The BTeV Project at Fermilab Talk to DOE/Fermi Group Jan. 11, 2001 Introduction – Joel Butler Tracking detectors – David Christian Particle Identification – Simon Kwan Trigger and Data Acquisition – Erik Gottschalk Offline Computing – Rob Kutschke Interaction Region and C0 – Peter Garbincius Cost and Summary – Joel Butler Discussion Outline

What is BTeV? BTeV is a colliding beam experiment in the C0 Interaction Region of the Tevatron Its goal is to do a detailed study of CP violation (more in a moment!) in decays of particles containing b- quarks. It will start around 2006 and will compete directly with an experiment at the LHC called LHCb. To compete with an experiment at much higher energy, we have to employ very aggressive technology. In many ways, it is as challenging as ATLAS and CMS. BTeV is one of the most technically challenging HEP experiments.

Quick B physics - I The b quark was discovered at Fermilab by a collaboration led by Leon Lederman (including Appel, Brown, & Kaplan). Vital Statistics of the b-quark: (anti quark in []’s) Charge 1/3 [-1/3] Baryon number 1/3 [-1/3] Mass about 5.5 X the proton [same] Decay Lifetime when at rest 1.6X seconds[same] It has a special property called Beauty that must be conserved in all strong (nuclear strength) interactions but not in weak decays. Beauty quantum number –1 [+1]

Quick B physics - II B-quarks always materialize in association with other quarks: Lightest B Mesons bubdbs bu Antimesons: bdbs B+B+ B-B- B0B0 B0B0 BsBs BsBs Baryons: bud Antibaryons: bb Upsilon: bc B Factory Energy is too low to make these, and many more!!!! Heavier B Mesons BcBc BcBc

Quick B physics - III At the Tevatron, B particles are produced by the strong nuclear interaction of a 1 TeV proton with a 1 TeV antiproton. They must be produced in pairs, a b and an anti b-quark, to conserve the Beauty quantum number: B B But B’s decay into lighter quarks, which form lighter mesons and baryons, by the weak interaction, which doesn’t conserve the Beauty quantum number. If this were not so, B’s would be STABLE particles!

Quick B physics - IV When B’s decay, they can decay into many different “final states”, each called a decay mode. The fraction of times each “decay mode” occurs is called the “branching fraction” for that mode. Some modes have only two particles, others may have 5 or more. Nearly every type of particle in the high energy zoo can appear. B decays have another property. The lifetimes are “relatively long” because the weak interaction is “weak”. This enables B’s to travel a measurable distance – of order 1-10 mm from the main interaction – before they decay. So particles not coming from the main interaction, but appearing to come from a vertex separated from it are likely to be daughters of B decays

Quick B physics - V CP violation: the particles with b-quarks may not decay the same way as particles with b-antiquarks – an example of matter antimatter asymmetry. What could be different: The branching fraction of a B into a set of particles may be different from the branching fraction of an anti-B into the corresponding set of anti-particles; or The time structure of the decay, as measured by the distance traveled from the interaction vertex may not be the same Two important factoids: B’s are produced in only 0.1% of all collisions All decay modes expected to have large CP asymmetries are expected to have really small “branching fractions” These differences or “asymmetries”” between B’s and anti-B’s are the goal and we hope will tell us something about the evident matter-antimatter asymmetry of the universe.

What is BTeV? Because we are looking for a subtle effect in rare decays of rare events, BTeV must run at very high luminosity (intensity, collision rate) which means It must be radiation hard It must have an excellent trigger so it only needs to record a reasonable number of events It must have a high speed data acquisition system Because the key feature that distinguishes the particles from B decays from particles coming from the main interaction is that they decay away from the main vertex, we need precision tracking that has enough resolution to see the gap.

What is BTeV? Because the decays are so complicated and some have big asymmetries and some do not, we need to know the type of each particle in the decay. This means we need to be able to Identify charged hadrons – pions, kaons, protons (and their antiparticles) identify muons and electrons Reconstruct photons To make sure that there is nothing missing, we have to measure the momentum of all particles and show that they actually add up to the mass of a B. This requires a magnet- in our case a large dipole – and a superb downstream tracking system to measure the bend of each charged particle in the magnet

The BTeV Detector -PbWO 4 crystals Inside the beam pipe This detector, its trigger and its data acquisition system, will be capable of addressing whatever problems are likely to arise in bottom and charm quark physics.