Pauli exclusion principle (PEP) violation

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2 Pauli exclusion principle (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: 1. searches for PEP-forbidden electronic states 2. searches for PEP-forbidden nuclear states 3. searches for PEP-forbidden electronic transitions 4. searches for PEP-forbidden nuclear transitions

3 Experimental tests for PEP violation Since 1948 many experimental tests of CNC processes have been performed The first test was the search for possible PEP-forbidden (PEPf) electronic states The best sensitivities obtained for 4 classes of experiments for PEPf states are: Experiment Result Ref. searches for PEPf electronic states in atoms searches for PEPf nuclear states searches for PEPf electronic transitions searches for PEPf nuclear transitions [ 12 C']/[ 12 C] < A.S. Barabash et al., JETPL 68 (1998) 112 [Be']/[Be] < D. Javorsek II et al., PRL 85 (2000) 2701 [ 5 He']/[ 4 He] < E. Nolte et al., J. Phys. G 17 (1991) S355 δ 2 < δ 2 < δ 2 < C. Curceanu et al., JP:Con.Se. 306(2011) H. Ejiri et al., NPB(Proc.Sup.) 28A (1992) 219 R. Bernabei et al., EPJC 62 (2009) 327 δ 2 < δ 2 < R. Bernabei et al., EPJC 62 (2009) 327 G. Bellini et al., PRC 81 (2010) 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

4 Charge Non-Conserving (CNC) processes Electric Charge Conservation (CC) is a fundamental law in QED This law is correlated with gauge invariance and photon mass (Weinberg theorem) The possibility that CC may be broken in future unified theories and the relative implications have been discussed in last years since the first experimental test in 1959 At present no self-consistent theories have been developed, but in some modern theories (for example extra-dimensions) these processes can be possible In 1978 Zeldovich, Voloshin and Okun considered problems due to a phenomenological description of CNC processes; they demonstrated that CNC can not be due to a spontaneus breaking if photon mass is zero CNC processes are possible if photon mass is not zero

5 Experimental tests for CNC processes Since 1959 many experimental tests fot CNC processes have been done The first test was the search for electron decay, but other possible processes have been considered The best sensitivities obtained for some CNC precesses are: [S.N.Gninenko, arxiv: ] Process τ (yr) Ref. CNC-β decay ( 71 Ga) > M. Torres et al. MPLA 19 (2004) 639 p anything > V.I. Tretyak & Yu.G. Zdesenko PLB 505 (2001) 59 p invisibile > S. N. Ahmed et al. PRL 92 (2004) n invisibile > T. Araki et al. PRL 96 (2006) pp invisibile > H.O. Back et al. Phys. Lett. B 563 (2003) 23 nn invisibile > T. Araki et al. PRL 96 (2006) nnp invisibile > R.Bernabei et al., EPJA 27,s01(2006)35 npp invisibile > R.Bernabei et al., EPJA 27,s01(2006)35 ppp invisibile > R.Bernabei et al., EPJA 27,s01(2006)35 e - invisible > P.Belli et al. PLB 460(1999)236 e - ν e γ > H. O. Back et al. PLB 525(2002)29 CNC-Elect. Capt. ( 129 Xe) > P.Belli et al. PLB 465(1999)315

6 Roma2,Roma1,LNGS,IHEP/Beijing + by-products and small scale expts.: INR-Kiev + neutron meas.: ENEA-Frascati + in some studies on bb decays (DST-MAE project): IIT Kharagpur, India DAMA/CRYS DAMA/R&D DAMA/LXe low bckg DAMA/Ge for sampling meas. DAMA/NaI DAMA/LIBRA

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

8 phe/kev DAMA/LIBRA set-up 25 x 9.7 kg NaI(Tl) in a 5x5 matrix Two Suprasil-B light guides directly coupled to each bare crystal Two PMTs working in coincidence at the single ph. el. threshold All the materials selected for 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 Calibrations in the same running conditions as production runs Installation in air conditioning + huge heat capacity of shield Monitoring/alarm system; many parameters acquired with 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 Installation Glove-box for calibration Electronics + DAQ

9 The new DAMA/LIBRA set-up ~250 kg NaI(Tl) (Large sodium Iodide Bulk for RAre processes) installing DAMA/LIBRA detectors assembling a DAMA/ LIBRA detector filling the inner Cu box with further shield 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 Residual contaminations in the new DAMA/LIBRA NaI(Tl) detectors: 232 Th, 238 U and 40 K at level of g/g closing the Cu box housing the detectors

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

11 PEP forbidden transitions (1/2) Underground experimental site and highly radiopure set-up allow to reduce background due to PEP-allowed transitions induced by cosmic rays and due to environmental radioactivity 1) Search for non-paulian nuclear processes Example of a process PEP violating: deexcitation of a nucleon from the shell N i to the N 0 lower (full) shell PEPf transition The energy is converted to another nucleon at shell N through strong interaction, resulting to excitation to the unbound region (analogy: Augér emission) PLB 408 (1997) 439 This process was studied in 1997with DAMA/NaI set-up obtaining a sensitivity of > y for 23 Na (68% C.L.) > y for 127 I (68% C.L.) internal s

12 PEP forbidden transitions (2/2) 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 PEP violating electron example of a PEP violating transition of Iodine electron to the full L-shell followed by the atomic shells rearrangement The total released energy (X-ray + Augér electrons) is approximately equal to L- shell ionization potential ( 5 kev) In 1999 DAMA searched for this process in DAMA/NAI obtaining the sensitivity: τ > yr (68% C.L.) [P. Belli et al., PLB 460 (1999) 236]

13 PEP-violating nuclear processes (1/2) 570h running time, optimized for very high energy Above 10 MeV background due to very high energy muons possibly surviving the mountain. EPJC 62 (2009) 327 For PEP violating nuclear processes: events where just one detector fires Mainly particles from internal contaminants Continous line: bkg muon events evaluated by MC not present in the inner core (veto) For E > 10 MeV: 17 events in the upper/lower plane of detector (10 cryst.) 0 events in the central planes of detector (14 cryst.)

14 PEP-violating nuclear processes (2/2) EPJC 62 (2009) 327 I II II II I III III III III IV III III III III III III III III III III I II II II I a) Fermi momentum distribution with k F = 255 Mev/c Lower limit on the mean life for non-paulian proton emission in frame b) (90% C.L.): > 2 x y for 23 Na > 2.5 x y for 127 I b) 56 Fe momentum distribution accounting for correlation effects cautious approach:

15 PEP-violating electron processes EPJC 62 (2009) 327 Exposure: 0.53 ton yr PV > 4.7 x s (90% C.L.) considering normal electromagnetic dipole transition to Iodine K-shell: 0 6 x s d e2 < (90% C.L.). excluded one order of magnitude more stringent than the previous one (ELEGANTS V) This limit can also be related to a possible finite size of the electron in composite models of quarks and leptons providing superficial violation of the PEP [PRL 68(1992)1826] The obtained upper limit on the electron size is: r 0 < cm (energy scale E > 3.5 TeV)

16 Possible electron decay CNC: e - ν e γ e - ν e ν ν electron disappearance e - nothing e - +(A,Z) ν e +(A,Z)* [CNC electron capture] (A,Z) ν e +(A,Z+1)*+ν e [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... η(p nothing) = y [S.L.Dubovsky, JHEP 01(2002)012] η(e nothing) = yr

17 CNC Electron capture (1/5) e - +(A,Z) ν e +(A,Z)* This process is more probable by K-shell electrons! In NaI(Tl) detectors the possible excited states that can be produced by this process are: 127 I four possible excited states: 57.6 kev, kev, 375 kev and 418 kev 23 Na one excited state at 440 kev We search for γ emitted in de-excitation processes kev ( 212 Pb) Exposure 0.87 ton yr kev ( 228 Ac) Na: E K = 1.1 kev I: E K = 33.3 kev DAMA/LIBRA high-energy distribution This process is followed by relaxation of the atomic shells with emissions at energy = electron disappeared bounding energy E b We choose preliminarly to study the production of 127 I in the excited level 418 kev To improve our sensitivity and reduce the background we search for events in coincidence Each CNC electron capture in Iodine produces X-rays/Augér electrons at 33.3 kev and γ emission due to deexcitation processes of 127 I (for example for the 418 kev level γ energies 418 kev, 203 kev and 360 kev)

18 CNC Electron capture (2/5) With Montecarlo simulation ( events) we obtain: EGSnrc Montecarlo simulation Expected distribution for events in coincidence with multiplicity 2 Peak at 33.3 kev Fixing the energy window keV in one detector We expect a peak at energy 418 kev due to 127 I deexcitation EGSnrc Montecarlo simulation Efficiency for this coincidence is 4.5% Selection of events in coincidence with multiplicity 2 in DAMA/LIBRA (0.87 ton yr exposure) in the energy window kev for the first one and kev for the second one gives candidates events for this process Using 1ζ-approach we obtain for the expected signal S < 162 events (68% C.L.) Considering that each Iodine has 2 electron in K-shell we obtain: η > yr (68% C.L.)

19 CNC Electron capture (3/5) Comparison of experimental data distribution with Montecarlo expectation No correlated events in coincidence! Montecarlo expectation Experimental data The experimental data with multiplicity 2 don t show the expected structures for events in coincidence: No evidence for any signal!

20 CNC Electron capture (4/5) χ 2 /dof=1.04 Data selection with multiplicity 2 and the first event in the energy window kev reduces the background of a factor larger than 10 3 Fittting data with a sum of an exponential function for the continous background and the expected peak we obtain: S = - (260 ± 296) events Using Feldman and Cousins procedure: S < 264 events (90% C.L.), corresponding to: τ> yr (90% C.L.) The obtained limit is the best one available for this process in NaI(Tl) Best limits previously obtained for this process by: DAMA/NaI for the production of excited levels of 127 I: η> yr [P.Belli et al., PRC 60(1999)065501] DAMA/LXe for the production of excited levels of 129 Xe: η> yr [P.Belli et al., PLB 465(1999)315]

21 CNC Electron capture (5/5) The transition probability for the CNC process can be written in therm of a process mediated by photon exchange or by W-boson exchange: The CC process can be estimated theoretically (i-initial state, f-final state, n all the possible intermediate states) Considering the excited state at 418 kev and the obtained limit: τ > yr (90% C.L.) [Nuclear Data Sheet 112(2011)1647; T. Kibèdi et al., NIMA 589(2008)202]

22 e - γν e (1/3) [J.N. Bahcall, Rev. Mod. Phys. 50, 881 (1978)] This process has been here considered to complete the study on electron decay although the presence of a residual contamination of 212 Pb in the set-up (peaked at kev) limits the sensitivity in the vicinity of the peak at E γ m e c 2 /2 = 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>=σ i ε i N i /Σ i N i =12.2% DAMA/LIBRA preliminary Exposure 0.87 ton yr Preliminary analysis exploits the total DAMA/LIBRA published exposure: 0.87 ton yr 212 Pb γ-emission at kev estimated by MC considering the experimental energy resolution Fit of the energy distribution in the region [193, 293] kev with a sum of: (i) an exponential; (ii) energy distribution due to 212 Pb decay; (iii) the possible signal due to the CNC process searched for obtained activity of the possible e ν e γ decay (χ 2 /d.o.f. = 1.2): A = - (1.2±1.3) mbq By Feldman & Cousins procedure: A<0.42 mbq (68% C.L.) and:

23 e - γν e (2/3) Further analysis: we selected the 7 detectors (of the 25 ones in DAMA/LIBRA) which have the lower contribution from 212 Pb 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 The fit (χ 2 /d.o.f. = 1.1) gives for the possible e ν e γ decay the activity: A= (1.0 ± 2.2) mbq Using Feldmann and Cousins procedure: A<1.3 mbq at 68% C.L. Largely comparable with the limit obtained above with total exposure Our best limit: τ > yr ε 2 e γν < It is the best-one with NaI(Tl) detectors, the previous one was: η > yr [E.L. Koval chuk et al. JETP Lett. 29, 145 (1979)] Best limits previously obtained by: kg LXe (99.5% 129 Xe) DAMA/Lxe: τ > yr (90% C.L.) [P.Belli et al., PRD 1(2000)117301] kg HP-Ge HD-MW: τ > yr (68% C.L.) [H.V. Klapdor-Kleingrothaus et al., PLB 644(2007)109] - ~4 ton PXE scintillator BOREXINO: τ > yr (90% C.L.) [H. O. Back et al., PLB 525(2002)29]

24 e - γν e (3/3) This process gives the most restrictive limit on ε 2 (< [PLB 525(2002)29]) but from some theoretical considerations this may be not the best way to test CNC: Photon mass non-zero needs a non-spontaneous symmetry breaking to preserve QED The emission of two or more photons is more probable than the emission of one photon Electron decay in neutrinos with a coupling constant g (very little) should be accompained by a huge amount of photons each one transporting a very little amount of energy Electron decay probability: it has been demonstrated that [L. B. Okun et al., Phys. Lett. B 78 (1978) 597 ; M. B. Voloshin et al., Sov. Phys. JETP Lett. 28 (1978) 145 ] Thus, this may be not the best way to study for Charge Non-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.

25 For the PEP-forbidden transitions the obtained limits on electron transition probability by DAMA/LIBRA is the best available in literature. For nuclear transition BOREXINO obtained a more stringent limit in 2010 Process Electron transition Nuclear transition δ 2 (yr) DAMA/LIBRA [EPJC 62 (2009) 327] δ 2 (yr) (best limit by other experiments) [Ref.] < (90% C.L.) < (68% C.L.) ELEGANTSV [NPB(PS) 28A(1992)219] < (90% C.L.) < (90% C.L.) BOREXINO [PRC 81 (2010) ] We obtain the best limits available on the life-time of CNC processes for NaI(Tl) detectors and the best limits available on CNC electron capture. Process τ (yr) (this work) τ (yr) (previous best limit) [Ref.] e - νγ > (90% C.L.) [H. O. Back et al., PLB 525(2002)29] > (68% C.L.) (in NaI) > (68% C.L.) [E.L. Koval chuk et al., JETPL29(1979)145 ] EC-CNC ( 127 I) > (90% C.L.) > (90% C.L.) [P.Belli et al., PRC 60(1999)065501]

26 To compare experimental sensitivity on CNC studied in different processes in 1978 Bahcall proposed a parametrization for CNC admixtures in weak interactions [J.N. Bahcall, Rev. Mod. Phys. 50, 881 (1978)] The violation parameter is given by ε 2 λ CNC /λ CC η CC /η CNC Process ε 2 (this work) ε 2 (previous best limit) [Ref.] e - νγ < (68% C.L.) < (90% C.L.) [H. O. Back et al., PLB 525(2002)29] EC-CNC γ < (90% C.L.) < (90% C.L.) [P.Belli et al., PRC 60(1999)065501] EC-CNC W < (90% C.L.) < (90% C.L.) [P.Belli et al., PRC 60(1999)065501] For CNC Electron Capture the process can be mediated by photon or W-boson and the η CC is given by theoretical estimation with an high uncertainty on parameters used for In this work we studied the possible production of 127 I at the excited level 418 kev, to optimize the ε 2 determination it s needed to study the lower excited level (for 127 I the 57.6 kev excited level)

27 Perspectives for further CNC investigations with DAMA/LIBRA (1/2) Other possible studies: Complete the search for 23 Na and 127 I 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 Exclusion Principle violation Possible studies on electron disappearance from L-shelll can be pursued Considering η e invisible (from K-shell) η e invisible (from L-shell) [PLB 460 (1999) 236] and that the electron PEP-forbidden transitions give the same experimental signal of electron disappearance for this electron s decay From η e invisible (K-shell) < s we can estimate an experimental sensitivity for η e invisible (from L-shell) years

28 [S.L.Dubovsky, JHEP 01(2002)012] Perspectives for further CNC investigations with DAMA/LIBRA (2/2) Search for particle disappearance can constrain theoretical models with extradimensions where particles are considered localized in a three-brane world. In this scenario particles at low energy are described by the eigenvalue: E=E 0 -iγ/2 where Γ is a resonance which can be interpreted as a four-dimensional metastable particle Particles disappearance is due to tunneling from the three-brane world to the extra-dimension. Γ depends on the number of extradimensions n For electron disappearance considering k Planck mass GeV the best available limit on η e nothing constrains the number of extradimension to n > 2 (η e nothing for n=3 is yr) The estimated sensitivity on η e nothing could be used to give a more stringent limit on the number of extradimensions

29 Perspectives for PEP investigations with DAMA/LIBRA PLB 460 (1999) 236 Search for non-paulian electronic transitions to L-shell Accessible sensitivity with DAMA/LIBRA η e invisible years 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 energy thresholds The lowering of the software energy threshold of the experiment down to about 1 kev may give the possibility to investigate for the first time processes involving Sodium K- shell ( 1 kev)

30 If something in fundamental physics can be tested, then it absolutely must be tested [L.B. Okun]