MESON2008-Krakow-5/10 June 2008 Paolo CameriniMESON2008-Krakow-5/10 June 2008 Paolo CameriniMESON2008-Krakow-6/10 June 2008 Paolo Camerini

� Hypernuclear spectroscopy

▪ Study of Λ-N and Σ-N interaction ▪Single particle models predictions ▪ Hypernuclear structure ▪ Study of Λ/Σ -nucleus potentials ▪astrophysical

implications

Physics topics (FINUDA @DAΦΦΦΦNE)

� Hypernuclear decays

Λ →πN (mesonic weak decay) and ΛN→nN, ΛNN→nNN (non mesonicweak decay)

• baryon-baryon strangeness changing weak processes in nuclear matter• mesons medium modifications • short range correlations •quark d.o.f.

Strangeness Exchange reactionsK- + N→Y(Λ/Σ) + π

If Y remains bound a hypernucleus forms

K-stop + →→→→ + ππππ-ZA ΛZA

MESON2008-Krakow-5/10 June 2008 Paolo CameriniMESON2008-Krakow-5/10 June 2008 Paolo CameriniMESON2008-Krakow-6/10 June 2008 Paolo Camerini

�Search for:

� High N/Z (neutron rich) hypernuclei: K- + AZ→ AΛ(Z -2)+ ππππ+ (6ΛH ,7ΛH…)

Info on: neutron halo, low density Λ-n interaction, Λ−Σ coupling

� (Deeply) bound kaonic clusters: ΛΛΛΛp,ΛΛΛΛd,...detectionK-

-A potential, K mass/condensation in nuclear matter, nuclearcompressibility, chir.symm. rest.,

� Study of K- multinucleon absorption (ΛΛΛΛp,ΛΛΛΛd..detection)

� Σ−hypernuclei� rare decays� K+ charge exchange reactions

Physics topics (FINUDA @DAΦΦΦΦNE)

3

Target setup : 3 targets 12CTarget setup : 3 targets 12C

PR C64(2001)044302PR C64(2001)044302

12ΛC is the hypernucleus more

extensively studied up to now

12ΛC is the hypernucleus more

extensively studied up to now

Three 12C targets should provide:• calibration data to be compared with previous

measurements• improvement of the precision of the measurement

on all the hypernucleus observables

Three 12C targets should provide:• calibration data to be compared with previous

measurements• improvement of the precision of the measurement

on all the hypernucleus observables

NP A479(1988)161cNP A479(1988)161c

( ) CK 12, Λ++π

( ) CK stop12, Λ

−− π

3 MeV FWHM3 MeV FWHM

1.5 MeV FWHM1.5 MeV FWHM

core excitedstates

core excitedstates

5

Target setup : 7Li and 6LiTarget setup : 7Li and 6Li

2 MeV FWHM2 MeV FWHM

NP A691(2001)123cNP A691(2001)123c

7ΛLi low-lying states are the most extensivelystudied with high resolution γ spectroscopy

7ΛLi low-lying states are the most extensivelystudied with high resolution γ spectroscopy

With the FINUDA resolution the g.s. doubletshould be clearly separated from theexcited states at 2 MeV and 3.7 MeV

With the FINUDA resolution the g.s. doubletshould be clearly separated from theexcited states at 2 MeV and 3.7 MeV

• non mesonic decay variables of 7ΛLi will be

measured for the first time• Search for Σ−hypn (A near to 4He)• search for the neutron-rich hypernucleus 7

ΛHwill be attempted

• non mesonic decay variables of 7ΛLi will be

measured for the first time• Search for Σ−hypn (A near to 4He)• search for the neutron-rich hypernucleus 7

ΛHwill be attempted

( ) CK 12, Λ++π

• 6ΛLi is unstable by nucleon emission, it constitutes a

doorway for light systems 5ΛHe, 4ΛHe, 4ΛH

• the reaction K-+6Li→ 6ΛH+π+ could give access to the

unexplored field of neutron-rich hypernuclei

• 6ΛLi is unstable by nucleon emission, it constitutes a

doorway for light systems 5ΛHe, 4ΛHe, 4ΛH

• the reaction K-+6Li→ 6ΛH+π+ could give access to the

unexplored field of neutron-rich hypernuclei

light K--nucleus systems may favour theformation of deeply bound kaonic nuclei

K-stop + 6Li→ (ppnnnK-) + p

K-stop + 7Li→ (ppnnnnK-) + p

light K--nucleus systems may favour theformation of deeply bound kaonic nuclei

K-stop + 6Li→ (ppnnnK-) + p

K-stop + 7Li→ (ppnnnnK-) + p

6

Target setup : 6LiTarget setup : 6Li Spectroscopized

p He5 +Λ

ΓΓΓΓππππ−−−− about 102/pb-1

n p He4 ++Λ

τΓΓΓΓp (in coinc.) about 10/pb-1

ΓΓΓΓn (in coinc.) a few/pb-1

4He+ ππππ - spectr. (102/pb-1) calibration

K - + 6Li π π π π - +K - + 6Li π π π π - +

π π π π -

p p H4 ++Λ

d+d spectr. (∼0.3/pb-1 if B.R. ∼10-3)

p+ 3H spectr.(0.2/ pb-1 if B.R. ∼10-3) ππππ++n+3H many events (∼ 102/pb-1)how distinguishable?

7

Target setup : 51V, 27AlTarget setup : 51V, 27Al

PRL 34(1975)683PRL 34(1975)683

6 MeV FWHM6 MeV FWHM

1.9 MeV FWHM1.9 MeV FWHM

Only a very old measurement on 27Al atthe coarse resolution of 6 MeV FWHM

Only a very old measurement on 27Al atthe coarse resolution of 6 MeV FWHM

• The excitation spectrum of 51V shows peaks of single particle orbits with a resolution of 1.9 MeV FWHM

• The measurement of the capture rate of the groundstate formation with K-

stop will indicate the possibility ofcontinuing the study on medium-heavy A hypernuclei

• The excitation spectrum of 51V shows peaks of single particle orbits with a resolution of 1.9 MeV FWHM

• The measurement of the capture rate of the groundstate formation with K-

stop will indicate the possibility ofcontinuing the study on medium-heavy A hypernuclei

8

Hypernuclear physics at DAΦNEThe FINUDA Collaboration

Hypernuclear physics at DAΦNEThe FINUDA Collaboration

µ+

π-

• Torino University, Polytechinc and I.N.F.N., Torino, Italy

• Laboratori Nazionali di Frascati I.N.F.N., Italy

• Trieste University and I.N.F.N. Trieste, Italy

• Pavia University and I.N.F.N. Pavia, Italy

• Bari University and I.N.F.N. Bari, Italy

• Brescia University and I.N.F.N. Pavia, Italy

• TRIUMF, Vancouver, Canada

• Shahid Beheshty University, Teheran, Iran

• University of Tokyo, Japan

•KEK, Japan

•RIKEN,Wako,Japan

•Seoul National University, Korea

9

FINUDA saw the light in May 2003 FINUDA saw the light in May 2003

11

12

Average daily integrated luminosity: >8 pb-1

Average daily integrated luminosity: >8 pb-1

13

Machine & Apparatus commissioning: Bhabha events and KSMachine & Apparatus commissioning: Bhabha events and KS

e+

e−

Bhabha trigger:• 2 hits on tofino back to back• low threshold on tofino• multiplicity (2-7) on tofone• Time correlation tofino-tofone

Bhabha trigger:• 2 hits on tofino back to back• low threshold on tofino• multiplicity (2-7) on tofone• Time correlation tofino-tofone

( )γ−+−+ → eeee

−+→

→Φ

ππS

SL

K

KK

Rough (one helix, ≥ 4 hits) reconstruction procedure

Rough (one helix, ≥ 4 hits) reconstruction procedure

Luminosity and Φ production monitor

Luminosity and Φ production monitor

Bhabha (e+e-→ e+e-γ) and KS → π+π−

events entered the triggerBhabha (e+e-→ e+e-γ) and KS → π+π−

events entered the trigger

15

Machine & Apparatus commissioning: Φ vertex and acceptanceMachine & Apparatus commissioning: Φ vertex and acceptance

x vertexhorizontal

x vertexhorizontal

z vertexlongitudinal

z vertexlongitudinal

Φ vertex positionΦ vertex position

beam boosteffect

beam boosteffect

longitudinalmisalignementlongitudinal

misalignement

Φ vertex on-linemonitoring

Φ vertex on-linemonitoring

beamaxis

beamaxis

z

azimuthaluniformityazimuthaluniformity mechanical

structuresmechanicalstructures

16

17

Machine & Apparatus commissioningmachine energy and spectrometer calibration

Machine & Apparatus commissioningmachine energy and spectrometer calibration

π-

π+

e−

e+

492 MeV/c

−+−+ → eeee−+

−+

→→Φ→

ππS

LS

KKKee

512 MeV/c

Two arm full fittingTwo arm full fitting

vertexvertex

18

Machine & Apparatus commissioning:machine energy and spectrometer calibration

Machine & Apparatus commissioning:machine energy and spectrometer calibration

e+ e− invariant mass (GeV/c)

Φ → KSKL

Ks → π+ π−

e+ e− → e+ e−

Φ → ρ0π0

ρ0 → π+ π−

Minv = 1.019±0.015 GeV/c2Minv = 1.019±0.015 GeV/c2

Minv = 0.496±0.002 GeV/c2

KS=0.4977 GeV/c2

Minv = 0.496±0.002 GeV/c2

KS=0.4977 GeV/c2

Φ → ρ0π0

ρ0 → π+ π−

Φ → KSKL

Ks → π+ π−

Two arm full fittingTwo arm full fitting

Note:Peaks ratio�energy cal.

19

12.5 mrad

Machine & Apparatus commissioning: beam boostMachine & Apparatus commissioning: beam boost

e+e+

ΦΦΦΦ12.5 mrad

Nominal beamboost :12.8 MeV/c

Nominal beamboost :12.8 MeV/c

Φpr

FINUDAFINUDA

pΦ simulated by Monte Carlo12.3 MeV/c

pΦ simulated by Monte Carlo12.3 MeV/cDAΦNE LayoutDAΦNE Layout

pΦ measured by Bhabha events

9.7 MeV/c

pΦ measured by Bhabha events

9.7 MeV/c

Very important for K stop point reconstructionVery important for K stop point reconstruction

20

In-beam apparatus calibration : K+K- eventsIn-beam apparatus calibration : K+K- events

Hypernuclear trigger:• 2 hits on tofino over threshold (kaon)• extended back to back• multiplicity (>2) on tofone• Time correlation tofino-tofone (<10ns)

Hypernuclear trigger:• 2 hits on tofino over threshold (kaon)• extended back to back• multiplicity (>2) on tofone• Time correlation tofino-tofone (<10ns)

Tofino ∆ETofino ∆E

m.i.p.’sm.i.p.’s

∆E (arbitrary units)

ISIM ∆E/∆XISIM ∆E/∆X

K+K-K+K-

K-

K+

Φ

over thresholdover threshold

very effective slow kaon recognition

very effective slow kaon recognition

beam boost

K stop calculationGEANE tracking

K stop calculationGEANE tracking

only two measured points

on ISIM

only two measured points

on ISIM

K+K-K+K-

22

boost

In-beam apparatus calibration : K+K- stop pointsIn-beam apparatus calibration : K+K- stop points

K- stop pointsin targets

K- stop pointsin targets

total K-

stop pointstotal K-

stop points

K- stop pointsin ISIM

K- stop pointsin ISIM

a supplementarysilicon target for free

a supplementarysilicon target for free

K- stop points in other volumes

K- stop points in other volumes

Kaons crossingLithium

Kaons crossingLithium

boost

Beam pipeBeam pipe

Φ Φ

23

In-beam apparatus calibration : TOFIn-beam apparatus calibration : TOF

24

In-beam apparatus calibration : momentum resolutionIn-beam apparatus calibration : momentum resolution

µ+

π+

235.8 MeV/c

204.8 MeV/c

( )MeV/c)236(

%5.63=→ ++

µ

µ

pνµK ( )

MeV/c)205(%6.21

=→ ++

0π

0

pππK

25

In-beam apparatus calibration : momentum resolutionIn-beam apparatus calibration : momentum resolution

Κ+ → µ+νµ236MeV/c

Κ+ → π+π0

205MeV/c

K+ two body decays: referencefor spectrometer calibrationK+ two body decays: referencefor spectrometer calibration

∆p/p≈0.6% FWHM ∆MH= ∆Tπ ~1.25 MeV FWHM∆p/p≈0.6% FWHM ∆MH= ∆Tπ ~1.25 MeV FWHM

Further improvements• detector alignment• detector time calibration• P.R. or fit ambiguities• Magnetic field mapping

Further improvements• detector alignment• detector time calibration• P.R. or fit ambiguities• Magnetic field mapping

26

σ = 147 µmσ = 147 µm

STRAW

VDET: σ ≈ 30 µm LMDC: σ(ρ,φ) ≈ 150 µm; σz 1% wire length

STRAW: σ(ρ,φ) ≈ 150 µm; σz = 500 µm, ∆p/p~0.4% (FWHM)

High momentum (and mass) resolution (tracker resolution + He bag+ thin tgts) and low thresholds (π:~60MeV/c, p:~120MeV/c)

σ = 153 µmσ = 153 µm

LMDC

Mean resolution of all cells over all angles and over all z with cosmic rays

The tracking region and the neutron detectorThe tracking region and the neutron detector

Global Calibration resultsGlobal Calibration results

27

vertex detector PIDK identification with inner

Vertex detector dE/dx

VDET Residual distribution

The interaction-target region The interaction-target region

VDET: σz ~ 30 µm

energy res.~ 25% (K)

28

Progress in Particle Identification

Suppression of MIPand p contamination on d and t discrimination with 3 and 4 layers !

d

p

π+μ+

d

p

d

d

t

Contamination in deuteron selection , as example

Contamination in triton selection

29

30

31

pπ -

π -

μ+

FINUDA FRONTAL VIEW

Wire chambersStraw tubes

ΛΛΛΛ-identification

VERTEX REGION

π -

π -

p

K+

ΛΛΛΛ

μ+

K-

Vertex detector

Beam pipe

12C

12C

51V 27Al

12Ci

7Li

6Li6Li

Plastic Scintillators

Example of Λ decayingOutside the tgt

32

Λ momentum

K- N →ΛπK- NN →ΛN

ΛΛΛΛ-identification

coincidence π- p with Λvertex reconstruction σσσσ=2.9MeV/c2 overallσσσσ=2.3MeV/c2 (long tracks only)

ΛΛΛΛ mass resolutionΛΛΛΛ mass resolution

33

Summary of the FINUDA Detector performancesSummary of the FINUDA Detector performances

• clean K- vertex identification (VDET P.I.D.+ r resol. + K+ tagging)• ππππ,K,p,d,… P.I.D. (VDET)•High momentum (and mass) resolution (tracker resolution + He bag

+ thin tgts) and low thresholds (π:~60MeV/c, p:~120MeV/c)•Neutron detection capabilities (outer scintillator barrel)•Selective trigger•Multiple targets (A-dependence)

• clean K- vertex identification (VDET P.I.D.+ r resol. + K+ tagging)• ππππ,K,p,d,… P.I.D. (VDET)•High momentum (and mass) resolution (tracker resolution + He bag

+ thin tgts) and low thresholds (π:~60MeV/c, p:~120MeV/c)•Neutron detection capabilities (outer scintillator barrel)•Selective trigger•Multiple targets (A-dependence)

-

• large solid angle (~2πsr) • large solid angle (~2πsr) • multitracking capabilities • multitracking capabilities

Simultaneous study of formation and decay hadronic systems with strangeness via full event recontruction

Simultaneous study of formation and decay hadronic systems with strangeness via full event recontruction

34

SOME RESULTS SOME RESULTS

1) Hypernuclear spectroscopy of 12ΛC

2) Hints on hypernuclear decay, rare decays

3) Search for Σ bound states

4) Search for deeply bound kaonic nuclei

1) Hypernuclear spectroscopy of 12ΛC

2) Hints on hypernuclear decay, rare decays

3) Search for Σ bound states

4) Search for deeply bound kaonic nuclei

35

Hypernuclear formation event

µ+

π-

K-

K+

Φ

µ+

π-6Li

µ++ ν+µ→K

−Λ

− π+→+ ZZKAA

Hypernuclear trigger:• 2 high-threshold b.t.b. tofino hits (K+K-)

• >2 hits on tofone• Tofino-Tofone time correlation (<20 ns)

Hypernuclear trigger:• 2 high-threshold b.t.b. tofino hits (K+K-)

• >2 hits on tofone• Tofino-Tofone time correlation (<20 ns)

36

Hypernuclear decay event

π-

µ+

K+

K-

F

p

37

++++

npd

tp

dd

Candidate for rare decay : 4ΛHe —>d+dCandidate for rare decay : 4ΛHe —>d+d

d

d

µ+

6Li

Hyperfragments production

Hyperfragments production

pd = 570 MeV/cback to back topologypd = 570 MeV/cback to back topology

++

++

+

Λ

Λ

Λ

ppH

npHe

pHe

4

4

5+→+ −− πLiK 6

→ΛHe4

39

M.C. simulations of π± inclusive spectra from background reactions

in 12C

ππππ+ momentum MeV/c

K- p→Σ- π+K- p→Σ+ π-

Σ+ → n π+

K- (NN)→Σ+ NΣ+ → n π+

TOT

K- n→Λ π-

Λ→p π-

K- p→Σ+ π-

K- p→Σ- π+

Σ- → n π-K- n→Σ0 π-

TOT

K- (NN)→Σ- NΣ- → n π-

ππππ- momentum MeV/c

The 12C (K-stop , ππππ) backgroundsThe 12C (K-

stop , ππππ) backgrounds

40

K+→µ+νK+→π+ π0

Σ+→π+n

Quasifree-Σ− production

Quasifree-Σ+,0 decay

K-stop+ 12C ⇒ ππππ++++ + X

K-stop+ 12C ⇒ ππππ−−−− + XK-

stop+ 12C ⇒ ππππ−−−− + X

Quasifree-Σ+,0 production

Quasifree-Σ− decay

12ΛC

???

Quasifree-Λ production

Exp. data on 12C targetExp. data on 12C target

Inclusive(K-stop, ππππ)Inclusive(K-

stop, ππππ)

41

Hypernuclear Physics: FINUDA can simultaneously provide the full pattern:

prompt ππππ−−−−, and p and ππππ−−−− from Hyp. decay and measure their spectra

Incl.ππππ−−−−

Hypernuclear

spectroscopy

ππππ-ππππ-

coinc.

pππππ−−−− (MeV/c)

Spectrum ofππππ- in

coincidene

Counts

/ 2 M

eV/c

7ΛΛΛΛLi

ππππ-pcoinc.

Proton spectrum in coincidence with

a π- from the Hyp. ground state.

NMW Hypernuclei

decay

Mesonic Hyp.

decay

12C (raw) excitation spectrum

K− + 12C → 12ΛC + π−K− + 12C → 12

ΛC + π−

Inclusive spectrum of negative pions from 12C targets. Hypernuclear peaks are visible even without any background subtraction

0

100

200

300

400

500

600

700

0.18 0.2 0.24 0.26 0.28 0.3 0.320.22

Cou

nts/

1 M

eV/c

p- momentum (GeV/c)

K- (NN)→Σ- N

Σ- → n π-

g.s.

High resolutionLong tracks only

44

12ΛC spectroscopy

FINUDA RESULTSFINUDA RESULTS ( ) CK stop12, Λ

−− π

2.1±0.27

0.27±0.066

-1.6±0.25

-3.8±0.14

-5.9±0.13

-8.4±0.22

-10.94±0.061

-BΛ (MeV)#

Best published result on 12ΛC (KEK E369)R ≈ 1.45 MeV FWHM

Production reaction: (π+,K+)

Preliminary FINUDA result on 12ΛC :R≈ 1.29 MeV FWHM

Production reaction: (K-stop, π-)

PR C64(2001)044302PR C64(2001)044302

Capture Rates for 12ΛC in FINUDA:

#1 ground state: ~ 2.5x10-3/K-stop #6 excited state: ~ 5.8x10-3/K-

stop

Capture Rates for 12ΛC in FINUDA:

#1 ground state: ~ 2.5x10-3/K-stop #6 excited state: ~ 5.8x10-3/K-

stop

45

Inclusive ππππ- spectra

Mettere figure su tutti I nuclei???

5ΛHe formation

Λ in p-orbit

Λ in s-orbit

#1

#3

#5

6Li

7Li 27Al

51V

−Λ +πLi6

pHe+Λ5

Neutron-rich hypernuclei Hypernuclei with a large neutron excess have been theoretically predicted (L. Majling, NPA 585 (1995) 211c).

The Pauli principle does not apply to the Λ inside the nucleus + extra bindingenergy (Λ “glue-like” role,dynamical contraction of the core nucleus) ⇒ a

larger number of neutrons can be bound with respect to ordinary nuclei (extension of the neutron drip line)

• Hypernuclear physics:

ΛN interactions at low densities, the role of 3-body forces (Λ−Σ coupling)• Neutron drip-line:

response of neutron halo on embedding of Λ hyperon, hypernuclear species with unstable nuclear coreT. Yu. Tretyakova and D. E. Lanskoy, Nucl. Phys. A 691: 51c, 2001.

• Astrophysics:

Feedback with the astrophysics field: phenomena related to high-density nuclear matter in neutron stars (role of Σ).S. Balberg and A. Gal, Nucl. Phys. A 625: 435, 1997.

1) strangeness exchange+ charge exchangeK- + p → Λ + π0

‌→ π0 + p → n + π+

π- + p → π0 + n‌→ π0 + p → K+ + Λ

2) strangeness exchange + Λ-Σ couplingK- + p → Σ- + π+

‌→ Σ- + p → Λ + n

π- + p → Σ- + K+

‌→ Σ- + p → Λ + n

Neutron-rich hypernuclei Production mechanisms (2 steps→low yield)

•K - + p → Σ + + π -

Σ + → π+ + n(130 < pπ < 250 MeV/c)

•K - + pp→ Σ + + n Σ + → π+ + n

(100 < pπ < 320 MeV/c)

Backgrounds:

Selection on impact parameter to minimize background

FINUDA(1st run):Study of inclusive π+ spectra

Neutron-rich hypernuclei

6.1�10-5/K-stop(2.0 ±0.4stat syst)�10-5/K-

stop12

ΛBe

-(4.5 ±0.9stat syst)�10-5/K-stop

7ΛH

-(2.5 ±0.4stat syst)�10-5/K-stop

6ΛH

From litterature

FINUDA valueSystem

6.1�10-5/K-stop(2.0 ±0.4stat syst)�10-5/K-

stop12

ΛBe

-(4.5 ±0.9stat syst)�10-5/K-stop

7ΛH

-(2.5 ±0.4stat syst)�10-5/K-stop

6ΛH

From litterature

FINUDA valueSystem

0.4

0.1

+−

0.4

0.1

+−

0.3

0.1

+−

PLB 640 (2006)145

FINUDA value 90% C.L.

1st data takingK- + 6Li � 6

ΛH + π+ (N/Z= 5) NEW

K- + 7Li � 7ΛH + π+ (N/Z= 6) NEW

K- + 12C � 12ΛBe + π+ (N/Z= 2)

K- + 6Li � 6ΛH + π+ (N/Z= 5) NEW

K- + 7Li � 7ΛH + π+ (N/Z= 6) NEW

K- + 12C � 12ΛBe + π+ (N/Z= 2)

Upper limits

Neutron-rich hypernucleiππππ+ spectra (production)

in coincidence with low-energy ππππ- (mesonic decay)Data Taking

2006-2007

Work in pro

gress

Higher statistics allows to effectively suppress backgrounds by asking the presence of a mesonic decay π-…

…statistical significance of a peak?

65

R.Bertini et al., Phys. Lett. 90B (1980) 375

Search for Σ bound statesSearch for Σ bound states

1) ΣN→ΛN conversion (strong int.) releases80 MeV and the Λ has considerableprobability to escape the nucleus

2) Strong mechanisms of suppression of theΣN→Λn conversion should be introducedto justify the existence of Σ−hypernuclei

1) ΣN→ΛN conversion (strong int.) releases80 MeV and the Λ has considerableprobability to escape the nucleus

2) Strong mechanisms of suppression of theΣN→Λn conversion should be introducedto justify the existence of Σ−hypernuclei

Experimental evidence of Σ−hypernuclei9

ΣBe, 12ΣC, 12

ΣBe, 12ΣC was claimed

PL 90B(1980)29, PL136B(1984)29, PL 158B(1985)19

Experimental evidence of Σ−hypernuclei9

ΣBe, 12ΣC, 12

ΣBe, 12ΣC was claimed

PL 90B(1980)29, PL136B(1984)29, PL 158B(1985)19

The evidence was definitely disclaimed by a high statistics experiment at BNL AGSPRL 83(1999)5238

The evidence was definitely disclaimed by a high statistics experiment at BNL AGSPRL 83(1999)5238

( )±−πKBe9 ,

R.Bertini et al., Phys. Lett. 136 (1984) 29

ΓΓΣΣ expected ~ 25 expected ~ 25 MeVMeVΓΓΣ Σ measured ~ 7 measured ~ 7 MeVMeV

66

Present knowledge on Σ hypernucleiPresent knowledge on Σ hypernuclei

PL B 231(1989)355, PRL 80 (1998) 1605PL B 231(1989)355, PRL 80 (1998) 1605

4ΣHe4ΣHe

• Only one Σ−hypernucleus has been definitelyobserved

4ΣHe (Σ≡Σ0,Σ+)

• It is considered an exception, connected withthe special structure of this system

• There is practically no evidence on heaviersystems

• Only one Σ−hypernucleus has been definitelyobserved

4ΣHe (Σ≡Σ0,Σ+)

• It is considered an exception, connected withthe special structure of this system

• There is practically no evidence on heaviersystems

Conversion reaction (Σ + N → Λ + N): 25 MeV

Local density approximation: 14 MeV

Pauli blocking factor: 11 MeVVarious mechanisms suppress the width: 5 MeV

Conversion reaction (Σ + N → Λ + N): 25 MeV

Local density approximation: 14 MeV

Pauli blocking factor: 11 MeVVarious mechanisms suppress the width: 5 MeV

Visible if: Peaks separation ≥ widthPeaks separation ≥ spectrometer resolution

Visible if: Peaks separation ≥ widthPeaks separation ≥ spectrometer resolution

No experimental evidence on heavier nuclei (inclusive expts)

FINUDA can detect the formation and decay of Σ-hypernuclei via (K-stop,Λπ)

reaction (Λ inv. mass reconstruction and secondary vertex)

FINUDA can detect the formation and decay of Σ-hypernuclei via (K-stop,Λπ)

reaction (Λ inv. mass reconstruction and secondary vertex)

67

K-stop + A → ΣB + π±

prompt

Σ + N → Λ + N

+Λ+→+Λ+→

++Λ+→

++Λ+→

+

→+

Σ

Σ

−Σ

Σ

−Σ

Σ

+Σ

−+

+

−

−

pBC

nCC

C

pBC

C

nBeBe

Be

CK

prompt

prompt

prompt

stop

1012

1012

12

1012

12

1012

12

12

0

0

0 π

π

π

Σ-hyp simulated eventΣ-hyp simulated eventReaction stepsReaction steps

How to look for Σ bound states in FINUDAHow to look for Σ bound states in FINUDA

Λ emittedΛ emitted

150-180 MeV/c150-180 MeV/c

Final state : π+prompt, p, π−, nFinal state : π+

prompt, p, π−, n

68

69

Monte Carlo simulations of Σ-hypernuclei

+Λ+→+Λ+→

++Λ+→

++Λ+→

+

→+

Σ

Σ

−Σ

Σ

−Σ

Σ

+Σ

−+

+

−

−

pBC

nCC

C

pBC

C

nBeBe

Be

CK

prompt

prompt

prompt

stop

1012

1012

12

1012

12

1012

12

12

0

0

0 π

π

π

binding energies and width are taken from: E.Oset et al., Phys. Rept. 188 (1990) 79

bound nucleons have Fermi mom.Σ mom. distr. prob. dens. funct.final state particles tested for Paulikinematics of f.s.p. feeds GEANT3 (geom., en. loss, trajectories)

E.Oset, A.Ramos, I.Vidana, private communication

2p

1s

tot

70

Kstop+ 12C →

−−Σ

+−Σ

+→Λ

+Λ+→

+

π

π

p

nBeBe

Be prompt

1012

12

2p

1s

tot

2p

1s

tot

2p

1s

tot

71

π-

π+prompt

p

Candidate for Σ bound state in 12CCandidate for Σ bound state in 12C

short tracksshort tracks

Minv(p,π−) = 1114 MeV/c2Minv(p,π−) = 1114 MeV/c2

Momenta at K- vertex• (π+) 176 MeV/c• (p ) 500 MeV/c• (π−) 158 MeV/c

Momenta at K- vertex• (π+) 176 MeV/c• (p ) 500 MeV/c• (π−) 158 MeV/c

K-stopped + 12C → 12

Σ-Be + π+prompt

12Σ-Be → 10Be + Λ + n

Λ → p + π-

K-stopped + 12C → 12

Σ-Be + π+prompt

12Σ-Be → 10Be + Λ + n

Λ → p + π-

72

Candidate for Σ bound state in 12CCandidate for Σ bound state in 12C

Interaction-vertex regionInteraction-vertex region

front viewfront viewside viewside view

π-π-

π+prompt

π+prompt

pp

K- interactionpoint

K- interactionpoint

Λ decayΛ decay

Λ decayΛ decay

π+prompt

π+prompt

π-π-

pp

K- interactionpoint

K- interactionpoint

73

Recently added: Conversion Reaction:

Σ N → Λ NFinal π’s q.f. scattering:

π N → π Ν

Recently added: Conversion Reaction:

Σ N → Λ NFinal π’s q.f. scattering:

π N → π Ν

K- n→Λ π-

Λ→p π-

K- p→Σ+ π-

K- p→Σ- π+

Σ- → n π-K- n→Σ0 π-

TOT

Monte Carlo simulations of background reactions for 12C

K- p→Σ- π+K- p→Σ+ π-

Σ+ → n π+

K- (NN)→Σ+ NΣ+ → n π+

TOT

ππππ- momentum Mev/c

ππππ+ momentum Mev/c

K- (NN)→Σ- NΣ- → n π-

74

Monte Carlo simulations of background reactions for 12C

Recently added:Conversion Reaction:

Σ N → Λ NFinal π’s q.f. scattering:

π N → π Ν’

Recently added:Conversion Reaction:

Σ N → Λ NFinal π’s q.f. scattering:

π N → π Ν’

K- n→Λ π-

Λ→p π-

K- p→Σ+ π-

K- p→Σ- π+

Σ- → n π-K- n→Σ0 π-

TOT

K- p→Σ- π+K- p→Σ+ π-

Σ+ → n π+

K- (NN)→Σ+ NΣ+ → n π+

TOT

ππππ- momentum Mev/c

ππππ+ momentum Mev/c

K- (NN)→Σ- NΣ- → n π-

Σ+,0-hyp region

Σ--hyp region

75

coincidence spectracoincidence spectra

Quasifree-Σ+,0 production

Quasifree-Σ− decay

12ΛC

???

Quasifree-Λ production

inclusive spectruminclusive spectrum

K-stop+ 12C ⇒ π− + X

ππππ-prompt x ππππ-ππππ-prompt x ππππ-

ππππ-prompt x pππππ-prompt x p

K- + 12C → 12Σ+C + π-

prompt

12Σ+C → 10B + Λ + p

Λ → π- + p

K- + 12C → 12Σ+C + π-

prompt

12Σ+C → 10B + Λ + p

Λ → π- + p

…cutting the (π- p) invariant mass distribution at Λ mass…cutting the (π- p) invariant mass distribution at Λ mass

ππππ-prompt x ππππ- x pππππ-prompt x ππππ- x p

76

K-stop+ 12C ⇒ π− + Λ (π−,p) + X

π−

Λ

π− p

K-stop⇒•

Searching for 12Σ+CSearching for 12

Σ+C

Λ cut

Measured spectraMeasured spectra

77

K-stop+ 12C ⇒ π− + Λ (π−,p) + X

quasifree-Λ production

quasifree-Σ production

π−

Λ

π− p

K-stop⇒•

Simulated backgroundSimulated background Measured spectraMeasured spectra

Searching for 12Σ+CSearching for 12

Σ+C

78

1s1p

BΣ+=0

BΣ0=0

K-stop+ 12C ⇒ π− + Λ + X

~7~2 [~7]1p

~7

6.7 [6.8](*)

~13 [~18]

7.5 [11.2](*)

1s

Γ[MeV]

Σ+ [Σ0]

B[MeV]

Σ+ [Σ0]

(*) Oset et al., Phys.Rep.,188(1990)79Initial evidence of:

Σ-Be, Σ+,0C, Σ+,0LiInitial evidence of:

Σ-Be, Σ+,0C, Σ+,0Li12 12 6

79

Σ identification via

Σ � Σ (π,n)

80

Alternative approach: study of π peak after Σ formation

81

End of lesson 5