Markus Büscher [email protected] DPG Frühjahrstagung Mainz 2004 1 Isospin breaking a 0 -f 0...

Markus Bü[email protected]

DPG Frühjahrstagung Mainz 20041

Isospin breaking a0-f0 mixing

Markus BüscherForschungszentrum Jülich

Germany

... a tool to investigate (not only!) the structure of the light scalar mesons



Nature of these states??„Genuine“ qq4-quark statesKK molecules

The light scalar resonances

COSY

S

I

K*(?)

K*(?) K*(?)

K*(?)

a0-(?) a0

0(?) f0(?) a0+(?)

f0(?)

Nonet of light scalar mesons JP=0+ f0(500) (““)

f0(980)a0(980)

f0(1370)K0*(1430)a0(1450)f0(1500)f0(1710)

Possible candidates

9 states}10 states}



Observables?

KK

(KK/) = (0.183±0.024) (“seen“/“dominant“)

(KK/) = ... (“seen“/“dominant“)

a0– a0

0 f0 a0+

I3= –1 0 +1

m = (984.7±1.2) MeV/c2 (“average“) = (50...100) MeV/c2 (“estimate“)

m = (980±10) MeV/c2 (“estimate“) = (40...100) MeV/c2 (“estimate“)

a0

f0

Observables at COSY (yet unknown): Mass distributions Branching ratios to KK and (Differential) production cross sections Isospin ratios (e.g. pn vs. pp reactions) a0-f0 mixing Polarization observables

COSY limit

a0



The Accelerator: COSY-Jülich

COSY (Cooler Synchroton)at FZ-Jülich:

• (polarized) p & d beams

• phase-space cooling– electron & stochasting cooling

• p = 0.30 – 3.70 GeV/c– pp pp X (mX 1.1 GeV/c2)– dd X (mX 1.03 GeV/c2)– pp pK+ Y* (mY* 1.5 GeV/c2)

• internal & extracted beams



The detectors: ANKE & WASA

WASA ANKE

In operation since1998

Ready for experimentsin 2006

-currently at CELSIUS (Uppsala)-nearly 4 coverage-charged and neutral particle i.d.-frozen pellet target (L ~ few1032 cm-2s-1)

-forward spectrometer (small acceptance)-optimized for K+/K- detection-cluster jet target (L ~ few1031 cm-2s-1)



The a0/f0(980) at COSYReaction Where? Result Goal

pp pp K+K- COSY-11ANKE

a00/f0 contribution??

pp d K+K0 ANKE a0+ channel

dominates

d + WASA First „simple“ experiment

for WASA (2006)

pn d K+K- ANKE (Feb. 2004)

d 0 WASA Angular asymmetriesa0-f0 mixing

pd 3He K+K- MOMO a00/f0 contribution??

3H K+K0

dd 4He K+K- ANKE Winter ’04/05?

4He 0 WASA Isospin violationa0-f0 mixing



p(2.65 GeV)pdK+K0 at ANKE

Fit:Fit:[(KK)S d]P + [(KK)P d]S

tot(pp dK+K0) = (38 ± 2stat ± 14sys) nb

Q = 46 MeV

•K+d coincidence measurement•Identification of ppdK+X events via TOF, E and particle momenta•Identification of ppdK+K0 events via dK+ missing mass

Dominance of a0+ channel

K+ d

m(K

+)+

m(K

0)

83%

V.Kleber et al., PRL 91, 172304 (2003)



a0-f0 mixing in dd 4He 0

Strength of a0-f0 mixing unknown• Probably larger than 0- mixing• Close & Kirk: mixing intensity = 8±3% (data from WA102) but critizised by Achasov & Kiselev, Oller

dd 4HeX cross section unknown• Our estimate: (dd 4He a0

0) ~ (50 ... 200) pb• Pilot measurement: dd 4He a0

0/f0 4He K+ K–

Similar to dd 4He 0 experiment @IUCF

Direct production of a00 in dd 4He a0

0 ( 0) is forbidden if isospin is conserved

(12.7 ± 2.2) pb

(15.1 ± 3.1) pb

E.J.Stephenson et al.,Phys. Rev. Lett. 91, 142302 (2003)

ANKE

Dominant channel dd 4He f0(I=0) 4He a0

0(I=1) 4He 0 ??



dd (0) vs. dd 0

CSB in propagationof a0/f0

production

Details in: C.Hanhart, nucl-th/0306073

20m

Production

nPropagatioCSB

00 /fa

N

m

1

0000 /fa/fa

00/faN m m-

1

t

1

<<d d

a0

0

d d

f0

a0

0

d d

0

d d

0

?

or 0/



More a0-f0 mixing ...

f0 a0

K0

K0

_

Further enhancement: “Kaon loops“

f0 a0

K–

K+

8 MeV

“normal“ CSB

o(1%)

N.N.Achasov et al., PLB 88, 367 (1979)

CS

B a

mp

litu

de

d d

f0

a0



a0/f0 mixing in pn interactions Look, e.g., for angular asymmetries around 90°in pn d+Meson reactions

V.Grishina et al., PLB 521, 217 (2001) V.Kudryavtsev et al., PRC 66, 015207 (2002)

no mixing

„direct“a0-f0 or -

mixing

Kaon loops

angular distribution of the a0 mass distributionpn pn(d) 0

a00 a0

0



People ...M.Büscher, C.Hanhart, V.Hejny, S.Krewald, A.Sibirtsev, H.Ströher

IKP, FZ Jülich

U.-G.MeißnerHISKP, Universität Bonn / IKP, FZ Jülich

V.KleberIKP, Universität zu Köln

P.Fedorets, L.Kondratyuk, A.KudryavtsevITEP, Moscow, Russia

V.GrishinaINR, Moscow, Russia

A.Dzuba, V.Koptev, S.Mikirtychiants, M.NekipelovPNPI, Gatchina, Russia

and the ANKE collaborationExperimentTheory http:www.fz-juelich.de/ikp/anke



I.d. of ppdK+K0 events @ ANKE

K+

d

T = 2.65 GeV

t

p• K+-d coincidence measurement

• Identification of ppdK+X events via TOF, E and particle momenta

• Identification of ppdK+K0 events via dK+ missing mass

Background < 10%

COSY

beam

Spectrometer dipole



First Results on the a0+

V.Kleber et al., PRL 91, 172304 (2003)

nucl-ex/0304020

Q = 46 MeV

Fit:Fit:[(KK)P d]S + [(KK)S d]P

tot(pp dK+K0) = (38 ± 2stat ± 14sys) nb

(pp da0+ dK+K0) =

83% · tot

p p d K+K0 (ANKE)



p(2.65 GeV)ndK+K- at ANKE

• D2 as an effective neutron target• K+ K- d coincidence measurement• unobserved spectator proton

First data on -mesonproduction on neutrons

Narrow a00/f0 signal

at small K+K- masses??

K+ d

K-

m(K

+)+

m(K

- )

inv. mass (K+K-)

verypreliminary!!

Markus Büscher [email protected] DPG Frühjahrstagung Mainz 2004 1 Isospin breaking a 0 -f 0...

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