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Pauli exclusion principle (PEP) violationThe 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
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:
Experimental tests for PEP violation
Experiment Result Ref.
searches for PEPf
electronic states in atoms
[12C']/[12C] < 2.5∙10-12
[Be']/[Be] < 9∙10-12
A.S. Barabash et al., JETPL 68 (1998) 112
D. Javorsek II et al., PRL 85 (2000) 2701
searches for PEPf nuclear
states[5He']/[4He] < 2∙10-15 E. Nolte et al., J. Phys. G 17 (1991) S355
searches for PEPf
electronic transitions
δ2< 4.7∙10-29
δ2< 1.1∙10-46
δ2 < 1.3∙10-47
C. Curceanu et al., JP:Con.Se. 306(2011)012036
H. Ejiri et al., NPB(Proc.Sup.) 28A (1992) 219
R. Bernabei et al., EPJC 62 (2009) 327
searches for PEPf nuclear
transitions
δ2 < 3-4∙10-55
δ2< 4.1∙10-60
R. Bernabei et al., EPJC 62 (2009) 327
G. Bellini et al., PRC 81 (2010) 034317
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
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 (Weinbergtheorem)
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 bepossible
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
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:
Experimental tests for CNC processes
Process τ (yr) Ref.
CNC-β decay (71Ga) >1.4∙1027 M. Torres et al. MPLA 19 (2004) 639
p→anything >4∙1023 V.I. Tretyak & Yu.G. Zdesenko PLB 505 (2001) 59
p→invisibile >2.1∙1029 S. N. Ahmed et al. PRL 92 (2004) 102004
n→invisibile >5.8∙1029 T. Araki et al. PRL 96 (2006) 101802
pp→invisibile >5.0∙1025 H.O. Back et al. Phys. Lett. B 563 (2003) 23
nn→invisibile >1.4∙1030 T. Araki et al. PRL 96 (2006) 101802
nnp→invisibile >1.4∙1022 R.Bernabei et al., EPJA 27,s01(2006)35
npp→invisibile >2.7∙1022 R.Bernabei et al., EPJA 27,s01(2006)35
ppp→invisibile >3.6∙1022 R.Bernabei et al., EPJA 27,s01(2006)35
e-→invisible >2.4∙1024 P.Belli et al. PLB 460(1999)236
e-→νeγ >4.6∙1026 H. O. Back et al. PLB 525(2002)29
CNC-Elect. Capt. (129Xe) >3.7∙1024 P.Belli et al. PLB 465(1999)315
[S.N.Gninenko, arXiv:0707.3492]
DAMA/R&DDAMA/LXe low bckg DAMA/Ge
for sampling meas.
DAMA/NaI
DAMA/LIBRA
http://people.roma2.infn.it/dama
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/LXe: results on 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]
• CNC decay 139La 139Ce [UJP51(2006)1037]
DAMA/R&D set-up: results on CNC processes
• 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]
DAMA/NaI: results on CNC processes and PEPv
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
5.5-7.5 phe/keV
DAMA/LIBRA set-up
• 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
Glove-box for
calibration
Electronics + DAQ
Installation
Glove-box for
calibration
Electronics + DAQ
Installation
• 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
The new DAMA/LIBRA set-up ~250 kg NaI(Tl)(Large sodium Iodide Bulk for RAre processes)
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:
232Th, 238U and 40K at level of 10-12 g/g
installing DAMA/LIBRA detectors
assembling a DAMA/ LIBRA detector
filling the inner Cu box with further shield
closing the Cu box
housing the detectors
...calibration procedures
• Radiopurity,performances, procedures, etc.: NIMA592(2008)297
• Results on DM particles: DM Annual Modulation Signature: EPJC56(2008)333, EPJC67(2010)39
Results on rare processes: PEP violation in Na and I: EPJC62(2009)327
1) Search for non-paulian nuclear processes
This process was studied 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.)
Example of a process PEP violating:deexcitation of a nucleon from the shell Ni to theN0 lower (full) shell
The energy is converted to another nucleon atshell N through strong interaction, resulting toexcitation to the unbound region (analogy:Augér emission)
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
PEPf
transition
internal ’s
PLB 408 (1997) 439
Electronic configuration schema of I anion (54 electrons) in Na+I- crystal
K
L
M
s p d
example of a PEP violating transition of Iodine electron to the full L-shell followedby the atomic shells rearrangement
The total released energy (X-ray + Augér electrons) is approximately equal to L-shell ionization potential ( ≈ 5 keV)
PEP violating electron
PEP forbidden transitions (2/2)
2) Search for non-paulian electronic transitions to L-shell
In 1999 DAMA searched for this process in DAMA/NAI obtaining the sensitivity:
τ > 4.2×1024 yr (68% C.L.) [P. Belli et al., PLB 460 (1999) 236]
PEP-violating nuclear processes (1/2)
Above 10 MeV background due to very high energy muons
possibly surviving the mountain.
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.)
EPJC 62 (2009) 327570h running time, optimized for very high energy
For PEP violatingnuclear processes:events where just one detector fires
Mainly particlesfrom internal contaminants
I II II II I
III III III III
III III III III III
III III III III III
I II II II I
Lower limit on the mean life for non-paulianproton emission in frame b) (90% C.L.):
> 2 x 1025 y for 23Na > 2.5 x 1025 y for 127I
cautious approach:
PEP-violating nuclear processes (2/2)
IV
a) Fermi momentum distribution with
kF = 255 Mev/c
b) 56Fe momentum distribution accounting
for correlation effects
EPJC 62 (2009) 327
Exposure: 0.53 ton × yr
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
de2 < 1.28 10-47 (90% C.L.).
PV > 4.7 x 1030 s (90% C.L.)
excluded
considering normal electromagneticdipole transition to Iodine K-shell:
0 ≈ 6 x 10-17 s
one order of magnitude more stringent
than the previous one (ELEGANTS V)
PEP-violating electron processes
The obtained upper limit on the electron size is:
r0 < 5.710-18 cm (energy scale E > 3.5 TeV)[PRL 68(1992)1826]
EPJC 62 (2009) 327
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]
electron disappearance
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) = 9.2×1034 y η(e → nothing) = 9.0×1025 yr[S.L.Dubovsky, JHEP 01(2002)012]
CNC Electron capture (1/5)e-+(A,Z) → νe+(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: 127I four possible excited states: 57.6 keV, 202.8 keV, 375 keV and 418 keV23Na one excited state at 440 keV
We search for γ emitted in de-excitation processes
238.6 keV(212Pb)
338.3 keV(228Ac)
DAMA/LIBRA high-energy distribution
This process is followed by relaxation of the atomic shellswith emissions at energy = electron disappeared boundingenergy Eb
Na: EK = 1.1 keV
I: EK = 33.3 keV
We choose preliminarly to study the production of 127I 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 de-
excitation processes of 127I (for example for the 418 keV level γ energies 418 keV, 203 keV and 360 keV)
Exposure 0.87 ton × yr
CNC Electron capture (2/5)With Montecarlo simulation (3600000 events) we obtain:
Expected distribution for
events in coincidence
with multiplicity 2
Peak at 33.3 keV Fixing the energy
window 24.7-41.9keV
in one detector
We expect a peak
at energy 418 keV
due to 127I de-
excitation
Selection of events in coincidence with multiplicity 2 in DAMA/LIBRA (0.87 ton×yr
exposure) in the energy window 24.7-41.9 keV for the first one and 371.6-464.4 keV for
the second one gives 26273 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 > 1.9 × 1024 yr (68% C.L.)
Efficiency for this
coincidence is 4.5%
EGSnrc Montecarlo simulation EG
Sn
rcM
on
teca
rlo s
imu
latio
n
CNC Electron capture (3/5)
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!
No correlated events in coincidence!
Comparison of experimental data distribution
with Montecarlo expectation
CNC Electron capture (4/5)Data selection with multiplicity 2 and the first event
in the energy window 24.7-41.9 keV reduces the
background of a factor larger than 103
Fittting data with a sum of an exponential function
for the continous background and the expected peak
we obtain: S = - (260 ± 296) events
χ2/dof=1.04
Best limits previously obtained for this process by:
DAMA/NaI for the production of excited levels of 127I: η> 2.4·1023 yr
[P.Belli et al., PRC 60(1999)065501]
DAMA/LXe for the production of excited levels of 129Xe: η>3.7·1024 yr
[P.Belli et al., PLB 465(1999)315]
The obtained limit is the best one available for this process in NaI(Tl)
Using Feldman and Cousins procedure:
S < 264 events (90% C.L.), corresponding to:
τ>1.2 × 1024 yr (90% C.L.)
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:
[Nuclear Data Sheet 112(2011)1647; T. Kibèdi et al., NIMA 589(2008)202]
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 > 1.2 × 1024 yr (90% C.L.)
Preliminary analysis exploits the total DAMA/LIBRA published
exposure: 0.87 ton × yr212Pb γ-emission at 238.6 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 212Pb
decay; (iii) the possible signal due to the CNC process searched
for obtained activity of the possible e → νeγ decay
(χ2/d.o.f. = 1.2): A = - (1.2±1.3) mBq
By Feldman & Cousins procedure: A<0.42 mBq (68% C.L.) and:
[J.N. Bahcall, Rev. Mod. Phys. 50, 881 (1978)]
Exposure 0.87 ton × yr
This process has been here considered to complete the study on electron decay although the presence of a
residual contamination of 212Pb in the set-up (peaked at 238.6 keV) limits the sensitivity in the vicinity
of the peak at Eγ ≈ 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%
DAMA/LIBRA
preliminary
e-→γνe (1/3)
Further analysis: we selected the 7 detectors (of the 25 ones in DAMA/LIBRA) which have thelower 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
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.
Largely comparable with the limit obtained above with total
exposure
Best limits previously obtained by:
- 6.5 kg LXe (99.5% 129Xe) DAMA/Lxe: τ > 2.0×1026 yr (90% C.L.) [P.Belli et al., PRD 1(2000)117301]
-10.96 kg HP-Ge HD-MW: τ > 1.9×1026 yr (68% C.L.) [H.V. Klapdor-Kleingrothaus et al., PLB 644(2007)109]
- ~4 ton PXE scintillator BOREXINO: τ > 4.6×1026 yr (90% C.L.) [H. O. Back et al., PLB 525(2002)29]
Our best limit: τ > 4.0×1025 yr
ε2e→γν < 2.6×10−98
It is the best-one with NaI(Tl) detectors, the previous one
was: η > 3.5×1023 yr [E.L. Koval’chuk et al. JETP Lett. 29, 145 (1979)]
Exposure 0.25 ton × yr
e-→γνe (2/3)
e-→γνe (3/3)This process gives the most restrictive limit on ε2 (<2.3·10−99 [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 beaccompained by a huge amount of photons each one transporting a very little amount ofenergy
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 isnecessary to remind that any “a priori” argument could give wrong results.So experimental tests of the underlying principles of physics should be continueddespite temporary difficulties and lack of theoretical motivation.
Process τ (yr) (this work) τ (yr) (previous best limit) [Ref.]
e-→νγ>1.3×1025 (68% C.L.)
>4.6×1026 (90% C.L.) [H. O. Back et al., PLB 525(2002)29]
(in NaI) >3.5×1023 (68% C.L.) [E.L. Koval’chuk et al., JETPL29(1979)145 ]
EC-CNC (127I) >1.2×1024 (90% C.L.) >2.4·1023 (90% C.L.) [P.Belli et al., PRC 60(1999)065501]
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.
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
Processδ2 (yr) DAMA/LIBRA
[EPJC 62 (2009) 327]δ2 (yr) (best limit by other experiments) [Ref.]
Electron
transition<1.28×10-47 (90% C.L.) <1.1·10-46 (68% C.L.) ELEGANTSV [NPB(PS) 28A(1992)219]
Nuclear
transition<3-4×10-55 (90% C.L.) <4.1·10-60 (90% C.L.) BOREXINO [PRC 81 (2010) 034317]
Process ε2 (this work) ε2 (previous best limit) [Ref.]
e-→νγ <2.6×10-98 (68% C.L.) <2.3×10-99 (90% C.L.) [H. O. Back et al., PLB 525(2002)29]
EC-CNC γ <2.5×10-25 (90% C.L.) <9.6·10-26 (90% C.L.) [P.Belli et al., PRC 60(1999)065501]
EC-CNC W <5.0×10-39 (90% C.L.) <4.8×10-40 (90% C.L.) [P.Belli et al., PRC 60(1999)065501]
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 ε2 ≈ λCNC/λCC ≈ ηCC/ηCNC
For CNC Electron Capture the process can be mediated by photon or W-boson and
the ηCC is given by theoretical estimation with an high uncertainty on parameters
used for
In this work we studied the possible production of 127I at the excited level 418 keV,
to optimize the ε2 determination it’s needed to study the lower excited level (for 127I
the 57.6 keV excited level)
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
Possible studies on electron disappearance from L-shelll can be pursued
Considering ηe→invisible (from K-shell) ≈ 0.024 ηe→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 ηe→invisible (K-shell) < 4.7 × 1030 s we can estimate an experimental
sensitivity for ηe→invisible (from L-shell) ≈ 1025 years
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
[S.L.Dubovsky, JHEP 01(2002)012]
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=E0-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 ≈ 1019 GeV the best
available limit on ηe→nothing constrains the number of extradimension to n > 2
(ηe→nothing for n=3 is 9×1025 yr)
The estimated sensitivity on ηe→nothing could be used to give a more stringent
limit on the number of extradimensions
Perspectives for further CNC investigations with DAMA/LIBRA (2/2)
Search for non-paulianelectronic transitions to L-shell
Accessible sensitivity with
DAMA/LIBRA ηe→invisible ≈ 1025 years
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)
Perspectives for PEP investigations with DAMA/LIBRA
Search for non-paulian electronic transitions to K-shellDAMA/LIBRA upgrade (2010)
• Replacement of all the PMTs with higher Q.E. ones
• Goal: lowering the energy thresholds
PLB 460 (1999) 236
“If something in fundamental physics can be tested, then it absolutely must be tested“ [L.B. Okun]