Physics Performance of LHC-B

Neville Harnew

University of Oxford

Beauty-97, Los Angeles

October 13-17 1997

Outline• Introduction

• The LHC-B Experiment

New Developments :

The Trigger

The RICH

• Physics Performance

• Summary

• LHC will provide an intense source of B-hadrons : bbb

Unprecedented source of bb pairs.

• Probe consistency of the Standard Model :

CKM Physics

CP Violation

Bs-Bs mixing

Rare B decays, FCNC’s

• LHC-B specialised detector :

Measure xs, ’,

in SINGLE EXPERIMENT.

• Precision probe of new physics beyond SM.

MOTIVATION FOR B PHYSICS AT LHC-B

Measure angles Side VV**

tdtd ( ’ )

Unitarity Triangle Unitarity Triangle

V*ubVud+V*

cbVcd+V*tbVtd) = 0 V*

udVtd+V*usVts+V*

ubVtb) =0

(, i)(, i)) (1-, i)

0 Re 1 0 Re 1

’

Im Im

V*ub V*

td

Test of Standard Model

2 unitarity conditions of CKM matrix out of 6which give triangles which do not have a side much shorter than the other two :

112

11

2

11

23

22

32

AiA

A

iA

VVV

VVV

VVV

tbtstd

cbcscd

ubusud

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Production angle b vs b

Advantages

• bb production sharply peaked forward-backward

• Low luminosity is sufficient (1.5x1032 cm-2s-1) Less radiation >80% single interactions

• Threshold for pt trigger can be set low, 1.1-1.25 GeV/c

• Fast B hadrons < pB >Accepted ~ 80 GeV/c Mean flight path of B’s ~ 7 mm • Open geometry allows for easy installation and maintenance

• Vertex detector close to interaction region.

Disadvantages

• Minimum bias also peaks forward• High occupancy, high track density• Needs more sophisticated trigger than high pt

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Advantages of LHC-B

Rhobust and efficient 4 Level Trigger system

Level 0 : Muon pT > 1.25 GeV/c Electron pT > 1.4 GeV/c Dihadron pT > 3 and 2 GeV/c Level 1 : Vertex and track trigger Level 2 and 3 : Software triggers

Very good particle identification :

Muon system Electron (e-separation > 100) p/K// separation with two RICH detectors (3 /K separation between ~2 to 150 GeV/c)

Good decay time resolution

Decay distance resolution ~ 120 m

Decay time resolution ~ 0.04 ps

Bunch crossing rate 40 MHzBunch crossing with single interaction 9 MHzb-hadron production rate 75 kHz

inelastic = 80 mb , bb = 500 b

Nominal luminosity = 1.5 x1032 cm-2s-1

(Max luminosity = 5 x1032 cm-2s-1 )

• Interaction rate (single interaction) = 9 MHz

• Fraction of bunch crossings with no interaction = 0.68

• Fraction of bunch crossing with one interaction = 0.26

Choice of Luminosity

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Number of interactions vs. Luminosity

Probability of B interaction vs. Luminosity

BEvent

• Full GEANT simulation• dN/dAR2 particles/cm2 (<5% occupancy)

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LHC-B -VertexTitle:(si_detector_elements.eps)Creator:Adobe Illustrator(r) 6.0Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.

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Precision vertexing :

zprimarym

tBs mixing

ps

Level 1Trigger Device

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Vertex detector L1 trigger provides ~10 suppression withefficiency 75% for B- and 90% for BsDs -

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• Track-finding with 3 successive planes of r-strip detectors : reconstruct primary vertex by histogramming combinations with opposite ( sectors).• Calculate impact parameters (IP) wrt primary and cut on this quantity• Add -strip information for tracks with large IP• Construct 2-track vertices in space

LHC-B Level 1 Vertex Trigger

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LHC-B RICH /K Separation

3 /K separation between ~2 to 150 GeV/c

LHC-B RICH DETECTOR CHARACTERISTICS

RICH-1 :

• Combined Aerogel and gas (C4 F10)• Approx 125 HPDs, 250000 pads. C4 F10 : n=1.0014 ; <> ~ 55 Thresholds : 2.7 GeV/c, K 9.4 GeV/c Aeogel : n=1.03 ; <> ~ 15 Thresholds : 0.6 GeV/c, K 2.0 GeV/c

RICH-2 :

• Gas (CF4)• Approx 125 HPDs, 250000 pads. CF 4 : n=1.0005 ; <> ~ 30 Thresholds : 4.6 GeV/c, K 16.3 GeV/c

RICH 1,2 Detectors provide/K separation in LHC-B between 1 and 150 GeV/c

LHC-B will develop HPD in collaboration with industry

• 2000 Si pads per HPD, 2x2 mm pads• Amplifier/Shaper/L0-Pipeline inside the gas envelope• Large area coverage (11 cm diameter photocathode)• 80% photocathode active area (HPD)• 90% packing active area

PATTERN RECOGNITION IN RICH-1

• Aerogel: n=1.03, <>=15

• C4F10: n=1. 0014, <>=55

• B event

• Reconstruction efficiency and purity both better than 90% (for and K)

• Random hits - Rayleigh scattered ’s

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Scalein cm

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LHC-B Prototype RICH

• Aerogel and C4F10 Cerenkov rings for 10 GeV/c Pions : 1/4 scale prototype

• Aerogel : approx 1.4 mean no. of photons observed, 2.0 expected (N0 ~ 100 cm-1 prelim.)

• C4F10 : approx 7.9 mean no. of photons observed, 6 expected (N0 ~ 230 cm-1 prelim.)

• First Ring Imaging Counter using hybrid photo diodes

• SEE TALK BY N.BROOK

Scale in mm

PRELIM

LHC-B Event Rates (LoI)

L=1.5x1032, 1 year running (=107s)

Event Sample VisibleB.R.

DecayAccept.

EfficiencyLevel-1 Level-2

Eventson Tape

Measuredquantity

B0 +

2.0 x 10-5 17.8% 20.6% 33.1% 110k B0 J/ Ks

0 () 2.1 x 10-5 14.0% 73.5% 34.5% 340k

B0 J/ Ks0 (ee) 2.1 x 10-5 12.4% 44.6% 34.5% 183k

B0 D0K* (KK) 8.0 x 10-7 12.8% 15.4% 43.3% 3k

Bs0 Ds

K+ 1.1 x 10-5 12.6% 14.6% 47.5% 13k

Bs0 Ds

+K

5.3 x 10-6 12.6% 14.6% 47.5% 6k

Bs0 J/

() 4.2 x 10-5 14.2% 71.8% 42.0% 246k

Bs0 J/ (ee) 4.2 x 10-5 12.5% 44.0% 42.0% 133k

Bs0 Ds

+ 1.4 x 10-4 13.0% 14.7% 46.8% 171k xs

Bs0 Ds

++ 3.5 x 10-4 9.6% 12.0% 50.8% 277k xs

Bs0 + 4.0 x 10-9 19.2% 84.3% 33.5% 30 FCNC

B0 + K* 2.9 x 10-6 14.3% 70.0% 42.2% 17k FCNCB0 J/ K* () 6.3 x 10-5 13.7% 75.3% 42.8% 1270k controlB0 J/ K* (ee) 6.3 x 10-5 12.1% 45.5% 42.8% 679k control

recon 0.3, tag 0.4 not included • These are LoI values, tabulated values are conservative Expect improvement with new L1 trigger scheme

-

LHC-B PHYSICS PERFORMANCE

• xS measurement

• sin2

• sin 2

• Note : All sensitivities quoted are still LoI.New calculations in progress : Improvement expected.

B0

B

J/

, e

+, e+

+

K

D0

, e

Ks0

Lepton Tag

Kaon Tag

B Flavour Tagging

eg. B J/ Ks0

Signal B

Tag B

Bs-Bs Oscillations• Look at time evolution of BsDs

No CP violation expected

• Time evolution of Bs (Bs) given by : Rt) exp(-t/s) (cosh(s/2 t) 1-2cos(mst) )

• Fit ms , s , s ; xs= ms /s

• LHC-B in one year: 35k tagged BsDs

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LHC-B xs reach

Bs tag

Bs tag

Xs

Proper time distributions for reconstructed Ds- (ie. Bs decay)

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Interference via Bd0 Bd

0 mixing and decay

LHC-B Events on tape J/: 340k J/e+ e : 183k L=1.5x1032, 1 year =107s, BR x (e BR) =2.1x10-5

recon 0.3, tag 0.4

Reconstructed and tagged events=55k/year

Measure decay asymmetry : N(B0 J/s

0 )(t) - N(B0 J/s0 )(t)

N(B0 J/s0 )(t) + N(B0 J/s

0 )(t)

Nb(t) - rNb(t) = a sin(m t)

Nb(t)+ rNb(t) d

a : fitted parameter sin 2 a / (1-r=Bd/Bd tagged ratio (found from control sample)=wrong tag fraction=0.290 (0.00

And sin ) = 0.023 (statistics dominated)

Sin 2from BJ/s0

BJ/s0

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J/

s0

d

e+ e

LHC-B Events on tape : 110k L=1.5x1032, 1 year =107s, BR=2x10-5 NB

recon 0.3, tag 0.4

Reconstructed and tagged events=14k/year

Measure decay asymmetry :

Nb(t) - rNb(t) = a cos(m t) + b sin(m t)

Nb(t)+ rNb(t) d d

a, b fitted parameters (if no penguin, a=0)r=Bd/Bd tagged ratio (found from control sample)

Background : Predominantly BdK BsKBsK

Particle ID with RICH is vitally important

If a=0, then : sin 2 = b/(1-=wrong tag fraction=0.260 (0.00

And sin ) = 0.039 (statistics dominated)

Sin 2from B

4 channels : BsDs-K+ , BsDs

+K-

BsDs+K- , BsDs

-K+

Reconstructed and tagged events=3000/year

Measure decay time evolution for Bs , Bs Ds-K+

Nb,bt) exp(-t/s) (cosh(s/2 t) A sinh(s/2 t) a cos(mst) b sin(mst))

Measure decay time evolution for Bs , Bs Ds+K-

Coefficients a, b a’, b’ a, b, a’, b’ fitted parameters b, b’ give sin

Sin from BDsK

Background

to BsDsK is

BsDs

Mass resolution

m=8.5 MeV

and particle ID

(RICH) vital.

Measure 6 relative branching fractions

BdD K*, D K*, D CP K*

BdD K*, D K*, D CP K*

LHC-B sin 2) = 0.14 - 0.24

(dependent)

Small CP violation in BsJ/s/Bs time-dependent asymmetry. Reconstruct 44k events with a tag.LHC-Bsin 2) = 0.02 (xs=25)

Sin from BsJ/

Sin 2from BdDK*

Error on depends on xs … eg. 10o o, 80o o

LHC-B ) = 6o - 16o

(This measurement is unique to 2nd generation

hadron-machine dedicated CP experiments)

(600, 200, 50 events/year per channel)

LHC-B CP Reach Summary : One year’s running at 1.5 x 1032 cm-2s-1

CPParameter

Decay mode No. ofEvents

Uncertainty inone Year

Importantdetectorproperties

sin 2 Bd J/ Ks 55k (sin2)= 0.023

sin 2 Bd

14k (sin2)= 0.039 Particle ID

Bd D

0.9k () = 7 -12 Particle ID

' Bs Ds

3.3k () = 6 -16 Particle ID (Decay time)

sin Bs J/ 44k ( (Decay time)

xs Bs

Ds 35k < 55

(Decay time)

(sin2) assumes penguin contribution known, and BR(Bd x

• All measurements are statistics, not systematics, limited.• Table is based on LoI (Summer 1995). Expect improvement with new L1 trigger.

• LHC provides an opportunity to study CP (and other physics) in B-decay with very high statistics

• LHC-B: Optimized Forward Detector

- Flexible, efficient, robust triggers

- Particle ID

- Excellent decay-time precision

• CKM-PHYSICS: Angles and sides of Unitarity Triangle overconstrained through measurements of 'xs .

Different decay channels, triggers, tags allow redundancy and control of systematics

• “LOW” Luminosity:

- LHC-B can “choose”: LLHCB = 1.5 x 1032 cm-2 s-1

- No Pile-up

- Exploit initial (& subsequent) LHC running

• End 1995 : LoI approved

Feb 1998 : Technical Proposal submitted

2005 : Beam (Day 1 experiment)

LHC-B can run for MANY YEARS at optimal luminosity to study CP-violation

SUMMARY