1. Probing SUSY CP Violation
in Stop Decays at the LHC
The University
of Manchester
Frank Deppisch
frank.deppisch@manchester.ac.uk
University of Manchester
in collaboration with
Olaf Kittel (Granada U.)
arXiv:0905.3088 [hep-ph]
SUSY09, Boston, 7 June 2009

2. CP Violation
CP violation in
quark sector
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3. CP Violation
CP violation in
quark sector
CP violation in
neutrino sector?
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4. CP Violation
CP violation in
quark sector
CP violation in
neutrino sector?
Baryon Asymmetry
of the Universe
 B = n B / n  = 6.1 0.3⋅10−10
−0.2
→ New mechanism of CP Violation required
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5. CP Violation
CP violation in
quark sector
CP violation in
neutrino sector?
Baryon Asymmetry
of the Universe
 B = n B / n  = 6.1 0.3⋅10−10
−0.2
→ New mechanism of CP Violation required
Supersymmetry
Possible new CP phases in SUSY and SUSY-breaking
Gaugino mass terms → φM1 , φM3
Higgs mixing term → φµ
3rd generation trilinear scalar coupling terms → φAt,b,τ
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6. Bounds from Electric Dipole Moments
Stringent bounds from electron and
neutron EDMs ∣d ∣4⋅10−27 e⋅cm
e
−26
∣d n∣6⋅10 e⋅cm
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7. Bounds from Electric Dipole Moments
Stringent bounds from electron and
neutron EDMs ∣d ∣4⋅10−27 e⋅cm
e
−26
∣d n∣6⋅10 e⋅cm
Generally constrain SUSY phases
to be small (or SUSY scale large), e.g. φµ < π/10
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8. Bounds from Electric Dipole Moments
Stringent bounds from electron and
neutron EDMs ∣d ∣4⋅10−27 e⋅cm
e
−26
∣d n∣6⋅10 e⋅cm
Generally constrain SUSY phases
to be small (or SUSY scale large), e.g. φµ < π/10
… unless cancellations occur between contributions
 =1 °
 =1 °
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9. Triple Product Asymmetries
CP-even observables at colliders sensitive to phases
masses
branching ratios
cross sections
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10. Triple Product Asymmetries
CP-even observables at colliders sensitive to phases
masses
branching ratios
cross sections
CP-odd observables are needed
to confirm CP Violation
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11. Triple Product Asymmetries
CP-even observables at colliders sensitive to phases
masses
branching ratios
cross sections
p1
CP-odd observables are needed p3
to confirm CP Violation p2
Momentum triple product
Time Reversal
T = p1⋅ p 2× p 3 
− p2
→ T-odd → CPT Invariance → CP-odd
− p3
− p1
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12. Triple Product Asymmetries
CP-even observables at colliders sensitive to phases
masses
branching ratios
cross sections
p1
CP-odd observables are needed p3
to confirm CP Violation p2
Momentum triple product
Time Reversal
T = p1⋅ p 2× p 3 
− p2
→ T-odd → CPT Invariance → CP-odd
− p3
CP-odd asymmetry − p1
N T 0− N T 0 ∫ sign T ∣M∣ d Lips
2
A= =
N T 0 N T 0 ∫∣M∣2 d Lips
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13. Stop Production at the LHC
Framework
mSUGRA decorated with CP phases at EW scale
Benchmark Scenario
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14. Stop Production at the LHC
Framework
mSUGRA decorated with CP phases at EW scale
Benchmark Scenario
Stop pair production at
Stop boost distribution
the LHC Cross section
∗
pp   i  i
t t
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15. CP-odd Asymmetries in Stop Decays
Stop cascade decay sensitive
to φAt, φµ(, φM1) from spin-spin correlations
t
1
0
2 L/R
l
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16. CP-odd Asymmetries in Stop Decays
Stop cascade decay sensitive
to φAt, φµ(, φM1) from spin-spin correlations
Triple product asymmetries not t
1
Lorentz-invariant
0
2 L/R
l
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17. CP-odd Asymmetries in Stop Decays
Stop cascade decay sensitive
to φAt, φµ(, φM1) from spin-spin correlations
Triple product asymmetries not t
1
Lorentz-invariant
0
2 L/R
l
Asymmetry reduction with stop boost
Effect of stop boost
on asymmetry
1 ∞ d
A = ∫0
lab
A d 
t
 d 
t
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18. mSUGRA Parameters
left-h. slepton,  1  2 t , 2   L l
t   l right-h. slepton, 1  2 t , 2   R l
t   l
∣A0∣=500 GeV , tan =5
 A =3 /4  , =0
t
Minimally required luminosity at the LHC to observe 1σ effect
Based only on theoretical significance
(statistical fluctuation of signal) S ≈∣A∣  L
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19. CP Phase Sensitivity
Asymmetry in the lab frame [%]  1  2 t , 2   R l
t   l Min. luminosity required at LHC
m0 =70 GeV , m1 /2 =270 GeV
∣A0∣=500 GeV , tan =5
Asymmetry largely independent of φM1 in mSUGRA
Large asymmetries possible for small φAt and φµ
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20. Conclusion
CP Violation in Stop decays at the LHC
Via 2nd Lightest Neutralino
Top-Neutralino Spin-Spin Correlations
Sensitive to CP phases φAt and φµ in mSUGRA
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21. Conclusion
CP Violation in Stop decays at the LHC
Via 2nd Lightest Neutralino
Top-Neutralino Spin-Spin Correlations
Sensitive to CP phases φAt and φµ in mSUGRA
Triple Product Asymmetries
CP-odd observables → Signal of CP Violation
Alternative Sensitivity than EDMs
Detectable at LHC
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22. Conclusion
CP Violation in Stop decays at the LHC
Via 2nd Lightest Neutralino
Top-Neutralino Spin-Spin Correlations
Sensitive to CP phases φAt and φµ in mSUGRA
Triple Product Asymmetries
CP-odd observables → Signal of CP Violation
Alternative Sensitivity than EDMs
Detectable at LHC
Motivation for experimental analysis
Reconstruction Efficiencies
Epsilon Product of Four Momenta
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