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Studies of radiative  meson decays with KLOE . P.Gauzzi (La Sapienza University and INFN – Rome) Contributed papers : ABS183, ABS184, ABS185. 31 st International Conference on High Energy Physics 24-31 July 200 2 , Amsterdam. Outline Scalars:  f 0 (980)  a 0 (980)

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Studies of radiative meson decays with kloe l.jpg
Studies of radiative  meson decays with KLOE

P.Gauzzi

(La Sapienza University and INFN – Rome)

Contributed papers: ABS183, ABS184, ABS185

31st International Conference on High Energy Physics

24-31 July 2002, Amsterdam

  • Outline

  • Scalars: f0(980)

  • a0(980)

  • Pseudoscalars:   

  • Conclusions


Da ne l.jpg
DANE

  • Frascati -factory: e+e- collider

  • s 1020 MeV  M ; peak3000 nb

  • 2001 performance:peak average

  • L(cm2 s1)5·1031 3.5·1031

  • day L dt (pb1)3 1.8

  • 2002 data taking started on

  • May 1st :same luminosity of 2001, background reduction of a factor 2—3

  • Collected data:

  • 2000: 25 pb-1  7.5 x 107f

  • (analysis completed)

  • 2001: 190 pb-1  5.7 x 108f

  • (analysis in progress)


Slide3 l.jpg
KLOE

  • Drift chamber:

  • gas: He-iC4H10

  • dpT/pT= 0.4%

  • xy150 m ; z2 mm

  • E.m. calorimeter (Pb-Sci.Fi.):

  • sE/E = 5.7% / (E(GeV))

  • st = 54 ps/(E(GeV))50 ps

  • 98% of 4

Magnetic field:0.52 T


Scalar mesons j pc 0 l.jpg

  • f0(980) (I=0) f000+-  = 40—100 MeV

  • a0(980) (I=1) a0 “ “

  • not easily interpreted as mesons (3P0 nonet)

  • Other interpretations: states (Jaffe ’77)

  • molecules (Weinstein-Isgur ’90)

  • Br(f0(980)) and Br(a0(980)) and the mass spectra are

  • sensitive to the nature of these scalar particles:

Scalar mesons (JPC= 0++)

Br(f0) 5  10-5 3  10-4 10-5

Br(a0) 2  10-5 2  10-4 10-5

  • Studied decays (data sample: 16 pb-1 from the 2000 data,~5107)

  • f0 ; f000  5  final state

  • a0 ; a00  (39%)  5 

  • a0 ; a00 +-0 (23%)  2 ch. tracks +5 

  • first observation 

Previous meas.

at VEPP2M


5 final state l.jpg
5  final state

  • cross sect.(nb)

  • Signal: 00 (f0 ; (500) ; 00) ~ 0.35

  •  00  0

  • 0 ( a0 ;  00) ~ 0.1

  •  

  • Background: e+e-0 00 (0) ~ 0.5

  • 3 (with accidental ’s) (~17)

  •  000 (with 2 lost) (~14)

  • Sample selection:

    • exactly 5 prompt photons

    • E > 7 MeV

    • |cos| < 0.93 to avoid the quadrupole region

    • 5Ei > 700 MeV to reject KLKS neutrals


Slide6 l.jpg

0

0

00

  • Constrained kinematic fit

  • to improve resolutions

  • Photon pairing

  • |M - M| < 5(M)

  • Reject events with:

  • |M - M| < 3(M)

  •  3102 events

    • <> = 40%

1+cos2

Estimated backgr. (~20%)

e+e-0 00 33924

0 16616

 000 15912


Fit to m spectrum l.jpg

radiative g

radiative g

gKK

gf0KK

gf0

f

0

0

K+

f

g

f0

K-

0

0

Fit to M spectrum

  • Model :

  • 1) f0 dominated by kaon loop

  • (Achasov-Ivanchenko, Nucl.Phys.B315(1989))

  • 2) f0 propagator with finite width corrections

  • 3) (500) B-W with M=478 MeV and =324 MeV

  • (Fermilab E791-Phys.Rev.Lett.86(2001)770)

  • 4) point-like coupling of (500) to 

  • (Gokalp,Yilmaz,Phys.Rev.D64(2001))

  • 5)  + interference term parameterizations

  • from Achasov-Gubin, (Phys.Rev.D63(2001))

  • Two fits:

  • Fit A : | (f0) + (00 )|2

  • Fit B : | (f0)+ () + (00 )|2

  • Free parameters: Mf0, g2f0KK, g2f0/g2f0KK, g and

  • Br(0000)


Fit results l.jpg

  •  contribution negligible

  • Br(00) = (1.09  0.03  0.05)  10-4 (Fit B)

  • (SND: (1.220.10 0.06)  10-4 ; CMD-2: (1.080.170.09)  10-4)

Fit results

A B

2/ndf 109.5/33 43.2/32

Mf0 (MeV) 9624 973 1

g2f0KK/(4) 1.290.14 2.79 0.12

(GeV2)

g2f0KK/g2f0 3.220.29 4.000.14

g — 0.060 0.008

  • Large f0- destructive interference at M < 700 MeV

    (see also the work of Gokalp and Yilmaz (Phys.Rev.D64(2001)on the SND spectrum)


0 with l.jpg

Events

cos

0 (with )

  • Constrained kinematic fit

  • to improve resolutions

  • Photon pairing: (1) 00 ; (2) 0

  •  reject00 events

  • M  < 760 MeV (reject f0 events)

  • |M - M| < 3(M)

  •  916 events <> = 32 %

Events

M (MeV/c2)

  • Estimated backgr.: (~30%)

  • e+e-0 00 546

  • 00 15216

  •  000 9810

  •   52

  • Data —MC

Br(0)=(8.510.510.57) 10-5

SND :(8.8 1.40.9)  10 –5 ;CMD-2: (9.0 2.41.0)  10 –5


0 5 0 l.jpg
0 +-5 (+-0)

  • No background with the same final state

  • Backgr.: 2 Tracks + 3/4 photons (e+e-0 ; +-0)

  • ( ; +-0)

  • 2 Tracks + 6 photons

  • (KSKL+-000)

  • 1 vertex in IR with 2 tracks

  • 5 prompt  (E>10 MeV, |cos|<0.93)

  • Constrainedkinematic fit

  • M+-< 425 MeV (reject KS  p+p-)

  •  197 events <>=19%

  • estimated backgr. 44 events

Br(0)=(7.960.600.47)  10-5


Fit to the m spectra l.jpg

a0 shape

dBr/dm10-6 (MeV-1)

Fit to the M spectra

  • Same model as for the f0 (kaon loop)

  • Combined fit, relative normalization fixed

  • to Br()/Br(+-0)

  • Free parameters:

  • g2a0KK, ga0/ga0KK and Br(000)

  • Ma0=984.8 MeV (PDG) fixed

  • 2/ndf 27.2/25

  • g2a0KK/(4) (GeV2) 0.40  0.04

  • ga0/ga0KK1.35  0.09

  • Br(000) (0.5  0.5)  10-5

5

+-5

Br(a00)= (7.4  0.7)  10-5

M (MeV/c2)


Summary of fit results l.jpg

  • f0 parameters are compatible with model

  • a0 parameters seem not compatible with model

Summary of fit results

  • Comparison with predictions from Achasov-Ivanchenko, Nucl.Phys.B315(1989)

KLOE

f0 model

g2f0KK/(4) 2.790.12 2.3 (=g2a0KK/4) 0.15 (=g2a0KK/4) 0.3 (=2g2a0KK/4)

(GeV2)

gf0 /gf0KK 0.500.01 0.3—0.5 2 0.5

Br(00)1041.090.07 ~ 1 ~ 0.15 ~ 0.2

a0 model

g2a0KK/(4) 0.400.04 2.3 (=g2f0KK/4) 0.15 (=g2f0KK/4)

(GeV2)

ga0/ga0KK 1.350.09 0.91 1.53

Br( a0)1040.740.07 ~ 2 ~ 0.2


Slide13 l.jpg
 / 

  • The mass eigenstates ,  are related to the SU(3) octet-singlet

  • 8, 1 through the mixing angle P

  • Recent studies based on PT and phenomenological analyses

  • suggested a two mixing angle scenario

  • In the quark flavour basis the two mixing angles are almost equal

  •  mixing is described by only one parameter (P)

  • Pcan be extracted from the ratio(Bramon et al., Eur.Phys.J.C7(1999)) :

  • Br() can probe the gluonic content of 


Slide14 l.jpg
 / 

  • Same final state +- 3:

  • ;+-0;0 Br  3  10-3

  •  ; +- ;  Br  2  10-5

  • Backgr.: KLKS(with KLdecaying near the IP), +-0

  • Data sample : 16 pb-1 from the 2000 data (~5107 )

  • 1 vertex in IR with 2 tracks

  • 3 prompt  (E>10 MeV, |cos|<0.93)

  • Constrainedkinematic fit

  • :

  • 320 < Erad<400 MeV

  • E++E-< 550 MeV (reject +-0)

  •  N() = 50210  220 events  = 37 %


Slide15 l.jpg
 / 

  • :

  • Main background is 

  • Selection: elliptic cut in the plane

  • of the two most energetic photons

N() = 120 12 5 events  = 23 %

  • F =0.95 (interference with e+e-( )

M (MeV)


Slide16 l.jpg

(2)

(1)

 / 

  • Mixing angle: P=(41.8  1.7)

  •  P=(-12.9 1.7)

  • Using Br() = (1.297  0.003) % (PDG)

  •  Br() = (6.10 0.67  0.45)  10-5

  • PDG : (6.7 )  10-5

  • Gluonic content of :

  • Consistency check: if Z=0  |Y|=cosP

  • other constraints on X and Y from:

  • (1) /(0

  • (2) /(0


Conclusions l.jpg
Conclusions

  • With the 2000 data KLOE studied the radiative decays of the

  •  into scalar and pseudoscalar mesons

  • We measured the branching ratios of :

  • 00  Phys.Lett.B537(2002)

  • 0  “ “ B536(2002)

  • reducing the experimental uncertainties

  • We evaluated the couplings of f0 (a0) to KK and to  () from

  • the fit to the invariant mass spectra

  • Pseudoscalar mixing angle in the quark flavor basis,

  • and best measurement of Br()  Phys.Lett.B541(2002)

  • Other KLOE results: KSe (Phys. Lett.B535(2002)),

  • (KS+-()) / (KS00) (Phys.Lett.B538(2002))

  • Analysis on 2001 data (190 pb-1) is in progress,

  • results on f0+- are also expected, other 300 pb-1 from 2002

  • data taking are foreseen


Comparison with other experiments l.jpg
Comparison with other experiments

 decays

other

f0KLOE SND(1) CMD-2(1) WA102(2) E791(3)

Mf0 (MeV)9731 9705 9757 9878 9774

g2f0KK/(4) 2.790.12 2.470.73 1.480.32 0.390.06 0.020.05

(GeV2)

g2f0KK/g2f04.000.14 4.60.8 3.610.62 1.630.46 0.20.5

g0.060 0.008

a0KLOE SND E852(4) Crystal Barrel(5)

Ma0 (MeV)984.8 (fixed) 995 9913 9996

g2a0KK/(4) 0.400.04 1.4 0.220.03

(GeV2)

ga0/ga0KK 1.350.09 0.750.52 1.050.06 0.93—1.07

  • f0   ;  contribution negligible (CMD2: combined f000f0+-)

  • (2) WA102 (CERN): centrally produced K+K-,+- in pp at 450 GeV/c

  • (3) E791 (Fermilab): f0 production in DS-+

  • (4) E852 (BNL): a0 production in -p+-n and -p0n at 18.3 GeV/c

  • (5)


Scalar mesons j pc 019 l.jpg

  •  f0(980) a0(980) are not easily interpreted as qq mesons

  • Other interpretations: qqqq states (Jaffe ’77)

  • KK molecules (Weinstein-Isgur ’90)

Scalar mesons (JPC= 0++)

  • f0(980) (I=0) f000+-  = 40—100 MeV

  • sizeable ss contents; strongly coupled to KK

  • a0(980) (I=1) a0 “ “

  • coupled to KK

  • Possible interpretation (3P0 nonet):

  • f0-a0 mass degeneracy

  • f0 decay is OZI suppressed

  • small  partial width (0.3—0.4 keV)

  • small masses wrt the 3P2 nonet ( ~ 1500 MeV)

  • other candidates for the 3P0 nonet (a0(1450), f0(1370), f0(1710))


0 0 rejection l.jpg
00 rejection

Data

  • 0

  • 000

  • 00

|M(1)- M (2)| (MeV)

M (MeV)

(0 wrong pairing)

  • Parabolic cut to reject 0

  •  M < 760 MeV to reject f0 + 0 wrong pairing

  • 00 MC-simulation with the experimental M spectrum


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