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"1.4 Indirect solar WIMP search with neutrinos

 

Large celestial bodies like the Sun have the potential to be natural attractors for (Weakly-interacting massive particles) WIMPs $^{48}$, hypothetical particles that are thought to constitute dark matter. The Sun, as part of the galactic disc, revolves around the galactic center and thereby plows through the WIMP halo, which is thought to be at rest. This leads to scattering of WIMPs on the nuclei of the Sun. If the scatter is connected to a substantial loss of kinetic energy by the WIMP so that it falls below the escape velocity, it will get gravitationally bound to the Sun. With time and further scatters the WIMPs eventually sink to the core of the Sun, where they accumulate and thermalize. The resulting over density of WIMPs leads to self-annihilation processes yielding SM particles in great abundances. Of these only neutrinos can possibly leave the Sun. This process is schematically illustrated in figure 1.4.

 

Indirect searches for solar WIMP dark matter are sensitive to the WIMP-nucleon scattering cross-section which initiates the capture process. Here the mass of $\simeq 2 · 10^{30}$ kg for the Sun is forming a huge target driving the capture of WIMPs and their accumulation. The neutrinos yielded in the annihilation processes should then be observable at Earth in neutrino telescopes like IceCube. Even if the detection of neutrinos has challenges of its own, a neutrino signal detection from the direction of the Sun would be very significant in its interpretation for WIMP dark matter.".

"1. Introduction

 

The IceCube neutrino observatory $^{1, 2}$ is a cubic kilometer photomultiplier (PMT) array embedded in glacial ice at the geographic South Pole. The complete array is made of 5160 downward-facing Hamamatsu R7081 photomultipliers deployed on 86 vertical strings at depths between 1450 and 2450 meters in the icecap. IceCube detects neutrinos by observing Cherenkov light induced by charged particles created in neutrino interactions as they transit the ice sheet within the detector; the energy and momentum of these charged particles reflect the energy and momentum of the original neutrino.

 

At the TeV energies typical of such neutrino telescopes, the primary neutrino interaction channel is deep-inelastic scattering with nuclei in the detector material. In both neutral and charged-current interactions, a shower of hadrons is created at the neutrino interaction vertex. In charged-current interactions, this shower is accompanied by an out-going charged lepton. This lepton, in particular for electrons, may also lose energy rapidly and itself trigger another overlaid shower. Cherenkov light is radiated by this primary lepton and any accompanying showers with a total amplitude proportional to the integrated path length of charged particles above the Cherenkov threshold. This, in turn, is proportional to the total energy of these particles $^3$.

 

The light production from electromagnetic (EM) showers is both maximal and has low variance with respect to deposited energy $^3$. As such, it forms a natural unit of re- constructed shower energy.".

"Current status

 

High-energy neutrinos from the Sun provide one of the cleanest potential discovery channels for weakly-interacting dark matter (DM). Weakly-interacting DM particles passing through the Sun are expected to scatter on solar nuclei. Some of these collisions reduce the kinetic energy of the DM particle enough for it to become gravitationally bound to the Sun, causing it to return on a bound orbit and undergo subsequent scattering, eventually thermalising and settling down to the solar core. If DM is able to annihilate, either with itself of with anti-DM captured in a similar manner, high-energy SM particles will be produced in the solar core. Even if neutrinos are not amongst those particles produced in the annihilation hard process, they will still be generated with quite high energies in the decay and subsequent interaction of other SM particles with nuclei in the Sun. Unlike the other SM particles, these GeV-scale neutrinos are then able to travel unhindered from the centre of the Sun to the surface, and across space to Earth, where they may be detected with terrestrial experiments.

 

The directionality of the signal is the primary means by which it can be distinguished from the atmospheric neutrino background, caused by cosmic ray interactions with the Earth’s atmosphere. The only known background to the signal is therefore the analogous production of high-energy neutrinos in the atmosphere of the Sun, due to interactions of cosmic rays with solar nuclei.

 

The capture of dark matter by the Sun typically becomes the rate-limiting step in the production of any signal, rather than the annihilation. Searches for high energy neutrinos from the Sun are therefore most useful for constraining the interaction cross section of dark matter with nuclei. Spin-dependent interactions are particularly relevant, as the Sun consists mostly of hydrogen, which possesses nuclear spin.".

 

...

 

Page 3:

 

"Improved background calculations

 

Previous predictions of the background rate of high-energy neutrinos from the Sun, due to interactions of cosmic rays with nuclei in the solar atmosphere, were computed more than a decade ago.$^{6,7,8}$ However, two more recent recalculations have appeared.$^{9,10}$ Compared to the older predictions, the new calculations make use of modern knowledge on neutrino oscillations, production and interaction cross-sections. One of these$^{10}$ also makes use of up-to-date models of the solar composition and structure, and carries out extensive Monte Carlo simulations of neutrino production, interaction and oscillation. Both studies (and another at the same time, based on the old flux estimates$^{11}$) show that the solar atmospheric background lies barely an order of magnitude below current sensitivity limits for some models (Fig. 2). This suggests that future neutrino telescopes might be able to directly measure this irreducible ‘neutrino floor’, and that the improved calculations of the background rates should be included in future phenomenological studies of DM scattering and annihilation in the Sun.".

 

9. C. A. Argüelles, G. de Wasseige, A. Fedynitch, and B. J. P. Jones, Solar atmospheric neutrinos and the sensitivity floor for solar dark matter annihilation searches, JCAP 7 (2017) 024, [arXiv:1703.07798].

10. J. Edsjö, J. Elevant, R. Enberg, and C. Niblaeus, Neutrinos from cosmic ray interactions in the Sun, JCAP 6 (2017) 033, [arXiv:1704.02892].

"If we compare the he neutrino fluxes at production (solid lines) to the ones after passage through the Sun (dashed lines), we see that we get a dip at low impact parameters. This is the effect of the attenuation that happens due to interactions when the neutrinos pass through the Sun, as we saw already in figure 4. As the density of the Sun is significantly higher in the centre, the effect is very strongly pronounced for low impact parameters. We can also see that the effect of attenuation is higher for higher energies as expected.

 

We can also see how the production fluxes depend on the impact parameter. We can see that for higher energies these are quite peaked at large impact parameters, which is expected as the density where the cascade happens is lower for these Sun grazing CRs, and hence the fluxes are higher. We also get a small contribution from muons decaying outside of the Sun at high impact parameters and high energies.3 The total flux from the Sun is obtained by integrating over the impact parameters including the fact that the solid angle is larger for large impact parameters. Hence, the high impact parameter part of these figures will be most important for the total flux from the Sun.".

"Solar atmospheric neutrinos provide a natural background to solar dark matter searches and limit their sensitivity as recently pointed out $^{[5, 6, 7]}$.".

 

7. J.Edsjö, J.Elevant, R.Enberg and C.Niblaeus, [astro-ph/1704.02892v1].

"We now use Eq. (36) to translate the distribution in E-L space into a radial distribution. The results for elastic scattering are shown in Fig. 5 for the times $t = 10^{−10} t\odot$ (left), $t = 10^{−8} t\odot$ (middle) and $t = 10^{-6} t\odot$ (right). The distribution is compared to the isothermal one of Eq. (33), with the angular degrees of freedom integrated over. One can see that the distribution has essentially reached equilibrium already at $t = 10^{−8} t\odot$, changing only slightly at $t = 10^{-6} t\odot$. The Boltzmann distribution gives a fairly accurate description of the distribution, although the numerically computed one is slightly shifted towards larger radii, and its peak is not as pronounced.

 

Moving on to the case of inelastic DM, we will again focus our discussion on the illustrative case of m$_χ$ = 100 GeV and δ = 100 keV.".

Page 39: "While the large ice overburden above the detector provides a shield against downward going, cosmic ray induced muons with energies $\begin{smallmatrix}\lt\\\sim\end{smallmatrix}$ 500 GeV at the surface, most analyses focus on upward going neutrinos employing the entire Earth as a filter. Additionally, low energy analyses use DeepCore as the fiducial volume and the surrounding IceCube strings as an active veto to reduce penetrating muon backgrounds. The search for WIMP annihilation signatures at the center of the Earth takes advantage of these two background rejection techniques as the expected signal will be vertically up-going and of low energy."

 

Page 40: "4. Background

 

As signal neutrinos originate near the center of the Earth, they induce a vertically up-going signal in the detector. This is however a special direction in the geometry of IceCube, as the strings are also vertical. While in other point source searches, a signal-free control region of the same detector acceptance can be defined by changing the azimuth, this is not possible for an Earth WIMP analysis. Consequently, a reliable background estimate can only be derived from simulation.

 

Two types of background have to be taken into account: the first type consists of atmospheric muons produced by cosmic rays in the atmosphere above the detector. Although these particles enter the detector from above, a small fraction will be reconstructed incorrectly as up-going.

 

The second type of background consists of atmospheric neutrinos. This irreducible background is coming from all directions.".

 

Page 43: "8. Conclusion

 

Using one year of data taken by the fully completed detector, we performed the first IceCube search for neutrinos produced by WIMP dark matter annihilations in the center of the Earth. No evidence for a signal was found and 90% C.L. upper limits were set on the annihilation rate and the resulting muon flux as function of the WIMP mass. Assuming the natural scale for the velocity averaged annihilation cross section, upper limits on the spin-independent WIMP-nucleon scattering cross section could be derived. The limits on the annihilation rate are up to a factor 10 more restrictive than previous limits. For indirect WIMP searches through neutrinos, this analysis is highly complementary to Solar searches. In particular, at WIMP masses around 50 GeV, due to resonant capture by iron nuclei in the Earth the sensitivity of this analysis exceeds that of searches for WIMP annihilations in the Sun. The corresponding limit on the spin independent cross section presented here is the best set presently by IceCube. The next analysis combining several years of data will further improve the sensitivity.".

"1.4 Indirect solar WIMP search with neutrinos

Large celestial bodies like the Sun have the potential to be natural attractors for (Weakly-interacting massive particles) WIMPs $^{48}$, hypothetical particles that are thought to constitute dark matter. The Sun, as part of the galactic disc, revolves around the galactic center and thereby plows through the WIMP halo, which is thought to be at rest. This leads to scattering of WIMPs on the nuclei of the Sun. If the scatter is connected to a substantial loss of kinetic energy by the WIMP so that it falls below the escape velocity, it will get gravitationally bound to the Sun. With time and further scatters the WIMPs eventually sink to the core of the Sun, where they accumulate and thermalize. The resulting over density of WIMPs leads to self-annihilation processes yielding SM particles in great abundances. Of these only neutrinos can possibly leave the Sun. This process is schematically illustrated in figure 1.4.

Indirect searches for solar WIMP dark matter are sensitive to the WIMP-nucleon scattering cross-section which initiates the capture process. Here the mass of $\simeq 2 · 10^{30}$ kg for the Sun is forming a huge target driving the capture of WIMPs and their accumulation. The neutrinos yielded in the annihilation processes should then be observable at Earth in neutrino telescopes like IceCube. Even if the detection of neutrinos has challenges of its own, a neutrino signal detection from the direction of the Sun would be very significant in its interpretation for WIMP dark matter.".

"1. Introduction

The IceCube neutrino observatory $^{1, 2}$ is a cubic kilometer photomultiplier (PMT) array embedded in glacial ice at the geographic South Pole. The complete array is made of 5160 downward-facing Hamamatsu R7081 photomultipliers deployed on 86 vertical strings at depths between 1450 and 2450 meters in the icecap. IceCube detects neutrinos by observing Cherenkov light induced by charged particles created in neutrino interactions as they transit the ice sheet within the detector; the energy and momentum of these charged particles reflect the energy and momentum of the original neutrino.

At the TeV energies typical of such neutrino telescopes, the primary neutrino interaction channel is deep-inelastic scattering with nuclei in the detector material. In both neutral and charged-current interactions, a shower of hadrons is created at the neutrino interaction vertex. In charged-current interactions, this shower is accompanied by an out-going charged lepton. This lepton, in particular for electrons, may also lose energy rapidly and itself trigger another overlaid shower. Cherenkov light is radiated by this primary lepton and any accompanying showers with a total amplitude proportional to the integrated path length of charged particles above the Cherenkov threshold. This, in turn, is proportional to the total energy of these particles $^3$.

The light production from electromagnetic (EM) showers is both maximal and has low variance with respect to deposited energy $^3$. As such, it forms a natural unit of re- constructed shower energy.".

"Current status

High-energy neutrinos from the Sun provide one of the cleanest potential discovery channels for weakly-interacting dark matter (DM). Weakly-interacting DM particles passing through the Sun are expected to scatter on solar nuclei. Some of these collisions reduce the kinetic energy of the DM particle enough for it to become gravitationally bound to the Sun, causing it to return on a bound orbit and undergo subsequent scattering, eventually thermalising and settling down to the solar core. If DM is able to annihilate, either with itself of with anti-DM captured in a similar manner, high-energy SM particles will be produced in the solar core. Even if neutrinos are not amongst those particles produced in the annihilation hard process, they will still be generated with quite high energies in the decay and subsequent interaction of other SM particles with nuclei in the Sun. Unlike the other SM particles, these GeV-scale neutrinos are then able to travel unhindered from the centre of the Sun to the surface, and across space to Earth, where they may be detected with terrestrial experiments.

The directionality of the signal is the primary means by which it can be distinguished from the atmospheric neutrino background, caused by cosmic ray interactions with the Earth’s atmosphere. The only known background to the signal is therefore the analogous production of high-energy neutrinos in the atmosphere of the Sun, due to interactions of cosmic rays with solar nuclei.

The capture of dark matter by the Sun typically becomes the rate-limiting step in the production of any signal, rather than the annihilation. Searches for high energy neutrinos from the Sun are therefore most useful for constraining the interaction cross section of dark matter with nuclei. Spin-dependent interactions are particularly relevant, as the Sun consists mostly of hydrogen, which possesses nuclear spin.".

...

Page 3:

"Improved background calculations

Previous predictions of the background rate of high-energy neutrinos from the Sun, due to interactions of cosmic rays with nuclei in the solar atmosphere, were computed more than a decade ago.$^{6,7,8}$ However, two more recent recalculations have appeared.$^{9,10}$ Compared to the older predictions, the new calculations make use of modern knowledge on neutrino oscillations, production and interaction cross-sections. One of these$^{10}$ also makes use of up-to-date models of the solar composition and structure, and carries out extensive Monte Carlo simulations of neutrino production, interaction and oscillation. Both studies (and another at the same time, based on the old flux estimates$^{11}$) show that the solar atmospheric background lies barely an order of magnitude below current sensitivity limits for some models (Fig. 2). This suggests that future neutrino telescopes might be able to directly measure this irreducible ‘neutrino floor’, and that the improved calculations of the background rates should be included in future phenomenological studies of DM scattering and annihilation in the Sun.".

9. C. A. Argüelles, G. de Wasseige, A. Fedynitch, and B. J. P. Jones, Solar atmospheric neutrinos and the sensitivity floor for solar dark matter annihilation searches, JCAP 7 (2017) 024, [arXiv:1703.07798].

10. J. Edsjö, J. Elevant, R. Enberg, and C. Niblaeus, Neutrinos from cosmic ray interactions in the Sun, JCAP 6 (2017) 033, [arXiv:1704.02892].

"If we compare the he neutrino fluxes at production (solid lines) to the ones after passage through the Sun (dashed lines), we see that we get a dip at low impact parameters. This is the effect of the attenuation that happens due to interactions when the neutrinos pass through the Sun, as we saw already in figure 4. As the density of the Sun is significantly higher in the centre, the effect is very strongly pronounced for low impact parameters. We can also see that the effect of attenuation is higher for higher energies as expected.

We can also see how the production fluxes depend on the impact parameter. We can see that for higher energies these are quite peaked at large impact parameters, which is expected as the density where the cascade happens is lower for these Sun grazing CRs, and hence the fluxes are higher. We also get a small contribution from muons decaying outside of the Sun at high impact parameters and high energies.3 The total flux from the Sun is obtained by integrating over the impact parameters including the fact that the solid angle is larger for large impact parameters. Hence, the high impact parameter part of these figures will be most important for the total flux from the Sun.".

"Solar atmospheric neutrinos provide a natural background to solar dark matter searches and limit their sensitivity as recently pointed out $^{[5, 6, 7]}$.".

7. J.Edsjö, J.Elevant, R.Enberg and C.Niblaeus, [astro-ph/1704.02892v1].

"We now use Eq. (36) to translate the distribution in E-L space into a radial distribution. The results for elastic scattering are shown in Fig. 5 for the times $t = 10^{−10} t\odot$ (left), $t = 10^{−8} t\odot$ (middle) and $t = 10^{-6} t\odot$ (right). The distribution is compared to the isothermal one of Eq. (33), with the angular degrees of freedom integrated over. One can see that the distribution has essentially reached equilibrium already at $t = 10^{−8} t\odot$, changing only slightly at $t = 10^{-6} t\odot$. The Boltzmann distribution gives a fairly accurate description of the distribution, although the numerically computed one is slightly shifted towards larger radii, and its peak is not as pronounced.

Moving on to the case of inelastic DM, we will again focus our discussion on the illustrative case of m$_χ$ = 100 GeV and δ = 100 keV.".

Page 39: "While the large ice overburden above the detector provides a shield against downward going, cosmic ray induced muons with energies $\begin{smallmatrix}\lt\\\sim\end{smallmatrix}$ 500 GeV at the surface, most analyses focus on upward going neutrinos employing the entire Earth as a filter. Additionally, low energy analyses use DeepCore as the fiducial volume and the surrounding IceCube strings as an active veto to reduce penetrating muon backgrounds. The search for WIMP annihilation signatures at the center of the Earth takes advantage of these two background rejection techniques as the expected signal will be vertically up-going and of low energy."

Page 40: "4. Background

As signal neutrinos originate near the center of the Earth, they induce a vertically up-going signal in the detector. This is however a special direction in the geometry of IceCube, as the strings are also vertical. While in other point source searches, a signal-free control region of the same detector acceptance can be defined by changing the azimuth, this is not possible for an Earth WIMP analysis. Consequently, a reliable background estimate can only be derived from simulation.

Two types of background have to be taken into account: the first type consists of atmospheric muons produced by cosmic rays in the atmosphere above the detector. Although these particles enter the detector from above, a small fraction will be reconstructed incorrectly as up-going.

The second type of background consists of atmospheric neutrinos. This irreducible background is coming from all directions.".

Page 43: "8. Conclusion

Using one year of data taken by the fully completed detector, we performed the first IceCube search for neutrinos produced by WIMP dark matter annihilations in the center of the Earth. No evidence for a signal was found and 90% C.L. upper limits were set on the annihilation rate and the resulting muon flux as function of the WIMP mass. Assuming the natural scale for the velocity averaged annihilation cross section, upper limits on the spin-independent WIMP-nucleon scattering cross section could be derived. The limits on the annihilation rate are up to a factor 10 more restrictive than previous limits. For indirect WIMP searches through neutrinos, this analysis is highly complementary to Solar searches. In particular, at WIMP masses around 50 GeV, due to resonant capture by iron nuclei in the Earth the sensitivity of this analysis exceeds that of searches for WIMP annihilations in the Sun. The corresponding limit on the spin independent cross section presented here is the best set presently by IceCube. The next analysis combining several years of data will further improve the sensitivity.".

Draft: Proofread, (hopefully) mostly accurate; more edits coming.

Allure: Can the Sun / Earth have a dark matter core?

Perhaps a more interesting question is: What is the approximate distribution of dark matter within the Sun (I haven't researched the Earth portion of your question yet, or finished this edit.).

Allure: If dark matter interacts with ordinary matter at all, it should most likely occur where ordinary matter is densest.

That does not appear to be a certainty in the case of the Sun, the center is so dense that cosmic rays are restricted by the core; altering or obscuring the measurement of dark matter.

The thesis "A search for solar dark matter with the IceCube neutrino detector", by Dr. Marcel Zoll, explains it this way on page 15 (page 32 of the .PDF):

Allure: ... Sun, or even the Earth can have dark matter cores too - they're just less likely to have such cores. If the Sun / Earth does have such a core dark matter would be much easier to study since they're so nearby.

The light production from electromagnetic (EM) showers is both maximal and has low variance with respect to deposited energy $^3$. As such, it forms a natural unit of re- constructed shower energy.".

It's possible that studying the Sun would be easier than studying the Earth (with it's weaker gravity) - but I'm not far enough into researching your answer to say for certain.

Allure: Is there any observational evidence that the Sun / Earth is 100% ordinary matter? If no, what is the observational limit of the Sun / Earth's dark matter fraction?

No, see below.

Allure: I've seen popular-level articles (example) about such theories, but they're all rather speculative.

Allure: If dark matter interacts with ordinary matter at all, it should most likely occur where ordinary matter is densest. Hence we have papers about neutron stars possibly containing dark matter cores (example).

In "Neutrino telescope searches for dark matter in the Sun" (14 Oct 2017), by Dr. Pat Scott, he writes on page 1:

In "Neutrinos from cosmic ray interactions in the Sun" (10 Jul 2017), by Edsjö, Elevant, Enberg, and Niblaeus, on page 23, they write and include this image:

While that paper also discusses the Earth I have not prepared that portion of the answer to your question. As usual more information is available in the quoted papers.

In "The distribution of inelastic dark matter in the Sun" (19 Feb 2018), by Blennow, Clementz, and Herrero-Garcia, on page 17 they write:

On page 20 they write:

Allure: "Can the Sun / Earth have a dark matter core?"

Perhaps a more interesting question is: What is the approximate distribution of dark matter within the Sun. The exact center of the Sun has none, for the Earth the results are inconclusive.

Allure: "If dark matter interacts with ordinary matter at all, it should most likely occur where ordinary matter is densest."

In the case of the Sun, the center is so dense that dark matter is subjected to self-annihalation. The thesis "A search for solar dark matter with the IceCube neutrino detector", by Dr. Marcel Zoll, explains it this way on page 15 (page 32 of the .PDF):

Allure: "... Sun, or even the Earth can have dark matter cores too - they're just less likely to have such cores. If the Sun / Earth does have such a core dark matter would be much easier to study since they're so nearby."

The light production from electromagnetic (EM) showers is both maximal and has low variance with respect to deposited energy $^3$. As such, it forms a natural unit of re- constructed shower energy.".

Studying the Sun has proven to be easier than studying the Earth (with it's weaker gravity, and due to detector alignment with the center of the Earth you can't do multiple comparisons that entirely eliminate the background).

Allure: "I've seen popular-level articles (example) about such theories, but they're all rather speculative."

Allure: "If dark matter interacts with ordinary matter at all, it should most likely occur where ordinary matter is densest. Hence we have papers about neutron stars possibly containing dark matter cores (example)."

In "Neutrino telescope searches for dark matter in the Sun" (14 Oct 2017), by Dr. Pat Scott, he wrote on page 1:

In "Neutrinos from cosmic ray interactions in the Sun" (10 Jul 2017), by Edsjö, Elevant, Enberg, and Niblaeus, on page 23, they wrote and include this image:

In "The distribution of inelastic dark matter in the Sun" (19 Feb 2018), by Blennow, Clementz, and Herrero-Garcia, on page 17 they wrote:

On page 20 they wrote:

Those two images are in agreement with the prior one included from "Neutrinos from cosmic ray interactions in the Sun".

Allure: "Is there any observational evidence that the Sun / Earth is 100% ordinary matter? If no, what is the observational limit of the Sun / Earth's dark matter fraction?"

In the article "Searches for Dark Matter in the center of the Earth with the IceCube detector", an included paper in: "IceCube Neutrino Observatory - Contributions to ICRC 2017 Part IV: Searches for Beyond the Standard Model Physics", by the IceCube Collaboration, the authors wrote:

Page 39: "While the large ice overburden above the detector provides a shield against downward going, cosmic ray induced muons with energies $\begin{smallmatrix}\lt\\\sim\end{smallmatrix}$ 500 GeV at the surface, most analyses focus on upward going neutrinos employing the entire Earth as a filter. Additionally, low energy analyses use DeepCore as the fiducial volume and the surrounding IceCube strings as an active veto to reduce penetrating muon backgrounds. The search for WIMP annihilation signatures at the center of the Earth takes advantage of these two background rejection techniques as the expected signal will be vertically up-going and of low energy."

Page 40: "4. Background

As signal neutrinos originate near the center of the Earth, they induce a vertically up-going signal in the detector. This is however a special direction in the geometry of IceCube, as the strings are also vertical. While in other point source searches, a signal-free control region of the same detector acceptance can be defined by changing the azimuth, this is not possible for an Earth WIMP analysis. Consequently, a reliable background estimate can only be derived from simulation.

Two types of background have to be taken into account: the first type consists of atmospheric muons produced by cosmic rays in the atmosphere above the detector. Although these particles enter the detector from above, a small fraction will be reconstructed incorrectly as up-going.

The second type of background consists of atmospheric neutrinos. This irreducible background is coming from all directions.".

Page 43: "8. Conclusion

Using one year of data taken by the fully completed detector, we performed the first IceCube search for neutrinos produced by WIMP dark matter annihilations in the center of the Earth. No evidence for a signal was found and 90% C.L. upper limits were set on the annihilation rate and the resulting muon flux as function of the WIMP mass. Assuming the natural scale for the velocity averaged annihilation cross section, upper limits on the spin-independent WIMP-nucleon scattering cross section could be derived. The limits on the annihilation rate are up to a factor 10 more restrictive than previous limits. For indirect WIMP searches through neutrinos, this analysis is highly complementary to Solar searches. In particular, at WIMP masses around 50 GeV, due to resonant capture by iron nuclei in the Earth the sensitivity of this analysis exceeds that of searches for WIMP annihilations in the Sun. The corresponding limit on the spin independent cross section presented here is the best set presently by IceCube. The next analysis combining several years of data will further improve the sensitivity.".

The results did not exceed statistical error, leaving them inconclusive.

The paper "Neutrinos from cosmic ray interactions in the Sun" is also recommended on page 70 of "The IceCube Neutrino Observatory Contributions to ICRC 2017 Part III: Cosmic Rays" (over 300 authors), in the article "Solar atmospheric neutrino search with IceCube", by Seongjin In and Carsten Rott:

"Solar atmospheric neutrinos provide a natural back- ground to solar dark matter searches and limit their sensitivity as recently pointed out $^{[5, 6, 7]}$.".

The paper above, "Neutrinos from cosmic ray interactions in the Sun" is also recommended on page 70 of "The IceCube Neutrino Observatory Contributions to ICRC 2017 Part III: Cosmic Rays" (over 300 authors), in the article: "Solar atmospheric neutrino search with IceCube", by Seongjin In and Carsten Rott, they wrote:

"Solar atmospheric neutrinos provide a natural background to solar dark matter searches and limit their sensitivity as recently pointed out $^{[5, 6, 7]}$.".