Probing hadronic axions with the CAST calorimeter · 2018. 6. 8. · Probing hadronic axions with...

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18 May 2006 D. W. Miller, Chicago 1 High-Energy Axion Detection: Probing hadronic axions with the CAST calorimeter I. Origin of hadronic axion models and constraints II. Axion emission by nuclear de-excitation III. The CAST γ-calorimeter & results Juan I. Collar, David W. Miller, Joaquin D. Vieira The University of Chicago

Transcript of Probing hadronic axions with the CAST calorimeter · 2018. 6. 8. · Probing hadronic axions with...

  • 18 May 2006 D. W. Miller, Chicago 1

    High-Energy Axion Detection: Probing hadronic axions with

    the CAST calorimeter

    I. Origin of hadronic axion models and constraints

    II. Axion emission by nuclear de-excitationIII. The CAST γ-calorimeter & results

    Juan I. Collar, David W. Miller, Joaquin D. VieiraThe University of Chicago

  • 18 May 2006 D. W. Miller, Chicago 2

    KSVZTree-level couplings to quarks

    suppressed→ Evades constraints of DFSZ model→ Nucleon coupling still possible

    Origin of hadronic axions

    • The PQ / Weinberg & Wilczek axion was pinned to the weak scale, resulting in ma~ 0.1-1 MeV– Quickly ruled out experimentally

    (e.g. quarkonium and kaon decays)

    • New models developed to evade such constraints:– Adjustment of the PQ scale (fa→ >106 GeV)– Modification of couplings

    DSFZAxion couples to Fermions and photons

    → Less experimentally favored

  • 18 May 2006 D. W. Miller, Chicago 3

    Hadronic axion window

    • SN1987A hadronic axion constraints (via gaNN)– For ~10-2 < ma< ~2-5 eV, axions

    would have carried away too much energy from SN1987a

    • The so-called “hadronic axion window” is ~2-5 < ma< ~20 eV

    “Experiments probing distinct properties of axions, even if redundant in the context of a

    particular model, provide independent constraints on theories incorporating the PQ symmetry.”[1]

    Telescope/lab limits in gaγγ vs ma space[1] F. T. Avignone, III, et al. PRD37, 618 (1988)

  • 18 May 2006 D. W. Miller, Chicago 4

    Axion-nucleon coupling: gaNN• gaNN derives from axion-light meson mixing

    –– independentindependent of the U(1)PQ charges that are implicit in KSVZ (i.e. hadronic) axion models

    • As a pseudoscalar object, carries JP = 0-, 1+, 2-, …– M1 nuclear transitions could (should?!) emit axions

    • Axion-nucleon coupling explicitly as

    Where g0 and g3 are the isoscalar and isovector axial-current contributions, respectively

    aggiagiL

    NN

    NaNNNaNN

    )(

    3305

    5

    ψτγψψγψ

    +−=−=

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    Nuclear de-excitation via axions• For anyany (e.g. thermally)

    excited M1 nuclear transition

    drrrNDrdE

    dΦ sunRa

    Ea

    a 2

    02 4 )(

    41 πρ

    π⋅⋅= ∫

    ]s [g 1 1-1-γγ τ

    BNN aNa ⋅⋅ΓΓ⋅=

    ( )

    2

    10

    10

    3

    )(2/121

    ⎥⎦

    ⎤⎢⎣

    ⎡−+−

    +⎟⎟⎠

    ⎞⎜⎜⎝

    ⎛=

    ΓΓ

    ημβμβ

    πα γγgg

    kkaa

    DD = Gaussian DopplerBroadening term

    Axion emission per gram solar mass, per sec

    BB = the Boltzmannfactor for thermally excited nuclear state

    NNNN = # density of the isotope

    Axion-photon branching ratio

    ττγγ = lifetime of excited nuclear state

    ALL of the decay channel-specific axion physics is contained in β and η→ nuclear structure dependent

    terms

  • 18 May 2006 D. W. Miller, Chicago 6

    Decay channels and signal• A few M1 transition decays

    available from solar core: p + d → 3He + a (5.5 MeV)7Li* → 7Li + a (0.48 MeV)23Na* → 23Na + a (0.44 MeV)

    • Give mono-energetic axions at the decay energy– Detector signal will of course

    include effects such as escape peaks (for Ea > 1.2 MeV)

    • γ-ray energy axions have improved probability of conversion for a helioscope

    [ ] 222

    2 )cos(21)2/( aaa EqLqBgP ∝−=→ γγγ

    Low-E axions(5 keV)

    High-E axions(1-60 MeV)

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    The CAST high-energy calorimeterDetector design goals• Maximize sensitivity to γ-ray

    conversion photons– A dense crystal works well

    • Maintain minimalist design due to CAST constraints– Minimal lead shielding +

    muon veto• Search for several decay several decay

    channels and other possible channels and other possible new new pseudoscalarpseudoscalar bosonsbosons– So maintain good photon

    efficiency & dynamic range for E > 100 MeV

    Chicago calorimeter

    adjustable platform for alignment

    MicroMegas Detector (transparent above

    ~102 keV)X-ray Telescope

  • 18 May 2006 D. W. Miller, Chicago 8

    Large scintillating crystal (CdWO4)Very pure & high γ efficiencyLow-background PMTOffline particle identificationEnv. radon displacementPlastic muon vetoThermal neutron absorberLow 0.2 MeV energy threshold~100 MeV dynamic rangeCompact XIA Polaris - Digital Gamma Spectrometer

    CWO PMT Power

    Lead shielding

    Low-backgroundAncient Lead

    Plastic scintillatorMuon veto

    22 cm58 cm

    The CAST high-energy calorimeter

  • 18 May 2006 D. W. Miller, Chicago 9

    Front ViewFront View

    Side ViewSide View

    ~4~4ππPlastic Muon Plastic Muon

    VetoVeto

    CWO CWO CrystalCrystal

    Light Light guideguide

    Brass support Brass support tubetube

    Shielded Shielded electronicselectronics

    UltraUltra--low low bckgbckg PbPb

    GammasGammas(from magnet bore)(from magnet bore)

    Pb shieldingPb shieldingMuon veto PMTMuon veto PMT

    Characteristic pulse

    ~16μsrate~4 Hz

    Radon Radon displdispl. & . & borated borated thermalthermal

    n absorbern absorber

    Large CWO (good particle Large CWO (good particle ID, ID, radiopureradiopure, efficient), efficient)

    LowLow--BCKG BCKG PMTPMT

    22 cm

    58 cm

  • 18 May 2006 D. W. Miller, Chicago 10

    Particle identification

    α / γ separation from detector calibrations

    αγ

    We actually expect veryfew α events since CWO so pure

  • 18 May 2006 D. W. Miller, Chicago 11

    A. Data acquisition– Digital waveform acquisition @ 40 MHz– Muon veto coincidence rejection (95%

    of μ events)B. Offline processing

    – Livetime calculation via LED pulser– Particle identification cuts– Correction for detector systematics

    (temp, position)– BCKG: 2·10-6 cm-2 s-1 kev-1

    C. Background subtractionD. Limits on possible anomalous events

    – Look for Gaussian signals at low energies

    – Look for complex signal shape (including photon escape peaks) at higher energies

    Calorimeter data and operation

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    • Signal: Gaussian peaks E < 10 MeV– E > 10 MeV the functional

    changes due to photonuclear reactions

    • Obtain 95% CL (2σ) for allowed anomalous events at each energy

    • Any signal after subtraction could be a hint towards new physics…

    Tracking dataBackground data

    Best fit (signal)Best fit (bckg)Best fit (sig+bckg)

    95% CL peak

    Looking for evidence in the data

  • 18 May 2006 D. W. Miller, Chicago 13

    • This is tricky…– Production mechanism

    (generally) relies on nuclear coupling

    – Detection mechanism relies on photon coupling

    • It is possible but unlikely that there are cancellations in the PQ symmetry that cause gaγγ~0 but gaNN≠ 0 …in which case we can stop talking now [2]

    aaa

    γaγγ mP

    Φ≤

    → )(γ

    To derive this limit we must: (a)(a)calculate the expected axion flux or (b)(b) make an assumption about

    what it is.

    aγγaaaγ gP m2)( Φ≥Φ →γ

    Limits on axion physics

    [2] D. B. Kaplan, Nucl. Phys. B260, 215 (1985)

    (a) In order to calculate Фa:

    ⎟⎟⎠

    ⎞⎜⎜⎝

    ΓΓ

    ⎟⎟⎠

    ⎞⎜⎜⎝

    ⎛ΓΓ=Φ

    γγτπa

    total

    M12

    1 4

    1

    Ea r

    Гa/ Гγ most difficultp + d → 3He + a : we have concentrated most on this reaction…assumption (b) used, now direct calc.7Li* → 7Li + a23Na* → 23Na + a

    Calcs in progress

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    Improved “limits” using

    max Φaassumption for 5.5 MeV axion

    Self-consistent improved limits possible for several energies of interest, e.g. 5.5 MeV, by using Фa, MAX … but we are in

    the process of calculating Фa for several channels

    (b) Assume Фa, MAX :aaa

    γaγγ mP

    Φ≤

    → )(γ

    Results from the calorimeter: 5.5 MeV(a) Of course, we want an

    expression for Фa• η, β almost impossible to calculate (3-body nuclear decay)• Perhaps we can simplify the expression??? Not sure yet.

  • 18 May 2006 D. W. Miller, Chicago 15

    Conclusions

    • Axion-nucleon coupling will give rise to axion-emission through M1 transitions

    • We have built a gamma-ray detector that is sensitive to several axion decay channels

    • In a generic search in the range 0.3 – 60 MeV, no statistically significant signal has been seen

    • To correctly set limits on the axion parameters (fPQ) more careful calculations of nuclear structure dependent parameters are necessary…IN PROGRESS!

  • 18 May 2006 D. W. Miller, Chicago 16

    Backup slides

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    Details for this data set

    15/09 – 08/11Data taking period (2004)

    0.13Ratio Norm BCKG to Total BCKG

    299 hrs (12 days)Systematics Time (valves open, quenches…)

    117.3 hrs (5 days)117.3 hrs (5 days)Normalized Background TimeNormalized Background Time

    898 hrs (37 days)Total Background Time

    60.3 hrs (2.5 days)60.3 hrs (2.5 days)Tracking TimeTracking Time

    1257 hrs (53 days)1257 hrs (53 days)Total Running TimeTotal Running Time

  • 18 May 2006 D. W. Miller, Chicago 18

    Data processing and results

    0.2633.82100Raw data

    0.10.11.431.4337.437.4FULL DATA TREATMENTFULL DATA TREATMENT

    1.43 0.1

    2.42 0.167

    2.42 0.167

    BCKG BCKG Count rate Count rate

    (Hz)(Hz)

    IntegInteg. . ΦΦ0.30.3--50 50 MeVMeV

    (cm(cm--2 2 secsec--11))

    % data % data keptkept

    37.4PSD analysis and cuts

    (incl. removal of livetime pulser)

    63.4Recursive 40K peak gain shifting

    (temperature correlated)

    63.4Anti-coincidence with muon veto

    ResultResultData treatmentData treatment

  • 18 May 2006 D. W. Miller, Chicago 190.1

    1

    1 10

    MCNP calculated full-energy (peak)efficiency for collimated axion-induced gammas

    CdWO4(r=2.15,l=12)CdWO4(r=2.15,l=7.5)CdWO4(r=2.15,l=5.)

    peak

    effi

    cien

    cy

    E (MeV)

    chosen size (cost and self-absorption also an issue)0

    50

    100

    150

    200

    250

    300

    350

    400

    1.6 1.8 2 2.2 2.4 2.6 2.8

    CWO crystal (l=7.5cm) in Pb shielding (R=4.75cm)response to 1 MeV isotropic bckg

    and collimated axion beam signal (MCNP MonteCarlo)

    peak bckgtotal bckgsignal

    % in

    crea

    se re

    lativ

    e to

    R=1

    .75

    cm

    crystal radius (cm)

    (slig

    htly

    larg

    er

    than

    bor

    e)

    signal/ noiseworse for larger r ->

    0.01

    0.1

    1

    1 10

    efficiency for different crystals

    BGO(r=2.15,l=12)C6F5I(r=2.15,l=20)BaF2(r=2.15,l=12)YAG:Ce(r=2.15,l=12)YAP:Ce(r=2.15,l=12)

    GSO:Ce(r=2.15,l=12)NaI(r=2.15,l=12)CdWO4(r=2.15,l=12)LSO(r=2.15,l=12)PWO(r=2.15,l=12)

    full-

    ener

    gy e

    ffici

    ency

    (1 =

    100

    %)

    gamma energy (MeV)

    (beh

    ind

    LSO

    )

    Crystal selection and Monte Carlo

    • Tested: CWO, BGO, BaF2• MC: CWO, BGO, BaF2,

    PWO, YAG, LSO, NaI,…

  • 18 May 2006 D. W. Miller, Chicago 20

    Detector Parameters

    Resolution versus energy Efficiency for full energy deposition

  • 18 May 2006 D. W. Miller, Chicago 21

    Energy Spectrum• Without position normalized background

    data– Apparent agreement, butbut systematic effect systematic effect

    due to the pointing positiondue to the pointing position of the magnet, as in TPC

    • With position normalization– Error bars increase by factor x2– Systematic effect of position is removedeffect of position is removed

  • 18 May 2006 D. W. Miller, Chicago 22

    Software cuts• Use γ calibrations to

    determine software cuts– Keep 99.7%!!!!!!

    • Of the events above 300 keV…threshold set due to noise events + BCKG

    • Set cuts for:– Energy– Shape of Pulse

    • PID = pulse identification parameter

    – Pulse rise time

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    Look for evidence buried in data• Signal: mono-energetic peaks

    below 10 MeV– Width determined by measured

    detector resolution• Obtain 95% CL (2σ) for

    allowed anomalous events at each energy

    • Above 10 MeV the functional form used becomes more complex (effect of photonuclear reactions)

    • Dedicated search for specific energy, including escape peaks in fit, yields better sensitivity than simple gaussian and full-E efficiency (a first-order approach).

    Example illustrated here iExample illustrated here is s emission at 5.5 MeV emission at 5.5 MeV

    (p + d (p + d →→ He + a He + a …….. a .. a →→ γγγγ))G. Raffelt and L. Stodolsky,

    Phys. Lett. B119, 323 (1982).

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    Residual spectraDifference between signal (solar tracking) and background

    Low energy0.3 – 3 MeV

    Mid energy3 – 10 MeV

    High energy10 – 50 MeV

    3 energy regions to allow for different binning based on detector resolution

  • 18 May 2006 D. W. Miller, Chicago 25

    From counts to photons

    • Use the 95% CL allowed counts at each energy and convolve with– Detector efficiency (ε) – livetime (t)

    γtΦ=Φ

    detlivetime

    counts

    ε