1 outline ● Part I: some issues in experimental b physics ● why study b quarks? ● what does it take? ● Part II: LHCb experiment ● Part III: LHCb first physics + outlook

2 Part I: experimental issues

3 flavour physics ● weak interaction: quark flavour transitions ● important observables in weak decays of hadrons ● mass, lifetimes, mixing, branching fractions ● angular distributions, asymmetries ● CP asymmetries u d W Vud “CKM matrix”

4 why study the b quark? ● heaviest quark to from bound states ● very rich phenomenology ● 100s of decay modes, some very rare ● large CP violating effects ●... ● NP physics “at leading order”, especially in “loops” ● all decays are CKM suppressed ● long lifetime (1.5 ps --> ct ≈ 500 mm) ● precise predictions: m >> L QCD ● especially true for ratios and asymmetries

5 why look at rare things? ● processes dominated by loop diagrams are very sensitive to high mass scales ➔ new particles in loops change branching fractions, mixing frequencies, CP asymmetries, etc ● 'low-energy' flavour physics results (Babar, Belle, Tevatron,...) put strong constraints on flavour structure of TeV-scale NP

6 low-E constraints in one implementation of MSSM

7 why look at unitary triangles? ● 'unitary triangles' are a tool to visualize constraints from different measurements on V ckm “if SM, then V unitary, then “ ● SM tests ● over-constrain triangles by measuring both sides and angles ● measure angles in more than one way, e.g. 'tree' and 'penguin'

8 constraints from processes dominated by 'tree diagrams', unlikely to be affected by NP

9 constraints from processes involving mixing, likely to be affected by NP

10 consistency is good but not perfect (~5%)... plenty of room for NP? current dogma: at 'tree' level the SM holds perfectly... NP effects are not very large

11 B hadrons: masses and lifetimes 1.5ps 5.3 GeV lifetimes of b and c baryons just about the size of coordinate resolution of particle detectors

12 mixing ● Niels on Monday: neutral mesons (K 0,D 0,B 0,B s ) 'mix' ● flavour composition oscilates with time ● mixing frequency determined by 'box' diagram ● physics is such that ● Bs mixes very fast ● Bd mixes about as quickly as it decays ● D0 mixes very slowly number of oscillations per lifetime

13 B decays: 'tree' topologies ● semi-leptonic b qq c, u W-W- l-l- n e.g. B 0 --> D + m - n ● hadronic note: sign of charge of lepton same sign as charge of b quark b qq c, u W-W- u,c d,s e.g. B 0 --> D ( * )+ p - B 0 --> K + p -

14 B decays: 'loop' topologies ● EW-penguin ● 'strong' penguin b qq s, d W-W- g, Z 0 e.g. B 0 --> K *0 m + m - b --> s “flavour changing neutral current” b qq s, d W-W- g q' q e.g. B 0 --> K + p - B s --> K + K -

15 b hadron production ● at Y(4S) resonance (Argus, Cleo, Babar, Belle,...) ● at high-energy collidors (LEP,Tevatron, LHC,...) ● all B hadron species (Bd, Bs, Bc, Lb,...) ● larger boost ● much larger cross-section ● more mess in particular at hadron colliders e+ e- --> Y(4S) --> B 0 B 0 or B + B -

16 comparing b factories ● some relevant parameters: ● different b-species Y(4S) high-energies

17 observables ● masses, lifetime ● not 'predictable', but ratios related in models of bound-states ● absolute branching fractions ● usually hard to predict ● some exceptions, a.o. – fully leptonic, B + --> tn, B s,d --> m + m - – inclusive semi-leptonic (b->cln) or radiative (b--> X g) ● partial decay widths --> angular distributions ● sometimes very clean predictions, e.g. K*mm ● CP asymmetries

18 CP observables Mainly two types 1. 'charge asymmetries' ● relative phase of two amplitudes depends on time ● often very clean predictions ● measuring this requires propertime and flavour tag ● requires two amplitudes with different 'strong' and 'weak' phases ● strong phases cannot be predicted, but sometimes extracted by combining different measurements 2. time-dependent asymmetries: if B d,s and B d,s -bar have common final state, interference through mixing B0B0 f B0B0

19 time-dependent CP violation ● Niels on Monday: if f is a CP eigenstate B s ® J/yj ● the physics is in S, e.g. ● sensitivity to S determined by ● statistics, background ● 'dilution' from finite proper-time resolution ● 'dilution' from wrong tagging of flavour of B

20 propertime measurement BsBs DsDs K+K+ K+K+ K-K- p-p- to measure lifetime, B needs to move the faster it moves, the better the lifetime resolution

21 SLAC CERN built for a lot of boost! built for a bit of boost...

22 dilution from propertime resolution ● finite resolution 'dilutes' the wiggles ● 'dilution' given by ● compare again Babar and LHCb sensitivity decreases very strongly as function of “Dm s” Babar (or Belle) can never measure mixing in Bs mesons smearing t

23 flavour tagging ● flavour tagging: determine if B created as b or as anti-b b BsBs J/y f b s ● same-side tagging: exploit the other s quark s ● two methods ● opposite-side tagging: exploit the other b quark b

24 opposite-side tagging ● look for high pT charged Kaon or lepton from other b quark b BsBs J/y f b s b c s m-,e-m-,e- K+K+

25 same-side tagging ● look for charged Kaon (or pion for Bd) close in phase space b BsBs J/y f b s b K-K- s

26 tagging dilution ● flavour tag is often wrong ● OST: lepton from D decay, B 0 mixing,... ● SST: wrong kaon ● dilution quantified as probability to 'find' a tag ● flavour tagging is much harder at hadronic factories: ● or sometimes as 'tagging power' or 'effective efficiency': miss-tag-rate: probability that tag is wrong

27 key features of a beauty experiment BsBs DsDs K+K+ K+K+ K-K- p-p- 1. good vertex resolution ➔ to identify B and D hadrons ➔ to resolve fast oscillations B tag

28 key features of a beauty experiment BsBs DsDs K+K+ K+K+ K-K- p-p- 1. vertex resolution ➔ to identify B and D hadrons ➔ to resolve fast oscillations 2. momentum resolution ➔ to separate topologically similar final states B tag

29 key features of a beauty experiment BsBs DsDs K+K+ K+K+ K-K- p-p- 1. vertex resolution ➔ to identify B and D hadrons ➔ to resolve fast oscillations 2. momentum resolution ➔ to separate topologically similar final states B tag 3. K/p separation ➔ to separate topologically similar final states ➔ to tag B flavor K-K-

30 key features of a beauty experiment BsBs DsDs K+K+ K+K+ K-K- p-p- 1. vertex resolution ➔ to identify B and D hadrons ➔ to resolve fast oscillations 2. momentum resolution ➔ to separate topologically similar final states B tag 3. K/p separation ➔ to separate topologically similar final states ➔ to tag B flavor K-K- 4. muon, electron and photon ID ➔ for various other interesting final states ➔ to tag B flavor 5. highly selective trigger ➔ to reduce rate to acceptable level ➔ based on muons, electrons, high pT hadrons, large IP tracks