Sep 15, 2008

Recent results of muon neutrino disappearance from the MINOS experiment

Bob Armstrong (IU)

We will present measurement of dijet angular distribution using variable chi, defined as the exponential of absolute rapidity difference between two leading jets in an event.

    The measurement was done using dataset collected by the D0 experiment during the 2004-2005 running at the Fermilab Tevatron Collider and corresponds to an integrated luminosity of 0.7 fb-1. The distributions are presented in ten dijet invariant mass bins starting from 0.25 TeV and going all the way over 1.1 TeV.

    This is the first time in a collider based experiment where we directly probe dijet invariant mass beyond 1 TeV. The data are in good agreement with the prediction of the perturbative QCD, and are used to constrain several models of new physics beyond standard model.

Sep 29, 2008

I will present highlights of the CKM 2008 conference held in Rome in September.   I will introduce briefly the  various topics and show some of the most interesting results presented at the conference.

Oct 6, 2008

An analysis of J/psi and Upsilon production at LHC is expected to be one of the first physics results to come out of ATLAS. An overview of the theoretical models will be given, followed by discussion of the expected ATLAS performance for quarkonium reconstruction and its ability to distinguish various proposed production mechanisms, as well as the expected precisions for measurements of the cross-section and polarisation of quarkonia with early data. The uses of J/psi and Upsilon for commissioning and data quality monitoring of the detector will also be highlighted.

Oct 27, 2008

Sep 22, 2008

Oct 13, 2008

Oct 20, 2008

Many extensions of the Standard Model result in neutral particles that are weakly coupled and have decay lengths comparable with LHC detector dimensions. Examples are gauge-mediated SUSY extensions of the MSSM, split SUSY, and the Hidden Valley Scenarios. In the Hidden Valley models long lived  particles that decay to quark and tau pairs can be produced in SUSY processes, Z’ decays and Higgs Boson Decays.

    A common feature of many of these models is that a Higgs boson, by mixing with other scalar fields, can decay to long-lived neutral particles which then decay to four jets with displaced vertices. Such long-lived states, which may decay anywhere within the detector volume, challenge both the trigger and reconstruction capability of LHC detectors. In this talk I will discuss signature-driven triggers we have developed to select such events in the ATLAS detector.

Nov 3, 2008

The Standard Model describes the unification of electromagnetic and weak interactions. It was thoroughly tested over past thirty years, and represents one of the major successes of modern physics. This theory predicted the existence and the masses of the weak bosons. The last remaining piece of the puzzle is the Higgs boson whose existence is crucial for our understanding of the origin of particle masses.

    Direct searches at LEP put a lower limit on the Higgs boson mass, and together with precision measurement constrained it to ~<200 GeV. The D0 and CDF experiments at the Tevatron recently excluded a new interval in the Higgs mass. In this time when we are entering LHC era, we are coming closer to the discovery or exclusion of the SM Higgs boson.

  I will discuss current searches for the SM Higgs boson with the D0 experiment at Tevatron, highlighting the most important techniques. I will also draw a parallel with future searches at LHC, showing what we can learn from Tevatron experience.

Nov 10, 2008

For a decade, the PEP-II/BaBar B-factory has been a flagship experiment in precision measurements in the flavor sector, notably in the decays of B and charm mesons. Before its shutdown in April, the B-factory took a new direction and secured the world's largest samples of Upsilon(3S) and Upsilon(2S) mesons and performed an extensive scan above the Upsilon(4S) resonance.

    I will talk about the motivation for this change of course and our new results in both the search for the ground state of bottomonium and the search for evidence of new physics at a low mass scale, including both the Higgs and dark matter.

Nov 17, 2008

Nov 24, 2008

Dec 1, 2008

The B_c meson is an unique laboratory for studying QCD since it consists of two heavy quarks and decays via the weak interaction, allowing for the study of the weak decay properties in the framework of non-relativistic QCD.

    I review a measurement of the B_c lifetime at CDF using semileptonic B_c decays to J/psi particles and leptons. The result is compared to previous measurements of the B_c lifetime, and the measured quantities are used while discussing possible constraints on the theoretical predictions of the lifetime.

November 18, 2008 11:00 AM (Special Seminar)

Dec 8, 2008

We have studied two cosmic ray physics problems in the MINOS far detector.

    In the first, we have measured the muon charge underground as a function of energy and then projected our results back to the surface. In the range of surface energies between 1-7 TeV, we find the data are consistent with the charge ratio being energy independent. When the MINOS results are compared with measurements at lower energies, a clear rise in the charge ratio is apparent. A qualitative model shows that the rise is consistent with an increasing contribution of kaon decays to the muon charge ratio.

    In the second problem, we studied charge-separated atmospheric neutrino-induced muons. We find oscillation parameters consistent with the more precise accelerator-based measurements.

The existence of dark matter and dark energy comes from observing conventional matter and its gravitational effects, noting a discrepancy between the two, and postulating an extra source of stress-energy to compensate.  

    However, it might instead be the case that the laws of gravity could be modified to explain this discrepancy, and several theories have attempted to do this.  This approach, while potentially fruitful, runs a risk of introducing instabilities in other gravitational interactions.  

    I will briefly review such theories, and then present results concerning the stability of modified gravity theories of recent interest.

After a brief review of the theoretical predictions and experimental difficulties presented by fully leptonic charged B decays, I will review the latest search for charged B decays into lepton neutrino pairs, where the lepton can be an electron, muon, or tau, in the recoil of a semileptonically decaying charged B.  This search uses the full data set collected at the BaBar experiment.

December 5, 2008 11:00 AM (Special Seminar)