Diapositiva 1

1
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
2
Outlook

• Nuclear Double Beta Decay
• Neutrino Physics
• Nuclear Matrix Elements
• Experimental Approaches
• Sensitivity
• Experimental Techniques
• Present Situation
• Future Experiments
• Conclusion

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
3
Nuclear Double Beta Decay
Rare Nuclear Decay (A,Z) ? (A,Z2) 2e- ...
occurs in a number of even-even nuclei in A even
multiplets

• bb-2n two neutrino mode
• (A, Z) ? (A, Z2) 2e- 2ne
• allowed in Standard Model
• second order weak transition

• bb-0n neutrinoless mode
• (A, Z) ? (A, Z2) 2e-
• not allowed in Standard Model (DL2)
• neutrino is a massive Majorana particle

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
4
Neutrinoless Double Beta Decay (DBD)
Many models beyond SM with lepton number
violation can contribute!

• Left-right symmetric models
• R-parity violating ...
• R-parity conserving supersymmetric models
• ...
• Light neutrinos

Exchange of a virtual neutrino (Racah sequence
Furry 1939) Lepton number violation (DL
2) Helicity mismatch mass mechanism neutrino
must be massive a Majorana particle these
conditions hold even if other mechanisms are
possible and may dominate
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
5
present knowledge

• neutrino flavour oscillation
• neutrinos mix and have masses
• oscillation experiments measure Dmik2 mi2-mk2
  and sin22qik f( Ulk 2)
• direct (kinematic) neutrino mass measurements
• mb S Uek2 mk lt 2.2 eV
• cosmology (WMAP2dFGRS...)
• mS 3mn lt 0.7 eV (model dependent...)

• still missing
• absolute mass scale (i.e. mass of the lightest
  neutrino)
• neutrino mass hierarchy m1 m2 lt m3 or m3 lt
  m1 m2
• neutrino nature (Dirac/Majorana)
• CPV
• LNV

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
6
Neutrino mass hierarchy
Inverse
Normal
??
??

?m2sol
??
?m2atm
(Mass)2
?m2atm
??

?m2sol
??
??
sin2?13
Quasi-degenerate mlow2 gtgt Dm2atm gtgt Dm2sol
mlow
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
7
Neutrino mass hierarchy
A.Strumia and F.Vissani. hep-ph/0503246
ltmngt eV
ltmngt f( mlow,Uek )
lightest neutrino mass eV

• Quasi degenerate and inverse hierarchy TESTABLE
• Normal hierarchy UNTESTABLE
• ltmngt threshold 10 meV

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
8
bb-0n decay rates
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
9
Nuclear Matrix Elements

• phase space G0n(Qbb,Z) can be precisely
  evaluated
• large uncertainties in NME calculation M0n also
  affect ltmngt
• about factor of 100 in FN
• of the order of 2-3 in ltmngt

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
10
Nuclear Matrix Elements (2)

• Different approaches
• Quasi Random Phase Approximation (most used
  many versions)
• Shell Model
• Operator Expandion Model
• ...
• Large spread of values even within the same
  method

• Democratic approach
• difficult to quantify with absolute confidence
  the range of uncertainties in nuclear matrix
  elements calculated with different theoretical
  models or approximations
• it is assumed that the published range of
  calculated matrix elements defines a plausible
  approximation to the uncertainty in our knowledge
  of the matrix elements

Bachall, Murayama and Pena-Garay Phys. Rev. D 70
(2004) 033012
Criticized in V.A.Rodin et al, nucl-th/0503063
which calibrate their model parameters on the
available experimental results for 2n-DBD,
obtaining a lower spread in the final predictions
as a function of different model ingredients
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
11
Nuclear Matrix Elements (3)
The uncertainty in the calculated NME for
neutrinoless DBD could constitute the principal
obstacle to answering some basic questions about
neutrinos. Comparable efforts and resource
investments are therefore needed both on the
experimental and theoretical frameworks

• Ongoing activities
• International WG on NME calculation
• Sharing of information
• Dedicated resources
• Cross check with the direct measurements
• two neutrino DBD rates
• b/EC decays
• induced reactions
• .

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
12
Candidate nuclei

• Selection of nuclei for bb-0n experiments
• Mean Nuclear Factor of Merit (FN) as high as
  possible
• Large transition energy to minimize background
  contributions
• Large isotopic abundance
• Possibility to enrich nuclei in bb isotope
• Chemical purification of materials available
• ......

AVLIS, ICR?
Ultracentrifuge
Ultracentrifuge
Ultracentrifuge
Ultracentrifuge??
Ultracentrifuge
Ultracentrifuge
AVLIS, ICR?
F.T. Avignone II et al., New Journal of Physics 7
(2005) 6
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
13
Experimental approach inhomogeneous

• Source ? detector
• source in thin foils
• electron energies and track analyzed

• topology (background rejection)
• angular correlation
• single electron energies
• any isotopes with solid form possible
• relatively small amount of material
• poor efficiency
• enriched materials needed
• (generally) poor energy resolution

• Detector types
• TPC
• scintillators
• drift chambers
• semiconductor detectors

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
14
Experimental approach homogeneous

• Source detector (calorimetry)
• detector measures sum energy E Ee1 Ee2
• bb-0n signature a peak at Qbb
• scintillators, bolometers, semiconductors, gas
  chambers
• large masses
• high efficiency
• many isotopes possible
• no blanks
• depending on technique
• high energy resolution (bolometers,
  semiconductors)
• moderate topology recognition (Xe TPCs,
  semiconductors)

• Other approaches (geochemical, milking)
• do not separate bb-0n and bb-2n (inclusive
  measurements)

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
15
Experimental sensitivity
Experimental sensitivity to t½0n with no bb-0n
decay observed Nbb (bkgDE M tmeas)½ at 1s
We need very massive detectors (1 ton scale)
We need enriched materials
We need very low radioactive background
We need high energy resolution detectors
(critical also for background)
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
16
Background sources

• their relevance depends on adopted technique
• all experiments are somehow affected by them
• possible background sources
• internal to source (and detector for
  calorimeters)
• primordials (238U, 232Th, 40K)
• cosmogenic activation
• external
• primordials in surrounding materials
• neutrons
• cosmic rays
• specific
• quenched a's for scintillators
• primordials on surface for bolometers

For future experiments we need material
contamination lt 10-12 g/g U and Th (?10-14 g/g)
Experiments made in deep underground Labs
New and different approaches to validate
materials
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
17
bb-2n background
116Cd measured with scintillator CdWO4

• bb-2n is a background source
• detector energy resolution critical

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
18
bb-2n background
bb 76Ge ? HPGe diodes
bb 100Mo ? Tracking exp
bb 116Cd ? CdWO4 scintillators
bb 130Te ? TeO2 bolometers
bb 136Xe ? Xe TPCs
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
19
Present/past experimental situation

• positive result
• running experiments

2006
1.46
2.7
1.2
2.9
2006
11.1
5.6
0.6
2.5
2006
8.33
24
0.17
1.0
s scintillation i ionization t tracking b
bolometric
Range of uncertainties in NME
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
20
Heidelberg/Moscow 76Ge

• 5 HP-Ge crystals, enriched to 87 in 76Ge
• total active mass of 10.96 kg ? 125.5 moles of
  76Ge
• run from 1990 to 2003 in Gran Sasso Underground
  Laboratory
• total statistics 71.7 kgy
• 820 molesy
• main background from U/Th in the set-up
• b0.11 c/keV/kg/y at Qbb

21
Heidelberg/Moscow 76Ge 0n-DBD evidence

• First claim in January 2002 (Klapdor-Kleingrothaus
  HV et al. hep-ph/0201231) with a statistics of
  55 kg y and a 2.2-3.1 statistical significance
• claim confirmed in 2004 with the addition of a
  significant (1/4) new statistics

1990 2003 data, all 5 detectors exposure 71.7
kgy t½0n 1.2 1025 years ltmngt 0.44 eV
H.V.Klapdor-Kleingrothaus et al., Phys. Lett. B
586 (2004) 198

• The claim has drawn criticism and has been
  refuted by other members of the HM coll.
• signal is still faint (4 s) to be blindly
  accepted as unquestionable evidence
• still some weak points in the published analysis
• presence of not understood peaks around the
  signal (comparable significance)
• impossibility to check an energy window larger
  than the published one
• disagreement on the evaluated significance level
• all future experiment will certainly have to
  check this result

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
22
Low Temperature Detectors (LTD)

Detection Principle DTE/C C thermal
capacity low C low T (i.e. Tlt1K) dielectrics,
superconductors ultimate limit to E
resolution statistical fluctuation of internal
energy UltDU 2gt kBT 2C
Thermal coupling

• Thermal Detectors Properties
• good energy resolution
• wide choice of absorber materials
• true calorimeters
• slow tC/G1103 ms

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
23
CUORICINO
Installed in Hall A _at_ LNGS

• TeO2 thermal calorimeters
• Active isotope 130Te
• natural abundance a.i. 33.9
• transition energy Q?? 2533 keV
• encouraging predicted half lifeltm?gt0.3 eV ?
  ?1/20?1025 years
• Absorber material TeO2
• low heat capacity
• large crystals available
• radiopure

Cuoricino tower 62 TeO2 crystals

• intermediate size bb experiment
• important test for
• radioactivity
• performance of large LTD arrays

24
CUORICINO results

• total statistics 8.3 kgy (duty cycle 64)
• energy resolution FWHM ?E 7.5 keV at Qbb
• anticoincidence applied to reduce surface U/Th
  background and external ?s
• background mainly from U/Th on Cu and TeO2
  surfaces (? and b)
• b0.18 0.02 c/keV/kg/y at Qbb

anticoincidence sum spectrum 8.33 kgy ?1/2 ?
2.41024 years at 90 C.L. ltm?gt 0.2 1.0 eV
208Tl

• experiment still running
• 3 y sensitivity
• t1/2 6.11024 y
• ltmngt 0.1 0.6 eV

60Co
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
25
NEMO3 100Mo and 82Se

• Tracking detector for bb-2n and bb-0n
• at Frejus (4800 m.w.e.)
• 10 kg of enriched material in foils
• 6180 geiger cells ? drift wire chamber
• 1940 plastic scintillators PMTs
• iron (g) water with B (n) shielding anti-Rn
  box
• e, e, g and a identification

sources in foils

• 100Mo (6.9 kg)
• 82Se (0.9 kg)
• 130Te (0.45 kg)
• 116Cd (0.4 kg)
• 150Nd (37g)96Zr (9.4 g)48Ca (7.0g)
• natTe (0.5 kg)
• Cu (0.6 kg)

?2
?1
calorimeter (scintillators)
tracking volume (drit wire chamber)
26
NEMO3 100Mo and 82Se results
100Mo
82Se
2 neutrinos DBD
2 neutrinos DBD
T1/2 7.11 0.02 (stat) 0.54 (syst) ? 1018
y Phys Rev Lett 95, 182302 (2005)
T1/2 9.6 0.3 (stat) 1.0 (syst) ? 1019
y Phys Rev Lett 95, 182302 (2005)
Neutrinoless DBD
Neutrinoless DBD
T1/2gt5.81023 y mnlt0.6-1.0 eV
T1/2gt2.11023 y mnlt1.2-2.5 eV
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
27
Next generation bb-0n experiments

• sensitivities of few 0.01 eV on ltmngt
• hierarchy problem solution
• good chances to observe bb-0n (LNV, Majorana n's)
  
• confirmation/rejection of the 76Ge result
• confirmation sensitivities of few 100 meV on
  ltmngt are enough check different isotopes
• rejection much better sensitivities on ltmngt
  must be achieved
• new results on 76Ge crucial

• How?
• promote as many as possible experiments on
  different isotopes
• reduce uncertainties in nuclear matrix FN
• increase sensitivity
• ? experimental masses
• ? detector resolutions
• ? isotopic abundances
• ? radioactive backgrounds

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
28
Next generation bb-0n experiment sensitivities
Present
Future
0.0270
4.56
1.45
s scintillation i ionization t tracking b
bolometric
0.0560
2.64
0.73
, i
0.2400
1.55
0.24
latest experimental results
nuclear matrix elements FN selected by Elliott
Vogel
S.R. Elliott P. Vogel, Ann. Rev. Nucl. Part.
Sci. 52 (2002) 115
ltmngt range with selected FN elements
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
29
Next generation proposed projects
projected experimental parameters
nuclear matrix elements FN selected by Elliott
Vogel

• projected background levels
• large spread
• too large gap with respect to present

ltmngt evaluated according to staudt et al
Europhys. Lett. 13 (1990) 31
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
30
Calorimetric experiments ionization detetors

• Germanium diode experiments
• well known technique
• high energy resolution
• large masses
• segmentation and PSD to reduce background
• cost of enrichment
• standard cooling in ultra low background
  cryostats
• Majorana experiment
• naked crystals in cryogenic liquids
  (scintillating)
• GERDA or Genius/GEM
• CdTe or CdZnTe diode experiments (COBRA)
• many isotopes at once
• segmentation (tracking) to reduce background
• new technique, still poor energy resolution and
  small masses
• COBRA K. Zuber, Phys. Lett. B 519 (2001) 1,First
  results H.Kiel, D. Münstermann, K. Zuber, Nucl.
  Phys. A 723,499 (2003). 40x40x40 cm box 370 kg
  CdZnTe

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
31
GERDA
Proposal hep-ex/0404039

• goal analise HM evidence in a short timeusing
  existing 76Ge enriched detectors (HM, Igex)
• experimental approach
• naked Ge crystals in LN2 or LAr
• radioactive shildigs
• 1.5 m LN2(LAr) 10 cm Pb 2 m water
• 2-3 orders of magnitude better bkg than
  present Status-of-the-Art
• active shielding with LAr scintillation
• 3 phases experiment
• Phase I
• radioactivity tests
• 20 kg 76Ge from HM and Igex
• expected bkg 0.01 c/keV/kg/y (intrinsic)
• check at 5s HM evidence
• 15 kgy ? 61 bb events on 0.5 bkg events
• Phase II
• add new enriched segmented detectors with
  special care for activation (38 kg)
• expected background 0.001 c/keV/kg/y
• t1/2 gt 21026 y with 100 kgy
• ltmngt lt 0.09 0.29 eV

• Approved by LNGS S.C.
• site Hall A northern wing
• 38 kg enriched 76Ge for phase II ready for
  crystallization
• aggressive time schedule

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
32
Majorana
White paper nucl-ex/0311013

• concept cosmogenics main background source
  (IGEX)
• 500 kg Ge crystals in ultra low background
  cryostats
• electroforming copper with lt10-14 g/g U and Th
• segmentation and PSD to reduce bkg
• 2 experimental phases 180 kg - 500 kg

• Phase I
• 180 kg 86 76Ge (centrifugation)
• Modules with 57 crystals each (40 cm x 40 cm
  Cryostat)
• Three modules for 180 kg
• Eight modules for 500 kg (phase II)
• Maximal use of copper electroformed underground
• Background rejection methods
• Granularity
• Pulse Shape Discrimination
• Single Site Time Correlation
• Detector Segmentation
• Underground Lab
• 6000 mwe
• Class 1000

• FULL EXPERIMENT
• (9 years from start in 2006)
• expected bkg 1.21 c/ton/y in ROI
• mainly Th from Cu structure
• t1/2 gt 4 1026 y in 3 years
• ltmngt lt 0.07 0.21 eV

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
33
Majorana (2)
57 crystal module
segmentation concept
shield design
34
Calorimetric experiments bolometers

• true calorimeters
• wide isotopes choice 48Ca, 76Ge, 100Mo, 116Cd,
  130Te, 150Nd
• high energy resolution
• large masses
• segmentation to reduce background
• fully sensitive to surface radioactivity
• difficult to reduce the amount of close
  materials (holders, wires, cryostats,...)
• very slow detectors
• hybrid detectors can do particle identification
  (i.e. e/g - a)
• heat scintillation detection
• heat ionization detection (with PSD
  segmentation)
• CUORE (130Te)
• Edelweiss (76Ge) G.Chardin NIM A 520 (2004) 145
• MOON (100Mo)???

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
35
CUORE
Proposal hep-ex/0501010

• Cryogenic Underground Observatory for Rare Events
• array of 988 TeO2 crystals 555 cm3 (750 g)
• 741 kg TeO2 granular calorimeter
• 600 kg Te 203 kg 130Te
• bb-0n, Cold Dark Matter, Axions searches

single dilution refrigerator ( 10 mK)
SINGLE HIGH GRANULARITY DETECTOR
Crystals grouped in a cylindrical matrix of 19
towers
Single tower thirteen (4 crystal) modules
36
CUORE (2)

• enrichment still open option full detector /
  only core (2nd phase)
• compact and granular self shielding detector
• work in progress to reduce surface radioactivity
• advanced cleaning techniques
• new surface sensitive detectors for active bkg
  rejection under test
• Present status
• approved LNGS S.C. Site Hall A southern wing
• approved and funded by INFN for the Italian part
• proposal to DOE and NuSAG for the American part
• positive NuSAG report
• underground building is designed and under
  construction
• dilution refrigerator funded tender in progress
• material selection and cleaning procedure
  settling
• Full experiment
• CUORE experiment due to start data taking in
  01/01/2010 _at_ LNGS

DE
5 y sensitivities
37
Calorimetric experiments scintillators

• large masses (solid or liquid)
• well known simple techniques
• wide isotopes choice 48Ca, 100Mo116Cd, 136Xe,
  160Gd
• immersion in clean liquids to reduce background
  (Borexino, SNO...)
• PSD to reduce background
• poor energy resolution
• in some cases difficult to have radiopure
  crystals
• background from PMTs
• CAMEO (116Cd)
• CANDLES (48Ca)
• XMASS (136Xe)
• Xenon in Borex (or SNO) (136Xe) B.Caccianiga
  Astropart. Phys. 14 (2000) 15
• nanocrystals in SNOlab (48Ca, 82Se, 96Zr, 116Cd,
  130Te, 150Nd) SNO
• Corea project CaMoO4, PbMoO4, SrMoO4

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
38
Xe scintillators

• XMASS (Xenon MASSive detector) _at_ KAMIOKA
• concept a self shielding detector for DM, ??
  bb
• presently running 100 kg prototype (with light
  guide)
• 10 t natural LXe
• considering only bb-2n bkg
• ltmngt lt 0.01 0.02 eV in 5 years
• but self shielding at 3 MeV is not effective
• PMT bkg limits bb-0n sensitivity
• ongoing
• Background reduction
• 3ppt in 85Kr, 10-14 g/g in U/Th
• RD for a 800 kg detector
• design and development of new PMT
• Primary goal still WIMP detection

Proposals for inclusion of large 136Xe samples in
radioclean environments such as SNO or
BOREX have also been submitted
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
39
Tracking experiments

• background reduction by vertex and track
  reconstructrion
• mass mechanism demonstration by electron angular
  correlation
• poor energy resolution
• small masses enrichment necessary
• MOON (100Mo)
• DCBA (82Se, 150Nd)
• SuperNEMO (82Se, 150Nd)
• EXO, calorimeter tracking (136Xe)

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
40
SuperNemo

• concept scale NEMO setup
• tracking calorimeter
• already tested technology (NEMO)
• event topology (Detection of the 2 electrons)
• single and sum energy angular correlation
• particle identification
• Background control
• source purification
• background level measurement
• external background reduction (Rn)
• Isotope selection 82Se
• transition energy 2 995 keV
• natural i.a. 8.7
• bb-2n 0.9 1020 y

• Planar geometry
• source (40 mg/cm2) 12m2
• tracking volume 3000 channels
• calorimeter 1000 PMT
• Modular
• 5 kg of enriched isotope/module
• 100 kg 20 modules
• 60 000 channels for drift chamber
• 20 000 PMT
• energy resolution DE 2.6 _at_ 3 MeV
• efficiency 40
• Canfranc-Spain (LNGS/LSM)

2006-2008 RD 2009 first module 2011 all
modules 2016 final results
3 years RD aiming at a 50 meV ltmngt sensitivity
accepted by IN2P3 s.c.

• 5 kg of 82Se funded by ILIAS (Europe)
• Enrichment
• 1 kg of 82Se in 2005
• 2 kg of 82Se in 2006
• 5 kg of 82Se in 2007
• Possible new enrichment facility in France (CEA)
  to produce few hundreds kg of 150Nd (SILVA
  project)

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
41
EXO

• concept scale Gotthard experiment adding Ba
  tagging to suppress background (136Xe?136Ba
  2e)
• single Ba detected by optical spectroscopy
• two options with 63 enriched Xe
• High pressure Xe TPC
• LXe TPC scintillation
• calorimetry tracking
• expected bkg only by bb-2n
• energy resolution DE 2

• Present RD
• Ba spectroscopy in HP Xe / Ba extraction
• energy resolution in LXe (ion.scint.) OK
• Prototype scale
• 200 kg enriched L136Xe without tagging
• all EXO functionality except Ba id
• operate in WIPP for two years
• Prototype goals
• Test all technical aspects of EXO
• (except Ba id)
• Measure 2n mode
• Set decent limit for 0n mode
• (probe Heidelberg- Moscow)

LXe TPC

• Full scale experiment at WIPP or SNOLAB
• 10 t (for LXe volume 3 m3)
• b 410-3 c/keV/ton/y
• t1/2 gt 1.31028 y in 5 years
• ltmngt lt 0.013 0.037 eV

42
Present status of experiments
background reduction
NME??
New EPC site Zalenagorsk
Indication from NuSAG
XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006
43
Conclusions

• Neutrinoless Double Beta Decay is a unique tool
  to study neutrino properties
• Absolute Mass Scale
• Nature (Majorana/Dirac)
• Lepton Number Violation
• CP Violation
• Parameter constraints for GUTs and SUSY models
  can be obtained
• Still large uncertainties due to spread in NME
  calculations
• Experimental situation
• one claimed evidence for bb0n of 76Ge
• 2 medium size (1-10 kg) ongoing experiments
  (NEMO CUORICINO)
• 1 improved sensitivity 76Ge experiment in
  preparation (GERDA)
• intermediate future goal ltmngt lt 100 meV
• 2-3 intermediate size (200 kg) approved
  experiments
• ultimate future goal ltmngt 10 meV
• many proposals with different techniques and
  isotopes
• promote as many as possible experiments on
  different isotopes
• reduce uncertainties in nuclear matrix FN
• many activity in background reduction and control

XXVI Physics in Collision 2006 Buzios Brasil
6/9 July 2006