The ATLAS B-Physics programme

The ATLAS B-physics programmeJames R Catmore ([email protected])

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ATLAS & the LHC

Triggering

B-physics programme

The ATLAS B-Physics programme

James R Catmore

ATLAS group, University of Lancaster

United Kingdom

Institute of Physics HEPP Conference 2005, Dublin, Republic of Ireland


2/14

ATLAS & the LHC

Triggering

B-physics programme

Overview of ATLAS

Weight: 7000 tonnes

Radius: 11m

Length: 46m

Muon chambers

Barrel toroid

Inner detector

EM calorimeterForward calorimeter

Hadronic calorimeter

End-cap toroid


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ATLAS & the LHC

Triggering

B-physics programme

The LHC Environment

• pp collisions: 14 TeV centre of mass energy • Luminosity:

– 2007: 100 days @ 0.5 x 1033 cm-2s-1 Tuning– 2008-2009: 200 days @ 2 x 1033 cm-2s-1 “Low”– 2010+: 1034 cm-2s-1 “High”– Drops by factor ~2 during 10 hour run

• 1 proton bunch crossing every 25ns– 4.6/23 pp collisions/crossing @ low/high luminosity– ~1% of pp collisions produce a bb pair

• At luminosity 2 x 1033 cm-2s-1 – bb events produced with rate of 106 Hz– 10Hz output to permanent storage for B-physics

so highly selective and adaptable B-physics

trigger required


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ATLAS & the LHC

Triggering

B-physics programme

The ATLAS Trigger System

Calorimeters

Muon Systems

Tracking

Pipeline memory

LVL1

Read-out buffers

LVL2

Event Builder

Distributed storage & analysis

(“Grid”)

Event filter

Region of interest data

1 GHz interaction rate

75 kHz 1 kHz 100 Hz


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ATLAS & the LHC

Triggering

B-physics programme

B-physics trigger strategies

As luminosity drops during the run, more triggers are turned on

Trigger LVL1 Example channels

Di-muon

L 2.1033

(L ≈ 1034)

2 muons

pT > 5 GeV (barrel)

3 GeV (end-caps)

Bd→ J/ψ(μμ)K0S

Bs→ J/ψ(μμ)φ

B→μμ B→K0*μμ B→μμ

Λb→Λ0 J/ψ(μμ) Λb→Λ0 μμ

EM+μ

L < 2.1033

1 muon

pT > 6 GeV

1 EM cluster

ET > 2GeV

Bd→ J/ψ(μμ)K0S+ b→ eX

Bd→ J/ψ(ee)K0S + b→ μX

Bd→K0* Bs→+ b→ μX

Hadronic

L < 2.1033

1 muon

pT > 6 GeV

1 jet cluster

ET > 2GeV

Bs→Ds(φ(KK))π

Bs→Ds (φ(KK)) a1(ρ0π+)

B+ → K+K+- Bd → +-

(+ b→ μX)


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ATLAS & the LHC

Triggering

B-physics programme

The current ATLAS B-physics studies

Event type Channel Physics motivationsDecays to charm Bd→ J/ψ(μμ)K0

S

Bs→ J/ψ(μμ)φ Bs→ J/ψ(μμ)η

sin 2β and test of CPV from NP

ΔΓS, φS - test of CPV from NP

Λb→Λ0 J/ψ(μμ)

Bc+→ J/ψ(μμ)π+

QCD: production polarization, test of CPV

QCD, heavy-heavy decays, VcbV

Rare decays Bs→μμ Bd→μμ

Bd→K0*μμ ; Bs→φμμ

Bd→K0*γ ; Bs→φγ

Λb→Λ0 μμ

Branching ratio

Branching ratio, AFB,

B.R., angular studies; CPV

Branching ratio, AFB

Hadronic

channels

Bs→Dsπ, Bs→Dsa1

Bd→ππ

B+ → K+K+-

Bs oscillation; Vts/Vtd

CP violation, decay parameters

Branching ratio, test of NP

NLO QCD: b-production

B →l + B+→ J/ψ(μμ)K+

B+→J/ψ(μμ)K0* , Bs→ J/ψ(μμ)b-cross section and b-b correlations


7/14

ATLAS & the LHC

Triggering

B-physics programme

Bs meson physics

• B mesons mix:

• Mixing parameters:

– ΔMs Bs→Dsπ, Bs→Dsa1

– ΔΓs , φs Bs→ J/ψ(μμ) φ, Bs→ J/ψ(μμ) η

,s

,s


8/14

ATLAS & the LHC

Triggering

B-physics programme

Physics with BS→J/ψφ

• Aim: measurement of ΔГs and φs

• S → V V decay so three final state helicity configurations:

• To extract φs we must separate out the helicity amplitudes → angular analysis: 3 angles in inner detector

J/J/ψψ φφBB00

SS

BB00SS

μμ++μμ--

KK++KK--

A┴ A║ A0…so final state is made up of linear combinations of helicity amplitudes which are CP-eigenstates with different parities

p pB0

S

K+J/

- φ

1

2


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ATLAS & the LHC

Triggering

B-physics programme


Accurately modelled by EvtGen


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ATLAS & the LHC

Triggering

B-physics programme


• Experimental technique:

– Identify BS→J/ψφ decays, collect angular distribution

– Fit distribution against theoretical expression to extract the parameters, using a Maximum Likelihood Estimator

– Magnitudes and forms of εtag, εrec ,, ρ, b estimated with simulation

– Correlations between parameters are of critical importance

0

0

2211

2211

1

min

0

0

)(,,

)(,,

t

trectagrectag

it

irectagirectagN

idttdttbetWtW

dtttbetWtWL

i

i


11/14

ATLAS & the LHC

Triggering

B-physics programme



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ATLAS & the LHC

Triggering

B-physics programme


xs - φs region

Allowed by Standard Model (updated 2003)

New physics: Left-right symmetric model (NP-LR)Fleischer, Ball, 2000

ATLAS (3yr @ 1033cm-2s-1)

Statistics: 300 000

LHCb (5yr @ 5 x 1032cm-2s-1) performance as given in 2000

Statistics: 240 000


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ATLAS & the LHC

Triggering

B-physics programme

Rare Decays

• FCNC processes b→d, b→s

– forbidden at tree level: occur at lowest order as loops

– sensitive to deviations from S.M.

e.g. B→μμ

Signal

Bs→μ+μ-

Signal

Bd→μ+μ-

BG

1 yr

1034cm-2s-192 14 660

3 yrs

1033cm-2s-127 4 93

ATLAS measurement

Combing the two samples:

4.3σ significance for Br(Bs→μμ)

95% C.L. upper limit for Br(Bd→μμ) = 3x10-10

Standard Model:Br(Bd→μμ) ≈ 1.5 x 10-10

Br(Bs→μμ) ≈ 3.5 x 10-9


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ATLAS & the LHC

Triggering

B-physics programme

Conclusions

• ATLAS is well placed to perform a diverse range of precise measurements on B-physics events

• A flexible trigger strategy will allow efficient use of beam-time

• Precise measurements to test sensitivity of CPV or other NP indicators in charm and charmless decays will be carried out

• In rare muonic decays already after 1yr @ 1034cm-2s-1 sensitivity down to BR ~ 3 x 10-10

• Rare semi-muonic and rare radiative decays: statistics allow the testing of the sensitivity of angular distributions to NP

• QCD tests: b-quark, b-b production, origin of b polarization, doubly HF production mechanisms (Bc)


15/14

ATLAS & the LHC

Triggering

B-physics programme

Additional Slides


16/14

ATLAS & the LHC

Triggering

B-physics programme

Is it a B or a B? (Tagging)

b/b? b/b?

Signal B/B-meson

Jet charge tag

b/b? b/b?

Lepton tag from semi-leptonic decay

For Bd→ J/ψ(μ6μ3)K0S

Tagging efficiency εtag = 0.64

Wrong-tag fraction Wtag = 0.42

εtag(electron) = 0.012

εtag(muon) = 0.025

Wtag(electron) = 0.27

Wtag(muon) = 0.24Signal B/B-meson


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ATLAS & the LHC

Triggering

B-physics programme

Measuring sin(2β) with Bd→ J/ψ K0S

• Decay into a CP eigenstate (CP=-1)

• So far the study assumed no direct CP violation, the plan is to include it

2sinsin/ dsdmixCP KJBA

N

i

t

tii

it

ii

dttdttbetWtW

dtttbetWtWL

i

i

1 0

0

21

21

min

0

0

where W+ = Pdf (Bd→ J/ψK0S)

W- = Pdf (Bd→ J/ψK0S)


18/14

ATLAS & the LHC

Triggering

B-physics programme

Measuring sin(2β) with Bd→ J/ψ K0S

• To achieve high sensitivity:– Triggers selecting J/ψ→μμ, J/ψ→ee– Combined tagging techniques: lepton tag and jet-charge tag

J/ψ→μ(6)μ(3) J/ψ→μ(6)μ(5) J/ψ→e(1)e(1)

No. of reconstructed events

Signal/Background

δstat[sin 2β]: lepton tag

δstat[sin 2β]: j.c. tag

δstat[sin 2β]: combined tag

490 000

23

0.023

0.015

0.0126

250 000

32

0.030

0.019

0.016

15 000

16

0.018

-

0.018

δstat[sin 2β] J/ψ→μ(6)μ(3) + J/ψ→e(1)e(1)

δstat[sin 2β] J/ψ→μ(6)μ(5)

δsystematic

0.010

0.016

0.005

3 years @ 1033 cm-2 s-1:


19/14

ATLAS & the LHC

Triggering

B-physics programme

CP violation with Bd→π+π-

– Penguin diagrams contribute without suppression so large hadronic uncertainties

– Difficult to isolate the decay from other similar decays (Bd→K+π-, Bs→K+K-, Bs→K- π+, Λb→pπ-, Λb→pK-)

– Low branching ratio

• Maximum likelihood:

2sin d

mixCP BA

• Decay into a CP = +1 state:

MtAMtA

tt

ttA dir

CPmixCPCP

cossin

sin2coscos22sin;sinsin2T

PA

T

PA dir

CPmixCP

arg(P/T)


20/14

ATLAS & the LHC

Triggering

B-physics programme

CP violation with Bd→π+π-

%0|| TP

%30|| TP

%100|| TP


21/14

ATLAS & the LHC

Triggering

B-physics programme

Bs meson physics: ΔMs measurement

• Bs→Ds(φ(KK))π, Bs→Ds (φ(KK)) a1(ρ0π+) : B(t=0) = Bs

– p-(t), p+(t) = probability of decay in the state B(t) = Bs , B(t) = Bs

2cos

2cosh

22s

sst tMtetp

t

tM

tptp

tptptr

s

s

2cosh

cos

TheoryExperiment

1 year @ 1033 cm-2 s-1:

• Measurement highly dependent on the trigger scheme

• ΔMs determination not sensitive to value of ΔΓs with these channels


22/14

ATLAS & the LHC

Triggering

B-physics programme


ATLAS LHCb

No of events 300 000 240 000

Proper time res. 0.063 ps 0.031 ps

Background ~15% ~3%

Tag efficiency 63% j.c. 40% lp & K

Wrong-tag 38% 30%

σstat: ΔГs,Гs

σstat: A┴, A║

σstat: φs(x=20)

σstat: φs(x=40)

12%, 0.7%

0.8%, 3%

0.03

0.05

9%, 0.6%

0.7%, 2%

0.02

0.03


23/14

ATLAS & the LHC

Triggering

B-physics programme

More Rare Decays

Semi-muonic decays: Bd→μμK0*, Bd→μμφ

(a) Branching ratios: enhancement

from beyond the S.M.

(b) Forward-backward asymmetryb s

?

)cos(

0

1 )cos(

)cos(

1

0 )cos(

1)(

2

2

ddsd

d

ddsd

d

dsdsAFB

Three points: mean values of AFB in three q2/MB

2 experimental regions with error bars

SM

MSSM C7g >0

MSSM C7g <0

K*0

Bd

Documents

The ATLAS B-Physics programme