· · 2010-07-08Giornata di Seminari - INFN sez. Trieste - 05/07/2010 - S.Piano -...

Giornata di Seminari - INFN sez. Trieste - 05/07/2010 - S.Piano - L’esperimento FINUDA

L’esperimento

FINUDA

Stefano PianoINFN sez. Trieste

FINUDA Collaboration


Bari University & INFN Bari

Brescia University & INFN Pavia

Pavia University & INFN Pavia

Torino University & INFN Torino

Trieste University & INFN Trieste

Torino Polytechnic & INFN Torino

L.N.F. / INFN Frascati

RIKEN

KEK

Seoul National University

Teheran Shahid Beheshty University

University of Victoria

JINRDubna

LNF -

INFNFrascati

DAΦNE

The FINUDA Collaboration


FINUDA physics program-

Λ

HYPERNUCLEAR SPECTROSCOPY

essential tool

for testing :•

theoretical models

of Λ-N

potentials

•

single particle

nuclear model predictions •

bound

states with strangeness

-

Λ

HYPERNUCLEAR SPECTROSCOPY

essential tool

for testing :•

theoretical models

of Λ-N

potentials

•

single particle

nuclear model predictions •

bound

states with strangeness

-

HYPERNUCLEAR DECAYS•

study of baryon-baryon weak processes

in nuclear

matter: Λ →πN

and ΛN→NN

-

HYPERNUCLEAR DECAYS•

study of baryon-baryon weak processes

in nuclear

matter: Λ

→πN

and ΛN→NN

-

SEARCH FOR:•

Neutron-rich hypernuclei

•

Rare decays•

Sigma hypernuclei

•

Deeply bound kaonic nuclei•

K-

multi-nucleon absorption

-

SEARCH FOR:•

Neutron-rich hypernuclei

•

Rare decays•

Sigma hypernuclei

•

Deeply bound kaonic nuclei•

K-

multi-nucleon absorption

ON DIFFERENT NUCLEISIMULTANEOUSLY


Hypernuclear

Physics at DAΦNE e+e-

collider

e+e-

Φ(1020) K+K-

~16 MeV

The K-

can be stopped in thin targets (~ 0.1

÷

0.3 g cm-2)

to produce hypernuclei

decay High resolution

spectroscopy

K-stop

+ + π-ΛZAZA

The Φ

decay is a source of:

• neutral and charged kaons

• collinear and tagged

• low energy (~16 MeV)


FINUDA DetectorDetector capabilities:

Selective trigger based on fast scintillation detectors (TOFINO, TOFONE)

Clean K- vertex identification(ISIM P.ID.+

x,y,z

resolution

+

K+

tagging)π±, K, p, d, t … P.I.D. (dE/dx)High momentum resolution

(6‰ FWHM) (tracker resolution+ He bag + thin targets)

Neutron detection (TOFONE)Time-Of-Flight (TOFONE-

TOFINO)


(BR 49% -

Ekin

~ 16 MeV)

12 scintillators (TOFINO)8 silicon microstrips layer (ISIM)8 targets10 silicon microstrip layer (OSIM)

some hundreds

Φ/s

Φe+ e-

K-/+

K+/-

crossing angle: 12.5 mrad

Interaction Region


FINUDA detectors performancess.c. solenoid: B = 1.0 T; field homogeneity within 2%

interaction/target region: K+/K-identification, hypernucleus production and detection

tracking devices: measurement of trajectories and momenta of charged particles (Δp/p 5‰)

external scintillator barrel: trigger and neutron detection

He chamber: minimization of particle multiple scattering

TOFout

:

σt

= 500 ps

FWHMefficiency ≥

10%;

ΔE = 8 MeV

Δp/p:

He atmosphere

= 5‰air

= 2%

VDET:

σz

= 30 μm;

ΔE = 25% FWHM (K)TOFin

:

σt

= 250 ps

LMDC:

σ(ρ, φ) = 150 μm;

σz

≤

1% wire length STB:

σ(ρ, φ) = 150 μm;

σz

500 μm

TOF

out

time resolutionTOFout

time resolution

VDET z resolutionVDET z resolution

PID in VDETPID in VDET


different targets in the same run➥

high degree of flexibility

simultaneous tracking of μ+

from the K+

decay ➥

energy and rate calibration

transparency ➥

“high”

resolution spectroscopyvery thin targets (0.1 ÷

0.3 g/cm2)

1

2 3

4

5

67

8

1 cm

coincidence measurement with large acceptancecomplete event ➥

decay mode study

4ΛHe → dd

FINUDA Key Features


2×6Li, 7Li, 3×12C, 27Al, 51V

Three

12C targets

for:•

calibration

data to

be

compared

with previous

measurements•

improvement

of the precision

of the measurement

on all

the hypernucleus observables

•

Other items of

physics

(deeply

bound kaonic states, multinucleon

K-absorption

) )

6Li6Li

7Li

51V 27Al

12C

12C 12C

Medium-heavy

targets:A-dependence

and feasibility

of higher

A studies

Light targets:

ideal for

weak

decay

studies.6

Λ

Li unstable

by

nucleon

emission, used

as doorway

for

light systems

5Λ

He, 4Λ

He, 4Λ

H.Light K--nucleus

systems

may

favour

the

formation

of

deeply

bound

kaonic states

The interaction-target region for the first data taking

•Average daily integrated luminosity ~ 2 pb-1

• Total integrated luminosity 257 pb-1


6Li 7Li

7Li

6Li

9Be

9Be

13C

D2

O

The interaction-target region for the second data taking

• 6Li e 7Liused

also

during

the first data taking;

•9Be: •hypernuclear

spectroscopy

with

high resolution

and high statistics• weak

decays

•D2

O:

important

comparison

with

“quasi” deuteron

in 6Li .

•13C:•hypernuclear

spectroscopy

with

high resolution

and high statistic•Comparison

with

12C from

the first data taking

2×6Li, 2×7Li, 13C, 2×9Be, D2

O

•Average daily integrated luminosity ~ 7 pb-1

• Total integrated luminosity 966 pb-1


Hypernuclear

event

π−

μ+

μ+

Κ+

Κ−

π−

Φ

K−

+ A →

Λ

A + π−K−

+ A →

Λ

A + π−

Presenter

Presentation Notes

This is the, let me say, typical event. Here you can see the π– from a hyperfragment formation reaction on 6Li target; on the opposite side we have the μ+ following the K+ decay.


12C (raw) excitation spectrum

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

momentum (GeV/c)

K−

+ 12C →

12

Λ

C + π−K−

+ 12C →

12Λ

C + π−

Raw spectrum of

negative pions

coming out the 12C targets.

Hypernuclear peaks are visible

already without any background subtraction


the measurement of the π-

momentum is possible thanks to the FINUDA capabilities of tracking and resolution

How did we detect an hypernucleus?

by conserving energy and momentum

the “strangeness exchange”

reaction it is not

the only possible way in which a negative pion

can be present

in the interaction K-N final state

1

2

3

4

Detecting Hypernuclei

−π

+μ


FINUDA vs. KEK-E369

H. Hotchi

et al., Phys. Rev. C 64 (2001) 044302 H. Hotchi

et al., Phys. Rev. C 64 (2001) 044302

ΔE ~ 1.5 MeV

FWHMΔE ~ 1.5 MeV

FWHM

12C(π+,K+)12C12C(π+,K+)12CC12Λ

ΔE ~ 1.3 MeV

FWHMΔE ~ 1.3 MeV

FWHM

12C(K-

,π-)12C12C(K-

,π-)12C−stopK C12

Λ

M.Agnello

et al., Phys. Lett. B 622 (2005) 35M.Agnello

et al., Phys. Lett. B 622 (2005) 35

Presenter

Presentation Notes

In order to see where we stand, we looked at the results obtained at KEK. Here you can see the comparison between our background subtracted spectrum and the published data. At present our energy resolution is of about 1.4 MeV. Our final value performance should be around 800 keV, so we hope to resolve the structures suggested in this region.


simulation of the background -

by means of MC simulations -

we reproduced the BΛ

distribution of the pions

coming from the possible reactions

Background simulation

BΛ

distribution of the pions


anti-boost side boost side

1) we fit the experimental distribution with the sum of N gaussians (for the signal) and 4 histograms for the background (the mean and the sigma of the gaussians are free to move around the input values)2) we repeat the fit with a more sophisticated fit tool fixing also the mean values and the sigma of the gaussians [ROOT TFractionFitter]

Fitting the Data


the muons curves in a different way and do not cover all the “roads”

(possible source of systematics)

the MC tracks are “cleaner”

than the real ones,quality cuts act in a different way in real data and MC

(possible source of systematics)

road = a given combination of detectors (OSIM, inner Drift Chambers, outer Drift Chambers)

nΛ

=n. of hypernucleiNK-=n. of stoppped kaonscR = capture rate

(formation probability per stopped kaon)επ

= all other efficiencies (trigger, geometrical acceptance, reconstruction, cuts)

εD

= overall detector efficiency

Capture Rate


FWHMFWHMfrom 1.65 to 1.95 from target to targetfrom 1.65 to 1.95 from target to target

BΛ

energy measurements-

absolute scale of the energy known at the level of 0.2 MeV-

possible systematic of the fit of 0.2-0.3 MeV -

global error of about 0.5 MeV

Hypernuclear

Spectroscopy: 7Li


capture Rate per stopped Kcapture Rate per stopped K

--

#1: 0.041 #1: 0.041 ±±

0.006 0.006 ±±

0.005 %0.005 %

#2: 0.058 #2: 0.058 ±±

0.008 0.008 ±±

0.006 %0.006 %

#3: 0.043 #3: 0.043 ±±

0.006 0.006 ±±

0.005 %0.005 %

#4: 0.052 #4: 0.052 ±±

0.007 0.007 ±±

0.006 %0.006 %

H. Tamura et al.

Nucl. Phys. A 754

(2005) 58c

excitation energies

are referred tothe ground state BΛ

= -5.58 ±

0.03 MeV[M. Juric et al. Nucl. Phys. B 52

(1973) 1]

Total in the bound region: 0.14 ±

0.02 ±

0.02 %

Hypernuclear

Spectroscopy: 7Li


Hypernuclear

Spectroscopy: 9Be


H. Tamura et al.

Nucl. Phys. A 754

(2005) 58c

excitation energies

are referred to the ground stateBΛ

= -6.61 ±

0.04 MeV

[M. Juric et al. Nucl. Phys. B 52

(1973) 1]

capture Ratecapture Rate#1: 0.022 #1: 0.022 ±±

0.006 0.006 ±±

0.002 %0.002 %

#2: 0.036 #2: 0.036 ±±

0.008 0.008 ±±

0.004 %0.004 %

#3: 0.027 #3: 0.027 ±±

0.006 0.006 ±±

0.003 %0.003 %

Total in the bound region: 0.058 ±

0.014 ±

0.006

Hypernuclear

Spectroscopy: 9Be


Hypernuclear

Spectroscopy: 13C


excitation energies

are referred to the ground stateBΛ

= -11.22 ±

0.08 MeV[M. Juric et al.

Nucl. Phys. B 52

(1973) 1]


0.001 0.001 ±±

0.001 %0.001 %

#2: 0.014 #2: 0.014 ±±

0.002 0.002 ±±

0.002 %0.002 %

#3: 0.018 #3: 0.018 ±±

0.002 0.002 ±±

0.002 %0.002 %

#4: 0.024 #4: 0.024 ±±

0.003 0.003 ±±

0.003 %0.003 %

#5: 0.035 #5: 0.035 ±±

0.005 0.005 ±±

0.004 %0.004 %

Total in the bound region: Total in the bound region: 0.062 0.062 ±±

0.0080.008

±±

0.008 %0.008 %

Hypernuclear

Spectroscopy: 13C


Hypernuclear

Spectroscopy: 16O


Total in the bound region: Total in the bound region: 0.027 0.027 ±±

0.0050.005

±±

0.003 %0.003 %


0.002 0.002 ±±

0.001 %0.001 %

#2: 0.021 #2: 0.021 ±±

0.004 0.004 ±±

0.002 %0.002 %

Hypernuclear

Spectroscopy: 16O


bound region

binding energy of the ground state

ground state

Conclusions

The capture rate (formation probability),per stopped K-, has been measured in the same experiment

for different targets*

-

First measurements for

7Li,

9Be and 13C

*(27Al and 51V will also be added to the analysis

CAPTURE RATE (PER STOPPED KAON) VS A

NPA 835 (2010) 414


•

Mesonic

weak decay like Λ

free weak decay:–

Λ → pπ-

B.R. 63.9% (Гπ-

)–

Λ → nπ0

B.R. 35.8% (Гπ0

)

–

lifetime τΛ

free

= 263 ps–

nucleons emitted with a momentum q ~ 100MeV/c

–

The

mesonic

weak decay

is suppressed in

nuclear matter due to the

Pauli blocking

of the nucleon in the final state

The two main decay mechanism inside a hypernucleus

are

Mesonic Weak decay

Non Mesonic Weak Decay (NMWD)

Decay modes of

Λ

hypernuclei


Non Mesonic

Weak Decay•

Λ

embedded in a nucleus

–

Λn → nn

(Гn

) “neutron-induced

decay”–

Λp → np

(Гp

) “proton-induced

decay”–

ΛNN → nNN

(Г2

) “two nucleons-induced

decay”

Total width decay ГT

=

ГM

+ ГNM

ГM

=

Гπ-

+ Гπ0

ГNM

=

Гn

+ Гp

+ Г2

mom

entu

m

270

MeV

/c

NΛ

N N

π

The non mesonic

decay

is the dominant decay channel for medium-heavy

nuclei

(A≥12)

(~ 415 MeV/c)


Hypernuclear

decay study in FINUDAStrategy: coincidence measurement

p

π-

charged Non-Mesonic channel

K-

stop

+ AZ → AΛ

Z + π-

AΛ

Z →A-2(Z-1) + p + n

charged Mesonic channel

K-

stop

+ AZ → AΛ

Z + π-

AΛ

Z →A(Z+1) + π-

S-EX 260-280 MeV/c

MVD80-110 MeV/c

NMWD 170-600 MeV/c

π-

π-


12Λ

C

11Λ

B

kinetic energy (MeV)

Hypernuclear

decay study in FINUDA: strategy

MWD NMWD

NMWD

decay

π-

and p spectra

(Λqf

decay)/K-np background subtracted & acceptance

corrected

Inclusive production π-

spectra

K-np background corrected

π-p

p

12Λ

C

11Λ

B 11Λ

B

Presenter

Presentation Notes

Ricordare la soglia per la rivelazione dei pi- mesonici: 80 MeV/c ovvero 22 MeV. Per la slide successiva: componenti del fondo: Lqf, K- decay in flight (dipende dalla posizione del bersaglio, boost o no boost)


T. M

otob

a (P

rivat

e C

omm

unic

atio

n)

Mesonic weak decay spectra: 7Λ

Li•

Correspondence with the calculated strenght 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 spinJπ

(7

Λ

Lig.s.

) = 1/2+ (Sasao, PLB 579 (2004) 258.)

•



A. Gal, Nucl. Phys. A 828 (2009) 72.

•

Formation of different excited states of the daughter nucleus

• Initial hypernucleus spinJπ

(7Λ

Lig.s.

) = 1/2+ (Sasao, PLB 579 (2004) 258.)

7Be: 3/2-gs

& 1/2-

(429keV)

3-body decays

PLB 681

(2009)1

39

Presenter

Presentation Notes

Gal: only major contributions are reported (with a common arbitrary width of 1 MeV) accounting for at least 20%(?) of the total decay rate; each of the 2 bars in 25-27 MeV stands for states spread over roughly 2-3 MeV) Motoba: empirical level energies where known and calculated where not known, in the Priv. Comm; only calculated levels in the old calculations. FINUDA resolution @ 38 MeV: 4.2 MeV FWHM; part under acceptance threshold: negligible


T. M

otob

a (P

rivate Com

mun

ication)

•



A. Gal, Nucl. Phys. A 828 (2009) 72.

•

Initial hypernucleus spinJπ

(9

Λ

Beg.s.

) = 1/2+

O.Hashimoto NPA 639 (1998) 93c.

•



A. Gal, Nucl. Phys. A 828 (2009) 72.


(9Λ

Beg.s.

) = 1/2+

O.Hashimoto NPA 639 (1998) 93c.


Be

9B: 3/2-gs

& 1/2-(2.75 MeV)

FINUDA

ΔT ~ 4 MeV

FWHM @38 MeV

PLB 681

(2009)1

39

Presenter

Presentation Notes

Our spectrum is consistent with the interpretation from (pi+,K+) exp. According to which 9LBe g.s. is dominantly a 1s-L coupled to 8Be(0+)g.s.


•


H. Bando et al, Pers. Meson Science (1992) p.571A. Gal, Nucl. Phys A 828 (2009) 72.

•

Two contributions of the 11C ground state 5/2-

and its 7/2-

excited state


(11Λ

Bg.s.

) = 5/2+ : experimental confirmation(Sato et al., PRC 71 (2005) 025203)

by different observable


B

T. M

otob

a (P

rivate Com

mun

ication)

11C: 3/2-gs

& 7/2-

(~6.5 MeV)

PLB 681

(2009)1

39

Presenter

Presentation Notes

5/2+: Zieminska (1975) emulsion data, Sato (KEK) (2005) by comparing the measured decay rate with calculations of Motoba (Perspectives 1992) Risoluzione in T @ 38 MeV=4.5 MeV


•


T. Motoba et al, Nucl. Phys. A 489 (1988) 683.A. Gal, Nucl. Phys. A 828 (2009) 72.

• 15Λ

Ng.s spin not known. Jπ

(15Λ

Ng.s.

) = 3/2+

D.J.Millener, A.Gal, C.B.Dover Phys. Rev. C 31 (1985) 499. Spin ordering not obtained from γ-rays of 16

Λ

O M.Ukai et al. Phys. Rev.C 77 (2008) 054315.

• First experimental determination of Jπ

(15Λ

Ng.s.

) = 3/2+ from decay rate value (and spectrum shape)


N

T. M

otob

a N

PA 489 (198

8) 683

.

15O: 1/2-gs

& sd

(~6 MeV)15O: 1/2-gs

& sd

(~6 MeV)

PLB 681

(2009)1

39


present data

T. Motoba

PTPS 117 (1994) 477

previous data

A.Gal

NPA 828 (2009) 72

A

Mesonic decay ratio: Γπ−

/ ΓΛ

fit from measured values for A=4-12 hypernuclei

strong nuclear structure effects

Presenter

Presentation Notes

Ricordare le ref. dei previous data! Su 5LHe: Szymanski e Kameoka; su 11LB: Noumi, Sato (Montwill non riportato ma si confonde con gli altri sulla scala del grafico) Errori: statistico: 17%, 28%, 20%, 35%; sistematico:4%, 6%, 15%, 13%.


12Λ

C

Acceptance

corrected

•

Spectrum of negative pions

for events in which a proton is detected in coincidence with a π-

•

Asking for the proton coincidence a clear peak emerges at

272 MeV/c

(ground state)

Non Mesonic weak decay spectra: the method

Proton energy spectrum from 12Λ

C p-induced NMWD before and after

the acceptance correction

339

events

Not acceptance

corrected

Presenter

Presentation Notes

The coincidence requirement reduces the background due to Lqf production in the inclusive pi-spectra, so that the hypernucleus formation peak(s) emerge(s) Protoni da Lqf (100 MeV/c) sotto soglia di rivelazione (~200 MeV/c)


NMWD p

Coincidence spectra: 12Λ

C, all targets

π-

normalization region

simulation + reconstruction + selection + normalization

Non Mesonic weak decay spectra: the methodbackground reaction: K-

np

Σ-

p

Σ-

n π-

coincidence

p

Data

subtraction

M. Agnello et al., NPA 804 (2008),151


Ahigh

: spectrum area above μ1N + FSI 2N(>70 MeV) ~ 5% 2NtotG,Garbarino, A.Parreno

and A.Ramos, Phys.Rev.Lett. 91 (2003) 112501.Phys.Rev. C 69 (2004) 054603.

assumption

Alow

Ahigh

μ

from fit

NMWD p

gaussian

fitfree μ 12

Λ

C

FSI & ΛNN contribution evaluation: the method

Alow

: spectrum area below μ1N + 2N + FSI

W.Alberico

and G.Garbarino, Phys. Rev. 369 (2002) 1.assumption2N / NMWD independent on A

Presenter

Presentation Notes

As model independent as possible method. Nevertheless, to relate the spectra area directly to the amplitude G1p, G2np it is necessary to make some assumption … light assumption! NEGLIGIBLE!!


N(Λp np)+Alow

+ Ahigh

Alow=

0.5 N(Λnp nnp) + NpFSI-lowN(Λp np) +

N(Λnp nnp) + NpFSI-low + Np

FSI-high

Alow

, Ahigh

proportional to A =

c’

+ A

d’Alow

+ Ahigh

Alow=

a’

+ A

b’a

+

A b

a=a’/c’= 0.65±0.14

b=b’/c’=0.009±0.013

d’/c’

< 10-3

Alow

Alow

+ Ahigh

= R(A)

FSI linear on A up to A=16

PLB 685 (2010) 247


R(A) = 0.5 + Γ2

/Γp

1 + Γ2

/Γp

+ bA

Γ2

/Γp =R(A) -

bA

-

0.5

1 –

R(A) -

bAΓ2

/Γp

not dependent on A

Γ2

/Γp

: eight values weighted mean = 0.43±0.25

ΓNMWD

Γ2 =Γn

/Γp

+ 1 + Γ2

/Γp

Γ2

/Γp = 0.24 ±

0.10

Bhang et al., EPJ A33 (2007) 259.

from the linear fit

systematics: all p-shell


• p-induced NMWD proton spectra from 5Λ

He to 16Λ

O

• FSI & 2N: “model–independent”

analysis by the exploitation of a large systematics

•

first experimental indication of the relevant rôle

played by the two–nucleon induced mode in the NMWD of hypernuclei

• contribution as large as almost 27% 24% of all the non–mesonic weak decays

• very large contributions from 2N suggested by theoretical calculation (Γ2

/ΓNMWD

~ 0.19 -

0.29)

W.Alberico, A.De

Pace, G.Garbarino

and A.Ramos, Phys. Rev. C 61 (2000) 044314.

G. Garbarino, A.Parreno

and A.Ramos, Phys. Rev. C 69 (2004) 054603.

E. Bauer and G. Garbarino

, NPA 828 (2009) 29.

• Γ2

/ΓNMWD

experimental indications:

present value: 0.24±0.10 PLB 685 (2010) 247H. Bhang et al., EPJ A33 (2007), 259: ~ 0.4 12

Λ

CJ.D.Parker et al., PRC 76 (2007), 035501: ≤

0.24 (95% CL) 4Λ

He

NMWD, FSI & 2N: results


d

dμ+

6Li

Hypernuclear

rare

decay

⎪⎩

⎪⎨

⎧

++++

npdtpdd

Hyper-fragments

production

Hyper-fragments

production

p

d

= 570

MeV/cback to

back

topologypd

= 570

MeV/cback to

back

topology

⎪⎩

⎪⎨

⎧

++

++

+

Λ

Λ

Λ

ppHnpHe

pHe

4

4

5+→+ −− πLiK 6

4Λ H →e

Capture rate:10-5

– 10-4

per K-

stop


Light hypernuclei

rare 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

•

4Λ

He

hyperfragments

production, from

all

targets–

4Λ

He

→ dd•

d momentum: 570 MeV/c

–

4Λ

He

→ pt•

p momentum: 508 MeV/c

•

5Λ

He hypernucleus formation–

From

6Li targets: K- 6Li →

5Λ

He

+ p + π

-

(π-

momentum: 275.15 MeV/c)–

From

7Li targets: K- 7Li → 5Λ

He

+ d + π

-

–

NM two-body

decay: 5Λ

He

→

dt•

d momentum: 597 MeV/c

dE/dx

p.id. TOF p.id.

p t

dd

p t

mips


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 binding energy

(Λ

“glue-like”

role) ⇒

a larger number

of neutrons can be bound

with respect to ordinary nuclei.

•

Hypernuclear physics:ΛN interactions at low densities, the role of 3-body forces

•

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.

S. Balberg

and A. Gal, Nucl. Phys. A 625: 435, 1997.


1)

strangeness

+ double charge

exchangeK-

+ p → Λ + π0

‌→ π0

+ p → n

+ π+

π-

+ p → π0 + n‌→ π0

+ p → K+

+ Λ2)

strangeness

exchange with Λ-Σ

couplingK-

+ p → Σ-

+ π+

‌→ Σ-

+ p → Λ + nπ-

+ p → Σ-

+ K+

‌→ Σ-

+ p → Λ + n

Neutron-rich hypernuclei Two production mechanisms:

Presenter

Presentation Notes

In the last years the study of nuclei beyond the neutron drip line has attracted much interest. Hypernuclei offer the opportunity to produce nuclear systems with an extreme neutron to proton ratio. The production of the neutron rich hypernuclei could be explained with 2 different production mechanisms: the so called strangeness and double charge reactions the strangeness exchange with Λ-Σ coupling We concentrated our efforts on this channel and we looked for a π+ trajectory reconstructed in the apparatus This is the measured spectrum, where the π+ were identified by their energy loss and their time-of-flight.


Neutron-rich hypernucleiK-

+ 6Li 6ΛH + 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)

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

stop12ΛBe

-(4.5 ±0.9stat syst)·10-5/K-stop

7ΛH


6ΛH

From litterature

FINUDA valueSystem

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

stop12ΛBe


7ΛH


6ΛH

From litterature

FINUDA valueSystem

0.40.1

+

−

0.40.1

+

−

0.30.1

+

−

PLB 640 (2006)145

FINUDA value

90% C.L.


Neutron-rich hypernucleiπ+ spectra (production) in coincidence with π-

(decay)Data Takin

g

2006-2007


Investigation

of

hyperon-nucleon/nucleus

interaction

via production of hypernuclei:

-

A

success story in the Λ-sector

(several

Λ-hypernuclei

found, precious

info on Λ-N/A potential)-

A troubled

story in the Σ-sector:

(large

width

expected

from

ΣN → ΛN abs)

-Contradictory

claims:▪Σ-hyp. claimed

on 6Li, 9Be, 12C,16O, 4He

[1]

▪

No

evidence

on 6Li,9Be(K-,π); CH, Si, Ni, In, Bi

(π-,K+) [2]

4Σ+/0

He: presently

the only

well established

Σ-hypernucleus

[1] Bertini et

al, PLB136 (‘84),Yamazaki

et

al i PRL54(‘85),Paul et

al NPA479(‘88),…[2] Sawafta

et

al, NPA639 (1998);Bart et

al,PRL83 (1999); Hayano

et

al, PLB231 (1989), Noumi

et

al, PRL89 (2002); Saha

et

al.,PRC70 (2004)…

Experiments essentially based on A(K-,π) and A(π-,K+)

inclusive reactions.

Study of the K-stop

A→ΣπΑ'

Reaction at DAφNE


K+

K-n

π- μ+

π+ π+

π-μ+

FINUDA spectrometer Central region

TGTS: 2×6Li,

2×7Li, 13C, 2×9Be, D2

O

FINUDA studied the Σ

production via the (semi) exclusive

K-stop

A→ nπ+π−A’

reaction.

Study of the K-stop

A→ΣπΑ'

Reaction at DAφNE

μ+ ν K+

Φ K-

A

π-

n

π+ A’ Σ− Σ+


Background reactions Inclusive vs. exclusive π-

spectra

K-

n→Λ π-

Λ→p π-

K-

p→Σ+ π-

K-

p→Σ-

π+

Σ-

→ n π-K-

(NN)→Σ-

NΣ-

→ n π-

K-

n→Σ0 π-

Sum

K-

n→Σ-

π0

Σ-

→ n π-

(K-stop

,nπ-

π+)

(K-stop

,π-

)

Σ

Bound region

π−

momenta

from 12C (K-stop

,π-) quasifree

reactions (simulated)

QF Σ

thresh


Σ+

formation Σ-

decay

K-

p→Σ+ π-

π-

momenta

from K-stop

6Li nπ+π−X with FINUDA

K-

p→Σ-

π+

Σ-

→ n π-

main contributions

to π-

spectrum: Σ

production and decay

π−

momenta

from K-stop

6Li nπ+π−X

MeV/c

K-

n→Σ-

π0

π0 p nπ+

Σ-

→ n

π-Backgrounds also from2-step/complex reactions,

involving e.g.Σ

N → Λ N (conversion

reaction)π

N → π’ N (SCX)

and possible contaminations

…

K-

p→Σ-

π+

Σ-

p→ ΛnΛ → pπ-


min miss mass expectedM(X)=M(5He)

2σ

cut3σ

cut

unphysical region

S/B~0.7Σ−

signalS/B~1.0

nπ±

combinatorial + incoherent background

1.

Discard events with unphysical missing mass

(γ

contamination,rescattered

neutrons)

Σ+

signal

nπ-

invariant mass nπ+

invariant mass

Study of K- 6Li → nπ+π-

X : X : Σ±

identificationidentification


S/B~1.2 S/B~1.8

miss. mass cut

min miss mass expectedM(X)=M(5He)

2σ

cut3σ

cut

unphysical region

1.

Discard events with unphysical missing mass

(γ

contamination,rescattered

neutrons)

nπ-

invariant mass


X : X : Σ±

identificationidentificationnπ+

invariant mass

Σ+

signalΣ−signal


S/B~1.2 S/B~1.8

Thr

Σ-

Σ-

decay

Thr

Σ+

Σ+

decayΣ+

formation Σ-

formation

Σ−

:remove

π-

from

Σ+

production Σ+

:remove

π+

from

Σ−

production

nπ-

invariant mass nπ+

invariant mass


X : X : Σ±


Σ+

signalΣ−signal


S/B~2.8S/B~1.9

Σ+

formationΣ-

decay

Mom π-

> Thr

Σ+

Σ-

formation Σ+

decay

Mom π

+> Thr

Σ-

Σ−

:remove

π-

from

Σ+

production Σ+

:remove

π+

from

Σ−

production

nπ-

invariant mass nπ+

invariant mass


X : X : Σ±


Σ+

signalΣ−signal


Taglio 2

Cut on the other

pion

S/B~2.8S/B~1.9

Improve

S/B by

applying

further

quality

cuts

on track fitting

and vertex

selection

nπ-

invariant mass nπ+

invariant mass


X : X : Σ±


Σ+

signalΣ−signal


Taglio 2S/B~2.9S/B~2.0

nπ-

invariant mass nπ+

invariant mass

Improve

S/B by

applying

further

quality

cuts

on track fitting

and vertex

selection


X : X : Σ±


Σ+

signalΣ−signal


Taglio 2S/B~2.9S/B~2.0

Cut on Cos Θnπ

(Σ

momentum

below

~170MeV/c)Cos Θnπ

<-0.2

nπ-

invariant mass nπ+

invariant mass


X : X : Σ±


Σ+

signalΣ−signal


S/B~3.9S/B~2.8

Cut on Cos Θnπ

(Σ

momentum

below

~200MeV/c)Cos Θnπ

<-0.2

σ~3.4MeV/c2 σ~3.4MeV/c2

nπ-

invariant mass nπ+

invariant mass


X : X : Σ±


Σ+

signalΣ−signal


7Li: π-

momentum in coincidence with Σ+

Search

for

possible

bound

states

on 6Li,7Li,9Be, 13C, 16O Via K-

A→ nπ+π-

XX

reaction

6Li: π-


-BΣ+

~5.4 MeV

ΓΣ+

~ 3.4 MeV

Significance

Z2σ

~4Significance

Z2σ

<1

Exponential + gauss. fit


Search

for

possible

bound

states


A→ nπ+π-

XX

reaction

-BΣ+

~7.6

MeV

ΓΣ+

~6.6 MeV

Significance

Z2σ

~5

-BΣ+

~ 4.7MeV ΓΣ+

~4MeV

9Be: π-

momentum in coincidence with Σ+ 13C: π-


Significance

Z2σ

~2


Search

for

possible

bound

states


A→ nπ+π-

XX

reaction

-BΣ+

~8.3 MeV

ΓΣ+

~5 MeVSignificance

Z2σ

~3

16O: π-



Search

for

possible

Σ-bound

states


A→ nπ+π-

XX

reaction

Significance

Z2σ

<1

6Li: π+

momentum in coincidence with Σ-

Significance

Z2σ

<1

7Li: π+



Search

for

possible

Σ-bound

states


A→ nπ+π-

XX

reaction

Significance

Z2σ

<2 Significance

Z2σ

<2

9Be: π+

momentum in coincidence with Σ- 13C: π+



Search

for

possible

Σ-bound

states


A→ nπ+π-

XX

reaction

Significance

Z2σ

<1

16O: π+



6Li data vs. 4He data6Li [1] DAFNE 4He[2] KEK

Yield (Σ−) No signal No signalYield (Σ+) ~2x10-3/K-

stop ~6x10-3/K-stop

[Σ+/Σ0]

B (Σ+) ~5.4 MeV 3.2 +0.4-1.4 MeV

Γ (Σ+) ~3.4 MeV 4.6 +2.1-1.8 MeV

[1] This work[2] Hayano

et al., PLB231(’89)

-6Li data appear consistent

to

4He data

[2]:

Binding

Energy, width

and Yield-isospin

dependence

similar

to

that

already

observed

on 4He (no

signals

of

Σ-

bound

states)

-Analysis is ongoing: refining data, further checks, better background description.

Summary and conclusions

NPA 835 (2010) 398


Akaishi & Yamazaki: What a Deeply Bound Kaon Nuclear State is

•

Nuclear bound states formed by a single (double) K-

and few nucleons, S = -1•

Deeply bound due to the strength of the KN strongly attractive interaction, I = 0

–

Simplest case: (KN) bound state: Λ(1405)•

The presence of Λ(1405) prevents a reliable perturbative

treatment

•

More composite states: can be interpreted as molecules formed by

Λ(1405)+xN–

covalent bonding K--nucleons, much stronger than the nuclear force–

The Λ(1405) should persist as such in a nuclear system

High nuclear density in a low temperature system !!!

ρ0 = 0.14 fm-3

Akaishi & Yamazaki (PLB535(2002), 70; PRC65(2002)…)

ρ0 = 1.39 fm-3

¯¯


Experimental approaches to DBKS•

Missing mass spectroscopy–

Measurement of the momentum of monochromatic recoiling particlesin the A(K-,N)X reaction

•

KEK-PS E471 (K-stop

)•

AGS E930 (K-in-flight

)•

FINUDA (K-stop

)•

KEK-PS E549 (K-stop

)

•

Invariant mass spectroscopy–

Based on the kaonic nuclear state decaying into YN pairs

•

(K-pp) → Λ + p•

(K-ppn) → Λ + d•

(K-ppnn) → Λ + t •

Typically: –

pΛ,p

~ 500 MeV/c–

pΛ,π

< 200 MeV/c–

p decay p

~ 500 MeV/c

–

Full event reconstruction desirable (necessary)–

Angular correlation between the emitted pairs necessary (desirable)

•

FOPI (heavy ion collisions) •

FINUDA (K-stop

)•

OBELIX (p He)•

KEK-PS E549 (K-stop

)

(d,t)

¯


Inclusive proton spectra (FINUDA)

No mono-energetic emission of N and YOnly on 6Li FINUDA

observes a bump (FINUDA Coll., NPA 775 (2006), 35)

:

two

nucleon

absorption

reaction

on quasi-deuteron: K-”d”→ Σ-+p

[6Li = α

+ d]

6Li 7Li

9Be 13C 16O

4HeE471


Inclusive proton spectra (FINUDA)

No mono-energetic emission of N and YOnly on 6Li FINUDA

observes a bump (FINUDA Coll., NPA 775 (2006), 35)

:

two

nucleon

absorption

reaction

on quasi-deuteron: K-”d”→ Σ-+p

[6Li = α

+ d]

6Li 7Li

9Be 13C 16O

4HeE549


Experimental approaches to DBKS•

Missing mass spectroscopy–

Measurement of the momentum of monochromatic recoiling particlesin the A(K-,N)X reaction

•

KEK-PS E471 (K-stop

)•

AGS E930 (K-in-flight

)•

FINUDA (K-stop

)•

KEK-PS E549 (K-stop

)

•

Invariant mass spectroscopy–

Based on the kaonic nuclear state decaying into YN pairs

•

(K-pp) → Λ + p•

(K-ppn) → Λ + d•

(K-ppnn) → Λ + t •

Typically: –

pΛ,p

~ 500 MeV/c–

pΛ,π

< 200 MeV/c–

p decay p

~ 500 MeV/c

–

Full event reconstruction desirable (necessary)–

Angular correlation between the emitted pairs necessary (desirable)

•

FOPI (heavy ion collisions) •

FINUDA (K-stop

)•

OBELIX (p He)•

KEK-PS E549 (K-stop

)

(d,t)

¯


Λ

identification with FINUDAFINUDA FRONTAL VIEW

VERTEX REGION


2NA: K- pp identification with

FINUDAΛp Invariant Mass to measure K-pp:

1.

Data taking 2003-2004:–

200 pb-1

2.

reconstruction of Λ’s–

pΛ

>

300 MeV/c–

6 MeV

FWHM

3.

Λ

and p angular correlation–

Events with a Λ-p coincidence: ~ 5%

–

Light targets only (3x

12C, 2x 6Li, 1x 7Li)

–

Λ

p should be oppositely emitted, apart from FSI

1

2

cosθYN

< -0.8


Λp invariant mass in FINUDA•

High resolution tracks only

•

A bump is observed–

Two nucleon absorption

•

K-

+ (pp) → Λp peak expected at 2.34 GeV

•

K-

+ (pp) → Σ0p → Λγ p 74 MeV

lower distribution, and

broadened–

Kaon nuclear bound state formation

•

K-

(pp) → X → Λp→ Σ0p → Λγ p

B = 115+6-5 (stat)+3

-4 (sys)

MeVΓ= 67+14

-11

(stat)+2-3 (sys)

MeV

fit region

FINUDA Coll., PRL 94(2005)212303

Acc

epta

nce

corr

ectio

n

M =

(2255 ±

9) MeV/c2

mK

+2mp

~ 20

0 ev

ents

in th

e pu

blis

hed

pape

r

SEMISEMI--EXCLUSIVE ANALYSISEXCLUSIVE ANALYSIS


FINUDA: 6Li(K-stop

,Λp)X

2006-2007 Data Taking• 8x statistics on: 6Li (7Li, 9Be)-

Improved tracking efficiency

-

Extended range of the reconstructed momentum-

Improved selections (missing mass)

-

Statistics large enough to study single tgt

spectra

not a

ccep

tanc

e co

rrect

ed

not a

ccep

tanc

e co

rrect

ed

not a

ccep

tanc

e co

rrect

ed

unphysical region


FINUDA: 6Li(K-stop

,Λp)X

FINUDA Coll., PRL 94(2005)212303

New inv mass spectra compatible with published one

New data Old dataSame cuts applied

A=6Li,7Li,12CA=6Li

not a

ccep

tanc

e co

rrect

ed

not a

ccep

tanc

e co

rrect

ed

not a

ccep

tanc

e co

rrect

edno

t acc

epta

nce

corre

cted

unphysical region


3NA: FINUDA study of 6Li(K-stop

,Λd)X•

Λd invariant mass to measure K-

ppn

absorption

•

Use of 6Li target: low background

•

6Li is

a well

known

[α+d] cluster–

Bump

observed

at MΛd

= 3251 MeV,

ΓΛd

=37 MeV–

25 events

in the peak,

statistical

significance 3.9σ

–

Yield: (4.4±1.4)x10-3/K-stop FI

NU

DA

Col

l., P

LB 6

54 (2

007)

80


FINUDA: study of A(K-,Λt)X

(A=6Li,7Li,9Be) (I)

•

K-

A → Λ t X•

A = 6Li,7Li,9Be

•

FINUDA thresholds:–

Λ

140 MeV/c

–

t 430 MeV/c

•

Λ

signal background free•

Λ, t pairs emitted back-to-back

•

High momenta

for Λ, t

FIN

UD

A C

oll.,

PLB

669

(200

8) 2

29

Only one measurement exists so far, from bubble chamber: 3 events by kin fit40 events observed in FINUDACapture rate: ~1x10-3/K-

Direct measurement of K-

absorption on 4He


FINUDA: study of A(K-,Λt)X

(A=6Li,7Li,9Be) (II)•

Many body K-

absorption role–

Simulations of different phase space reactions with cos(ΘΛt

)<-0.9 (filtered through apparatus acceptance)

–

Λ

and t momentum distribution compatible with:

a)

Four nucleon absorption with (Λt) or (Σt)

emissionb)

Four nucleon absorption with (Λt)N

emissionc)

NOT with (Λt)π: too small Λ

momentumd)

2-step pickup reaction (suppressed?)

K-

A → Σ0

t A’Σ0

→ Λ γ

a) b)

d)e)


DBKS and K-(multiN) conclusions•

[K-pp] → Λp:

–

MΛp

signal on different targets–

CosΘΛp ~ 1–

FSI alone cannot explain at the same time

MΛp

and CosΘΛp–

Needed a realistic model: K-

dynamics (bound state) + proton pairs momenta–

What is the role of short-range correlated proton pairs ?(R. Subedi

et al., Science 320(2008)1476)–

The models should explain most the observables !•

[K-ppn] → Λd:

–

CosΘΛd ~ 1–

Identified the QF-3NA–

Identified other two final states (analysis in progress)–

K-

is absorbed on quasi “α” (6Li = α

+ d)–

The role of Σ0

seems negligible•

[K-ppnn] → Λt:

–

CosΘΛt ~ 1–

Direct measurement of K-

absorption on 4He–

Capture rate: ~1x10-3/K-

•

Near Future: –

acceptance correction and final analysis of Λp

(and Λd)•

bump position and width with A from 6 to 16 –

neutron on coincidence with Λ, Λp and Λd•

participant (energy carrier) and spectator•

role of K-

α

absorption on Λp and Λd spectra


Summary•

1993 FINUDA experiment proposal (preprint LNF-93/021, 11 May 1993)

•

2003-04 FINUDA 1st data taking (200 pb-1 integrated luminosity)•

2006-07 FINUDA 2nd data taking (968 pb-1integrated luminosity)

•

2008 FINUDA 3rd data taking proposed in 2009 (for 1 fb-1 integr. lum. )

•

The proposed 3rd data taking could not find room in the LNF planning:“…

The FINUDA collaboration was placed in stand-by, until the

uncertainties on the roll-in of KLOE (entailing the switch of the IR) could be removed. It now appears clear that the roll-in of KLOE in late 2009 will take place, which suppresses the time window that FINUDA could have used. …”37th MEETING OF THE LNF SCIENTIFIC COMMITTEE (December 1 -2, 2008)

•

As a consequence, at beginning of 2009, decision was taken to de- commission the experiment


Conclusions

•

The FINUDA main task (the simultaneous study of spectroscopy and decay of hypernuclei

in a broad range of

A) has been achieved, with the ability of the apparatus to measure also MWD and rare decays into d-d

and p-t

of light

hypernuclei, not foreseen in the proposal.

•

FINUDA capability to reconstruct secondary verteces, short tracks and light ions allowed the study of the interaction of stopped K-

on multi-nucleons aggregates and the Σ±

hypernuclei

production.

•

Some other items, as the search of neutron rich hypenuclei, and the decay of hypernuclei

into two neutrons, cannot be

fully pursued because of the lack of statistics.

· · 2010-07-08Giornata di Seminari - INFN sez. Trieste - 05/07/2010 - S.Piano -...

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Transcript of · · 2010-07-08Giornata di Seminari - INFN sez. Trieste - 05/07/2010 - S.Piano -...