2 The CDF Experiment at Fermilab Contents - Harvard University ...

Section 2: B Mixing and CP Violation 93
oscillation frequency, m s . Additionally, new physics contributing to the B s mixing `box'
diagram would cause a larger m s than Standard Model predictions even if the new physics
does not aect the angles of the unitarity triangle. Therefore, it is imperative to measure
m s as a prerequisite for any serious testing of the self-consistency of the CKM matrix.
To measure the B s oscillation frequency, one needs
1. proper time of the B s decay
2. decay avor of the B s meson, obtained from the B s decay products
3. production avor of the B s meson, inferred either from the decay products of the other
b-quark in the event (in pp collisions, b b are produced in incoherent pairs), or from the
byproducts of the b ! B s hadronization; this process is called avor tagging.
In preparation for the B s mixing measurement, the Harvard group is involved in the
following tasks:
Generic decay reconstruction tool: Postdoc Maksimovic wrote a generic tool able
to reconstruct an arbitrary decay.
Study of combinatorial background for the PAC: Maksimovic utilized this tool
to isolate a sample of events with a lepton and a D s decay in the opposite hemisphere
(to or K K), which provided a basis for a study of combinatorial background in
fully reconstructed B s ! D s (n) events, conrming the prior estimate of S=B between
1:2 and 2:1.
Vertex nding in D s X events: Maksimovic isnow focussed on investigating a technique
to nd the decay point ofaB s ! D s X decay using new Run II software framework
and tools adapted to Run I data.
Since the B s production avor is determined by the sti trigger lepton in the opposite
hemisphere (characterized by avery high purity of the avor tag), the B s decay vertex
is the only ingredient missing in a B s mixing analysis. Given that D s X sample is a
superset of D s (n) sample designated for B s mixing, this approach has a potential to
be the rst analysis to actually measure m s in Run II.
Other tagging studies: Maksimovic isinvolved in other studies of the `opposite side
tagging' (avor tagging involving decay products of the b-hadron in the opposite hemisphere),
using the samples of B 0;+ ! `+D () decays.