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Pauli exclusion principle (PEP) violation

Pauli exclusion principle (PEP) violation

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Pauli exclusion principle (PEP) violation

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  1. Pauliexclusionprinciple (PEP) violation • The exclusion principle was postulated by Pauli in 1925 to explain atomic spectra and regularities of the Periodic Table of the elements. • In modern Quantum Field Theory the PEP is related to the spin statistics and automatically arises from the anti-commutation property of the fermion creation and destruction operators • Although all the well known successes of the PEP in explaining phenomena the exact validity of the PEP is still an open question • Despite the fact that the foundation of PEP lies deep in the structure of Quantum Field Theory a simple and easy explanation is still missing • General principles of quantum theory do not require that all the particles must be either fermions or bosons, but also generalized statistics could be considered • Similar arguments have inspired many experimental tests of the PEP validity with improved sensitivities since the first pioneering experiments in 1948 [Ph.Rev.73(1948)1472] In particular, four classes of experiments have been considered so far: • searches for PEP-forbidden electronic states • searches for PEP-forbidden nuclear states • searches for PEP-forbidden electronic transitions • searches for PEP-forbiddennucleartransitions

  2. Experimentaltestsfor PEP violation • Since 1948 manyexperimentaltests of CNC processeshavebeenperformed • The first test was the searchforpossiblePEP-forbidden (PEPf) electronic states • The best sensitivitiesobtainedfor4 classes of experiments for PEPf states are: It is worth noting that in 1980 Amado & Primakoff [PRC 22(1908)1338] criticized the possibility of testing the Pauli principle by looking for PEP-forbidden transitions. However their arguments can be evaded either as demonstrated in PRL 68(1992)1826 or PRD39(1989)2032 (for example extra dimensions could lead to apparent PEP violations) Thus experimental tests of PEPf transitions can also investigate the deep structure of matter and/or of space-time

  3. ChargeNon-Conserving (CNC) processes • ElectricChargeConservation (CC) is a fundamentallaw in QED • Thislawiscorrelatedwithgaugeinvariance and photon mass (Weinbergtheorem) • The possibilitythat CC maybebroken in future unifiedtheories and the relative implicationshavebeendiscussed in last yearssince the first experimental test in 1959 • At present no self-consistenttheorieshavebeendeveloped, but in some moderntheories (forexample extra-dimensions) theseprocesses can bepossible • In 1978 Zeldovich, Voloshin and Okunconsideredproblems due to a phenomenologicaldescriptionof CNC processes; theydemonstratedthat CNC can notbe due to a spontaneusbreakingifphoton mass is zero CNC processes are possibleifphoton mass isnot zero

  4. Experimentaltestsfor CNC processes • Since 1959 manyexperimentaltests fot CNC processeshavebeendone • The first test was the searchfor electron decay, butotherpossibleprocesseshavebeenconsidered • The best sensitivitiesobtainedfor some CNC precesses are: [S.N.Gninenko, arXiv:0707.3492]

  5. Roma2,Roma1,LNGS,IHEP/Beijing + by-products and small scale expts.: INR-Kiev + neutronmeas.: ENEA-Frascati + in some studies on bbdecays (DST-MAE project): IIT Kharagpur, India DAMA: an observatory for rare processes @LNGS DAMA/CRYS DAMA/R&D low bckg DAMA/Ge for sampling meas. DAMA/LXe DAMA/NaI DAMA/LIBRA

  6. DAMA/LXe: resultson CNC processes • Electron decay into invisible channels [Astrop.P.5(1996)217] • Nuclear level excitation of 129Xe during CNC processes [PLB465(1999)315] • N, NN decay into invisible channels in 129Xe [PLB493(2000)12] • Electron decay: e-νeγ[PRD61(2000)117301] • CNC decay 136Xe  136Cs[Beyond the Desert(2003)365] • N, NN, NNN decay into invisible channels in 136Xe • [EPJA27 s01 (2006) 35] DAMA/R&D set-up: resultson CNC processes • CNC decay 139La 139Ce [UJP51(2006)1037] DAMA/NaI: resultson CNC processes and PEPv • Possible Pauli exclusion principle violation [PLB408(1997)439] • CNC processes [PRC60(1999)065501 ] • Electron stability and non-paulian transitions in Iodine atoms (by L-shell) [PLB460(1999)235]

  7. DAMA/LIBRA set-up • 25 x 9.7 kg NaI(Tl) in a 5x5 matrix • TwoSuprasil-B light guidesdirectlycoupledtoeach bare crystal • TwoPMTsworking in coincidence at the single ph. el. threshold • All the materialsselectedfor low radioactivity • Multicomponent passive shield (>10 cm of Cu, 15 cm of Pb + Cd foils, 10/40 cm Polyethylene/paraffin, about 1 m concrete, mostly outside the installation) • Three-level system to exclude Radon from the detectors 5.5-7.5 phe/keV • Calibrations in the same running conditions as production runs • Installation in air conditioning + huge heat capacity of shield • Monitoring/alarm system; manyparametersacquiredwith the production data • Pulse shape recorded by Waweform Analyzer Acqiris DC270 (2chs per detector), 1 Gsample/s, 8 bit, bandwidth 250 MHz • Data collected from single photoelectron up to MeV region, despite the hardware optimization was done for the low energy

  8. The newDAMA/LIBRAset-up~250 kg NaI(Tl) (LargesodiumIodideBulk forRAreprocesses) installing DAMA/LIBRA detectors detectors during installation; in the central and right up detectors the new shaped Cu shield surrounding light guides (acting also as optical windows) and PMTs was not yet applied assembling a DAMA/ LIBRA detector filling the inner Cu box with further shield Residualcontaminations in the new DAMA/LIBRA NaI(Tl) detectors: 232Th, 238U and 40K at levelof 10-12 g/g closing the Cu box housing the detectors

  9. ...calibrationprocedures Results on rare processes: PEP violation in Na and I: EPJC62(2009)327 • Radiopurity,performances, procedures, etc.:NIMA592(2008)297 • Results on DM particles: DMAnnual Modulation Signature: EPJC56(2008)333, EPJC67(2010)39

  10. PEP forbidden transitions (1/2) Undergroundexperimentalsite and highlyradiopureset-up allow to reduce background due to PEP-allowedtransitionsinduced by cosmicraysand due to environmentalradioactivity 1) Search for non-paulian nuclear processes Exampleof a processPEP violating: deexcitationof a nucleonfrom the shell Nito the N0 lower (full) shell The energyisconvertedtoanothernucleon at shell N through strong interaction, resultingtoexcitationto the unboundregion (analogy: Augéremission) PEPftransition PLB 408 (1997) 439 Thisprocesswasstudied in 1997 with DAMA/NaI set-up obtaining a sensitivity of  > 0.7 × 1025 y for 23Na (68% C.L.)  > 0.9 × 1025 y for 127I (68% C.L.) internal’s

  11. PEP forbidden transitions (2/2) PEP violating electron 2) Search for non-paulian electronic transitions to L-shell Electronic configuration schema of I anion (54 electrons) in Na+I-crystal M L K s p d exampleof a PEP violatingtransitionofIodine electron to the full L-shellfollowedby the atomicshellsrearrangement The total releasedenergy(X-ray+ Augérelectrons) isapproximatelyequaltoL-shellionizationpotential ( ≈ 5 keV) In 1999 DAMA searched for thisprocess in DAMA/NAI obtaining the sensitivity: τ> 4.2×1024yr (68% C.L.) [P. Belli et al., PLB 460 (1999) 236]

  12. PEP-violatingnuclearprocesses (1/2) EPJC 62 (2009) 327 570h runningtime, optimizedforvery high energy Above 10 MeVbackground due to very high energy muons possibly surviving the mountain. For PEP violatingnuclearprocesses: eventswhere just one detector fires Continousline: bkgmuoneventsevaluatedby MC notpresent in the innercore (veto) • Mainly • particles • from internal contaminants For E > 10 MeV: 17 events in the upper/lowerplaneof detector (10 cryst.) 0 events in the centralplanesof detector (14 cryst.)

  13. PEP-violatingnuclearprocesses (2/2) EPJC 62 (2009) 327 IV Fermi momentumdistributionwith kF= 255 Mev/c b) 56Fe momentumdistribution accounting forcorrelationeffects • Lower limit on the mean life for non-paulian proton emission in frame b) (90% C.L.): • > 2 x 1025 y for 23Na • > 2.5 x 1025 y for 127I cautiousapproach:

  14. PEP-violating electron processes EPJC 62 (2009) 327 Exposure: 0.53 ton × yr tPV> 4.7 x 1030 s (90% C.L.) consideringnormalelectromagneticdipoletransitiontoIodineK-shell: t0 ≈6 x 10-17 s de2 < 1.28  10-47 (90% C.L.). oneorderofmagnitude more stringentthan the previousone (ELEGANTS V) excluded Thislimit can also be related to a possible finite size of the electron in composite models of quarks and leptonsprovidingsuperficialviolation of the PEP The obtained upper limit on the electron sizeis: r0 < 5.710-18 cm (energy scale E > 3.5 TeV) [PRL 68(1992)1826]

  15. electron disappearance Possible electron decay CNC: • e-→νeγ • e-→νe ν ν • e-→nothing • e-+(A,Z) → νe+(A,Z)* [CNC electron capture] • (A,Z) → νe+(A,Z+1)*+νe [CNC β-decay] Searches for invisible decays are also related with extra-dimensions: • Probably, our world is a brane inside higher-dimensional space • Particles can escape from the brane to extra dimensions • “The presence and properties of the extra dimensions will be investigated by looking for any loss of energy from our 3-brane into the bulk” [N.Arkani-Hamed et al., PLB 429(1998)263] • Thus we could expect disappearance of e, p, n... τ(p→nothing) = 9.2×1034 y τ(e → nothing) = 9.0×1025yr • [S.L.Dubovsky, JHEP 01(2002)012]

  16. CNC Electron capture (1/5) e-+(A,Z) → νe+(A,Z)* Thisprocessis more probablebyK-shellelectrons! In NaI(Tl) detectorsthe possibleexcitedstatesthat can beproducedbythisprocess are: 127I fourpossibleexcitedstates: 57.6 keV, 202.8 keV, 375 keV and 418 keV 23Na oneexcited state at 440 keV Wesearchforγemitted in de-excitationprocesses Exposure 0.87 ton × yr 238.6 keV (212Pb) 338.3 keV (228Ac) Na: EK = 1.1 keV I: EK = 33.3 keV DAMA/LIBRA high-energydistribution Thisprocessisfollowedbyrelaxationof the atomicshellswithemissions at energy = electron disappearedboundingenergyEb Wechoosepreliminarlytostudy the production of127I in the excitedlevel 418 keV Toimproveoursensitivity and reduce the background wesearchforevents in coincidence Each CNC electron capture in Iodineproduces X-rays/Augérelectrons at 33.3 keV and γemission due tode-excitationprocessesof127I (forexamplefor the 418 keVlevelγenergies 418 keV, 203 keV and 360 keV)

  17. CNC Electron capture (2/5) With Montecarlo simulation (3600000 events) weobtain: EGSnrc Montecarlo simulation Weexpect a peak at energy 418 keV due to127I de-excitation Expecteddistributionforevents in coincidencewithmultiplicity 2 EGSnrc Montecarlo simulation Peak at 33.3 keV Fixing the energywindow 24.7-41.9keV in one detector Efficiencyforthiscoincidenceis 4.5% Selectionofevents in coincidencewithmultiplicity 2 in DAMA/LIBRA (0.87 ton×yrexposure) in the energywindow 24.7-41.9 keVfor the first one and 371.6-464.4 keVfor the secondonegives 26273 candidateseventsforthisprocess Using 1σ-approachweobtainfor the expectedsignal S < 162 events (68% C.L.) ConsideringthateachIodinehas 2 electron in K-shellweobtain: τ > 1.9 × 1024yr (68% C.L.)

  18. CNC Electron capture (3/5) Comparison of experimental data distribution with Montecarlo expectation No correlatedevents in coincidence! Montecarlo expectation Experimental data The experimental data withmultiplicity 2 don’t show the expectedstructuresforevents in coincidence: No evidenceforanysignal!

  19. CNC Electron capture (4/5) Data selection with multiplicity 2 and the first event in the energywindow 24.7-41.9 keVreducesthe background of a factorlargerthan 103 Fittting data with a sum of an exponentialfunction for the continous background and the expectedpeakweobtain: S = - (260 ± 296) events χ2/dof=1.04 UsingFeldman and Cousins procedure: S < 264 events (90% C.L.), corresponding to: τ>1.2 × 1024yr (90% C.L.) The obtainedlimitis the best oneavailableforthisprocess in NaI(Tl) Best limitspreviouslyobtainedforthisprocessby: DAMA/NaIfortheproductionofexcitedlevelsof127I: τ> 2.4·1023yr [P.Belliet al., PRC 60(1999)065501] DAMA/LXefortheproductionofexcitedlevelsof129Xe: τ>3.7·1024yr [P.Belliet al., PLB 465(1999)315]

  20. CNC Electron capture (5/5) The transitionprobabilityforthe CNC process can bewritten in thermof a processmediatedbyphotonexchange or byW-bosonexchange: The CC process can beestimatedtheoretically (i-initial state, f-final state, n all the possible intermediate states) Considering the excited state at 418 keV and the obtainedlimit: τ > 1.2 × 1024yr(90% C.L.) [Nuclear Data Sheet 112(2011)1647; T. Kibèdiet al., NIMA 589(2008)202]

  21. e-→γνe (1/3) [J.N.Bahcall, Rev. Mod. Phys. 50, 881 (1978)] Thisprocesshasbeenhereconsidered to complete the study on electron decayalthough the presence of a residualcontaminationof 212Pb in the set-up (peakedat 238.6 keV) limits the sensitivity in the vicinity of the peakatEγ ≈ mec2/2 = 255.5 keV searched for . Electrons decays in NaI(Tl) crystals, Cu surrounding the crystals (a total copper mass of 1646 kg has been considered) and crystals light guides (total light guides mass is 50 kg) [the relative contribution are 22% for copper and 2.6% for light guides] are considered. Effective efficiency: <ε>=ΣiεiNi/ΣiNi=12.2% Preliminary analysis exploits the total DAMA/LIBRA published exposure: 0.87 ton × yr 212Pb γ-emission at 238.6 keVestimatedby MC considering the experimentalenergyresolution Fit of the energy distribution in the region [193, 293] keV with a sum of: (i) an exponential; (ii) energy distribution due to 212Pb decay; (iii) the possible signal due to the CNC process searched for obtained activity of the possible e → νeγdecay (χ2/d.o.f. = 1.2): A = - (1.2±1.3) mBq By Feldman & Cousins procedure: A<0.42 mBq (68% C.L.) and: Exposure 0.87 ton × yr DAMA/LIBRA preliminary

  22. e-→γνe (2/3) The fit (χ2/d.o.f. = 1.1) gives for the possible e → νeγ decay the activity: A=−(1.0 ± 2.2) mBq Using Feldmann and Cousins procedure: A<1.3 mBq at 68% C.L. Largelycomparable with the limitobtainedabove with totalexposure • Further analysis: we selected the 7 detectors (of the 25 ones in DAMA/LIBRA) which have the lower contribution from 212Pb residual contamination in the set-up;exposure is 0.25 ton × yr • The same fitting procedure used above has been applied in the same energy range Exposure 0.25 ton × yr Our best limit: τ > 4.0×1025yr ε2e→γν< 2.6×10−98 Itis the best-one with NaI(Tl) detectors, the previousonewas: τ > 3.5×1023yr[E.L. Koval’chuket al. JETP Lett. 29, 145 (1979)] Best limits previously obtained by: - 6.5 kg LXe (99.5% 129Xe) DAMA/Lxe:τ> 2.0×1026yr (90% C.L.) [P.Belli et al., PRD 1(2000)117301] • 10.96 kg HP-GeHD-MW: τ> 1.9×1026yr (68% C.L.) [H.V.Klapdor-Kleingrothauset al., PLB 644(2007)109] • ~4 ton PXE scintillator BOREXINO: τ> 4.6×1026yr(90% C.L.) [H. O. Back et al., PLB 525(2002)29]

  23. e-→γνe (3/3) • Thisprocessgives the mostrestrictivelimit on ε2(<2.3·10−99[PLB 525(2002)29]) but from some theoreticalconsiderationsthismay be not the best way to test CNC: • Photon mass non-zeroneeds a non-spontaneoussymmetrybreakingtopreserve QED • The emissionoftwo or more photonsis more probablethan the emissionofonephoton • Electron decay in neutrinoswith a couplingconstant g (verylittle) shouldbeaccompainedby a hugeamountofphotonseachonetransporting a verylittleamountofenergy Electron decayprobability: ithasbeendemonstratedthat • [L. B. Okun et al., Phys. Lett. B 78 (1978) 597 ; M. B. Voloshinet al., Sov. Phys. JETP Lett. 28 (1978) 145 ] Thus, thismaybenot the best way tostudyforChargeNon-Conservation; but, despite problems with a theoretical treatment of this electron’s decay mode, it is necessary to remind that any “a priori” argument could give wrong results. So experimental tests of the underlying principles of physics should be continued despite temporary difficulties and lack of theoretical motivation.

  24. For the PEP-forbiddentransitionsthe obtainedlimits on electron transitionprobability by DAMA/LIBRA is the best available in literature. Fornucleartransition BOREXINO obtained a more stringentlimit in 2010 Weobtain the best limitsavailableon the life-time of CNC processesfor NaI(Tl) detectors and the best limitsavailable on CNC electron capture.

  25. To compare experimentalsensitivity on CNC studied in differentprocesses in 1978 Bahcallproposed a parametrization for CNC admixtures in weakinteractions [J.N. Bahcall, Rev. Mod. Phys. 50, 881 (1978)] The violationparameterisgivenbyε2 ≈ λCNC/λCC ≈ τCC/τCNC • For CNC Electron Capture the process can bemediatedbyphoton or W-boson and the τCCisgivenbytheoreticalestimationwithan high uncertainty on parametersusedfor • In this work westudied the possible production of127I at the excitedlevel 418 keV, tooptimize the ε2determinationit’s neededtostudy the lowerexcitedlevel (for127I the 57.6 keVexcitedlevel)

  26. Perspectives for further CNC investigations with DAMA/LIBRA (1/2) Other possible studies: • Complete the search for 23Na and 127I CNC Electron-Capture investigating other excited states • Search for possible nucleons disappearance (neutron, proton, diproton...) • Study for possible electrons disappearance CNC processes are correlated to other fundamental questions, in particular searches for invisible decays are related also with: extra-dimensions and Pauli ExclusionPrincipleviolation Possiblestudies on electron disappearance from L-shelll can bepursued Consideringτe→invisible (from K-shell) ≈ 0.024 τe→invisible (from L-shell) [PLB 460 (1999) 236]and that the electron PEP-forbiddentransitionsgive the sameexperimentalsignal of electron disappearance for this electron’s decay Fromτe→invisible (K-shell) < 4.7 × 1030 s we can estimate an experimentalsensitivityforτe→invisible (fromL-shell) ≈ 1025years

  27. Perspectives for further CNC investigations with DAMA/LIBRA (2/2) [S.L.Dubovsky, JHEP 01(2002)012] Searchforparticledisappearance can constraintheoreticalmodelswithextradimensionswhereparticles are consideredlocalized in a three-brane world. In this scenario particles at low energy are describedby the eigenvalue: E=E0-iΓ/2 whereΓis a resonancewhich can be interpretedas a four-dimensionalmetastableparticle Particlesdisappearanceis due totunnelingfrom the three-brane world to the extra-dimension. Γdepends on the number of extradimensions “n” For electron disappearanceconsidering k ≈ Planck mass ≈ 1019GeV the best availablelimit on τe→nothingconstrains the number of extradimension to n > 2 (τe→nothingfor n=3 is 9×1025yr) The estimatedsensitivity on τe→nothingcouldbeusedtogive a more stringentlimit on the numberofextradimensions

  28. Perspectives for PEP investigations with DAMA/LIBRA PLB 460 (1999) 236 Search for non-paulian electronic transitions to L-shell Accessiblesensitivitywith DAMA/LIBRA τe→invisible ≈ 1025years Search for non-paulian electronic transitions to K-shell DAMA/LIBRA upgrade (2010) • Replacement of all the PMTs with higher Q.E. ones • Goal: lowering the energythresholds The lowering of the software energythreshold of the experimentdown to about 1 keV may give the possibility to investigate for the first time processes involving Sodium K-shell (≈1 keV)

  29. Thankyouforattention! “If something in fundamental physics can be tested, then it absolutely mustbetested“ [L.B.Okun]