HybridPhotonDetectorsfortheLHCbRICHSystem

NickStylesOnbehalfoftheLHCb‐RICHgroup

NewDevelopmentsinPhotodetec>on2008,Aix‐Les‐Bains

TheLHCbExperiment•  LHCbisadedicatedB‐PhysicsexperimentattheLarge

HadronColliderpar>cleaccelerator,aimstomakeprecisionmeasurementsofCPViola>onandRareDecays

•  Anessen>alpartoftheLHCbexperimentisthePar>cleIden>fica>onsystem,basedaround2RingImagingCherenkovDetectors

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250mrad

100mrad

M1

M3M2

M4 M5

RICH2

HCALECAL

SPD/PSMagnet

T1T2

T3

z5m

y

5m

!!5m

10m 15m 20m

TTVertexLocator

RICH1

PrinciplesoftheRICHSystem

•  Chargedpar>clestraverseradiatorvolume(Aerogel,C4F10,CF4)

•  CherenkovphotonsemiSedwithanangledependentonvelocityofpar>cle: cosθc=1/βn

•  SphericalmirrorsfocusCherenkovphotonsintoaring

•  photodectorrequirements–  Singlephotonsensi>vity–  Excellentspa>alresolu>on–  200–600nmwavelengthrange

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RICH1

HPDs•  PhotoelectronsemiSedfrom

S20‐typemul>alkaliphotocathode,acceleratedthrough20kVpoten>al

•  Focusingfieldbringsphotoelectronsonto300μmthickpixelatedsiliconsensor,reverse‐biasedat80V

•  Approx.5000signalelectronsper20keVphotoelectron

•  8192pixels,8‐foldlogicalORappliedtoproduce1024500μm2super‐pixels

•  Sensorchipbump‐bondedtoelectronicsreadoutchip

•  484HPDsrequiredtofillbothRICHdetectors

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HPDQualityControl•  Acerproduc>on,HPDsare

testedatdedicatedfacili>esinEdinburghandGlasgow

•  Comprehensivesetoftests:–  Photocathode:DarkCount,

ResponsetoPhotons–  Anode:Threshold,Noise,

Dead&NoisyPixels,IVCurve–  ElectronOp2cs:HVStability,

Demagnifica>on–  HPDBody:SensorPosi>on,

PhysicalDimensions–  VacuumQuality:Ion

Feedback(acerpulse)

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PixelThreshold

Threshold(e‐)

HPD

s

PixelThreshold

PhotonDetectorTestFacilityResults

•  557HPDsproducedandtestedintotal

•  HPDsareclassifiedaccordingtotheirperformanceinthetes>ng

•  Morethan97%ofHPDsproducedaresuitableforuseintheRICHdetectors

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5kHz/cm2=1%probabilityfor1Hit/HPD/event

IonFeedback

DarkCount

QEMeasurements•  QuantumefficiencymeasuredbyDEPandconfirmedatEdinburghPhotonDetectorTestFacility

•  SteadyincreaseinmeanQEasHPDproduc>onprogressed

•  MeanHPDQEissignificantlyaboveourbaselineexpecta>ons

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QESpectrum

QEperbatch

MinTyp

RICHTestbeamSetup

•  CERNSPSacceleratorusedtoprovide80GeV/cπ‐beam,25nsbeamstructure

•  3fullypopulatedHPDcolumnsplacedinscaled‐downRICHdetector•  N2andC4F10usedasgasradiators•  Tes>ngHPDsincondi>onsclosetothoseofLHCbrunning•  2BareHPDanodesaspar>cletrackers

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Radiator Vessel

Detector Housing

Quartz Window

Mirror

HPDs

HPD column

Beam

Aluminum Foil

CourtesyofPPARC

HPDTestbeamPerformance

•  TestbeamdataprovidesCherenkovringsforN2andC4F10,withtrackinginforma>onforpar>cledirec>on

•  Studiesperformed:–  Cherenkovangleresolu>on

inc.pixelisa>oneffects–  Hitmul>plici>es–  Chargesharinginpixelchip–  Alignment–  Socwaretests

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C4F10

RICHCommissioning•  RICH2nowfully

populatedwithHPDs•  AllRICHsubsystems

opera>onal–  HighVoltage–  LowVoltage–  Cooling–  DAQ–  Experimentcontrolsystem–  Monitoring

•  Takingcommissioningdataonaregularbasis

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RICH1HPDplane

RICHCommissioning(2)

•  RICH1&RICH2dataanalysedbothonlineandoffline

•  Evolu>onofHPDperformancerou>nelymonitored:–  LeakageCurrent–  DarkCount–  IonFeedback(vacuum

quality)

•  Stresstestfullreadoutelectronicschain

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Integratedcon>nuousrunforbothRICH2HPDpanels,over2.3Millionchannelsreadoutsimultaneously

IonFeedback

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•  AnumberofHPDshaveshownlargeincreaseinIonfeedbackratesincePDTFtests–  Someenter‘GlowDischarge’regime,causingsatura>onofpixelchip–  TheseHPDshavebeenreplacedfromsupplyofspares

•  Situa>onisbeingmonitored•  MajorityofHPDss>llbehavingexcellently

RICHTimeAlignment•  Fine>mealignmentofL0

boardsrequired,inordertomaximisephotoncollec>onefficiency

•  Use100pspulsedlaser•  Delayoflaserpulsevariedin

stepsof2nswithrespecttoHPDreadout

•  Buildup>mingprofileofRICH2,plus144individualscansforHPDpairs

•  Define‘switchon’and‘switchoff’pointsfor>mingplateau

•  L0boardscanbeindividuallyshicedtomaximise>mingoverlap

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10 20 30 40 50 ns

Board#

16ns

10

20

30

40

50

16ns

Conclusions

•  557HPDsintotaldeliveredandtested•  HPDsbehavedexcellentlyinPDTFtests•  AllRICHHPDcolumnsfullypopulated

•  RICHestakingHPDdataonaregularbasis•  Evolu>onofHPDperformanceismonitoredwithbothonlineandofflinetools

•  TheRICHsystemisreadyfordatatakingwithLHCbbeamlaterthisyear

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SPARESLIDESExtras

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RICHColumns•  HPDsaremountedoncolumns

forintegra>onintoRICHdetectors

•  2HPDsperLevel0electronicsboard,with>ming>edtogether

•  Pairedbychipleakagecurrent,inordertomaximize>mingoverlap

•  L0boardbuffersandsendsoutHPDdata,receivesclockandtriggersignals

•  LowVoltage(chipelectronics)andHighVoltage(HPDelectrosta>cs)providedbyHVandLVdistribu>onboards

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IonFeedbackEvolu>on

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•  HPDshaveshownincreasesinIonFeedbackovertheirlife>me•  Natureofincreaseandpossiblecausescurrentlyunder

inves>ga>on

Produc>onofanHPD

•  Siliconsensorbump‐bondedtoreadoutchip(VTT,Finland)

•  Chipassemblypackagedwithinbrazedandgold‐platedceramiccarrier(HCM,France)

•  CompletedanodeencapsulatedwithinHPDtubebody,quartzwindowinstalled,photocathodedeposited,vacuumbake‐out(DEP,Netherlands)

•  TestedatPhotonDetectorTestFacili>es(Scotland)

•  IntegratedintoRICHdetectors(CERN)

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