Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 1 / 19 IOP HEPP Annual Meeting

Analysis of the B0D0K*0 decays at LHCb

Outline:• The LHCb detector• B0 D0K0* event selection• B0 D0K0* sensitivity studies• Conclusion

Jacopo Nardulli RAL

IOP HEPP Annual Meeting

Lancaster 31/3 2/4

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 2 / 19 IOP HEPP Annual Meeting

LHC tunnel

CMSALICE

ATLAS

LHCb CERN

Geneva airport

The Large Hadron Collider (LHC)Start: 2008

LHC LHCb:p-p collisions with 14 TeV L ~ 2 .1032 cm-2s-1 (mostly single interactions)Bunch crossing @ 40MHz (25 ns ) ~ 14 Million collisions per second

1 in 160 collisions is B physicsInelastic pp collisions/crossing

LHCb

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 3 / 19 IOP HEPP Annual Meeting

Physics motivations

B-factories and the Tevatron Winter 2007

LHCbLHCb L=10 fb L=10 fb-1-1

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%6.3/)(

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ηησρρσ

Unitarity Triangle prospectsfrom LHCb only (2014)

In this talk I’ll concentrate on a clean mode for γ extraction: B0D0K0*

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%17/)(

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ηησρρσ

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 4 / 19 IOP HEPP Annual Meeting

B production

• B hadrons are mostly produced in the forward direction (along the beam)

• Choose a forward spectrometer10–300 mrad

• Both b and b in the acceptance: important to tag the B flavour at production to study CP violation

(PYTHIA)

b–b correlation

Parton 1 Parton 2

p p

Boostb

b-

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 5 / 19 IOP HEPP Annual Meeting

p p

~ 300 mrad

10 mrad

Forward spectrometer (running in pp collider mode)

LHCb Detector

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 6 / 19 IOP HEPP Annual Meeting

Vertex locator around the interaction region

LHCb Detector

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 7 / 19 IOP HEPP Annual Meeting

Tracking system and dipole magnet to measure angles and momenta p/p ~ 0.4 %Magnetic field regularly reversed to reduce experimental systematics

LHCb Detector

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 8 / 19 IOP HEPP Annual Meeting

Two RICH detectors for charged hadron identificationProvide > 3σ \K separation for 3 < p < 100 GeV

LHCb Detector

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 9 / 19 IOP HEPP Annual Meeting

Calorimeter system to identify electrons, hadrons and neutralsImportant for the first level of the trigger

e

h

LHCb Detector

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 10 / 19 IOP HEPP Annual Meeting

Muon system to identify muons, also used in first level of trigger

LHCb Detector

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 11 / 19 IOP HEPP Annual Meeting

Decays of interests are B0 D0K*0 with D0 K± π± and K*0 K+π-

B0 D0K*0 with D0 K±π±

analogously we have B0 D0 K*0 with K*0 K-π+ and B0 D0 K*0

Finally there are also the decays to CP eigenstates: D0 K+K- or D0 π+π-

A bit of theoryDecays of interests

• Extraction of γ through CP modes originally proposed by Gronau - London - Wyler: Phys. Lett. B253, 483 (1991)• Possibility of using not only CP modes proposed by Atwood - Dunietz - Soni Phys.Rev.Lett. 78 3257 (1997)

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 12 / 19 IOP HEPP Annual Meeting

• LHCb cannot easily measure CP odd states GLW alone is not enough

• Combining GLW and ADS solves problem (using also non CP modes)

• We have 6 equations and 5 unknowns: rB, δB, δD, γ and N Kπ

• NCP is determined from NKπ taking in account the different BR and efficiencies

• Method described in LHCb note 2005-066.

A bit of theory

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 13 / 19 IOP HEPP Annual Meeting

D0D0 b u

s

d

c

d

b c

s

d

u

d K(*)0 K(*)0B0 B0

VcbVub

4.01

|)(|

|)(|0*00

0*00

≈≈ →

→=

cb

ubB V

V

KDBA

KDBAr

λ

•Both diagrams colour-suppressed similar magnitude and large interference

• Decays of D0, D0 to same final state gives access to interference

• Modes with K*0→ K+π- are self-tagging: sign of kaon charge distinguishes B0

K*0→ K-π+ from B0

• Branching fractions involved all rather small

A bit of theory

K+u

D0 c ds

uu - D0

-du

u

s

u K+c

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 14 / 19 IOP HEPP Annual Meeting

K

h

h

πK*0

B0dPV

D0

Decay topology and event selection

Analysis described in LHCb public note: 2007-050

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 15 / 19 IOP HEPP Annual Meeting

Mass resolution

B0 K* D0

B0 mass K0* mass D0 mass

μ ~ 5276 MeVσ ~ 14 MeV

μ ~ 892 MeVσ ~ 32 MeV

μ ~ 1864 MeVσ ~ 8 MeV

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 16 / 19 IOP HEPP Annual Meeting

Monte Carlo Selection Results(on 2/fb of data)

Channel Annual yield B/S

B0D0(K+π-)K0* 3350 < 2.1

B0D0(K+π-)K0* 536 < 12.8

B0D0(K+K-)K0* 474 < 4.1

B0D0(+π-)K0* 134 < 14

• Most of the background arises from π/K misidentifications, where we have a ρ0 instead of a K*0. Other background comes from D* resonances•The limits are calculated, assuming Poisson statistics, after none of the original 34 M bbar passes the event selection.

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 17 / 19 IOP HEPP Annual Meeting

TOY MC Results: 1000 experiments (2/fb each)

rB Input : 0.4

δB Input : 10o

γ Input : 60o

δD Input : 12o

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 18 / 19 IOP HEPP Annual Meeting

Scans

δB ScanrB Scan δD Scan

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 19 / 19 IOP HEPP Annual Meeting

Summary

• The B0D0K0* decays offer a “penguin free” way to extract the CKM angle γ• An event selection has been studied on Monte Carlo data, which will allow LHCb to achieve a good S/B for all studied decay channels. It was found that low background levels are crucial in particular for B decays with D0 CP modes. Therefore a tighter event selection has been developed for these rarer decay modes. • Using B0D0(hh)K0*

decays, γ can be determined with a statistical error better than 10 degrees with one year of data at nominal luminosity for rB > 0.3.

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 20 / 19 IOP HEPP Annual Meeting

Back Up Slides

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 21 / 19 IOP HEPP Annual Meeting

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 22 / 19 IOP HEPP Annual Meeting

Particle identification through RICH system p/K/π separation

Invariant mass (no PID)

ππ hypothesis

Clean samples through expected PID performance of RICH system

Invariant mass (with PID)

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 23 / 19 IOP HEPP Annual Meeting

Results : a badly behaved case (2/fb)

rB Input : 0.4

δB Input : 120o

γ Input : 60o

δD Input : 3o

Jacopo Nardulli Lancaster 1/04/2008B0 D0K0* Analysis in LHCb 24 / 19 IOP HEPP Annual Meeting

Sensitivity studies

• A TOY for the extraction of γ in the B0D0K*0 has been developed• In the TOY the following equations are parameterized

• We have 6 equations and 5 unknowns: rB, δB, δD, γ and NKπ

• NCP is determined from NKπ taking in account the different BR and efficiencies