Transcript No Slide Title

High precision and new
CP violation measurements
with LHCb
Michael Koratzinos, CERN
EPS HEP 99
Tampere ,15 July 1999
The LHCb Experiment
Brazil
USA
Finland
Ukraine
France
UK
Germany
Switzerland
Italy
Poland
PRC
Netherlands
Romania
Russia
Spain
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
• 2000-2002: 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, 1012 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 Bs DSK: m = 11 MeV/c2
The LHCb Detector
Angles of CKM Unitarity Triangles
(and decay modes to measure them discussed in this talk)



Vtd Vtb +Vcd Vcb +Vud Vub = 0
Bd r


Vcb
Vtd
Bs DSK
(1,0)
Bd J/yKS
Vub

Vtd
Vts


(0,0)
Bd D

BsKK
Bd 
(r,)
Vub

Vtd Vud +Vts Vus +Vtb Vub = 0

Bs J/yf
Bd sector
Here we will have results from earlier generation experiments but LHC will
provide high statistics
•B0 J/yKs (measures sin(2)); sin20.05 by 2005
•High statistics at LHC (LHCb: 45k tagged events per year) can reduce
this ultimately to 0.006  Can probe direct CP violation
•B0   (measures (2 +2) or (-))
•B factories total: <1000 events by 2005;
LHCb: 7k events/year (assuming Br=0.7X10-5)
Need to know P/T
to better than 10%
•Particle ID essential
•BUT Penguin diagram uncertainty: theory brick wall at 2-5 degrees
if P/T 10% - Challenge to theory!
•B0  r : Alternative channel for  that bypasses the penguin problem;
multi parameter fit, so need statistics (>5k events) [LHCb: 1k events/year]
•B0d D*+ ,a1+ measures (2) - need large statistics; LHCb can get
>500k events/y (D*+ and D*a1+) ;   100 in 1 year. Theoretically clean.
Bs sector
•No results from B factories
•Measurements require sensitivity to Bs oscillations - good proper
time resolution is needed
•Bs  J/y measures sin(2) no particle ID needed, also
good for ATLAS/CMS
•Bs  DsK measures  (2 ); Ds background , so use RICH
•Bs  KK use theory to relate to Bd   allows  and 2 to
be determined simultaneously
Bs  J/y
•
•
LHC-wide precision measurement
equivalent of Bd  J/y KS
B  J /y K :V V   exp 2i  
CP asymmetry allows to extract the
B  J /y f : V V   exp2i 
d
phase of Bs mixing amplitude, i.e. angle 
S
2
*
tb td
2
*
tb ts
s
[B physics working group]
• decay into spin-1 particles:
J/yf 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
Current
limit
Good place to look
for new physics
Bs  DsK+, Ds+K
Extraction of 2 from 4
time-dependent decay rates,
then use  from J/yf to get 
 Theoretically clean
Essential features:
• hadron trigger
• proper time resolution
• mass resolution
kill Bs Ds 
background
• K/ separation (RICH)
No penguin
diagram
contributions
 ~ 10o
in one year
~ 2.5 k events / year with S/B > 10
(reconstructed & tagged)
Can only be done at LHCb
depends on , Dms,
and strong phase
(will be extracted as well)
Bs  KK
Used in conjunction
with B   to
extract  and 
LHCb: 4k reconstructed
and tagged events/y
Dms=20ps-1
Can only be done at LHCb
•Need Hadron trigger
•Need Particle ID
•Need good proper time resolution
Under certain assumptions,
20 for =760 in 5 years
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 Bd sector will benefit from high statistics
•B0 J/yKs can probe direct CP violation
•B0   large theoretical uncertainties due to penguin diagrams
•B0  r multi parameter fit avoids the penguin problem
•B0d D*+ ,a1+ theoretically clean measurement for 
•The Bs sector will be exploited to good effect
•Bs  J/y LHC-wide precision measurement
•Bs  DsK theoretically clean measurement, LHCb specific
•Bs  K K LHCb specific measurement