DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from...

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DIS 2004, Strbske Pleso,A pril 2004 1 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb detector CP violation in Standard Model Few examples of measurements of B s mesons: - Δm s from B s 0 - B s 0 mixing in B s 0 D s π - CP asymmetries in B s 0 D s K - CP asymmetry in B s 0 J/ψ φ • Conclusions Marek Szczekowski Soltan Institute for Nuclear Studies, Warsaw

Transcript of DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from...

Page 1: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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

Page 2: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

Page 3: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

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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

Page 5: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

Page 6: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

Page 7: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

Page 8: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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 ?

Page 9: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

Page 10: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

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• 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 /,

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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

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• 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

Page 14: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

Page 15: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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• 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

Page 16: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

Page 17: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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

Page 18: DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb.

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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