1 Introduction - Caltech High Energy Physics - California Institute of ...

10 Introduction
Measuring γ
Table 1-6 lists two expected statistical errors on the measurement of γ with 10 ab −1 . The more conservative
error estimate of 2 ◦ − 3 ◦ is obtained employing only methods and decay modes that have already been
observed and used in γ-related measurements. These are B ± → DK ± with D 0 → K − π + , D 0 → CP -
eigenstates, and D 0 → KSπ + π − .The sensitivities are estimated from the quoted experimental references.
The range in the estimates is due to current uncertainties in the ratio between the interfering b → u and
b → c amplitudes, taken to be between 0.1 and 0.2. The mode D 0 → KSπ + π − is especially important in
that it reduces the 8-fold asymmetry to a 2-fold asymmetry.
The less conservative estimate of 1.2 ◦ − 2 ◦ is based on cautious assumptions about the sensitivities that
could be obtained with modes that have yet to be fully explored experimentally. One category of such
modes is additional multi-body D decays to final states such as π + π − π 0 , K + K − π 0 , KSK + K − , KSK + π − ,
KSπ + π − π 0 , K + π − π 0 ,andK + π − π + π − . The second category is B 0 → DK (∗)0 , with a time-dependentand
time-independentanalysis. The third category is B → D + KSπ − decays [16], which also requires a timedependent
analysis.
It should be noted that there are additional modes and methods, not included in the γ sensitivity estimates of
Table 1-6, that can be used to measure γ. These methods presently suffer from difficulties in obtaining a clean
extraction of γ, which will likely be resolved in the future. Examples include sin(2β + γ) inB → D (∗)+ π − ,
B → D (∗)+ ρ − , where BABAR has already published measurements of CP asymmetries and constraints on γ. It
is not clear, however, whether the ratio between the interfering b → u and b → c amplitudes can be measured
with sufficient precision for these measurements to be competitive with the B → DK measurements at high
luminosity. The estimates also exclude the possible contribution of B ± → DK ± π 0 , where experimental
issues are yet to be resolved and the level of interference is not yet known.
1.2.3 Physics Performance Projections
Various benchmark physics measurements, discussed in Sections 1.2.1 and 1.2.2, have been used to illustrate
the physics reach of a Super B Factory on the basis of integrated samples. In some cases, comparisons with
hadronic experiments are also possible. A set of assumptions has been made concerning the pace at which
these projects reach their design luminosity goals, as summarized in Table 1-7. These assumptions then form
the basis for time varying projections of effective tagged samples in a number of important channels (observed
yield weighted by effective tagging efficiency). Finally, the effective tagged sample sizes, when combined with
measured or simulated single event sensitivities can be used to project the errors on benchmark observables.
In the case of the e + e − collider options the samples are assumed to be continuations of the event samples
obtained at PEP-II through the end of the already planned program. In all cases, PEP-II is assumed to
cease operations at the point when installation of the upgraded collider must begin. Integrated luminosities
in these periods are taken from the published PEP-II plan.
Figure 1-3 shows the time evolution of the error on the sine coefficient for time-dependent CP violation in
various b → s Penguin modes. In this case the error reaches below 0.04 in most case within two years, which
is the regime that is relevant for definitive demonstration of potential New Physics in such modes. Figure 1-7
shows the error evolution for the electromagnetic Penguin mode B 0 → K 0 Sπ 0 γ.
Figure 1-4 shows the effective tagged sample accumulations and expected evolution of the error on the
sine amplitude in time-dependent CP asymmetries for B 0 → π + π − . In this case both LHCb and BTEV
are capable of measurements, as well as a Super B Factory. However, only a Super B Factory is capable
of doing the complete isospin analysis of the two-body modes in order to obtain the correction from the
determination of αeff in the CP asymmetry from the charged mode to the unitarity angle α. The evolution
of this correction as a function of time is shown in Figure 1-5. The error on sin 2α falls below 0.05 within
two years of startup for the Super B Factory.
The Discovery Potential of a Super B Factory