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ATLAS Forward Protons:Fast Time-of-Flight

DetectorsMichael Rijssenbeek – Stony Brook Universityfor the ATLAS Forward Proton group

• Quartic - the ATLAS Forward Proton Fast ToF Detector

see also next talk: Diamond detectors by Gabriele Chiodini (Universita del Salento)

2AFP Time-of-Flight

ATLAS Forward Timing Detectors

Collaborating Institutions:Canada: U Alberta (CFD, HPTDC), U Toronto (Detector mounting); France: Saclay (SAMPIC RO chip)Germany: U Giessen (Radiators)Italy: Lecce, Roma2 (Diamond R&D)Portugal: Lisbon U (Trigger)

USA: U Texas at Arlington (Detectors, MCP-PMT), Oklahoma State U (RO – Optoboards), U New Mexico (Irradiation), SLAC (Readout), Stony Brook U (Electronics, Readout, RPs)

AFP Time-of-Flight Project Leader: Andrew Brandt (UTA)

Many Thanks to all my colleagues for fruitful collaboration and help!

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3AFP Time-of-Flight

AFP – ATLAS Forward ProtonsAFP measurements:• Tag and measure momentum of intact protons from interactions

seen in the central ATLAS detector• Soft QCD (Diffraction) in special low/medium-luminosity runs

– avoid backgrounds from additional interactions in the same BX μ≃1• cross sections are rather high: many pb’s• need clean interactions in ATLAS, i.e. low pile-up

– need ~3 weeks-equivalent of data taking at μ≃1 (or ~1 week at μ≃3 ?)• at μ>1, require proton time-of-flight measurement to correlate forward

protons with interaction vertex measured in central ATLAS detector σt=30 ps ⇔ σz=7 mm

• Hard Central Diffraction in standard running (μ~50)– huge background from pile-up: 1 proton per side in each BX from soft

QCD (Single Diffraction, etc.)• pile-up suppression requires precise proton time-of-flight measurement.• any increase spatial and temporal granularity improves efficiency and

rejection17JUL13

AFP

206

AFP

214

AFP

214

AFP

206

4AFP Time-of-Flight

Fast Time-of-FlightMain CEP background: overlap of SD protons with non-diffractive events = ‘pile-up’ backgroundReduce by:– central mass matching:

• Mcentral = MAFP = (s ξLeft ξRight)½

– ToF:• zvtx = c(tLeft – tRight)/2

• E.g.: σt = 10 ps σzvtx = 2.1 mm

–not a new idea; FP420:

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σt =20 ps: 0.1σt =10 ps: 0.5MX >800: 0.05

5AFP Time-of-Flight

Diffractive Protons in AFPNumber of protons per 100 fb–1 (~1 LHC yr) per Si pixel (50 μm × 250 μm):

– Proton energy loss ξis related to x:

– Central Mass M is related to both protons’ energylosses ξ1, ξ2 :

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AFP 1 22

e.g. 0.01 160 GeV

beamM p

M

----- detector area

(20 mm × 20 mm)

6AFP Time-of-Flight

Hamburg Beam PipeATLAS design: Be floor and windows in Al structure• Tilted windows (11) minimize beam coupling and losses• Beryllium windows and floor, and Al structure

minimize interactions and multiple scattering• Ample space for tracking and timing devices

Results of detailed RF simulations:• Impedance Zlong is at the level of 0.5%/station at 1 mm from the beam

• Similar for Ztrans

• Power loss (heating) is manageable ~30 W, mostly in conical sections• Bellows are not yet included, but we are confident we can minimize

their effect17JUL13

ALUMINUM - AUSTENITIC STEEL FLANGEs

ALUMINUM

BERYLLIUM

450 mm

thin

AFP Time-of-Flight

AFP Roman Pot & StationAFP Pot adaptation from TOTEM design–shown with a possible timing detector …

Copy RP Station design of ALFA & TOTEM:–Ample operational experience –Known cost and construction & installation procedures

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AFP Pot

beamAFP timing

TOTEM horizontal RP

station(beam view)

8AFP Time-of-Flight

Major Development Challenges

• MCP-PMT Rate and Lifetime: – Have tube capable of 5 MHz and 5 C/cm2 (equivalent to 50

fb–1 !) – expect further 2-3× improvement

• HPTDC board capable of 15 MHz• 5 ps resolution CFD• Clock Distribution Circuit <5 ps

• All achieved !

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9AFP Time-of-Flight

AFP Fast Time-of-FlightQUARTIC concept: Mike Albrow for FP420 (joint ATLAS/ CMS effort) (2004) based on Nagoya Detector. – Initial design (~2006):

4 trains of 8 Q bars: 6mm × 6mm ×100mm

– mounted at Cherenkov angle θČ 48°≃

– Isochronous – Cherenkov light reaches tube at ~same time for each bar in a train

– arrival time of proton is multiply measured: bar + readout resolution less stringent!• e.g 30 ps / bar 11 ps for train of 8 bars

2011 DOE Advanced Detector Research award for electronics development:

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proton

Č ph

oton

s

MCP-PMT

trains

1 2 3 4

θČ

SMApigtails

PA-b Programmable Gain Amp CFD Daughter Board

HPTDC Board8-Channel Preamplifier (PA-a)

Detector & PMT R&D: U Texas at Arlington (A. Brandt et al.); Electronics R&D: Stony Brook (M.R. et al)

AFP Time-of-Flight

Electronics Layout Phase 0Baseline layout (8×8 channels/side):

if the CFD is sufficiently radiation-hard, it can be located at 214 m

if the HPTDC is sufficiently radiation-tolerant, it can be located at 214 m

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QuarticFeed

through

(32 ch REDEL-HV)8× HV

64× Signal

8× Temp

2× Pressure

(SMA)

(μD)

AFP2crate

SignalsAtt

DCS

Trigger

RR13 ?crate

USA15cratesTrigger (LMR600)

TDCToT

OptoBoard

DCSDCS

BOC-RODor RCE

CTF

DCS

iseg HV

LV+6V 5A

(50 Ω)CFDToT

LE

Data

LV+6V 20A

DCS

PA-a

PA-b

214 m 214 m 240 m 0 m

11AFP Time-of-Flight

Beam Test – FNAL 2012 (A.Brandt, UTA)

30 mm long Quartz bar // beam read by SiPM: σt ≃ 10 ps for a SiPM (CFD only!)– excellent resolution! – not very radiation hard

2 mm wide × 6 mm deep (in beam direction) Quartz bar positioned at 48° with beam (Cherenkov angle),read by 10 μm pore MCP-MAPMT– single bar: σt ≃ 20 ps (CFD only!)

• 4 bars at 48° (~32 mm): expect ~10 ps

– single bar with HPTDC: σt ≃ 26 ps• 6 bar train measurement (Test Beam): ~11 ps

– rad hard tube (no degradation seen yet up to 5 C)

Multiple measurements ‘tunable’ resolution, size, and interaction length …

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SiPM1 – SiPM3

SiPM3 – Qbar3

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MCP-PMT Life Time (A.Brandt, UTA)

• Historically MCP-PMT’s have not been extremely robust, their performance (QE) degrades from positive ion feedback

• UTA Formed a collaboration with Arradiance and Photonis for coating …

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12

Hamamatsu ion barrier SL10

Arradiance 10 (25) m pore Planacon

15

16

17

18

19

20

215E4 Gain

1E5 Gain

Laser Rate (MHz)

δt (

ps)

20 ps single bar resolution at 5MHz proton rate (10 pe per proton) at 5E4 gain; x3-5 better with 10 m pore tube

• Lehman et al. (Panda): As of 5/13 no loss in QE with Q>5 C/cm2!

• >10× improvement over typical tube 1C~10 fb-1

• expect 3× more with next version

13AFP Time-of-Flight

T958 DAQ FNAL 2012

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2 3 4 5 6 7 Avg

Using a 20-ch, 20 GHz, 40 GS/s (25ps/point) 500k$ LeCroy 9Zi scope! Thanks for the loan LeCroy !

Time difference between SiPM and average of 6 Q-bars: σt = 20 ps (SiPM: σt =14-15 ps) (A. Brandt, UTA)

14AFP Time-of-Flight

Timing System ResolutionReached and extrapolated timing resolution:– Currently at 11-12 ps (Fall 2012 Test beam) with 6 bars; – ultimate performance of this system is probably about 8 ps

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Component σt (ps)

Current

σt (ps)

Projected

Action

Radiator/MCP-PMT(~10 pe’s with 10 µ pore MCP)

19 17 Optimize radiator

CFD 5 5 Larger dynamic range HPTDC 18 <9 New HPTDC chipReference Clock 3 3 -Total/bar 27 20Total/ detector (6 ch) 11 8 -

15AFP Time-of-Flight

Time of Flight in Roman Pot• Bend the Quartic bars by 90°

–disadvantage: loose light in the bend–advantage: extra degree of freedom in

projecting the bar onto the MA-PMT !

• Note: the Quartic concept is modular; –make ‘trains’ of ‘arbitrary’ length (limited by λint) choose σt

–choose granularity: make trains of arbitrary width• beam test: 2 mm wide bar has same resolution as a 6 mm wide bar

–optimize ToF detector’s size vs. σt vs. λint!

• Possibility: make the light guide part of the bar into a mirrored air-guide!–reduce amount of material exposed to particles–reduce dispersion compared to quartz

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Quartz vs. Air Light Guide …Simulations by Libor Nozka (Prague):• run 0: straight Q-bar 150 mm long• run 5: Bent Q-Bar 30/120 mm with mirror

on elbow (R=90%)• run 6: Q-bar 30 mm + bent Air guide

120 mm with mirror on elbow (R=90%)

(R = reflectivity of air guide)

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straight Q-bar 15 cm

bent Q-bar 3+12 cm Q-bar 3 cm + bent airguide12

cm

ns

ns ns

this design gives σt 20≃ ps in beam test

17AFP Time-of-Flight

Diffractive Protons in AFPNumber of protons per 100 fb–1 (~1 LHC yr) per Si pixel (50 μm × 250 μm):

– Proton energy loss ξis related to x:

– Central Mass M is related to both protons’ energylosses ξ1, ξ2 :

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detector area (20 mm × 20

mm)

1 22

e.g. 0.01 160 GeV

beamM p

M

18AFP Time-of-Flight

Efficiency & BackgroundsRoyon, Sampert confirm pixellation of ~10 rows is adequate:– inefficiency per train:

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7 trains:2, 6×3.25 mm

10 trainsof 2 mm width

20 trainsof 1 mm width

19AFP Time-of-Flight

New Nuclear Interaction Studies

Concerns:–Scattering in first (upstream) station

• this destroys proton which will neither be tracked nor timed global inefficiency

• In case where this proton was kinematically disallowed it might create another proton inside the 2nd station’s acceptance

–Scattering in the thin ‘floor’, spraying ‘sideways’ into the detector inside

–At 14 TeV find about λInt≃2% per Q-bar (~8 mm of quartz)• 15% of events have an interaction by bar 8• These interactions have a high multiplicity

–Too many particles in quartz bar (shower) would saturate amps• dynamic range about 8-10• O(10s) particles, which would saturate amps and cause that bar (and

following) timing to be mismeasured– Time over Threshold functionality allows some recovery …

All above influence the timing detector optimization17JUL13

Tom Sykora et al.

20AFP Time-of-Flight

Severe Backgrounds at the LHC

Sources:1. IP: single diffraction pile-up2. secondary interactions in upstream beam elements3. Beam Halo

Low-μ (special) runs: backgrounds are OK– see: ALFA runs at β* = 90 m, 1 km

– OK for the soft diffraction program of AFP

High-μ (standard) runs: backgrounds are very high– see: TOTEM standard-optics runs (Joachim Baechler’s talk)

• evidence that the source is primarily IP and secondary interactions in collimators (1 & 2)

– we are analyzing recently recovered ALFA run at β*=0.55 m (15’ run, 2 Mevts)

– we are simulating the high-μ environment with β*=0.55 m optics …

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dominant !

Horizontal RP Rate at 14 s

56-F 45-N 45-F

Rate for 1368 b with beam separation

2 MHz 1 MHz 3 MHz(incl. showers from N)

separation lumi factor

1 / 15.7 1 / 18.6 1 / 22.6

Rate for 1368 b without separation

31 MHz 19 MHz 68 MHz(22.6* 3 MHz)

Rate for 1 bwithout separation

23 kHz 14 kHz 50 kHz

Hits per bxw/o separation

2.0 1.2 4.4(50 kHz/11.2kHz)

Beam conditions (fill # 3288):1.6 x 1011 p/bE = 4 TeVb* = 0.6 men = 2.8 mm radm = 31 (without separation)L = 6.7 x 1033

expected SD rate per arm within acceptance: ~ 0.4 / bx (event rate / bunch crossing)

Revolution frequency: 11.2 kHzaverage crossing rate : 11.2 * 1368 = 15.3 MHzaverage interaction rate (without separation) : 15.3 * 31= 47.4 MHz

Expected ratesafter LS1 are different(L, bunch scheme)

insertion at low β*beam heating – LHC vacuum – RP optimization-

rates

from: Joachim

Baechler’s talk of

yesterday

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22AFP Time-of-Flight

Summary• AFP has a baseline fast timing detector

–10 ps or better resolution for 8 Q-bars–Long-lifetime MCP-PMT–Electronics

• Optimization in progress:–Needs for μ≃1 physics–Backgrounds and efficiency …–Housing in a Roman Pot ?–Triggering

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Backup Slides

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AFP – HBP plus Tracker …

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thin floor sensors

evaporativecooling

readout flex

ATLASA

FP206

AFP

214

AFP

214

AFP

206AFP

AFP Time-of-Flight

AFP POT Modifications • AFP needs changes in the POT design:

– the TOTEM design has a different thin window size, not optimally matched to our acceptance

– the TOTEM floor is a groove in the pot bottom: • requires a bump-out of the tracking sensor, • making it difficult to insert a Quartic detector close to the beam …

• We have more time than TOTEM use to investigate improvements– We should make the AFP pot a bit larger (to ~144 mm) by reducing the 2.5 mm

gap between the bellows and the pot itself to ~1 mm. • Making it even larger than that requires a different ‘Tee’ design and RF calculations will

have to be repeated to validate a larger cylinder. Unless absolutely necessary, I would prefer to keep the pot to 144 mm ID.

– We should investigate alternative pot and window materials, coatings, etc. • e.g., a Be window of 200-400 μm thickness welded to an Al pot (cfr. Daniela) would be a

huge improvement over the current TOTEM pot in terms of conductivity, radiation length (MS), and interaction length.

• Need our own feedthrough plate with the services as we require them, adapting the plate as designed for TOTEM to AFP needs.

• Possibly the plate for the ‘timing’ will be different from the plate for the ‘tracking’17JUL13 25