High precision and new CP violation measurements with LHCb Michael Koratzinos, CERN EPS HEP 99 Tampere,15 July 1999

Brazil France Germany Italy Netherlands PRC Romania Spain Switzerland Ukraine UK USA The LHCb Experiment Poland Russia Finland

The LHCb collaboration: brief history & future Aug 1995: Letter of Intent (~30 institutes, 171 collaborators) Feb 1998: Technical Proposal (42 institutes, 336 collaborators) July 1998: Experiment approved : Technical Design Reports 2005: Ready to take data from day one of LHC operation

Overview LHCb is an experiment that will probe the Standard Model in the LHC era by performing accurate CP violation measurements in the B sector. The strength of the experiment is that it provides a complete package: it will not only measure accurately some CP violation parameters, it will measure enough parameters and in enough different ways to overconstrain the Standard Model. However, here I will give a selected overview on a small number of channels, concentrating on channels that are either difficult for earlier generation experiments or can be done with much greater precision in LHC.

Strengths of the LHCb experiment Statistics LHC is a copious B factory (  b  500  b, bb per year) Trigger designed to be highly efficient for B physics Particle ID - essential for background suppression in some channels Two RICH counters ensure good K-  separation in the required momentum range (1 to 150 GeV) Accurate vertexing - essential for good proper time resolution Silicon vertex detector in a Roman Pot (first tracking measurement close to vertex) Good mass resolution - in B s  D S K:  m = 11 MeV/c 2

The LHCb Detector

Angles of CKM Unitarity Triangles (and decay modes to measure them discussed in this talk) V td V tb  +V cd V cb  +V ud V ub  = 0V td V ud  +V ts V us  +V tb V ub  = 0     V ub   V cb  V td   V ub   V td  V ts  B d  J/  K S B d  D   B d  B s  J/  B s  D S K (,)(,) (0,0) (1,0) B s  KK B d 

Here we will have results from earlier generation experiments but LHC will provide high statistics B 0  J/  K s (measures sin(2  ));  sin2   0.05 by 2005 High statistics at LHC (LHCb: 45k tagged events per year) can reduce this ultimately to   Can probe direct CP violation B 0   (measures (2  +2  ) or (  -  )) B factories total: <1000 events by 2005; LHCb: 7k events/year (assuming Br=0.7 X ) Particle ID essential BUT Penguin diagram uncertainty: theory brick wall at    2-5 degrees if  P/T  10% - Challenge to theory! B 0   : Alternative channel for  that bypasses the penguin problem; multi parameter fit, so need statistics (>5k events) [LHCb: 1k events/year] B 0 d  D *   +,a 1 + measures (  ) - need large statistics; LHCb can get >500k events/y (D *   + and D *  a 1 + ) ;    10 0 in 1 year. Theoretically clean. B d sector Need to know P/T to better than 10%

B s sector No results from B factories Measurements require sensitivity to B s oscillations - good proper time resolution is needed B s  J/  measures sin(2  ) no particle ID needed, also good for ATLAS/CMS B s  D s K measures  (  2  ); D s  background, so use RICH B s  KK use theory to relate to B d   allows  and 2  to be determined simultaneously

equivalent of B d  J/  K S CP asymmetry allows to extract the phase of B s mixing amplitude, i.e. angle  B s  J/  This channel: good place to look for new physics This channel: good place to look for new physics decay into spin-1 particles: J/  can be CP-odd or CP-even (depending on angular orbital momentum)  need angular analysis to separate contributions Good proper time resolution needed can be done by ATLAS/CMS/LHCb with similar sensitivity Assumption: the decays to the 2 CP eigenstates have the same strong phase, i..e. r is real Assumption: the decays to the 2 CP eigenstates have the same strong phase, i..e. r is real LHC-wide precision measurement Good place to look for new physics Current limit [B physics working group]

Extraction of    from 4 time-dependent decay rates, then use   from J/  to get   Theoretically clean hadron trigger proper time resolution mass resolution K/  separation (RICH) hadron trigger proper time resolution mass resolution K/  separation (RICH) kill B s  D s  background Essential features: B s  D s  K +, D s + K  ~ 2.5 k events / year with S/B > 10 (reconstructed & tagged) depends on ,  m s, and strong phase (will be extracted as well) No penguin diagram contributions  ~ 10 o in one year Can only be done at LHCb

B s  KK Used in conjunction with B   to extract  and  Can only be done at LHCb Need Hadron trigger Need Particle ID Need good proper time resolution LHCb:  4k reconstructed and tagged events/y Under certain assumptions,    2 0 for  =76 0 in 5 years  m s =20ps -1

Conclusions LHCb will perform precision physics in the LHC era Its key features of Efficient trigger Excellent Particle identification Good mass and decay time resolutions will help to perform a multitude of measurements to probe the Standard Model The B d sector will benefit from high statistics B 0  J/  K s can probe direct CP violation B 0   large theoretical uncertainties due to penguin diagrams B 0   multi parameter fit avoids the penguin problem B 0 d  D *   +,a 1 + theoretically clean measurement for  The B s sector will be exploited to good effect B s  J/  LHC-wide precision measurement B s  D s K theoretically clean measurement, LHCb specific B s  K K LHCb specific measurement