# Presentation: 831762

## Weighing the neutrino

- CENPA

- Center for Experimental Nuclear Physics and Astrophysics
- University of Washington

- J. F. Wilkerson
- February 27, 2004
- APS Neutrino Mass Working Group

- - Motivation
-  Techniques
-  kinematical
-  cosmological/astrophysical
-  double beta decay
- - Future expectations

## The absolute scale of  masses

- Addresses key physics issues
- hierarchical or quasi-degenerate neutrino mass spectrum
- understanding the scale of new physics beyond SM
- potential insight into origin of fermion masses
- Impacts cosmology and astrophysics
- early universe, relic neutrinos (HDM), structure formation, anisotropies of CMBR
- supernovae, r-process, origin of elements
- potential insight on understanding the origin of UHE cosmic rays

## sub-eV absolute  mass measurements

- sub-eV absolute  mass measurements

- hierarchical

- quasi-degenerate

- Given the surprise of large mixing in the lepton sector, there is limited theoretical insight into which scenario occurs in nature.

## Probes of absolute  mass

**Direct kinematical techniques**
- time of flight (supernovae)
- particle decay kinematics
**Cosmology and Astrophysics**
- Cosmic Microwave Background
- Galaxy clusters
- Galaxy large scale structure
- Lyman- forest
- UHE cosmic-rays
- Supernovae generation mechanisms
**Neutrinoless**** ********-decay**

## Direct measurements of neutrino mass

**Techniques**
**time of flight from supernovae**
- Not expected to be able to reach sub-eV sensitivity
- Much more likely that a direct measurement or limit will be used to help understand supernovae dynamics.
**particle decay kinematics**
- beta decay (and electron capture) spectrum shape
- muon momentum in pion decay
- invariant mass studies of multiparticle semileptonic decays

- SN1987a

- 3H -decay

## Past: history of direct  mass measurements ( flavor eigenstates)

- Past: history of direct  mass measurements ( flavor eigenstates)

- points without error bars represent upper limits

- me < 2.2 eV (95% CL)
-  (Mainz 2000)

-  m < 18.2 MeV (95% CL)
-  (ALEPH 1998)

- m < 170 keV (90%CL)
-  (PSI 1996)

- But  oscillations with large mixing angles - forces one to consider
- direct techniques
- in terms of  mass
- eigenstates!

## -decay endpoint measurement

- Essentially a search for a distortion in the shape
- of the b-spectrum in the endpoint energy region

- For 3  mass spectrum, with quasi-degenerate states, the beta spectrum simplifies to an “effective mass” : m2=  |Uei |2 mi

## Mainz Neutrino Mass Experiment

- Quench condensed solid T2 source
- Early results (94) showed systematic effects, traced to source film roughening transition.
- (fixed by lowering temperature)
- 95-97 significant background reduction, signal improvement

## Mainz Results

- Weinheimer et al., Phys. Lett. **B460** 219 (1999)

- Recent data (Q5 and greater) exhibit good reduced 2 and are stable over a varying fit interval.
- Change made to “sweep” spectrometer backgrounds between data points starting at run Q5.
- Detailed studies published on source systematics.
-   m= -1.2 ± 2.2 ± 2.1 eV
-      m≤ 2.2 eV (95%CL)
- A solid result.

## Neutrinos and Cosmology

- Amount of hot dark matter must be limited to avoid excessivefree streaming in the early universe that would suppress small-scale power of the observed matter distribution

## Cosmology - WMAP and Large Scale Surveys

- WMAP CMB data combined with the recent data from large galaxy surveys (SDSS, 2dF) yields constraints on m when either assuming quasi-degenerate masses or one heavy neutrino and 3 or more light neutrinos.

- S. Hannestad and G. Raffelt, hep-ph/0312154

##  Cosmological Results seem robust...

- 	Different analyses, with varying assumptions and priors, yield similar results range from m < 0.23 eV to m < 0.6 eV  (95% CL)
- 	O. Elgaroy et al., “A new limit on the total neutrino mass from the 2dF galaxy redshift survey,”Phys. Rev. Lett. 89, 061301 (2002) [astro-ph/0204152].
- 	S. Hannestad, “Cosmological limit on the neutrino mass,” Phys. Rev. D 66 (2002) 125011 [astroph/0205223].
- 	S. Hannestad, “Neutrino masses and the number of neutrino species from WMAP and 2dFGRS,” JCAP 0305 (2003) 004 [astro-ph/0303076].
- 	O. Elgaroy and O. Lahav, “The role of priors in deriving upper limits on neutrino masses from the 2dFGRS and WMAP,” JCAP 0304 (2003) 004 [astro-ph/0303089].
- 	D. N. Spergel et al., “First year Wilkinson Microwave Anisotropy Probe (WMAP) observations: Determination of cosmological parameters,” Astrophys. J. Suppl. 148 (2003) 175 [astroph/0302209].
- 	V. Barger, D. Marfatia and A. Tregre, “Neutrino mass limits from SDSS, 2dFGRS and WMAP,” [hep-ph/0312065].

**But these limits depend on the validity of the assumed standard cosmological model. **
- S. W. Allen et al. [astro-ph/0306386], include x-ray galaxy cluster data and find: m = 0.20 ± 0.10 eV

## Cosmology - future prospects

- With Planck and a completed SDSS there are predictions that one may be able to observe neutrino masses. †
- Together Planck + SDSS might yield a msensitivity of 0.12 eV
- However, interpretations of these measurements are extremely model dependent.
-  degeneracies of m with other cosmological parameters
-  certain implicit assumptions (scale invariance, bias is small)
-  dependence on priors selected
- It is possible that direct sub-eV neutrino measurements, free of model dependencies, will be used as input to the cosmological models allowing us a better understanding of the underlying cosmology

- † S. Hannestad, Phys. Rev. D 67 (2003) 085017 [astro-ph/0211106].

## Future -decay endpoint measurements

- Ultimate sensitivity of spectrometers
- require instrumental resolution of ~ m/Eo
- spectral fraction per decay that falls in the last m of the spectrum is ~ (m/Eo )3
- source thickness is set by the inelastic scattering cross-section (3.4 x 10-18 cm2 ), n ≤ 1
- If one wants ~1 event/day in last m of the spectrum
- for a 10 m magnetic spectrometer** **m~ 1.7 eV
- for a 3 m dia. solenoid retarding field spectrometer** **m~ 0.3 eV
- Calorimetic detector sensitivity
- evade source-thickness limit, because no e-loss problem
- limited by response time, and eventually pileup
- requires fine segmentation, many detectors

- See Wilkerson and Robertson, Direct Measurements of Neutrino Mass, Sect 3.6

## KATRIN - Karlsruhe Tritium Neutrino Experiment

*KATRIN - Ka**rlsruhe **Tri**tium **N**eutrino Experiment*
* *
*direct measurement of the ****-mass in the sub-eV range *

## KATRIN Collaboration

## The KATRIN experiment

- ~70 m beamline, 40 s.c. solenoids

-   *located at Tritium Laboratory      *
*                 **Karlsruhe (TLK) *
*  *
-     - TLK: worldwide unique facility
-     tasks: closed ITER fuel cycle
-                 KATRIN: high purity T2

## KATRIN sensitivity & discovery potential

- LoI 9/2001

- reference

*statistical & systematic error*
*  *
*will contribute ~ equally*
* *
*KATRIN sensitivity **no ****- **mass signal*

*m(****)  <  0.2 eV (90% CL)*

*KATRIN discovery potential*
* *
*(evidence for ****mass signal)*

*m(****)  =  0.35 eV (5****)*

*m(****)  =  0.30 eV (3****)*

## 4. Project organisation

*4. Project** **organisation*

## KATRIN time schedule

- 2001		first presentation (internat. workshop Bad Liebenzell)
-     			founding of KATRIN Collaboration
-                         		submission of Letter of Interest (hep-ex 0109033)
- 			BMBF start up funding (astroparticle physics)
- 2002/03       	background studies, R&D works, design optimisation
-   			international KATRIN review panel, UK groups join,
-                             	pre spectrometer on site, transport section element ordered
-                      HGF review, funding applications DOE, PPARC,...
-  			validate UHV concept and novel electromagnetic design,
-                            	specifications & tender for WGTS and main spectrometer
- 2005/2007	set up and commissioning of key components (tritium source,                  		transport section, spectrometer, detector)
- 2008  		system integration, test runs & first measurements
-   			total measuring time 5 years

## Summary

- All 3 masses can be probed through the electron neutrino
- Present direct kinematic limit on mass of 1, 2, and 3
- Tritium b-decay: m < 2.2 eV; m ≤ 6.6 eV
- Cosmology: m ≤ 1 eV
- Direct measurements combined with oscillation and 0 decay results can discriminate between a variety of 3 and 4 neutrino mass spectrum scenarios.
- KATRIN should be able to achieve sub-eV mass sensitivity of 0.20 eV, an order of magnitude improvement over current direct measurements.
- Sub-eV direct lab limits yield model independent results that will likely be serve as strong constraints on astrophysics and cosmology.

## Slide 22

## 187Re -decay microbolometers

-  lowest Q-value: 2.6 keV
-  63% abundance
-  5/2+ Æ 1/2- first forbidden transition   (requires shape correction)

- Fiorini, INFN Milano - AgReO4

- Gatti, INFN Genoa - Re crystal

- 10 calorimeters (250 g, E ~ 25 eV, trise ~ 1 ms) m sensitivity: 10 eV in 1 year