Petr Shatunov

Study of e+e-→ωπ0→π0π0γ in the energy range 1.05-2.00 GeV with the SND detector

The cross section for the process e+e- --> omega pi0 --> pi0 pi0 gamma has been measured in the energy range 1.05--2.00 GeV. The experiment has been performed at the e+e- collider VEPP-2000 with the SND detector. The measured e+e- --> omega pi0 cross section above 1.4 GeV is the most accurate to date. Below 1.4 GeV our data are in good agreement with the previous SND and CMD-2 measurements. Data on the e+e- --> omega pi0 cross section are well described by the VMD model with two excited rho-like states. From the measured cross section we have extracted the gamma^* --> omega pi0 transition form factor. It has been found that the VDM model cannot describe simultaneously our data and data obtained from the omega --> pi0 mu+ mu- decay. We have also tested CVC hypothesis comparing our results on the e+e- --> omega pi0 cross section with data on the tau- --> omega pi- nu_{tau} decay.

Recomissioning and Perspectives of VEPP-2000 e+e- Collider

VEPP-2000 is electron-positron collider exploiting the novel concept of round colliding beams. After three seasons of data taking in the whole energy range of 160-1000 MeV per beam it was stopped in 2013 for injection chain upgrade. The linking to the new BINP source of intensive beams together with booster synchrotron modernization provides the drastic luminosity gain at top energy of VEPP-2000.

Comissioning of Upgraded VEPP-2000 Injection Chain

The upgrade of VEPP-2000 ee collider injection chain includes the connection to BINP Injection Complex (IC) via newly constructed transfer line K-500 as well as upgrade of the booster synchrotron BEP to the energy of 1 GeV. Modernization has started in the middle of 2013 and now the electron and positron beams with highly increased production rate together with top-up injection from BEP are ready to feed VEPP-2000 ring and provide design luminosity at the whole energy range limited only by beam-beam effects. The design and operation experience of IC damping ring, 250 m transfer channel and booster BEP dealing with 2.6 T magnets at top energy will be presented.

The Injection Septum Magnet for the Collector Ring (FAIR)

Collector Ring [1] is one of the key installations of the FAIR project (Darmstadt, Germany). It is dedicated for stochastic cooling of incoming beams of antiprotons and rare ions. Additionally there is a mode of operation for experiments in the ring. Beams for all modes of operation are injected through one transfer channel. Extremely high acceptance of the ring (240 mm*mrad) leads to large apertures of all magnetic elements including the septum magnet. Meanwhile planned parameters of the magnetic field and magnetic field quality are comparatively strict. The present state of the design of the pulsed injection septum for the CR is presented in this article together with the concept of the injection system. THE SCHEME OF INJECTION The cycle of the Collector ring operation for the antiprotons consists of injection, cooling and extraction. The full cycle takes 10 seconds. The analogous cycle for the rare isotope beams takes only 1.5 seconds. Additionally there are options of the RIBs injection for further experiments in the so-called isochronous lattice [2]. All beams that are cooled and later extracted have the rigidity of 13 T·m. The isochronous mode experiments are planned for the discrete set of beam energies: γ=1.84, γ=1.67, γ=1.43. Each regime of the RIBs has one lattice option. For better flexibility for antiprotons two lattices are foreseen – with positive and negative slip-factor η. The full list of all mentioned regimes is shown in the Table 1. Table 1: The list of the CR operation regimes The particles type The lattice name The cycle length Emittance P-bars P-bar 1 10 sec 240 mm·mrad P-bars P-bar 2 10 sec 240 mm·mrad RIB RIB 1.5 sec 200 mm·mrad RIB ISO 1.84 100 mm·mrad RIB ISO 1.67 100 mm·mrad RIB ISO 1.43 100 mm·mrad In all regimes of operation the injecting beam comes from the TCR1 channel [3]. The angle between the channel and the CR orbit is 7.842538o. This angle is mainly compensated by the Injection Septum (IS). The final compensation is done by the fast kicker magnets (KM) [4]. The kicker magnets are grouped by three in two sections with the magnetic length of 60 cm and the maximum magnetic field of 0.054 T. After KM the injected beam trajectory coincides with the main CR orbit. The distance between the end of the IS and the KM is about 15m. Three quadrupole magnets are placed in this region that produce enough betatron phase advance for the proper angle compensation in KM. In this region beam moves by the trajectory shifted from the main orbit so all the structure elements here have an enlarged aperture. The horizontal aperture in the CR01QS01, CR01QS02 and CR04QS02 quads is 270 mm. The scheme of the injection region is shown at the Figure 1. INJECTION SEPTUM MAGNET DESIGN As it is mentioned above the task of the septum magnet is to compensate the angle between the TCR1 channel and the orbit of the CR. Taking into account that the angle that can be later compensated with the KM varies from 8 to 13 mrad for the different modes of operation the angle of the injection septum should be ≈128 mrad. This angle is gained by the three pulsed magnets of similar desing that all together are called Injection Septum. The principal scheme of the IS magnet is the following: pulsed magnetic field, several turns of the primary coil winded around the yoke of the magnet; the secondary coil is combined with the septum electrode; the straight ceramic vacuum chamber is used to avoid the heat losses during the pulse. The basic layout of the IS magnet together with the injecting and circulating beams cross-sections are shown at the Figure 2. Beams sizes and positions are shown for the point at the exit of the last magnet by the way of the beam. Additionally the flange that combines the vacuum chamber of the IS and of the CR is shown. At the top and the bottom of the yoke two special cleats that tighten the laminated yoke in longitudinal direction are provided. The 3D model of the set of 3 IS magnets together with the vacuum chamber is shown at the Figure 3. Parameters of the IS magnet are provided in the Table 2. The magnetic field and the magnetic length of the IS magnets are mainly limited by the following factors: the length of the injection straight section which is 5 meters and parameters of the power source. ______________________________________________ * The work is carried out with the financial support of FAIR-Russia Research Center † email address p.yu.shatunov@inp.nsk.su Proceedings of IPAC2016, Busan, Korea TUPMB017 07 Accelerator Technology T09 Room-temperature Magnets ISBN 978-3-95450-147-2 1145 C op yr ig ht

Recent Beam-Beam Effects at VEPP-2000 and VEPP-4M

Budker INP hosts two e + e − colliders, VEPP-4M operating in the beam energy range of 1–5.5 GeV and the low-energy machine VEPP-2000, collecting data at 160– 1000 MeV per beam. The latter uses a novel concept of round colliding beams. The paper presents an overview of observed beam–beam effects and obtained luminosities. VEPP-4M Being a rather old machine with a moderate luminosity, VEPP-4M has several unique features, firstly a very low beam-energy spread, and a system for precise energy measurement, providing an interesting particle physics program for the KEDR detector. Over recent years VEPP4M was taking data at a low energy range with two bunches in each beam. The luminosity at this range is limited by beam–beam effects with the threshold beam– beam parameter ξy ≤ 0.04 [1]. In this case the luminosity