L0/L1 trigger development of ALICE PHOS detector

188 Pages·2011·12.65 MB·English

by  Lijiao Liu

L0/L1 trigger generation by the ALICE
PHOS detector
Lijiao Liu
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Dissertation for the degree philosophiae doctor (PhD)
at the University of Bergen
October 2011
Contact: LijiaoLiu
InstituteofPhysicsandTechnology
UniversityofBergen
Allégaten55
5007Bergen
Norway
Email: [email protected]
Privateemail: [email protected]
Acknowledgements
I started my PHD program in spring 2008, now it comes to the end with the submission of
the thesis. Working on the interesting and challenge project brings me to a large group of
internationalcolleagues,withwhomIenjoyedverynicecooperationandfruitfulexchangeof
ideas. WhenIthinkback, mystudyinBergeniswonderful, exciting, andworthcherishing,
even though there have been moments of hard work and exhaust. I appreciate that I have
experiencedalotduringthework.
Attheveryfirst, IwouldliketothankmysupervisorDieterRöhrichandKjetilUllaland
for giving me the chance to work in the group and guiding me on both my work and life.
DieteralwayssupportsmeandgivesmehelpwheneverIneed. AndIalwaysadmirehisway
of explaining complicated physics in easily understandable and short words. His relax and
kind personality deeply impresses me too. Kjetil has been a main source of knowledge and
inspiration for me. He has had many long and priceless discussions with me, both on work
and life, which greatly help me get through my PHD period. I’m always influenced by his
intelligence,optimisticandhappiness. DiscussingwithhimhighlightsmydaywhenI’mlack
of motivation or unhappy. Dieter and Kjetil, thanks a lot! I appreciate deeply being your
studentandIwishIcouldbeyourstudentagain!
IowemyspecialthankstoprofessorsGuangmingHuangandDaicuiZhou,whogaveme
thechancetoapplythepositionofworkingontheproject. Daicuifirstlyprovidedthechance
oftheposition.WhenIhesitated,Guangmingencouragedandconvincedmetoapply,making
me experienced a wonderful life in Bergen. Moreover, I appreciated a lot of dinner time at
CERNwithDaicui. WhenI’minBergen,youtwostillcareaboutmeverymuch,treatmeas
astudent,afriendandadaughter.
IwouldalsoliketothankJohanAlmeandKetilRøed,whohelpedmealotatthebegin-
ningofmywork. ItwasunforgettablethatJohansentmethedocumentationformyworkon
Chinese New Year and regards for my birthday the same day on 2008. Ketil was a nice of-
ficemate,gavemeinvaluablehelp. Youtwoalwaysgavemedetailedandpatientanswers,no
matterhowstupidmyquestionswereandhowbusyyouwerewithyourthesis. Iappreciated
alot!Thanksagain!
IwouldliketothankHongyanYang,LiangSunandYunCheng,whohelpedmestartthe
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ii Acknowledgements
studylifeinBergen.Withoutyou,IcouldnotgetusedtomylifeinBergenassoonaspossible.
IhavehadthepleasureofworkingcloselywithDongWang,whohasbeenmyfriendfor
10years. Wehavesharednotonlyalotoftasks, butalsoalotofnicemomentsofcooking,
havingdinnerandhiking. Hehasbeenanimportantmotivatorinmyworkandanicefriend
inmylife. ThesamethankgoestoMeidanaHuang, whoisaniceroommate, anintelligent
colleagueonmyworkandthebestfriendinmylife.Wewenttogetherforconferences,shared
a lot of nice moments at CERN. Dana, thank you! You have made my life enjoyable and
colorful.Iwon’tfeellonelybecauseofyou!
ThanksalsogotoJoakimNystrand,Per-ThomasHille,ØysteinDjuvsland,SveinLindal,
HenrikQvigstadandKyrreSkjerdalforansweringmyquestionsnicelyandgivingmecount-
less ride at CERN. I appreciated a lot! Jiri Kral deserves a lot of thanks for answering my
stupid questions with great patience and helping with my work. So does Yuri Kharlov, who
answerspatientlymyemailingreatdetail,helpingmeunderstandeasily.Aspecialthankgoes
toHåvardHelstrupalso,whohelpedmewiththesetupoftheDAQsystematthelabefficiently.
MygratefulthanksgotoDominikFehlkertoo,withwhomIsharedalotoffunnytimeand
havingfruitfuldiscussionaboutwork. I’mimpresseddeeplybyhispatienceandconsiderate-
ness. Iwon’tforgetthefirsttimeheshowedmeandDanathesetupatthelabatCERN,the
nice invitation for fishing and the computer games during rest time, the nice accompany for
walkingushome,nottomentioncountlessrideaftergroupparties.DagToppeLarsendeserves
muchofmyappreciationforencouragingmewhenI’mdepressed,forhelpingmewithLatex,
Aliroot,andforreadingthroughmythesisandcorrectinginabettershape. Specialthanksgo
toShimingYang,whohasgivenmealotofhelponwork,wehavealotofnicediscussionon
both life and work. Thanks also go to Kalliopi Kanaki, Sebastian Bablok, Gaute Øvrebekk,
ØysteinSennesetHaaland,HegeErdal,CamillaHanquistStokkevåg,YngveSkogseide,Njål
Brekke,ArildVelure,EivindLarsen,Per-IvarLønne,KristianYtre-Hauge,ThomasChristoph
Solem,andAndreasSamnøy. Thanksyouallwithyourgreathelponbothworkandlife. Ad-
ditionally,IwouldliketothankmyothercolleaguesinPHOSgroup,microelectronicsgroup
andNuclearPhysicsgroupwhohavecontributedthehelpinonewayoranother. AlthoughI
havenottalkedmuchwithsomeofyou,thesmilesonyourfacesencouragemealot.Working
togetherwithyouisalwaysinterestingandenjoyable.
MydeepgratitudegoestoBiancaRossforalwayscaringmuchaboutme,invitingmeto
her many nice dinner parties. Your concern could not mean more to me. I won’t forget the
words she encourages me every time she meets me. I won’t forget the regards when I was
at CERN for work and Spring Festival. I won’t forget the electronic card for my Birthday.
Bianca, thanks you very much, I love you! I have never met a lady with such a broad and
goldenheartasyoubeforeever,yourfascinatingpersonalityinfluencesme.
IalsohadchancetomeetalotofcolleaguesandfriendsfromHuazhongNormalUniversity
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atCERN,thankyouall,alotofdinnertimewithyoumademystaysatCERNveryenjoyable
andmemorable!
ManythanksgotomyChinesefriends(toomanytobelistedhere)inBergen,weshared
alotofwonderfultimeinBergen. Thanksallofyoutokeepmehappyinaforeigncountry.
AlsothanksmyfriendsinChinaforencouragingmeandsupportingme.
Finally,Iowethankstomyparents,sisters,brothers-in-law,brothers,nephewsandniece,
yourloveandconstantsupportaregreatstrengthformetogothroughtheseyears.Ihavebeen
farawayfromyouforfouryears,Imissedalotoffamilyactivitiesinthepast10years. You
alwaysunderstandmewithoutcomplaining.Thanks,Iloveyou!

Abstract
Quark-GluonPlasma(QGP)isaphasethatexistsaboveacriticaltemperatureandcorrespond-
ingenergydensityaccordingtothetheoryofQuantumChromo-Dynamics(QCD).Thestudies
oftheQGPhelpustounderstandtheearlyevolutionofouruniverseandtheStandardModel.
A large Ion Collider Experiment (ALICE) aims to study the properties of the QGP. A QGP
cannotbeobserveddirectlybecauseitisashortlivedstate.Signaturessuchasjetquenching,
flowpatternandhigh p suppressionindicatetheexistenceofaQGP.Varioussub-detectors
T
are designed for detecting these signatures. The PHOton Spectrometer (PHOS), one of the
sub-detectors, isahigh-resolutionelectromagneticcalorimeterdedicatedtotheprecisemea-
surementofdirectphotonandneutralmesonyieldsina p rangeupto100GeV/c.
T
Four online systems are developed to monitor, control and read out the different sub-
detectors. The trigger system is one of them. The task of the trigger system is to select
events of interest and to reduce the overall data flow in the ALICE experiment. Three lev-
elsoftriggersandaHighLevelTrigger(HLT)aredesignedtomakeoptimaluseofdifferent
sub-detectors, which vary in readout time. The PHOS detector generates two levels of trig-
gers: i) the Level-0 (L0) trigger selects high p clusters in Pb+Pb and in p+p collisions; ii)
T
theLevel-1(L1)triggercorrespondstoamoresophisticatedshoweranalysiswhichrefinesthe
eventselection.
The main objective of the thesis has been to develop the PHOS trigger firmware, to im-
plementitinanFPGAandtocommissionit. TheALICEL0triggerhasalatencyof1.2μs,
limitingthetimeforgeneratingL0triggersinthePHOSdetector.Thealgorithmsarebasedon
thedigitizedsignalfromAvalanchePhoto-Diodes(APDs). Asliding-windowclusterrecon-
structoristhecriticalpart. Alotofeffortshavebeenmadetofulfillthetimingrequirement.
TheALICEL1triggerhasalatencyof6.5μs,leavingmoretimetorefinetheeventselection.
TherearethreetypesofL1triggersforPHOS:onebasicL1triggerandtwoadvancedones:
total energy trigger and isolated photon trigger. The firmware development focuses on the
L0generation(chapter5). Thetiminganalysis(chapter5),testingandcommissioningofthe
PHOSL0trigger,whichisthemaineffortduringthePhDprojectaswell,havebeenperformed
(chapter 7). The generation of L1 triggers is discussed in chapter 6, where the firmware for
the basic L1 trigger is implemented. The algorithms and related resource consumption for
v
vi Abstract
theadvancedL1triggersareanalyzed, buttheyhavenotbeencommissionedyet. Addition-
ally,simulationshavebeendonetoanalyzehowseveralfactorsaffectthetriggerperformance
(chapter6).
The outline of this thesis is given as follows: After a very brief overview of the physics
goal,thesub-detectorsandtheonlinesystemsoftheALICEexperimentaredescribedinchap-
ter1.ThePHOSdetectorisspecifiedthoroughlyinchapter2.Chapter3introducesthetrigger
and readout electronics, based on which the firmware for the triggers (chapter 5) is imple-
mented for the PHOS detector. In chapter 4, the requirements of the ALICE PHOS triggers
are given in detail. The principle of issuing triggers is discussed elaborately based on the
layoutofthedetector,irrespectiveofthetriggerelectronics.Chapters5and6discussthegen-
erationofL0andL1triggersrespectively.Chapter7givesthecommissioningresults.Finally,
theconclusionandanoutlookaregiveninchapter8.
The trigger firmware is implemented by two types of electronics boards, Trigger Region
Unit(TRU)andTrigger-OR(TOR),I’mresponsiblefortheTORsince2008. TheL0trigger
commissioning has started in Oct. 2008, and it is still ongoing. In addition, I performed
the timing analysis, the energy and trigger channel correlation analysis and the L0 trigger
performance analysis. Because the L1 algorithm was implemented in the TOR, I analyzed
algorithms,resourceandtimingconsumptionofallthreetypesL1triggers,andsimulatedthe
L1triggerperformance.
Contents
Acknowledgements i
Abstract v
Contents vii
ListofFigures xiii
ListofTables xvii
1 TheALICEexperiment 1
1.1 Quark-GluonPlasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 TheLargeHadronCollider . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 TheALICEexperimentalsetup . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 TheALICEdetectorsystems . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4.1 InnerTrackingSystem . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4.2 TimeProjectionChamber . . . . . . . . . . . . . . . . . . . . . . . 7
1.4.3 TransitionRadiationDetector . . . . . . . . . . . . . . . . . . . . . 7
1.4.4 Time-Of-Flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4.5 PhotonSpectrometer . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4.6 HighMomentumparticleidentificationdetector . . . . . . . . . . . . 8
1.4.7 Electro-MagneticCalorimeter . . . . . . . . . . . . . . . . . . . . . 8
1.4.8 ALICECosmicRayDetector . . . . . . . . . . . . . . . . . . . . . 8
1.4.9 Forwardmuonspectrometer . . . . . . . . . . . . . . . . . . . . . . 9
1.4.10 Forwarddetectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5 TheALICEonlinesystems . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.5.1 ExperimentControlSystem . . . . . . . . . . . . . . . . . . . . . . 10
1.5.2 TriggerSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.5.3 DataAcquisitionSystem . . . . . . . . . . . . . . . . . . . . . . . . 13
1.5.4 HighLevelTriggerSystem . . . . . . . . . . . . . . . . . . . . . . . 15
vii
viii CONTENTS
1.5.5 DetectorControlSystem . . . . . . . . . . . . . . . . . . . . . . . . 15
2 ThePHOSDetector 17
2.1 Photonphysics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2 ThecomponentsofthePHOSdetector . . . . . . . . . . . . . . . . . . . . . 19
2.2.1 PWOcrystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2.2 AvalanchePhotoDiode. . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.3 ChargeSensitivePre-Amplifier . . . . . . . . . . . . . . . . . . . . 21
2.2.4 TheLEDSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2.5 ThelayoutofPHOS . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3 IntrinsicperformanceofthePHOSdetector . . . . . . . . . . . . . . . . . . 22
3 ThePHOStriggerandreadoutelectronics 27
3.1 PHOSelectronicstopologyanddataflow . . . . . . . . . . . . . . . . . . . . 27
3.2 FrontEndCard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.2.1 Shapers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2.2 ALTRO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2.3 Analog-sum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2.4 BoardController(BC) . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3 TriggerRegionUnit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.1 TheTRUoverview . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.2 TheTRUresources . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4 TriggerOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4.1 TheTORoverview . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4.2 TheTORresources . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.5 DCSboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.6 ReadoutControlUnit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.7 BusyBOX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4 ThePHOStriggerrequirementsanddesign 45
4.1 ThePHOStriggerrequirement . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2 Triggergeneration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.2.1 TheprincipleofissuingL0triggers . . . . . . . . . . . . . . . . . . 47
4.2.2 TheprincipleofissuingL1triggers . . . . . . . . . . . . . . . . . . 49
4.2.3 HardwareRequirements . . . . . . . . . . . . . . . . . . . . . . . . 50
5 ThegenerationofPHOSLevel-0trigger 55
5.1 ThefirmwaredevelopmentofLevel-0trigger . . . . . . . . . . . . . . . . . 55
5.1.1 TechnicalrequirementsofL0 . . . . . . . . . . . . . . . . . . . . . 56