DIRECT DETECTION OF NUCLEAR DARK MATTER USING TONNE-SCALE - - PowerPoint PPT Presentation
DIRECT DETECTION OF NUCLEAR DARK MATTER USING TONNE-SCALE EXPERIMENTS What is Nuclear Dark Matter? Signal and sensitivity in DEAP-3600 and XENON1T Can it be distinguished from a vanilla WIMP signal? arXiv:1610.01840 ALISTAIR
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arXiv:1610.01840
Many dark matter models which mirror the SM sector, e.g., asymmetric models (difference between DM and anti-DM), composite particles (WIMPonium, dark atoms etc.) Nuclear Dark Matter (NDM) - dark matter which consists of bound states of strongly-interacting dark nucleon constituents with short-range interactions In this model: heavy scalar mediator with SM assumed (SI), no analogue of long range EM interactions between protons - this means dark nucleon number, k, can be large > 108. arXiv:1411.3739
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The composite nature of these particles effects how they scatter off SM nuclei in direct detection experiments Composite DM particles made up of k nucleons will have an elastic cross-section which is coherently enhanced by
Due to its spatially extended nature a form factor for the NDM particle appears. If the radii of the NDM states are larger than the SM nuclei, direct detection experiments will probe the dark form factor at lower values of the momentum transfer compared to the SM form factor.
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Mass of single dark nucleon With NDM being a composite rather than point particle the differential rate is modified. Dark nucleon number NDM form factor The second form factor allows the characteristic zeros to appear inside a detector’s energy window. Coherent enhancement
v>vmin
knkm1
v>vmin
χnmA2σ0FN(q)2
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(keV)
R
E
20 40 60 80 100 120 140
)
R
(E
2
F
5 −
10
4 −
10
3 −
10
2 −
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1 −
10 1
Ar-40
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k = 10
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k = 10
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k = 10
Spherical top hat function assumed for the density, leading to a spherical Bessel function form factor:
Fk(q) = 3j1(qRk) qRk
Rk = k1/3R1
Approximate radius of a single DN, taken to be 1 fm Form factors for various k-DN states plotted with the Helm parameterisation for Argon-40
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WIMP = 103 = 104 DEAP-3600 20 40 60 80 100 120 140 10-12 10-11 10-10 10-9 10-8 10-7 10-6
The finite resolution of the detectors smooth the shape into peaks and troughs. Values of k with m1 = 1 GeV are plotted with a WIMP spectrum of 100 GeV.
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WIMP = 103 = 104 XENON1T 10 20 30 40 50 60 10-10 10-9 10-8 10-7 10-6 10-5
XENON1T efficiency and resolution taken from: E. Aprile et al., Physics reach of the XENON1T dark matter experiment, JCAP 1604 (2016) 027
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DEAP-3600 XENON1T LUX WIMPs NDM 1 10 100 1000 104 105 106 10-52 10-50 10-48 10-46 10-44 10-42 10-40 10-38 mDM/GeV σ0/cm2
90% CL sensitivity to NDM with m1 = 1 GeV and mDM=k*m1. The k2 enhancement of the cross section results in a sensitivity orders of magnitude below the equivalent WIMP. LUX (old) limit (1.4E4 kg.day): D. S. Akerib et al. Phys. Rev. Lett. 116 (2016) 161301, DEAP limit (3000 kg.year): P. A. Amaudruz et al. ICHEP 2014, XENON limit (2000 kg.year): E. Aprile et al. JCAP 1604 (2016) 027
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λ = −2 ln " Poisson{Nobs, N NDM
exp
(σNDM , k, m1)}QNobs
i=1 fNDM(Ei|k, m1)
Poisson{Nobs, N WIMP
exp
(σWIMP , m)}QNobs
i=1 fWIMP(Ei|m)
# λ = −2 ln "QNobs
i=1 fNDM(Ei|k, m1)
QNobs
i=1 fWIMP(Ei|m)
#
p = Z ∞ g(λ|Nobs)dλ
To determine whether a NDM signal can be distinguished from a WIMP signal we look at the most indistinguishable case. For each value of k to be tested we find the WIMP signal which takes the greatest number of events to be ruled out. Define a likelihood ratio test statistic: The most indistinguishable case occurs when the expected number of events for both hypotheses is the same. Since each cross section can be varied independently the problem becomes simple shape analysis: Probability of mis-identifying NDM as WIMPs: Probability of correctly identifying NDM under the NDM hypothesis:
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20 40 60 80 100 120 10-12 10-11 10-10 10-9 10-8 10-7 k = 1412 mWIMP = 29.9 GeV 1234 Events Required 20 40 60 80 100 120 10-12 10-11 10-10 10-9 10-8 10-7 k = 5012 mWIMP = 23.4 GeV 23 Events Required
Tables of NDM and WIMP spectra were built and a grid search was performed to find the most indistinguishable WIMP for each NDM. In each case p was determined via Monte-Carlo and the WIMP which required the maximum number of events to be distinguished at a given confidence level was found.
WIMP tracks the majority of the NDM signal. First trough appears close to the beginning of the window. As the WIMP spectrum is exponentially falling the position of the first trough (and consequently rising edge) is the most important feature.
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20 40 60 80 100 120 10-11 10-10 10-9 10-8 10-7 k = 17785 mWIMP = 34.1 GeV 71 Events Required 20 40 60 80 100 120 10-11 10-10 10-9 10-8 10-7 k = 28187 mWIMP = 25.4 GeV 43 Events Required 20 40 60 80 100 120 10-11 10-10 10-9 10-8 10-7 k = 501245 mWIMP = 42.3 GeV 134 Events Required 20 40 60 80 100 120 10-11 10-10 10-9 10-8 10-7 k = 107 mWIMP = 44.1 GeV 384 Events Required
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Number of events required to identify NDM against the most indistinguishable case. Peaks and troughs correspond to where the first NDM trough appears in the energy window for each experiment. Flat region appears when the NDM shape is no longer resolvable. This
it has a lower energy resolution than DEAP-3600.
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WIMPs NDM 3σ CL 2σ CL 1σ CL DEAP-3600 10 100 1000 104 105 106 107 50 100 150 200 mDM/GeV
WIMPs NDM 3σ CL 2σ CL 1σ CL XENON1T 10 100 1000 104 105 106 107 50 100 150 200 mDM/GeV
The maximum number of events it’s possible to see for each detector assuming the cross-section is at the value of the old LUX limit (Phys. Rev. Lett. 116 (2016) 161301). In either detector it only possible to distinguish NDM at the 2 sigma level for limited regions of the parameter space.
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Probability of positively identifying a WIMP in at least one detector: Regions of the k parameter space become available at the 3 sigma confidence level. Probability of misidentifying NDM in DEAP XENON1T
We have set a constraint on NDM using the 1.4E4 kg.day LUX limit, and calculated the sensitivity of the current running experiments DEAP-3600 and XENON1T The sensitivity on the zero momentum transfer cross-section of NDM is orders of magnitude lower than the equivalent WIMP sensitivity - this is due to the k
2 enhancement of the scattering cross-section.
The ability to distinguish between WIMPs and NDM depends on both the energy threshold (position of first trough) and energy resolution (shape of oscillations). It is possible to see “hints” of NDM at 2 and 3 sigma in DEAP-3600 and XENON1T. Future experiments should be able to distinguish NDM from WIMPs at 3 sigma over the entire k range.
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