Joint High Energy Physics/Theory Seminars
HEP/theory seminar mailing list
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2009/2010
Organizers: Ashutosh Kotwal, Kate Scholberg and Tom Mehen
Held in Duke Physics Room 278 (old Room 246) (Unless otherwise noted)Regular times for Fall '09 semester: alternating between Mondays 11 am and Mondays 1 pm.
Regular time for Spring '10 semester: Wednesdays 1:30 pm.
August 5: Denis Perevalov, U. of Alabama, 3 pm
MiniBooNE is an experiment operated at Fermilab looking for neutrino oscillations at Delta m^2 ~ 1eV^2. MiniBooNE uses a neutrino beam produced from 8 GeV protons from the Fermilab Booster incident on a Be target. The Cerenkov detector located 541m from the target is a 12m diameter sphere filled with mineral oil and instrumented with 1280 inner and 240 veto PMTs. Neutral current elastic scattering (NCE) is one of the most important neutrino interactions in MiniBooNE. To date we have recorded about 94.5K NCE interactions candidates in the neutrino mode with about 65% NCE purity, which represents the world's largest sample of such interactions. The MiniBooNE NCE cross-section has been measured and will be presented as well as the measurement of the axial vector mass (M_A) and the strange quark contribution to the nucleon spin (Delta s).
August 31: Ke Han, Yale U., 11 am
Strange Quark Matter (SQM) is a proposed state of hadronic matter made up of roughly one-third each of up, down, and strange quarks in a single hadronic bag. For the last three decades, a wide range of experimental searches for strangelets (small lumps of SQM with baryon number less than $10^6$) have been conducted but all failed to give a definite answer to the existence of SQM. We report results from a search for strangelets in a lunar soil sample, in which the predicted strangelet concentration is about $10^4$ times higher than that on the Earth. The search used the tandem Van-de-Graaff accelerator at Yale as an ultra-sensitive mass spectrometer. We have searched over a range in mass from A=42 to A=70 amu for nuclear charges 5, 6, 8, 9, and 11. No strangelets were found in the experiment. For strangelets with nuclear charge 8, a concentration in lunar soil higher than $10^{-16}$ per normal atom is excluded at the 95% confidence level. The implied limits on the strangelet flux in cosmic rays are the most sensitive to date for the covered range and are relevant to both recent theoretical flux predictions and a strangelet candidate event found by the AMS-01 experiment.
September 8: Geumbong Yu, Duke U., 1 pm: NON-STANDARD DAY
We report on the first direct search for charged Higgs bosons decaying into c-sbar in t-tbar events produced by p-pbar collisions at sqrt(s) = 1.96 TeV. The search uses a data sample corresponding to an integrated luminosity of 2.2/fb collected by the CDF II detector at Fermilab and looks for a resonance in the invariant mass distribution of two jets in the lepton+jets sample of t-tbar candidates. We observe no evidence of charged Higgs bosons in top quark decays. Hence, 95% upper limits on the top quark decay branching ratio are placed at B(t -> H+ b) <0.1 to 0.3 for charged Higgs boson masses of 60 to 150 GeV/$c^2$ assuming B(H+ -> c=sbar) = 1.0. The upper limits on B(t -> H+ b) are also used as model-independent limits on the decay branching ratio of top quarks to generic scalar charged bosons beyond the standard model.
September 14: Oleg Perevozchikov, U. of Tennessee, Knoxville, 11 am
I will present the results of the search for the electron antineutrinos from the Sun with Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND). There is no known direct production of the electron antineutrinos in the Sun. However, in the some theoretical models with the large neutrino magnetic moment antineutrinos from the Sun can be produced e.g. via Spin Flavor Precession mechanism (SFP). Search for solar antineutrinos potentially can provide new information about fundamental properties of neutrinos. The most sensitive one-kiloton antineutrino detector KamLAND gives the possibility to search for such antineutrinos. The analysis described in this dissertation is based on 1425.9 days of data collection in KamLAND. The search for the electron antineutrinos have been made within 8.8-16.3MeV antineutrino energy range, that is above energies of reactor antineutrinos and where properties of the solar B8 neutrinos are well studied. Based on the number of observed candidates and estimated background rates the upper limit on the electron antineutrino flux and probability of conversion electron neutrinos produced in the Sun to electron antineutrinos was set. The same limit can be used on the diffuse Supernovae neutrino flux. The estimated background rates during this study can make significant impact on the design of the future neutrino scintillator detectors.
September 28: Laura Loiacono, University of Texas at Austin, 1 pm
Neutrino interactions at low neutrino energies are of three types: quasi-elastic, resonance, and deep inelastic scattering. The admixture of these types are of interest to long baseline neutrino oscillation experiments which require precise neutrino energy reconstruction of charged current neutrino interactions in the low energy region. Relatively few low energy neutrino cross section measurements exist and are dominated by uncertainties in the neutrino flux from low energy neutrino beams.
Currently, the MINOS neutrino oscillation experiment and the MINERvA neutrino interaction experiment utilize the low energy neutrino beam produced by the NuMI beam line at Fermilab. The NuMI beam line has 3 muon monitors which can be used to measure the muon flux from the beam line. The muon flux is related to the neutrino flux because one muon is produced for every muon neutrino in pion and kaon decays. We measure the neutrino flux generated by the NuMI beam line by measuring the daughter muon flux produced in pion and kaon decays. This flux will be used to measure neutrino cross-sections via sigma_nu = N_nu/phi_nu, where the numerator is the number of neutrino events seen in the MINOS Near Detector. Preliminary measurements of the neutrino flux obtained from the muon monitoring system will be presented.
February 3: Colin Anderson, Yale University, 1:30 pm
Many current generation and planned oscillation experiments are searching for electron neutrino appearance. These experiments must contend with the background posed by neutral current single pi0 (NC 1pi0) production. If one the two photons from the pi0 decay fails to be detected, the pi0 may be misidentified as a single electron--the sought after signal in such oscillation searches. In order to maximize their sensitivity to such parameters as the mixing angle theta_13 or the CP-violating phase delta_CP, rigorous constraints on the pi0 background will have to be established. However, the predictions of the myriad models of single pion production vary widely and previous measurements are relatively scant. A measurement of the absolute NC 1pi0 cross section will prove valuable in constraining both models of production as well as the background to nu_e appearance searches. Since releasing the results of its principal oscillation analysis, the MiniBooNE experiment has focused on using its enormous set of recorded neutrino and antineutrino interactions to produce multiple cross section measurements. Among these measurements are absolute differential cross sections for NC 1pi0 production for both neutrinos and antineutrinos, which will be presented here. These cross sections are the first absolute and first differential cross sections for NC 1pi0 production and they encompass samples of neutrino and antineutrino events that are roughly an order of magnitude larger than any other sample at O(1 GeV). Liquid Argon Time Projection Chambers (LArTPCs), an emerging neutrino detector technology with robust particle identification capabilities, will also be discussed.
May 5: Jon Link, Virginia Tech, 1:30 pm
Mega-Curie electron capture neutrino sources have the potential to be among the most intense sources of neutrino flux. They have previously been used to calibrate the solar neutrino detectors Gallex and Sage. Advances in neutrino physics and detector technology have opened up new possible uses for these sources. I will examine the prospects for producing mega-Curie scale sources in the US using the High Flux Isotope Reactor at Oak Ridge National Lab, and I will outline a two experiments that could be done with such sources: a sterile neutrino oscillation search using the LENS solar neutrino technology, and a precision neutrino magnetic moment search using a liquid noble gas detector.
May 11: Christopher Hays, Oxford U, 1:30 pm
Various studies of collider and cosmological data have found multi-lepton sources that are not described well by the usual models. These studies have motivated a theory of a new force at the O(1 GeV) energy scale that interacts with standard-model particles only through a high-mass intermediary. This new 'dark' force could produce multiple leptons at small relative angles, dubbed 'lepton jets,' at hadron colliders. I describe a general CDF search for high-momentum muon pairs with sensitivity to any new low-mass resonance. I also briefly discuss the possibility that the Higgs boson is a source of high-momentum dimuons, with a mass lower than the usual LEP bounds and more consistent with supersymmetry and the global electroweak fits.
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