SuperB Workshop Frascati March 16, 2006 CP Measuring Violation in decay at Super B t David Hitlin SuperB Workshop Frascati March 16, 2006 David Hitlin Frascati SuperB Workshop March 17, 2006

Outline At SuperB we can make measurements sensitive to CP,T or CPT violation in t production or in t decay Eugenio Paoloni has covered the question of CP violation in t production, which can be parametrized as a t EDM I will discuss CP violation in t decay The efficacy of polarized beams in making such measurements Technical options in producing polarized beams Comparision of a t/charm factory with SuperB These measurements require longitudinal polarization David Hitlin Frascati SuperB Workshop March 17, 2006

CPV in t decay Unpolarized t’s Polarized t’s Measure B’s of t decays with two or more hadrons Interpretation of any observed CPV requires understanding of inelastic final state interactions Measure CP or T-violating correlations in t+t- decays Polarized t’s Search for T-odd rotationally invariant products, e.g. in t+ and t-decays such as Search for T-odd correlation between t polarization and m polarization in decay David Hitlin Frascati SuperB Workshop March 17, 2006

CP violation in t decay Y.S. Tsai, Phys Rev D55, 3172 (1995) Longitudinal polarization The t polarization is For while for For while for 0.6 0.95 0.9 0.8 0.7 we- we+ 0.99 David Hitlin Frascati SuperB Workshop March 17, 2006

There was transverse polarization at SPEAR Polarization produced by quantized synchrotron radiation emission Up-down asymmetry in the yield of backscattered g’s is proportional to the transverse beam polarization David Hitlin Frascati SuperB Workshop March 17, 2006

Transverse polarization at PEP-II is small PEP-II transverse polarization is small due to longer polarization buildup time and more dense depolarizing resonances LER 0.8% max HER 3.5% max Polarization maxima may not coincide with required CM energy David Hitlin Frascati SuperB Workshop March 17, 2006

Longitudinal beam polarization The ILC baseline >80% linearly polarized e- source Unpolarized e+ source, with an upgrade possible to 60% linear polarization Since a polarized e- source alone is sufficient to make the proposed measurements, and a high intensity unpolarized e+ source is already a substantial technical challenge, I would recommend that we include longitudinally polarized e- capability in the SuperB baseline design, with a polarized e+ source as a possible upgrade David Hitlin Frascati SuperB Workshop March 17, 2006

The ILC polarized electron source Positron-style room-temperature accelerating section diagnostics section standard ILC SCRF modules sub-harmonic bunchers + solenoids laser E=70-100 MeV Rapid, random helicity flip at source for control of systematics Parameter Symbol Value Units Electrons per bunch1 4x1010 Number Bunches per pulse 2820 Microbunch repetition rate fmicro 3 MHz Pulse Repetition Rate 5 Hz DR energy Acceptance DE/E 1 % (FW) DR Transverse Acceptance A=2J 0.09 m-rad Electron Energy E0 GeV Electron Polarization Pe >80 % OK for storage ring injection An issue for linear collider SBF 1 twice IP requirement David Hitlin Frascati SuperB Workshop March 17, 2006

The ILC polarized positron source upgrade Produce polarized 20 MeV photons in a helical undulator Double-wound superconducting solenoid Rotated permanent magnet dipoles sections Laser Compton scattering ~60% polarization can be achieved David Hitlin Frascati SuperB Workshop March 17, 2006

An ILC design with a polarized positron source Primary e- source e- DR Target e- Dump Photon Beam Dump e+ Auxiliary e- Source Photon Collimators Adiabatic Matching Device e+ pre-accelerator ~5GeV 150 GeV Helical Undulator In By-Pass Line Photon Target 250 GeV Positron Linac IP Beam Delivery System 100 GeV Electron Linac Parameter Value Units Positrons per bunch number Bunches per pulse 2820 Pulse Repetition Rate 5 Hz Positron Energy GeV Undulator Length (unpolarized source) 100 m Photon Energy (1st harmonic cutoff) 10.7 MeV Max Photon Beam Power (unpolarized source) 147 kW Max Target Absorption 11 Positron Polarization (upgrade) 60 % David Hitlin Frascati SuperB Workshop March 17, 2006

Spin control in the damping ring(s) Must rotate longitundinal polarization from source to transverse for insertion into damping ring Coming out of DR, rotate back to longitudinal with complete control of spin orientation David Hitlin Frascati SuperB Workshop March 17, 2006

The Emma rotator Provides complete control of longitudinal polarization orientation at the IP without emittance dilution All current designs I am aware of are designed for flat beams The reflection sections provide a unity transformation in the horizontal plane and a -1 transformation in the vertical plane, avoiding transverse betatron coupling by the rotation in the solenoids Would the concept work with round beams? David Hitlin Frascati SuperB Workshop March 17, 2006

The extra wrinkle For control of experimental systematics, it is necessary to randomly switch the polarization for + to – helicity For the polarized electron beam, this is easily done at the source itself by controlling the circular polarization of the laser, and thereby the polarization of the electrons emitted from the photocathode This has already been demonstrated at the SLC and in E158 For a polarized positron beam with photons produced by an undulator, the helicity of the 20 MeV g’s is determined by the (fixed) helicity of the undulator The desired control of polarization can be achieved by an additional LTR bypass that has random control of kickers David Hitlin Frascati SuperB Workshop March 17, 2006

A polarized positron system David Hitlin Frascati SuperB Workshop March 17, 2006

Comparison of t/charm and SBF BEPCII L=1033 SBF L=1036 SBF(4GeV) L  1035 FOM for measuring CPV in t decay (Tsai): z component of t polarization averaged over cross section: For equal longitudinal polarization Machine FOM/FOM BEPCII BEPCII@ =4 GeV 1 SBF @ U(4S) 178 SBF @ =4 GeV 100 David Hitlin Frascati SuperB Workshop March 17, 2006

Conclusions SuperB with a longitudinally polarized electrons can perform unique searches for New Physics in the lepton sector CP violation searches in both t production and decay are possible Tests of CPT (not discussed here) are feasible as well Production, preservation and control of longitudinally polarized electrons, with polarization ≥80%, is feasible This requires spin rotators in the LTR (injection) and RTL (reinsertion) lines, and must be factored into the design of the damping rings in a linear collider design or the rings in a storage ring design to avoid spin-depolarizing resonances There is some additional benefit in also having longitudinally polarized positrons, at the ~10-20% level Polarized positron capability is probabily best considered as an upgrade David Hitlin Frascati SuperB Workshop March 17, 2006