MV for 1X 4 = 6.70 MV/m

16 MV for 2X4 = 4.65 MV/m

16 MV for 1X4 = 9.3 MV/m

=> 6.70 MV/m => 4.65 MV/m


Tracker

Baseline Option:

Sci Fi tracker – 5 stations with 3 crossing double planes of 350 m fibres readout by VLPC (High Q.E. and high gain) as in D0.

Pro: we are essentially sure that this will perform well enough for MICE. Con: 43000 channels make it quite expensive (4.1 M€)

2 cost saving alternatives, under energic investigation :

Option 1 Sci-Fi -- Reduce channel count by multiplexing channels (1/7) Pro: cheaper by factor 4. Con: less sure to work in presence of Bkg and a few dead channels.

Option 2 Use a Helium filled TPC with GEM readout (‘TPG’) Pro: very low material budget (full TPG = 2 10-4 X0) and lots of points/track (100) cheaper (<0.5 M€ of new money) Con: long integration time (50 s vs 10 ns) => several muons at a time + integrated noise effect of x-rays on GEMs themselves unknown.


Sci Fi tracker – 5 stations with 3 crossing double planes of 350 m fibres readout by VLPC (High Q.E. and high gain) as in D0 … see MUSCAT also

Pro: we are essentially sure that this will perform well enough for MICE.

Con: 43000 channels make it quite expensive, if read out individually (4.1 M€)

Tracker Baseline Option:


concept

Sci-Fi studies with

G4MICE

background simulated 1000 times largerthat extrapolated from measurements does NOT degrade resolution seriously(No multiplexing here!)

further improvements from the RF cavitywill be seeked (TiN coating) etc…

looks good. if this is confirmed, one could envisage running with higher gradients. This is possible if -- 8 MW power to one 4-cavity unit-- LN2 operation

in

out


Cost saving alternatives: Option 1

Multiplex Sci-Fi -- Reduce channel count (1/7)

Seven 350 m fibres multiplexed by a 7:1 multiplexing wave guide into one VLPC pixel.

only be about a 10% loss of light in the outer ring of fibres due to a slight mismatch.

Pro: cheaper by factor 4 …. save 3 M !!!!!

Con: less sure to work in presence of bkgd and of a few dead channels.

OK if backgrounds from the RF cavities stays at a low level


Cost saving alternatives: Option 2

TPG ………… a 90% Helium filled TPC 1 m long and 30 cm Ø

Novel: GEM amplification and hexaboard R/O

Pro: very low material budget (full TPG = 2 10-4 X0)

lots of points/track (>100) oustanding pattern recognition

cheap (<0.5 M€ of new money)

Con: long integration time (50 s vs 10 ns)

=> several muons at a time + integrated noise

effect of x-rays on GEMs themselves …. still to be ested


at noise rate similar to that simulated for fibers, no difficulty finding tracks and measuring them.

resolution somewhat better than sci-fi (which is good enough)

difficulty: nobody knows the effect of RF photons on the GEM themselvestests in 2003, decision October 2003



trigger ... simple doubles & triples .... 70 ps rms ..... 1% ID ( 1400 ps TOF ..) + 5° timing wrt the RF phase

TOF0 Bicron BC-420 plastic scintillator Hamamatsu R4998 PMTs

TOF1&2 BC-404 fine mesh Hamamatsu R5505 OK in 1 Tesla fringe fields thou reduced gain BESS] + dedicated laser calib system [HARP]

12124040 cm2

basic TOF designupstream t0 tin tout



Particle Identification

Both residual beam pions

and muon decay electrons

fake different kinematics spoil and bias the emittance measurements

must have < 0.1% of either in the sample

PID rejection must be strong & redundant both up and down stream


Upstream Particle Identification

Even with a solenoid decay channel, the beam is not pure. Entering electrons and protons have different cooling properties and must be rejected (easy)

Pions are more of a problem since they can decay in flight with a daugther of different momentum ………………. big bias in emittance!

need less than 1 ‰ pion contamination in final sample.

TOF in the beam line with 10m flight path and 70 ps resolution providesseparation better than 1% @ 300 MeV/c (t = 1400 ps ! ) it is sufficient that the beam has fewer than 10% pions

A small beam Cherenkov is foresen to complete the redundancy in this system (overlaps …. or higher …) a 5 ” Ø vessel of liquid C6F14 (n=1.25), 30 cm long in total


Downstream PID

0.5% of decay in flight ………… large bias if a forward-decay e is kept as two systems are foreseen to get to eliminate electrons below 10-3 :

Electromagnetic Calorimeter (mip = em shower 27 MeV, use also z profile)Aerogel Cherenkov ( n=1.02, blind , threshold well above beam momentum )

Positive Identification of a particle in the calorimeter consistent with a muon AND no electron signal in the Cherenkov


PRECISION

1. statistical errors

--emittance is measured to 10-3 with ~106 muons.

-- ratio of emittances to same precision requires much fewer (105) a nice unexpected

surprise (re)measuring again the same , after little material … in & out strongly correlated

statistical fluctuations largely cancel in the ratio

-- Due to RF power limitations we can run about 10-3 duty factor 1ms/s -- To avoid muon pile up we want to run at ~1 muon per ISIS bunch

(1/330ns) 3000 muons /s -- The emittance generation must cover cooling acceptance uniformly -- 25% of incoming muons within acceptance

-- about 1/6 mimic a bunch on crest => MICE cools 100 muons/s . A 10-3 measurement of emittance ratio will take 103 s … 1/3

hour !!

N.B. this assumes a beam line with a solenoid to be obtained from PSI. A quadrupole channel has more background and less rate, and would lead

to a time longer by a factor ~10.


1. statistical errors

--emittance is measured to 10-3 with ~106 muons. --ratio of emittances to same precision requires much fewer (105) a nice surprise, unexpected measuring again the same , after little material … in & out strongly correlated

statistical fluctuations largely cancel in the ratio -- To avoid muon pile up we want to run at ~1 muon per ISIS bunch (1/330ns) 3000/s -- The emittance generation must cover keeps 25% of incoming muons within acceptance about 1/6 are on crest … a bunch … => 100 good muons per second. -- Due to RF power limitations we can run about 10-3 duty factor 1ms/s

A 10-3 measurement of emittance ratio will take 106 s < one hour

N.B. this assumes a beam line with a solenoid to be obtained from PSI. A quadrupole channel has more background and less rate, and would lead to a time longer by a factor ~10.


. MICE measures e.g. (out in)exp = 0.894 ± 0.001 (statistical)

compares with (out in)theory. = 0.885

and and tries to understand such atries to understand such a ~ 0.01 0.01 differencedifference

in emittance in emittance reduction reduction

SIMULATIONSIMULATION

REALITYREALITY

MEASUREMENTMEASUREMENT

A.A. theory systematics: modeling of cooling cell is not as reality

B. B. experimental systematics:modeling of spectrometers is not as reality

MICE-FICTION:MICE-FICTION: systematic errors

ACCURACY


No systematic must affect the expected 10% cooling effect by more than 10–3 absolute, i.e., 1% of its value.

The errors of class AA (modeling the cooling cell ) Errors in this category include: Uncertainties in the thickness or density of the liquid-hydrogen absorbers and other material in the beam Uncertainties in the value and phase of the RF fields Uncertainties in the value of the beta function at the location of the absorbers Misalignment of the magnetic elements Uncertainty in the beam energy scale Uncertainties in the theory (M.S. and dE/dx and correlation thereof)

All errors of type A become more important near the equilibrium emittance.

The errors of class B B (modeling the pair of detectors ): systematic differences between incoming and outgoing measurement devices different efficiency different misalignments possible differences in the magnetic field of the two spectrometers will constrain them heavily .... got a full arsenal of ancillary measurements

Step III or run MICE empty with no RF or analyse cooling vs muon phase (free) or .....


3 hall probes

Positioning holes

SC Coils

Magnetic

sensors

Magnetic measurements

design of system and procedures by Saclay (Rey, Chevallier)

NIKHEF will provide the probes (Linde)

Most critical is the control of the magnetic fields. For this reason MICE will be equipped with a set of magnetic measurement devicesthat will measure the magnetic field with a precision much better than 10–3.


- STEP I: 2004

STEP II: summer 2005

STEP III: winter 2006

STEP IV: spring 2006

STEP V: fall 2006

STEP VI: 2007 full power


The statistical precision will be very good and there will be many handles against systematics.

We believe that the systematic errors on the measurement of the ratio of emittances can be kept below 10-3

This will require careful integration of the acquisition of data from the spectrometers and from the cooling cell.

A lot remains to be done in this area, admittedly, to make surethat MICE has foreseen the necessary diagnostics by the time it turns on.




Next Future

1. Prototype critical detectors (trackers) in 2003

Test beds … Fermi … KEK …. CERNPS … bkgrounds

…… Sci Fi …..TPG

2. Choose helicometer option Oct 31 (CollMeet)

3. Start build late this year … more standard items

………trigger&TOF, PID subdetectors

4. Be there first …. …. well understood by the

time the cooling engine

arrives


Conclusions

The MICE detector system

an integrated tool … a pair of challenging particle

detectors…

capable to measure reduction of emittance

at 1% level

appears feasible

first to be studied

a full cell of the US NuFact design studyII including a number of beam & optics conditions beyond

the baseline

The collaboration has organised responsibilities, determined the basic costs and time line of the construction and commissioning of the two detectors .


requirements on detector system:

1. tag each particle considered: select muon, in & out !

in …… reject e, p, => TOF 2 stations 10 m flight with 70 ps resolution

& up-Cerenkov 1/2” Ø, 30 cm liquid C6F14 (n=1.25) cell

out …… reject e => down-Cerenkov + em Calorimeter 2. measure all its six parameters i.e. x,y,t, px/pz , py/pz , E/pz

3. each with resolution better than 10% of width at equilibrium emittance (correction less than

1%) … … ie adequate not to smear (spoil sensitivity

to) variances & covariances …...

emittance !!!

4. Be robust against noise from RF cavities


Further Explorations

We have defined a baseline MICE, which will measure the basic cooling properties of the StudyII cooling channel with high precision, for a moderategradient of ~8 MV/m, with Liquid Hydrogen absorbers.

Many variants of the experiment can be tested.

1. other absorbers: Various fillings and thicknesses of LH2 can be envisaged The bolted windows design allows different absorbers to be mounted.

2. other optics and momentum: nominal is 200 MeV/c and 42 cm. Exploration of low (down to a few cm at 140 MeV/c) Exploration of momentum up to 240 MeV/c will be possible by varying the currents.

3. the focus pairs provide a field reversal in the baseline configuration, but they have been designed to operate also in no-flip mode which could have larger acceptance both transversally and in momentum (Fanchetti et al) (We are not sure this can be done because of stray fields…)

4. Higher gradients can be achieved on the cavities, either by running them at liquid nitrogen temperature (the vessel is adequate for this) (gain 1.5-1.7) or by connecting to the 8 MW RF only one of the two 4-cavity units (gain 1.4)


Time Lines … to be reformulated

Time lines for the various items of MICE have been explored – procurement delays and installation – the critical items are solenoids and RF cavities.

If funding is adequate, the following sequence of events can be envisaged * -> consistent with the logistics of the beam line upgrade at RAL and of the various shut downs.

Muon Ionization cooling will have been demonstrated ands measured precisely by

2007

At that time MINOS and CNGS will have started and mesured m13

2 more precisely J-Parc-SK will be about to start up ( LHC will be about to start as well

It will be timely (…and not too soon!) to have by then a full design for a neutrino factory, with one of the main unknowns (practical feasibility of ionization cooling) removed.


- STEP I: 2004

STEP II: summer 2005

STEP III: winter 2006

STEP IV: spring 2006

STEP V: fall 2006

STEP VI: 2007

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