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Performance Studies for Performance Studies for thethe LHCb LHCb ExperimentExperiment

Marcel Merk

NIKHEF

Representing the LHCb collaboration

19 th International Workshopon Weak Interactions and NeutrinosOct 6-11, Geneva, Wisconsin, USA

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Direct Measurement of angles: (sin(2)) ≈ 0.03 from J/ Ks in B

factories Other angles not precisely known

Knowledge of the sides of unitary triangle:

(Dominated by theoretical uncertainties) (|Vcb|) ≈ few % error

(|Vub|) ≈ 5-10 % error

(|Vtd|/|Vts|) ≈ 5-10% error

(assuming ms < 40 ps-1)

In case new physics is present in mixing, independent measurement of can reveal it…

B Physics in 2007B Physics in 2007

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Large bottom production cross section:

1012 bb/year at 2x1032 cm-2s-1

Triggering is an issue All b hadrons are produced:

Bu (40%), Bd(40%), Bs(10%), Bc and b-baryons (10%) Many tracks available for primary vertex Many particles not associated to b hadrons b hadrons are not coherent: mixing dilutes tagging

B Physics @ LHCB Physics @ LHC

√s 14 TeV

L (cm-2 s-2) 2x1032 cm-2 s-1

bb 500 b

inel / bb 160

bb production:(forward)

LHCb: Forward Spectrometer with:• Efficient trigger and selection of many B decay final states• Good tracking and Particle ID performance • Excellent momentum and vertex resolution• Adequate flavour tagging

Bs KK

,K

Ds

B Decay eg.: Bs->Dsh

bb

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Simulation and ReconstructionSimulation and ReconstructionAll trigger, reconstruction and selection studies are based on fullPythia+GEANT simulations including LHC “pile-up” events andfull pattern recognition (tracking, RICH, etc…)

Sensitivity studies are based on fast simulations using efficiencies and resolutions and from the full simulation

No true MC infoused anywhere !

VELORICH1

TT

T1T2

T3

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Evolution since Technical ProposalEvolution since Technical Proposal

• ReducedReduced materialmaterial

• ImprovedImproved level-1 triggerlevel-1 trigger

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Track finding strategyTrack finding strategy

VELO seeds

Long track (forward)

Long track (matched)

T seeds

Upstream track

Downstream track

T track

VELO track

T tracks useful for RICH2 pattern recognition

Long tracks highest quality for physics (good IP & p resolution)Downstream tracks needed for efficient KS finding (good p resolution)Upstream tracks lower p, worse p resolution, but useful for RICH1 pattern recognition

VELO tracks useful for primary vertex reconstruction (good IP resolution)

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ResultResult of track findingof track findingTypical event display:

Red = measurements (hits)

Blue = all reconstructed tracks

Efficiency vs p : Ghost rate vs pT :

Eff = 94% (p > 10 GeV)

Ghost rate = 3%(for pT > 0.5 GeV)

VELO

TT

T1 T2T3On average:

26 long tracks11 upstream tracks4 downstream tracks5 T tracks26 VELO tracks

2050 hits assigned to a long track: 98.7% correctly assigned

Ghosts:Ghosts:Negligible effect onNegligible effect onb decay reconstructionb decay reconstruction

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Experimental ResolutionExperimental Resolution

p/p = 0.35% – 0.55%

p spectrum B tracks

IP= 14 + 35 /pT

1/pT spectrum B tracks

Momentum resolution Impact parameter resolution parameter resolution

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Particle IDParticle ID

B->hh decays:

RICH 1 RICH 2

(K->K) = 88%

(p->K) = 3%

Example:

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TriggerTrigger40 MHz

pil

e-u

p

1 MHz

40 kHz

200 Hz output

Level-1:Impact parameterRough pT ~ 20%

HLT:Final state

reconstruction

CalorimeterMuon system

Pile-up system

Vertex LocatorTrigger TrackerLevel 0 objects

Full detectorinformation

L0L0

Level-0:Level-0:ppTT of of

, e, h, , e, h,

ln pT ln pT

ln

IP/

IP

ln

IP/

IP

L1L1

Signal

Min.Bias

B-> Bs->DsK

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Flavour tagFlavour tag

l

B0

B0D

K-

bb

s

u

s

u

Bs0

K+

tagging strategy: opposite side lepton tag ( b → l ) opposite side kaon tag ( b → c → s ) (RICH, hadron trigger) same side kaon tag (for Bs) opposite B vertex charge tagging

43542

eff [%]Wtag [%] tag [%]

63350

Bd

Bs K K

Combining tagseffective efficiency:

eff = tag (1-2wtag )2

sources for wrong tags:

Bd-Bd mixing (opposite side)b → c → l (lepton tag) conversions…

Knowledge of flavour at birth is essential for the majority of CP measurements

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Efficiencies, event yields and BEfficiencies, event yields and Bbbbb/S ratios/S ratios

Nominal year = 1012 bb pairs produced (107 s at L=21032 cm2s1 with bb=500 b)Yields include factor 2 from CP-conjugated decaysBranching ratios from PDG or SM predictions

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CP Sensitivity studiesCP Sensitivity studiesCP asymmetries due to interference of Tree, Mixing, Penguin, New Physics amplitudes:

1. Time dependent asymmetries in Bs->DsK decays. Interference between b->u and b->c tree diagrams due to Bs mixing

Sensitive to + s (Aleksan et al)

2. Time dependent asymmetries in B-> and Bs->KK decays. Interference between b->u tree and b->d(s) penguin diagrams

Sensitive to , d, s (Fleischer)

3. Time Integrated asymmetries in B-> DK* decays. Interference between b->u and b->c tree diagrams due to D-D mixing Sensitive to (Gronau-Wyler-

Dunietz)

Time dependent asymmetry in Bd->J/ Ks decays

Sensitive to d

Time dependent asymmetry in Bs->J/ decays

Sensitive to s

Mixing phases:

Measurements of Angle

treemix pen

new+ + +

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BBss oscillation frequency: oscillation frequency: mmss Needed for the

observation of CP asymmetries with Bs decays

Use Bs Ds

If ms= 20 ps1

Can observe >5 oscillation signal if

well beyond SM prediction

(ms) = 0.011 ps1

ms < 68 ps1

Proper-time resolutionplays a crucial role

Full MC

Expected unmixed Bs Ds

sample in one year of data taking.

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Mixing PhasesMixing Phases Bd mixing phase

using B->J/ Ks

Bs mixing phase

using Bs->J/

s/s) = 0.018

Background-subtracted BJ/()KS CP asymmetry after one year

If ms= 20 ps1:

(sin(s)) = 0.058NB: In the SM, s = 2 ~ 0.04

(sin(d)) = 0.022

Angular analysis to separate Angular analysis to separate CP even and CP oddCP even and CP odd

Time resolution is important:Time resolution is important:

Proper time resolution (ps)Proper time resolution (ps)

= 38 fs= 38 fs

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1. Angle 1. Angle from B from BssDDssKK

(after 5 years of data)

() = 1415 deg

After one year, if ms= 20 ps1, s/s = 0.1, 55 < < 105 deg,

20 < T1/T2 < 20 deg:

No theoretical uncertainty;insensitive to new physics in B mixing

Simultaneous fit of Simultaneous fit of BBss->D->Dss and and BBss->D->DssKK:: Determination of mistag fractionDetermination of mistag fraction Time dependence of backgroundTime dependence of background

Time dependent asymmetries:Time dependent asymmetries:

BBss(B(Bss)) ->D->Dss--KK++: : →→ T1/T2T1/T2 + ( + (++ss))

BBss(B(Bss)) ->D->Dss++KK--: : →→ T1/T2T1/T2 – ( – (++ss)) AADs-K+Ds-K+

AADs+K-Ds+K-

(2 Tree diagrams due to Bs mixing)(2 Tree diagrams due to Bs mixing)

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Measure time-dependent CP asymmetries in B and BsKK decays:

ACP(t)=Adir cos(m t) + Amix sin(m t)

Method proposed by R. Fleischer:SM predictions:

Adir (B0 ) = f1(d, , ) Amix(B0 ) = f2(d, , , d)

Adir (BsKK ) = f3(d’, ’, ) Amix(BsKK ) = f4(d’, ’, , s)Assuming U-spin flavour symmetry

(interchange of d and s quarks): d = d’ and = ’4 measurements (CP asymmetries) and

3 unknown (, d and ) can solve for

2. Angle 2. Angle from B from B and B and BssKKKK

d exp(i) = function of tree and penguin amplitudes in B0

d’ exp(i’) = function of tree and penguin amplitudes in Bs KK

(b->u processes, with large b->d(s) penguin contributions)(b->u processes, with large b->d(s) penguin contributions)

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2. Angle 2. Angle from B from B and B and BssKKKK (cont.) (cont.) Extract mistags from BK and BsK

Use expected LHCb precision on d and s

pdf for

pdf for d

blue bands from BsKK (95%CL)red bands from B (95%CL)ellipses are 68% and 95% CL regions(for input = 65 deg)

“fake” solution

d vs

() = 46 deg

If ms= 20 ps1, s/s=0.1, d =0.3, = 160 deg, 55 < < 105 deg:

U-spin symmetry assumed;sensitive to new physics in penguins

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Application of Gronau-Wyler method to DK* (Dunietz):

Measure six rates (following three + CP-conjugates):1) B D(K)K*, 2) B DCP(KK)K* , 3) B D (K) K*

No proper time measurement or tagging requiredRates = 3.4k, 0.6k, 0.5k respectively (CP-conj. included), with

B/S = 0.3, 1.4, 1.8, for =65 degrees and =0

3. Angle 3. Angle from B from B D DKK** and B and B D DKK**

A1 = A1

√2 A2√2 A2

A3

A3

2

55 < < 105 deg20 < < 20 deg

() = 78 deg

No theoretical uncertainty;sensitive to new physics in D mixing

(Interference between 2 tree diagrams due to D0 mixing)(Interference between 2 tree diagrams due to D0 mixing)

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Measurement of angle Measurement of angle : New Physics?: New Physics?

1. Bs->DsK 2. B->, Bs->KK 3. B->DK*

not affected by new not affected by new physics in loop diagramsphysics in loop diagrams

affected by possibleaffected by possible new physics in penguinnew physics in penguin

affected by possible affected by possible new physics innew physics inD-D mixingD-D mixing

Determine the CKM parameters A,,independent of new physics

Extract the contribution of new physics to the oscillations and penguins

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Possible sources of systematic uncertainty in CP measurement: Asymmetry in b-b production rate Charge dependent detector efficiencies…

can bias tagging efficiencies can fake CP asymmetries

CP asymmetries in background process

Experimental handles: Use of control samples:

Calibrate b-b production rate Determine tagging dilution from the data:

e.g. Bs->Ds for Bs->DsK, B->K for B->, B->J/K* for B->J/Ks, etc Reversible B field in alternate runs Charge dependent efficiencies cancel in most B/B asymmetries Study CP asymmetry of backgrounds in B mass “sidebands” Perform simultaneous fits for specific background signals:

e.g. Bs->DsinBs->DsK , Bs->K & Bs->KK, …

Systematic EffectsSystematic Effects

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ConclusionsConclusions LHC offers great potential for B physics from “day 1”

LHC luminosity

LHCb experiment has been reoptimized: Less material in tracking volume Improved Level1 trigger

Realistic trigger simulation and full pattern recognition in place

Promising potential for studying new physics