David Hitlin

1
CP
Measuring Violation in decay at
Super
B
t
David Hitlin SuperB WorkshopFrascatiMarch 16,
2006
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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

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CPV in t decay

• Unpolarized ts
• Measure Bs of t decays with two or more
  hadronsInterpretation of any observed CPV
  requires understanding of inelastic final state
  interactions
• Measure CP or T-violating correlations in tt-
  decays
• Polarized ts
• 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

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CP violation in t decay

• Y.S. Tsai, Phys Rev D55, 3172 (1995)
• Longitudinal polarization
• The t polarization is
• For while
  for
• Forwhile for

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There was transverse polarization at SPEAR

• Polarization producedby quantized
  synchrotronradiation emission

Up-down asymmetry in the yieldof backscattered
gs is proportional to the transversebeam
polarization
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Transverse polarization at PEP-II is small

• PEP-II transverse polarizationis small due to
  longer polarization buildup timeand more
  densedepolarizing resonances
• LER 0.8 max
• HER 3.5 max
• Polarization maximamay not coincide
  withrequired CM energy

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Longitudinal beam polarization

• The ILC baseline
• gt80 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

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The ILC polarized electron source
Rapid, random helicity flipat source for control
of systematics
Parameter Symbol Value Units
Electrons per bunch1 4x1010 Number
Bunches per pulse 2820 Number
Microbunch repetition rate fmicro 3 MHz
Pulse Repetition Rate 5 Hz
DR energy Acceptance DE/E 1 (FW)
DR Transverse Acceptance A2J 0.09 m-rad
Electron Energy E0 5 GeV
Electron Polarization Pe gt80
OK for storagering injection An issue for
linearcollider SBF
1 twice IP requirement
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The ILC polarized positron source upgrade

• Produce polarized 20 MeV photons in a helical
  undulator
• Double-woundsuperconductingsolenoid
• Rotated permanentmagnet dipoles sections
• Laser Compton scattering

60 polarization can be achieved
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An ILC design with a polarized positron source
Parameter Value Units
Positrons per bunch number
Bunches per pulse 2820 number
Pulse Repetition Rate 5 Hz
Positron Energy 5 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 kW
Positron Polarization (upgrade) 60
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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

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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?

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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 gs 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

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A polarized positron system
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Comparison of t/charm and SBF

• BEPCII L1033 SBF L1036 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_at_ 4 GeV 1
SBF _at_ U(4S) 178
SBF _at_ 4 GeV 100
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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