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Open Access Publications from the University of California

Scholarly Works (33 results)

  • Article
Lawrence Berkeley National Laboratory (2006)

IceCube is a 1 km$^3$ neutrino observatory being built to study neutrino production in active galactic nuclei, gamma-ray bursts, supernova remnants, and a host of other astrophysical sources. High-energy neutrinos may signal the sources of ultra-high energy cosmic rays. IceCube will also study many particle-physics topics: searches for WIMP annihilation in the Earth or the Sun, and for signatures of supersymmetry in neutrino interactions, studies of neutrino properties, including searches for extra dimensions, and searches for exotica such as magnetic monopoles or Q-balls. IceCube will also study the cosmic-ray composition. In January, 2005, 60 digital optical modules (DOMs) were deployed in the South Polar ice at depths ranging from 1450 to 2450 meters, and 8 ice-tanks, each containing 2 DOMs were deployed as part of a surface air-shower array. All 76 DOMs are collecting high-quality data. After discussing the IceCube physics program and hardware, I will present some initial results with the first DOMs.

    Cover page: First Results from IceCube
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2018)
    The STAR collaboration has observed an excess production of e+e- pairs in relativistic heavy ion collisions, over the expectations from hadronic production models. The excess pairs have transverse momenta pT<150MeV/c and are most prominent in peripheral gold-gold and uranium-uranium collisions. The pairs exhibit a peak at the J/ψ mass, but include a wide continuum, with pair invariant masses from 400MeV/c2 up to 2.6GeV/c2. The ALICE Collaboration observes a similar excess in peripheral lead-lead collisions, but only at the J/ψ mass, without a corresponding continuum. This paper presents a calculation of the cross section and kinematic for two-photon production of e+e- pairs, and find general agreement with the STAR data. The calculation is based on the starlight simulation code, which is based on the Weizsäcker-Williams virtual photon approach. The STAR continuum observations are compatible with two-photon production of e+e- pairs. The ALICE analysis required individual muon pT be greater than 1 GeV/c; this eliminated almost all of the pairs from two-photon interactions, while leaving most of the J/ψ decays.
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2017)
      Ultra-peripheral collisions are the energy frontier for photon-mediated interactions, reaching, at the Large Hadron Collider (LHC), γ−p center of mass energies five to ten times higher than at HERA and reaching γγ energies higher than at LEP. Photoproduction of heavy quarkonium and dijets in pp and pA collisions probes the gluon distribution in protons at Bjorken-x values down to 3×10−6, far smaller than can be otherwise studied. In AA collisions, these reactions probe the gluon distributions in heavy ions, down to x values of a few 10−5. Although more theoretical work is needed to nail down all of the uncertainties, inclusion of these data in current parton distribution function fits would greatly improve the accuracy of the gluon distributions at low Bjorken-x and low/moderate Q2. High-statistics ρ0 data probe the spatial distribution of the interaction sites; the site distribution is given by the Fourier transform of dσ/dt. After introducing UPCs, this review presents recent measurements of dilepton production and light-by-light scattering and recent data on proton and heavy nuclei structure, emphasizing results presented at Quark Matter 2017 (QM2017).
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2023)
        High-energy vector meson photoproduction is an important tool for studying the partonic structure of matter at low Bjorken x. In the Good-Walker (GW) paradigm, the cross section dσ/dt for coherent production of vector mesons or other final states depends the average transverse distribution of gluons, while the incoherent cross section depends on fluctuations in the nuclear structure, due to variations in nucleon positions, and/or gluonic hot spots. However, predictions of the the GW paradigm seemingly conflict with data from multiple experiments which observe coherent production of vector mesons accompanied by nuclear excitation, or in peripheral relativistic heavy-ion collisions. These data are consistent with a simpler, semiclassical approach. I will discuss this contradiction and explore how and why GW fails. I will also contrast the significant differences in incoherent photoproduction on Au197 and Pb208 targets in the GW approach with the much smaller expected differences in their low-x gluon content.
          Cover page: Challenges to the Good-Walker paradigm in coherent and incoherent photoproductionCreative Commons 'BY' version 4.0 license
          • Article
          LBL Publications (2004)

          At very high energies, the Landau-Pomeranchuk-Migdal effect reduces the cross sections for electron bremsstrahlung and photon $e^+e^-$ pair production. The fractional electron energy loss and pair production cross sections drop as the energy increases. In contrast, the cross sections for photonuclear interactions grow with energy. In solids and liquids, at energies above $10^20$ eV, photonuclear reactions dominate, and showers that originate as photons or electrons quickly become hadronic showers. These electron-initiated hadronic showers are much shorter (due to the absence of the LPM effect), but wider than purely electromagnetic showers would be. This change in shape alters the spectrum of the electromagnetic and acoustic radiation emitted from the shower. These alterations have important implications for existing and planned searches for radiation from $\nu_e$ induced showers above $10^20$ eV, and some existing limits should be reevaluated.

            Cover page: Cascades from nu_E above 1020 eV
            • Article
            LBL Publications (2004)
              Cover page: e+e- pair production from 10 GeV to 10 ZeV
              • Article
              Lawrence Berkeley National Laboratory (2002)
                Cover page: Heavy Nuclei, From RHIC to The Cosmos
                • Article
                LBL Publications (2006)
                  Cover page: Recent Results from RHIC &amp; Some Lessons for Cosmic-Ray Physicists
                  • Article
                  • Peer Reviewed
                  UC Berkeley Previously Published Works (2018)
                  In "ηc production in photon-induced interactions at the LHC," [Phys. Rev. D 97, 094009 (2018)PRVDAQ2470-001010.1103/PhysRevD.97.094009] Goncalves and Moreira discuss inclusive and exclusive ηc production at pp and pA collisions at LHC energies. The exclusive channels are via two-photon and photon-Odderon interactions. This comment points out that there is a large additional source of almost-exclusive ηc in ultraperipheral collisions: from the radiative decay of J/ψ that are produced in photon-nucleon interactions. Although the J/ψ→γηc branching ratio is small, the J/ψ production cross-section is large enough that it dominates over the exclusive channels considered in [1], and is comparable to the nonexclusive production. In J/ψ→γηc, the photon is very soft and therefore easy to miss, and the ηc will have very similar kinematics to the J/ψ.
                    Cover page: Comment on “ηc production in photon-induced interactions at the LHC”
                    • Article
                    Lawrence Berkeley National Laboratory (2002)
                      Cover page: Electrodynamics at the highest energies
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