HADRONIC CROSS SECTION MEASUREMENTS AT SND

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1 e + e Collisions from Phi to Psi 3 (PHIPSI3) International Journal of Modern Physics: Conference Series Vol. 3 () 6388 ( pages) c The Authors DOI:./S HADRONIC CROSS SECTION MEASUREMENTS AT SND Int. J. Mod. Phys. Conf. Ser..3. Downloaded from by on //8. For personal use only. M. N. ACHASOV,,V.M.AULCHENKO,, A. YU. BARNYAKOV, K. I. BELOBORODOV,,A.V.BERDYUGIN,,D.E.BERKAEV,, A. G. BOGDANCHIKOV,A.A.BOTOV,T.V.DIMOVA,,,V.P.DRUZHININ,, V. B. GOLUBEV,,L.V.KARDAPOLTSEV,,A.S.KASAEV,A.G.KHARLAMOV,, A. N. KIRPOTIN,I.A.KOOP,,A.A.KOROL,,S.V.KOSHUBA,D.P.KOVRIZHIN, E. A. KRAVCHENKO,,A.S.KUPICH,K.A.MARTIN,,A.E.OBRAZOVSKY, E. V. PAKHTUSOVA, YU. A. ROGOVSKY, A. I. SENCHENKO,S.I.SEREDNYAKOV,, YU. M. SHATUNOV,D.A.SHTOL,D.B.SHWARTZ,,Z.K.SILAGADZE,, A. N. SKRINSKY,I.K.SURIN, YU. A. TIKHONOV,, YU. V. USOV andi.m.zemlyansky Budker Institute of Nuclear Physics, Novosibirsk, 639, Russia Novosibirsk State University, 639 Novosibirsk, Russia Novosibirsk State Technical University, Novosibirsk, 639, Russia baiert@inp.nsk.su Published 8 December The preliminary results on multihadron processes obtained with the SND detector at the e + e collider VEPP- in the energy range from to GeV are presented. The results are interesting in connection with their contribution to the total hadronic cross section, the muon g- and a possibility to study excited vector mesons properties. The nucleon anti-nucleon production was also studied. Keywords: detector, hadrons, cross section.. Introduction Starting from, SND detector is carrying out the experiments at the VEPP- collider in the energy range from 3 MeV to GeV. The SND (Fig. ) isthe general purpose non-magnetic detector for low energy e + e -colliders. It consists of the 9 layers drift-chamber, the aerogel Cherenkov counters, the three-layer spherical electromagnetic calorimeter with 68 NaI(Tl) crystals and the muon system. During - years SND collected about pb integrated luminosity at the energy range.. GeV. This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 3. (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited

2 M. N. Achasov et al. Int. J. Mod. Phys. Conf. Ser..3. Downloaded from by on //8. For personal use only. Fig.. The SND detector: - beam pipe, - tracking system, 3 - aerogel cherenkov counter, - NaI(Tl) crystals, - phototriodes, 6 - iron muon absorber, muon detector, - focusing superconducting solenoids.. Multihadron processes Process e + e ωπ. This process was studied in the π π γ final state. The cross section measured using 3 pb data set is presented in Fig.. Uptodate, this is the most accurate measurement of this process above. GeV. The fit to the cross section was done with a sum of ρ(77), ρ() and ρ(7) contributions. Using SND data and CVC hypothesis the probability of τ ωπ ν τ decay was calculated B(τ ωπ ν τ )=(.96 ±. ±.)%. This value is in good agreement with the PDG data 3 B(τ ωπ ν τ )=(.9 ±.8)%. The e + e ωπ cross section can be expressed in term of the γ ωπ transition form factor F ωπγ : σ ωπ (E) = πα E 3 F ωπγ(e ) P f (E), where P f (E) is the phase space factor. From the measured cross section the energy dependence of the transition form factor was obtained (Fig. 3). This dependence at lower energies was measured earlier by NA6 experiment in ω π µ + µ decay. The solid curve represents the results of the VMD prediction with the parameters obtained from our cross section fit. The dashed curve shows the ρ(77) contribution only. One can conclude that it is hard to describe the data from e + e annihilation and NA6 experiment simultaneously within VMD model. Process e + e ηγ. This process was studied in the 7γ final state. Data set of 3 pb integrated luminosity was analyzed. About 6 events of the process were selected. The obtained cross section is shown in Fig.. The approximation was performed taking into account ρ(77), ρ() and ρ(7) contributions. This is the first measurement of the e + e ηγ process in the energy range above. GeV. Process e + e π + π π π. This process dominates in the energy region between and GeV. The data set of 3 pb was analyzed. The measured cross section is shown in Fig.. The main contributions come from the ρ() and ρ(7) resonances. This process can proceed via several intermediate states 6388-

3 Hadronic cross section measurements at SND Cross section (nb).6.. SND 3 SND CMD- DM ωπγ () ) / F ωπγ (q F SND 3 SND NA E (GeV) q (GeV) Int. J. Mod. Phys. Conf. Ser..3. Downloaded from by on //8. For personal use only. Fig.. The cross section for the e + e ωπ π π γ process obtained with SND detector in comparison with previous SND 6, CMD- 7 and DM- 8 measurements. The solid line is the result of the approximation by a sum of ρ(77), ρ () and ρ (7) contributions Fig. 3. The γ ωπ transition form factor. The circles represent our data, triangles are previous SND data and squares are dataof NA6 experiment. The solid curve represents a sum of contributions of ρ, ρ and ρ resonances, the dashed curve shows the ρ(77) contribution only. Fig.. The cross section of the e + e ηγ obtained by SND detector. The solid line is result of the approximation by a sum of ρ(77), ρ () and ρ (7) contributions ωπ,a π, ρ + ρ,ρf,andρf. The contributions corresponding to ωπ and non-ωπ final states were separated. They shown in Fig. 6. Process e + e π + π π. The measured e + e π + π π cross section is shown in Fig. 7. The result was obtained using pb data set. The contributions from the ω () and ω (6) resonances are seen. The result is in good agreement with previous SND 3 and BABAR data. Process e + e ηπ + π. This process was studied in the η γ decay mode. The data set of 3 pb was used. The measured cross section is shown in Fig. 8. The fit to the cross section was done with a sum of the ρ(77), ρ() and ρ(7) contributions. Using SND data and CVC hypothesis the probability of τ ηπ π ν τ decay was calculated to be B(τ ηπ π ν τ )=( )%. This value is in a reasonable agreement with the PDG 3 data: B(τ ηπ π ν τ )= (.39 ±.)%. Process e + e N N. The e + e n n and e + e p p processes were studied in the near-threshold region. The analysis of these processes was done on

4 M. N. Achasov et al. σ (nb) 3 3 BABAR DM CMD99 SND SND SND 6 8 E (MeV) σ (nb) 8 ωπ 6 non ωπ E (MeV) Int. J. Mod. Phys. Conf. Ser..3. Downloaded from by on //8. For personal use only. Fig.. The cross section for the e + e π + π π π process obtained with SND detector (solid circles and squars) in comparison with previous experiments: BABAR 9,DM,CMD-,and SND. σ,nb BaBar - SND(3) - SND() 6 8 E b (MeV) Fig. 7. The cross section for the e + e π + π π process obtained with SND detector in comparison with previous SND and BABAR data. σ B, nb Fig. 6. The cross sections corresponding to ωπ and non-ωπ intermediate states. 3 SND@VEPPM BaBar SND@VEPP SND@VEPP FIT s, MeV Fig. 8. The cross section for the e + e ηπ + π process obtained with SND detector in comparison with previous SND and BABAR data 6. The curve is the result of the approximation by a sum of the ρ(77), ρ () and ρ (7) contributions. the base of pb data set. The cross sections measured by SND are shown in Fig. 9 and Fig.. There no contradiction with previous data. 3. Conclusions During last 3 years experiments were carried out with SND detector in the c.m. energy range from 3 to MeV with about of 8 pb total integrated luminosity. The preliminary results were obtained in the energy range from to MeV for the following hadronic processes: e + e ωπ,ηγ,π + π π π,π + π π,ηπ + π,n n, p p. The obtained results are in agreement with previous measurements

5 Hadronic cross section measurements at SND σ(nb). SND SND FENICE E CM (MeV) Int. J. Mod. Phys. Conf. Ser..3. Downloaded from by on //8. For personal use only. Fig. 9. The cross section for the e + e n n process obtained with SND detector for two data sets separately in comparison with FENICE 7 data. Fig.. The cross section for the e + e p p process obtained with SND detector for two date sets separately in comparison with BABAR 8 data. Acknowledgments This work is partially supported in the framework of the State order of the Russian Ministry of Science and Education and by RFBR grants No. --6-a, -- -a, mol-a, a, 3--8-a and scientific school grant 3... References. M.N. Achasov et al., Nucl. Instrum. Meth.A98, 3 (9). V.M. Aulchenko et al., Nucl. Instrum. Meth.A98, (9).. Yu.M. Shatunovet al., Project of a new electron positron collider VEPP-, in Proc. of the 7th European Particle Accelerator Conference (Vienna, Austria, ), p J.Beringer et al. (Particle Data Group), Phys. Rev. D 86, ().. R.Arnaldi et al., Phys. Lett. B677, 6 (9).. M. N. Achasov et al., Phys. Lett. B 86, 9 (). 6. M.N.Achasov et al., Phys.Lett.B 86, 9 (). 7. R.R.Akhmetshin et al., Phys.Lett.B 6, 73 (3). 8. D.Bisello et al., Nucl.Phys.Proc.Suppl., (99) 9. V.P.Druzhinin, in Proc. of LP7 International Symposium, 3 (7) [hepex/7.3].. Bisello al., Nucl. Phys. Proc. Suppl (99).. R.R.Akhmetshin et al., Phys. Lett. B (999).. M.N.Achasov et al.,j. Exp. Theor. Phys. 96, 798 (3). 3. M.N.Achasov et al.,phys. Rev. D. 66, 3 ().. B.Aubert et al., Phys. Rev. D. 7, 7 ().. M.N.Achasov et al., JETP Lett. 9, 8 (). 6. B.Aubert et al., Phys. Rev. D 76, 9 (7). 7. A.Antonelli et al., Phys. Lett. B 33, 83 (993). 8. B. Aubert et al., Phys. Rev. D 73, (6)