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Heavy Flavour Physics with the
LHCb Experiment at the LHC
Jimmy McCarthy,
Luca Pescatore
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Matter vs Anti-Matter
 Every particle has an anti-particle:
 Same mass
 Same lifetime
 Opposite charge
e
electron
up quark u+2/3
e+
positron
u-2/3
up anti-quark
 sds
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How do you make antimatter?
 Einstein had an idea...
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E=mc Energy  matter
Energy
e4
e+
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When matter meets antimatter
 Annihilation!
e-
Energy
e+
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Naturally occurring anti-matter
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Naturally occurring anti-matter
 Lots of energy at
the big bang
 Particles and
anti-particles created
in equal quantities
 They annihilate!
 Where is all the
anti-matter?
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What’s the difference?
 The answer lies in CP (charge-parity) violation!
 The parity operation is a reflection (mirror image)
 Charge-conjugation inverts the charge of a particle
(positive ↔ negative)
 Combined operation converts matter ↔ anti-matter.
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P
C
P
C
CP
CP
Violation
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Finding CP Violation
 Only occurs in heavy quarks.
 Can’t see a quark on its own
 Forms particles called mesons (quark anti-quark pair) or baryons (3
quarks)
 First investigated in particles containing “strange” quarks:- Kaons
Particle
K+ u s
K0 d s
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Anti-Particle
K- u s
K0 d s
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At the LHC
 At LHCb we now look at the b quark.
Particle
B+ u b
B0 d b
Anti-Particle
B- u b
B0 d b
 Look at the difference between B+ and B- decays
 CP Asymmetry:
 e.g B±  π+π-π±
ACP = +0.622±0.08
 Problem solved?
 With all sources of CP violation we know about there is 109 more
matter than we can explain...
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Search for new physics
 Can search for new particles in an indirect way.
 Look at processes with penguin diagrams!
 New particles can appear in these loops and change the
behaviour of decays
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The LHCb Experiment
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Birmingham in LHCb
 Joined relatively recently: March 2011
 Still a small group
 2 academic staff
 1 post-doc
 4 PhD students.
 Working in rare decays and charmless B decays
 Involve penguin processes
 Also working in the simulation of the LHCb detector.
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The LHCb Detector
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The VErtex LOcator (VELO)
 Helps us detect B mesons.
 B mesons have long lifetimes (10-12s!).
 They travel a few mm before decaying.
 Can observe a secondary vertex.
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The VErtex LOcator (VELO)
 Need a very good tracking detector:
 Very close to the interaction.
 Not too close or it suffers
radiation damage.
 The VELO can be retracted:
 6cm apart when not in use.
 8mm from the interaction for collisions.
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Ring Imaging Cherenkov Detectors (RICH)
 LHCb needs very good particle identification (PID)
 Can we distinguish protons, pions and kaons?
 RICH detectors rely on Cherenkov Radiation:
 A charged particle travelling through a medium will emit a
cone of light if it travels faster than the speed of light in that
medium.
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Ring Imaging Cherenkov Detectors (RICH)
 Angle of the cone is related to the speed of
the particle.
 Plotting momentum of particle against
Cherenkov angle is different for different
particles.
 Use different radiators for
different momentum ranges.
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Now you know...
 What is heavy flavour physics?
 Why do we do heavy flavour physics?
 How do we do heavy flavour physics?
 What is LHCb?
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