# SND Experiment

Spherical Neutral Detector in Budker INP, partially unmounted (2008).

Spherical Neutral Detector (SND) is a detector for particle physics experiments, successor of the Neutral Detector (ND),[1] created by the team of physicists in the Budker Institute of Nuclear Physics (BINP), Novosibirsk, Russia. There are three major periods in evolution of the SND experiment;

## Physics

Previous experiment with ND[3] (predecessor of SND) has shown that the e+e annihilation in the final states with neutral particles in the energy range 2E=0.4-1.4 GeV is mediated by the processes which need to be studied in more details. In particular,

• quark structure of the light scalar mesons can be studied in electric-dipole radiative decays ${\displaystyle \phi \to a_{0}(980)\gamma ,~~f_{0}(975)\gamma }$;
• precise measurement of the e+eannihilation cross section into hadrons is the important component in definition of the muon anomalous magnetic dipole moment;[4]
• precise measurement of the hadronic cross sections is necessary to study the radial excitation of the light vector mesons ρ, ω, and φ;
• measurement of the higher order quantum electrodynamic (QED]) processes is important for the QED theory test.

This physics can be studied with dedicated detector at higher statistics, for this purpose the SND was constructed with many improvements relative to ND;

• the solid angle is covered up to 96% of 4π sr,
• the NaI(Tl) calorimeter has uniform spherical shape with fine segmentation in azimuthal and polar angles and 3 layers in radial direction,
• drift chamber is used as a central tracker,
• external anti-coincidence flat scintillation counters are enhanced by the coordinate system made of arrays of strimmer tubes.

## Experimental program

Experimental program of the SND is presented in Ref.[5] and consists of items as follow.

${\displaystyle e^{+}e^{-}\to \rho ,\omega ,\phi \to \pi ^{0}\gamma ,\eta \gamma }$
${\displaystyle \phi \to \eta ^{\prime }\gamma }$
${\displaystyle \phi \to a_{0}(980)\gamma ,~~f_{0}(975)\gamma ,~~\pi \pi \gamma ,~~\eta \pi \gamma }$
${\displaystyle \rho ,\omega \to \pi \pi \gamma }$
${\displaystyle \phi \to \omega \pi ^{0},~~\pi \pi ,~~\eta \pi \pi }$
${\displaystyle \rho \to \pi ^{+}\pi ^{-}\pi ^{0}}$
${\displaystyle \omega \to \pi ^{+}\pi ^{-}}$
• Electromagnetic decays
${\displaystyle \rho ,\omega ,\phi \to \eta e^{+}e^{-},~~\pi ^{0}e^{+}e^{-}}$
${\displaystyle e^{+}e^{-}\to 2\pi ,~~3\pi ,~~4\pi ,~~5\pi }$
${\displaystyle e^{+}e^{-}\to \omega \pi ,~~\eta \pi \pi ,~~\phi \pi }$
${\displaystyle e^{+}e^{-}\to K^{+}K^{-},~~K_{S}^{0}K_{L}^{0},~~KK\pi }$
• Test of QED processes
${\displaystyle e^{+}e^{-}\to 3\gamma ,~~e^{+}e^{-}\gamma }$
${\displaystyle e^{+}e^{-}\to 4\gamma ,~~e^{+}e^{-}\gamma \gamma ,~~e^{+}e^{-}e^{+}e^{-}}$
${\displaystyle e^{+}e^{-}\to 5\gamma ,~~3\gamma e^{+}e^{-},~~4e\gamma }$
• Search for rare decays
${\displaystyle K_{S}^{0}\to \gamma \gamma ,~~3\pi ^{0},~~2\pi ^{0}\gamma ,~~\pi ^{0}\gamma \gamma ,~~\pi ^{0}e^{+}e^{-}}$
${\displaystyle \eta \to 3\gamma ,~~e^{+}e^{-},~~4e}$
${\displaystyle e^{+}e^{-}\to \eta ^{\prime },~~a_{0},~~f_{0},~~a_{2},~~f_{2}}$

## Detector

The SND and its upgraded version are described in Refs.[5] and,[2] respectively. The detector design is illustrated in the R-θ view and 3-D plot of the NaI(Tl) calorimeter segmentation. Unique features of the SND and its sensitivity to the neutral particles are defined by the state-of-art NaI(Tl) calorimeter.

## Results

Data collected in the SND experiment from 1995 to 2000 corresponds to the integrated luminosity 30 pb−1 spread in the energy range 2E=0.4-1.4 GeV. Review of results of this experiment is presented in Refs. [6] and .[7] Results are included in the PDG Review.[8] Complete list of publications from SND also covers recent results of the experiment in the energy range 2E=1.0-2.0 GeV started in 2009.

## References

1. ^ Golubev, V. B.; et al. (1984). "The neutral detector at VEPP-2M". Nuclear Instruments and Methods in Physics Research Section A. 227 (3): 467–469. Bibcode:1984NIMPA.227..467G. doi:10.1016/0168-9002(84)90202-X.
2. ^ a b Abramov, G. N.; et al. (2001). "SND Upgrade". Invited talk at the e+e Physics at Intermediate Energies Workshop, SLAC, Stanford, California, April 30 - May 2. 675: 391–397.
3. ^ Dolinsky, S. I.; et al. (1991). "Summary of experiments with the neutral detector at the e+e storage ring VEPP-2M". Physics Reports. 202 (3): 99–170. Bibcode:1991PhR...202...99D. doi:10.1016/0370-1573(91)90127-8.
4. ^ (g-2) Design Report, BNL, 1995.
5. ^ a b V. M. Aulchenko et al., "Beginning of the Experiments with SND Detector at e+e Collider VEPP-2M", preprint BINP 95-56 (1995); Proceedings of the 6th International Conference on Hadron Spectroscopy (HADRON 95), Manchester, England, 10-14 Jul 1995, p.295-297.
6. ^ Achasov, M. N.; et al. (2002). "Review of experimental results from SND detector". AIP Conf. Proc. 619: 30–39. arXiv:. doi:10.1063/1.1482433.
7. ^ Achasov, M. N.; et al. (2000). "New Data from SND Detector in Novosibirsk". Nucl. Phys. A. 675: 391–397. arXiv:. Bibcode:2000NuPhA.675..391A. doi:10.1016/S0375-9474(00)00295-5.
8. ^