DIS 2004, Strbske Pleso,April 2004 1

LHCb experiment sensitivity to CKM phasesand New Physics from mixing and CP violation

measurements in B decays

• LHCb detector• CP violation in Standard Model• Few examples of measurements of Bs mesons:

- Δms from Bs0 - Bs

0 mixing in Bs0

Ds π

- CP asymmetries in Bs0

Ds K

- CP asymmetry in Bs0

J/ψ φ• Conclusions

Marek SzczekowskiSoltan Institute for Nuclear Studies, Warsaw

DIS 2004, Strbskie Pleso,April 2004 2

LHCb detector

pp collisionsat s = 14 TeV

σbb 500 µb

σinelastic 80 mb

L = 2 1032 cm-2s-1

nB /107s in 4π ~1012

B+ / Bd / Bs / Λb

40 / 40 / 10 / 10 %

Tracking

π/K/p separation

e/γ/π0 identification

hadron identification

muon identification

DIS 2004, Strbskie Pleso,April 2004 3

Example of B event

• Selection of a specific B decay event from large background effective trigger

• Reconstruction of final state measurement of momenta and identification of particles

• Measurement of proper time of B decay: t mL / pc decay length L (<L> ~ 1 cm in LHCb) momentum p from decay products (range ~ 1–100 GeV)

• Tagging state of B0 : was it originally produced as B0 or B0 ? e.g. charge of lepton or kaon from decay of the other b hadron can be used

Bs0

π± or K±

Ds±

K+

K-

π±b-hadron

lepton K-

primary vertex

σz ~ 50 μm

σz ~ 140 μm

σz ~ 440 μm

L

<nch>b 34

DIS 2004, Strbskie Pleso,April 2004 4

Tracking in LHCbVELO: silicon strips21 stationssensors R and φ

TT stations:silicon strips

Outer Tracker:straw drift chambers

Inner Tracker:silicon strips

δp/p = 0.35 –0.55 %

tracks from B decays

DIS 2004, Strbskie Pleso,April 2004 5

Time and mass resolutions

Bs DsK

στ = 40 fs σM(Ds) = 5.5 MeV/c2 σM(Bs) = 13.8 MeV/c2

for Δms=30 ps-1 oscillations havea period of 210 fs sufficient resolution

very good mass resolutionuseful in background rejection

DIS 2004, Strbskie Pleso,April 2004 6

π/K/p separation

separation of Bs DsK

andBs Dsπ

RICH 1 RICH 2

(K K) = 88%

(π K) = 3%

Example:

Two RICH systems are essential

DIS 2004, Strbskie Pleso,April 2004 7

Trigger

pil

e-u

p

Efficiency: 30 – 60 %

Level-0:Level-0:ppTT of of

, e, h, , e, h,

Level-1:Impact parameterRough pT ~ 20%

HLT:Final state

reconstruction

40 MHz

1 MHz

40 kHz

200 Hz output

• σbb ~ 500 μb, < 1% of inelastic cross-section• with high background multi-level trigger is needed to select interesting events: - L0: high pT electrons, muons or hadrons - L1: vertex structure and pT of tracks - High Level Trigger: full reconstruction

DIS 2004, Strbskie Pleso,April 2004 8

Flavour physics puzzle

The fundamental question: what distinguishes different generationsof quarks and leptons ? - three families of particles have the same quantum numbers, but very different properties (hierarchical masses, small mixing angles) - in Q.M. we expect similar energy levels and large mixing for a set of states with the same quantum numbers.THESE FACTS SUGGEST THAT THERE IS AN ORDERED STRUCTUREBEHIND THE FLAVOUR. - hidden flavour quantum numbers that distinguish different generations - new quantum number new symmetry: A FLAVOUR SYMMETRY - allows the top quark Yukawa coupling - forbids all other Yukawa couplings massless quarks - no mixing between states with different quantum numbers - experiments show that new symmetry has to be only approximate, small breaking allows small quark masses and some mixing. WHAT IS THIS SYMMETRY ?

DIS 2004, Strbskie Pleso,April 2004 9

CP violation and unitarity triangles• Nine unitarity relations of the Cabibbo-Kobayashi-Maskawa (CKM) matrix

• Two are the most relevant in the analysis of CP violation in B-meson sector:

• The unitary triangle in 2007 when LHCb will start to take data:

measurement of the angle will be crucial

β - large Bd-Bd mixing phase (Vtd)

χ - small Bs-Bs mixing phase

(Vts)

γ - bu decay phase (Vub)

Bs mesons provide access to the second unitarity triangle

DIS 2004, Strbskie Pleso,April 2004 10

Formalism for CP violation sshl BqBp

qpB

22)(

1Two mass eigenstates Bl and Bh:

Time dependent rates for initial flavour eigenstates Bs and Bs decaying tofinal states f and f :

)()(2

)(

2

tItIeA

t tf

f )()(

2)(

22

tItIeq

pAt tf

f

)()(2

)(

2

tItIeA

t tf

f )()(

2)(

22

tItIep

qAt tf

f

where

tttI

2sinh)(2

2cosh1)(

2

mtmttI sin2cos12 f

f

A

A

p

q

f

f

A

A

q

p

Asymmetry:

tAt

mtAmtAtA

mixdir

f

2sinh

2cosh

sincos

1

12

2

dirA

1

22

mixA

1

22

AIn S.M.:

iep

q

DIS 2004, Strbskie Pleso,April 2004 11

• Present limits: (95% CL)

• Channel with largest sensitivity for LHCb:

Bs Ds+

• Decays Bs0 Ds.

- π+ and Bs0 Ds.

+ π - are flavour specific:

no CP asymmetry

can be used to extract • ~ 80,000 reconstructed events/year

with S/B ~ 3 expected• High branching ratio and fully reconstructed

decay for Ds.- K- K+ π -

Decay length resolution ~ 200 m proper time resolution ~ 40 fs

Δms and ΔΓs from Bs-Bs mixing

29.0/,4.14 1 sss psm

00 ff AA

Acos(Δmst) free parameter A=1 for true Δms

)cos()2

cosh(2

~

2

tmt

eA

sstD

D

s

s

sssm /,

DIS 2004, Strbskie Pleso,April 2004 12

Error on the amplitude A of oscillations vs ms: 5 measurement in one year for ms up to 68 ps-1 sensitivity limit much larger than SM prediction (14.4 –26 ps-1)

To observe mixing we must know what was originally produced: Bs

0 or Bs0

tagging of production state: efficiency = 54.6 ± 1.2 % mistag rate = 30.0 ± 1.6 %

Reconstructed proper-time for Bs0 decays

tagged as not mixedshows clear oscillations

LHCb Δms limits from Bs-Bs mixing

Rate (Bs0 Ds

-π+)

Err

or o

n am

plit

ude

A

ms

ms[ps-1] 15 20 25 30ms) 0.009 0.011 0.013 0.016

DIS 2004, Strbskie Pleso,April 2004 13

• With the same topology Bs Ds is a background for Ds K with ~ 12 –15 higher branching ratio

• the background can be eliminated by cut on difference in log-likelihood between K and hypotheses in RICH

After cuts contamination only ~ 10%

Since Ds has no CP asymmetry, it can be used to control systematic errors:eg to measure any possible productionasymmetry of Bs and Bs

Dsπ vs. DsK

DIS 2004, Strbskie Pleso,April 2004 14

CP asymmetries in Bs Ds K+

• CP violation asymmetry arises from interference between two tree diagrams via Bs mixing:

Bs Ds+K with Bs Bs Ds

+K and Bs DsK+ with Bs Bs Ds

K+

• |T1| |T2 | large asymmetries

• CP asymmetries measure ( is the phase of Vub)if will be determined in Bs J/ decays

a clean method to measure γ since only tree diagrams contribute• Insensitive to new physics, new particles appear in loops• Branching ratio for Ds

KKgives ~ 5400 events/year

T1

T2

Four distinct decay modes, flavour-nonspecific channels common to B0 and B0 decays:

Bs0 Bs

0

Bs0 Bs

0

K+

K+

K-

K-

Ds-

Ds+

Ds+

Ds-

b

b b

b

ss

s s s

ss

s

s

s s

s

u

u

u

u

c

c

c

cVcb Vub

Vub*Vcb*

Vcs*Vus*

VcsVus

Bs0

Bs0

Δms

f = Ds.-K+

f = Ds.+K-

T1

T2

T1

T2

T1

T2

DIS 2004, Strbskie Pleso,April 2004 15

• Large ms rapid oscillations have

to be resolved

• Unknown strong phase difference

between tree diagrams

• forDsKasymmetry the phase is

arg(λ) = (

• for Ds+Kasymmetry the phase is

arg(λ) = (

• With fits to two time-dependent

asymmetries it is possible to extract

bothand(

Asymmetries for 5 years of LHCb data taking

() ~ 14 in one year

Asymmetries in Bs DsK

Δms=25 ps-1

DIS 2004, Strbskie Pleso,April 2004 16

CP asymmetry in Bs J/

• Dominated by single amplitude no CP violation in decay• Bs counterpart of the golden mode B0 J/KS

• CP asymmetry arises from interference of Bs J/ and Bs Bs J/

in S.M. asymmetry very small sin 2~ 0.04 sensitive probe for contributions from New Physics:

observation of sizeable asymmetry implies existence of NP• 120,000 events/year with J/ or ee, KK

• For VV decays final state is admixture of CP-even and CP-odd contributions

separation requires angular analysis of decay products

• Likelihood is sum of CP-odd and CP-even terms

L(t) = R L(t) (1+cos2tr)/2 + (1R) L(t) (1cos2tr)

tr is the transversity angle

• Fit for sin 2, R and s/s (s/s 0.1 expected)

(sin 2) ~ 0.06, (s/s) ~ 0.02 in one year

Bs0

J/ψ

cc

ss

s

bVcb*

Vcs

Bs0

Bs0

ΔmsfCP= J/ψ

A

A

DIS 2004, Strbskie Pleso,April 2004 17

LHCb Physics Reach in 1 year (2fbLHCb Physics Reach in 1 year (2fb–1–1))

ChannelChannel Yield Yield PrecisionPrecision Bd J/Ks 240 000 0.6o

Bs DsK

Bd , Bs KKBd D0 K*

Bd D0 K*

Bd DCP0 K*

5400 26000, 37000

5003400600

14o

6o

8o

Bs J/ 120 000 2o

|V|Vtdtd/V/Vtsts Bs Ds 80 000 ms up to 68 ps

rare rare decaysdecays

Bd K 35 000 (ACPdir) 0.01

DIS 2004, Strbskie Pleso,April 2004 18

Conclusions

• To discover new physics or help interpret new physics discovered in other experiments a comprehensive study of heavy flavour physics is needed:

- measure α, β, γ, χ in many decays with high precision - look at rare decays and mixing

• LHCb will be able to explore flavour physics with the required sensitivity and flexibility needed to discover, confirm or clarify new phenomena.

• The LHCb experiment will be ready for first LHC collisions in 2007