MLgeneralexam

Backgrounds in the Karlsruhe Tritium Neutrino Experiment: 

Backgrounds in the Karlsruhe Tritium Neutrino Experiment Michelle Leber General Exam August 2, 2006

Outline: 

Outline What is a neutrino and why is its mass interesting? What techniques can measure neutrino mass? The KATRIN tritium -decay experiment Backgrounds in KATRIN affecting neutrino mass measurements

Pauli’s Puzzle: 1930: 

Pauli’s Puzzle: 1930 Two particles are observed in the final state. Energy and momentum appear to not be conserved. Spin Statistics of Nuclei are not understood. (14N) Nuclear ß-decay:

The neutrino: 

The neutrino Pauli postulate a third particle is emitted Electrically Neutral Light: Spin 1/2 Fermi develops a theory of ß-decay and uses this to explain the shape of the electron’s energy spectrum. The “neutrino” must be lighter than the electron.

Parity Violation: 

Parity Violation Polarized 60Co nuclei ß-decay, emitting electrons preferentially away from the magnetic field. Under parity, spin does not change sign, but the electron’s momentum does. Figure from Los Alamos Science

Standard Model of Particle Physics: 

Standard Model of Particle Physics Neutrinos interact via the weak interaction mediated by W+ and Z0 Interaction projects out left-handed particle states to violate parity maximally Neutrinos are only left-handed and massless!

Helicity vs. Chirality: 

Helicity vs. Chirality Helicity Conserved Frame dependent In the Standard Model, only massless, left-chirality neutrinos exist. Figure from Los Alamos Science

Meanwhile, Solar Neutrinos...: 

Meanwhile, Solar Neutrinos... Are missing! The sun is a source of low energy Many experiments observed a deficit of neutrinos from the sun

Neutrino Oscillations: 

Neutrino Oscillations If neutrinos have different mass and flavor eigenstates (like quarks) than solar can be oscillating to other flavors Different solar experiments have different flavor sensitivity SuperK: Elastic Scattering Radiochemical: Charged Current

Atmospheric Neutrinos: 

Atmospheric Neutrinos Cosmic Rays create mesons in the upper atmosphere that decay to high energy neutrinos Figure from Los Alamos Science

Atmospheric Neutrinos: 

Atmospheric Neutrinos Cosmic Rays create mesons in the upper atmosphere that decay to high energy neutrinos Two µ-type neutrinos for every e-type Figure from Los Alamos Science

Atmospheric Neutrinos: 

Atmospheric Neutrinos Zenith Angle dependence of the ratio Neutrinos coming up through the earth travel farther than just through the atmosphere Disappearance experiment Super-Kamiokande hep-ex/0604011

Solar Neutrinos: 

Solar Neutrinos SNO was first to measure CC, NC, and ES Appearance of flavors other than electron in SNO NC: CC: ES:

Solar Neutrinos: 

Solar Neutrinos SNO was first to measure CC, NC, and ES Appearance of flavors other than electron in SNO SNO Collaboration, Phys. Rev. C72 (2005)

Current State of Neutrino Physics : 

Current State of Neutrino Physics Neutrinos can be summarized by rotations from mass to flavor states. Mass eigenvalues and differences are the 3 other parameters of the system.

Current State of Neutrino Physics : 

Current State of Neutrino Physics Solar Experiments and KamLAND measure SNO Collaboration, Phys. Rev. C72 (2005)

Current State of Neutrino Physics : 

Current State of Neutrino Physics Solar Experiments and KamLAND measure SNO Collaboration, Phys. Rev. C72 (2005) Atmospheric Experiments measure Super Kamiokande Collaboration, Phys. Rev. Lett. 93(2004)

Current State of Neutrino Physics : 

Current State of Neutrino Physics Oscillations show neutrinos are not massless! But cannot measure the mass scale Figure from Scott Dodelson

Why is neutrino mass important?: 

Why is neutrino mass important? Particle Physics: Neutrino mass is much smaller than other fermions Neutrinos are uncharged and can be their own antiparticle This may mean neutrinos acquire mass differently than other particles New physics? Figure from APS “Neutrino Matrix”

Why is neutrino mass important?: 

Why is neutrino mass important? Cosmology Neutrinos are second only to photons as most abundant particles in the universe Large Scale Structure Leptogenesis Neutrino mass can help explain the abundance of matter over antimatter in the universe Supernovae

Techniques to measure neutrino mass: 

Techniques to measure neutrino mass Neutrinoless Double Beta Decay Cosmology Beta Decay

Neutrinoless Double Beta Decay: 

Neutrinoless Double Beta Decay If neutrinos are their own antiparticle (Majorana) Figure from Los Alamos Science

Neutrinoless Double Beta Decay: 

Neutrinoless Double Beta Decay Rate depends on effective mass and nuclear matrix element Phases can lead to cancellations Figure from Los Alamos Science

Large Scale Structure: 

Large Scale Structure Neutrinos with mass are hot dark matter that freely stream out of dense regions Colombi, Dodelson, & Widrow 1995 Cold Dark Matter (no neutrino mass) Hot + Cold Dark Matter (non-zero neutrino mass)

Neutrino Signature in Cosmology: 

Neutrino Signature in Cosmology Massive neutrinos suppress matter power spectrum at small scales Lowering matter density has same effect CMB: Measure of matter density Figure from Scott Dodelson

Bounds from cosmology: 

Bounds from cosmology Bounds fluctuate because of model dependencies S. Hannestad, Annu. Rev. Nucl. Part. Phys. (2006) 1

Beta decay: 

Beta decay Neutrinos with mass modify the shape of the electron’s energy spectrum near the endpoint.

Beta decay: 

Beta decay Electron’s energy spectrum: For degenerate neutrino mass region (3 flavors) measure an effective mass:

Beta decay: 

Beta decay Electron’s energy spectrum: For degenerate neutrino mass region (3 flavors) measure an effective mass: Compare to With phases! No phases!

Advantages of Tritium: 

Advantages of Tritium Low endpoint energy (18.6 keV) and relatively short half life (12.3 yrs) Allowed nuclear transition Low charge of the source Atomic structure of tritium and 3He are simple

The Mainz Experiment: 

The Mainz Experiment eV (90% CL)

Slide32: 

 meV KKDC†  † Klapdor-Kleingrothaus H V, Krivosheina I V, Dietz A and Chkvorets O, Phys. Lett. B 586 198 (2004). What we know Future Experiments KATRIN Tritium -decay Constraints on  mass

How does KATRIN measure neutrino mass?: 

How does KATRIN measure neutrino mass?

Slide34: 

KATRIN Overview

Slide35: 

KATRIN’s Signal Emerging from Spectrometer Signal in Detector

KATRIN’s Sensitivity: 

KATRIN’s Sensitivity Maximize the luminosity of the source Small analyzing window reduces rate Sensitive to near endpoint accessible

Slide37: 

Gaseous T2 Source Column density d: 5 X 1017 T2/cm2 (+ 0.1%) OD: 9 cm Purity> 95% T2 (+ 1%) 40 g T2 /day Expect 100x more decays/sec than Mainz KATRIN Design Report 2005 Gas has less complicated final states, systematics than solid source

KATRIN’s Sensitivity: 

KATRIN’s Sensitivity Maximize the luminosity of the source Excellent energy resolution accessible

Slide39: 

Two superconducting solenoids make a guiding magnetic field Electron source in left solenoid Electrons emitted in forward direction are magnetically guided Adiabatic transformation: Parallel beam at analyzing plane Principle of MAC-E Filter Magnetic Adiabatic Collimation + Electrostatic Filter J. Beamson et al., J. Phys. E13 (1980) 64

Slide40: 

Principle of MAC-E Filter Retarding electrostatic potential is an integrating high-energy pass filter Parallel energy analysis Magnetic Adiabatic Collimation + Electrostatic Filter

Slide41: 

Transmission Function with Pinch Energy resolution depends on starting angles of electrons in the source Pinch Magnet rejects high angle electrons

KATRIN’s Sensitivity: 

KATRIN’s Sensitivity Maximize the luminosity of the source Excellent Energy resolution Minimize Backgrounds (<10 mHz)

Spectrometer-related backgrounds: 

Spectrometer-related backgrounds Limit to 9 mHz 10X larger diameter spectrometer than Mainz Not well understood Field emission Delta rays induced by cosmic rays Natural radioactivity

Wire Electrode: 

Wire Electrode Reject low energy electrons from the spectrometer walls

Detector-related backgrounds: 

Detector-related backgrounds Limit to 1 mHz 20X larger area detector than Mainz Cosmic Rays Natural Radioactivity Cosmogenics

Slide46: 

Detector Parts of the Detector: 6 Tesla magnet Active shielding Passive shielding from External particles Vacuum tube Quartz insulator Post acceleration electrode Mechanical support Silicon diode detector

Slide47: 

Detector Parts of the Detector: 6 Tesla magnet Gate valves Pumps Rail system for moving magnet

Slide48: 

Detector Parts of the Detector: 6 Tesla magnet Active shielding Passive shielding from External particles Vacuum tube Quartz insulator Post acceleration electrode Ceramic insulators Guided magnetic flux

Statistical Errors: 

Statistical Errors Decreasing the background rate below 10 mHz will improve the statistical error

Background Investigations: 

Background Investigations Ionizations in the Source Detector Backgrounds Prespectrometer Backgrounds

Will ionization in the source be a background for KATRIN?: 

Will ionization in the source be a background for KATRIN?  e- Delta electrons produced by cosmic rays ionizing the gaseous source are indistinguishable from beta decay electrons

Generation of Cosmic Rays: 

Generation of Cosmic Rays Da Silva, Angela Jane. Ph. D. diss., University of British Columbia

Acceptance from the Source: 

Acceptance from the Source Electrons that reach the detector Originate in guided magnetic flux Radius of curvature of 18 keV electron in 3.6 T field is 0.12 mm Have opening angle  < 51 Have energy > Spectrometer Threshold Count electrons with these properties

Verification of Muon Spectra: 

Verification of Muon Spectra Line is input to Geant4 simulation Points are measurements from PDG S. Eidelmann et al., Phys. Letters B, 592, 1 (2004)

Muon Stopping Power: 

Muon Stopping Power Red line calculated from experiments D. E. Groom et al., Atomic Data and Nuclear Tables, 78, 2 (2001) 183-356 Points from Geant4 simulation

Proton Stopping Power: 

Proton Stopping Power Red line calculated from experiments ICRU, Stopping Powers and Ranges for Protons and Alpha Particles, ICRU Report 49 (1993) Points from Geant4 simulation

Rate from Cosmic Muons: 

Rate from Cosmic Muons Spectrum of delta rays ~ 1/T2 Rate of delta electrons with energy between 18.5 keV and 25 keV 1.33 + 0.02 Hz Limit total background rate to 10 mHz

Ongoing Work: 

Ongoing Work Detector Backgrounds

Detector Backgrounds: 

Initially investigated by F. Schwamm with prototype detector Major backgrounds from radioactivity in ceramic mount and cosmic rays Regions of interest: 15.9-19.4 keV 36.9-39.5 keV 47.1-49.5 keV Detector Backgrounds Figure from Frank Schwamm’s Dissertation

Goals of Detector Simulation: 

Goals of Detector Simulation Identify major sources of background Optimize Active and Passive Shielding to reduce background Optimize post-acceleration voltage and identify Region of Interest (ROI) Understand detector-related backgrounds so neutrino mass data taking can start late 2009.

Simple Geant4 Detector: 

Stainless Steel Magnet Case Nb-Ti-Cu Magnet Coils Copper Shield Plastic Scintillator Stainless Steel Vacuum Tube Copper High Voltage Electrode Silicon Diode Detector Simple Geant4 Detector

Simple Geant4 Detector: 

Stainless Steel Magnet Case Nb-Ti-Cu Magnet Coils Copper Shield Plastic Scintillator Stainless Steel Vacuum Tube Copper High Voltage Electrode Silicon Diode Detector Simple Geant4 Detector

Typical 1 GeV µ- Event : 

Typical 1 GeV µ- Event Red: Negative (e-, µ-) Green: Neutral (’s, ’s, Neutrons) Blue: Positive (e+, µ+) Yellow: Nuclei (’s, ionized atoms)

Cosmic Secondaries below 100 keV: 

Cosmic Secondaries below 100 keV Copper Shield Lead Shield Fewer photons from lead shield.

Secondary Photon Spectrum inside Shield: 

Secondary Photon Spectrum inside Shield More Bremsstrahlung photons in copper shield.

Geant4 Silicon Detector: 

Geant4 Silicon Detector Silicon wafer mounted in copper 100 copper pins Stainless Steel CF Flange

Geant4 Detector Region: 

Geant4 Detector Region

Slide68: 

Assumptions Impurities can vary for the same material Assays of sample materials will be necessary Average impurity assumed for simulation shown at right

Sources of Detector Backgrounds: 

Sources of Detector Backgrounds Preliminary: Muons are the largest background Insulators for HV electrode do not introduce large background

Background Spectra: 

Background Spectra Preliminary: Continuum decreases at higher energy

Detector Backgrounds: 

Detector Backgrounds Compare to Lead Shield Include Cosmogenics Copper, Stainless Steel, Silicon Other natural Radioactivity: 40K, 210Pb Continue to update the geometry as the design changes Fiber Optics in scintillator Detector pixelization

Future Work: 

Future Work

Detector Simulation Verification: 

Detector Simulation Verification Near Future Measurements with silicon detectors and scintillators in the Majorana lab Long Term KATRIN detector will be assembled and tested at UW, including the 6 Tesla magnet. I will help with the commissioning and the simulation will be verified with this setup.

Spectrometer Background Measurements: 

Spectrometer Background Measurements Near Future (Oct. 2006) Measure prespectrometer backgrounds with wire electrode in monopole mode Optimize the wire electrode voltage setting Possibly use pixelization of detector and scintillators to trace position in spectrometer of background Is it cosmic rays? Is it field emission? Is it natural radioactivity?

Prespectrometer Test Set-up: 

Prespectrometer Test Set-up

Spectrometer Background Simulations: 

Compute energy and angle of emitted delta rays with Geant4 Low energy delta rays are not collimated in direction of incident muon Tracking of particles in E&M fields must be done separately Spectrometer Background Simulations

Overall Contribution: 

Overall Contribution Impact the design of KATRIN’s detector region and shielding Impact the running phase by guiding the choice of ROI and optimizing wire electrode setting Identify possible limiting backgrounds for the experiment, e.g. source ionization

Conclusions: 

Conclusions KATRIN has the ability to probe regions of neutrino mass interesting for particle physics and cosmology. Optimum sensitivity can only be reached if backgrounds are limited to 10 mHz. Simulations and verification can help lead to an understanding of our backgrounds so neutrino mass data taking can begin in late 2009.

Slide79: 

John Wilkerson, Hamish Robertson, Peter Doe, Tom Burritt, Joseph Formaggio, Jason Detwiler, Noah Oblath, Rob Johnson, Brandon Wall, Mike Marino, Alexis Schubert, Sky Sjue, Sean McGee, Keith Rielage, Laura Stonehill, Minesh Bacrania, Claire Cramer, and Ferenc Gluck. Thanks!