Radiative Decays @ LHCb

Radiative Decays @ Radiative Decays @ LHCbLHCb

Vanya BELYAEV (NIKHEF/Amsterdam & ITEP/Moscow)Vanya BELYAEV (NIKHEF/Amsterdam & ITEP/Moscow)On behalf of LHCb CollaborationOn behalf of LHCb Collaboration

Outline

• Radiative penguins & photon polarization in Radiative penguins & photon polarization in

b→ s b→ s transitionstransitions

• Event Selection Event Selection

• Probing for the photon polarization in Probing for the photon polarization in BBss → →

• Early dataEarly data

•SummarySummary

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Loops and Penguins

•Rare (Rare (≡≡“loop-induced” “loop-induced” ) and especially ) and especially penguin-mediatedpenguin-mediated decays are essential decays are essential part of part of LHC(b)LHC(b) physics program: physics program:•Electroweak penguinElectroweak penguin BB00 →K →K*0*0 ++--

• talk by talk by Will ReeceWill Reece

• Gluonic penguin Gluonic penguin BBss→ → • Talk by Olivier Leroy , also charmless B-decays, talk by Lorence CarsonTalk by Olivier Leroy , also charmless B-decays, talk by Lorence Carson

•Hunting for “Hunting for “SUSY/HiggsSUSY/Higgs penguin”: penguin”: BBss → →++--

• talk by talk by Diego Martinez SantosDiego Martinez Santos

And the radiative penguins are here And the radiative penguins are here … …

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LHC(b)LHC(b) penguinariumpenguinarium

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Radiative penguins

•Radiative penguin decays of Radiative penguin decays of BB++&B&B00 mesons mesons have been discovered by have been discovered by CLEOCLEO and both and both inclusive inclusive b→sb→s and exclusive decays have and exclusive decays have been intensively studied by been intensively studied by CLEOCLEO, , BaBaRBaBaR and and BelleBelle

• Br(b →sBr(b →s) ) is one of the most efficient killer for is one of the most efficient killer for New Physics Models New Physics Models

• BelleBelle has observed has observed BBss → →

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BelleBelle: O(1 : O(1 BBss→→)/day at Y(5S))/day at Y(5S)


Why penguins are attractive?

• The clear picture in SM:The clear picture in SM:

•One diagram dominanceOne diagram dominance

•One Wilson coefficient One Wilson coefficient CC77effeff(())

• Reliable theoretical description at Reliable theoretical description at (N)NLO (N)NLO allows allows the numerically precise predictionsthe numerically precise predictions

• LoopsLoops

•New Physics contribution can be comparable and New Physics contribution can be comparable and even dominating to (small) even dominating to (small) SMSM amplitudes amplitudes

•NP appears not only in modifications of NP appears not only in modifications of BrBr, but also , but also in asymmetries and the angular effects in asymmetries and the angular effects

•““Sensitive also to spin structure of NPSensitive also to spin structure of NP””


• Not so rare decaysBr(B→K*0 ) = (4.3±0.4)x10-5

Br(Bs→ ) = (3.8±0.5)x10-5

•1-amplitude dominance

•strong phase appears at order of s or 1/mb

→“Direct” asymmetries are small (<1%) for b→s & a bit larger O(10%) for b→d

•Photons are polarized• Mixing asymmetries

vanishes, *BUT*

Exclusive radiative penguins

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Suppressed by : s , 1/mb or |VCKM|

Vanya Belyaev: Radiative decays @ LHCbVanya Belyaev: Radiative decays @ LHCb 66

Mixing asymmetries are vanished, but …

• B→ B→ ffCPCP is not is not CPCP eigenstate! eigenstate! RR//LL ≈m ≈mss/m/mbb

•Take it into account:Take it into account:

• SM:SM:

•C = 0 direct CP-violationC = 0 direct CP-violation

•S = S = sin2sin2sinsin

•AA = = sin2sin2coscos 10.9.2k+9

not not suppressed!suppressed!


B0→ KS 0

BaBarBaBar BelleBelle(sin2(sin2 ) ~ 0.4 ) ~ 0.4

88

s/s≠ 0

• CC is practically zerois practically zero• 1 diagram dominance 1 diagram dominance

•SS is a product of is a product of CPCP-eigenstate fraction -eigenstate fraction andand (small) (small) phase difference of phase difference of BBss oscillation and oscillation and b→sb→s penguin penguin

•double smallness is double smallness is SMSM

•AA is just a fraction of is just a fraction of CPCP-eigenstate -eigenstate

• ≡≡ Fraction of wrongly polarized photonsFraction of wrongly polarized photons

•No “other” suppression factors, only No “other” suppression factors, only ss//ss

Essentially Essentially we study we study CPCP-violation -violation in in BBss→→ as as an instrument an instrument to to probe Lorentz structure of probe Lorentz structure of b→sb→s transitionstransitionsF.Muheim, Y.Xie & R.Zwicky, F.Muheim, Y.Xie & R.Zwicky, Phys.Lett.B664:174-179,2008Phys.Lett.B664:174-179,2008


Expected performance for Bs→ at LHCb

• What we “What we “know”know” now: now:

•The yield is 11k per 2 fbThe yield is 11k per 2 fb-1-1 (and 70k of (and 70k of BB00→ K→ K*0*0) )

• Background is Background is

• <6k @ 90%CL<6k @ 90%CL

• The mass resolution ~96 MeV/The mass resolution ~96 MeV/cc22

• Ecal resolutionEcal resolution

• The proper time resolution: The proper time resolution: ~78fs~78fs

• 50/50 50/50 11=52fs, =52fs, 22=114fs=114fs

L.Shchutska L.Shchutska et alet al, CERN-LHCb-2007-030, CERN-LHCb-2007-030

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LHCbLHCb: O(3 : O(3 BBss→→)/hour at )/hour at 2x102x103232

Full Monte Carlo simulationFull Monte Carlo simulation


Trigger

• Hardware Hardware L0L0 trigger for photons with high trigger for photons with high EETT

• Next trigger levels (software) :Next trigger levels (software) :

•Photon confirmation (& suppression of Photon confirmation (& suppression of mergedmerged ) ) and single (or pair) detached track reconstructionand single (or pair) detached track reconstruction

• ~ 70%~ 70%

•Full reconstruction of Full reconstruction of BBss → → candidatecandidate

•Reconstruction of Reconstruction of -candidate -candidate

•““inclusive inclusive ” trigger ” trigger

More details in dedicated talk More details in dedicated talk by Leandro de Paulaby Leandro de Paula


Large overlap, Large overlap,

high redundancy & high redundancy & robustness: robustness: ~ 95% ~ 95%

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)


Signal proper time resolution


Sensitivity to sin2

• To evaluate our sensitivity to To evaluate our sensitivity to sin2sin2

• toy Monte Carlo (10toy Monte Carlo (1044 experiments) experiments)

• Unbinned maximum likelihood fitUnbinned maximum likelihood fit

•Proper lifetime & error Proper lifetime & error

•Reconstructed mass Reconstructed mass

• Per-event proper time errorsPer-event proper time errors

• Resolutions & Efficiencies from Resolutions & Efficiencies from full MC full MC

• Parameterize the background from mass-sidebands Parameterize the background from mass-sidebands

• Important ingredient – proper time acceptance Important ingredient – proper time acceptance functionfunction

L.Shchutska L.Shchutska et alet al, CERN-LHCb-2007-147 , CERN-LHCb-2007-147

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m(Bm(Bss) = 5.367 GeV/) = 5.367 GeV/cc22

(B(Bss) = 1.43 ps) = 1.43 ps

ss = 0.084 ps = 0.084 ps-1-1

mmss = 17.77 ps = 17.77 ps-1-1


Proper time acceptance

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a = 0.74 psa = 0.74 ps-1-1

c = 1.86c = 1.86

dN/dt dN/dt ss(t) (t)


Proper time acceptance

•It is a vital to know it with very high precisionIt is a vital to know it with very high precision

•5% bias in “5% bias in “aa” -> bias in ” -> bias in sin2sin2 ~ 0.2 ~ 0.2

•We are planning to calibrate it using three We are planning to calibrate it using three techniques:techniques:

• BB00→ K→ K*0*0

• BBss→ → J/ J/

• “ “per-event-acceptanceper-event-acceptance” (“swimming” method)” (“swimming” method)

•The acceptance could be extracted from data for all The acceptance could be extracted from data for all casescases

•E.g. with ~E.g. with ~OO(1%) precision for (1%) precision for BB00→ K→ K*0*0


Background parameterization

•Fit separately left and Fit separately left and

right sidebandsright sidebands

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LeftLeft RighRightt


Results: (A(A,,CC,,SS))

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(A(A)=0.22)=0.22 ((SS)=)=((CC)=0.11)=0.11

Vanya Belyaev: Radiative decays @ LHCbVanya Belyaev: Radiative decays @ LHCb 1818

2fb2fb-1-1

• Already with “early” Already with “early” data the data the measurements of measurements of direct CP-asymmetry in direct CP-asymmetry in B→ KB→ K*0*0

•Double ratio:Double ratio:

•Measurement of Measurement of B→B→KK

“early measurements”

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The first 13 minutes @The first 13 minutes @

nominal luminosity nominal luminosity

B→ KB→ K*0*0

Conclusions

• LHCbLHCb has good potential for measurement has good potential for measurement of photon polarization in of photon polarization in BBss→→ decay decay

•For 2 fbFor 2 fb-1-1: :

(A(A)=0.22, )=0.22, ((SS)=)=((CC)=0.11)=0.11

•The determination of proper time acceptance The determination of proper time acceptance function from data in under the study: function from data in under the study:

•Three methodsThree methods

•The result has The result has moderatemoderate dependency on dependency on B/SB/S

Stay tuned and wait for more newsStay tuned and wait for more news


Backup slidesBackup slides10.9.2k+9 Vanya Belyaev: Radiative decays @ LHCb 2121

Example of models

•Anomalous right-handend top couplings Anomalous right-handend top couplings J.P.Lee’03J.P.Lee’03

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= -cos 2= -cos 2


B: proper-time in sidebands

•Fit separately left and right sidebandsFit separately left and right sidebands


Signal proper time resolution as function of Signal proper time resolution as function of coscos


Signal proper time resolution as function of Signal proper time resolution as function of coscos

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-1.0 : --1.0 : -0.50.5

-0.5 : -0.15-0.5 : -0.15

-0.15 : 0.3-0.15 : 0.3 0.3: 1.00.3: 1.0


The shape of background

•Vary the “short/long”-lived componentsVary the “short/long”-lived components

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Relative changeRelative change Absolute changeAbsolute change


Stability tests: B/S

•There is some dependency on There is some dependency on B/SB/S level: level:

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Conservative Conservative UL @ 90% UL @ 90% CLCL


Results: pulls

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AA

CCSS


Resolution and ss//ss

•Vary the proper time resolutionVary the proper time resolution

•Use simple model with two Gaussians and vary Use simple model with two Gaussians and vary the proportionthe proportion


Acceptance function


Background parameterization


Likelihood


Documents

Radiative Decays @ LHCb