fpcp04, daegu, 9 oct 2004p j dornan - imperial college london1 b-physics at the lhc p j dornan...

FPCP04, Daegu, 9 Oct 2004

P J Dornan - Imperial College London

1

B-Physics at the LHCB-Physics at the LHC

P J DornanP J Dornan

Imperial College, LondonImperial College, London



2

Why b-physics at the Why b-physics at the LHCLHC

Millions of b’sMillions of b’sWith full luminosity, 1034, gives 5.1013 bb pairs per year- But events much too difficult to analyse, ~25 interactions

per crossing- So - need to run at lower luminosities for most b-physics

- In the early period max luminosity expected ~ 1033 - ATLAS/CMS

- but will eventually be able to exploit full luminosity for certain rare decays

- LHCb currently plan to run at 2.1032 by detuning the beam

Signal/Background improves with increasing Signal/Background improves with increasing energyenergy

inel = 80 mb, bb = 500 b

All b-species produced, BAll b-species produced, B++, B, B00, B, Bss, B, Bcc, b-baryons, b-baryonsAt these energies b’s are getting ‘light’ At these energies b’s are getting ‘light’

Thus bb pairs produced dominantly forward - backward

-

-



3

General PurposeGeneral PurposeATLAS, CMS – 4 ‘standard’ colliding beam detectors

Main aim to search for new states - Higgs and those from BSM so will always aim to run at maximum luminosity, 1033 -> 1034

SpecialisedSpecialisedLHCb – forward spectrometer (10 – 300 mrads), designed specifically for b-physics. Will always run at low luminosity, nominally 2.1032

General Purpose and LHCb operate in complementary kinematic regions

The ExperimentsThe Experiments

b b

b

No



4

Experimental Experimental RequirementsRequirements

An excellent vertex detectorAn excellent vertex detectorB-states identified by displaced secondary vertices

Good K-Good K- separation separationDifficult for general purpose detector - a weakness of ATLAS/CMSAn essential feature of LHCb

A good trigger for A good trigger for interestinginteresting b-physics b-physicsFar too many b’s produced to trigger on all of them. Therefore trigger

must reject many b-states and concentrate on those from which CP/CKM physics will result

This is probably the greatest challenge for a hadronic b-This is probably the greatest challenge for a hadronic b-experimentexperiment

-- and has caused failures in the past-- and has caused failures in the past



5

ATLASATLAS



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ATLAS TrackerATLAS Tracker

Tracker

Pixel Detector

Pixel Detector designed for b-physics

Radius of inner layer = 5 cm.

3 layers, but middle will not be available at start-up



7

ATLAS Pit TodayATLAS Pit Today



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CMSCMS



9

CMS TrackerCMS Tracker

CMS Silicon Tracker

Pixel DetectorAll Silicon2 Pixel Layers Radii 4 and 7 cm Low luminosityRadii 7 and 11 cm high luminosity



10

CMS TodayCMS Today

Tracker being assembled

In the pit



11

LHCbLHCb



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LHCB – VELOLHCB – VELO



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LHCb - VELOLHCb - VELO

Proper time resolution ~ 40 fs



14

LHCb - RICH1LHCb - RICH1

RICH1 detector

Vertex locator



15

LHCb – RICH1&2LHCb – RICH1&2



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LHCb RICH performanceLHCb RICH performance

MomentumMomentum



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TriggersTriggers

LHCb much better for hadronic B-decays

All comparable for B -> J/decays

ATLAS/CMS better for Rare Decays ->(X)

Vital - Still Evolving - Algorithms depend upon important Vital - Still Evolving - Algorithms depend upon important physics channelsphysics channels

Basic philosophyBasic philosophy



18

What physics channels?What physics channels?

Must be interesting and extractable at the trigger levelMust be interesting and extractable at the trigger level

* * * 0ud ub cd cb td tbV V V V V V * * * 0td ud ts us tb ubV V V V V V

Unitarity Triangles

Bd0

Bd0

BS0 DS

Bd0 J/ KS

0

Bd0 DK*0

BS0 DSK

Bd0 BS

0 K+K-

Bd0 D*

BS0 J/

Rare DecaysBs(d) X, b s



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Flavour TaggingFlavour Tagging

In many cases need to In many cases need to know the flavour of know the flavour of the B when producedthe B when produced

Use Decays of the other B state - Opposite Side tagLepton b -> e,

Kaon b -> c -> s

Or from the accompanying /K with the signal B – Same Side tag

Or use vertex charge

l

B0

B0

D

K-

b

b

d

u

d

u

B0

+Prelim. LHCb with Opposite side only

Obtain eD2 = 6.4%



20

BBss Oscillation - Oscillation - mmss

With With mmdd yields V yields Vtdtd

Oscillation is fast (>14.4 psOscillation is fast (>14.4 ps-1-1))Need excellent momentum and position resolution, i.e. a fully resconstructable final state and excellent vertex resolution

Use BUse Bss-> D-> Dss(LHCb) Obtain ~80,000 fully reconstructed/year, S/B ~3. Proper time resolution ~40fs

Expected unmixed Bs Ds sample

in one year of data taking (fast MC)

Expect to make a 5 measurement in 1 year to 68 ps-1



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sin2sin2 - B - B00 -> J/ -> J/ K Kss

Classic channel for CP violation studyClassic channel for CP violation studyStill important for LHC experiments to measure with the best possible precision.

Measure time dependent asymmetryMeasure time dependent asymmetry

AAmixmix yields yields sin2sin2AAdirdir direct CP violation - BSM direct CP violation - BSM

Assuming AAssuming Adirdir = 0 = 0

ATLAS quote ATLAS quote (sin2(sin2) = 0.013 after 3 years at 10) = 0.013 after 3 years at 103333

LHCb quote LHCb quote (sin2(sin2) = 0.022 after 1 year at 2.10) = 0.022 after 1 year at 2.103232

( ) cos( ) sin( )dir mixCP CP CP dA t A m t A m t

LHCb



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Sin2Sin2 - B - B00 -> -> ++==

Actually measure Actually measure ----

a very good channel for a very good channel for LHCbLHCb

High pT hadron to give trigger

RICH is essential

ButBut Penguins complicate Penguins complicate the analysisthe analysis

Can reach 5° < () < 10° in one year if P/T known to 10%



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Sin2Sin2 - B - B00 -> ->

Three final statesThree final states

Requires time dependent Dalitz plot analysis

But needs detailed understanding of the acceptance

An analysis is being developedAn analysis is being developed-- looks promising



24

LHCbLHCb

Will be a major result for LHCb - relies on the hadronic triggerWill be a major result for LHCb - relies on the hadronic trigger

Many waysMany waysBut none are simple - involve measuring low decay rates, time dependent analyses in the Bs system, theoretical uncertainties

Many approaches necessary to check consistency

4 time dep rates yields

Relate with U-spin yields

4 time dep rates yields 2

6 decay rates yields 0*0

10

0*000*00

*0

00

,,.4

.3

,.2

,.1

KDB

KDBKDB

DB

KKBB

KDBKDB

CP

s

ssss



25

Features of LHCb for Features of LHCb for DeterminationDetermination

Vertex Resolution - Time Vertex Resolution - Time Dependent BDependent Bs s AsymmetriesAsymmetries

Separation BSeparation Bss-> D-> Dss/B/Bss --> D> DssK - RICH particle ID and K - RICH particle ID and mass cutsmass cuts

BsDsKBsDs

BsDsK

BsDs

( )~ 12

( )s s

s s

Br B D

Br B D K



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Bd D0 K*0 signal RICH minimises background

Bs KKSeparationWith RICH



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LHCb Expected performance LHCb Expected performance for for

2400 events per year3° < ) < 16°

5000 events per channel per year3° < ) < 16°

~500,000 events per year. ) ~ 10

Some BR’s very small, 10-7 -> 10-8

) ~ 10 ° per year0*01

0

0*000*00

*0

00

,,.4

.3

,.2

,.1

KDB

KDBKDB

DB

KKBB

KDBKDB

CP

s

ssss



28

BBss Mixing phase Mixing phase ss= -2= -2

Use BUse Bs s -> J/-> J/

BBss analogue of golden analogue of golden channel, Bchannel, B00 -> J/ -> J/KKss

Asymmetry very small in SM, s ~ -0.04so very sensitive to new physics

But two vectors in final state But two vectors in final state therefore need a time therefore need a time

dependent angular analysisdependent angular analysisSensitivity depends on ms

For ms = 20, Expect ) ~ 2° per year

Analysis also yields s

and s



29

BBs,ds,d -> -> XX

Atlas/CMS can here use the high luminosity, so can Atlas/CMS can here use the high luminosity, so can do better than LHCbdo better than LHCb

Full TrackerFull Tracker

= 46 = 46 MeVMeV

CMS – Mass resolutionNeed 30 fb-1 for a 5 observation

BBss -> -> BBss -> -> XX

14041110-6Bd0

29019951.5x10-6Bd0K*

95022210-7Bd0

BGsignalBRchannel

ATLAS statistics with 30 fb-1

F-B Asymmetry sensitive to some SUSY scenarios



30

BBcc

Production less peaked forwardProduction less peaked forwardBetter for ATLAS/CMS

For Bc -> J/

p (GeV)

ATLAS, (M(Bc) = 74 MeV Expect between 5 – 10K Bc -> J/ for each of ATLAS, CMS & LHCb per year

Also BAlso Bcc -> J/ -> J/ gives V gives Vbcbc



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An Event in LHCbAn Event in LHCb



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The major problem - The major problem - TriggeringTriggering

B-rates at the LHC are very highB-rates at the LHC are very highThe final states of interest are a very small proportion

For highest efficiency, the High Level Triggers (HLT)) must For highest efficiency, the High Level Triggers (HLT)) must focus very directly on the focus very directly on the predictedpredicted properties of the properties of the final states of interest and aim to distinguish them from final states of interest and aim to distinguish them from the the predictedpredicted backgrounds using the backgrounds using the predictedpredicted properties of the detectorproperties of the detector

Predictions in the forward area depend upon knowledge of the pdf’s at very low x where they are least reliable

The simulation will not be perfect!

The performance of the trigger is key to the The performance of the trigger is key to the success of the experimentsuccess of the experiment

Planned on the simulationToo loose -> low efficiencyToo tight -> potential bias



33

Triggering LHCbTriggering LHCb

Dimuon TriggersDimuon TriggersMuch physics, J/ X decays, rare decaysStrong signature, low rates

Safe for LHCb and ATLAS & CMS, Safe for LHCb and ATLAS & CMS,

Triggers for hadronic final statesTriggers for hadronic final statesMuch of the physics is here - quite probably any new

physics will at the few % level - probing this is the justification for LHCb

But rates are low - or very low

NeedNeedStatistical precision -> highly efficient triggerSystematic precision -> minimal biases and these must be

accurately quantified

Highly demanding for the triggerHighly demanding for the trigger



34

The ProblemThe Problem

Crossing rate at LHC = 40 MHz

Running at 2.1032 and a 25 nsec bunch spacing expect crossings with interactions at 10 MHz

- of which 200kHz will have bb pairs!

But those useful for CP/CKM physics and having all decay products in the detector is very much less

e.g. For B0 J/()Ks(-) it is 0.02 Hz – or 1 per minute.

For Bs0 it is ~1 per week



35

Current LHCb PlanCurrent LHCb Plan

3 Level Trigger3 Level Trigger

Level 0 - reduce rate from 10 Level 0 - reduce rate from 10 Mhz to 1 MhzMhz to 1 Mhz

Pile-up veto, a high pt hadron, electron, muon, photonIncreases b purity from 1% to 3%

Level 1 – reduce rate from 1 Level 1 – reduce rate from 1 Mhz to 40 kHzMhz to 40 kHz

Demand tracks with finite impact parameter and high pt

Divide bandwidth between generic and specific, cuts for special channels, electron, photon, dimuonb-purity now at 9%

High Level trigger – reduce rate High Level trigger – reduce rate from 40 kHz to 200 Hz to tapefrom 40 kHz to 200 Hz to tape

Fast reconstruction, using all detectors except RICH – so far

Bandwidth Division at Level1

To maintain efficiency at this rate, HLT must use tight ‘offline’ type cuts.Efficiency for channels not used to define HLT can be low



36

Possible ImprovementPossible Improvement

Keep present philosophy but add a new inclusive stream Keep present philosophy but add a new inclusive stream with simple cuts and a high output ratewith simple cuts and a high output rate

To be based on detection of just a single muon with minimal pt and impact parameter cuts - small modification of level 1 bandwidth

This would beThis would beInclusive - trigger on the ‘other’ bYields tagged eventsRobustUse to reduce/estimate systematic uncertaintiesAccess to states not chosen for HLT optimisation Ks ….Output rate- whatever can be handled - would be 2 – 5 kHz with ~50% events with bb

Under active investigationUnder active investigation - Current 200 Hz stream would - Current 200 Hz stream would be preserved - now Hot Streambe preserved - now Hot StreamInclusive stream to be reconstructed at many sitesInclusive stream to be reconstructed at many sites

Possible futureLevel 1 bandwidth



37

The LHCThe LHC

StatusStatusDelays due to problems with the cryolines

Poor quality control by the company charged with installation of work by its sub-contractorsFirst collisions are still scheduled for ‘summer’ 2007Great pressure to maintain this date

ComponentsComponentsAlmost all ontimeCryodipoles, which were a problem now stacking up on the surface waiting for the repair of the cryolines



38

SummarySummary

The LHC has great potential to make major advances The LHC has great potential to make major advances in precision CPV b-physicsin precision CPV b-physics

All species of b-hadron state are producedAll species of b-hadron state are producedThousands of events for many important channels Thousands of events for many important channels

with small branching ratios make measurements with small branching ratios make measurements at the few % level possible. at the few % level possible.

ButButThe hadronic environment will be difficultThe hadronic environment will be difficult

still a lot of background - mostly from still a lot of background - mostly from uninteresting b-statesuninteresting b-states

Efficient, well understood triggering will be all Efficient, well understood triggering will be all importantimportant

fpcp04, daegu, 9 oct 2004p j dornan - imperial college london1 b-physics at the lhc p j dornan...

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