exclusive + – + – and + 0 – 0 production in two photon

April, 23-27DIS 2003

Exclusive +–+– and +0–0 production in two photon collision at L3 (page 1)

O. Fedin PNPI, Russia

Exclusive + – + – and + 0 – 0

production in two photon

collisions at LEP

Exclusive + – + – and + 0 – 0

production in two photon

collisions at LEP

O. Fedin, S. Nesterov, G. Sultanov, I. Vorobievrepresenting the L3 collaboration

April, 23-27 DIS 2003




Outline e+e– e+e– + – + – e+e– e+e– + 0 – 0

Exclusive and –production at Q2

0

Exclusive production for

1.2 < Q2 < 30 GeV2 [Subm. to Phys. Lett.]

+ – + – and + 0 – 0 at W > 2.4 GeV




Exclusive production at Q2 0 high energy data (161 < s < 208 GeV),

integrated luminosity 686.7 pb-1

e+e– e+e– + – + –

*4 tracks with zero charge* no photons* dE/dx CL(4) > 6%

e+e– e+e– + 0 – 0

* two tracks with zero charge*dE/dx CL(2) > 6%* 4 photons E > 100 MeV*two best 0 from constraint fit

p2t(4) < 0.02 GeV2

Sample of + – + – — 69542 events (66838 in 1.0 < W<3.0 GeV)Sample of + 0 – 0 — 5253 events (4740 in 1.0 < W < 3.0 GeV)




Efficiency and detector acceptance

Trigger efficiency calculated from the data: 91.8% for + – + –

51.8% for + 0 – 0

Detector acceptance and selection efficiency determined from MC (EGPC generator [F.Linde, PhD Thesis, 1988] )




Two pion mass spectra




Partial Wave Analysis methodPerformed in 1.0 < WGeV

Model with in different spin-parity states and isotropic 4M.Althoff et al. Z.Phys. C16, 1982]

*ABW12BW34JPJz+ perm.* A4

JP,Jz) = (0+, 0), (2+, 2), (0–, 0), (2+, 0), (2–, 0(1,2)) and 4 isotropic, no interference, significant only 0+ and (2+, 2); 4isotropic is effective background

MC integration of |A|2

Likekihood fit to the data in each Wbin




Fit results for

• M– and M

M–spectrum Mspectrum




Fit results for •Angle of pion in C.M.S. of with respect to the beam axis (Adair angle)

angle of in CMS angle of in CMS




Cross section for

• Total and dominant partial waves cross sections• Isospin ratio of the cross section is incompatible with I=0, 1




Cross section for

Broad enhancement near threshold of




Exclusive production for 1.2 < Q2 < 30 GeV2

Single tag e+e– e+e–tag e+e–

tag

*tagged electron 25 mrad < < 68 mrad

*p2t (etag––) < 0.2 GeV2

*Etag > 80% Ebeam

Z-pole (s 91 GeV) 1.2 < Q 2 < 8.5 GeV2, L e+e– = 148.7 pb-1

high energy data (s 195 GeV) 8.8 < Q 2 < 30 GeV2, L e+e– = 706.0 pb-1

at Z-pole sample of 851 events with WGeV at high energy sample of 498 events with W > GeV




M( + –) spectrum




Box method [D.M.Schmidt et al. NIM A328(1993)]

2 million MC events for channel

* 0 0

* 0 + –

* + – + –

Likelihood fit to the data




Fit results for 0 0

• M( + –) in different Q2 and W regions

Points represent the data, histogram shows fit results, hatched area shows 0 0 component




• Production angle and angle between decay planes

Points represent the data, histogram shows fit results, hatched area shows 0 0 component

Fit results for 0 0




Cross section of * 0 0

Z-pole data High energy data

• Broad enhancement near threshold of as seen in measurements at Q2 0

• Interval 1.1 < W< 3.0 GeV is chosen for Q2-dependence




Agrees well with GVDM form factor, pole is not sufficient

Fit with 1/(Qn(Q2+<W>2)2) n = 2.4 0.3(<W> = 1.945)Agrees with QCD expectation

n= 2 [M.Diehl et al. PRD 62 073014]

Cross section of * 0 0




High W two pion mass spectra

M = 763 4 GeV = 170 21 GeV

Mf2 = 1282 15 GeV f2 = 273 130 GeV

M = 1738 19 GeV = 130 61 GeV

• (770), f2(1270), (1700) are clearly seen




Breit-Wigner fit for high W

M = 763 4 GeV

= 170 21 GeV

Mf2 = 1282 15 GeV

f2 = 273 130 GeV




SummaryExclusive production at Q2

* Dominance of(JP, Jz) = (2+, 2) spin-parity state * Broad enhancement of near threshold* Cross section ratio is incompatible with isospin

I=0,1Exclusive production at high Q2

* Broad enhancement of near threshold as for Q2 ~ * Good agreement with the QCD expectation for differential cross

section de+e/dQ2

* GDVM form factor describes well Q2 dependence of

* Measurements of the at Q2 ~ and for Q2 > 1.2 GeV are consistent

* Low and high Q2 data are consistent with the same QCD prediction

High Wregion

* In + – + – (770), f2 (1270) and (1700) are clearly seen* In + 0 – 0 (770) and f2 (1270) are seen




Cross section + – + –

Comparison of total + –+ – cross section

exclusive + – + – and + 0 – 0 production in two photon

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