KATRIN experiment: fjrst neutrino mass result and future prospects Alexey Lokhov on behalf of KATRIN collaboration 13th European Research Conference on Electromagnetic Interactions with Nucleons and Nuclei Paphos, Cyprus Institut für Kernphysik Westfälische Wilhelms-Universität Münster
Outline Neutrino masses in particle physics and cosmology ● Neutrino mass measurements ● Complementary ways to the neutrino mass scale – Tritium b -decay spectrum – KATRIN experiment ● Setup – MAC-E-Filter Principle – Experimental response – First Tritium – First neutrino mass result – Current status and future – Conclusion and Outlook ● 2
Neutrino masses in particle physics and cosmology neutrino oscillation Discovery of the neutrino oscillations neutrino oscillation ● n 2 n m cos q n t sin q non-zero neutrino masses – n 3 -sin q Physics Nobel Prize 2015: cos q – D m 2 ij m( n j ) 0 D m 2 ij m( n j ) 0 Prof. Dr. T . Kajita, Prof. Dr. A.B. McDonald but unknown absolute scale but unknown absolute scale Neutrino mass ordering m( n j ) not accessible by osc. exp. m( n j ) not accessible by osc. exp. ● A small n mass generation mechanism is needed, likely ● beyond the Standard model Higgs The most abundent massive particle in the Universe – ● 336 n cm -3 only weak interaction with matter – 3
Three ways to assess the absolute neutrino mass scale 1) Cosmology very sensitive, but model dependent compares power at different scales current sensitivity: m( n i ) 0.12 eV (Planck) 2) Search for 0 nbb Sensitive to Majorana neutrinos, model-dependent Upper limits by EXO-200, KamLAND-Zen, GERDA, CUORE: m bb < 0.1-0.4 eV 3) Direct neutrino mass determination No further assumptions needed, use E 2 = p 2 c 2 + m 2 c 4 m 2 ( n ) Time-of-flight measurements ( n from supernova) Kinematics of weak decays / beta decays, e.g. tritium, 163 Ho best upper limits m( n ) < 2 eV (Mainz & Troitsk) N. Aghanim et al. (Planck), (2018), arXiv:1807.06209; M. J. Dolinski, A. W. Poon, and W. Rodejohann, Annual Review of Nuclear and Particle Science 69, 219 (2019); Eur. Phys. J. C 40, 447 (2005); Phys. Rev. D 84, 112003 4
Tritium b -decay ● continuous b -spectrum described by Fermi´s Golden Rule, measurement of efgective mass m( n e ) based on kinematic parameters & energy conservation 3 d Γ 2 ) 2 | 2 − m n i 2 ⋅ F ( E,Z ) ⋅ √ ( E 0 − E ) dE = C ⋅ p ⋅( E + m e ) ( E 0 − E ) ⋅ ∑ | U ei ⋅q( E 0 − E − m n i ⋅ i = 1 3 m (n e )≝ √ ∑ 2 | 2 | U ei ⋅ m i count rate (arb. units) i = 1 6 4 2 0 5 10 15 electron energy (keV) 5
Tritium b -decay Need: low endpoint energy Tritium 3 H – 18.6 keV Need: low endpoint energy Tritium 3 H – 18.6 keV ● continuous ß-spectrum described by Fermi´s Golden Rule, measurement of short half-life (superallowed) – 12.3 yr short half-life (superallowed) – 12.3 yr efgective mass m( n e ) based on kinematic parameters & energy conservation d Γ ( 163 Ho electron capture) 2 2 i C p ( E m ) ( E E ) ( E E ) m ( 163 Ho electron capture) F ( E , Z ) ( E E m ) q e 0 0 i 0 i d E very high energy resolution & very high energy resolution & very high luminosity & MAC-E-Filter KATRIN 3 very high luminosity & MAC-E-Filter KATRIN 2 2 m ( ) U m (cryogenic bolometers n (cryogenic bolometers e ei i very low background ECHo, HOLMES) i 1 very low background ECHo, HOLMES) count rate (arb. units) 6 4 2 0 5 10 15 electron energy (keV) 6
Tritium b -decay – T 2 3 He + FSD n e 0.05 Rotational recoil calculated f inal s tate d istribution of T 2 and e - vibrational excitations 0.04 electronic ground state probability 3 H ro-vib excitations 0.03 excited 3 He + n e electronic states Electronic excitations and e - 0.02 ionization due 57 % 43 % to Migdal effect → new electronic 0.01 3 wavefunction 0 2 4 20 30 40 50 H excitation energy (eV) atomic source (T) would have simpler FSD but difficult to handle – PROJECT 8 A. Ashtari Esfahani et al. (Project 8), J. Phys. G 44,054004 (2017), arXiv:1703.02037 7
The KATRIN experiment at Karlsruhe Institute for Technology Gaseous T 2 source Transport section Pre-Spectrometer Main Spectrometer Detector Diagnostics 70 m 8
The KATRIN Windowless Gaseous Molecular Tritium Source beam tube Ø = 9 cm , L = 10 m guiding field 3.6 T (2.52 T) temperature T = 30 K ± 30 mK, T 2 flow rate 5·10 19 molecules/s (40 g of T 2 / day) T 2 purity 95% ± 0.1 % T 2 inlet pressure 10 -3 mbar ± 0.1 % column density 5·10 17 T 2 /cm 2 luminosity 1.7·10 11 Bq 9
MAC-E-Filter: high-resolution b - spectroscopy M agnetic A diabatic C ollimation & E lectrostatic Filter: Analyzing plane electrode Giant spectrometer: solenoid solenoid high energy resolution & acceptance U 0 U s detector B max B min B s µ = E ┴ / B = const. adiabatic conversion E ┴ → E ‖ Inner electrode system: background suppression & potential shaping Momentum tranfsormation without the E-field 10
Response function of KATRIN Shooting electrons from monoenergetic pulsed UV-laser photoelectron source through tritium column density (Eur. Phys. J. C77 (2017) 410, Astropart. Phys. 89 (2017) 30) Normal integral MAC-E-Filter mode Differential Time-of-flight mode (Nucl. Inst. Meth. A 421 (1999) 256, New J. Phys. 15 (2013) 113020) 1-fold, 2-fold, 3-fold inelastic scattering Deconvoluted differential energy loss function (arXiv:1909.06048, subm. to Phys. Rev. Lett.) 11
Measuring the response with 83m Kr E B D ● MAC-E filter characteristics well understood min E filter width E B ● (also used to study plasma) max L3-32 line: 30.47 keV J P = 5 / 2 - J P = 1 / 2 - L3-32 E g = 32.15 keV g J P = 7 / 2 + E g = 9.4 keV g J P = 9 / 2 + KATRIN Collab., “High-resolution spectroscopy of gaseous 83m Kr conversion electrons with the KATRIN experiment”, arXiv:1903.06452 “Calibration of high voltages at the ppm level by the difference of 83mKr conversion electron lines at the KATRIN experiment”, Eur. Phys. J. C (2018) 78:368 Retarding energy (eV) 12
Model of the experimental spectrum Beta spectrum: R b (E,m 2 ( n e )) E 0 Ä single tritium scan E 0 and fit Experimental response: f(E-qU) 13
First Tritium (2-week engineering run in 2018) systematic uncertainty ± 0.1% reference First Tritium: - low tritium concentration : ~1% DT and ~99% D 2 - functionality of all system components at nominal column density r d (5·10 17 cm -2 ) - stability of the source parameters → sub per mille level KATRIN Collab., “First operation of the KATRIN experiment with tritium”, arXiv:1909.06069 14
KATRIN neutrino mass run # 1 4-week long measuring campaign in spring 2019 with high-purity tritium - April 10 – May, 13 2019: 780 h - high-purity tritium ( e T = 97.5 % by laser-Raman spectr.) - high source activity (22% nominal): 2.45 · 10 10 Bq - high-quality data collected - full analysis chain using two independent methods 15
Tritium scanning strategy 274 scans of tritium b -spectrum : 22 HV set points 5 HV set points - alternating up- / down- scans - 2 h net scanning time single tritium scan E 0 - analysis: 27 HV set points and fit - [ E 0 – 40 eV , E 0 + 50 eV] still limited bg-slope Measurement point distribution maximises n -mass sensitivity - focus on region close to E 0 16
Fitting tritium b -decay spectrum High-statistics b -spectrum - 2 million events in in 90-eV-wide interval (522 h of scanning, 274 indiv. scans) - fit with 4 free parameters: m 2 ( n e ), R bg , A s , E 0 neutrino mass square m 2 ( n e ) excellent goodness-of-fit c 2 = 21.4 for 23 d.o.f. (p-value = 0.56) Bias-free analysis - blinding of FSD - full analysis chain first on MC data sets - final step: unblinded FSD for experimental data (arXiv:1909.06048, subm. to Phys. Rev. Lett.) 17
Analysis methods and n -mass result two independent analysis methods to propagate uncertainties & infer parameters - Covariance matrix: covariance matrix + c 2 -estimator - MC propagation: 10 5 MC samples + likelihood (-2 ln L ) - both methods agree to a few percent n -mass and E 0 : best fit results m 2 ( n e ) = -1.0 +0.9 -1.1 eV 2 KATRIN collab. E 0 = (18573.7 ± 0.1) eV arXiv:1909.06048 subm. to Phys. Rev. Lett. → Q-value: (18575.2 ± 0.5) eV E.G. Myers, A. Wagner, H. Kracke, → Q-value[ Δ M( 3 H, 3 He)]: (18575.72 ± 0.07) eV B.A. Wesson, Phys. Rev. Lett. 114, 013003 (2015) 18
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