High precision and new CP violation measurements

with LHCb

Michael Koratzinos, CERN

EPS HEP 99Tampere ,15 July 1999

Brazil

France

Germany

Italy NetherlandsPRC 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

• 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 (b500 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 Vtd Vud

+Vts Vus+Vtb Vub

= 0

Vub

Vcb

Vtd

Vub

Vtd

Vts

Bd J/KSBd D

Bd

Bs J/

Bs DSK

(,)

(0,0) (1,0)

BsKKBd

Here we will have results from earlier generation experiments but LHC will provide high statistics

•B0 J/Ks (measures sin(2)); sin20.05 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)

•Particle ID essential

•BUT Penguin diagram uncertainty: theory brick wall at 2-5 degrees if P/T 10% - Challenge to theory!

•B0 : Alternative channel for that bypasses the penguin problem; multi parameter fit, so need statistics (>5k events) [LHCb: 1k events/year]

•B0d D*+ ,a1

+ measures () - need large statistics; LHCb can get >500k events/y (D*+ and D*a1

+) ; 100 in 1 year. Theoretically clean.

Bd sector

Need to know P/Tto better than 10%

Bs sector•No results from B factories

•Measurements require sensitivity to Bs oscillations - good proper time resolution is needed

•Bs J/ 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

• equivalent of Bd J/ KS

• CP asymmetry allows to extract the phase of Bs mixing amplitude, i.e. angle

Bs J/

iVVJB

iVVKJB

tstbs

tdtbSd

2exp:/

2exp:/2*

2*

• 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

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 Bs Ds background

Essential features:Bs DsK+, Ds

+K

~ 2.5 k events / year with S/B > 10 (reconstructed & tagged)

depends on , ms,and strong phase(will be extracted as well)

No penguindiagram

contributions

~ 10o in one year

Can only be done at LHCb

Bs 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,20 for =760 in 5 years

ms=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 Bd sector will benefit from high statistics

•B0 J/Ks can probe direct CP violation •B0 large theoretical uncertainties due to penguin diagrams •B0 multi parameter fit avoids the penguin problem•B0

d D*+ ,a1+ theoretically clean measurement for

•The Bs sector will be exploited to good effect•Bs J/LHC-wide precision measurement•Bs DsK theoretically clean measurement, LHCb specific•Bs K K LHCb specific measurement