Probing hadronic axions with the CAST calorimeter · 2018. 6. 8. · Probing hadronic axions with...
Transcript of 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-excitationIII. The CAST γ-calorimeter & results
Juan I. Collar, David W. Miller, Joaquin D. VieiraThe University of Chicago
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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
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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)
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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
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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
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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
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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
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Particle identification
α / γ separation from detector calibrations
αγ
We actually expect veryfew α events since CWO so pure
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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
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• 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
gΦ
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
gΦ
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.
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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!
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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
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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
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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,…
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Detector Parameters
Resolution versus energy Efficiency for full energy deposition
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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
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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
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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