Heavy quark physics
at the LHC and elsewhere
Guy Wilkinson
University of Oxford
Edinburgh, February 2006
Talk Roadmap
Motivation & context
• Why quark flavour physics?
• And why flavour physics in the LHC era?
• What is the CKM model, and what state is it in?
B-physics: precision tests of the CKM triangle & beyond
The Tevatron and the LHC (especially LHCb):
• Bs mixing
•  measurements: tree and loop
• Probing the weak phase in Bs mixing
• Very rare decays
We will
concentrate
on these
Super B-factories: potential and prospects
Beyond the b’s: flavour physics in the charm & kaon sector
Why do we care about flavour physics?
Quark flavour physics at heart of many of HEP’s big questions:
• Why are there three generations ?
• Why is there an extreme hierarchy in mass (m t ~ 170 GeV !)
• What is origin of CP violation ?
• Can we understand the cosmic baryon-antibaryon asymmetry ?
• Is there a relation between the quark & neutrino mixing matrices?
Complementary to direct searches for new physics at the LHC
• Powerful way to look for new physics
b
t
s
d
u
u
s
new
particles?
• Elucidate flavour structure of
the new physics when found
(not dissimilar to ILC)
Unitarity Triangle, Summer 2005
Remarkably self-consistent: certainly the CKM model is the
dominant mechanism of CP violation in nature! This
conclusion is only possible thanks to work of B factories.
What is the CKM Model ?
In Standard Model, charged-current quark-coupling described by
the CKM matrix, which has 4 parameters, 1 of which is complex
Wolfenstein parameterisation: A, ρ, λ and η. Non-zero value
of η is source of all CP violation in the Standard Model.
VCKMVCKM* = 1 implies:
α

This is the unitarity triangle
β
Existing triangle measurements: the essentials
A lot of information in these ρ-η plane plots! For clarity lets
focus in on most important experimental constraints.
α
‘B’

‘G’
β
In (rough) order of importance:
• Side ‘B’ fixed by ratio of b→ul/b→cl (theory limited)
• Angle β from measurement of CP asymmetry in Bd→J/ψK0
• Side ‘G’ constrained by measurements (limits) on Bd(s) mixing
• Recent B-factory results give first indications on α and 
Good agreement, but hints of inconsistencies
Overall consistency of measurements is impressive. A closer
look, however, reveals that agreement is not quite perfect….
Indirect 0.791±0.034
Direct 0.687±0.032
>2 sigma
difference
Although at 1st order the CKM description is vindicated, are
there 2nd order corrections from New Physics contributing?
Generic Strategy to Hunt for New Physics
New heavy particles (eg. sparticles) if they exist, are expected
to lurk in box and Penguin processes. Here contributions may
be comparable to, or exceed, the Standard Model amplitudes
Tree
Box
b
b
t
Penguin loop
b
t
d
t
u
d,s
b
d,s
We must hunt both Boxes (eg. mixing) & Penguins (eg. B→)
Trees still play vital role in global strategy – provide pure CKM
benchmark values to compare other measurements against.
Example: ‘b→ul/b→cl’ side is tree; sin2β from J/ψK0 is box.
Time line of B physics facilities and goals
B-factories Tevatron
(double
existing
data set)
2008
2010
Super
B-factory
LHC
Selected list of most important aims
(in ~ order of likely achievement):
• Improved measurements of 
• Observation of Bs mixing
• Very high precision sin2β
• Precision measurements of 
• Measurement of Bs mixing phase
• Observation of very rare decays
Study prospects in a few of above
Time line of B physics facilities and goals
B-factories Tevatron
(double
existing
data set)
2008
2010
Super
B-factory
LHC
Selected list of most important aims
(in ~ order of likely achievement):
• Improved measurements of 
• Observation of Bs mixing
• Very high precision sin2β
• Precision measurements of 
• Measurement of Bs mixing phase
• Observation of very rare decays
Study prospects in a few of above
Bs Mixing
Next important constraint on triangle likely to be ‘mixing side’
α

 |Vtd|/|Vts|
β
b
d,s
t
t
b
d,s
Vtd,ts
Measure Δmd (slow) & Δms (fast!), frequency
of oscillations. Ratio of frequencies, with
hadronic correction (error ~ 6%) → |Vtd|/|Vts|
Δmd known. Present 95% CL limit on Δms
is > 16.6 ps-1 (LEP/SLD alone >14.5 ps -1)
Standard model expectation
Bs Mixing: the experimental challenges
Bs mixing search now being spear-headed by CDF and D0.
Immediate challenge
is to accumulate enough
events. Two choices:
1) Fully hadronic Bs
decays, eg. Bs→Ds
2) Semi-leptonic, eg. Bs→Dslν
Note both are flavour specific, eg. we know b or b at decay.
But we also need to ‘tag’ Bs, to know flavour at time of birth.
Reduces effective statistics by a lot! eg. εeff = 1.6% at CDF.
2) has higher yield and dominates present results; but worse
proper time resolution will limit performance at high Δms.
Bs mixing: future prospects
Present Tevatron analyses use 400-600 pb-1 of data.
More data, and improved analyses, will give real possibility
of observation (if within Standard Model region!) soon-ish.
If the Tevatron fails, LHC
should do the job. eg. LHCb:
• Can observe Δms=40 ps-1
with 1/8 year of running.
• Sensitivity up to Δms=68 ps-1
in one year of running
Of course this assumes aligned
and understood detector etc
(4-8 fb-1 expected by 2009)
Place your bets now for winner!
B-physics at the LHC
B physics advantages of LHC vs Tevatron:
• 10x higher b-production cross-section
• Higher luminosity (ATLAS/CMS)
• One dedicated B-physics experiment
ATLAS/CMS: excellent B-physics
for channels involving leptons
ATLAS
CMS
LHCb
B-physics at the LHC vs the B-factories
ee  (4S)  BB
PEPII, KEKB
ppbbX (√s = 14 TeV, tbunch=25 ns)
LHC (LHCb–ATLAS/CMS)
Production bb
1 nb
~500 b
Typical bb rate
10 Hz
100–1000 kHz
bb purity
~1/4
Pileup
b-hadron types
0
B+B– (50%)
B0B0 (50%)
b-hadron boost
Small
bb/inel = 0.6%
Trigger is a major issue !
0.5–5
B+ (40%), B0 (40%), Bs (10%)
Bc (< 0.1%), b-baryons (10%)
Large (decay vertexes well
separated)
Production
vertex
Not reconstructed
Reconstructed (many tracks)
Neutral B mixing
Coherent B0B0 pair
mixing
Event structure
BB pair alone
Incoherent B0 and Bs mixing
(extra flavour-tagging dilution)
Many particles not associated
with the two b hadrons




LHCb Spectrometer
Dipole
magnet
VELO
collision
point
~1 cm
B
Crucial for B physics:
• optimised geometry and choice of luminosity
• trigger efficient in hadronic & leptonic modes
• excellent tracking and vertexing (m, )
• excellent particle ID
LHCb VELO (Silicon Vertex Locator)
VELO is laid out as a series of R and Φ measuring stations approaching
0.8 cm to the beam line, situated in vacuum chamber (inside beam-cavity!)
VELO key to LHCb physics programme:
• Provides ‘lifetime trigger’ which gives
high efficiency for all decay modes
• Gives excellent proper time resolution;
vital for high performance Bs physics
BsDs
proper
time
resolution
t ~ 40 fs
Example of LHCb RICH in action
RICH sytem will allow clean separation of different Bhh
modes. Not possible elsewhere at hadron colliders.
Situation at Tevatron:
CDF
data
BsKK
signal
Bd
signal
Bd
signal
Towards a precise measurement of 
LHCb has a wide variety of strategies for measuring :
1) Tree level methods – vital for benchmarking entire triangle
Example: approaches involving B→DK decays
2) Methods involving loops – sensitive to new physics
Example: two-body modes
Such redundancy is essential in
the hunt for new physics!
How well do we need to do? Well 1)
suggests that we make measurement
with precision equal to or better than
that from indirect prediction…
γ = (61.4 ± 6.5)°
B →DK - interfering B diagrams
Two interfering tree diagrams (theoretically clean).
s
B-
b
u
c
u
u
b
BD0
u
Vub – phase ~ 
u
c
D0
s
u
For decays common to Do and Do we access interference
effects which depend on  ! Other parameters exist in game
(‘rb’, ‘δb’) and need several decays to overconstrain problem.
• Many common D0/D0 final states exist
• Charged B’s: no flavour tagging or proper time
analysis required. It is merely a counting experiment!
B →DK - some specific examples
LHCb aspects particularly suited to B→DK: trigger & RICH
Do decay mode
Statistics in
recent B-factory
publications
Expected
annual yield
at LHCb
CP-self conjugate
(‘3-body Dalitz’)
Ks (KsKK)
~200
5000
~30
8000
~10
2000
CP-eigenstates (‘GLW’)
KK ()
Doubly Cabibbo
suppressed (‘ADS’)
K (K)
Lack of tagging requirement means full statistics can be used!
Example of B→DK analysis: D(Ks)K
Pioneered by B-factories: look at Dalitz space of D decay
products for B+ and B- decays. Rich resonance decay
structure allows for reasonable sensitivity with ~200 events.
Belle sees
clear difference
where it should !
Expected variation of
sensitivity in Dalitz space
B-factory samples have statistical error of ~ 20o. Scope for 5o
LHCb error, but needs good understanding of D decay model
Other approaches (eg. ‘ADS’) cleaner and more precise.
All DK methods measure same parameters, but have
differing systematics → combine for final precision of ~1o ?
Accessing  with B→hh Decays
B0→ and Bs→KK receive important contributions from Penguin graphs.
b→u transitions in tree gives rise to  dependence in the time dependent
CP asymmetries. Individually, however, hadronic uncertainties don’t allow
Penguin/tree contributions to be decoupled, and hence  to be extracted.
Penguin
b
d,s + +
u  ,K
u - , Kd,s
u
+, K+
d,s
t
B0, Bs
d,s
(Recall role
of RICH in
separating
modes)
Tree
B0,
b
Bs
d,s
~
u
d,s
- , K-
However, B0→ and Bs→KK identical under swapping d↔s (‘U-spin’).
Hadronic effects should be same (or very similar) for both. Combined
analysis allows  to be extracted with high sensitivity to New Physics !
Accessing  with B→hh Decays
For both decays measure ACPd,s = Ad,scosΔmd,st + Bd,ssinΔmd,st
Suitable combination of
parameters gives  to ±5o
Enough constraints exist
in analysis that stability to
U-spin symmetry assumption
can be assessed.
Bd →
Hadronic amplitude which we
assume to be same for two cases
Large event yields, RICH
and good proper time
resolution allow for good
precision on all parameters.
Comparison with tree-level
Bs→KK
measurements a very important test!
 [degrees]
Beyond the triangle 1: the Bs mixing phase
Other angles exist beyond those of familiar unitarity triangle ! At order λ3
CKM element Vts is real; at order λ5 it has a very small phase, c ,
(c  0.02 radians). Phase accessible through Bs mixing.
Analogous to β measurement in
system (~ Vtd).
In Bs case, new physics contributions may be
much more evident, because of tiny SM signal !
B0
Golden channel for c : Bs→J/ψΦ. Every LHC
experiments expect 50-150k events.
Vector-vector final state → angular analysis
needed to separate CP-odd and even amplitudes.
LHCb is sensitive at level of SM expectation, but
may need several years for 5σ observation.
b
d,s
t
t
Vtd,ts
b
d,s
Beyond the triangle 2: very rare decays
In addition to studying consistency of triangle, we may look
for certain B decays heavily suppressed in Standard Model.
Clean Standard Model prediction:
Br (Bs  μ+μ-) ~ 4 × 10 -9
Large enhancements possible, eg. MSSM:
Br ~ tan6β / M2H !
Distinctive leptonic
signature good
for all experiments
1 year
Bs  + –
signal (SM)
b, b
background
LHCb
2 fb–1
17
< 100
ATLAS
10 fb–1
7
< 20
CMS (1999)
10 fb–1
7
<1
Motivation & Prospects for a Super-B Factory
Spectacular success of BaBar/Belle demonstrates power of
Upsilon(4s) environment. Aim for order in magnitude
improvement in precision:
• High statistics for precise CKMology
• Precise measurements to elucidate
flavour structure of new physics
• Very high sensitivity in flavour violating
tau decays, eg. →μ
• Particular strengths: ability to reconstruct
modes with neutrinos and EM neutrals
Two proposals: SuperKeK & Frascati. Briefly discuss former.
Projections for luminosity at SuperKEKB
Design lumi = 4 x 1035 cm-2 s-1
Aim for 100x present yield
SuperBelle detector
SC solenoid
1.5T
 / KL detection
14/15 lyr. RPC+Fe
g tile scintillator
CsI(Tl) 16X0
g pure CsI (endcap)
Aerogel Cherenkov counter
+ TOF counter
g “TOP” + RICH
Tracking + dE/dx
small cell + He/C2H6
gremove inner lyrs.
Use fast gas
New readout
and
computing
systems
Si vtx. det.
4 lyr. DSSD
g 2 pixel/striplet lyrs.
+ 4 lyr. DSSD
Decays with neutrinos,  and 0’s feasible
• B decays with neutrinos
B g D, , ul B meson beam !
Charged Higgs
Vub
e
(8GeV) Υ(4S)
• B decays with , 0
B g Xs, 00 etc.
direct CPV
D etc.
B
e+(3.5GeV)

B
full (0.1~0.3%)
reconstruction
BgD etc.
f2(a) isospin analysis
Not possible at LHCb ! Methods established at BaBar/Belle.
What can a Super B-factory do?
Pursue hints of new physics
seen at BaBar/Belle which
are difficult to pursue at LHC
Central values as now,
with Super-B precision
Example: sin2β measured
with J/ψ Ks and ΦKs
B0 g J/Ks
b→ΦKS has b→s Penguin
sin2βJ/ψK0 = 0.69 ± 0.03
sin2βΦK0 = 0.47 ± 0.19
Mode unsuited to LHCb
(poor vertex constraint)
B0 g fKs
(0.03 stat error on Δsin2β)
More to quark flavour physics than B’s !
All discussion so far has focused on B decays. Why is this?
Because in B system there is a multitude of observables
that can be cleanly related to CKM / SM predictions
But there is still much to learn from other quark systems:
• D0 system: very small mixing and CP violation expected.
New physics may couple differently to up-type quarks !
• Kaon system: historical view is that despite being birthplace
of CP physics, interpretation of measurements is messy.
Not always true !
New opportunities in charm physics
Mixing and CP violation expected to be small in Standard Model, but are
coming within range of new experiments, eg. LHCb and SuperBfactory.
Clear signatures can be looked for. For instance, for direct CP violation
compare D0 and D0 decays to CP eigenstates, such as KK,  .
Current precision 10-2.
In SM we expect
effects of order 10-3.
LHCb will accumulate
5 x 108 D*→D0(hh) p.a.,
>100x Tevatron yields.
Clear discovery potential!
K→ and the unitarity triangle
Two ultra-suppressed kaon decays provide extremely clean
constraints on unitarity triangle. Standard Model predicts:
BR(K++) = (8.0 ± 1.1)×10-11
BR(KL0) = (3.0 ± 0.6)×10-11
Irreducible theory error on
0 = 1% ; on + = 5%
Prospects for K+→+
Decay already observed! 3 events at E787/949 (now defunct)
Rate consistent with SM.
P-326: proposed CERN
experiment (in NA48 hall)
Data taking in ~2010
+
K+

With 100 events !

Reconstruct missing mass. Vetoes vital!
Prospects for K0→0: E391a at KEK
First dedicated K0→ experiment. Challenging signature!
• 2 photons only
• Missing pt
missing pt (GeV/c)
Requirement for selection:
No events !
z position of vertex (cm)
Prospects for K0→0: upgrade for J-PARC
E391 aims to reach 10-9 (Grossman-Nir limit) with present data.
E391 situated on
12 GeV KEK PS.
Upgraded experiment
planned for J-PARC
(30 GeV protons)
→ 100x KL flux
Intention is to have
sensitivity at SM BR.
~3 years of operation
Conclusions and Outlook
Now know that observed CP violation is described to first
order by CKM model. But still expect new physics to show!
Augment existing triangle constraints with new, very
precise measurements involving tree and loop:
Bs mixing;  (tree and loop)
Additional measurements beyond the triangle:
Bs mixing phase ; very rare decays (eg. Bs→μμ)
LHC studies can be complemented by super-clean, super-B !
Charm and kaon mesons still have role to play.
Backup Slides
Choice of Geometry and Running Luminosity
Forward spectrometer geometry
exploits correlated production
(excellent for flavour tagging)
De-focus beams locally to lower
luminosity to ~2 x 1032 cm-2 s-1
Inelastic pp collisions/crossing
LHCb
Forward layout also allows planes of
silicon to approach very close to beam
Optimises fraction of 1-interaction
events → cleaner to analyse. Also
allows for acceptable occupancy
and radiation levels.
Trigger
•
bb ~ 500 b, < 1% of inelastic cross-section
• Use multi-level trigger to select interesting events:
 high pT electrons, muons or hadrons
 vertex structure and pT of tracks
 full reconstruction
~ 200 Hz
to tape in
exclusive
decays



30–60%
efficiency
LHCb Ring Imaging Cherenkov (RICH) System
PID mandatory for suppressing same
topology backgrounds in many final states,
and for adding kaons to flavour tagging.
Wide momentum span in PID requirements
→ 2 RICHes with 3-radiators
Cherenkov rings in RICH 1
Kaon ID: ~88%
Pion mis-ID: 3%
Good performance
for 2<p<100 GeV/c