Cosmic-ray boosted dark matter in Xe-based direct detection experiments Tarak Nath MaityIDaRanjan LahaIDa

2025-04-27 0 0 591.62KB 15 页 10玖币

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Cosmic-ray boosted dark matter in Xe-based direct

detection experiments

Tarak Nath Maity ID ,a∗Ranjan Laha ID a†

aCentre for High Energy Physics, Indian Institute of Science, C. V. Raman Avenue, Bengaluru 560012, India

Abstract

LUX-ZEPLIN (LZ) collaboration has achieved the strongest constraint on weak-scale dark mat-

ter (DM)-nucleon spin-independent (SI) scattering cross section in a large region of parameter space.

In this paper, we take a complementary approach and study the prospect of detecting cosmic-ray

boosted sub-GeV DM in LZ. In the absence of a signal for DM, we improve upon the previous

constraints by a factor of ∼2 using the LZ result for some regions of the parameter space. We also

show that upcoming XENONnT and future Darwin experiments will be sensitive to cross sections

smaller by factors of ∼3 and ∼10 compared to the current LZ limit, respectively.

1 Introduction

A multitude of cosmological and astrophysical observations indicate that the biggest slice (∼85%) of

the matter density of the Universe is made up of DM [1–3]. While the presence of DM is revealed

through gravitational observations, its true nature is yet to be known. Typically it is assumed that

DM might be a particle in nature, and depending on the nature of the particle, the allowed DM mass

range varies. Additionally, it is phenomenologically interesting to have an interaction between diﬀerent

Standard Model (SM) states and DM. This relation is also common in a myriad of well-motivated

particle physics models [4–7]. Many ongoing and upcoming searches are speciﬁcally looking for this

connection [8–14].

Direct detection (DD) experiments look for the recoil of SM states through its scattering with am-

bient DM particles, and is mostly relevant for weakly interacting massive particles (WIMPs) searches.

One type of DD experiments hunt for recoil of the target nucleus, kept in underground laborato-

ries [15–22]. Among various target materials, xenon stands out to be quite beneﬁcial due to its

properties like shelf shielding, higher mass number, inert chemical nature, and others. Interestingly,

Xe target experiments continue to set the leading limits in large regions of DM parameter space [20–22].

The main target material in a two-phase time projection chamber (TPC) is liquid xenon (LXe). The

possible DM interaction with LXe is detected through light yields (S1) and charge yields (S2). Com-

bining the S1 and S2 signal topologies, it is possible to reconstruct the event’s three-dimensional

∗tarak.maity.physics@gmail.com

†ranjanlaha@iisc.ac.in

arXiv:2210.01815v2 [hep-ph] 7 Feb 2024

position and eﬃciently discriminates between nuclear recoil (NR) and electron recoil (ER) signatures,

etc. The NR backgrounds arise from neutrons, neutrino-nucleus interactions, etc., whereas the ER

background arise and from β-decays, γproduced by radioactivity, neutrino-electron interactions, etc.

Experiments like Xenon, LZ, and PandaX are exploring possible DM events in the presence of these

backgrounds.

Recently, LZ collaboration has published its ﬁrst result [23]. The experiment is situated at 4850

ft underground in the Davis Cavern at the Sanford Underground Research Facility (SURF) in Lead,

South Dakota, USA. The total mass of LXe is 10 t, out of which only the inner ﬁducial 5.5 t is used

for DM searches to reduce the backgrounds. With 60 live days of data, LZ has reached the current

strongest constraint 6 ×10−48cm2at DM mass 30 GeV. Compared to the previous strongest bound,

this is 6.7 and 1.7 times better at DM mass ∼30 GeV and ∼1000 GeV, respectively.

While the LZ result focuses on the searches for WIMP-like DM, in this paper, we take a complemen-

tary approach to investigate scenarios of sub-GeV DM interacting with nucleons via spin-independent

(SI) interactions. Non-relativistic sub-GeV DM, typically moving with velocity ∼10−3, will not be

able to impart enough energy to produce an observable NR in the LZ experiment. However, an en-

ergetic sub-GeV DM may produce suﬃciently large NR. One of the simplest ways to produce such

boosted DM is to consider the interaction between high-energy cosmic-rays (CRs) and DM, known as

CR boosted DM (CRDM), proposed for the ﬁrst time in Ref. [24] for nuclear scattering and Ref. [25]

for electron scattering. Further this technique has received considerable attention [26–66]. These

boosted DM particles reach the underground detector with much higher energy which helps to over-

come the energy threshold although with much lower ﬂux. Even with this lowered ﬂux, it is possible

to probe new regions of DM-nucleon scattering cross-section, since the bounds for sub-GeV DM using

other techniques are weak. The paradigm of CRDM premises only on the assumption of DM-nuclear

interactions, which is also true for many DD experiments. A large class of particle physics models

predicts such interaction for sub-GeV DM [67–72].

Knowledge of the CR spectrum is an important ingredient in computing CRDM ﬂux. The direct

CR ﬂux measurements (PAMELA [73], AMS-02 [74,75], CREAM-I [76], etc.) are done with balloons

and satellite detectors near the top or outside the atmosphere. This has been used as input CR ﬂux

in Ref. [24]. However above 100 TeV CR ﬂuxes are small hence direct measurements are not a

feasible choice. In this case, CR is measured indirectly through the air shower induced by it. We

utilize the parametric ﬁt of CR ﬂux measurement (obtained by combining direct and indirect CR

ﬂux measurements) given in Ref. [77] as the input CR ﬂux. Then we explore the signature of the

CR-induced DM in the LZ experiment. We ﬁnd a factor ∼2 improvement compared to previous limit

of XENON1T near DM mass ∼1 MeV. We also present the projections of the upcoming XENONnT,

LZ, and Darwin in probing the DM-nucleon cross-section for sub-GeV DM. We ﬁnd that there can be

a factor ∼10 improvement for Darwin compared to the current LZ limits.

The paper is organized as follows. In Sec. 2, we brieﬂy sketch the CRDM framework. In Sec. 3, we

present limits from LZ and future xenon-based experiments. We conclude in Sec. 4.

2 Overview of CRDM

Let us consider a DM particle (χ) of mass mχ, scattering with a CR particle of mass mi. After

scattering, the CR induced DM ﬂux is [24]

dϕχ

dTχ

=Deﬀ

ρlocal

mχX

σχiG2

i(2mχTχ)Z∞

Tmin

dTi

Tmax

χ(Ti)

dϕCR

dTi

,(1)

where Tχand Tiare the DM and CR kinetic energies respectively. The eﬀective distance, Deﬀ ,

depends on the distance to which DM ﬂux is integrated. The local DM density is denoted by ρlocal

χ,

ﬁxed to 0.3 GeV/cm3. In the sum, we have included the contributions of p, He, C, O, and Fe. DM-

nucleus scattering cross section is represented by σχi and G2

i(2mχTχ) is the nuclear form factor. The

diﬀerential CR ﬂux is represented by dϕCR

i/dTi. The minimum CR energy required to produce a DM

of kinetic energy Tχis

Tmin

i=Tχ

2−mi 1±s1 + 2Tχ

mχ

(mi+mχ)2

(2mi−Tχ)2!,(2)

with + and −sign applicable to Tχ>2miand Tχ<2mirespectively. The maximum kinetic energy

transferred to DM by the CR DM collision is given by

Tmax

χ=2mχT2

i+ 2miTi

2mχTi+ (mi+mχ)2(3)

The eﬀective distance is

Deﬀ =1

ρlocal

χZdΩ

4πZlos

ρχdℓ, (4)

where ρχis the Milky-Way (MW) DM density proﬁle under consideration. The angular region of the

integration is represented by dΩ. For traditional Navarro-Frenk-White DM density proﬁle [78] (with

parameters taken from Ref. [79]), the eﬀective distance (given in Eq. (4)) turns out to be ∼1 kpc and

∼10 kpc for integrating up to 1 kpc and 10 kpc around the Sun respectively [24]. In our numerical

calculation we ﬁx Deﬀ to 10 kpc. We have used the Global ﬁt model presented in Ref. [77] inspired

by various CR measurement. This CR spectra retain the various spectral features which arise due to

the contribution from diﬀerent possible CR sources. We do not consider spatial-dependent CR ﬂux;

including them, will strengthen our limits and sensitivities by factor of ∼3 [56], hence our results are

conservative.

The CRDM particles will also interact with the nuclei while traversing from the top of the atmosphere

to the underground detector. CRDM will lose its energy for a reasonably large cross-section due

to scattering with these nuclei. The subsequent attenuation of CRDM ﬂux has been studied in

Refs. [24,56,80].1We calculate the DM kinetic energy at a depth z,Tz

χ, utilizing [64]

dT z

dz =−X

mjZωmax

dωχ

dσχj

dωχ

ωχ,(5)

where ρis the average mass density of the medium, mjis the mass of the target nucleus and ωχis the

energy loss of DM particles due to collision. For elastic scattering, the maximum energy loss, ωmax

χ, can

1See Refs. [81–85] for attenuation of non-boosted DM with large DM-SM scattering cross sections.

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摘要：

Cosmic-rayboosteddarkmatterinXe-baseddirectdetectionexperimentsTarakNathMaityID,a∗RanjanLahaIDa†aCentreforHighEnergyPhysics,IndianInstituteofScience,C.V.RamanAvenue,Bengaluru560012,IndiaAbstractLUX-ZEPLIN(LZ)collaborationhasachievedthestrongestconstraintonweak-scaledarkmat-ter(DM)-nucleonspin-indepe...

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Cosmic-ray boosted dark matter in Xe-based direct detection experiments Tarak Nath MaityIDaRanjan LahaIDa

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