Some of the conclusions reached at “Beyond 1034: Physics at a 2nd Generation B Factory”
(A personal summary - I. Shipsey)
- By about the end of 2002 the B factory experiments will have accumulated a sample of at least 100 million BB pairs each, Sin(2beta) will have been well-measured by BaBar, Belle, CDF, D0 and Hera-B. Direct CP violation may be seen by BaBqr and Belle, but whether it has been seen or not, we will need much larger data samples in order to probe the phases in loop decays and gain an understanding of the physics underlying CP violation and flavor mixing.
If direct CP violation occurs at a level comparable to that foreseen by the Standard Model through the Kobayashi-Maskawa mechanism, data samples of a few billion B \bar B events will be needed before the systematic study of phase structure through statistically significant measurements of CP asymmetries become possible. Even if an asymmetry is revealed in one mode, asymmetries in more modes will be required before we understand the pattern of phases. In addition, statistically significant measurements of rates in many rare, and less rare, processes will be required in order for reliable theoretical predictions of CP
asymmetries to be made.
There is therefore a strong case to upgrade PEP-II and KEK-B to the highest possible luminosities (roughly 3 x 10^34). Note: three years at 3 x 10^34 , plus earlier accumulated data leads to a sample of about 1 billion BBbar pairs by about 2008.
- It is hard to justify the expense of a new machine unless the luminosity is at least a factor 10 higher than any existing e+e- machine can reach, and there are powerful tests of the Standard Model and searches for physics beyond the SM that can only be made at an e+e- machine with the very large B samples that would be obtained.
- It is not possible now to know how Babar, Belle, BTeV and LHC-b will fare over the next decade. In addition it is difficult to assess the role B physics will play if super symmetry is discovered, and can be readily studied directly, at the LHC. Therefore making the physics case for a new machine is difficult at this time.. One can make some general statements about the physics case however:
- By 2005 or so experiments at hadron colliders (BTev, LHC-B, CMS, ATLAS) will be coming on-line. There will be no shortage of produced B’s in these experiments but the background environment is difficult. Reconstructing final states containing a gamma, pi^0, eta, eta prime or omega will be challenging. On the other hand, access to the B_s and /\_b will give the hadron collider experiments a unique reach. The hadron colliders will provide important information for understanding flavor mixing and CP violation, but it is likely to be complementary to the information from e+e-.
- Taking experimental sensitivity studies at face value for the hadronic B experiments is the only option when comparing the capabilities of e+e- and hadron machines. At 3 x 10^35 an e+e- collider has the same number of measured B's as the hadron machines. Hadron machines will have to contend with significant backgrounds, which degrade the statistical power of the measurements. Therefore, for measurements involving a B0 or B+ the e+e- machine would be expected to have a comparable or greater physics reach at this luminosity.
- At 3 x 10^ 36 the statistical reach is a factor 10 greater than the hadron machine for measurements involving a B+ or B^0, and complementary for measurements involving the B_s.
- A conceptual design of a machine that may reach beyond 1x10^36 was presented. The machine is a challenging design. Estimating the time needed for accelerator R&D, construction of the machine and a detector is difficult, but 8-10 years is probably a reasonable estimate.
- The detector for such a machine will be challenging.
- Community wide support would be needed to build such a machine.
- It would be natural for this machine to turn on after a few years of running by PEP-II and KEK-B at their highest upgraded luminosities, This means the machine should turn on around 2008. Therefore R&D on such a machine should begin soon.
- Quite possibly, a unique and powerful physics case could be constructed for such a machine. Promising topics were identified and working groups formed. These included:
i. b-->snu nubar and other rare decays containing neutrals
ii. Precision V_ub
iii. A theoretically clean determination of gamma at the Y(4S) especially using B-->DK methods
iv. A theoretically clean determination of gamma at the Y(5S) using B-->DsK methods
v. CP asymmetries in a very large range of rare decays including final states with neutrals.
Example: new physics sensitive search for gamma in the Kpi/pipi system
vI. impact oftmeasurements in (I-IV) on CKM matrix
vii. Detector
viii. Machine
4)There will be a report back at the "second workshop" which will be a part of the Fourth International Conference on B Physics and CP Violation (BCP4) at Ise Shima, Japan, Feb 19-23 2001.
In conclusion, PEP-II and KEK-B are powerful tools at the high sensitivity frontier and there is a strong case to upgrade PEP-II and/or KEK-B to the highest possible luminosity. The utility of the e+e- approach to B physics likely does not cease at 3x10^34. A very high luminosity e+e- B Factory is a potentially even more powerful tool at the high sensitivity frontier. It is a natural successor to the fully upgraded PEP-II, and may be necessary to achieve a full understanding of CP violation. This idea is new and not yet ripe for judgment, however it is a topic that has already attracted considerable interest within the community and is being considered for further study at Snowmass 2001. Taking this idea to Snowmass will depend on the level of interest from the community at BCP4.