Direct CP asymmetries and charmless branching fractions with BABAR

1
Direct CP asymmetries and charmless branching
fractionswith BABAR
ICHEP 2002

• Adrian Bevan

For the BABAR Collaboration
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Overview

• Motivation Direct CP Violation (CPV)
• New Physics sensitivity
  e.g. XSg, fK
• Penguins
• Event Selection Methods
• Results Charmless decays, Kg, D0CPK-
• Summary and outlook

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Direct CP Violation

• need interference between diagrams with different
  strong (?i) and weak phases (?i)
• Direct CPV only seen in ?' few 10-6
• theory predicts large asymmetries in B/0 (few to
  80)
• Diagrams from New Physics (e.g. SUSY) can modify
  SM asymmetries/branching fractions

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• Experimentally - look for CP asymmetries
• Neutral B time dependent asymmetry
• Charged B time integrated asymmetry (no
  mixing) also used for some B0 results (e.g.
  K0p0)

C?0 direct CPV e.g. for ??, pp
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Searching for direct CPV

• Large ACP requires amplitudes of similar order
• b?u suppressed tree charmless decays
• large predicted ACP
• b?s,d penguins radiative decays
• small predicted ACP
• Understand penguins
• Access to a and g
• Sensitive to New Physics effects via loops
• minimal SUGRA B?Xs?, ?K, K0?
• R-parity Violating SUSY ?KS
• SUSY searches K?

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Experimental Issues

• small branching fractions
• large continuum background (u,d,s,c)
• other B background
• charge bias
• detector trigger, tracking reconstruction
• event selection, particle ID, analysis
• Proof of principle
• ACP in J/yp, J/yK PRD 65 091101 (2002)
• AJ/y? 0.01 ? 0.22 ? 0.01
• AJ/yK 0.003 ? 0.030 ? 0.004

small systematic error few per mille
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Event Selection Techniques

• Use beam energy to constrain mass energy

DE s 15-80 MeV larger with neutrals
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Event Selection Techniques

• B events are spherical
• u,d,s,c is jet-like
• Fisher Discriminants
• Thrust
• Sphericity
• Fox-Wolfram moments
• flavour-tagging (e, ?, K, slow ? from other B)
• Maximum Likelihood fits or cut based analysis
• off-resonance ?E sidebands are used to
  parameterise light quark background

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RESULTS
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Two body decays
can measure ? eg. B???-, ??0, ?0?0 ?
eg. B?K?-, K0? using Fleischer Mannel bound
ACP can be sizeable
see Jim Olsens talk
Plots have an optimised cut on likelihood ratio
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New results
88?106 B pairs
Preliminary
60?106 B pairs
Mode NEVENTS Branching ratio (?10-6) ACP
B0?Kp- 589 ?30 (17.9?0.9 ?0.6) -0.102 ?0.050 ?0.016
B?Kp0 (12.8 ?1.2 ?1.0) -0.09 ?0.09 ?0.01
B?pp0 (5.5 ?1.0 ?0.6) -0.03 ?0.18 ?0.02
B0?K0p0 (10.4 ?1.5 ?0.8) 0.03 ?0.36 ?0.09
B0?KK- lt0.6 (90 C.L.) -
B?KK0 lt1.3 (90 C.L.) -
B?K0p (17.5 ?1.8 ?1.3) -0.17 ?0.10 ?0.02
hep-ex/0206053
All upper limits are _at_ 90 C.L.
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B?hhh, h?, K

• Motivation
• measure ? using a full Dalitz plot
• look for direct CPV in charge asymmetry
• Method
• cut based analysis across the Dalitz plot for
  branching ratio

sum over Dalitz plot

• B backgrounds J/?K, D?/DK, X-feed D???, K?, KK
• subtract open charm from J/?, ?(2s) and D0
• measure Br(B-?D0p-) as a cross check

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B?KKK
B?KKK
Preliminary
B?Kpp
D0
B?Kpp
BB
y(2s)
J/y
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56.2?106 B pairs
Branching fractions measured across the Dalitz
plot
(90 C.L.)
(90 C.L.)

• Main systematic uncertainties
• PID 3 6
• tracking 2.4

Preliminary
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B???K(), ?K, ???

• B???K(), suppressed tree ACP 430 (theory)
• B??K, ???, penguin ACP 6 (theory)

sensitive to ?
sensitive to ?,g
preliminary
PRD 65 (2002) 051101
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B0?wK0
Preliminary
60?106 B pairs
First Observation!
6.6 s significance (statistical)

• penguin
• sensitive to a, g
• expect small ACP
• ML fit
• dominant systematic
• uncertainty
• background shape
• neutral eff
• tracking

Signal region
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B??K(), ??

• Motivation
• ACP 2 in SM
• New Physics
• (ACP up to 30)
• sin2? if no new physics

see Doug Wrights talk
PRD 65 (2002) 051101
PRL 87 151801 (2001)
preliminary
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B-?D0(CP)K-
see Erich Varnes talk

• ACP may be large
• access to g

• Do reconstructed
• in Kp, Kppo, Kppp
• in KK- (CP1 eigenstate)

Preliminary
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B ? K?
22.7?106 B pairs
Phys Rev Lett 88 101805 (2002)

• Acp 1 in SM.
• SUSY can enhance to 20
• Reconstruct

ACP(B?K?) -0.044 ? 0.076 ? 0.012 -0.170,
0.082 (90 C.L.)
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Other results see talk on a
88?106 B pairs

• via isospin analysis and
• direct CPV from time evolution
• of B? ??-

Cpp -0.30 ? 0.25 ? 0.03 Spp 0.02 ? 0.34 ? 0.03
Factorization predicts 0.4
Br(B0?pp-)(4.6 ? 0.6 ? 0.2)?10-6 Br(B?pp0)
(5.5 ?1.0 ?0.6)?10-6 Br(B0?p0p0) lt 3.6 10-6
Preliminary
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Summary and outlook

• First CP results from B0???
• Branching fractions and ACP measured in many
  decays
• ACP precision achieved 520
• No direct CPV signal yet
• watch for future updates