Jou nal o Physics: Con e ence Se ies
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Pe spec i es o lowe ing CUORE h esholds wi h Op imum T igge
To ci e his a icle: V Dompè e al 2020 J. Phys.: Con . Se . 1643 012020
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Jou nal o Physics: Con e ence Se ies 1643 (2020) 012020
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doi:10.1088/1742-6596/1643/1/012020
1
Pe spec i es o lowe ing CUORE h esholds wi h
Op imum T igge
V Domp`e1,2, D Q Adams3, C Alduino3, K Al onso4, F T A ignone
III3, O Azzolini5, G Ba i6, F Bellini7,8, G Bena o9, A Be sani10, M
Biassoni11, A B anca11,12, C B o e io11,12, C Bucci2, A Camina a10, A
Campani10,13, L Canonica2,14, X G Cao15, S Capelli11,12, L
Cappelli2,9,16, L Ca dani8, P Ca ni i11,12, N Casali8, D Chiesa11,12, N
Cho 3, M Clemenza11,12, S Copello1,2, C Cosmelli7,8, O C emonesi11,
R J C eswick3, J S Cushman17, A D’Addabbo2, D D’Aguanno2,18, I
Da inei8, C J Da is17, S Dell’O o19, S Di Domizio10,13, A
D obizhe 9,16, D Q Fang15, G Fan ini1,2, M Fa e zani11,12, E Fe i11,12,
F Fe oni1,7,8, E Fio ini11,12, M A F anceschi20, S J F eedman9,16,a, B
K Fujikawa16, A Giache o11,12, L Gi oni11,12, A Giuliani21, P Go la2, C
Go i11,12, T D Gu ie ez22, K Han23, K M Heege 17, R G Huang9, H
Z Huang4, J Johns on14, G Keppel5, Yu G Kolomensky9,16, A
Lede 14, C Ligi20, Y G Ma15, L Ma ini9,16, M Ma inez7,8,24, R H
Ma uyama17, Y Mei16, N Moggi6,25, S Mo gan i8, T Napoli ano20, M
Nas asi11,12, C Nones26, E B No man27,28, V No a i21, A Nuccio i11,12,
I Nu ini1,11,12, T O’Donnell19, J L Ouelle 14, C E Paglia one2,18, M
Palla icini10,13, L Pa a ina2, M Pa an11,12, G Pessina11, V
Pe inacci8, C Pi a5, S Pi o2, S Pozzi11,12, E P e i ali11, A Puiu11,12,
C Rosen eld3, C Rusconi2,3, M Sakai9, S Sangio gio27, B Schmid 16, N
D Scielzo27, V Singh9, M Sis i11,12, D Spelle 17, L Ta a ello29, F
Te ano a11,12, C Tomei8, M Vigna i8, S L Wagaa achchi9,16, B S
Wang27,28, B Welli e 16, J Wilson3, K Wilson3, L A Winslow14, T
Wise17,30, L Zano i11,12, S Zimme mann31 and S Zucchelli6,25
1INFN – G an Sasso Science Ins i u e, L’Aquila I-67100, I aly
2INFN – Labo a o i Nazionali del G an Sasso, Asse gi (L’Aquila) I-67100, I aly
3Depa men o Physics and As onomy, Uni e si y o Sou h Ca olina, Columbia, SC 29208,
USA
4Depa men o Physics and As onomy, Uni e si y o Cali o nia, Los Angeles, CA 90095,
USA
5INFN – Labo a o i Nazionali di Legna o, Legna o (Pado a) I-35020, I aly
6INFN – Sezione di Bologna, Bologna I-40127, I aly
7Dipa imen o di Fisica, Sapienza Uni e si `a di Roma, Roma I-00185, I aly
8INFN – Sezione di Roma, Roma I-00185, I aly
9Depa men o Physics, Uni e si y o Cali o nia, Be keley, CA 94720, USA
10 INFN – Sezione di Geno a, Geno a I-16146, I aly
11 INFN – Sezione di Milano Bicocca, Milano I-20126, I aly
12 Dipa imen o di Fisica, Uni e si `a di Milano-Bicocca, Milano I-20126, I aly
13 Dipa imen o di Fisica, Uni e si `a di Geno a, Geno a I-16146, I aly
14 Massachuse s Ins i u e o Technology, Camb idge, MA 02139, USA
27 h In e na ional Nuclea Physics Con e ence (INPC2019)
Jou nal o Physics: Con e ence Se ies 1643 (2020) 012020
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doi:10.1088/1742-6596/1643/1/012020
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15 Shanghai Ins i u e o Applied Physics, Chinese Academy o Sciences, Shanghai 201800,
China
16 Nuclea Science Di ision, Law ence Be keley Na ional Labo a o y, Be keley, CA 94720, USA
17 W igh Labo a o y, Depa men o Physics, Yale Uni e si y, New Ha en, CT 06520, USA
18 Dipa imen o di Ingegne ia Ci ile e Meccanica, Uni e si `a degli S udi di Cassino e del Lazio
Me idionale, Cassino I-03043, I aly
19 Cen e o Neu ino Physics, Vi ginia Poly echnic Ins i u e and S a e Uni e si y,
Blacksbu g, Vi ginia 24061, USA
20 INFN – Labo a o i Nazionali di F asca i, F asca i (Roma) I-00044, I aly
21 CSNSM, Uni . Pa is-Sud, CNRS/IN2P3, Uni e si ´e Pa is-Saclay, 91405 O say, F ance
22 Physics Depa men , Cali o nia Poly echnic S a e Uni e si y, San Luis Obispo, CA 93407,
USA
23 INPAC and School o Physics and As onomy, Shanghai Jiao Tong Uni e si y; Shanghai
Labo a o y o Pa icle Physics and Cosmology, Shanghai 200240, China
24 Labo a o io de Fisica Nuclea y As opa iculas, Uni e sidad de Za agoza, Za agoza 50009,
Spain
25 Dipa imen o di Fisica e As onomia, Alma Ma e S udio um – Uni e si `a di Bologna,
Bologna I-40127, I aly
26 Se ice de Physique des Pa icules, CEA / Saclay, 91191 Gi -su -Y e e, F ance
27 Law ence Li e mo e Na ional Labo a o y, Li e mo e, CA 94550, USA
28 Depa men o Nuclea Enginee ing, Uni e si y o Cali o nia, Be keley, CA 94720, USA
29 INFN – Sezione di Pado a, Pado a I-35131, I aly
30 Depa men o Physics, Uni e si y o Wisconsin, Madison, WI 53706, USA
31 Enginee ing Di ision, Law ence Be keley Na ional Labo a o y, Be keley, CA 94720, USA
aDeceased
E-mail: [email p o ec ed]
Abs ac . CUORE is a c yogenic expe imen ha ocuses on he sea ch o neu inoless double
be a decay in 130Te and i is loca ed a he G an Sasso Na ional Labo a o ies. I s de ec o
consis s o 988 TeO2c ys als ope a ing a a base empe a u e o ∼10 mK. I is he i s on-
scale bolome ic expe imen e e ealized o his pu pose. Thanks o i s la ge a ge mass
and ul a-low backg ound, he CUORE de ec o is also sui able o he sea ch o o he a e
phenomena. In pa icula he low ene gy pa o he spec a is in e es ing o he de ec ion o
WIMP-nuclei sca e ing eac ions. One o he mos impo an equi emen s o pe o m hese
s udies is ep esen ed by he achie emen o a s able ene gy h eshold lowe han 10 keV. He e,
he CUORE capabili y o accomplish his pu pose using a low ene gy so wa e igge will be
p esen ed and desc ibed.
1. In oduc ion
The double be a decay is a a e second o de weak ansi ion ha can occu o a numbe o
hea y e en-e en nuclei. In many cases, he single be a decay is supp essed o ene ge ically
o bidden. Two decay modes a e conside ed o his a e p ocess: he wo-neu ino double be a
decay (2νββ) and he neu inoless double be a decay (0νββ). In he i s case, wo neu inos
accompany he emi ed elec ons and i has been obse ed in se e al nuclei. Depending on he
s udied iso ope, he measu ed alues o he hal li es o his decay ange be ween 1019 - 1021
yea s[1]. The neu inoless double be a decay has ne e been obse ed ye . Only wo elec ons a e
emi ed in his case, he e o e i is a lep on numbe iola ing p ocess, o bidden by he S anda d
Model. The e a e di e en easons why he s udy o his p ocess is in e es ing. Fi s o all, he
obse a ion o such p ocess would be a di ec sign o new physics beyond he S anda d Model.
The mos in e es ing aspec ega ds he possibili y o p obe he neu ino Di ac o Majo ana
na u e: in ac , he 0νββ decay can only occu i he neu ino is a Majo ana pa icle [2]. The
obse a ion o his decay would also gi e in o ma ions on he neu ino absolu e mass scale and
hie a chy. Fo all hese easons, se e al expe imen s a e cu en ly in es iga ing he 0νββ decay
27 h In e na ional Nuclea Physics Con e ence (INPC2019)
Jou nal o Physics: Con e ence Se ies 1643 (2020) 012020
IOP Publishing
doi:10.1088/1742-6596/1643/1/012020
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o di e en candida e nuclei. Depending on he conside ed iso ope, he cu en limi s on he
0νββ decay hal li e es ablish ha i canno be less han 1025 - 1026 yea s[1]. The pe o mance
o such expe imen s is desc ibed by hei sensi i i y o he hal li e o he decay, which can be
app oxima ed as[3]:
S0ν=T0ν
1/2∝·η·sM·
b·∆E(1)
As shown by eq. 1, he sensi i i y depends on se e al ele an pa ame e s: he de ec ion
e iciency , he iso opic abundance ηo he 0νββ emi e , he exposu e in e ms o he mass
Mand he li e ime , he alues o ene gy esolu ion ∆E and he backg ound bin he egion
o in e es . The egion o in e es (ROI) is an ene gy ange ha includes he ansi ion ene gy
( he Q alue) o he decay. A high sensi i i y expe imen aims a simul aneously op imizing he
majo i y o hese pa ame e s.
2. The CUORE expe imen
CUORE (C yogenic Unde g ound Expe imen o Ra e E en s) is an expe imen sea ching o
0νββ decay in 130Te[4]. The choice o his iso ope is due o i s high na u al iso opic abundance
η= 34.167%, and he Q alue = 2527.515 keV, ha alls in a low backg ound egion o he
gamma spec um, namely be ween he 208Tl peak, which is he cu o o he na u al be a gamma
adioac i i y, and i s Comp on edge. The CUORE de ec o consis s o an a ay o 988 c yogenic
TeO2c ys als o a o al mass o 742 kg, wi h 206 kg o 130Te. This candida e iso ope o
he 0νββ emission is embedded in he de ec o i sel : his p o ides a high de ec ion e iciency,
close o 80%. The c ys als a e ope a ed as bolome e s: his echnique exploi s he he mal
a ia ion expe ienced by he abso be c ys al when a pa icle passes h ough i and deposi s
ene gy[4]. The ampli ude o he he mal aise is p opo ional o he ene gy deposi ion and
depends on he empe a u e by means o he hea capaci y o he abso be . Since he he mal
a ia ion would be unmeasu able a oom empe a u e, he CUORE bolome e s a e ope a ed a
a wo king empe a u e o ∼10 mK. Such c yogenic empe a u e is eached and main eined by
means o a cus om buil mul i-s age c yos a [5]. In o de o wo k a low backg ound condi ions,
CUORE is ins alled a he G an Sasso Na ional Labo a o ies in I aly a a 3600 m.w.e. dep h,
o supp ess he backg ound om cosmic ays. Accu a e p ocedu es o a oid con amina ions
we e applied du ing he CUORE cons uc ion, assembly and cleaning o he ma e ials. The
bolome e s p o ec ion om ex e nal adioac i i y is p o ided by lead shields ins alled in o he
CUORE c yos a ; pa o his lead has ex emely low adioac i i y since i belongs o Ancien
Roman age[6].
Figu e 1. The 988 CUORE c ys als, be o e he c yos a was closed.
27 h In e na ional Nuclea Physics Con e ence (INPC2019)
Jou nal o Physics: Con e ence Se ies 1643 (2020) 012020
IOP Publishing
doi:10.1088/1742-6596/1643/1/012020
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Figu e 2. The ROI (2465 - 2575 keV) bes i . The Qββ alue is enligh ened by he ed band,
which wid h e e s o he sys ema ics unce ain y on he econs uc ed ene gy[7].
2.1. CUORE i s esul s
The CUORE physics da a collec ion s a ed in sp ing 2017. The i s ob ained esul s e e
o 7 weeks o da a aking collec ed du ing 2017, o a o al TeO2exposu e o 86.3 kg·y [7].
The i in he CUORE ROI is shown in igu e 2. F om his i , we ex ac ed a decay a e
o Γ0ν= (−1.0+0.4
−0.3±0.1(sys .)) ×10−25 y−1. The decay a e is p opo ional o he in e se
o he hal li e, and is also ela ed o he Majo ana neu ino mass mββ h ough he equa ion
Γ0ν∝G0ν(Q, Z)|M0ν|2|< mββ >|2; he e o e, we we e able o se a limi on 130Te 0νββ hal li e
o T0ν
1/2>1.5×1025 y (90% C.L.), and a co esponding limi on he e ec i e Majo ana neu ino
mass o mββ <110 −520 meV. Besides he sea ch o he 0νββ peak, i is possible o analyze
o he phenomena con ibu ing o he CUORE measu ed spec um. This can be pe o med
hanks o an accu a e Mon e Ca lo econs uc ion o he CUORE backg ound. This includes
de ailed in o ma ions achie ed by exploi ing he g anula i y o he de ec o , in pa icula he
knowledge o he numbe o c ys als in ol ed in he in e ac ions (e en mul iplici y), and by
sepa a ing he de ec o in o an inne and an ou e laye . A majo con ibu ion o he CUORE
Figu e 3. The CUORE measu ed spec um om 0 o he Qββ: he con ibu ion o 2νββ decay
o 130Te is d awn in cyan[8].

27 h In e na ional Nuclea Physics Con e ence (INPC2019)
Jou nal o Physics: Con e ence Se ies 1643 (2020) 012020
IOP Publishing
doi:10.1088/1742-6596/1643/1/012020
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con inuous ene gy egion om 0 o he Q alue is gi en by he 2νββ decay o 130Te ( ig.3). The
backg ound model econs uc ion allows o disen angle his con ibu ion, om which i was
possible o measu e he hal li e o 130Te 2νββ decay: T2ν
1/2= (7.9±0.1(s a .)±0.2(sys .))×1020
y[8].
3. Lowe ing he CUORE ene gy h esholds
The CUORE de ec o la ge mass and low backg ound le el make i sui able o he s udy o
o he a e e en s[9]. The WIMP di ec de ec ion could be sea ched o h ough he measu emen
o he nuclea ecoil due o WIMP - Te/O nuclei sca e ing, as well as h ough he obse a ion o
hei a e annual modula ion signal. The sola axions sea ch can also be pe o med by exploi ing
he in e se P imako e ec in he Coulomb ield o he TeO2c ys als. In addi ion, he cohe en
sca e ing o supe no a neu inos wi h Te/O nuclei could be de ec ed by CUORE. Since all hese
in e ac ions a e expec ed o p oduce signals a ene gies below ew ens o keV, a undamen al
equi emen o s udying hem is o achie e a su icien ly low de ec ion ene gy h eshold. In
CUORE, his can be accomplished by an imp o ed igge algo i hm, named Op imum T igge .
3.1. The Op imum T igge
The low ene gy egion o he CUORE spec um is s ongly a ec ed by noise con ibu ions,
e.g. om elec onic dis u bances and mechanical ib a ions. The CUORE s anda d de i a i e
igge i es when he baseline slope emains abo e h eshold o a ce ain amoun o ime[10].
Since i does no ca y any in o ma ion abou he signal pulse shape, i is no e y e icien in
dis inguishing be ween physical and non-physical pulses a low ampli udes. Indeed, he ene gy
h eshold canno go below ens o keV. In o de o lowe he ene gy h eshold, he non-physical
backg ound mus be iden i ied and ejec ed. This is accomplished by he Op imum T igge
(OT)[9]: he igge algo i hm is applied on a con inuous da a s eam, p e iously il e ed wi h
an op imum il e , wi h a ans e unc ion gi en by
H(ωk) = S(ωk)
N(ωk)e−jωk M(2)
whe e S(ωk) is he Disc e e Fou ie T ans o m o he signal shape, and N(ωk) is he de ec o
noise powe spec um. The il e ed da a a e cha ac e ized by a highe signal- o-noise a io and
educed noise luc ua ions ( ig. 4). The in o ma ions on he signal pulse shape ca ied by he
Figu e 4. Windows o da a samples in he p esence o a pulse. Raw da a a e ep esen ed by he
black solid line, while il e ed da a by he ed dashed line; he ed iangle is he OT posi ion[9].
27 h In e na ional Nuclea Physics Con e ence (INPC2019)
Jou nal o Physics: Con e ence Se ies 1643 (2020) 012020
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doi:10.1088/1742-6596/1643/1/012020
6
op imum il e allow o supp ess he non-physical pulses, which ha e a di e en pulse shape.
The igge ene gy h eshold is de ined, o each bolome e , as he ene gy co esponding o he
90% igge de ec ion e iciency. In o de o e alua e he e iciencies, we pe o m speci ic da a
acquisi ions whe e a de ined numbe o hea e pulses a di e en ampli udes a e i ed on each
bolome e . The e iciency cu e is hen cons uc ed o each c ys al by e alua ing he numbe o
pulse s de ec ed a each ene gy. A p elimina y s udy o he e iciencies o he s anda d igge
and o he OT has been pe o med wi h pa o he da a collec ed by CUORE du ing 2019[11];
om a compa ison o he s anda d and OT h esholds, we ob ain ha he usage OT signi ican ly
lowe s he ene gy h esholds ( ig. 5).
Figu e 5. Compa ison o he ene gy h esholds ob ained by he s anda d de i a i e igge
(blue dis ibu ion) and by he Op imum T igge ( ed dis ibu ion)[11].
4. Conclusions
CUORE is sea ching o 0νββ decay o 130Te. I s i s da a elease e e s o he analysis o a
TeO2exposu e o 86.3 kg·y : wi h only 7 weeks o da a aking, he s onges limi on 0νββ decay
hal li e and he mos p ecise measu emen o 2νββ decay hal li e o 130Te we e se . Thanks o
i s cha ac e is ics o la ge mass and low backg ound, CUORE is also sui able o he sea ch o
o he a e e en s, p o ided ha a su icien ely low ene gy h eshold is achie ed. The Op imum
T igge has been de eloped o his pu pose, and he i s es s on i s e iciencies showed ha i
signi ican ly imp o es he ene gy h eshold wi h espec o he s anda d igge ; u he s udies
on OT op imiza ion o CUORE a e cu en ly ongoing, exploi ing he highe s a is ics ha
CUORE is collec ing. Da a o an exposu e o ∼400 kg·y a e al eady a ailable o analysis.
Re e ences
[1] Tanabashi M e al. (Pa icle Da a G oup) 2018 and 2019 upda e Phys. Re . D 98, 030001
[2] Dell’O o S, Ma cocci S, Viel M, and Vissani F 2016 Ad . High Ene gy Phys. 2016 2162659
[3] Alduino C e al. (CUORE) 2017 Eu . Phys. J. C 77 532
[4] A usa D R e al. 2015 Ad . High Ene gy Phys. 2015 879871
[5] Alduino C e al. 2019 C yogenics 102 9-21
[6] Alessand ello A e al. 1998 Nucl. Ins um. Me h. A 412 454-464
[7] Alduino C e al. (CUORE Collabo a ion) 2018 Phys. Re . Le . 120 132501
[8] Adams D Q e al. (CUORE Collabo a ion) 2018 a Xi :1808.10342.
[9] Di Domizio S, O io F and Vigna i M 2011 J. Ins um. 6
[10] Di Domizio S, B anca A, Camina a A, Canonica L, Copello S, Giache o A, Gua dince i E, Ma ini L,
Palla icini M and Vigna i M 2018 J. Ins um. 13
[11] Campani A e al. J. Low Temp. Phys. P oceeding o LTD-18 Con e ence