P epa ed o submission o JINST
Fi s Demons a ion o a Combined Ligh and Cha ge
Pixel Readou on he Anode Plane o a LA TPC
SoLA Collabo a ion
N. An imo ,13 A. B anca,6,10 J. Bü gi,1L. Cali e s,1C. Cues a,3R. Diu ba,1P. Dunne,5
D. A. Dwye ,7J. J. E ans,9A. C. Eze ibe,12 A. Gauch,1I. Gil-Bo ella,3S. G eenbe g,2,7
D. Gu an i,6,10 A. Ka che ,7I. K eslo,1J. Kunzmann,1N. Lane,9S. Man hey Co chado,3
N. McConkey,11 A. Na e -Agasson,5,9S. Pa sa,1G. Ruiz Fe ei a,9B. Russell,8
A. Selyunin,13 S. Söldne -Rembold,5,9A. M. Szelc,4A. Tappe ,5F. Te ano a,6,10
C. Tognina,1G. V. S enico,4M. Webe ,1and I. Xio idis5
1Uni e si y o Be n, CH-3012 Be n, Swi ze land
2Uni e si y o Cali o nia Be keley, Be keley, CA 94720, USA
3CIEMAT, Cen o de In es igaciones Ene gé icas, Medioambien ales y Tecnológicas, E-28040 Mad id,
Spain
4Uni e si y o Edinbu gh, Edinbu gh EH9 3FD, Uni ed Kingdom
5Impe ial College o Science, Technology and Medicine, London SW7 2BZ, Uni ed Kingdom
6Is i u o Nazionale di Fisica Nuclea e Sezione di Milano Bicocca, 3 - I-20126 Milano, I aly
7Law ence Be keley Na ional Labo a o y, Be keley, CA 94720, USA
8Massachuse s Ins i u e o Technology, Massachuse s, MA 02139, USA
9Uni e si y o Manches e , Manches e M13 9PL, Uni ed Kingdom
10Uni e si à di Milano-Bicocca, I-20126 Milano, I aly
11Queen Ma y Uni e si y o London, London E1 4NS, Uni ed Kingdom
12Uni e si y o She ield, She ield S3 7RH, Uni ed Kingdom
13Visi o
E-mail: [email p o ec ed]
Abs ac : The no el SoLA concep aims o ex end sensi i i ies o liquid-a gon neu ino de ec o s
down o he MeV scale o nex -gene a ion de ec o s. SoLA plans o accomplish his wi h a liquid-
a gon ime p ojec ion chambe ha employs an anode plane wi h dual cha ge and ligh eadou ,
which enables p ecision ma ching o ligh and cha ge signals o da a acquisi ion and econs uc ion
pu poses. We p esen he esul s o a i s demons a ion o he SoLA de ec o concep wi h a
small-scale p o o ype de ec o in eg a ing a pixel-based cha ge eadou and silicon pho omul iplie s
on a sha ed p in ed ci cui boa d. We discuss he design o he p o o ype, and i s ope a ion and
pe o mance, highligh ing he capabili y o such a de ec o design.
Keywo ds: Noble liquid de ec o s (scin illa ion, ioniza ion, single-phase), ime p ojec ion cham-
be s, neu ino de ec o s
a Xi :2406.14121 2 [physics.ins-de ] 14 No 2024
Con en s
1 In oduc ion 1
2 Expe imen al Se up 2
2.1 Design o he SoLA p o o ype Time P ojec ion Chambe 2
2.2 Elec ic ield simula ion 5
2.3 C yogenics sys em 5
3 Resul s 6
3.1 P o o ype Ope a ion 6
3.2 Fi s cosmic- ay acks wi h dual-pixel ligh and cha ge eadou 8
3.3 Cha ge collec ion pe uni leng h 8
3.4 Ligh collec ion as a unc ion o SiPM g ound o se ol ages 9
4 Summa y 11
1 In oduc ion
The nex gene a ion o deep unde g ound de ec o s, namely DUNE [1], will enable a subs an ial
leap in he sensi i i y o neu ino physics expe imen h ough hei de ec o s’ mass and p ecision.
Thei baseline design is op imized o he de ec ion o GeV-scale neu inos p oduced by a pa icle
beam wi h he goal o measu e oscilla ion pa ame e s wi h unp eceden ed p ecision [2]. In addi ion,
he la ge mass and he unde g ound loca ion o he de ec o s p o ide a unique oppo uni y o expand
hei sensi i i y o lowe ene gy neu inos, wi h ene gies a he MeV-scale, o igina ing om na u al
nuclea p ocesses.
Sola neu inos p o ide an a enue o hese u u e de ec o s o explo e, p ima ily o de ec
neu inos gene a ed om he hep b anch [3,4]. I s disco e y di ec ly impac s he modeling o ou
Sun and he modeling o s ella e olu ion h oughou he Uni e se. The applica ion o liquid-a gon
de ec o s o sola -neu ino physics has been explo ed p e iously [5–7]. Such a de ec o was ound
o need an ene gy esolu ion a he MeV-scale o 7% o measu e sola neu inos [5], o ha e excellen
backg ound ejec ion capabili ies, and o ha e easonably low da a a es. These equi emen s a e
essen ial o success ully disc imina e he highe -ene gy ail o he hep neu ino spec um om
he dominan 8B neu ino spec um. Supe no a explosions ejec mos o hei ene gy in o m
o neu inos wi h ene gies simila o hose o hep neu inos. A de ec o ha is able o obse e
hep neu inos is by cons uc ion also he mos p ecise expe imen o de ec supe no a explosions.
Combining he da a wi h isible, X- ay, 𝛾- ay, and g a i a ional-wa e in o ma ion will p o ide a
comple e pic u e o he supe no a collapse [8].
One signi ican challenge is ela ed o eadou and compu ing. The whole DUNE Fa De ec o
si e needs o collec pe aby es o ligh and cha ge da a pe yea o accomplish i s calib a ion and
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neu ino p og ams om na u al sou ces [1]. P o iding a solu ion ha enables la ge mass de ec o s
while limi ing da a a es would signi ican ly inc ease he easibili y o low-ene gy sea ches in
liquid-a gon de ec o s.
The SoLA (sola neu inos in liquid a gon) collabo a ion p oposes o build mul ipu pose
liquid-a gon ime p ojec ion chambe s (LA TPCs) wi h se e al kilo ons o ac i e mass o de ec
beam neu inos, supe no a neu inos and sola neu inos, in pa icula hose p oduced in he hep
p ocess in he Sun [9]. The main ea u e o he SoLA p oposal consis s o a pixel-based dual-
eadou anode plane combining cha ge and ligh eadou o inc ease ene gy esolu ion, imp o e
backg ound ejec ion, and dec ease da a s o age equi emen s.
The cu en DUNE Fa De ec o modules ha e sepa a e cha ge eadou senso s and la ge a ea
ligh de ec o s ha can si behind he anode o on he ca hode [10,11]. The DUNE Nea De ec o
liquid-a gon modules ha e a pixel-based cha ge collec ing anode plane wi h la ge a ea dielec ic
ligh collec ing modules adjacen o he anode plane wi hin he elec ic ield o he LA TPC [12].
The SoLA design uniquely has disc e e, pixela ed ligh and cha ge eadou on a single, sha ed
p in ed ci cui boa d (PCB). The SoLA de ec o concep is based on he same de ec o echnology
o pixel-based LA TPCs being cons uc ed o he Nea De ec o si e a DUNE [12]. The pixel-
based cha ge eadou is able o do na i e h ee-dimensional econs uc ion. Fo he SoLA de ec o
concep , indi idual silicon pho omul iplie s (SiPMs) will be dis ibu ed in a uni o m pa e n among
he cha ge pixels on he anode plane, p o iding a localized ligh econs uc ion o accompany
he signals om he neighbo ing cha ge pixels. The de elopmen o SiPMs sensi i e o acuum
ul a iole (VUV) ligh is ins umen al o he SoLA p oposal. The combina ion wi h cha ge eadou
allows o g ea e sensi i i ies in econs uc ion h ough ligh and cha ge signal ma ching. I opens
possibili ies in online igge ing by sec o izing he de ec o and igge ing speci ic pixels only when
i s neighbo ing ligh de ec o sees a signal.
We aim o use he design concep o build an ≈10 liquid-a gon SoLA - ype de ec o wi h
an ac i e olume o abou 1.6×2×2.6m3. Ea ly planning has ound he Boulby Unde g ound
Labo a o y in he Uni ed Kingdom as a sui able loca ion. The Boulby Labo a o y is loca ed in a
wo king polyhali e and sal mine in he No h Eas o England a a dep h o 1.1km. The SoLA
de ec o concep could also be adap ed o he ins umen a ion o u u e Fa De ec o modules o
DUNE [9] as pa o he DUNE Phase-II p og amme [13,14].
In his pape , we desc ibe he design o he i s SoLA p o o ype TPC and p esen esul s om
he ope a ion o his p o o ype a he Uni e si y o Be n in Oc obe 2022.
2 Expe imen al Se up
2.1 Design o he SoLA p o o ype Time P ojec ion Chambe
The i s SoLA p o o ype TPC (P o o ype- 1) uses a PCB wi h a pixela ed cha ge eadou sys em
using he LA Pix chip [15] and neighbo ing Hamama su VUV SiPMs. The PCB ac s as he anode
plane and is placed wi hin an elec ic ield o measu e he ioniza ion cha ge in he liquid a gon.
The liquid a gon VUV scin illa ion ligh om cosmic- ay muons is measu ed by he SiPMs. The
dimensions o he TPC a e 11.8×10.8cm2in he 𝑥and 𝑦di ec ion, wi h a sensi i e anode a ea o
7×7cm2, and 5cm in he d i di ec ion (𝑧). The choice is d i en by he c yos a inne olume
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geome y, which has a diame e o 14 cm. This size is su icien o demons a e he SoLA concep
by collec ing ligh and cha ge om cosmic ays on he same plane.
The ac i e a ea o he LA TPC is di ided in o a g id o 16 iden ical cells. Each cell consis s
o a VUV SiPM (Hamama su S13370-6050CN, QE(𝜆=128𝑛𝑚)≈15%) and 16 cha ge-collec ion
pads, esul ing in a o al o 256 pixels (see Figu e 1). The ca hode is a 1cm hick me al pla e wi h
Figu e 1. (a) Schema ic o a single cell wi hin he sensi i e a ea o he LA TPC. Cha ge-collec ing pixels
a e loca ed di ec ly nex o he pin o each SiPM; (b) he comple e 1 p o o ype wi h all 16 cells.
(a) (b)
smoo h golden su ace and ounded co ne s o p e en discha ges o he c yos a walls o po en ials
up o 10 kV. The side panel PCBs on he ou walls unc ion as elec ic ield shaping su aces wi h
nine me alized bands linked h ough a esis o chain o c ea e a homogeneous elec ic ield along
he elec ons’ d i line om he ca hode o he anode.
Figu e 2shows he in e io o he TPC wi h he ca hode pla e, side panel PCBs, and he eadou
anode pla e. The assembled TPC connec ed o a hanging ix u e is shown in Figu e 2. The ounded
co ne ods ex ending ou o he TPC olume a e mechanical guides o inse ion in o he c yos a
and o adjus ing he posi ion and dis ances o he TPC om he c yos a ’s inne walls.
The VUV SiPMs collec he pho ons in Geige mode and ans e he analog ligh wa e o m
signal o a cold p e-ampli ie s age o e a sho (20 cm) double-laye ed lex PCB. The signal
is hen ans e ed ia a eed- h ough PCB using SAMTEC mic o-coaxial cables o a a iable
gain ampli ica ion (VGA) uni . The di e en ial ampli ied signal a his s age is ans e ed ia a
wis ed-pai ibbon cable o an analog- o-digi al con e e (ADC) uni .
The cha ge collec ed on he pixel pads is ead ou wi h he help o a LA Pix chip, a c yo-
a ed ASIC o pixela ed liquid-a gon TPCs, de eloped by LBNL [15]. Fou LA Pix chips a e
used o ead ou he 256 pixels on he anode plane. The LA Pix chip p o ides a sel - igge ing
digi iza ion and mul iplexed da a ans e o a eadou hub in wa m, e e ed o as he PACMAN.
The anode eadou plane consis s o h ee laye s o PCBs moun ed on op o each o he , as shown
in Figu e 3. The cha ge collec ion pads a e loca ed on he inne mos laye , which con ains cu ou
–3–
holes o accommoda e he SiPMs solde ed on he second laye . This con igu a ion ensu es ha he
su aces o he ce amic-packaged SiPMs a e le el wi h he cha ge collec ion pixels. This alignmen
Figu e 2. (le ) In e io o he SoLA - 1 TPC ime p ojec ion chambe wi h he ca hode pla e, he side
panels o 𝐸- ield shaping and he eadou anode pla e con aining he SiPMs and cha ge pixels. ( igh ) Fully
assembled SoLA - 1 TPC a ached o i s suppo s uc u e. The back side o he anode pla e wi h he ou
LA Pix chips and he back side o one o he E- ield shaping panels wi h a esis o chain is also isible.
Figu e 3. Top and side- iew o he anode eadou plane h ee-laye s ack: cha ge (A) and SiPM eadou (B),
and pixel ele a ion (C).
–4–
minimizes elec ic ield de o ma ions nea he edges o he SiPMs and cha ge collec ion pads. The
second laye hos s he SiPMs and hei eadou aces o he connec o s. I also con ains a ne wo k
o aces ha ansmi s he cha ge signals o he ou e mos laye , which hos s he LA Pix eadou
chips and cha ge eadou connec o .
The SiPMs ope a e a a bias ol age o 56 V a oom empe a u e and 46 V a liquid-a gon
empe a u e wi h an o e ol age be ween 3V and 4V. The se up is designed o p o ide g ound
o se bias ol ages on he SiPMs, such ha he op su ace o he SiPMs, acing he TPC in e io ,
could be se o a nega i e g ound o se ol age compa ed o he common g ound o he cha ge
pads. In his way, he po en ial on he SiPMs su ace can shape he elec ic ields owa d he pixels,
po en ially inc easing he cha ge collec ion e iciency.
2.2 Elec ic ield simula ion
To unde s and he impac o design choices on he cha ge collec ion, he elec ic ield in p oximi y
o he anode was e alua ed nume ically using he COMSOL so wa e [16] o di e en g ound
o se alues. Raising he g ound o se has o be done ca e ully since a s ong elec ic ield inside
he SiPMs may e ec hei ope a ion and cause damages. Mo eo e , i he g ound o se is oo la ge,
ield lines s a o come ou o he SiPMs and in o he pixels. Figu e 4shows he esul s o he
elec ic ield lines in wo di e en con igu a ions: g ound o se se o 0 V, ep esen ing he nominal
condi ions o he un, and -100 V, ep esen ing he maximum g ound o se o da a aking wi h he
SiPM on he h ee-laye ed PCB. Da a was aken a 0 V (nominal), -25 V, -50 V, -75 V, and -100 V
wi h ligh da a esul s discussed in Sec ion 3.
2.3 C yogenics sys em
A iple-laye c yos a was used o ope a e he SoLA p o o ype wi h liquid a gon. A acuum
jacke , he ou e mos laye , p o ides he mal insula ion o he wo inne olumes o he c yos a .
The middle olume is used as a cooling jacke wi h liquid a gon cons an ly lowing h ough his
laye . The inne mos olume o he c yos a is illed wi h liquid a gon once and sealed o he ull
du a ion o he un. Figu e 5shows a schema ic o he SoLA P o o ype- 1 in he c yos a .
The liquid a gon passes h ough a illing il e wi h coppe ge e s o emo e aces o oxygen
and humidi y o m he LA . This small se up is no equipped wi h e-ci cula ion capabili ies and
hus he pu i y o he LA will de e io a e o e ime, gi ing us a limi ed ime window o abou 24
hou s o b ing up he sys em and ake cosmic- ay da a.
The le el o liquid a gon inside he c yos a is con olled wi h h ee empe a u e senso s a
di e en heigh s connec ed o he slow con ol sys em. The slow con ol sys em and each eadou
sys em has an indi idual eed h ough on he c yos a o ans e da a. The bias ol age o he SiPMs
is ou ed h ough a sepa a e eed h ough in o de o allow di e en schemes o g ound o se s om
common g ound. The p essu e in he laye s o he c yos a is moni o ed wi h wo p essu e gauges,
moun ed on he op lange. The inne olume is kep a an o e p essu e o 50 mba o he du a ion
o he es . Figu e 6shows he op lange wi h he assembled SoLA P o o ype- 1 TPC sho ly
be o e inse ion in o he c yos a and he expe imen al se up du ing c yogenic ope a ion.
–5–
Figu e 4. COMSOL nume ical e alua ion showing he di ec ion and magni ude o he elec ic ield on he
SoLA TPC. (Top) SiPM op su ace po en ial is se o g ound. (Bo om) SiPM op su ace po en ial is se o
−100 V. (Le ) Su ace di ec ly on op o he anode plane. (Righ ) C oss-sec ion o he TPC cu ing h ough
he middle o he SiPMs and pixels.
3 Resul s
3.1 P o o ype Ope a ion
In his sec ion, we desc ibe he esul s ob ained wi h he ligh and cha ge eadou based on da a
collec ed du ing he c yogenics ope a ion a he Uni e si y o Be n du ing Oc obe 24–26, 2022.
A e he c yos a had been illed wi h liquid a gon and he empe a u e senso s had been subme ged,
he ca hode ol age was aised o a po en ial o 2.5kV o p o ide an elec ic ield o 500 V/cm.
The da a was collec ed o bo h he cha ge and he ligh eadou con inuously wi h sepa a e
sel - igge ing da a acquisi ion sys ems. In o de o synch onize, a pulse pe second signal om he
Global Posi ioning Sys em (GPS) was ed o bo h sys ems. In addi ion, a ligh igge signal was
sen o he cha ge eadou PACMAN, which is w i en in o he cha ge da a s eam as a 𝑡0ma ke
o iden i y he s a ime o an e en . This enables co ec associa ion o he cha ge packe s’ d i
ime. 14 ou o 16 SiPMs we e ope a ional and collec ed ull ligh wa e o m o each e en . Only
abou 50% o he cha ge collec ing pixels we e wo king on he low h eshold le el ha is needed.
The e was no c oss alk obse ed be ween he wo king cha ge collec ing pixels and he SiPMs.
The cha ge and ligh da a ha e uni e sal ime s amps associa ed wi h he signals measu ed on
–6–
Figu e 5. (a) Sec ion iew o he CAD d awing o he c yos a and he SoLA p o o ype. The blue egion
is indica ing he acuum jacke , he o ange egion is he middle olume, and he ed egion is he inne mos
olume wi h he p o o ype de ec o inside. (b) The c yos a wi h open lid, whe e he access o sepa a e
olumes is isible.
Figu e 6. (a) Top lange wi h all he eed- h oughs and he suspended SoLA P o o ype- 1 LA TPC sho ly
be o e inse ing i in o he c yos a . (b) Expe imen al se up du ing c yogenics ope a ion.
–7–
bo h eadou sys ems. These ime s amps a e used in o line da a p ocessing o associa e he ligh
and cha ge signals, c ea ing wha we de ined as “e en s”, wi h each e en co e ing a ime span o
200 𝜇s. The d i dis ance o 5cm equi es ≈60 𝜇s o an elec on o a el he ull d i leng h.
The e en window is he e o e long enough so ha all he cha ge ha is c ea ed h ough ioniza ion
a he ime 𝑡0can d i om he ca hode o he anode. I wo ligh signals occu in close p oximi y,
only he ea lies ligh signal is used o ma k he s a o an e en . This can po en ially cause some
e en misma ching which has o be aken in o accoun in he analysis.
The scope o his i s p o o ype is he p oo o he concep ual idea o ha ing ligh and cha ge
collec ion on he anode plane. I should ensu e ha he new VUV SiPMs a e ope a ional in liquid
a gon on he anode plane and show ha i is possible o do ligh and cha ge ma ching o cosmic
e en s.
3.2 Fi s cosmic- ay acks wi h dual-pixel ligh and cha ge eadou
An es ima ed 70,000 e en s we e collec ed du ing he Oc obe 2022 un. In Figu e 7, we show wo
e en s wi h cosmic- ay muon candida es passing h ough he de ec o o highligh he associa ion
be ween ligh and cha ge in o ma ion. The 𝑥and 𝑦axes ep esen he span o he anode plane,
while he 𝑧di ec ion indica es he d i dis ance be ween he anode and he ca hode. The pa e ns
o cha ge and ligh signals on he pixels clea ly indica e a muon ack candida e. The 𝑧𝑦 p ojec ion
is ob ained by d awing a line o he cha ge signals o he anode plane, using hei ligh igge ime
𝑡0 o calib a e hei d i dis ance o he anode. The posi ion in o ma ion p o ides an unambiguous
h ee-dimensional hi objec . The ack inding occu s by i ing a linea unc ion o he hi s in he
𝑥𝑦 and 𝑥𝑧 planes wi h es ic ions placed on he minimum numbe o hi s in he e en and he 𝜒2o
he hi s ela i e o he line o bes i in each o he wo planes.
This esul ep esen s he i s combined de ec ion o cha ge and ligh on a dual-pixel anode
plane in a LA TPC, which is a majo miles one o demons a ing he ully h ee-dimensional cha ge
and ligh associa ion o he SoLA concep o igge ing and econs uc ion pu poses [9].
3.3 Cha ge collec ion pe uni leng h
We e alua e he amoun o cha ge pe uni leng h (𝑑𝑄/𝑑𝑥) on selec ed e en s using h ough-going
acks selec ed by applying linea i s o he cha ge da a. These acks a e analyzed pixel-by-pixel
o measu e he o al amoun o cha ge each pixel eco ds om wha is likely a minimally ionizing
cosmic- ay muon. Figu e 8shows he dis ibu ion o cha ge pe uni leng h o h ough-going
acks o e a da a- aking pe iod o 10 minu es o he 0V g ound o se scheme. To ensu e ha
ioniza ion deposi s ha all be ween wo pixels a e coun ed co ec ly, he 𝑑𝑄/𝑑𝑥 is measu ed
by combining cha ge measu ed by pixels in o 1 cm clus e s. The alue o each indi idual pixel
channel is sub ac ed by he alue o said channel om a p e iously aken pedes al un o equalize
he baseline o said channels. Because app oxima ely hal o he pixels we e no unc ional, he
pu pose o his s udy is o show ha calo ime y wi h he cha ge in o ma ion can be ep esen ed
by a Landau-Gaussian unc ion. The measu emen s a e p esen ed in ADC/cm. The cha ge eadou
sys em used has been obse ed o ha e a 5% channel- o-channel a ia ion in cha ge collec ed,
he eby shi ing 𝑑𝑄/𝑑𝑥 [17]. The e o e, a sys ema ic unce ain y o ha scale has been added o
he dis ibu ion.
–8–
