Vanya Belyaev: Radiative decays @ LHCb - Beauty 2009

Radiative Decays @ LHCb
Vanya BELYAEV (NIKHEF/Amsterdam & ITEP/Moscow)
On behalf of LHCb Collaboration

Outline
• Radiative penguins & photon polarization in
b→ s g transitions
• Event Selection
• Probing for the photon polarization in Bs →fg fg
• Early data
• Summary
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Loops and Penguins
•Rare Rare ( (≡“loop “loop--induced” induced” ) and especially
penguin penguin--mediated mediated decays are essential part
of LHC(b) physics program:
• Electroweak penguin B0 →K *0
• talk by Will Will Reece Reece
• Gluonic penguin Bs→ ff
*0 m + m -
• Talk by Olivier Leroy , also charmless BB-decays,
decays, talk by Lorence Carson
• Hunting for “ “SUSY/Higgs
SUSY/Higgs penguin”: Bs →m + m- • talk by Diego Diego Martinez Martinez Santos Santos
And the radiative penguins are here …
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LHC(b) penguinarium
penguinarium
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Radiative penguins
• Radiative penguin decays of B + &B &B0 mesons have
been discovered by CLEO and both inclusive b→sg
and exclusive decays have been intensively
studied by CLEO CLEO, , BaBaR and Belle
• Br(b
Br(b →sg) ) is one of the most efficient killer for
New Physics Models
• Belle has observed Bs →fg fg
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Belle Belle: : O(1 Bs→fg fg)/day )/day at Y(5S)
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Why penguins are attractive?
• The clear picture in SM:
• One diagram dominance
• One Wilson coefficient C7 eff (m)
• Reliable theoretical description at (N)NLO allows the
numerically precise predictions
• Loops
• New Physics contribution can be comparable and even
dominating to (small) SM amplitudes
• NP appears not only in modifications of Br Br, , but also in
asymmetries and the angular effects
• “Sensitive Sensitive also also to to spin spin structure structure of of NP” NP
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• Not so rare decays
Br(B→K *0 g ) = (4.3±0.4)x10 -5
Br(B s→fg ) = (3.8±0.5)x10 -5
• 1-amplitude dominance
• strong phase appears at
order of a s or 1/m b
Exclusive radiative penguins
→“Direct” asymmetries are
small (

• B→ f CP
Mixing asymmetries are
vanished, but …
CP g is not CP CP eigenstate eigenstate! ! gR/gL ≈ms/m • Take it into account:
• SM:
• C = 0 direct CP CP-violation violation
• S = sin2 sin2y y sin sinf
• AD = sin2 sin2y y cos cosf
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/m b
not suppressed!
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B 0 → K S p 0 g
s(sin2 (sin2y ) ~ 0.4
BaBar Belle
8

• C is practically zero
• 1 diagram dominance
DG s/G s≠ 0
• S is a product of CP-eigenstate
CP eigenstate fraction and and (small) phase
difference of Bs oscillation and b→sg penguin
• double double smallness smallness is is SM
• AD is just a fraction of CP-eigenstate
CP eigenstate
• ≡ Fraction of wrongly polarized photons
• No No “other” “other” suppression suppression factors, factors, only only DG DGs/Gs Essentially we study CP-violation
CP violation in Bs→fg fg as an an instrument
instrument to probe
Lorentz structure of b→sg transitions
F.Muheim, Y.Xie & R.Zwicky R.Zwicky, , Phys.Lett.B664:174
Phys.Lett.B664:174-179,2008 179,2008
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Expected performance for B s→fg at LHCb
• What we “ “know” know” now:
• The yield is 11k per 2 fb fb-1 (and 70k of
• Background is
•

Trigger
• Hardware L0 trigger for photons with high E
•
T
Next trigger levels (software) :
• Photon confirmation (& suppression of merged merged p0 )
and single (or pair) detached track reconstruction
• e ~ 70%
• Full reconstruction of Bs →fg fg candidate
• Reconstruction of f-candidate candidate
• “inclusive inclusive ff” ” trigger
Large overlap,
high redundancy &
robustness: e ~ 95%
More details in dedicated talk by by Leandro Leandro de de Paula Paula
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Event selection
• B-decay products do not point to
reconstructed primary vertices
• Exclusively reconstructed B-candidate does
point to primary vertex
• B-candidate is
associated with the
primary vertex with
minimal impact
parameter (significance)
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Signal proper time resolution
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Sensitivity to sin2y
• To evaluate our sensitivity to sin2 sin2y
• toy Monte Carlo (10 (104 experiments)
experiments)
• Unbinned maximum likelihood fit m(B m(Bs) ) = 5.367 GeV GeV/c
• Proper lifetime & error
• Reconstructed mass
• Per Per-event event proper time errors
• Resolutions & Efficiencies from full MC
• Parameterize the background from mass mass-sidebands sidebands
• Important ingredient – proper time acceptance function
L.Shchutska et al al, , CERN CERN-LHCb LHCb-2007 2007-147 147
2
t(B (Bs) ) = 1.43 ps
DG DGs = 0.084 ps ps-1 Dms = 17.77 ps ps-1 10.9.2k+9
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a = 0.74 ps ps-1 c = 1.86
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Proper time acceptance
dN/ dN/dt dt es(t) (t)
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Proper time acceptance
• It is a vital to know it with very high precision
• 5% bias in “ “a” ” -> > bias in sin2 sin2y ~ 0.2
• We are planning to calibrate it using three techniques:
• B0→ K *0 g
• Bs→ f J/ J/y y
• “per per--event event--acceptance
acceptance” ” (“swimming” method)
• The acceptance could be extracted from data for all
cases
• E.g. with ~ ~OO(1%) (1%) precision for B0→ K *0 g
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Background parameterization
• Fit separately left and
right sidebands
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Left Right
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Results: s(A (AD ,C,S)
s(A (AD )=0.22
2fb 2fb-1 s(S)= )=s(C)=0.11 )=0.11
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The first 13 minutes @
nominal luminosity
“early measurements”
B→ K *0 g
• Already with “early”
data the
measurements of
direct CP CP-asymmetry
asymmetry
in B→ K *0 g
• Double ratio:
• Measurement of
B→fKg
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• LHCb
Conclusions
LHCb has good potential for measurement of
photon polarization in Bs→fg fg decay
• For 2 fb fb-1 :
s(A (AD )=0.22, s(S)= )=s(C)=0.11 )=0.11
• The The determination determination of of proper proper time time acceptance
acceptance
function function from from data data in in under under the the study: study:
• Three Three methods methods
• The result has moderate moderate dependency on B/S B/S
Stay tuned and wait for more news
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Backup slides
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Example of models
• Anomalous right right-handend handend top couplings J.P.Lee’03 J.P.Lee’03
lg = -cos cos 2y
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B: proper-time in sidebands
• Fit separately left and right sidebands
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Signal proper time resolution as function of cos cosQ
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Signal proper time resolution as function of cos cosQ
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-1.0 1.0 : -0.5 0.5 -0.5 0.5 : -0.15 0.15
-0.15 0.15 : 0.3 0.3: 1.0
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The shape of background
• Vary the “short/long”
“short/long”-lived lived components
Relative change
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Absolute change
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Stability tests: B/S
• There is some dependency on B/S B/S level:
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Conservative UL @ 90% CL
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Results: pulls
S
A D
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C

Resolution and DG DGs/Gs • Vary the proper time resolution
• Use simple model with two Gaussians and vary the
proportion
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Acceptance function
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Background parameterization
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Likelihood
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