Nygren TPC symposium

A New TPC Application…?: 

A New TPC Application…? Motivation: next generation 0 -  search Implications of 0v   0 are substantial: Neutrino = anti-neutrino (Majorana) Demonstration of lepton number violation Nearly direct measure of mv Significant contribution to cosmology, m

Experimental Status: 

Experimental Status Only one experiment claims detection: Heidelberg-Moscow subgroup, using 76Ge Current experiment is background limited Claim is not widely accepted Challenge: how to reach interesting scale? Cuore, Majorana, Genius, Gem, Moon,….. All rely solely on energy measurement...

Two Types of Double Beta Decay: 

Two Types of Double Beta Decay eutrino helicity must flip Neutrinoless double beta decay lifetime Neutrino mass for 48Ca

 detectors need high energy resolution: 

 detectors need high energy resolution Spectra from Ludwig DeBraekeleer http://www.wipp.carlsbad.nm.us/science/Workshop/workshoptalks/debraekeleer1/ppframe.htm Theory Practice Spectra from Klapdor Kleingrothaus et. al.  Future: Background rejection must be better by a factor of ~103 Sensitivity to mv  (time)-1/4

Basic Experimental Challenges: 

Basic Experimental Challenges How to ensure, before the experiment is built and made operational for an extended period, that the result will not be background limited? No consensus about background rejection! How to design an experiment that will reach the appropriate level of sensitivity at an affordable cost and human time-scale?

Scales...: 

Scales... Sensitive mass: To reach mv ~ 10 meV, 100’s of kg needed  condensed matter better than gas... Nuclear matrix elements remain uncertain…   safety margin probably a good idea Background rejection: Must be certain before start of experiment! Maybe a new or different approach is needed?

Strategy: Energy + Topology: 

Strategy: Energy + Topology Topology + energy measurement in a liquid medium containing the candidate nuclei Use dielectric or insulating liquid Image capture by ion transport of track Energy measurement by integrating Q of track How well can backgrounds be rejected by topology of low energy electrons in liquid?

 Topology in Magnetic Field: 

 Topology in Magnetic Field  topology in magnetic field is distinctive. Rejection of ,e backgrounds due to: Compton scatter, pair production, nuclear decay  decays, neutron scatters, , wimps,….  Radio-purity issues may be much less important

Topologies - with magnetic field: 

Topologies - with magnetic field Compton: Pair production ('V' shape):  Decay ('S' shape): 

Background Studies: 

Background Studies Background rejection by topology can be measured a priori, by introducing external gamma sources to an operational detector This should be well-established in advance, for a proposed next generation experiment!

B Field & Multiple Scattering: 

B Field andamp; Multiple Scattering Multiple scattering degrades topology - Rough Monte Carlo is encouraging…. Is overall efficiency high enough to be useful? How high a magnetic field? ~2T seems right, (event radius ~ 3mm) Algorithmic strategies to discard kinks due to hard scatters must be developed

Potentially Stronger Result: 

Potentially Stronger Result Background rejection, if high enough, will permit an experimental result that is an energy spectrum which contains both 2- and 0- decay events Energy resolution expected to be ~1- 2% Actual resolution is unknown at present

Detector Concept:: 

Detector Concept: Image capture by ion drift in liquid medium Strong magnetic field to visualize  topology Track lengths ~1.5 cm (Q value,  of liquid) Ionization level Gfi is low, but OK…maybe Low rate experiment permits slow drift velocity V = ~ 2 cm/second expected @ 4 kV/cm Spatial resolution of ~20 m expected @ 5 cm  new kind of TPC-like detector

… Detector Concept: 

… Detector Concept Pixellated readout plane Drift  B field  Basic Module holds ~1 liter of insulating liquid Pixel size is ~100 x 100 m2 HV: ~20 kV

Readout Plane: 

Readout Plane Pixel size is ~ 100 x 100 m2 Induced signal rises when ion cluster nears For vdrift = 2 cm/s,  ~ 5 msec  electronic bandwidth andlt; 1 kHz  low-noise low-power circuitry OK  Raster scan of integrated Q @ 400 Hz

Many Challenging Issues...: 

Many Challenging Issues... How useful is topology? Which isotope is practical? Is the chemistry of liquid acceptable? Is the ionization level high enough? Is energy resolution OK? (Gfi is f(E field)) Do ions display unique drift velocities? Is the intrinsic 'noise' of the liquid OK?

Challenges...: 

Challenges... How to measure the drift coordinate? Diffusion of track may be good enough,… Maybe the liquid scintillates a little,… Can practical detector modules be made? Pixel readout noise must be ~ 5 e- rms. Raw data rates, at module, ~50 Mbytes/s Filtered data, from module, ~ 10 kbytes/s Are negative ions better than positive?

Which isotope?: 

Which isotope? 48Ca is attractive: Lowest Z (20), Highest Q (4.3 MeV) However: natural abundance very low: 0.2% Not many insulating liquids with Ca in them Nuclear matrix element unfavorable

Other Possible Isotopes: 

Other Possible Isotopes 96Zr (2.8% abundance), Z=40, Q=3.35 MeV 82Se (8.7% abundance), Z=34, Q = 3.0 MeV Selenium 82 may be best choice… Enrichment methodology may exist for these isotopes, needs exploration...

Ion Drift in Insulating Liquids: 

Ion Drift in Insulating Liquids No basic reason why low drift velocity Vd is inappropriate for low rate experiments Is ion drift velocity Vd single-valued? Solvation may introduce range of values... Ion yield may be ~1 ion pair per 200 eV  ~15,000 ion pairs per 0 decay (82Se)  ~100 ion pairs per measurement along track

Detector R&D: Motivations : 

Detector Randamp;D: Motivations Double beta-decay process is regarded as a very high priority scientific objective Several nuclei should be studied to reduce systematic errors in interpretation of mv  Several experiments are justifiable Scaling of experiment from prototype to final size is an important consideration

R&D Plans...: 

Randamp;D Plans... Laboratory Randamp;D funds at LLNL have been awarded to study the general characteristics of imaging minimum ionizing tracks in dielectric liquids (LLNL: Adam Bernstein) Physical chemists have studied ion transport in dielectric liquids using relatively large pulsed radiation sources; - will seek experts

Summary: 

Summary Idea still rudimentary, but is possibly an innovation that can extend sensitivity of 0v Detector Randamp;D issues not costly to explore Good scaling behavior, as 1 N modules Other proposed next-generation techniques not shown to have adequate background rejection!