High-Energy Axion Detection: Probing hadronic axions with the CAST calorimeter

Transcription

1 High-Energy Axion Detection: Probing hdronic xions with the CAST clorimeter I. Origin of hdronic xion models nd constrints II. Axion emission by nucler de-excittion III. The CAST γ-clorimeter & results Jun I. Collr, Dvid W. Miller, Joquin D. Vieir The University of Chicgo 18 My 2006 D. W. Miller, Chicgo 1

2 Origin of hdronic xions The PQ / Weinberg & Wilczek xion ws pinned to the wek scle, resulting in m ~ MeV Quickly ruled out experimentlly (e.g. qurkonium nd kon decys) New models developed to evde such constrints: Adjustment of the PQ scle (f >10 6 GeV) Modifiction of couplings DSFZ Axion couples to Fermions nd photons Less experimentlly fvored KSVZ Tree-level couplings to qurks suppressed Evdes constrints of DFSZ model Nucleon coupling still possible 18 My 2006 D. W. Miller, Chicgo 2

3 Hdronic xion window SN1987A hdronic xion constrints (vi g NN ) For ~10-2 < m < ~2-5 ev, xions would hve crried wy too much energy from SN1987 The so-clled hdronic xion window is ~2-5 < m < ~20 ev Experiments probing distinct properties of xions, even if redundnt in the context of prticulr model, provide independent constrints on theories incorporting the PQ symmetry. [1] Telescope/lb limits in g γγ vs m spce 18 My 2006 D. W. Miller, Chicgo 3 [1] F. T. Avignone, III, et l. PRD37, 618 (1988)

4 Axion-nucleon coupling: g NN g NN derives from xion-light meson mixing independent of the U(1) PQ chrges tht re implicit in KSVZ (i.e. hdronic) xion models As pseudosclr object, crries J P = 0 -, 1 +, 2 -, M1 nucler trnsitions could (should?!) emit xions Axion-nucleon coupling explicitly s L NN = iψ = iψ N N γ g 5 NN N γ ( g + g τ 3) ψ 5 0 ψ 3 N Where g 0 nd g 3 re the isosclr nd isovector xil-current contributions, respectively 18 My 2006 D. W. Miller, Chicgo 4

5 Nucler de-excittion vi xions For ny (e.g. thermlly) excited M1 nucler trnsition dφ de 1 = 2 4π r D = Gussin Doppler Brodening term B = the Boltzmnn fctor for thermlly excited nucler stte τ γ R D N ρ( r) 4π r sun 2 N N = # density of the isotope = lifetime of excited nucler stte E 0 N = N N Γ Γ B γ τ γ Γ Γ 18 My 2006 D. W. Miller, Chicgo 5 [g dr Axion emission per grm solr mss, per sec γ = 1 2πα s γ ] Axion-photon brnching rtio k k 3 ALL of the decy chnnel-specific xion physics is contined in β nd η nucler structure dependent terms ( μ 1/ 2) 0 g 0 β + g 1 β + ( μ1 η) 2

6 Decy chnnels nd signl A few M1 trnsition decys vilble from solr core: p + d 3 He + (5.5 MeV) 7 Li* 7 Li + (0.48 MeV) 23 N* 23 N + (0.44 MeV) Give mono-energetic xions t the decy energy Detector signl will of course include effects such s escpe peks (for E > 1.2 MeV) γ-ry energy xions hve improved probbility of conversion for helioscope P γ = g 2 γγ Low-E xions (5 kev) ( B / 2) 2 q 2 High-E xions (1-60 MeV) [ ] 2 1 2cos( ql) E 18 My 2006 D. W. Miller, Chicgo 6

7 The CAST high-energy clorimeter Detector design gols Mximize sensitivity to γ-ry conversion photons A dense crystl works well Mintin minimlist design due to CAST constrints Miniml led shielding + muon veto Serch for severl decy chnnels nd other possible new pseudosclr bosons So mintin good photon efficiency & dynmic rnge for E > 100 MeV X-ry Telescope Chicgo clorimeter MicroMegs Detector (trnsprent bove ~10 2 kev) djustble pltform for lignment 18 My 2006 D. W. Miller, Chicgo 7

8 The CAST high-energy clorimeter Lrge scintillting crystl (CdWO 4 ) Very pure & high γ efficiency Low-bckground PMT Offline prticle identifiction Env. rdon displcement Plstic muon veto Therml neutron bsorber Low 0.2 MeV energy threshold ~100 MeV dynmic rnge Compct XIA Polris - Digitl Gmm Spectrometer Plstic scintilltor Muon veto CWO PMT Power 18 My 2006 D. W. Miller, Chicgo 8 Led shielding Low-bckground Ancient Led 58 cm 22 cm

9 Front View Muon veto PMT Pb shielding ~4π Plstic Muon Veto Gmms (from mgnet bore) CWO Crystl Ultr-low low bckg Pb Light guide Low-BCKG PMT 22 cm Rdon displ.. & borted therml n bsorber Chrcteristic pulse ~16μs rte~4 Hz 58 cm Lrge CWO (good prticle Shielded ID, rdiopure,, efficient) electronics Side View Brss support tube 18 My 2006 D. W. Miller, Chicgo 9

10 Prticle identifiction γ α α / γ seprtion from detector clibrtions We ctully expect very few α events since CWO so pure 18 My 2006 D. W. Miller, Chicgo 10

11 Clorimeter dt nd opertion A. Dt cquisition Digitl wveform 40 MHz Muon veto coincidence rejection (95% of μ events) B. Offline processing Livetime clcultion vi LED pulser Prticle identifiction cuts Correction for detector systemtics (temp, position) BCKG: cm -2 s -1 kev -1 C. Bckground subtrction D. Limits on possible nomlous events Look for Gussin signls t low energies Look for complex signl shpe (including photon escpe peks) t higher energies 18 My 2006 D. W. Miller, Chicgo 11

12 Looking for evidence in the dt Signl: Gussin peks E < 10 MeV E > 10 MeV the functionl chnges due to photonucler rections Obtin 95% CL (2σ) for llowed nomlous events t ech energy Any signl fter subtrction could be hint towrds new physics Trcking dt Bckground dt 95% CL pek Best fit (signl) Best fit (bckg) Best fit (sig+bckg) 18 My 2006 D. W. Miller, Chicgo 12

13 Limits on xion physics This is tricky Production mechnism (generlly) relies on nucler coupling Detection mechnism relies on photon coupling It is possible but unlikely tht there re cncelltions in the PQ symmetry tht cuse g γγ ~0 but g NN 0 in which cse we cn stop tlking now [2] Φ γ P γ ( m ) Φ Φ g 2 γγ To derive this limit we must: () clculte the expected xion flux or (b) mke n ssumption bout wht it is. γ gγγ P 18 My 2006 ( m ) Φ 7 Li* 7 Li + γ D. W. Miller, Chicgo 13 [2] D. B. Kpln, Nucl. Phys. B260, 215 (1985) () In order to clculte Ф : Φ = 1 4π r 2 E 1 τ γ Γ Γ M1 totl Г / Г γ most difficult Γ Γ p + d 3 He + : we hve concentrted most on this rection ssumption (b) used, now direct clc. 23 N* 23 N + γ Clcs in progress

14 Results from the clorimeter: 5.5 MeV Improved limits using mx Φ ssumption for 5.5 MeV xion () Of course, we wnt n expression for Ф η, β lmost impossible to clculte (3-body nucler decy) Perhps we cn simplify the expression??? Not sure yet. (b) Assume Ф, MAX : g γγ P Φ γ γ ( m ) Φ Self-consistent improved limits possible for severl energies of interest, e.g. 5.5 MeV, by using Ф, MAX but we re in the process of clculting Ф for severl chnnels 18 My 2006 D. W. Miller, Chicgo 14

15 Conclusions Axion-nucleon coupling will give rise to xion-emission through M1 trnsitions We hve built gmm-ry detector tht is sensitive to severl xion decy chnnels In generic serch in the rnge MeV, no sttisticlly significnt signl hs been seen To correctly set limits on the xion prmeters (f PQ ) more creful clcultions of nucler structure dependent prmeters re necessry IN PROGRESS! 18 My 2006 D. W. Miller, Chicgo 15

16 Bckup slides 18 My 2006 D. W. Miller, Chicgo 16

17 Detils for this dt set Dt tking period (2004) Totl Running Time Trcking Time Totl Bckground Time Normlized Bckground Time Systemtics Time (vlves open, quenches ) Rtio Norm BCKG to Totl BCKG 15/09 08/ hrs (53 dys) 60.3 hrs (2.5 dys) 898 hrs (37 dys) hrs (5 dys) 299 hrs (12 dys) My 2006 D. W. Miller, Chicgo 17

18 Dt processing nd results Result Dt tretment % dt kept BCKG Count rte (Hz) Integ. Φ MeV (cm -2 sec - 1 ) Rw dt Anti-coincidence with muon veto Recursive 40 K pek gin shifting (temperture correlted) PSD nlysis nd cuts (incl. removl of livetime pulser) FULL DATA TREATMENT My 2006 D. W. Miller, Chicgo 18

19 full-energy efficiency (1 = 100%) efficiency for different crystls BGO(r=2.15,l=12) C6F5I(r=2.15,l=20) BF2(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) NI(r=2.15,l=12) CdWO4(r=2.15,l=12) LSO(r=2.15,l=12) PWO(r=2.15,l=12) 1 10 gmm energy (MeV) (behind LSO) Crystl selection nd Monte Crlo Tested: CWO, BGO, BF 2 MC: CWO, BGO, BF 2, PWO, YAG, LSO, NI, MCNP clculted full-energy (pek) efficiency for collimted xion-induced gmms pek efficiency CdWO4(r=2.15,l=12) CdWO4(r=2.15,l=7.5) CdWO4(r=2.15,l=5.) chosen size (cost nd self-bsorption lso n issue) CWO crystl (l=7.5cm) in Pb shielding (R=4.75cm) response to 1 MeV isotropic bckg nd collimted xion bem signl (MCNP MonteCrlo) My 2006 D. W. Miller, Chicgo E (MeV) crystl rdius (cm) % increse reltive to R=1.75 cm pek bckg totl bckg signl (slightly lrger thn bore) signl/ noise worse for lrger r ->

20 Detector Prmeters Resolution versus energy Efficiency for full energy deposition 18 My 2006 D. W. Miller, Chicgo 20

21 Energy Spectrum Without position normlized bckground dt Apprent greement, but systemtic effect due to the pointing position of the mgnet, s in TPC With position normliztion Error brs increse by fctor x2 Systemtic effect of position is removed 18 My 2006 D. W. Miller, Chicgo 21

22 Softwre cuts Use γ clibrtions to determine softwre cuts Keep 99.7%!!!!!! Of the events bove 300 kev threshold set due to noise events + BCKG Set cuts for: Energy Shpe of Pulse PID = pulse identifiction prmeter Pulse rise time 18 My 2006 D. W. Miller, Chicgo 22

23 Look for evidence buried in dt Exmple illustrted here is i emission t 5.5 MeV (p + d He +.. γγ) G. Rffelt nd L. Stodolsky, Phys. Lett. B119, 323 (1982). Signl: mono-energetic peks below 10 MeV Width determined by mesured detector resolution Obtin 95% CL (2σ) for llowed nomlous events t ech energy Above 10 MeV the functionl form used becomes more complex (effect of photonucler rections) Dedicted serch for specific energy, including escpe peks in fit, yields better sensitivity thn simple gussin nd full-e efficiency ( firstorder pproch). 18 My 2006 D. W. Miller, Chicgo 23

24 Residul spectr Difference between signl (solr trcking) nd bckground Low energy MeV Mid energy 3 10 MeV High energy MeV 3 energy regions to llow for different binning bsed on detector resolution 18 My 2006 D. W. Miller, Chicgo 24

25 From counts to photons Use the 95% CL llowed counts t ech energy nd convolve with Detector efficiency (ε) livetime (t) t Φ counts livetime ε det = Φ γ 18 My 2006 D. W. Miller, Chicgo 25