BaBarW. Bhimji, D. Bowerman, P. D. Dauncey, U. Egede, R. Flack, G. Morton, J. A. Nash and D. J. Price

The BaBar detector is located at the PEP-II electron-positron collider at the SLAC laboratory in California. The BaBar collaboration is studying CP violation using B mesons. In 2001 it made the world’s first observation of this phenomenon in B decays through the measurement of the parameter sin2 of the CKM matrix. This parameter is indicative of the “indirect” type of CP violation. Within the last year, BaBar has produced the first evidence for the other, “direct”, type of CP violation in B mesons using charmless hadronic B decays.

The Group is heavily involved in such measurements of charmless decays. An example of a computer reconstruction of a charmless B decay observed in the BaBar detector is shown in Fig. XXX. These decays are sensitive to different CKM parameters from indirect CP violation, and allow estimates of sin2 and . So far, only one charmless mode has show significant direct CP violation so these parameters are not yet accurately determined. However, BaBar is scheduled to continue data-taking until 2008 and is expected to quadruple its data sample over that time. This will allow many more modes to be accurately measured, giving a major improvement in the state of knowledge of the CKM matrix parameters. The Group intends to continue to work in this important area over the coming years.

Figure XXX: An example of a B decay candidate in the channel KKKS as observed in the BaBar detector. The thin blue lines show the reconstructed charged particle trajectories, the green blocks indicate electromagnetic energy in the calorimeter, the pink dots show detected Cherenkov light which is used to identify the type of particles and the large blue blocks indicate hits in the outer flux return chambers.

Calice D. Bowerman, P. D. Dauncey, D. J. Price and O. Zorba

A high energy electron-positron linear collider with centre of mass energies up to 1000 GeV is seen as the next major accelerator for particle physics. Such a collider would allow precision measurements of any Higgs (or SUSY) particles in this mass range as well as having a significant discovery potential for other postulated particles.

To fulfil the physics potential of this machine, the calorimetry for a detector at such a collider needs to be able to reconstruct jet energies with resolutions exceeding anything previously achieved. The Calice collaboration has been formed to study both electromagnetic and

hadronic calorimetry for a linear collider detector. The experimental programme is to take large data samples of test beam data for accurate comparison with simulations.

The Imperial group has lead the design of the readout electronics for the prototype high-granularity electromagnetic calorimeter within this collaboration. Fig. YYY shows one of the custom-built readout boards. These have been used in the first set of beam tests early in 2005 with electrons of various energies. Fig. ZZZ shows the electromagnetic calorimeter at the beam test area. These tests will continue throughout 2005-7 at several locations around the world and will build up a unique dataset of electromagnetic and hadronic showers measured with state-of-the-art calorimetry. This will prove invaluable for designing a realistic calorimeter for the linear collider detector.

Figure YYY: Prototype version of the CALICE electromagnetic calorimeter readout board. This is a 9U VME board which can read out, digitise and store up to 1800 channels of calorimeter information at a rate above 1kHz.

Figure ZZZ: Test beam area at the DESY laboratory, showing the electromagnetic calorimeter in the beam line in January 2005. This first round of tests lasted six weeks and over 20 million electromagnetic showers were recorded.

Figure ZZZ: Test beam electromagnetic calorimeter in the beam line at the DESY laboratory. The readout electronics are shown protruding from the tungsten structure which housed the silicon diode detecting elements. This calorimeter was used in the first round of tests which lasted six weeks where over 20 million electromagnetic showers were recorded.