Claudio Campagnari

Professor of Physics

Addresses

UCSB

SLAC
5119 Broida Hall
Physics Department
University of California
Santa Barbara, CA 93106		 Stanford Linear Accelerator Center
Mail Stop 35 - UC Santa Barbara Group
2575 Sand Hill Road
Menlo Park, CA 94025
Office: Room 258 - Building 48 (ROB building)
(805)893-7567 (office)
(805)893-8959 (lab)
(650)926-2472 (office)
(805)893-8597 (fax) (650)926-8522 (fax)
claudio@charm.physics.ucsb.edu claudio@slac.stanford.edu

Teaching, Summer 2009

Physics 2

Research

BaBar is an experiment at the PEP II collider at the Stanford Linear Accelerator Center (SLAC) designed to study matter-antimatter asymmetry (aka CP-violation) in the decay of B-mesons. BaBar is a collaboration of several hundred physicists and engineers from all over the world. The UCSB BaBar group is led by Jeff Richman and me.

Between 1996 and 1999 we assembled the inner three layers of the BaBar Silicon Vertex Tracker (SVT) in our laboratories on the UCSB campus. The SVT is a five-layer, double-sided, micro-strip detector installed around the PEP II beampipe. The main purpose of the SVT is to precisely measure the position of decay vertices. Since the CP-violating effects must be measured as a function of the decay length, good performance of the SVT is crucial to the success of the BaBar program. A second goal of the SVT is to measure the trajectories of low momentum (around 100 MeV/c) tracks, since these curve in the solenoidal magnetic field and do not reach BaBar's drift chamber.

The SVT was installed in BaBar in April 1999, and has been working very well ever since. Our group remains involved in the operation and the maintenance of the SVT. Our students serve regular stints as SVT on-call experts. We have also made several contributions to tracking and calibration software, and to studies of the impact of future radiation damage and/or high machine background conditions. Between 2000 and 2003 I was the co-system manager of the SVT system. During that time, our group also built additional SVT modules that could be installed in the summer of 2005 to replace the modules in the horizontal plane of the machine, where the damage from radiation is most severe.

A second important aspect of my research at BaBar is physics analysis. My initial focus was on the flagship measurement at BaBar, namely the measurement of the CP violating parameter sin2beta. In collaboration with groups from Livermore and Italy, we first concentrated on the J/Psi Klong mode. This mode is much harder to reconstruct than the so-called golden mode, J/Psi Kshort. However, it is just as clean theoretically, and among the several modes used for the sin2beta measurement, it is second only to the golden mode in statistical power. Furthermore, because the CP of J/Psi Klong is opposite to that of J/Psi Kshort, the CP asymmetry as a function of time (or decay length) changes sign between J/Psi Kshort and J/Psi Klong.

The first step in this program was the establishment of the J/Psi Klong reconstruction. This resulted in the measurement of the B0 --> J/Psi Klong branching ratio which was published in Physical Review D ( Phys. Rev. D65, 032001 (2002) or hep-ex/0107025).

Subsequently, the J/Psi Klong sample was used for measuring sin2beta. As the reconstruction of J/Psi Klong matured, our group took on more responsibilities in other aspects of the sin2beta measurement. In 2001, my postdoc Owen Long became co-convenor of the sin2beta group. My student Stephen Levy wrote one of the two US PhD theses on the measurement of sin2beta.

The measurement of sin2beta represents the first evidence of CP violation outside the kaon system. Here are links to the 2001 and 2002 SLAC press-releases. Here are links to the BaBar sin2beta publications to which we contributed: We expect to submit one more update with over 200 fb^-1 of data in the summer of 2004.

More recently, I have been investigating the possibility of measuring the angle gamma of the unitarity triangle at BaBar. One of the more popular methods for measuring gamma is to exploit the quantum mechanical interference between B- --> D0 K- and B- --> D0bar K-, which can occur when the D0 and D0bar decay to a common final state, see figure below:

The measurement of gamma at BaBar is very difficult. This is basically because the B- -->D0bar K- amplitude is about ten times smaller than the B- --> D0 K- amplitude since it is both CKM and color suppressed (with respect to B- --> D0 K-). Somebody once said: beta is easy, alpha is hard, gamma is impossible! However, the prospects for measuring gamma have brightened somewhat in the past few years for three reasons:
  1. The B-factory experiments (BaBar and Belle) are collecting data faster than most people anticipated.
  2. In the past few years there have been quite a few new proposals for methods to measure gamma.
  3. New data on color-suppressed b->c transitions suggest that color suppression could not be as severe as previously thought.
It is doubtful that a precise measurement of gamma will come from a single measurement. However, it is possible that by combining several measurements from both BaBar and Belle in a few years we will end up with a very interesting measurement.

As a first step in the program to measure gamma, I have measured, in collaboration with UCSB postdoc Wouter Verkerke and (former) UCSB graduate student Stephen Levy, the branching ratio and polarization of B- --> D*0 K*- ( Phys. Rev. Lett. 92, 141801 (2004) or hep-ex/0308057).

Then, following the suggestions from Atwood, Dunietz, and Soni (ADS, Phys. Rev. Lett. 78 3257 (1997) or hep-ph/9612433) we have looked for the decay B- --> D0 K- or D0bar K- with the D0 or D0bar decaying into K+pi-. This final state can be reached through the favored B- --> D0 K- decay followed by the suppressed D0 --> K+ pi- decay, or through the suppressed B- --> D0bar K- decay followed by the favored D0bar --> K+pi- decay. Thus, the two interfering amplitudes are comparable in size, although they are both quite small. The analysis was done by myself and UCSB postdocs Wouter Verkerke and Owen Long. Unfortunately we did not see a signal in approximate 100 fb^-1 of data. This means that the interference between the two amplitudes is destructive and/or that the color suppressed amplitude is smaller than we had hoped. This work has been submitted for publication (hep-ex/0402024). We are now working on an update of this analysis with twice the data. We are also investigating the mode with a D*0 or D*0bar in place of the D0 or D0bar. Results should become available by the end of the summer of 2004.

Finally, with UCSB graduate students Adam Cunha and Bryan Dahmes, I am pursuing topics in rare B decays and I am carrying out a test of factorization in multi-body B decays. Results from these analyses should come out by the end of the summer of 2004.

The Compact Muon Solenoid (CMS) is one of the two huge multi-purpose detectors that are being built to study proton-proton collisions at the new Large Hadron Collider (LHC) at the Center for European Nuclear Research (CERN) in Geneva, Switzerland. The UCSB CMS group is led by Joe Incandela and me.

LHC and CMS are being built to explore the highest energies and the shortest length scales. It is expected that the LHC experiments will elucidate the electroweak symmetry breaking mechanism, and there is a very good chance that they will find new physics. These experiments will come on line in 2007-8.

Our group is responsible for the assembly of approximately one-half of the Tracker Outer Barrel (TOB). The other half of the TOB is being assembled at Fermilab. Joe Incandela is the leader of the US TOB group.

The TOB is a very large silicon detector for tracking charged particles in the large radius, central region of the detector. This is the area that has been traditionally covered by gaseous detectors (drift chambers) in collider experiments. However, such detectors would not work in the extreme conditions of the LHC, and therefore we have to build a silicon detector of an unprecedented scale. Construction of the TOB is underway in our laboratories on the UCSB campus.

As the beginning of LHC physics approaches, we are starting to turn our attention to software reconstruction and physics studies. This is an area where new members joining the group will have an opprtunity to contribute.

In a previous life, I worked on the search for the top quark as a member of the CDF collaboration at the Fermilab Tevatron Collider. Well, we found it.

Here is a copy of the paper published in Physical Review Letters (Postscript).

Here is the Review of Modern Physics article on the discovery of the top quark.

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