Can we determine the particle/antiparticle nature of Dark Matter? Bradley J. Kavanagh GRAPPA, University of Amsterdam LAW Physics - 17th January 2018 b.j.kavanagh@uva.nl @BradleyKavanagh 1
Dark Matter on all scales Hradecky et al. [astro-ph/0006397] Planck [1502.01589] Rubin, Ford & Thonnard (1980) 2 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Dark Matter near the Earth Global and local estimates of DM at Solar radius give: ρ χ ∼ 0 . 2 − 0 . 8 GeV cm − 3 E.g. Iocco et al. [1502.03821], Garbari et al. [1206.0015], Read [1404.1938] 8 . 5 kpc NOT TO SCALE 3 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Direct detection of Dark Matter m χ � 1 GeV v ∼ 10 − 3 c Detector Target nucleus χ 4 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Direct detection of Dark Matter m χ � 1 GeV v ∼ 10 − 3 c Detector 5 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Direct detection of Dark Matter m χ � 1 GeV v ∼ 10 − 3 c Detector Light (scintillation) Heat (phonons) Charge (ionisation) Measure rate of recoils and energy of recoiling nuclei Reconstruct the properties of DM (mass, cross section, etc.) 6 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Direct detection of Dark Matter m χ � 1 GeV v ∼ 10 − 3 c In practise, need to worry about backgrounds, Detector Light (scintillation) background rejection, detection efficiencies, energy resolutions, validation across multiple detectors, … Heat (phonons) Charge (ionisation) Measure rate of recoils and energy of recoiling nuclei Reconstruct the properties of DM (mass, cross section, etc.) 7 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Measuring the DM mass DM mass can be extracted from the slope of the recoil spectrum Characteristic recoil energy in keV Xe Ge Green [0805.1704] Peter, Gluscevic, Green, BJK , Lee [1310.7039] 8 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Measuring the local DM speed distribution With multiple experiments and more precise data, you could extract the DM mass and DM speed distribution simultaneously Using Xe, Ar and Ge targets: BJK, Green [1303.6868], but see also BJK, Fornasa,Green [1410.8051] and others 9 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Distinguishing Dirac from Majorana Dark Matter Cross sections for Dirac and Majorana DM should scale differently with number of protons and neutrons Queiroz, Rodejohann & Yaguna [arXiv:1610.06581] What are the prospects for distinguishing Dirac vs. Majorana DM in upcoming experiments BJK, Queiroz, Rodejohann & Yaguna [arXiv:1706.07819] Which experiments should we build to get the most out of a DM discovery? 10 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
3 highlights of this work 1) It may be possible to determine whether DM is its own antiparticle: using multiple ton-scale direct detection experiments! 2) To maximise our chances, we have to use particular combinations of detectors: should pursue Silicon detectors! 3) This work is 100% reproducible: check it, make fun of it, reuse it, whatever! 11 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Dirac vs. Majorana DM 12 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
DM-nucleon contact interactions Start thinking about how DM can interact with nucleons : N = ( p, n ) χ L ⊃ λ N, 1 χχ NN + λ N, 2 χγ µ χ N γ µ N + λ N, 3 χγ µ γ 5 χ N γ µ γ 5 N + λ N, 4 χγ 5 χ NN + λ N, 5 χγ µ χ N γ µ γ 5 N + ... 13 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
DM-nucleon contact interactions Start thinking about how DM can interact with nucleons : N = ( p, n ) χ L ⊃ λ N, 1 χχ NN + λ N, 2 χγ µ χ N γ µ N + λ N, 3 χγ µ γ 5 χ N γ µ γ 5 N Spin-dependent interaction + λ N, 4 χγ 5 χ NN + λ N, 5 χγ µ χ N γ µ γ 5 N + ... 14 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
DM-nucleon contact interactions Start thinking about how DM can interact with nucleons : N = ( p, n ) χ L ⊃ λ N, 1 χχ NN + λ N, 2 χγ µ χ N γ µ N + λ N, 3 χγ µ γ 5 χ N γ µ γ 5 N Spin-dependent interaction + λ N, 4 χγ 5 χ NN Velocity suppressed + λ N, 5 χγ µ χ N γ µ γ 5 N + ... 15 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
DM-nucleon contact interactions Start thinking about how DM can interact with nucleons : N = ( p, n ) χ L ⊃ λ N,e χχ NN + λ N,o χγ µ χ N γ µ N Standard spin-independent DM-nucleon couplings typically dominate. These operators couple to the number of nucleons in the target - expect a coherent enhancement of the cross section: σ ∼ [ λ p N p + λ n N n ] 2 But note that the scalar current operator is even under the exchange of particle and antiparticle , while the vector current operator is χ ↔ χ odd under the particle-antiparticle exchange. 16 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Majorana DM Start thinking about how DM can interact with nucleons : N = ( p, n ) χ L ⊃ λ N,e χχ NN + λ N,o χγ µ χ N γ µ N Vanishes for Majorana DM ≡ λ M N χχ NN Cross section for scattering with a nucleus A (in the zero-momentum transfer limit) is then: 4 µ 2 � 2 σ M = χ A λ M p N p + λ M � n N n π 17 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Dirac DM Start thinking about how DM can interact with nucleons : N = ( p, n ) χ L ⊃ λ N,e χχ NN + λ N,o χγ µ χ N γ µ N Both interactions are allowed λ N,e → λ N,e ± λ N,o Same as Majorana case, with . Cross section for scattering with a nucleus A (in the zero-momentum transfer limit) is then: 4 µ 2 �� � 2 � 1 � 2 + � σ D = χ A λ D p N p + λ D λ D p N p + λ D n N n n N n π 2 λ D N = ( λ N,e + λ N,o ) / 2 Cross section Cross section Half of DM is particles, for DM particles for DM antiparticles λ D N = ( λ N,e − λ N,o ) / 2 half is antiparticles 18 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Dirac DM (continued) We can try to manipulate the Dirac cross section, to get it into the same form as � 2 σ M ∼ λ M p N p + λ M � the Majorana cross section, . n N n 4 µ 2 �� � 2 � 1 � 2 + σ D = � χ N λ D p N p + λ D λ D p N p + λ D n N n n N n 2 π 2 µ 2 � � χ N ( λ D 2 + λ D 2 ) N 2 p + ( λ D 2 + λ D 2 n ) N 2 n + 2( λ D p λ D n + λ D p λ D = n ) N p N n p p n π 4 µ 2 [ λ p N p + λ n N n ] 2 + 2 λ p λ n ( f − 1) N p N n σ D = � � χ A π � 1 f = ( λ D p λ D n + λ D p λ D f ∈ [ − 1 , 1] n ) / (2 λ p λ n ) 2( λ D 2 + λ D 2 where and λ N = N ) N The DM-nucleus cross section scales differently with number of protons and neutrons for Dirac and Majorana DM! 19 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
Generalising to other spins We have discussed only spin-1/2 DM particles. However, similar logic applies for DM candidates of other spins. φ For example, in the case of scalar DM , the couplings leading to spin- independent scattering are: L ⊃ 2 λ N,e m φ φ † φ NN + i λ N,o φ † ( ∂ µ φ ) − ( ∂ µ φ † ) φ N γ µ N � � The second interaction is absent in the case of real scalar DM, so real and complex DM lead to different DM-nucleus cross sections! For vector DM, see e.g. [arXiv:0803.2360]. 20 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
A visual example ∆ = 20% � Calculate DM-nucleus cross section for Dirac DM. Here, assume the following couplings: Xe n ) = (6 . 7 , 2 . 0 , − 5 . 6 , − 1 . 0) × 10 − 9 GeV − 2 ( λ D p , λ D p , λ D n , λ D � λ �� [ �� - � ��� - � ] Assume DM-nucleus cross section is measured � to 20% precision. Attempt to fit assuming Majorana DM: - � 4 µ 2 �� � 2 � σ M = χ A λ M p N p + λ M n N n π - � - � - � � � � λ �� [ �� - � ��� - � ] 21 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
A visual example ∆ = 20% � Calculate DM-nucleus cross section for Dirac DM. Here, assume the following couplings: Xe Ar n ) = (6 . 7 , 2 . 0 , − 5 . 6 , − 1 . 0) × 10 − 9 GeV − 2 ( λ D p , λ D p , λ D n , λ D � λ �� [ �� - � ��� - � ] Assume DM-nucleus cross section is measured � to 20% precision. Attempt to fit assuming Majorana DM: - � 4 µ 2 �� � 2 � σ M = χ A λ M p N p + λ M n N n π - � - � - � � � � λ �� [ �� - � ��� - � ] 22 Bradley J Kavanagh (GRAPPA) DM Particle/Antiparticle LAW Physics - 17th Jan. 2018
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