R Lambert, CERNCERN CPV, 18th June 20101 Flavour-specific asymmetry and LHCb Robert W. Lambert On...

R Lambert, CERN CERN CPV, 18th June 2010 1

Flavour-specific asymmetryand LHCb

Robert W. Lambert

On behalf of the LHCb collaboration

Introduction

D exclusive asymmetry hep-ex 0904.3907

D Inclusive asymmetry hep-ex 1005.2757

What can we do at LHCb?

00 XDB ss

... bb

-31.41.5- 10 (syst)] 9.1(stat) 1.7[ s

-310 (syst)]46.12.51(stat) 57.9[ bA

Literature

Reading material: LHCb

– CERN-LHCb-2007-054 Public note from old Monte Carlo– CERN-THESIS-2008-045 Paul’s Thesis– CERN-THESIS-2009-001 Rob’s Thesis– CERN-THESIS-2010-076 Ken’s Thesis

Theory– hep-ph 0406300 U. Nierste – hep-ph 0612167 [JHEP] A. Lenz, U. Nierste– hep-ph 0605028 [PRL] Y. Grossman et al.– hep-ph 0604112 [PRL] Z. Ligeti et al.

Other measurements– hep-ex 0505017 [PRD] Belle– hep-ex 0202041 [PRL] Babar– hep-ex 0101006 [PRL] Cleo– Note 9015 CDF inclusive

Outline

1. Theory .. from an experimentalist

2. Experimental Status

3. Complications at LHCb

4. Why LHCb?

5. Measurements at LHCb

6. Real data highlights

7. Outlook and Prospects

8. Conclusions

Flavour-specific decays Favoured/Allowed Not allowed at tree Through mixing

Flavour specific asymmetry, afs, parameterises CPV in mixing

Flavour-specific asym.

fBBfBB

fBBfBBtAa

qqqqqfs

oror)(

ss DB0

fBB qq 00

ss DB0

The whole shebang

Three different parameters fully constrain b-mixing

afs is very small in the standard model

qqfs Ma

12Im ,2,arg2 1212

LqHq MMMm

104.01.2

101.10.5

Discovery Potential

afs is sensitive to new physics (NP): Sensitive to loop contributions Sensitive to new CPV phases

If we allow a single NP phase in the mixing

R Lambert, CERN CERN CPV, 18th June 2010

sinRecosIm12

Discovery Potential

Up to 200-times the SM ... but ... (4x10-3)< D measurement

sinRecosIm12

Discovery Potential

5101.2 3100.4

Experimental Status

B-factories

Babar, Belle, Cleo all use the di-muon sample Know the initial state (4S) Time-integrated number-counting of di-muons Possible muon detector asymmetry is important to measure

310)5.51.1(

factbdfs

lXlbbNNc b

hep-ph 0605028

Exclusive measurement

D have also made an exclusive measurement Search for the full decay chain in the data Requires full reconstruction Flavour-tagging provides extra information Lower and more easily understood backgroundsx Extra detector asymmetryx Lower statistics

3-1.41.5-

10 (syst)] 9.1(stat) 1.7[

hep-ex 0904.3907

CDF Inclusive

CDF use only the di-muon sample Don’t know the initial state (pp) Time-integrated number-counting Possible muon detector asymmetry is important to measure

3-10 (syst)]8.69.0(stat) 0.8[

582.0418.0

lXlbbNN

2fact-b using10) 9(ip).0 (syst)6.1 (stat)1.20.2( s

Note 9015

New D inclusive

D used primarily the di-muon sample Don’t know the initial state (pp) Time-integrated number-counting Possible muon detector asymmetry is important to measure

2fact-b using

10)75.046.1(

10 (syst)]46.12.51(stat) 57.9[

506.0494.0

lXlbbNN

hep-ex 1005.2757

New D inclusive

Key Systematics (it’s difficult to be inclusive!) Kaons decaying in-flight Punch-through of hadrons to muons

Key methods Rely on real data, cross-check with well-tuned Monte Carlo Use the inclusive single muon sample to get extra information Reverse magnets to remove most detector asymmetry Do many many cross-checks in different phase-space regions

Result, 3.2 s !

45.06.0 103.2

SM % 0.3) 1( bA

hep-ex 1005.2757

Summary

Before the New D Inclusive Measurement A lot of measurements All consistent with SM +/- 1%

The New D Inclusive Measurement First evidence of departure from the SM Statistics-limited, so may improve over the next year

A lot of theory interest , so, how will LHCb help?

... The situation is significantly more complicated ...

Complications

The simple formula

tmaatA

22/cosh

2222)(

10-3 -> 10 -5

fftAqfs

The simple formula

Polluting asymmetries are much larger than afs

Detector asymmetry dc ~(10-2)

Production asymmetry dp ~(10-2)

Background asymmetry db ~(10-3)

tmaatA

22/cosh

2222)(

10 -2 10 -2 10 -310-3 -> 10 -5

Very Complicated

fftAqfs

Detector Asymmetry, dc

Matter detector hadronic interactions are asymmetric

Magnet divides +/- charge, allowing +/- detector asymmetry We need to reverse the magnet regularly

MC Asymmetry in Muons

Left Right

+ve -ve

After 4Tm Magnet

Kaon PDG cross-section

0.1 1 10 100 1000

momentum in lab frame Plab / GeV c

mb. K-, p

Kaon interaction cross-section

K- pK+ p

An amazing machine

Unfortunately also not CP symmetric

Production Asymmetry, dp

LHC is a proton-proton collider: not CP-symmetric

LHCb is at high rapidity where production asymm. are largest

There is never a simple control channel to measure dp

-0.020

-0.015

-0.010

-0.005

0 50 100 150 200 250 300 350

Energy, E / GeVP

dp (B0 and B0)

Valence QuarkScattering

PYTHIA

Explicitly asymmetric at LHC

Why LHCb?

LHCb is a dedicated, precision, b-physics experiment

More statistics: we’re in the forward region, and at LHC

Being Timely

Proper Time: LHCb Velo precise down to 35 fs!

Being Precise

Particle ID: separation handled by dedicated subdetectors

Two RICHes, Calorimetry and Muon system

RICH 1(Vertical)

RICH 2(Horizontal)

Being Exclusive

Our forte: exclusive, reconstructed, b-decays

In particular, time-dependent measurements

Monte-Carlo!

~100k Ds in 5 fb-1 ~100k Ds in 0.05 fb-1

Measurements

Inclusive

Exclusive

Subtraction method

combine and

... bb

00 XDB ss

00 XDBd

ss DB0

00 XDB ss 00 XDBd

Inclusive at LHCb

Channel

Measured by D (see earlier)

Complications Physics! Production asymmetry: N(b)≠N(anti-b) [in acceptance] PYTHIA predicts dp(b) =

Mitigating factors None, difficult to interpret this measurement

... bb

sfsb aa

3103.04.3

45.06.0 103.2

~108 per fb-1

Inclusive at LHCb

Channel

Measured by D (see earlier)

Complications Physics! Production asymmetry: N(b)≠N(anti-b) [in acceptance] PYTHIA predicts dp(b) =

Mitigating factors None, difficult to interpret this measurement

... bb

3103.04.3

45.06.0 103.2

~108 per fb-1

sfsb aa

Hadronic at LHCb

Channel

KKDB ss0 ~105 per fb-1

CERN-THESIS-2008-045

CERN-LHCb-2007-017

Monte-Carlo!

Hadronic at LHCb

Channel

Measures

Complications Must fix either dc or dp in the fit – (db can be fit beforehand)

Mitigating factors Detector asymmetry small ~10-4 Fit afs and dp. – With excellent proper time resolution (35 fs)

tmaatA

22/cosh

2222)(

KKDB ss0

CERN-LHCb-2007-054

~105 per fb-1

Hadronic at LHCb

Channel

Measures

Complications Must fix either dc or dp in the fit – (db can be fit beforehand)

Mitigating factors Detector asymmetry small ~10-4 Fit afs and dp. – With excellent proper time resolution (35 fs)

tmaatA

22/cosh

2222)(

KKDB ss0

CERN-LHCb-2007-054

~105 per fb-1

Semi-leptonic

Channel (q = s/d)

00 XDB qq ~106 per fb-1

CERN-LHCb-2007-054

Monte-Carlo!

00 XDB ss

00 XDBd

Monte-Carlo!

Semi-leptonic

Channel (q = s/d)

Measures

Complications Missing neutrino makes proper-time resolution worse (≥120 fs?) Detector asymmetry large and difficult to measure

Mitigating factors Lots of statistics, but this makes dc even more important

00 XDB qq

tmaatA

22/cosh

2222)(

CERN-LHCb-2007-054

~106 per fb-1

Semi-leptonic

Channel (q = s/d)

Measures

Complications Missing neutrino makes proper-time resolution worse (≥120 fs?) Detector asymmetry large and difficult to measure

Mitigating factors Lots of statistics, but this makes dc even more important

00 XDB qq

tmaatA

22/cosh

2222)(

CERN-LHCb-2007-054

~106 per fb-1

The subtraction method

Take Bs/Bd with the same final states ( =KK p m) Background asymmetry: 2D fit in mass spectra Production asymmetry: fit with proper-time dependence Detector asymmetry: the same in each decay…

Do a simultaneous time-dependent fit

Measure the difference between Bs and Bd

Very comparible to the D measurement, but orthogonal to it!

)()(,dfs

45.06.0 105.2

Take Bs/Bd with the same final states ( =KK p m) Background asymmetry: 2D fit in mass spectra Production asymmetry: fit with proper-time dependence Detector asymmetry: the same in each decay…

Do a simultaneous time-dependent fit

Very comparible to the D measurement, but orthogonal to it!

)()(,dfs

45.06.0 105.2

Real data highlights

R Lambert, CERN 42CERN CPV, 18th June 2010

+,K+,K-

EVT: 49700980RUN: 70684

LHCb Preliminary

Real Data Bs

~800 mb-1

R Lambert, CERN 43CERN CPV, 18th June 2010

K-,K+,+

EVT: 141526660RUN: 70666

LHCb Preliminary

Real Data Bd

~800 mb-1

All D(s)->KKp

n.b. Selection with no requirement for a muon (need ~40 nb-1)

~2.6 nb-1

Sensitivities and Outlook

Sensitivity estimates

Full MC used to tune toy MC

Massive toy MC studies done in: CERN-LHCb-2007-054 CERN-THESIS-2008-045 CERN-THESIS-2009-001

Scaled to: Latest Monte Carlo efficiencies s(bb) = 500 mb

Stat. Error (500 mb)

100 pb-1 1fb-1

afss (Ds p) 2.1 x10-2 6.8 x10-3

DAfs (Dq mn) 2.0 x10-3 6.3 x10-4

All MC predictions!!Real data will be worse

Current Results

After 1fb-1 of LHCb

AssumeAb central valueand no NP in Bd

c.f. J/Y F

hep-ph 0612167

Directly Measure sin fs

s(fs) = 0.05c in 1 fb-1

Effectively Measures

s() = 0.5c in 1 fb-1

But they constrain NP differently Effective power enhanced NB physical limit of afs is at 4x10-3 < current D result!

/0 JBs

sinRecosIm12

MMCurrent measurements (pre D0 paper)

Red : Dms

Yellow: DGs

Black: fs

Blue: afs

Combining D

D and CDF

-2bs=fs

FPCP 2010

D and CDF

(add my own personal merging)

FPCP 2010

Conclusion

D have made an astounding new measurement (3.2 s!)

At LHCb the environment is more hostile, concentrate on:

Low detector asymmetry, great proper time resolution

Detector and production asymmetries fitted with the data

ss DB0

Stat. Error (500 mb)

100 pb-1 1fb-1

afss (Ds p) 2.1 x10-2 6.8 x10-3

DAfs (Dq mn) 2.0 x10-3 6.3 x10-4

sfsa from

dsfsA, from 00 XDB qq

All MC predictions!!Real data will be worse

-310 (syst)]46.12.51(stat) 57.9[ bA

Backups are often required

Cereal loops

Now in bitesize-chunks!

Act now and getyour first 105 decays free!

New Physics inspecial boxes!

Afs DG and Dms in every box!

Two excitingflavours!

Nomenclature

A decay to a given state which cannot be reached by the anti-flavour state (at tree level) = flavour-specific

CP-violating asymmetry in mixing, manifests directly in flavour-specific decays = Afs/afs flavour-specific asymmetry

Since this is most readily observed in semi-leptonic decays it is also referred to as Asl

a final state of given flavour. its charge conjugate.

After 1fb-1 of LHCb

LHCb measurement cuts at right-angles really depends what the value is, and if there is NP!

current favoured value Ab central value and no NP in Bd

Magnet divides +/- charge, allowing +/- asymmetry

by reversing magnet in D0: dc reduced from 3% -> ~0.1%

Asymmetry from Long Muon Tracks Reconstructed in MC

Left Right

-ve +ve

Left Right

+ve -ve

Before 4Tm Magnet After 4Tm Magnet

Matter detector hadronic interactions are asymmetric

Dominant systematic at order 1%

Kaon PDG cross-section

0.1 1 10 100 1000

momentum in lab frame Plab / GeV c

mb. K-, p

Kaon interaction cross-section

K- pK+ p

Resultant charge asymmetry (MC)

Systematics (1)

1. Detector asymmetry • Expect second order, so < 10-4

• Know the magnitude in real data from the pi momentum spectra• Detect any bias by binning in momentum• Correct with MC: Assuming the magnet is reversed!!

2. Production asymmetry• Separate using the time-dependence• Detect large bias from this by binning in eta• Measure production asymmetry, possible but very coarse

3. Background asymmetry • Fit simultaneously, simply, in the B-mass spectrum

ss DB0

Systematics (2)

1. Detector asymmetry only second order, so < 10-4

• Know the magnitude in real data from the daughter momenta• Detect any bias by binning in momentum• Correct with MC: Assuming the magnet is reversed!!

2. Production asymmetry• Separate using the time-dependence • Detect large bias from this by binning in eta• Measure in can help quantify any bias

3. Background asymmetry • Suppressed by the effective B/S < 0.1, in the signal region• Fit simultaneously, 2D fit, in the B-mass and D-mass spectra• Cancel detector-related part also, only production remains• Detect bias by binning in eta

00 XDB qq

ss DB0

Take Bs/Bd with the same final states ( =KK p m)

All production asymmetry is in x2/x3, just throw it away

dsdsfs

6.0 105.2 SM

Subtraction method

Channel (q = s/d)

Measures

Complications Requires weak constraints on DG and Dm

Mitigating factors Production asymmetry fit simultaneously Detector asymmetry cancelled

00 XDB qq

6.0 105.2 SM

KKDqCERN-LHCb-2007-054

Production Asymmetry

Tuned Pythia samples

*=standard decays, †=Stable Bd+Bs

Asymmetries agree with generic bb events

dp x1000 Min Bias (10M)* bb – inclusive (10M)* (20M) †

Pions -(4.23±0.16) -(2.16±0.09) -(2.27±0.07)

Kaons -(17.0±0.5) -(7.73±0.26) -(8.2±0.2)

Muons -- +(2.0±1.2) +(1.0±0.9)

Ds -- -(1.6±1.1) -(1.6±1.1)

Bs -- -(1.9±1.3) -(1.5±0.8)

Bd -- -(3.2±0.7) -(3.2±0.4)

00ds BB

R Lambert, CERNCERN CPV, 18th June 20101 Flavour-specific asymmetry and LHCb Robert W. Lambert On...

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