Simonetta Marcello Torino University Seminar @ JAEA Tokai- mura , October 26, 2010
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Transcript of Simonetta Marcello Torino University Seminar @ JAEA Tokai- mura , October 26, 2010
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Simonetta MarcelloTorino University
Seminar @ JAEATokai-mura, October 26, 2010
Hypernuclear Weak Decay
Measurements
with FINUDA Experiment
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OUTLINE
FINUDA Experiment
Study of Hypernuclear Weak Decays
Mesonic Weak Decays (MWD)
Non-Mesonic Weak Decays (NMWD)
Two body Rare Non-Mesonic Weak Decays
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DAFNE e+-e- Collider
e+- e- Beams of 510 MeV
at the c.m. energy of(1020) meson
circulating in two different rings
collide in two interaction regions
e-
e+
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DANE is a high luminosity Factory
L ~ 2.2x1032 cm-2s-1 ~ 900 /s 8 pb-1/day
DANE is a high luminosity Factory
L ~ 2.2x1032 cm-2s-1 ~ 900 /s 8 pb-1/day
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KLOECP, CPT violationchiral dynamics …
KLOECP, CPT violationchiral dynamics …
FINUDAStrangenessNuclear Physics
FINUDAStrangenessNuclear Physics
SIDDHARTAK-N scatteringSIDDHARTAK-N scattering
KSKL
34%
13%
K+K-
49%
Φ Decays
Decay BR (%) p (MeV/c)
K+ K- 49.2 127
K0L K0
S 34.0 110
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+-
0
2.3
Ekin 16 MeVLow Energy kaonscan be stopped in Nuclear Targets
• neutral and charged kaons
• collinear (Back-to-Back) and tagged
• monochromatic and low energy
• neutral and charged kaons
• collinear (Back-to-Back) and tagged
• monochromatic and low energy
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DAFNE Peak Luminosity history 2001-2007
FINUDA
DAFNE e+-e- Collider
RUN-1
RUN-2
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10FINUDA
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DAFNE e+-e- Collider
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DAFNE Peak Luminosity history 2000-2009
In the last years further improvement in the Luminosity has been achieved
L ~ 3÷4x1032 cm-2s-1 peak luminosity
In the last years further improvement in the Luminosity has been achieved
L ~ 3÷4x1032 cm-2s-1 peak luminosity
FINUDA
FINUDA
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RUN-2: October 2006 – June 2007
Integrated Luminosity ~ 1 fb-1Integrated Luminosity ~ 1 fb-1 HYP events: ~ 5 millionsHYP events: ~ 5 millions
Daily integrated luminosity [nb-1]
Integrated luminosity [nb-1]
Average daily integrated luminosity
~ 7 pb-1
Average daily integrated luminosity
~ 7 pb-1
Stable Data TakingStable Data Taking
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FINUDA Spectrometer @ DAΦNE
Structure of a collider experiment
Structure of a collider experiment
• Large acceptance: > 2 sr• B=1T omogeneous magnetic field within 2%
• Large acceptance: > 2 sr• B=1T omogeneous magnetic field within 2%
Mechanical frameVertex/target Drift Chambers,Straw tubes
Magnet end-caps
TOFONEdetector
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Fixed TARGET Experiment
K- are stopped in very thin targets
Different Targets at the same time
FINUDA is a target experiment with cylindrical geometry
e e Φ K K
127 MeV/c16 MeV
12.5 mrad
Φ
e-
e+
Not exactly at restboost of 12.3 MeV/c
π -
π -
p
K+
μ+
K-12C
12C
51V 27Al
12C
7Li
6Li6Li
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HYPERNUCLEAR PHYSICS
Spectroscopy
Weak Decays
HADRON PHYSICS with STRANGENESS
Bound Kaonic Clusters
• Detection and full reconstruction of particles
• Coincidence measurement with large acceptance
FINUDA Physics
SIMULTANEOUSLY
ON DIFFERENT TARGETS
• Very thin nuclear targets (0.1 ÷ 0.3 g/cm2)
• High Resolution Spectroscopy p/p = 0.6%
• Detection and full reconstruction of particles
• Very good identification
Kstop + AZ A
Z +
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Hypernuclear Event
K+
K-
6Li
Forward track
Kstop AZ A
Z
K
Forward track11
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Selective trigger based on fast scintillation
detectors
Clean K- vertex identification
ISIM P.ID.+ x,y,z resolution + K+ tagging
, K, p, d, t … Particle Identification (dE/dx)
High momentum resolution (6‰ FWHM)
tracker resolution+He bag+thin targets 6‰ for - @270 MeV/c for spectroscopy
1% for - @270 MeV/c for decay study
6% for - @110 MeV/c for mesonic decay study
2% for p @400 MeV/c for non-mesonic decay study
Time-Of-Flight (TOF system)
Neutron detection (external Scintillator barrel)
Selective trigger based on fast scintillation
detectors
Clean K- vertex identification
ISIM P.ID.+ x,y,z resolution + K+ tagging
, K, p, d, t … Particle Identification (dE/dx)
High momentum resolution (6‰ FWHM)
tracker resolution+He bag+thin targets 6‰ for - @270 MeV/c for spectroscopy
1% for - @270 MeV/c for decay study
6% for - @110 MeV/c for mesonic decay study
2% for p @400 MeV/c for non-mesonic decay study
Time-Of-Flight (TOF system)
Neutron detection (external Scintillator barrel)
Detector capabilities
Detector capabilities
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FINUDA Data Takings
RUN-2 2006-2007 Integrated Luminosity: ~ 1 fb-1 five millions of HYP events
RUN-2 2006-2007 Integrated Luminosity: ~ 1 fb-1 five millions of HYP events
Targets: 2x 6Li, 2x 7Li, 1x 13C, 1x 9Be, 1x 16OMedium-light targets to allow a wider spectrum of physics:
hypernuclear spectroscopy
NRH spectroscopy
hypernuclear decay modes
bound kaonic states
RUN-1 2003-2004 Integrated Luminosity: 190 pb-1 one million of HYP events
RUN-1 2003-2004 Integrated Luminosity: 190 pb-1 one million of HYP events
Targets: 2x 6Li, 1x 7Li, 3x 12C, 1x 27Al, 1x 51V
12C reference target for detector performance tuning
27Al -- 51V medium-heavy nuclei for spectroscopic studies
6Li -- 7Li sources of light hypernuclei
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Hypernuclear Weak Decays: Mesonic channels
Free Space
p + B.R. 63.9 % -free
n+ B.R. 35.8 % 0free
Q ~ 38 MeV ; pN = p~ 100 MeV/cΔ I = ½ RuleExp -
free0free
1.78
-free0
free 2 pure Δ I =
1/2
-free0
free 1/2 pure Δ I =
3/2
p +
n +
QM < 38 MeV ; pN ~ 100 MeV/c < kF = 270 MeV/c
Mesonic mode (MWD) is Pauli Blocked
But still possible in finite nuclei
In the Nuclear Medium
Hamiltonian describes transitions with
Δ I of 1/2 and 3/2 with comparable strengths
BUT an enhancement in Δ I = 1/2 component
is observed in free Y decays and K decays
Strong interaction corrections are added But not enough to account for such an enhancement
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Hypernuclear Weak Decays: Non-Mesonic channels
p n p
n n n n
p
One-Nucleon induced Decays
Nucleons can escape the nucleus
Non-Mesonic mode (NMWD) is not Pauli Blocked
NMWD dominates over the Mesonic one for all hypernuclei,
but the lighter ones, where is in competition with the MWD
Final State Interaction (FSI) cannot be neglected in NMWD
QM ~ 176 MeV ; pN ~ 415 MeV/c > kF = 270 MeV/c
Nucleon pairs mainly emitted back-to-back
Difficult to measure neutrons, low efficiency
N N n N N 2N Two-Nucleon induced Decay
QM ~ 176 MeV pN ~ 340 MeV/c
QM shared among the three Nucleons
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• Hypernuclear decays: only way to get information on N NN
• Extension of NN NN weak interaction with ΔS = 0, in particular on the
parity conserving part of the Hamiltonian (masked by strong interaction)
• No experimental observation of N NN using beams.
• Possible to study the reverse reaction pn p
but not feasible very low ~ 10-12mb
Hypernuclear Weak Decays
Tot = M + NM
M = - + 0 ; NM = p + n + 2N
= ℏ Tot hypernucleus lifetime
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Hypernuclear Weak Decays: Non-Mesonic channels
N
N
, K , K*
N
N
, K , K*
N
N
N
N
One-Nucleon induced Decays
Two-Nucleon induced Decay
One Meson Exchange Model
Massive mesons (, K, K*, and ) have been includedto explain interaction at short distances
One Pion Exchange Model Not enough to explain n / p ratio
Hybrid models adopting direct quark mechanisms in addition to meson-exchange potential have been used
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Mesonic Weak Decays
• -nucleus optical potential, the low energy probes the nuclear structure possibile to discriminate among different potential models
(instead of studying -nucleus scattering or X-rays from pionic atoms)
• Enhancement of the -mesonic decay rates due to the pion wave distortion higher momentum available for the Nucleon
• Jassignment hypernuclei, strong dependence of the two-body - decay Branching Ratios on the ground state spin: new indirect spectroscopic tool
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PHYSICS MOTIVATIONS
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PHYSICS MOTIVATIONS
Non-Mesonic Weak Decays
• 4-baryon strangeness changing weak interaction give the possibility to investigate both the parity violating and the parity conserving contributions to the Hamiltonian (in NN NN the latter one is masked by the strong interaction)
• I=1/2 rule
• n/p puzzle
• 2N and Final State Interactions (FSI) contributions
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Study of Weak Decays with FINUDA
p
-
charged Non-Mesonic channel
K- stop + AZ AZ + -
AZ A-2(Z-1) + p + n
NMWD 170-600 MeV/c
charged Mesonic channel
K- stop + AZ AZ + -
AZ A(Z+1) + -
S-EX 260-280 MeV/c MWD
80-110 MeV/c
-
-
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Coincidence measurement
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Mesonic Weak
Decays
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• MWD strictly forbidden in infinite nuclear matter (pN ~ 100 MeV/c)
• feels attraction in nuclear medium due to the p-wave part of the optical potential ( distortions) dispersion relation modified inside the nucleus pion carries lower energy for fixed momentum q: E≤ √(q2+m
2)
Energy conservation: higher momentum available for the final nucleon which has more chance to overcome the Fermi momentum
• theoretical calculations with pion distorted wave predict MWD to be less suppressed for p-shell (A~10)
Enhancement of MWD due to pion wave distortion: • Bando et al., Progr. Theor. Phys. Suppl. 72 (1984) 109• Oset et al., NPA 443 (1985) 704
Extensive calculations:• Motoba et al., Prog. Theor. Phys. Suppl. 117 (1994) 477• Gal Nucl. Phys. A 828 (2009) 72
Mesonic weak Decays p-shell hypernuclei
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Pauli Blocking is less effective in the medium !
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Study of Mesonic Decays
K- + AZ AZ + –
AZ A(Z + 1) + –
Hypernucleus Formationhigh – momentum ~ 270 MeV/cIn the bound region from the ground state peak
Hypernucleus Decaylow – momentum ~ 100 MeV/c
Not Pauli blocked in Light p-shell HypernucleiCan provide information on spin-parity of the initial hypernuclear ground state
AZ AZ + 0 0 not detected in FINUDA
Short track reconstructed by means of 2 layers of Si-Microstrips and 1 layer of Low Mass Drift Chambers
Δp/p =1% FWHMCuts are reduced
Δp/p =6% FWHMOnly 3 points
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MWD Measurements: strategy
12C
11B
Inclusive production - spectrum
background corrected
11B
-
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Background under formation peakK- (np) - p - n -
SHORT TRACKS (in Si-Microvertex)Detection of - down to ~ 80 MeV/c
LONG TRACKS (4 points)p/p ~ 1% in the region 260-280 MeV/c
Background under decay peakqf decay
Decay - spectrum background & acceptance corrected
Branching Ratio
BR – = – / TOT
BR – = N decays/ NHYP
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Study of Mesonic Decays
K- + 7Li 7Li + – (276 MeV/c)
K- + 7Li 5He + d + –
K- + 7Li 5He + p + n + –
7Li 7Be + – (107.7 MeV/c) 5
He 5Li + – (99.3 MeV/c)
7Li Target
Mesonic Weak Decay of Hypernuclei is important because it takes place
deeply inside the nucleus (since the is in s-shell s1/2 ) and involves a low
energy , so it can sensitively probe the structure of nuclear interior
Mesonic Decay Mesonic Decay
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T.
Mot
oba
(P
rivat
e C
omm
unic
atio
n))
7Be: 3/2-gs & 1/2- (429keV)
3-body decays
Agnello PLB 681 (2009) 139
Jassignment: 7Li
Gal NPA 828 (2009) 72
• Correspondence with the calculated strength functions
T. Motoba et al, Progr. Theor. Phys. Suppl. 117 (1994)
477
A. Gal, Nucl. Phys. A 828 (2009) 72
• Formation of different excited states of the daughter
nucleus
• Initial hypernucleus spin
Jπ (7Lig.s.) = 1/2+ Sasao, PLB 579 (2004) 258
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BR – = 0.315 ± 0.041
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9B: 3/2-gs & 1/2-(2.75 MeV)
T ~ 4 MeV FWHM @38 MeV
Agnello PLB 681 (2009) 139
T. M
oto
ba (P
riva
te C
om
mu
nic
ati
on
))
• Correspondence with the calculated strength
functions
T. Motoba et al, Progr. Theor. Phys. Suppl. 117
(1994) 477
A. Gal, Nucl. Phys. A 828 (2009) 72
• Initial hypernucleus spin
Jπ (Beg.s.) = 1/2+
O.Hashimoto NPA 639 (1998) 93c
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Jassignment: 9Be
BR – = 0.154 ± 0.040
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11C: 3/2-gs & 7/2- (~6.5 MeV)
Agnello PLB 681 (2009) 139 • Correspondence with the calculated strength functions
H. Bando et al, Pers. Meson Science (1992) 571
A. Gal, Nucl. Phys A 828 (2009) 72
• Two contributions of 11C 5/2- ground state
and 7/2- excited state
• Initial hypernucleus spin
Jπ (11ΛBg.s.) = 5/2+ : experimental confirmation
Sato et al., PRC 71 (2005) 025203 by different
observable
T. M
oto
ba
(Pri
vate
Com
mu
nic
ati
on
)
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Jassignment: 11B
BR – = 0.199 ± 0.039
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15O: 1/2-gs & sd (~6 MeV)
Agnello PLB 681 (2009) 139
• Correspondence with the calculated strength functions
T. Motoba et al, Nucl. Phys. A 489 (1988) 683
A. Gal, Nucl. Phys. A 828 (2009) 72
• 15ΛNg.s spin not known. Jπ (15
ΛNg.s.) = 3/2+
D.J.Millener, A.Gal, C.B.Dover Phys. Rev. C 31 (1985) 499
Spin ordering not obtained from -rays of 16O
M.Ukai et al. Phys. Rev.C 77 (2008) 054315.
• First experimental determination of
Jπ (15ΛNg.s.) = 3/2+ from decay rate value and spectrum
shape
T. M
oto
ba N
PA
48
9 (
19
88
) 6
83
.
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Jassignment: 15N
BR – = 0.085 ± 0.028
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present data
T. Motoba PTPS 117 (1994) 477
previous data
A.Gal NPA 828 (2009) 72
A
Mesonic decay ratio: - /
- / = tot / BR
tot / = (0.990±0.094) + (0.018±0.010) A
fit from measured values for A=4-12 hypernuclei [Sasao et al., PLB579(2004)258]
strong nuclear structure effect
distortion, MW
D enhancement
proved !
30
BR= N decays/ NHYP
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31
Non Mesonic Weak
Decays
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32
Hypernuclear Weak Decays: n / p Ratio
n p= 1/2 for pure ΔI = 1/2
n p= 2 for pure ΔI = 3/2
What about ΔI = ½ rule for decay in the medium ?
For a long time large experimental values have been measured (1 ÷ 2)
indicating a possible violation of ΔI = ½ rule in hypernuclear decays
and small theoretical values have been predicted (OPE model 0.1 ÷ 0.2)
n n np n pN N n N N
Most studied systems: 5He and 12
C
The analysis of n p ratio is influenced by the two-nucleon induced
process, whose experimental identification is rather difficult
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33
Hypernuclear Weak Decays: n /p Ratio
p n p
First measurement of nucleon-coincidence spectra and angular
correlation (BtoB) n p ≈ 0.4 - 0.5
N N n N Nn n n
New experimental measurements and progress in theoretical models
contributed to solve the n p ”Puzzle”
Theoretical improvements: havier mesons, interaction terms which
violate ΔI=1/2 rule, quark degree of freedoms for the short range baryon-
baryon interactionn p ≈ 0.3-0.7
5He
12C
Significant contribution of two-Nucleon induced decay and FSI
(non-BtoB kinematics) quenching of N yields ~ 40%Bhang et al., EPJ A33 (2007) 259
Outa et al., NPA754 (2005) 157c, Kang et al., PRL96(2006)062301
Sasaki et al., NPA669 (2000) 331Parreno and Ramos, PRC65(2002)015204
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Simulation of the background reactionK- n p Σ- p followed by the decay Σ- nπ-
Fermi momentum distribution for nucleonsselection criteria and quality cuts as for real data
Simulated background
π- and proton spectra from 12ΛC
NMWD
Spectrum of negative pions for events with a proton detected in coincidence red peak at 272 MeV/c (12
ΛC ground state)
π- spectrum in coincidence with p
RUN-1
12C
Not acceptance corrected 339
events 339 events
Not acceptance corrected
proton spectrain coincidencewith π- peak
Acceptance corrected
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35
proton spectrum in coincidence with π- peak
π- and proton spectra from 12ΛC
NMWD
background subtracted proton spectrum in coincidence with π- peak
π- spectrum in coincidence with p
RUN-1
12C
normalization region
M. Agnello et al., NPA 804 (2008),
151
Short tracks proton Threshold = 15 MeV
15 MeV
K- np - p
- n π-
coincidence
simulation + reconstruction + selection + normalization
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36
K- stopped in 7Li target can produce:
7ΛLi, (6
ΛHe+p), (5ΛHe+d), (4
ΛHe+t), (3ΛHe+α)
275 MeV/c peak is consistent with 7ΛLi g.s.
269 MeV/c peak is consistent with 5ΛHe+d
pmax = 272,67 MeV/c ΔBΛ = 3.98 MeV
π- and proton spectra from 7ΛLi NMWD
269 MeV/c
275 MeV/c
RUN-2
π- spectrum in coincidence with p
Simulated background
proton spectrum in coincidence with π- peak (275MeV/c) background subtracted proton
spectrum in coincidence with π- peak (275MeV/c)
Simulation of the backgroundK- np → Σ-p followed by Σ- → nπ-
Acceptance Corrected
7Li
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37
7Li - π- and proton spectra from 5ΛHe
NMWD
269 MeV/c
275 MeV/c
RUN-2
π- spectrum in coincidence with p
Acceptance Corrected
Simulated background
proton spectrum in coincidence with π- peak (269MeV/c)
background subtracted proton spectrum in coincidence with π- peak (269MeV/c)
K-stop + 7Li 5
ΛHe + d + π-
Enhancement of the low energy region FSI and 2 Nucleons induced effects Bulk of the signal at 80 MeV (~ Q/2 value of the reaction)
Simulation of the backgroundK- np → Σ-p followed by Σ- → nπ-
7Li
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38
6Li - π- and proton spectra from 5ΛHe
NMWD
Acceptance Corrected
Simulated background
proton spectrum in coincidence with π- peak
background subtracted proton spectrum in coincidence with π- peak
K-stop + 6Li 5
ΛHe + p + π-π- spectrum in coincidence with p
RUN-2
Simulation of the background for the 2 Nucleons absorption take into account the cluster substructure of 6Li as ( + d) molecule
Momentum distribution of the deuteron inside 6Li
T. Yamazaki and Y. Akaishi NP A792 (2007 )229
275 MeV/c
6Li
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5He
7Li
12C
Similar shape for 5He, 7Li and 12
C
Peak at ~ 80 MeV (Q/2 value), broadened by
N Fermi motion, visible even for 12C
no strong FSI effect in low energy region
FSI & 2N contribution in the low energy region?
39
5ΛHe, 7
ΛLi and 12ΛC proton spectra
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40
Comparison with KEK experimental data
FINUDA: NPA 804 (2008)151 KEK E462/E508: PLB 597 (2004)249
5ΛHe: FINUDA vs KEK 12
ΛC: FINUDA vs KEK
KEK: thick targets strong correction
FINUDA: thin targets & transparent detectors
KEK: p energy from TOF and range + dE/dx
poor energy resolution above 100 MeV, distortion
FINUDA: p momentum from magnetic analysis
2% energy resolution FWHM @ 80 MeV, no distortion
normalization beyond 35 MeV (KEK data threshold) Agreement for 5He, not for 12
C
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41
Comparison with theoretical calculations
Comparison with theoretical models
not satisfactory for 12C
New data important to constrain theories in low energy region12
ΛC: FSI and two-nucleons induced NMWD appear to be too strong to reproduce the data (low energy peak + excess smearing)
Theoretical curve
FINUDA proton spectra
5ΛHe
(Garbarino,Phys. Rev. C 69 054603 [2004])
KE
K
12ΛC
Garbarino,(P.R.C 69 054603 [2004])Theoretical curve
FINUDA proton spectra
KE
K
np nnp strongly quenches the nucleon yieldsH. Bhang et al., EPJ A33 (2007) 259
normalization beyond 15 MeV (FINUDA data threshold)
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Sim
on
ett
a M
arc
ello
.To
rino
Un
ive
rsity
-S
em
ina
r @
JA
EA
-Oct
ob
er
20
10
42
NMWD proton spectra p-shell hypernuclei
M.Agnello et al., PLB 685 (2010) 247
Background subtracted & acceptance corrected
5ΛHe 7
ΛLi 9ΛBe 11
ΛB
15ΛN12
ΛC 13ΛC 16
ΛO
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Alow
Ahigh
from fit12
C
FINUDA, PLB 685 (2010) 247 NMWD p
gaussian fitfree
Alow: spectrum area below 1N + 2N + FSI
Ahigh: spectrum area above 1N + FSI 2N(>70 MeV) ~ 5% 2Ntot
G,Garbarino, A.Parreno and A.Ramos, Phys.Rev.Lett. 91 (2003) 112501. Phys.Rev. C 69 (2004) 054603
assumption
W.Alberico and G.Garbarino, Phys. Rev. 369 (2002) 1
assumption
2N/NMWD & n/p not depend on A
43
NMWD: 2N
N N n N N
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FSI & NN contribution evaluation: systematics
44
5ΛHe 7
ΛLi 9ΛBe 11
ΛB
15ΛN12
ΛC 13ΛC 16
ΛO
NMWD: 2N
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FSI & NN contribution evaluation
Alow = 0.5 N(pnp) + N(npnnp) + NpFSI-low
Ahigh = 0.5 N(pnp) + NpFSI-high
N(p np)
N(npnnp)=
p
np≈
p
2N
np : pp : nn = 0.83 : 0.12 : 0.04
E. Bauer and G.Garbarino,
Nucl.Phys. A 828 (2009), 29.
assumption
N(p np) +Alow + Ahigh
Alow
=0.5 N(p np) +N(np nnp) + Np
FSI-low
N(np nnp) + NpFSI-low + Np
FSI-high
R =
45
NMWD: 2N
Alow
Ahigh
from fit
12C
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46
Rare Two-Body
Non Mesonic Decays
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Two body non mesonic decays of light hypernucleiNon-mesonic decays of light hypernuclei (A<12) are not the favoured decay
channels Mesonic decays play a larger role
Two-body non mesonic decay: large momentum transfer (QVal~170 MeV ) Unlikely to occur → rare events Expected branching ratios: at the level of 1.5% of all non-mesonic decays
calculations for 4ΛHe 3He n, p t, d d [Rayet Nuovo Cim. 42B (1968), 238]
Very few and sparse observations Mainly from bubble chamber/emulsion experiments, for 4
ΛHe Extremely poor statistics, a few events
No 4ΛHe →pt
A few 4ΛHe → 3He n : 8-14% of all identified NM decays of 4
ΛHe Corenmans et al. (1968), unpublished Block PRL 3(1959), 291
One 4ΛHe →dd event
Block et al. (1960) One 5
ΛHe →dt event Keyes et al. Nuovo Cimento (1976)
47
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Light hypernuclei decays in FINUDA
large angular coverage (~4π) Excellent particle identification for
charged hadrons Good momentum resolution Capability to fully reconstruct the
event topologies Set of several targets allowing the
production of different hypernuclei and hypernuclear fragments
• 4ΛHe hyperfragments production, from all targets– 4
ΛHe → d d• d momentum: 570 MeV/c
– 4ΛHe → p t• p momentum: 508 MeV/c
• 5ΛHe hypernucleus formation– From 6Li targets: K- 6Li → 5
ΛHe + p + π- (π- momentum: 275.15 MeV/c)
– From 7Li targets: K- 7Li → 5ΛHe + d + π-
– NM two-body decay: 5ΛHe → d t
• d momentum: 597 MeV/c
dE/dx p.id. TOF p.id.
p t
dd
p t
mips
48
4ΛHe → n 3He
Not detectable
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4ΛHe→dd
decays
Expected event features:
• 2 deuteron tracks of
570 MeV/c• Back-to-back
deuteron tracks
• possible 4ΛHe
formation π-
• for the formation of the 4
ΛHe g.s. hypernucleus in 4He target: pπ=255 MeV/c
d d
π-
Analyzed data: 954 pb-1, 2006-2007 data taking
49
Forward d p/p = 3%Backward d p/p = 4%
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4ΛHe→pt decays
Lower threshold for triton detection in FINUDA: 550 MeV/c508 MeV/c tritons cannot be observed !
Missing triton analysisone proton with momentum in the range (498-540) MeV/cone high momentum π-
Missing mass for the (A - Missing mass for the (A - 44ΛΛHe - p - He - p - ππ--) system compatible with one ) system compatible with one
(missing) triton + residual nucleus(missing) triton + residual nucleus
Large background contribution from K-(np) → Σ-p:
capture rate 1.62%/K-stop in 6Li (NPA 775 (2006), 35)
Stringent cuts to be applied on: secondary vertices ππ-- impact parameter (rejection 79%) angular distributions (backward peaked) (pπ-) invariant mass to reject from conversion reactions
50
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5ΛHe formation in
FINUDA
5ΛHe formation in FINUDA clearly observed in 6Li and 7Li
targets: peaks in the spectra in coincidence with a NM decay proton
5ΛHe formation: π- in the momentum
band (272-278) MeV/c
K- 6Li → 5ΛHe + p + π-
5ΛHe formation: π- in the momentum
band (267-273) MeV/c
K- 7Li → 5ΛHe + d + π-
6Li
5ΛHe
7Li
5ΛHe
7ΛLi
NPA804 (2008), 151
51
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5ΛHe → dt
decays
No events with detected d+t coincidence
Pion momentum in the selected bands granting hypernucleus formation
Deuteron momentum in a band across
597 MeV/c (570-630 MeV/c)
Missing triton analysis
Additional requirement:
hit on the vertex detectors
head-on with the deuteron
with large energy release
52
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Summary and Conclusions
FINUDA at DAFNE successfully collected ~ 1.2 fb-1 of K-stop on several nuclear
targets in two different data taking
Excellent tracking performance, PID and large acceptance
Several reactions have been measured and studied in coincidence
Good capabilities of FINUDA to detect events with well definite topologies
Systematic Study of the charged MWD channels of p-shell Hypernuclei:
7ΛLi, 9
ΛBe, 11ΛB and 15
ΛN
• Pion spectra measured for the first time with magnetic analysis• Shape of spectra compared with theoretical ones obtained with pion distorted wave
calculations
• J assignement of ground state: 1/2+ for 7ΛLi, 5/2 + for 11
ΛB have been confirmed, 3/2
+ for 15ΛN g.s. assigned for the first time
• Measurement of Branching Ratios Γ/ ΓTOT and evalaution of Γ/ Γ Λ
53
Mesonic Weak decays
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Summary and Conclusions
Measurement of the proton energy spectra from the NMWD
of 5ΛHe, 7
ΛLi, 9ΛBe, 11
ΛB, 12ΛC, 13
ΛC, 15ΛN, and 16
ΛO
down to 15 MeV, never reached before, crucial for FSI and Three-body decay
• 5ΛHe spectrum compatible with previous Exp and Theoretical calculations
• 12ΛC spectrum not compatible with Exp and Theoretical calculations
• First measurement of 7ΛLi
• Evaluation of the FSI and the Two-Nucleon induced NMWD
Γ2N/ΓNMWD = (0.24 ± 0.10) smaller than previous Experiments
In spite of limited statistics FINUDA could observe very clean signatures of Rare NMWD events with almost no background.
• First measurement of the ratio dd/pt of the decay modes of 4ΛHe.
First measurement of the BR (5ΛHe dt)
54
Non-Mesonic Weak decays
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55
The FINUDA Collaboration
•Bari University and INFN, Italy•Brescia University and INFN, Italy•KEK, Japan•Kyoto University, Japan•Laboratori Nazionali di Frascati INFN, Italy•Pavia University and INFN, Italy•RIKEN, Japan•Seoul National University, Korea•Shahid Beheshty University, Teheran, Iran •Torino University and INFN, Italy•Torino Polytechnic and INFN, Italy•Trieste University and INFN, Italy•TRIUMF, Vancouver, Canada
•Bari University and INFN, Italy•Brescia University and INFN, Italy•KEK, Japan•Kyoto University, Japan•Laboratori Nazionali di Frascati INFN, Italy•Pavia University and INFN, Italy•RIKEN, Japan•Seoul National University, Korea•Shahid Beheshty University, Teheran, Iran •Torino University and INFN, Italy•Torino Polytechnic and INFN, Italy•Trieste University and INFN, Italy•TRIUMF, Vancouver, Canada
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The END