Status and Perspective of the GERDA Neutrinoless Double...

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Karl Tasso Knöpfle MPI Kernphysik, Heidelberg on behalf of the GERDA collaboration http://www.mpi-hd.mpg.de/GERDA The 19 th Particles and Nuclei International Conference (PANIC11) Massachusetts Institute of Technology, Cambridge, July 24th 29th, 2011 T 2ν = 1.74·10 21 y ½ T 0ν = ? ½ Status and Perspective of the GERDA Neutrinoless Double Beta Decay Experiment

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  • Karl Tasso Knöpfle

    MPI Kernphysik, Heidelberg

    on behalf of the GERDA collaboration

    http://www.mpi-hd.mpg.de/GERDA

    The 19 th Particles and Nuclei International Conference (PANIC11)

    Massachusetts Institute of Technology, Cambridge, July 24th – 29th, 2011

    T2ν = 1.74·1021 y ½

    T0ν = ? ½

    Status and Perspective of the GERDA

    Neutrinoless Double Beta Decay Experiment

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Zürich, June 2011

    About 100 members, 19 institutions, 7 countries

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    introduction

    Introduction

    Construction and Status

    Results from Commissioning Runs

    Perspectives and Conclusion

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Introduction motivation for Ge-76 experiment

    Discovery of neutrinoless double beta decay would imply:

    ● Neutrino is its own anti-particle, has Majorana mass

    ● Access to absolute neutrino mass scale

    ● Lepton number violation ΔL = 2

    ● Further new physics beyond the standard model

    sum of kinetic energies

    exp. signature

    observed searched

    for

    Ge-76 : Qββ=2039 keV

    2νßß

    0νßß

    measured deduced

    phase space

    nuclear matrix element

    So far, best limits for neutrinoless double beta decay from

    Ge-76 experiments, IGEX and Heidelberg-Moscow (HdM),

    T1/2 > 1.9∙1025 y at 90% confidence limit,

    as well as claim for evidence by part of HdM collaboration

    KKDC, PL B586 (04) 198 ( 71.7 kg∙y, BI ~ 0.11 cts/(keV∙kg∙y)

  • Reach background index (BI) at Qββ = 2039 keV of 0.01 / 0.001 cts / (keV۰kg۰y)

    KKDC

    BI=0.01 phase I :

    use Ge-76 diodes of HD-Moscow & IGEX

    ~18 kg

    BI ~ 0.01 cts / (keV۰kg۰y)

    intrinsic background expected

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Introduction GERDA’s goals & sensistivity

  • Reach background index (BI) at Qββ = 2039 keV of 0.01 / 0.001 cts / (keV۰kg۰y)

    KKDC

    BI=0.01

    BI=0.001

    phase II :

    add new enriched Ge-76 detectors, 20 kg

    BI ~ 0.001 cts / (keV۰kg۰y)

    ► 37.5 kg enriched Ge-76 bought

    35 kg ∙ 3 y exposure

    phase I :

    use Ge-76 diodes of HD-Moscow & IGEX

    ~18 kg

    BI ~ 0.01 cts / (keV۰kg۰y)

    intrinsic background expected

    phase III: depending on results worldwide collaboration for real big experiment

    close contacts & MoU with MAJORANA collaboration

    ~ 0.12eV

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Introduction GERDA’s goals & sensistivity

  • 34

    00

    m w

    .e.

    GERDA in

    Hall A of

    LNGS

    LNGS: Laboratori Nazionali del Gran Sasso

    Gran Sasso

    GERDA strategy: underground site to suppress cosmics

    improved shield against external radiation

    discrimination between single- (0νββ) & multi-site events

  • f

    14.8m

    clean room with lock

    control rooms

    water plant &

    radon monitor

    water tank, Ø10m, part of muon-veto detector

    cryostat, Ø4m,

    with internal

    Cu shield

    muon & cryogenic

    infrastructure

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    LAr

    wate

    r

    wa

    ter

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Construction

    Introduction

    Construction and Status

    Results from Commissioning Runs

    Perspectives and Conclusion

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Construction delivery of cryostat

    6 mar 2008

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Construction water tank

    5 may 2008

    water tank roof

  • Construction clean room

    29 feb 2009

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Construction L’Aquila M=6.3 earthquake & aftershocks

    14.8m

    0.52g peak ground acceleration

    LNGS galleria

    0.03g

    negligible impact in underground lab

    6 April 2009

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Construction heat exchanger for active cooling & radon shroud

    18 jul 2009

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Construction muon veto instrumentation in water tank

    aug 2009

    1 of 66 PMTs

  • x

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Construction nitrogen flushed clean bench and commissioning locks

    18 may 2010

    1-string c-lock

    3-string c-lock

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    construction status of infrastruture

    Cryogenic system

    Commissioning lock

    Safety systems

    Water plant

    Maintaining quality of ultra-pure water (resistivity >17MΩ∙cm & TOC

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning

    Introduction

    Construction and Status

    Results from Commissioning Runs

    Perspectives and Conclusion

  • Runs started in June 2010

    using 3 refurbished Genius-TF natGe-diodes (7.61 kg)

    NB ► p-type / coaxial ► ‘low background’ diodes

    calibration: spectra with Th-228 radioactive source

    preamps

    (88K)

    2.33kg

    2.32kg

    2.96kg

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning calibration & resolution

  • run 12 (0.564 kg∙y)

    27 days run time

    energy / keV

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning measured background spectra

    GTF45

    GTF32

    GTF112

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning low energy spectral region

    ‘understood’

    Fit compatible with 1Bq(39Ar)/kg

    39Ar

  • run 12 (0.564 kg∙y)

    energy / keV

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning measured background spectra – discrete lines

    GTF45

    GTF32

    GTF112

    Rather weak discrete lines from Th/U background, Th / U / 40K lines suppressed by factors of ~4 / ~4 / ~20 wrt HdM.

    1525 keV line much stronger than expected,

    Bi-

    214

    609

    Tl-

    208

    2616

    1525

    K-4

    0

    39Ar

    39Ar

    39Ar

  • 42Ar 18

    32.9 y O+

    = 600

    15

    25

    GERDA proposal assumed : 42Ar / natAr < 3∙10-21

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    ~18%

    ~82%

    commissioning Ar-42 / K-42 decay schemes

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning study of Ar-42/K-42 via 1525 keV line

    run 1-3

    outer shroud only

    +3kV

    0V

    Count rate of 1525 peak factor ~14 larger than expected.

    OS (30μm Cu)

    Ø 80 cm

  • IS

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning study of Ar-42/K-42 via 1525 keV line

    run 1-3

    run 4

    with inner shroud

    IS/OS: OV/-400V

    run 1-3

    outer shroud only

    +3kV

    0V

    OS (30μm Cu)

    Ø 80 cm

    Ø 11cm

    Count rate of 1525 peak factor ~14 larger than expected.

    Additional inner shroud (IS) reduces counts by factor of 4-5.

    Still larger than expected! IS shields E- field and convection.

    NB: Similar observations at Qββ !

  • IS

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning study of Ar-42/K-42 via 1525 keV line

    run 5

    IS/OS -200V/+500V

    run 4

    with inner shroud

    IS/OS: OV/-400V

    +3kV

    0V

    Count rate of 1525 peak factor ~14 larger than expected.

    Biasing IS/OS such that positive ions are attracted by IS:

    Count rate increases to about previous value.

    Additional inner shroud (IS) reduces counts by factor of 4-5.

    Still larger than expected! IS shields E- field and convection.

    NB: Similar observations at Qββ !

    ► Clear evidence that 42K-ions drift in electric field.

    Potentially severe consequences for background at Qββ!

    Field-free configurations desirable!

    OS (30μm Cu)

    Ø 80 cm

  • Ar-42 specific activity deduced from almost field-free runs 10-12

    Published limit :

  • 42Ar 18

    32.9 y O+

    = 600

    15

    25

    high energy spectral part

    dependent on dead layer

    thickness

    15

    25

    for homogeneous distribution

    BI ~0.007 expected – has big

    uncertainties.

    However, if 42K ions are collected

    at detector surface, BI increases.

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning K-42 spectrum simulation

    no dead layer

    0.6mm

    1mm

    ~18%

    ~82%

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    commissioning background in Qββ-region

    Background rate significantly lower than

    in previous experiments (HdM, IGEX) -

    but still higher than Phase I goal of 0.01.

    Background most probably not only due to 42Ar/42K; could (partially) be due also to distant

    Th-232 source. ► Background at Qββ not yet understood - better statistics needed!

    runs 10-12 summed

    (76 days run time)

    Deduced background index

    in interval (Qββ ± 200) keV:

    0.06 ± 0.01 cts/(keV∙kg∙y)

    Tl-

    20

    8 2

    61

    5

    Bi-

    21

    4 1

    76

    5

    Qββ ± 200 keV

  • commissioning spectrum of enriched Ge-76 diodes, and MC 2ν2β & K-42 contributions

    absolutely normalized MC prediction for

    2ν2β decay spectrum with T1/2=1.74∙1021y,

    and 42K contribution normalized to 1525 line.

    data

    39Ar

    Most background between 39Ar endpoint & 1525 keV line accounted for by 2ν2β decays.

    (Basic background studies done better with non-enriched diodes:)

    2ν2β

    2ν2β + 42K

    15

    25

    Data obtained with string of 3 enriched 76Ge diodes

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    perspectives

    Introduction

    Construction and Status

    Results from Commissioning Runs

    Perspectives and Conclusion

  • perspectives measured pulse shapes

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    time / ns

    cu

    rre

    nt

    a.u

    .

    +3kV

    0V

    For Phase I detectors reduction of BI

    by a factor of up to 2 might be feasible.

    Blind analysis indispensible.

    • Exploitation of pulse shape analysis

  • perspectives

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    8 refurbished and tested diodes (HdM, IGEX) available

    ● 86% isotopically enriched in Ge-76

    ● 17.66 kg total mass

    ● 3-string lock under commissioning

    ● soon ready for start of Phase I physics run

    • Exploitation of pulse shape analysis

    • Deployment of full array of enriched diodes

  • perspectives

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    • Exploitation of pulse shape analysis

    • Deployment of full array of enriched diodes

    • Order of phase II detectors

    35452.9g of 6N enr Ge metal

    BEGe (point-contact) type of diode selected for

    Phase II – superb pulse shape discrimination!

    DEP: 90%

    0-like

    -bgd:

    11%

    D. B

    ud

    jas e

    t a

    l., JIN

    ST

    4 P

    10

    00

    7 (

    20

    09

    )

    Full production cycle tested with depleted

    material left over from enrichment process.

    Enriched material reduced and purified.

    Negotiations for Phase II detector order

    in progress.

  • perspectives

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    R&D for LAr

    instrumentation

    LArGe

    Suppression factor at Qββ of ~5000 measured with Th-228 calibration source.

    Alternative to scintillation light readout by PMTs: fibers coupled to SiPMs.

    9x8” PMTs

    M.Heisel, PhD thesis, Uni HD, 2011

    • Exploitation of pulse shape analysis

    • Deployment of full array of enriched diodes

    • Order of phase II detectors

    • Instrumentation of LAr for scintillation veto

  • * PR C81(10)028502

    • Construction completed.

    • All subsystems commissioned and running smoothly. • All phase I detectors (8 pcs ,~18 kg) refurbished & ready.

    • Commissioning with natural and enriched Ge diodes in progress.

    ► 42Ar isotopic abundance found to be about factor of 4

    larger than 90% limit reported previously – serious

    background for phase II. ► Best background index at Qββ of all Ge experiments so far,

    but still factor 6 above phase I goal - not yet fully under-

    stood why. LAr instrumentation might be needed already

    to reach goal of phase I.

    • Start of phase I physics run with enriched detectors soon. • Full production chain tested for phase II BEGe detectors. • Phase II detectors (~20 kg) to be ordered this year.

    goals: phase I : background 0.01 cts / (keV۰kg۰y)

    ► scrutinize KKDC result within ~1 year

    phase II : background 0.001 cts / (keV۰kg۰y)

    ► T1/2 > 1.5۰1026 y , 0.09< < 0.15 eV *

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    concluding remarks

  • Backup Slides

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

  • PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Introduction sensitivity for 0νββ decay experiment

    72 kg y

    background index (BI) [cts/(keV∙kg∙y)]

    instrumental spectral width

    exposure [kg y] sensitivity*

    molecular weight

    of source

    detection efficiency ( =1 if source=detector)

    3.3 keV

    0.1

    86%

    achieved with 76Ge

    *RevModPhys 80(08)481

    Qββ

    ?

    Bi-214 Bi-214

    KKDC: 71.7 kg∙y: T1/2 = 1.2 (0.7-4.2)·1025

    = 0.44 (0.24 – 0.58) eV (3σ)

    Heidelberg-Moskau Experiment.

    BI~0.12

  • Ø 10 m

    Ø 4 m

    H 1

    0 m

    H 2

    .5 m

    Ø 2.1 m

    water: γ & n shield,

    Cherenkov medium

    for μ veto

    LAr

    stainless

    steel cryostat

    w Cu shield,

    Rn tight

    10 cm electroformed Cu

    30 cm PE,

    active μ veto,

    Rn tight box

    *

    * LAr can be also active shield!

    GERDA: low Z shield, underground

    bare Ge diodes in high-purity LAr MAJORANA: high Z, deep underground

    Ge diodes housed in vacuum cryostat,

    ultra-high-purity electroformed Cu shield

    α(LAr) = 0.050/cm

    α(H2O) = 0.043/cm

    α(Cu) = 0.34/cm

    α(Pb) = 0.48/cm

    45 cm lead

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Introduction generic external background shields

  • GERDA

    storage tanks

    LAr for cool down and filling

    taken from storage tank. dep

    loyed

    LA

    r / t

    on

    s

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    Status cool down and filling of cryostat

    date

  • calibration: deviations from linearity

    preamps

    (88K)

    2.33kg

    2.32kg

    2.96kg

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle

    started in June 2010

    using 3 refurbished Genius-TF natGe-diodes (7.61 kg)

    NB ► p-type / coaxial ► ‘low background’ diodes

    commissioning calibration: linearity

  • muon induced rate ~ 0.01 cts/(keV∙kg∙year)

    veto efficiency >94% (system still incomplete)

    preamps

    (88K)

    2.33kg

    2.32kg

    2.96kg

    started in June 2010

    using 3 refurbished Genius-TF natGe-diodes (7.61 kg)

    NB ► p-type / coaxial ► ‘low background’ diodes

    commissioning muon veto

    PANIC11 28jul 2011 GERDA – status & perspectives K.T.Knöpfle