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

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

13

+-

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

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

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

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

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

• 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

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omm

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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

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

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

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

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 !

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BR= N decays/ NHYP

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Non Mesonic Weak

Decays

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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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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

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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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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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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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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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

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?

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5ΛHe, 7

ΛLi and 12ΛC proton spectra

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

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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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

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

FSI & NN contribution evaluation: systematics

44

5ΛHe 7

ΛLi 9ΛBe 11

ΛB

15ΛN12

ΛC 13ΛC 16

ΛO

NMWD: 2N

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

46

Rare Two-Body

Non Mesonic Decays

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

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

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%

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

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

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

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

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

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

56

The END