B-physics reach of the LHCb
Experiment
Paul Soler
University of Glasgow and
Rutherford Appleton Laboratory
RAL-Southampton Seminar
26 April 2002.
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/Y K) and will constrain unitarity triangles to unprecedented
accuracy.
RAL-Southampton Seminar,
26 April 2002
2
Physics aims (II)
CKM Matrix
VCKM

2
 1 2

  

 Vtd e ib



1
2
2
 Vts e idg

 Vub e ig 

2
A 


1


VudVub  VcdVcb  VtdVtb  0
*
*
*
_
b Bd-Bd Mixing Phase
_
dg Bs-Bs Mixing Phase
g Weak Decay Phase
Standard Model: apbg
dg2h ~ 0.03
VtbVub  VtsVus  VtdVud  0
*
RAL-Southampton Seminar,
26 April 2002
*
*
3
Physics aims (III)
Possible unitarity triangle measurements in LHCb
 Bs0  Kp , K  K  ,  , g , 
h
Bd0  p p 
1
Bd0  D p ,3p
Bd0  rp
B
Bs0  Dsp
a
0
g
Bd0  DK *0
B  Ds K
0
s
0
b
Bd0  J / K s0
RAL-Southampton Seminar,
26 April 2002
r
1
4
Physics aims (IV)



Babar, BELLE have established CP violations for B mesons with Bd -> J/Y K:
– sin 2b = 0.75+-0.09+-0.04 (Babar, 56 fb -1)
– sin 2b = 0.82+-0.12+-0.05 (BELLE, 42 fb-1)
Consistent with Kobayashi-Maskawa mechanism
Standard Model fit (0.5< sin 2b <0.8)
Possible situation in 2005
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26 April 2002
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Physics aims (V)
Aims for LHCb in 2008 (after 1 year data taking)
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26 April 2002
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Physics aims (V)
… or maybe g not consistent with SM fits
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26 April 2002
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B-meson Production (I)


LHC is the most intense source
of B mesons (Bd, Bu, Bs, Bc)
with sbb = 500 mb
Modest LHC luminosity
<L>LHCb = 2 x1032 cm-2 s-1
 1012 bb / 107 s
Channel
a modes
B0d  p  p 
Trigger Efficiency
Event yield
Sensitivity
30%
6.9k
210
B0d  D p, 3p
33%
725k
8
B0d  rp
20%
1.3k

b modes
B0d  J  Ks0
36%
45.6k
0.30.
g modes
Bs0  D s K
28%
2.4k
3
21%
0.4k

Bs0  D s p
28%
34.5k
up to xs ~90
dg modes
Bs0  J  
38%
44k
0.6o
Other decays
Bs0     
95%
10

B K g
8%
26k

B0d  D 0 K *0

Range of channels available
in LHCb:
Bs0 oscillations
0
d
*0
RAL-Southampton Seminar,
26 April 2002
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B-meson Production (II)

bb angular production
LHCb Detector
– forward single arm spectrometer

Experimental challenges
– Trigger: leptonic and hadronic final states
(eg Bd -> pp) amongst minimum bias
background
– Particle Identification:
p-K separation 1 GeV < p < 150 GeV
– Vertexing: proper time resolution
43 fs Bs -> Dsp(K)
30 fs Bs -> J/ 
– Experimental signature:
( B  f )  ( B  f )
A
(
t
)

time dependent asymmetry
( B  f )  ( B  f )
RAL-Southampton Seminar,
26 April 2002
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“LHCb-classic” Experiment

LHCb Detector: forward single arm spectrometer
Acceptance:
10-300 mrad bending
10-250 mrad non-bending
VELO
RICH1
RICH2
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26 April 2002
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Vertex Detector (VELO)
VErtex LOcator Design
Si strip detectors p-n, n-n,
Si detectors
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
Si Strip Layout
radial

 8 mm from beam during physics
 Radiation damage
 may have to replace detectors after a
few years
Liverpool, Glasgow participation

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26 April 2002
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Vertexing
Bs Ds K
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26 April 2002
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Particle Identification
Momentum vs polar angle
Momentum

Excellent Particle Identification
(p-K separation) required from
1 - 150 GeV/c

RICH system divided into 2
detectors and 3 radiators:
aerogel, C4F10, CF4
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26 April 2002
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RICH System Overview
RICH1
Photo detectors
RICH2

Acceptance
– 300 mrad RICH 1
– 120 mrad RICH 2

Radiators: thickness L,
refractive index n,
angle c, p/K threshold
Aerogel C4F10 CF4
L
n
5
85
167 cm
1.03 1.0014 1.0005
c
242
53
32 mrad
p
0.6
2.6
4.4 GeV
K
2.0
9.3
15.6 GeV
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26 April 2002
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Photon 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
C4F10
Aerogel
small rings large rings
LHCb environment: magnetic fields, charged
particles
Hybrid Photodiodes (HPD) baseline
CF4
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26 April 2002
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RICH Performance

Simulation
– based on measured test
beam HPD data
– global pattern recognition
– background photons
included

# of detected photons
–

3s p-K separation
3-80 GeV/c
(2s 1-150 GeV/c)
7
33
18
Aerogel
C4F10
CF4
Angular resolution [mrad]
– 2.00
1.45
0.58
Aerogel
C4F10
CF4
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26 April 2002
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Triggering (I)
5 kHz 200 Hz
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26 April 2002
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Triggering (II)
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26 April 2002
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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p+p- ~ 15% loss; BSDSK ~ 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p+p- efficiency of 30%.
Solution: include magnetic field in VELO + RICH1 region allows 25%
resolution in VELO Pt measurement
doubles Bp+p- efficiency or reduces trigger rate depending on need.
RAL-Southampton Seminar,
26 April 2002
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Re-optimisation (II)
BJ/Y()Ks is saturated
using L0().
Bp+p- is improved by a
factor >2 due to the
VELO Pt information.
10 kHz
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26 April 2002
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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.
RAL-Southampton Seminar,
26 April 2002
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Re-optimisation (IV)
“LHCb-classic”
“LHCb-light”
remove magnet tracking stations
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26 April 2002
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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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26 April 2002
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b from BJ/Y Ks
ACP  Adir cos( md t )  Amix sin( md t )

0 ?
• s(sin 2b) ~ 0.03 in 2006.
• s(sin 2b) ~ 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
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26 April 2002
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a from B0pp

Sensitive to CKM angle a
sa ~ 20 - 50 in 1 year
– depends on |P/T| and strong phase 

Backgrounds also have

4900 Bpp events/year
33000 BKp events/year for |P/T|

Tree T
Penguin P

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26 April 2002
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a from B0rp



r

Dalitz plot analysis
Fit tree and penguin parameters (angle a
+ 8 parameters)
sa ~ 2.50 – 5.00 in 1 year
B mass resolution: 42 MeV
(35 MeV when p0 mass constrained)
r0
r



1000 B0rp events/year
200 B0rp events/year
100 B0r0p0 events/year
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26 April 2002
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2bg from B0Dp




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)

s(mix+g) versus mix+g





sg ~ 10.00 in 1 year
Fit mix+g and strong phase strong
Get g using mix from B0J/YKs
73k B0D*(D(Kp)p)p events/year (S/B=5.6)
460k B0D*(D(incl)p)p events/year (S/B=4.4)
360k B0D*(D(incl)p)a events/year (S/B=4.0)
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26 April 2002
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g2dg from Bs -> DsK






Rate asymmetries measure angle g2dg
Time: 43 fs, B mass: 11 MeV
Expect 2100 BsDs-(KKp)K events/year
Expect 320 BsDs+(KKp)K events/year
s(g2dg)  0 .. 0
(depends xs, g, strong phase)
Get g using 2dg from BsJ/Y (next slide)
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26 April 2002
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dg from Bs -> J/Y







Expect 80K (32k tagged) events
Negligible background
J/Y mass resolution: 9 MeV
B mass resolution: 12 MeV
Time resolution: 32 fs
s(sin 2dg) ~ 0.03 (1 year,
depending on xs)
Standard Model: sin 2dg ~ 0.03
CP eigenstate
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|Vtd/Vts| from ms
Maximum
xs = ms/s = 75
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Rare 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 -> r +s|Vtd/Vts|2=11% 1 year
– Expected signal (bkgd) :
22400 (1400) 1 year

Bd -> K*g
– Standard Model branching ratio: 5 x 10-5
search for new physics in asymmetry dCP ~1% in SM
– Expected signal:
26000
1 year
RAL-Southampton Seminar,
26 April 2002
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LHCb Physics summary
Parameter
2(b+g)
2b+g
b
g-2dg
g
dg
Bs oscillations
xs
Rare Decays
BR
s(1 year)
LHCb feature
1300
460k
100k
2400
400
44000
2-5
2.5-5
~10
0.9
6-14
10
0.6
PID, hadron trigger
PID, hadron trigger
PID, hadron trigger
120000
up to 75
hadron trigger, st
<210-9
st
PID
Channels
Bdpp
|P/T| = 0
Bdrp
Bd  Dp
BdJ/Ks
Bs DsK
Bd  DK
Bs  J/
Evts/year
4900
Bs  Dsp
Bs  
Bd  K 
22400
RAL-Southampton Seminar,
26 April 2002
PID, hadron trigger, st
PID, hadron trigger
st
32
Conclusions






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 3s p-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
RAL-Southampton Seminar,
26 April 2002
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