Study of exclusive radiative Study of exclusive radiative

B decays with LHCbB decays with LHCb

Galina Pakhlova, (ITEP, Moscow)

for LHCb collaboration

Advanced Study Institute “Physics at LHC”, LHC Praha-2003,

B Physics Day, 11/07/2003

2

Physics motivationPhysics motivation

Constraint on CKM matrix elements |VConstraint on CKM matrix elements |Vtdtd/V/Vtsts|| from the ratios of decay from the ratios of decay rates rates

s

s

Search for New PhysicsSearch for New Physics Direct CP violation ACP < 1% in SM (tiny u quark contribution in loop) up to ~ 10% in SM extensions s

Mixing-induced CP violation ~0 in SM (different polarizations in and decays)

up to ~ 50% in SM extensions s

with e.g.

s (Dalitz plot

analysis of s to extract flavour blind

s ) Exotics, super rare decays

(s)l+ l-,

(s), etc

Test of QCD Test of QCD nb etc

bb s(d)s(d)

WW

t(c,u)t(c,u)

3

Experimental overviewExperimental overview

The first exclusive radiativeThe first exclusive radiativepenguin penguin was observed by was observed by CLEO CLEO inin 1993 1993

Belle Belle

Upper limit Upper limit BABAR BABAR

barionbarion

Upper Upper limit CLEO limit CLEO

Statistics at B-factories is still not sufficient for stringent Statistics at B-factories is still not sufficient for stringent test of SM in CP violation in radiative decays and for test of SM in CP violation in radiative decays and for observation of observation of b b d d

(4.3 (4.3 ± 0.4)×10± 0.4)×10-5-5 PDG PDG 20032003

(3.8 (3.8 ± 0.5)×10± 0.5)×10-5-5 PDG PDG 20032003

CPCP -0.01 -0.01 ± 0.07 ± 0.07 PDG PDG 20032003

(1.3 (1.3 ± 0.5)×10± 0.5)×10-5-5 PDG PDG

20032003

4

decaydecayvertexvertex

primaprimaryry

vertexvertex decaydecaydistancdistancee Impact Impact

Parameter (IP)Parameter (IP)

NNb hadronsb hadrons yearyear all types of b hadrons all types of b hadrons

bbbb/ / inel inel ~ ~

high charged and high charged and neutral neutral

multiplicitymultiplicity few primary verticesfew primary vertices

event at LHCbevent at LHCb

5

Challenge Challenge

Electromagnetic penguins are indeed Electromagnetic penguins are indeed rare B rare B decaysdecays

inclusive Br b s exclusive Br are ~10-100 smaller b d are further suppressed by |Vtd/Vts|2

fb Sf(b

Background sources Background sources Huge combinatorial background from generic bb events Minimum bias events X decays

separation using different shower shape

for X=V polarization can be exploited

6

Search for CP violationSearch for CP violation Direct CP violationDirect CP violation

no tag and lifetime analysis are required Systematic errors are of great importance:

fake (non-CP) asymmetries different and production rates in pp

interactions detector asymmetries

Hopefully can be calibrated with other final states

e.g. J/ Mixing-induced CP violationMixing-induced CP violation

need to tag flavour proper time resolution is critical

especially forSdue to fast oscillations (x s >19) to be

resolved

7

Can we measure radiative decays at Can we measure radiative decays at LHCb LHCb

Direct CPDirect CP

Energetic huge softandbackground can be effectively

removed dedicated trigger selects high ETphotons at Level 0

two charged tracks vertex reconstruction

S S ss decay & mixing-induced CP decay & mixing-induced CP

smallnarrowcut; small yield in decays: background conditions are more favourable

extremely small opening angle problem with

S vertex (proper time) resolution

b b dd smallnarrow cut problem with combinatorial background from

in progress (not presented here)

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reconstructionreconstruction

SelectSelect combinations combinations Tracks are consistent with Tracks are consistent with hypothesis hypothesis RejectReject tracks from all primary vertices tracks from all primary vertices ((

IPIP

>16)>16) produce secondary vertex produce secondary vertex (( PDG PDG MeV/c MeV/c22

EETT GeV GeV (close to L0 trigger requirement)(close to L0 trigger requirement)

E*E*TT GeV GeV Select primary vertex with Select primary vertex with minimum IP of minimum IP of

candidate candidate Require Require momentum and flight direction to be momentum and flight direction to be

consistent consistent ((mrad)mrad) helicity angle: in helicity angle: in rest frame rest frame |cos (p|cos (pBB, p, pKK)|<0.7)|<0.7

9

Background suppression (1)Background suppression (1)

No No IP IP cutcut

optimizedoptimized

IPIP> 16> 16

SSBB

c

oco

mb

mb

Require large IP of Require large IP of to all reconstructed primary vertex to all reconstructed primary vertex ((

IPIP> 16)> 16)

suppress primary tracks suppress primary tracks

especially effective background suppression in events with especially effective background suppression in events with multiple interactionsmultiple interactions

10

Background suppression (2)Background suppression (2)

Transverse energy Transverse energy E*E*TTininrest framerest framevs vs EET T in the in the lab framelab frame

EETTGeV GeV powerful against low energyand

E*E*TTGeVGeV rejects also soft candidates

EET T , GeV, GeV

E*

E* TT

G

eV

GeV

E*

E* TT

G

eV

G

eV

bb bb inclusiveinclusive

EET T , GeV, GeV

11

Background suppression (3)Background suppression (3)

reconstructed reconstructed momentummomentum

reconstructedreconstructeddecay decay vertexvertexreconstructedreconstructed

primary vertexprimary vertex

AngleAnglebetween between momentum momentum andand flight direction flight direction should be should be 0 for real 0 for real candidates (smeared by candidates (smeared by vertex resolution)vertex resolution) randomly distributed for randomly distributed for combinatorial backgroundcombinatorial background

One of the most powerful One of the most powerful cut!cut!

signalsignal ~ 60% ; ~ 60% ; bbbb < <

1%1%

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suppressionsuppression

Significant suppression of Significant suppression of fastfastis expected after application of is expected after application of special algorithm for special algorithm for separation based on separation based on shower shape shower shape (to be implemented soon) (to be implemented soon)

Contribution from Contribution from is is small and can be further small and can be further suppressed exploiting suppressed exploiting polarization :polarization :

helicity states helicity states 0 0

helicity:helicity: ininrest frame rest frame cos (pcos (pBB, , ppKK))

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: signal and background : signal and background summarysummary

~ 4 min LHCb~ 4 min LHCb

0 events0 events in in (4.5-6.0) GeV/c(4.5-6.0) GeV/c22 mass mass window window after trigger and off-line after trigger and off-line selectionselectionwith all available MC statistics with all available MC statistics ~ 10.3 M~ 10.3 M events events

~ 54 hours ~ 54 hours LHCbLHCb

MeV/MeV/cc22

In blue:In blue:contribution contribution fromfrom

after trigger and off-line cutsafter trigger and off-line cuts

ofofBrBrPDG PDG

20032003

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Annual yield and CP Annual yield and CP sensitivitysensitivity

Efficiency, [%]Efficiency, [%] NNyearyear CC

PPReconstructiReconstruction on

& & acceptanceacceptance

selectioselection n

triggetriggerr

totaltotal

4.54.5 9.29.2 3838 0.160.16 35 K35 K < < 0.010.01

BACKGROUND / SIGNALBACKGROUND / SIGNAL < 0.7< 0.7 @@ 90 % CL90 % CL

Assuming:Assuming:

Br Br = ( 4.3 = ( 4.3 0.4 ) 0.4 ) × × 1010-5-5

f f b b = 0.39= 0.39

N N N N

CP CP N N N N

15

SSreconstructionreconstruction

Two different tasksTwo different tasks Branching ratio measurementBranching ratio measurement

similar to reconstruction: Tracks are consistent with hypothesis Reject tracks from all primary vertices (

IP > 4) produce secondary Vertex ( PDG MeV/c2

ET GeV (close to L0 trigger requirements) E*T GeV Select primary vertex with minimum IP of

S candidate

S momentumandflight direction to be consistent

mrad ( worse S vertex resolution)

helicity : in rest frame |cos(pB,pK)| < 0.7 Search for mixing-induced CP:Search for mixing-induced CP: selection to be re-optimizedselection to be re-optimized

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ss background background

suppressionsuppression

narrownarrow< < MeV/cMeV/c22

Background is mainly due to real Background is mainly due to real Fortunately small Fortunately small yield from yield from decays.decays.

After After L0xL1L0xL1 trigger & off-line trigger & off-line cutscuts

bb inclusive:bb inclusive: 00 event event in mass window in mass window GeV/cGeV/c22

from from ~ ~ 10.3 M10.3 M events ( events ( ~ ~ 4 min4 min LHCbLHCb))

ss

ssassumingassumingBrBrBrBr

ss

17

s s after trigger and off-line cutsafter trigger and off-line cuts

Efficiency [%]Efficiency [%] NNyearyear reconstrreconstr

. & . & accept.accept.

selectiselection on

triggetriggerr

totaltotal

4.34.3 1515 3434 0.20.222

9.4 K9.4 K

BACKGROUND / SIGNALBACKGROUND / SIGNAL < 2.4 < 2.4 90 % CL90 % CL

limited by MC statistics, expected to be limited by MC statistics, expected to be betterbetter

Assuming:Assuming:

Br Br ss

= ( 4.3 = ( 4.3 0.4 ) 0.4 ) × × 1010-5-5

f f b b SS= 0.10= 0.10

MeV/cMeV/c22

~ 87 hours LHCb~ 87 hours LHCb

18

Search forSearch formixing induced CP mixing induced CP inin

SS

simplesimplevertex fitvertex fitfsfs

fsfs

““direction”direction”vertex fitvertex fitfs fs fs fs

S S proper time proper time

resolutionresolutionMain problem:Main problem:Proper time resolution is Proper time resolution is critical:critical: dominated by dominated by poor poor vertex resolutionvertex resolution kaons kaons are almost collinear are almost collinear no extrano extrainformation on information on

s s

vertex fromvertex from

Improvement can be Improvement can be achieved:achieved: Constrain the Constrain the

ss flight direction flight direction to to

ss momentum: ( momentum: (“direction” “direction” vertex fitvertex fit) ) Improve vertex resolution Improve vertex resolution by factor by factor >> 2.52.5

Select kinematical region with Select kinematical region with the better vertex (proper time) the better vertex (proper time) resolution: (resolution: (slow slow larger larger opening angle)opening angle)

19

sslifetime resolutionlifetime resolution

cuts re-optimizationcuts re-optimization for CP violation studyfor CP violation study

Achieved lifetime resolution isAchieved lifetime resolution is closeclose

to those forto those for charged modes charged modes..Estimation ofEstimation of CP violation CP violation

sensitivities sensitivities is in progressis in progress

Require:Require: cos cos , ,

EETT GeVGeV, , tighter tighter

cutcutNo cut No cut E*E*TT

SS

pro

per

tim

e r

esolu

tion

, p

rop

er

tim

e r

esolu

tion

, p

sp

s

cos cos

SSproper time proper time

resolution, psresolution, ps

Decay angle Decay angle (between(betweenmomentummomentumin rest frame ofin rest frame of

ss and and ss flight direction) is convenient variable to select flight direction) is convenient variable to select

the kinematical region that provides the betterthe kinematical region that provides the betterproper proper time resolutiontime resolution

fsfs

fsfs

20

ConclusionConclusion

record statistical sensitivity in direct CP violation(ACP )< 0.01 for one year LHCb. Stringent test of SM

extensions! systematic errors to be studied carefully

S S

precise measurement of the branching fraction with ~2% accuracy for one year LHCb For indirect CP violation

S proper time resolution is critical advanced fit vertex procedure and dedicated cut optimization allow

to hope on reasonable sensitivity Others channels of interest

|Vtd/Vts| direct CP

violation

s mixing-induced CP violation

why not under study