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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. The ILC polarized electron source
Positron-style room-temperature accelerating section
diagnostics section
standard ILC
SCRF modules
sub-harmonic bunchers + solenoids
laser
E= 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

9. 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

10. 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

11. 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

12. 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

13. 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

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

15. Comparison of t/charm and SBF
BEPCII L= SBF L= 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
=4 GeV 1
U(4S)
178
=4 GeV
100
David Hitlin Frascati SuperB Workshop March 17, 2006

16. 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