B-physics reach of the LHCb Experiment B-physics reach of the LHCb Experiment RAL-Southampton...

B-physics reach of the LHCb B-physics reach of the LHCb ExperimentExperiment

B-physics reach of the LHCb B-physics reach of the LHCb ExperimentExperiment

RAL-Southampton SeminarRAL-Southampton Seminar26 April 2002.26 April 2002.

Paul SolerUniversity of Glasgow and

Rutherford Appleton Laboratory

RAL-Southampton Seminar, 26 April 2002

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Physics aims (I)Physics aims (I)

To test the consistency of the Standard Model interpretation of CP violations and to search for new physics.

LHCb is a 2nd generation experiment that will determine CP violations in a variety of decays of Bd and Bs mesons to test consistency of Unitarity Triangles.

It will follow on from Babar, BELLE that have already established CP violations for Bd mesons (in the decay Bd -> J/ K) and will constrain unitarity triangles to unprecedented accuracy.


3

Physics aims (II)Physics aims (II)_ Bd-Bd Mixing Phase _ Bs-Bs Mixing Phase

Weak Decay Phase

12

1

21

22

2

its

itd

iub

CKM

eVeV

A

eV

V

Standard Model:

0*** tbtdcbcdubud VVVVVV 0*** udtdustsubtb VVVVVV

CKM Matrix


4

Physics aims (III)Physics aims (III)

0 1

1

0

B

0

0

0

3,

d

d

d

B

DB

B

00 / sd KJB

ss DB 0

KDB

DKB

ss

d

0

0*0

,,,,0 KKKBs

Possible unitarity triangle measurements in LHCb


5

Physics aims (IV)Physics aims (IV)

Possible situation in 2005

Babar, BELLE have established CP violations for B mesons with Bd -> J/ K:

– sin 2= 0.75+-0.09+-0.04 (Babar, 56 fb -1)

– sin 2 = 0.82+-0.12+-0.05 (BELLE, 42 fb-1) Consistent with Kobayashi-Maskawa mechanism Standard Model fit (0.5< sin 2<0.8)


6

Physics aims (V)Physics aims (V)

Aims for LHCb in 2008 (after 1 year data taking)


7

Physics aims (V)Physics aims (V)

… or maybe not consistent with SM fits


8

B-meson Production (I)B-meson Production (I)

LHC is the most intense source of B mesons (Bd, Bu, Bs, Bc) with bb = 500 mb

Modest LHC luminosity

<L>LHCb = 2 x1032 cm-2 s-1

1012 bb / 107 s

C h a n n e l T r i g g e r E f f i c i e n c y E v e n t y i e l d S e n s i t i v i t y m o d e s

0dB 3 0 % 6 . 9 k 2 1 0

3 ,DB 0d

3 3 % 7 2 5 k 8

0dB 2 0 % 1 . 3 k

m o d e s0s

0d KJB 3 6 % 4 5 . 6 k

m o d e s

KDB s0s 2 8 % 2 . 4 k

0*00d KDB 2 1 % 0 . 4 k

0sB o s c i l l a t i o n s

s0s DB 2 8 % 3 4 . 5 k u p t o x s ~ 9 0

m o d e s

JB 0s

3 8 % 4 4 k 0 . 6 o

O t h e r d e c a y s 0

sB 9 5 % 1 0

0*0d KB 8 % 2 6 k

Range of channels available

in LHCb:


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B-meson Production (II)B-meson Production (II)

LHCb Detector– forward single arm spectrometer

Experimental challenges– Trigger: leptonic and hadronic final states

(eg Bd -> ) amongst minimum bias background

– Particle Identification:

-K separation 1 GeV < p < 150 GeV– Vertexing: proper time resolution

43 fs Bs -> Ds(K)

30 fs Bs -> J/

– Experimental signature:

time dependent asymmetry

bb angular productionbb angular production

)()(

)()()(

fBfB

fBfBtA


10

““LHCb-classic” ExperimentLHCb-classic” Experiment LHCb Detector: forward single arm spectrometer

Acceptance:10-300 mrad bending

10-250 mrad non-bending

VELO

RICH2

RICH1


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Vertex Detector (VELO)Vertex Detector (VELO)

Si strip detectors p-n, n-n, single sided, double metal read-out 220 m thick, 1800 wedges

Level 1 trigger (L1) Alternate r and strip detectors

varying strip pitch 20 - 40 m in r Detector halves retracted by

30 mm in y during injection 8 mm from beam during physics Radiation damage may have to replace detectors after

a few years

Liverpool, Glasgow participation

VErtex LOcator DesignVErtex LOcator Design

Si Strip Layoutradial

Si detectors


12

VertexingVertexing

Bs Ds K


13

Particle IdentificationParticle Identification

Excellent Particle Identification (-K separation) required from 1 - 150 GeV/c

RICH system divided into 2 detectors and 3 radiators: aerogel, C4F10, CF4

Momentum vs polar angle

Momentum


14

RICH1 RICH2

RICH System OverviewRICH System Overview

Acceptance– 300 mrad RICH 1

– 120 mrad RICH 2

Radiators: thickness L, refractive index n, angle c, /K threshold

Aerogel C4F10 CF4

L 5 85 167 cm

n 1.03 1.0014 1.0005

c 242 53 32 mrad

0.6 2.6 4.4 GeV

K 2.0 9.3 15.6 GeV

Photo detectors


15

Photon DetectorsPhoton Detectors Photo detector area: 2.6 m2

Single photon sensitivity: 200 - 600 nm, quantum efficiency > 20%

Good granularity: ~ 2.5 x 2.5 mm2

Large active area fraction: 73% LHC speed read-out electronics: 40 MHz

LHCb environment: magnetic fields, charged

particles

Hybrid Photodiodes (HPD) baselineHybrid Photodiodes (HPD) baseline

CF4

Aerogellarge rings

C4F10

small rings


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RICH PerformanceRICH Performance Simulation

– based on measured test beam HPD data

– global pattern recognition – background photons

included

# of detected photons– 7 Aerogel 33

C4F10 18CF4

Angular resolution [mrad]

– 2.00 Aerogel 1.45C4F10 0.58CF4

3 -K separation3-80 GeV/c

(21-150 GeV/c


17

Triggering (I)Triggering (I)

5 kHz 200 Hz


18

Triggering (II)Triggering (II)


19

Re-optimisation (I)Re-optimisation (I)Problems LHCb design: Material budget too high:

After Outer Tracker (OT) and Vertex Locator (VELO) Technical Design Reports (TDR), the material upstream of RICH-2 has increased by 70% with respect to Technical Proposal.

Material up to RICH-2: ~ 0.6 X0, 0.2λI

=> Increased secondaries, reduced track finding & reconstruction efficiency, increased fake tracks

=> B+- ~ 15% loss; BSDSK ~ factor 3 loss ! Desirable to reduce trigger rate (or increase trigger

efficiency) at levels 0 & 1:Trigger rate after level 1 trigger 40 kHz with a B+- efficiency of 30%.

Solution: include magnetic field in VELO + RICH1 region allows 25% resolution in VELO Pt measurement

doubles B+- efficiency or reduces trigger rate depending on need.


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Re-optimisation (II)Re-optimisation (II)

BJ/()Ks is saturated using L0().BJ/()Ks is saturated using L0().

B+- is improved by a factor >2 due to the VELO Pt information.

B+- is improved by a factor >2 due to the VELO Pt information.

10 kHz


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Re-optimisation (III)Re-optimisation (III)Material reduction:

• Beam pipe: Al to Be-Al alloy• VELO: 0.19 X0, 0.04 I

Possibilities are being investigated for Be RF shield, thinner Si 300 220 , less stations, etc. 0.19 X0 0.11 X0 • RICH-1: 0.14 X0, 0.05 I

Possibilities are being investigated for composite mirror, light mirror supports. 0.14 X0 0.08 X0

• Outer Tracker: 0.03 X0 9 stations=0.27 X0, 0.11 I

Reduce to 4 stations 0.27 X0 0.12 X0 Preliminary indications show that tracking efficiency very similar to “classic” design.

Full re-optimisation studies to appear in a TDR at end of 2002.


22

Re-optimisation (IV)Re-optimisation (IV)

remove magnet tracking stations

“LHCb-light”“LHCb-classic”


23

Re-optimisation (V)Re-optimisation (V)

Complete redesign of RICH-1: magnetic field (~500 G) imposes two mirror system with magnetic shielding like RICH-2, but rotated in vertical direction

Large effort at Imperial College, Bristol and RAL to modify design.


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from Bfrom BJ/J/ K Kss

• (sin 2) ~ 0.03 in 2006. • (sin 2) ~ 0.02 after 1 year• Theoretically clean• High statistics to fit Adir: > 105 events/year• B mass resolution = 7 MeV• B time resolution = 36 fs

)sin()cos(?0

tmAtmAA dmixddirCP


25

Sensitive to CKM angle ~ 20 - 50 in 1 year

– depends on |P/T| and strong phase Backgrounds also have 4900 B events/year 33000 Bevents/yearfor |P/T|

from Bfrom B00

Tree T Penguin P


26

Dalitz plot analysis Fit tree and penguin parameters (angle

+ 8 parameters) ~ 2.50 – 5.00 in 1 year B mass resolution: 42 MeV

(35 MeV when 0 mass constrained)

from Bfrom B00

1000 B0 events/year

200 B0events/year 100 B0events/year


27

Theoretically clean Small CP asymmetry Hadron trigger B mass resolution: 13.6 MeV (excl)

220 MeV (incl) Time resolution: 60 fs (excl)

170 fs (incl)

from Bfrom B00DD

73k B0D*(D( events/year (S/B=5.6)

460k B0D*(D(incl events/year(S/B=4.4)

360k B0D*(D(incla events/year(S/B=4.0)

(mix+) versus mix+

~ 10.00 in 1 year

Fit mix+ and strong phase strong

Get using mix from B0J/Ks


28

from Bfrom Bss -> D -> DssKK

Rate asymmetries measure angle Time: 43 fs, B mass: 11 MeV Expect 2100 BsDs

-(KKK events/year Expect 320 BsDs

+(KKK events/year

depends xs, , strong phase) GetusingfromBsJ/ (next slide)


29

from Bfrom Bss -> J/ -> J/ Expect 80K (32k tagged) events Negligible background J/ mass resolution: 9 MeV B mass resolution: 12 MeV Time resolution: 32 fs sin1 year,

depending on xs) Standard Model: sin

CP eigenstate


30

|V|Vtdtd/V/Vtsts| from | from mmss

Maximum xs = ms/s = 75


31

Rare DecaysRare Decays Bs -> +-

– Standard Model branching ratio: 3.7 x 10-9 ideal to search for new physics - FCNC

– Combine with Bd -> +- to obtain |Vtd/Vts|2

– Expected signal (bkgd) : 11 (3.3) 1 year

Bd -> K*+-

– Standard Model branching ratio: 1.5 x 10-6

dimuon mass spectrum, forward-backward asymmetry

– combine with Bd -> +- |Vtd/Vts|2=11% 1 year

– Expected signal (bkgd) : 22400 (1400) 1 year

Bd -> K*– Standard Model branching ratio: 5 x 10-5

search for new physics in asymmetry CP ~1% in SM

– Expected signal: 26000 1 year


32

LHCb Physics summaryLHCb Physics summaryParameter Channels Evts/year (1 year) LHCb feature

2(+) Bd 4900

|P/T| = 0 2-5 PID, hadron trigger

Bd 1300 2.5-5 PID, hadron trigger

2+ Bd D 460k ~10 PID, hadron trigger

BdJ/Ks 100k 0.9

-2 Bs DsK 2400 6-14 PID, hadron trigger, t

Bd DK 400 10 PID, hadron trigger

Bs J/ 44000 0.6 t

Bs oscillations

xs Bs Ds 120000 up to 75 hadron trigger, t

Rare Decays

BR Bs <210-9 t

Bd K 22400 PID


33

ConclusionsConclusions LHCb is undergoing re-optimisation to acquire

efficiencies as stated in Technical proposal. Critical sub-detectors: Vertex Detector, RICH and

Trigger all have UK involvement. VELO can achieve 43 fs proper time resolution RICH design with two detectors and three radiators

provides 3 -K separation from 3-80 GeV/c LHCb can measure all angles of unitarity triangles

and test models of CP violation. LHCb in time to take data when LHC becomes

operational in 2007

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