DARWIN: towards the ultimate dark matter detector

TLDR: DARk matter WImp search with liquid xenoN (DARWIN) as mentioned in this paper is an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core.

Abstract: DARk matter WImp search with liquid xenoN (DARWIN(2)) will be an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core. Its primary g ...

Figures

Figure 1. (left) The attainable bound on spin-independent WIMP nucleon cross-section as a function of the WIMP mass of present and future nobel liquid detectors. Shown are upper limits from PandaXII [28], DarkSide-50 [31], XENON100 [25], and LUX [27] as well as the sensitivity projections for DEAP3600 [16], XENON1T [32], XENONnT [32], LZ [33], DarkSide-20k [34] and DARWIN [35], for which we also show the 1-σ (yellow band) and 2-σ (green band) regions. DARWIN is designed to probe the entire parameter region for WIMP masses above ∼5GeV/c2, until the neutrino background (ν-line, dashed orange [36]) will start to dominate the recoil spectrum. (right) Upper limits on the spin-dependent WIMP-neutron cross section of ZEPLIN-III [19], XENON100 [37] and LUX [38] as well as projections for XENON1T, XENONnT, LZ and DARWIN. DARWIN and the high-luminosity LHC will cover a common region of the parameter space. The 14TeV LHC limits for the coupling constants gχ = gq = 0.25, 0.5, 1.0, 1.45 (bottom to top) are taken from [39]. The LHC reach for spinindependent couplings is above 10−41 cm2. Argon has no stable isotopes with non-zero nuclear spins and is thus not sensitive to spin-dependent couplings. Figures updated from [35], using the xenon response model to nuclear recoils from [27] for the DARWIN sensitivity.

Figure 4. Sensitivity of DARWIN to solar axions (left) and axion-like-particles (ALPs) (right) which could constitute the entire galactic dark matter. While the increase in sensitivity compared to the XENON100 result [59] is only moderate for solar axions, due to the very weak dependence on the exposure (x−1/8), DARWIN could improve the sensitivity to galactic ALPs by almost two order of magnitude in a 200 t× y exposure. Direct upper limits from the dark matter experiments XMASS [60], EDELWEISS [61] and CDMS [62], indirect limits from solar neutrinos and red giants, as well as two generic axion models, DFSZ [63] and KSVZ [64], are also shown.

Figure 2. Sketch of the DARWIN detector inside a tank, operated as a water-Cherenkov muon veto. The need for an additional liquidscintillator neutron veto inside the water shield, as shown in the figure (‘inner shield’), is subject to further studies. The dual-phase time projection chamber is enclosed within a double-walled cryostat and contains 40 t of liquid xenon (50 t total in the cryostat). In the baseline scenario, the prompt and delayed VUV scintillation signals, induced by particle interactions in the sensitive volume, are recorded by two arrays of photosensors installed above and below the liquid xenon target.

Figure 8. A possible realisation of a ∼50 t (40 t) total (target) LXe mass DARWIN detector, inside a doublewalled stainless steel cryostat. The TPC is surrounded by highly reflective PTFE walls, closed by the cathode and anode electrodes on bottom and top, respectively. The sketch shows a TPC with two photosensor arrays made of circular PMTs with 3” diameter. The final sensor type, however, is not yet defined and all details regarding the cryostat and TPC are subject to R&D.

Figure 11. (left) Mean size of the S1 light signal in a dual-phase LXe TPC, expected from a nuclear recoil of 5 keVnr (left axis), plotted against the detector’s light yield for a 122 keV γ-line at a drift field of ∼500V/cm. The relative scintillation efficiency Leff of LXe for this study is taken from [23]. Also shown is the relative resolution (σ/S1) at 5 keVnr, assuming that it is dominated by a Poisson process (right axis). The LXe TPCs XENON100 [24] and LUX [169] have achieved light yields of ∼2.3PE/keVee and ∼4.6PE/keVee at this drift field, respectively, as indicated by the green lines. (right) Mean charge signal in electrons, before gas amplification, for a 5 keVnr recoil signal as a function of the electron lifetime τe. A drift field of ∼500V/cm is assumed. The charge yield Qy for LXe is taken from [157]. The right axis shows the relative Gaussian resolution for 1.3m and 2.6m electron drift, corresponding to the central and the maximal value in a DARWIN detector. Lifetimes of 2ms have already been achieved in LXe detectors (green line). In both cases, it is unrealistic that DARWIN can improve significantly with respect to the numbers already achieved, leading to S1 resolutions of about 40% for 5 keVnr recoil signals and to charge resolutions of about 20%.

Figure 6. Expected sensitivity for the effective Majorana neutrino mass. The sensitivity band widths reflect the uncertainties in the nuclear matrix element of the 136Xe 0νββ-decay. The ‘DARWIN’ sensitivity assumes a 30 t×y exposure of natural xenon and a background dominated by γ-rays from detector materials. The ’ultimate’ case with 140 t×y exposure assumes this background being absent, thus only 222Rn, 2νββ and 8B solar neutrinos contribute. For details, see [48]. Also shown are the expected regions for the two neutrino mass hierarchy scenarios.

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Year:2016
DARWIN:towardstheultimatedarkmatterdetector
DARWINCollaboration;Aalbers,J;Agostini,F;Alfonsi,M;etal;Barrow,P;Baudis,L;
Galloway,M;James,A;Kish,A;Mayani,D;Pakarha,P;Piastra,F;Wei,Y;Wulf,J
Abstract:DARk matterWImp searchwith liquidxenoN (DARWIN) willbe anexperimentfor the
directdetectionofdarkmatterusingamulti-tonliquidxenontimeprojectionchamberatitscore.Its
primarygoalwillbetoexploretheexperimentallyaccessibleparameterspaceforWeaklyInteracting
MassiveParticles(WIMPs)inawidemass-range, untilneutrinointeractionswiththetargetbecome
anirreduciblebackground.Thepromptscintillationlightandthechargesignalsinducedbyparticle
interactionsinthexenonwillbeobservedbyVUVsensitive,ultra-lowbackgroundphotosensors.Besides
itsexcellentsensitivitytoWIMPsaboveamassof5GeV/c(2),suchadetectorwithitslargemass,low-
energythresholdandultra-lowbackgroundlevelwillalsobesensitivetootherrareinteractions. Itwill
searchforsolaraxions,galacticaxion-likeparticlesandtheneutrinolessdouble-betadecayof(136)Xe,
aswellasmeasurethelow-energysolarneutrinouxwith<1%precision,observecoherentneutrino-
nucleusinteractions,anddetectgalacticsupernovae.WepresenttheconceptoftheDARWINdetector
anddiscussitsphysicsreach,themainsourcesofbackgroundsandtheongoingdetectordesignandRD;
eorts.
PostedattheZurichOpenRepositoryandArchive,UniversityofZurich
ZORAURL:https://doi.org/10.5167/uzh-129742
JournalArticle
AcceptedVersion
Originallypublishedat:
DARWINCollaboration;Aalbers,J;Agostini,F;Alfonsi,M;etal;Barrow,P;Baudis,L;Galloway,M;
James,A;Kish,A;Mayani,D;Pakarha,P;Piastra,F;Wei,Y;Wulf,J(2016). DARWIN:towardsthe
ultimatedarkmatterdetector.JournalofCosmologyandAstroparticlePhysics:1-36.

Prepared for submission to JCAP
DARWIN: towards the
ultimate dark matter detector
DARWIN collaboration
J. Aalbers,
a
F. Agostini,
b,n
M. Alfonsi,
c
F.D. Amaro,
r
C. Amsler,
d
E. Aprile,
e
L. Arazi,
f
F. Arneodo,
g
P. Barrow,
h
L. Baudis,
h
M.L. Benabderrahmane,
g
T. Berger,
i
B. Beskers,
c
A. Breskin,
f
P.A. Breur,
a
A. Brown,
a
E. Brown,
i
S. Bruenner,
j
G. Bruno,
n
R. Budnik,
f
L. Bütikofer,
d
J. Calvén,
k
J.M.R. Cardoso,
r
D. Cichon,
j
D. Coderre,
d
A.P. Colijn,
a
J. Conrad,
k
J.P. Cussonneau,
l
M.P. Decowski,
a
S. Diglio,
l
G. Drexlin,
m
E. Duchovni,
f
E. Erdal,
f
G. Eurin,
j
A. Ferella,
k
A. Fieguth,
w
W. Fulgione,
n
A. Gallo Rosso,
n
P. Di Gangi,
b
A. Di
Giovanni,
g
M. Galloway,
h
M. Garbini,
b
C. Geis,
c
F. Glueck,
m
L. Grandi,
o
Z. Greene,
e
C. Grignon,
c
C. Hasterok,
j
V. Hannen,
w
E. Hogenbirk,
a
J. Howlett,
e
D. Hilk,
m
C. Hils,
c
A. James,
h
B. Kaminsky,
d
S. Kazama,
h
B. Kilminster,
h
A. Kish,
h
L.M. Krauss,
p
H. Landsman,
f
R.F. Lang,
q
Q. Lin,
e
F.L. Linde,
a
S. Lindemann,
j
M. Lindner,
j
J.A.M. Lopes,
r
T. Marrodán Undagoitia,
j
J. Masbou,
l
F.V. Massoli,
b
D. Mayani,
h
M. Messina,
e
K. Micheneau,
l
A. Molinario,
n
K.D. Morå,
k
E. Morteau,
l
M. Murra,
w
J. Naganoma,
t
J.L. Newstead,
p
K. Ni,
s
U. Oberlack,
c
P. Pakarha,
h
B. Pelssers,
k
P. de Perio,
e
R. Persiani,
l
F. Piastra,
h
M.C. Piro,
i
G. Plante,
e
L. Rauch,
j
S. Reichard,
q
A. Rizzo,
e
N. Rupp,
j
J.M.F. Dos Santos,
r
G. Sartorelli,
b
M. Scheibelhut,
c
S. Schindler,
c
M. Schumann,
d
J. Schreiner,
j
L. Scotto Lavina,
l
M. Selvi,
b
P. Shagin,
t
M.C. Silva,
r
H. Simgen,
j
P. Sissol,
c
M. von Sivers,
d
D. Thers,
l
J. Thurn,
x
A. Tiseni,
a
R. Trotta,
u
C.D. Tunnell,
a
K. Valerius,
m
M.A. Vargas,
w
H. Wang,
v
Y. Wei,
h
C. Weinheimer,
w
T. Wester,
x
J. Wulf,
h
Y. Zhang,
e
T. Zhu,
e
K. Zuber
x
a
Nikhef and the University of Amsterdam, Netherlands
b
Department of Physics and Astrophysics, University of Bologna and INFN-Bologna, Italy
arXiv:1606.07001v1 [astro-ph.IM] 22 Jun 2016

c
Institut für Physik & Exzellenzcluster PRISMA, Johannes Gutenberg-Universität Mainz,
Germany
d
Albert Einstein Center for Fundamental Physics, Universität Bern, Switzerland
e
Physics Department, Columbia University, New York, NY, USA
f
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot,
Israel
g
New York University Abu Dhabi, United Arab Emirates
h
Physik-Institut, Universität Zürich, Switzerland
i
Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute,
Troy, NY, USA
j
Max-Planck-Institut für Kernphysik, Heidelberg, Germany
k
Department of Physics, Stockholm University, Sweden
l
Subatech, Ecole des Mines de Nantes, CNRS/In2p3, Université de Nantes, France
m
Institut für Experimentelle Kernphysik, Karlsruhe Institute of Technology (KIT), Germany
n
INFN-Laboratori Nazionali del Gran Sasso and Gran Sasso Science Institute, L’Aquila, Italy
o
Kavli Institute, Enrico Fermi Institute and Dept. of Physics, University of Chicago, IL, USA
p
Physics Department, Arizona State University, Tempe, AZ, USA
q
Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA
r
Department of Physics, University of Coimbra, Portugal
s
Department of Physics, University of California, San Diego, CA, USA
t
Department of Physics and Astronomy, Rice University, Houston, TX, USA
u
Astrophysics Group & Data Science Institute, Imperial College London, UK
v
Physics & Astronomy Department, University of California, Los Angeles, CA, USA
w
Institut für Kernphysik, Westfälische Wilhelms-Universität Münster, Germany
x
Institute for Nuclear and Particle Physics, TU Dresden, Germany
E-mail:
lior.arazi@weizmann.ac.il, laura.baudis@uzh.ch,
amos.breskin@weizmann.ac.il, decowski@nikhef.nl, marc.schumann@lhep.unibe.ch
Abstract. DARk matter WImp search with liquid xenoN (DARWIN
1
) will be an experiment
for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber
at its core. Its primary goal will be to explore the experimentally accessible parameter
space for Weakly Interacting Massive Particles (WIMPs) in a wide mass-range, until neutrino
interactions with the target become an irreducible background. The prompt scintillation
light and the charge signals induced by particle interactions in the xenon will be observed
by VUV sensitive, ultra-low background photosensors. Besides its excellent sensitivity to
WIMPs above a mass of 5 GeV/c
2
, such a detector with its large mass, low-energy threshold
and ultra-low background level will also be sensitive to other rare interactions. It will search
for solar axions, galactic axion-like particles and the neutrinoless double-beta decay of
136
Xe,
as well as measure the low-energy solar neutrino flux with <1% precision, observe coherent
neutrino-nucleus interactions, and detect galactic supernovae. We present the concept of the
DARWIN detector and discuss its physics reach, the main sources of backgrounds and the
ongoing detector design and R&D efforts.
Keywords: Direct dark matter detection, WIMPs, Neutrinos, Large detector systems for
particle and astroparticle physics, Time projection chambers, Liquid xenon detector, Axions,
Neutrinoless double beta decay, Supernovae
1
www.darwin-observatory.org

Contents
1 Introduction
1
2 The DARWIN project 3
3 Science channels 5
3.1 WIMP dark matter 5
3.2 Other rare event searches 7
3.2.1 Axions and axion-like particles 7
3.2.2 Solar neutrinos 8
3.2.3 Neutrinoless double-beta decay 9
3.2.4 Coherent neutrino-nucleus scattering 10
3.2.5 Galactic supernova neutrinos 11
4 Expected backgrounds 11
4.1 Neutron backgrounds 12
4.2 Xenon-intrinsic backgrounds 12
4.3 Neutrino backgrounds 13
5 Design considerations and associated research and development 14
5.1 Cryostat and time projection chamber 14
5.2 High voltage system 16
5.3 Cryogenic and purification systems 16
5.4 Signal readout 18
5.4.1 Photomultipliers 19
5.4.2 Novel photosensors 19
5.4.3 Liquid Hole-Multipliers: charge and light readout in a single-phase TPC 21
5.5 Calibration 22
5.6 Light and charge yield of electronic and nuclear recoils 24
5.7 Detector resolution 24
5.8 Data acquisition and trigger schemes 26
6 Summary and Outlook 27
1 Introduction
Astronomical and cosmological observations reveal that the vast majority of the matter and
energy content of our universe is invisible – or dark – and interacts neither strongly nor
electromagnetically with ordinary matter. Results from the Planck satellite [
1] show that
about 68% of the overall budget is dark energy, leading to the observed accelerated expansion
of the cosmos. Another 27% is composed of dark matter, a yet-undetected form of matter
whose presence is needed to explain the observed large-scale structures and galaxies. While
dark matter interacts gravitationally with baryonic matter, any additional interactions, if
existing, must be very weak with extremely small cross sections [
2]. Because the standard
model of particle physics does not accommodate dark matter, the observationally-driven need
– 1 –

for its existence is one of the strongest indications for physics beyond the standard model.
The direct detection and subsequent characterisation of dark matter particles is, therefore,
one of the major experimental challenges of modern particle and astroparticle physics [
3, 4].
Many theories beyond the standard model predict viable candidates; one particular
class, receiving the attention of most current and planned experiments, is that of Weakly In-
teracting Massive Particles (WIMPs) [3, 5]. Worldwide, more than a dozen experiments are
prepared to observe low-energy nuclear recoils induced by galactic WIMPs in ultra-sensitive,
low-background detectors [
6–9]. Since the predicted WIMP masses and scattering cross sec-
tions are model-dependent and essentially unknown, these searches must cover a vast param-
eter space [10, 11]. Most promising are detectors based on liquefied noble gas targets such
as liquid xenon (LXe) or liquid argon (LAr). This technology is by now well-established and
can be scaled up to ton-scale, homogeneous target masses [
12–14], taking data over several
years.
Two detector concepts are in use. The first uses a single-phase noble-liquid WIMP tar-
get, surrounded by photosensors to record the emitted scintillation light. Examples are the
XMASS detector, operating a 850 kg total LXe target [
15], as well as DEAP-3600 [16] and
miniCLEAN [
17], large LAr detectors currently under commissioning. The LAr instruments
employ the powerful rejection of electronic recoil background based on pulse shape discrim-
ination (PSD) [
18]. With a 3600 kg LAr target, the larger detector DEAP-3600 aims at a
sensitivity of ∼1 × 10
−46
cm
2
for spin-independent WIMP-nucleon interactions at a WIMP
mass of 100 GeV/c
2
.
The second concept is based on dual-phase noble gas time projection chambers (TPCs),
where the prompt scintillation light (S1) and the delayed proportional scintillation light signal
from the charge (S2) are measured. Both signals are employed for a precise reconstruction
of the event vertex and, thus, to suppress backgrounds by rejection of multiple-scatter inter-
actions, as WIMPs are expected to interact only once. The charge-to-light ratio, S2/S1, is
exploited to separate the expected signal, namely nuclear recoils (NR), from the dominant
electronic recoil (ER) background.
TPCs filled with LXe were pioneered by the ZEPLIN [
19, 20] and XENON10 [21, 22]
collaborations. The XENON100 experiment [
23, 24 ], a TPC with a 62 kg active target,
has reached its sensitivity goal and excluded spin-independent WIMP-nucleon cross sections
above 2 × 10
−45
cm
2
at a WIMP mass of 55 GeV/c
2
[25]. These constraints were superseded
by the results from the LUX collaboration [
26, 27], which operates a 250 kg TPC and excludes
spin-independent WIMP-nucleon scattering cross sections above 4 × 10
−46
cm
2
at 33 GeV/c
2
.
The second phase of PandaX has published first result from its run with a 500 kg active LXe
target [28]. Liquid argon dual-phase TPCs were pioneered by WArP [29] and ArDM [30]. In
addition to the S2/S1 discrimination, they also exploit the considerably more powerful PSD
rejection of ER background [18]. DarkSide-50, using 50 kg of active LAr mass, has presented
first results from a low radioactivity run [
31]. The experiment reduces its target radioactivity
by using underground argon in which the radioactive
39
Ar is depleted by a factor of 1.4×10
3
with respect to atmospheric argon.
Probing lower cross sections at WIMP masses above a few GeV/c
2
requires larger detec-
tors. XENON1T, the current phase in the XENON collaboration programme, aims to reach
spin-independent cross sections of 1.6 × 10
−47
cm
2
after 2 years of continuous operation of
its 2 t LXe target [
32]. The next phase, XENONnT, to be designed and constructed during
XENON1T operation, will increase the sensitivity by another order of magnitude, assuming
20 t×y exposure [
32]. A similar sensitivity is sought by LUX-ZEPLIN (LZ), the next phase
– 2 –

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Darwin: towards the ultimate dark matter detector" ?

DARk matter WImp search with liquid xenoN ( DARWIN ) will be an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core. Its primary goal will be to explore the experimentally accessible parameter space for Weakly Interacting Massive Particles ( WIMPs ) in a wide mass-range, until neutrino interactions with the target become an irreducible background. The prompt scintillation light and the charge signals induced by particle interactions in the xenon will be observed by VUV sensitive, ultra-low background photosensors. The authors present the concept of the DARWIN detector and discuss its physics reach, the main sources of backgrounds and the ongoing detector design and RD ; efforts. 

Q2. how many ion-like particles can be detected?

Light and charge yield of electronic and nuclear recoils 24 5.7 Detector resolution 24 5.8 Data acquisition and trigger schemes 26