CP Violation Reach at Very High Luminosity B Factories Abi Soffer Snowmass 2001 Outline: Ambiguities...
-
date post
19-Dec-2015 -
Category
Documents
-
view
214 -
download
0
Transcript of CP Violation Reach at Very High Luminosity B Factories Abi Soffer Snowmass 2001 Outline: Ambiguities...
CP Violation Reach at Very High Luminosity B Factories
Abi Soffer
Snowmass 2001
Outline:
• Ambiguities
• B DK
• B D* etc.
• B D*a0 etc. (“designer mesons”)
• Conclusions
Ambiguities
• Measurements of usually involve the decay rateei
cos(
• Compare cos(and cos(
• These are invariant under 3 symmetry operations (lacking a-priori knowledge of phases):
• Sexchange = – Different modes have different , resolving the ambiguity– Otherwise, may be small in B decays (doesn’t resolve, but helps)
• Ssign = – Gives non-SM value of
0 9090180 180
Allowed range
Result
Ssign
Proposed solution:
Proposed solution:
• S = (A.S., PRD 60, 54032)
– Gives non-SM value of
• SSsign can put back in allowed range, reducing resolution
0 9090180 180
Allowed range
Result
S
0 9090180 180
Allowed range
Result
Ssign
S
Effective error
Proposed solution:
No good solution w/o
additional info
Resolving the 8-fold Ambiguity
• A-priori knowledge that and || (sin()~0 not enough)resolves ambiguities
• Measurements that depend on more amplitudes may, in principle, partly resolve ambiguities.– Different modes with different values of – Amplitudes with several strong phases might break Sexchange , sorssign
• Even then, resolution may be impossible in practice, due to limited sensitivity: Ambiguities are always a statistical strain.
• If you also measure small magnitudes in addition to phases, parameters can conspire to give additional accidental ambiguities due to ~multiple solutions
• No case (to my knowledge) in which can be measured independently– Some strong phases may be measured, but not enough to resolve ambiguities
• Note that ambiguities are method-dependent, not machine-dependent
Sensitivity of Measurement in BDK• Interference through CP-eigenstate decays of D0 (M. Gronau, D. Wyler, PLB 265, 172)
Decay rate asymmetry not needed for measuring Interference between amplitudes of very different magnitudes
– Variations: D*0 K+, D0 K*+, D0 K*0 , D0(*) K** (resonance phase enhancement), allowed modes only
Factorization: ~
• The small amplitude can’t be measured directly (D. Atwood, I. Dunietz, A. Soni, PRL 78, 3257)
Decay rate asymmetry needed Similar magnitudes, large D large CP asymmetry, good chance of resolving
SexchangeD CP conserving
D decay phase
Combining the Methods
• Get the benefits of both methods, increase sensitivity (A.S., PRD 60, 54032):
• {, , B, D}
• amBr(B+ K+ (K+, etc.))
– a() theoretical expectation for am
• bmBr(B+ K+ (CP))
– b() theoretical expectation for bm
~
2222
2 )()()()(
m
m
m
m
m
m
m
m
b
bb
a
aa
b
bb
a
aa
Sensitivity Estimates
• 600 fb-1, symmetric B factory– B+ D(*)0 K(*)+, B0 D(*)0 K*0 (1-mode equivalent ~1900 fb-1)
– D0 K, K0, K3, 9 CP eigenstates
• Full CLEO-II MC to estimate backgrounds, effect of SVT & PID on bgd and efficiency put in by hand
• Cuts on E, mES, masses, D0 Dalitz, PID, Vtx
– am (B+ K+ (K+)) has large K+ Kbackground, 80% continuum
– Assume that a likelihood fit doubles S/sqrt(S+B)
• Generate the S+B yields of an average experiment for given values of , B, D, taking
– 0 130 events in am channels
– 700 1000 events in bm channels
• Use minuit to solve for , , B, D
– Full ambiguity – no external input regarding B, D
~
_
~
2 with 600 fb1
• Small D 8-fold ambiguity
• Larger D resolves Sexchange (in principle)
• ~ 90o Ssign & S overlap. NOTE: Sexchange still hurts
• Accidental ambiguity at 1.25 times true value. These are quite common.
~
~5o
2
2 with 600 fb1
• Small D 8-fold ambiguity
• Larger D resolves Sexchange (in principle)
• ~ 90o Ssign & S overlap. NOTE: Sexchange still hurts
• Accidental ambiguity at 1.25 times true value. These are quite common.
~
2 with 600 fb1
• Small D 8-fold ambiguity
• Larger D resolves Sexchange (in principle)
• ~ 90o Ssign & S overlap. NOTE: Sexchange still hurts
• Accidental ambiguity at 1.25 times true value. These are quite common.
~
2 with 600 fb1
• Small D 8-fold ambiguity
• Larger D resolves Sexchange (in principle)
• ~ 90o Ssign & S overlap. NOTE: Sexchange still hurts
• Accidental ambiguity at 1.25 times true value. These are quite common.
~
Quantifying Sensitivity, 600 fb1
• Due to ambiguities, the error is not very meaningful
• Instead, ask what fraction of SM-allowed region of (40o100o) is excluded by this experiment at the 2 > 10 level, given values of , B, D
Fraction of excluded range
180o < B, D < 180o
sin(B) < 0.25
Resolving in Principle & in Practice
• Allowed levels of D0 mixing (xD~0.01) affect from B DK by 5o10o (J.P. Silva, A.S., PRD61, 112001)
• Ssign resolved in principle
• In practice, resolving Ssign requires ~36 ab-1 with xD~0.01
• cos D can be very well measured at -c factory, reducing uncertainty, but not resolving an ambiguity
2 with 6 ab1
• Statistical error in measurement of is 1.5 – 3o
• Even with ambiguities, 2<10 region is very small
• Different DK modes with moderately different B efficiently resolve ambiguities
2=10
2=10
2=10
2=10
sin()
h+
D(*)
Final state
• h+ = + / + / a1+
(R. Aleksan, I. Dunietz, B. Kayser, F. Le Diberder, Nucl. Phys. B361, 141)
• Amplitude ratio r = O(0.01 – 0.04)
• Small asymmetry – increase statistics with partial reconstruction
udscc
B+B
D*+
BABAR 10 fb1
Partial reconstruction
• BABAR Book estimate (partial reconstruction, D* only):
(sin()) ~ 2 (sin())
• Add , a1, add full reconstruction* – this is a reasonable estimate
• ~30 fb1, sin() = 0.59 0.14 0.05
With 600 fb1, expect (sin()) ~ 0.07
• Toy Monte Carlo study: B D(*)+ full reconstruction (C. Voena)
With 600 fb1, expect (sin()) ~ 0.06
* Note: full & partial reconstruction analyses are statistically almost independent
sin() Sensitivity
sin() Sensitivity Enhancement
• In B D(*)+, measure terms1 r2 & r sin
• so sin1/r2
• Angular analysis in B D*+/a1+, rely only on terms
O(1) & O(r) (D. London, N. Sinha, R. Sinha, hep-ph/0005248)
• so tan 1/r
• Large sensitivity enhancement, even with partial amplitude overlap, many fit parameters, etc.– Requires more detailed Monte Carlo study (H. Staengle)
• Same idea can be applied to B D(**)+
– Interference due to overlapping D(**) resonances– Looking into uncertainty in Breit Wigner resonance shapes (Grossman,
Pirjol, A.S.)
sin() from B D(*)a0+
• Mesons with very small decay constants amplitude ratio r = O(1) (M. Diehl, G. Hiller, hep-ph/0105213)
• Estimate Br(B D(*)a0+) ~ (1 – 4) 10–6
– a0+
• Background estimate for mode (Br ~ 40%):– In 20 fb–1, BABAR has ~900 signal events in each of B D(*)+, with
~180 background (didn’t try too hard to reduce the background)• m(a0
+) > m(+) by ~200 MeV
• (a0+) ~ 1/3 – 2/3 of (+),
• Assume harder cuts (down to 700 B D(*)+ events), likelihood analysis
– Assume B D(*)a0+ background can be reduced to 7 events per 20 fb–1,
• In 10 ab–1,
– Some additional sensitivity from hadronic modes
• This mode is interesting, but probably can’t rely on it solely– Use all “designer mesons” states (but need to consider interference)
60
140to
60
35~;
3500
140to
3500
35~
B
S
B
S
Conclusions
600 fb1 at an e+e Y(4S) machine is likely to yield• ~ 5 10% from B DK
• sin(2+ ~ 0.05 from B D(*)+/+/a1+ (corresponding to 2+~3o).
NOTE: This is without the proposed sensitivity enhancements
• Machine-independent statements for these values of & 2+– Large :
• Sexchange & S’exchange in principle resolved, but significantly limit sensitivity
• S significantly limits sensitivity
– Small : Better sensitivity since ambiguities are far from true:
• Sexchange allows
• S allows • Ambiguities allow &
– In any case, Ssign allows true, S’sign allows true, limiting sensitivity
– Don’t forget accidental ambiguities– Possible theory advances Unless theory dictates
& can be trusted
…ConclusionsWith 6 ab1 at an e+e Y(4S) machine:
• ~ 1.5 3o from B DK
• 2+ ~ 1o from B D(*)+/+/a1+ (without sensitivity enhancements)
• sin(2+ with “designer modes” still very hard, not needed in light of other good measurements
• Errors small enough to resolve ambiguities very efficiently– Exact situation depends on the actual phase values – no guarantees