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C.Lazzeroni, University of Birmingham

Status and News

CEDAR Working Group CERN - 02/09/2008

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Situation in UKStatement of Interest (first step) submitted to 22nd July PPAN-STFC meeting : “Search for New Physics beyond the Standard Model with the NA62 experiment at CERN” and the CEDARFeedback:PPAN agreed that there was good and exciting science likely to emerge from the project and the proposal built upon the strong science role that the applicant has established.However PPAN was concerned by the lack of a developed science consortium for what was a significant package of research. For the project to be viable, PPAN believed that a stronger research community in the UK would need to be identified.

Effort is now concentrating on identifying other interested institutes: few universities already contacted - process will take some time...

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From last meeting

At the last meeting, 2 principal tasks were identified :1) choice of hydrogen gas and related infrastructure2) choice of photo-detectors

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L.G., 22 July 2008 K12 Beam Working Group – CEDAR Status4

Absolute necessity to minimize material on beam lineThe hope is that the 4x lower pressure allows thinner

windows(we hope 100 instead of 400 m Al)

Why hydrogen:

5 L.G., 22 July 2008 K12 Beam Working Group – CEDAR Status 5

Provide SC-GS with construction drawings and material certificates or definitions of

the materials used. This includes the type of steel, the windows material and thickness

(SC-GS may provide design input or help) and the type of seals.

The insulation material should not produce toxic black smoke. Note that polyurethane

foam is acceptable in small quantities whereas polystyrene is forbidden. A sample of the

insulation material should be made available for analysis by SC-GS.

Provide drawings and/or details of all electrical equipment (HV, motors).

Look at all possible leak scenarios and propose actions. This includes leaks into the

beam line, which must therefore use hydrogen rated pumps.

A hydrogen venting system must be available in TCC8 to cope with pressure changes

(including unforeseen pressure rises) and the placing of the hydrogen supply bottle must

be considered.

The relevant parts of the CEDAR counter should be housed in an inert enclosure. It

should be small enough (local !) that it does not become a confined space problem in

itself. Its walls should be thin to avoid danger in case of explosion.

Provide draft hydrogen filling and shutdown procedures, including emergency

scenarios

List of points to be addressed:

6 L.G., 22 July 2008 K12 Beam Working Group – CEDAR Status 6

0 1 2 3 4 50

20

40

60

80

100

Cedar N(He) versus W(H2) Comparison

Cedar-N, He

Cedar-W, H2

π+, 7-fold

K+, 7-foldCedar-N, He

Cedar-W, H2

[%]Efficiency

Diaphragm aperture [mm]

- MC

7 L.G., 22 July 2008 K12 Beam Working Group – CEDAR Status 7

100.0

±0.4

8 m

m

102.3

±0.4

5 m

m

Cedar-West (H2 filled)

Resolution is ok!

- MC

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Hydrogen CEDAR

Need to identify:- changes to be done(if any) to the CEDAR itself in order to use hydrogen gas rather than current gas- consequences in general infrastructure, connected to safety aspects

Decision to proceed to a First step: Prepare a CEDAR, as it is now, but filled with hydrogen Test it on beam line, at low intensity

Negotiation with beam division will start soon,to establish division of efforts and competences

9 L.G., 22 July 2008 K12 Beam Working Group – CEDAR Status 9

Original light spots

X (mm) X (mm)

Y (

mm

)

Y (

mm

)

20 x 7 mm2

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Photo-detector for the CEDAR

Current optics condenses the Cherenkov light from the diaphragm into 8 rectangular light spots ~10x30 mm2 each

Kaon rate = 50 MHz and ~100 photons per Kaon photon rate = 100 ph x 50 MHz / (300 mm2 x 8) ~ 2 MHz / mm2 (rate of singles from accidentals, after-pulses, dark noise not included)

Key points for the new detector: Single photon counting application Stand very high photon rate / unit area (occupancy in time and space) Reduced active area (beam activity) (minimum ~150 mm2 / spot due to optics phase space) UV/Blue light sensitivity with the highest efficiency (PDE) Excellent timing resolution on single photon Exposition to the halo of intense hadron beam (radiation damage)

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PMTs: R2248 vs R7600 R2248 R7600U/P square 10x10mm(8x8mm) 30x30mm(18x18mm) fill factor 64% 36% peak sens 420 nm 420 nm range 300-650 nm 300-650 nm - can be extended in UV QE 25% 25% - normal angle of incidenceGain (at 800 V) 1.1 x 106 2 x 106 Rise time 0.9 ns 1.4 ns Transit time 9 ns 9.6 ns TTS ~450 ps 350 ps Pulse width ~3 ns ~3 ns Av. current 0.03 mA 0.1 mA Dark current max 50 nA 20 nA or 500 counts cost (per 250) 850 CHF ??

R7600-100-M4 R7600-200-M4 R7600-00-M64 square 26x26 (18x18)mm 26x26(18x18)mm 26x26mm (18x18mm)fill factor 48% 48% 48%peak sens 350 nm 350 nm 420 nm range 270-650 270-650 300-650QE 35% 43% 25%Gain (at 800 V) 1.0-1.3 x 106 1.0-1.3 x 106 3.0 x 105 Rise time 1.4-1.2 ns 1.4-1.2 ns 1.0 nsTransit time 9.6-9.5 ns 9.6-9.5 ns 10.9 nsTTS 350 ps 350 ps 350 psPulse width ~3 ns ~3 ns ~3 nsAv. current 0.1 mA 0.1 mA 0.1 mADark current max 5 nA/ ch 5 nA/ ch 0.2 nA /chcross talk ? ? 2% cost (per 250) ? ? 1400 CHF

R2248 seems to be the best choice - test started by Placci

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PMTs options

R2248: 64 mm2 , 0.1 A/mm2 -> 6 A -> 1/5 max rated current

• Which is the limiting factor: cathode / divider / anode current ?• Is a safety factor needed ?Example: Assume we need to reduce the current by a factor of 6:

from 3 PMT per spot to 18 PMT per spot (144 PMT in total) light spot (30x10mm2) enlarged x 6 / 0.64 ~ x 9 with cones (100%eff.)

Photo-electon rate per spot: (12 photons per spots @ 50 MHz) x QE ~ 3 p.e @ 50 MHz 3 p.e. / 18 channels x 50MHz = 8.3 MHz per channel (R2248)

But can we work with no safety factor - with no additional optics ??Test needed

Would need optic system to increase the spot...

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ToDo

1) measure the limiting factors of the candidate PMT R2248: max anode/cathode currents

2) PMT single photo-electron pulse response: signal width, after-pulse features, time lag features

3) PMT performances as a function of high voltage (DV): timing features, collection efficiency, signal shape working at low G possible ?

Some data already exist, analysis in progressMore data needed

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Comparison SiPM vs PMTfor applications of photon counting and timing at high rates

20MHz limit to avoid signal pileup. Not mandatory: canuse proper shaping.SiPM can stand at least x10 more rate per unit areathan PMT

cell geometry

PMTHPK R7600(18x18 mm2)

SiPMHPK S10362-11-50C (1x1 mm2 )

Gain (G) ≥106 ≥106

Efficiency (on active area)

~25% @ 400nm ~40% (UBA)

~95% @ 400nm

Time resolution ~300ps 50ps to 100ps

Fill Factor 36% 40% to 80%

B-field immunity No Yes

Radiation damg. YesNo (also at single photon level ?)

Max average anode current

100 A(350 mm2 )

3 A(1 mm2 )

Reference device (eff. area)

After-pulse (thr. @ 1 p.e.)

1 % level 10 % level

Dark noise (1 p.e.) few kHz 0.5 MHz @room T

V/V for G/G=1% 3 x 10-4 6 x 10-4

T for G/G=1% 5o C 0.3 o C

See G.Collazuol talk atSORMA WEST 08 conf.

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SiPM

excellent efficiency and timing resolution for single photons very good rate capabilities and granularity cooling is necessary to reduce counts under control keep devices in the peripheral beam halo to reduce radiation damage dark count rate scales with active surface - small light spot

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Assume to collect light on a spot area of 12x12 mm2

covered by a matrix of 4x4 square SiPM's eachof dimension 3x3mm2 and 900 cells (100x100 mm2) -New design of suitable optics to concentrate Cherenkov light on 12x12 mm2 (about 1/2 of the original) Design cooling system

ToDo

From Francois:1 Hamamatsu SiPM is being tested which blue laser (405 nm) and connect to the NINO chip- analysis in progress

Test performances in the UV/Blue region:

Optics/cooling:

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FE electronics

Richard Stanley, electronic engineer from Birmingham,will visit Pisa in September with the aim of firstly learningwhat has been done already, and then helping with thereadout electronic, especially with the TELL1 FPGA

programming

pre-ampli + FADC + TELL1pre-ampli + NINO + TDC + TELL1

Need actual test of the chain with R2248 / SiPM - firstly in Lab, then on beam line

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Next Steps

• Test Beams 1) Test CEDAR prototype with Hydrogen (at low intensity) 2) Continue characterization of photo-detectors 3) Illumination with Cherenkov light for measuring : p.e. Yield and timing 4) Compare two solutions for electronics 5) Exposition of SiPM to K12 beam halo for measuring the radiation effects

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Spares

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PMTs for dummies...

• Limiting Currents: average/peak Anode ∝ p.e. Rate x Gain ~ exp (DV) average Cathode 1 photo-electron (p.e.) x Gain x qe = 1 x 106 x 1.6 10-19 = 200 fC Anode Current = rate/mm2 x QE x 2 10-13 = 2 MHz/mm2 x 0.25 x 2 10-13 = 0.1 A/mm2

• Transit time (TT) -> Pulse width ~ 1/ √DV - to be compared to photo-electron rate/channel - double pulse resolution: to be compared to rate/channel • TT spread (TTS) ∝ fluct. of flight time Cathd.-1stdynd. ~active Surf./ √DV -> time resolution ~ TTS/ √p.e. - to be compared to 100 ps necessary for tagging kaons• Rise time: ~ exp (-DV) - to be matched by FE electronics bandwidth

• Detection efficiency:• Sensitivity wavelength range: compare with Cherenkov spectrum• angle of incidence (photons) • collection efficiency (p.e.) ~DV first stage • Noise:• Dark current (uncorrelated)• After-pulses (correlated) • Cross-talk in Multi-Anode PMT (MAPMT) (correlated)

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Fast FE Electronics for counting and timing

Ideal FE for a high rate system:1) current amplifier or I-V converter: smallest Zin (to exploit the fast component) need low Gain ~ x20 (especially if SiPM working at low gain) high bandwidth

inherently fast (time resolution of the device not to be spoiled)2) RC shaper minimize signal occupancy (pile-up) per channel maximize the double pulse resolution (DPR < 5ns)3) sampling with FADC sampling (8 bits) at 1GHz: time resolution better than 20 ps rms and DPR better than 5ps are easy to obtain cost/channel < 180 $

Minimum number of channels to be evaluated on the basis of: Max level of inefficiency in kaon tagging due to pile-up: eg: DPR~5ns with >1p.e.@10 Mhz (signal) + >1p.e.@1 Mhz (noise) on 16 ch. inefficiencly due to pile-up ~ 5% Limit on time resolution: worsens with rate

NOTE: 1. up to now our tests with voltage amplifier + FADC sampling were successful even at very high rates (20MHz) 2. now we are testing the Time Over Threshold discrimination technique by exploiting the NINO chip (ALICE TOF, NA62 RICH) as an alternative FE chain: SiPM + Preamplif. + ToT Discrim. + TDC

to minimize the Kaon tagging inefficiency