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Searches for BSM Physics with the KATRIN Experiment

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Searches for BSM Physics with the KATRIN Experiment Searches for BSM Physics with the KATRIN Experiment Snowmass 2021 | NF03 Workshop | September 17, 2020 K. Valerius for the KATRIN collaboration • Active and sterile neutrinos (sub-eV … eV … keV scale) • Right-handed currents and exotic weak interactions • Cosmic relic neutrinos • Lorentz invariance violation KIT – The Research University in the Helmholtz Association www.kit.edu KATRIN in a nutshell Primary science mission: measurement of effective electron neutrino mass through direct, kinematic method (precision β-decay spectroscopy of molecular tritium) Requirements: strong tritium source (~1011 β-decays/sec) at high purity & stability, high energy resolution (ΔE ~ 1 eV at E0 ~ 18.6 keV), low background rate (~100 mcps or lower) katrin.kit.edu target m(�) sensitivity: 200 meV Deliverable: precision β-decay spectrum measurement close to endpoint (typically E0 - 40…100 eV; extendable to ~1600 eV at reduced source strength during commissioning or to full phase space with detector upgrade) 2 Snowmass NF03, Sept. 17, 2020 First neutrino-mass result Initial neutrino-mass data set (~ 4 weeks at reduced source strength) demonstrates excellent quality of measured spectra and model description Improved upper limit: m(�) < 1.1 eV (90% CL) [PRL 123 (2019) 221802] ➜ Precision β-decay spectroscopy opens up sensitivity to look for a range of BSM phenomena through distortions of the spectral shape 3 Snowmass NF03, Sept. 17, 2020 SearcheV-scale sterile neutrino search for light sterile neutrinos Mainz 95% C.L. RAA + GA 95% CL Troitsk 95% C.L. Neutrino-4 2 Prospect 95% C.L. KATRIN KSN1 95% C.L. (stat. and syst.) Initial 4-week data set: Demonstrate potential of KATRIN to DANSS 95% C.L. Projected KATRIN final sensitivity Stéréo 95% C.L. 95% C.L. (stat. and syst.) probe sterile neutrino hypothesis; complementarity with 3 High ∆= region: 10 short-baseline`L oscillation experiments üImprove exclusion with respect to DANSS, PROSPECT, Regionand SofTEREO high Δm2: 2 10 - üImproveExclude parameter space of exclusion with respectReactor Anomaly (RAA) to DANSS, PROSPECT, STÉRÉO ) 2 - Exclude large Δm2 solution preferred by reactor & gallium anomalies (eV 1 2 41 10 m 2 RegionLow ∆ =of`L lowregion: Δm : 100 - üImproveImprove limitsMAINZ byand MainzTROITSK andlimit Troitsk Preliminary - üNeutrino-4The NEUTRINO hint-4 regionhint at isthe edge of at the edgeexclusion limit of our 95% exclusion to be published soonPreliminary 10-1 -2 -1 0 10 10 10 Outlook: Large fraction of reactor/gallium anomalies and sin2(2 ) 26 Susanne Mertens ee Neutrino-4 hint will be probed with full KATRIN data set publication in preparation 4 see also Giunti++ 2020 Snowmass NF03, Sept. 17, 2020 keV-scale sterile neutrino search Search for more massive sterile neutrinos Proof of principle: Deep scan (1.6 keV below E0) with low-activity commissioning data üexcellent agreement of model and data (p-value = 0.6) 2 -3 Proof of principle: Deep scan (1.6 keV) üsensitivity to sin \ < 10 @ m4 = 0.4 keV ROI with low-activity commissioning data - publication in U preparation Future: Novel multi-pixel Silicon Drift Detector array (TRISTAN) ! Excellent agreement of model and data 2 -3 ühigh-statistics search sensitivity illustration Sensitivity to sin � = 10 at m4 = 0.4 keV ütarget sensitivity of sin2 \ < 10-6 Future perspectives: Novel multi-pixel Silicon Drift Detector array (TRISTAN) High-statistics search, coverage of entire spectrum 2 -6 Target sensitivity of sin � < 10 Mertens et al, JCAP 1502 (2015) T. Houdy et al 29 goal: operation in Susanne MertensMertens et al, J. Phys. G46 (2019) KATRIN by 2025 5 ➜ see separate LOI (Mertens et al.) in NF02 “Sterile Neutrinos” for details! Snowmass NF03, Sept. 17, 2020 3 Exotic weak interactions What if … … weak interactions were hiding a left-right symmetric sector? … additional, very light bosons might exist? FIG. 2. Parameters for the spectrum approximation of Eq. (A15) for various coupling structures. spectrum with vector or pseudoscalar boson X 5 Imprint of right-handed currents in tritium 10 E. Vector bosons emitted from neutrinos and electrons 102 2 β-spectrum difficult to observe unless E0 X /g ) ) e X 1 ¯ ⌫ 10− As mentioned above, a Z0 that is coupled to the classi- + fixed externally + e e ¯ ⌫ cally conserved electron-number current j has a quali- + Le + e ➜ e.g. Severijns++ 2006; Bonn++ 2011 + 4 + − He 10 tatively di↵erent behavior than a Z0 that only couples to + 3 He → electrons or neutrinos. With 3 H 3 7 A: ⌫¯γ ⌫X → Picture could change in presence of ( 10− 5 H Γ B: ¯eγ eX ↵ ↵ ↵ 3 5 ( = g j Z0 = g (¯⌫ γ P ⌫ +¯eγ e) Z0 (9) µ Le Le ↵ Le e L e ↵ Γ C: ⌫¯γµP ⌫X 10 L L sterile neutrinos and RH/LH interference 10− µ D: ¯eγµeX one finds that the amplitude for Z0 emission is approx- E: jµ X ➜ see Barry, Heek & Rodejohann 1404.5955; Le µ 13 imately constant in the limit of small mZ0 , contrary to 10− ↵ Ludl & Rodejohann 1603.08690; 3 2 1 0 1 2 3 4 the two cases discussed above, because j is a classically 10− 10− 10− 10 10 10 10 10 Le Steinbrink++ 1703.07667 boson mass mX (eV) conserved (non-anomalous) current. Fitting to the ap- proximate spectrum gives n 2.2 and K 5 10 24g2 − Le ➜ see Arcadi++3 1811.035303 + ' ' ⇥ FIG. 3. Ratio of the decay width Γ( H He + e− + for mZ0 eV, see Fig. 2. Similar to the scalar-neutrino ! 2 ⇠ ⌫¯e + X) (divided by the relevant coupling constant gX )with case there is still a logarithmic dependence on mZ0 that NB: Wider phase-space coverage of the β-spectrumrespect beyond to the SM m( width�) search as a function window of the new boson’swill is well known from Bremsstrahlung in QED. For larger mass mX .Thedi↵erent curves are for di↵erent underlying mZ0 & 10 keV, the behavior becomes identical to that of broaden the reach of BSM physics opportunities ➜ couplingextra structures,incentive see text for for details.detector upgradea Z0 coupled to neutrinos. D. Vector bosons emitted from electrons 6 Snowmass NF03, Sept. 17,III. 2020 eV-SCALE LIGHT BOSONS IN THE CURRENT KATRIN SETUP In a similar vein, we assume the following Lagrangian for the coupling of a Z0 with electrons: In order to compare the theoretical prediction for the µ light bosons to upcoming data taken by the Katrin ex- =¯eγ (g P + g P )eZ0 . (8) L eL L eR R µ periment in the current setting, we will apply several modifications to the analytical form given in Eq. (5) to In principle one can imagine di↵erent couplings for the account for experimental characteristics. We will refer chiralities, g = g , but we will take them to be equal eL eR to this as the experimental spectrum. In the following, for simplicity, 6 g = g g , corresponding to a eL eR eV we will introduce the modifications to the spectrum be- vector-like coupling. ⌘ fore stating the sensitivity of Katrin to constrain the For small m , the spectrum is identical to that of Z0 emission of a light boson in tritium b-decay. For better Eq. (7), i.e. with parameters n 4 and K 6.7 readability and overview, we summarize the possible pro- 10 22g2 (keV/m )2, see Fig. 2.' This is not' surpris-⇥ − eV Z0 duction mechanisms in Tab. I which we will later refer to ing upon noting that the electron-number current j↵ = Le ↵ ↵ when stating the results. ⌫¯eγ PL⌫e +¯eγ e is classically conserved, so a light Z0 coupled to it would not lead to a 1/m2 divergence (see Z0 Sec. IIE). This merely means that the 1/m2 divergence Z0 A. Experimental characteristics of thee ¯Z/ e coupling is exactly canceled by the 1/m2 0 Z0 divergence of the⌫ ¯eZ/0PL⌫e coupling. Since Katrin employs gaseous molecular tritium (T2), There are of course di↵erences between the Z0 coupling we have to use the molecular masses to calculate the end- to electrons and neutrinos, at least for larger Z0 masses 2 point: where the 1/mZ behavior is less dramatic. From Fig. 2 0 2 2 2 we can see that the two couplings become distinguishable m (mT 3He+ + m⌫ + mX ) + m Emax0 = T2 − e , (10) for boson masses above keV. e 2mT2 194 7. Physics beyond the neutrino mass as combinations of both, range from 1 to 106 [RW04, LVV08, F¨as+13]. In the scope of this thesis, also CnB-adopted MTDs are tested for their e↵ect on the sensitivity on ÷. However, the increase in sensitivity is found to be only minor. No order of magnitude increase can be achieved, even with a “CnB-focused” MTD. The reason is the dominant e↵ect of the background rate, which generally limits the Katrin sensitivity for the CnB(also see ref. [Hei15]). For larger neutrino masses, Search for capture of relic neutrinosthe statistical sensitivity is found to improve marginally by about a factor 1.4. While Katrin most likely will not be able to detect the CnB, it can rule out spe- culative models about the origin of the GZK cut-o↵ [HM05] and improve existing b-decay limits on ÷ by at least one order of magnitude. 7.3.Possibility Relic neutrinos of relic neutrino capture in KATRIN’s189 gaseous T2 source discussed in several Note that only the statistical sensitivity is investigated in this thesis. In order to works (e.g., Kaboth et al. 2010, Fässler et al. 2013,derive Heizmann an upper limit from 2018) the neutrino mass data, also systematic e↵ects need to be studied very carefully. E E (eV) − 0 20 15 10 5 0 5 1016 17− − − − 10− Robertson et al.
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