H. J. Karwowski - University of North Carolina

H. J. Karwowski
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H. J. Karwowski
University of North Carolina
United States

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Nuclear Experiment (19)
High Energy Physics - Experiment (11)
Nuclear Theory (5)
Physics - Instrumentation and Detectors (5)
High Energy Astrophysical Phenomena (3)
Solar and Stellar Astrophysics (2)
Astrophysics (1)

Publications Authored By H. J. Karwowski

We present a search for low energy antineutrino events coincident with the gravitational wave events GW150914 and GW151226, and the candidate event LVT151012 using KamLAND, a kiloton-scale antineutrino detector. We find no inverse beta-decay neutrino events within $\pm 500$ seconds of either gravitational wave signal. This non-detection is used to constrain the electron antineutrino fluence and the luminosity of the astrophysical sources. Read More

A search for double-beta decays of 136Xe to excited states of 136Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 0+1, 2+1 and 2+2 transitions of 0{\nu}\{beta}\{beta} decay were evaluated in an exposure of 89.5kg-yr of 136Xe, while the same transitions of 2{\nu}\{beta}\{beta} decay were evaluated in an exposure of 61. Read More

In the late stages of nuclear burning for massive stars ($M>8~M_{\sun}$), the production of neutrino-antineutrino pairs through various processes becomes the dominant stellar cooling mechanism. As the star evolves, the energy of these neutrinos increases and in the days preceding the supernova a significant fraction of emitted electron anti-neutrinos exceeds the energy threshold for inverse beta decay on free hydrogen. This is the golden channel for liquid scintillator detectors because the coincidence signature allows for significant reductions in background signals. Read More

We report new measurements of the doubly-polarized photodisintegration of $^3$He at an incident photon energy of 16.5 MeV, carried out at the High Intensity $\gamma$-ray Source (HI$\gamma$S) facility located at Triangle Universities Nuclear Laboratory (TUNL). The spin-dependent double-differential cross sections and the contribution from the three--body channel to the Gerasimov-Drell-Hearn (GDH) integrand were extracted and compared with the state-of-the-art three--body calculations. Read More

We search for electron anti-neutrinos ($\overline{\nu}_e$) from long and short-duration gamma-ray bursts~(GRBs) using data taken by the KamLAND detector from August 2002 to June 2013. No statistically significant excess over the background level is found. We place the tightest upper limits on $\overline{\nu}_e$ fluence from GRBs below 7 MeV and place first constraints on the relation between $\overline{\nu}_e$ luminosity and effective temperature. Read More

We describe a compact, ultra-clean device used to deploy radioactive sources along the vertical axis of the KamLAND liquid-scintillator neutrino detector for purposes of calibration. The device worked by paying out and reeling in precise lengths of a hanging, small-gauge wire rope (cable); an assortment of interchangeable radioactive sources could be attached to a weight at the end of the cable. All components exposed to the radiopure liquid scintillator were made of chemically compatible UHV-cleaned materials, primarily stainless steel, in order to avoid contaminating or degrading the scintillator. Read More

Affiliations: 1The KamLAND Collaboration, 2The KamLAND Collaboration, 3The KamLAND Collaboration, 4The KamLAND Collaboration, 5The KamLAND Collaboration, 6The KamLAND Collaboration, 7The KamLAND Collaboration, 8The KamLAND Collaboration, 9The KamLAND Collaboration, 10The KamLAND Collaboration, 11The KamLAND Collaboration, 12The KamLAND Collaboration, 13The KamLAND Collaboration, 14The KamLAND Collaboration, 15The KamLAND Collaboration, 16The KamLAND Collaboration, 17The KamLAND Collaboration, 18The KamLAND Collaboration, 19The KamLAND Collaboration, 20The KamLAND Collaboration, 21The KamLAND Collaboration, 22The KamLAND Collaboration, 23The KamLAND Collaboration, 24The KamLAND Collaboration, 25The KamLAND Collaboration, 26The KamLAND Collaboration, 27The KamLAND Collaboration, 28The KamLAND Collaboration, 29The KamLAND Collaboration, 30The KamLAND Collaboration, 31The KamLAND Collaboration, 32The KamLAND Collaboration, 33The KamLAND Collaboration, 34The KamLAND Collaboration, 35The KamLAND Collaboration, 36The KamLAND Collaboration, 37The KamLAND Collaboration, 38The KamLAND Collaboration, 39The KamLAND Collaboration, 40The KamLAND Collaboration, 41The KamLAND Collaboration, 42The KamLAND Collaboration, 43The KamLAND Collaboration, 44The KamLAND Collaboration, 45The KamLAND Collaboration, 46The KamLAND Collaboration, 47The KamLAND Collaboration, 48The KamLAND Collaboration, 49The KamLAND Collaboration, 50The KamLAND Collaboration, 51The KamLAND Collaboration, 52The KamLAND Collaboration, 53The KamLAND Collaboration, 54The KamLAND Collaboration, 55The KamLAND Collaboration, 56The KamLAND Collaboration, 57The KamLAND Collaboration, 58The KamLAND Collaboration, 59The KamLAND Collaboration, 60The KamLAND Collaboration, 61The KamLAND Collaboration, 62The KamLAND Collaboration, 63The KamLAND Collaboration, 64The KamLAND Collaboration, 65The KamLAND Collaboration, 66The KamLAND Collaboration, 67The KamLAND Collaboration, 68The KamLAND Collaboration, 69The KamLAND Collaboration, 70The KamLAND Collaboration, 71The KamLAND Collaboration

We report a measurement of the neutrino-electron elastic scattering rate of 862 keV 7Be solar neutrinos based on a 165.4 kton-day exposure of KamLAND. The observed rate is 582 +/- 90 (kton-day)^-1, which corresponds to a 862 keV 7Be solar neutrino flux of (3. Read More

Affiliations: 1Tohoku University, 2Tohoku University, 3Tohoku University, 4Tohoku University, 5Tohoku University, 6Tohoku University, 7Tohoku University, 8Tohoku University, 9Tohoku University, 10Tohoku University, 11Tohoku University, 12Tohoku University, 13Tohoku University, 14Tohoku University, 15Tohoku University, 16Tohoku University, 17Tohoku University, 18Tohoku University, 19Tohoku University, 20Tohoku University, 21Tohoku University, 22Tohoku University, 23Tohoku University, 24Tohoku University, 25Tohoku University, 26Tohoku University, 27Tohoku University, 28CEA-Saclay, 29CEA-Saclay, 30CEA-Saclay, 31CEA-Saclay, 32CEA-Saclay, 33CEA-Saclay, 34CEA-Saclay, 35CEA-Saclay, 36CEA-Saclay, 37CEA-Saclay, 38CEA-Saclay, 39CEA-Saclay, 40CEA-Saclay, 41CEA-Saclay, 42CEA-Saclay, 43Colorado State University, 44Colorado State University, 45University of Tokyo, 46Lawrence Berkeley National Laboratory and Berkeley University, 47Lawrence Berkeley National Laboratory and Berkeley University, 48Lawrence Berkeley National Laboratory and Berkeley University, 49Lawrence Berkeley National Laboratory and Berkeley University, 50Lawrence Berkeley National Laboratory and Berkeley University, 51Lawrence Berkeley National Laboratory and Berkeley University, 52Lawrence Berkeley National Laboratory and Berkeley University, 53Nikhef and the University of Amsterdam, 54North Carolina Central University, 55Osaka University, 56ITEP/INR RAS, 57IPCE RAS, 58Mephi, 59University of Hawaii, 60University of Hawaii, 61University of Hawaii, 62University of Hawaii, 63University of North Carolina, 64University of Tennessee, 65University of Washington, 66University of Washington

The reactor neutrino and gallium anomalies can be tested with a 3-4 PBq (75-100 kCi scale) 144Ce-144Pr antineutrino beta-source deployed at the center or next to a large low-background liquid scintillator detector. The antineutrino generator will be produced by the Russian reprocessing plant PA Mayak as early as 2014, transported to Japan, and deployed in the Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND) as early as 2015. KamLAND's 13 m diameter target volume provides a suitable environment to measure the energy and position dependence of the detected neutrino flux. Read More

We propose to test for short baseline neutrino oscillations, implied by the recent reevaluation of the reactor antineutrino flux and by anomalous results from the gallium solar neutrino detectors. The test will consist of producing a 75 kCi 144Ce - 144Pr antineutrino source to be deployed in the Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND). KamLAND's 13m diameter target volume provides a suitable environment to measure energy and position dependence of the detected neutrino flux. Read More

The first measurement of the three-body photodisintegration of longitudinally-polarized ^3He with a circularly-polarized \gamma-ray beam was carried out at the High Intensity \gamma-ray Source (HI\gamma S) facility located at Triangle Universities Nuclear Laboratory (TUNL). The spin-dependent double-differential cross sections and the contributions from the three-body photodisintegration to the ^3He GDH integrand are presented and compared with state-of-the-art three-body calculations at the incident photon energies of 12.8 and 14. Read More

The photofission cross-section of 238U was measured at sub-barrier energies as a function of the gamma-ray energy using, for the first time, a monochromatic, high-brilliance, Compton-backscattered gamma-ray beam. The experiment was performed at the High Intensity gamma-ray Source (HIgS) facility at beam energies between E=4.7 MeV and 6. Read More

Models of the r-process are sensitive to the production rate of 9Be because, in explosive environments rich in neutrons, alpha(alpha n,gamma)9Be is the primary mechanism for bridging the stability gaps at A=5 and A=8. The alpha(alpha n,gamma)9Be reaction represents a two-step process, consisting of alpha+alpha -> 8Be followed by 8Be(n,gamma)9Be. We report here on a new absolute cross section measurement for the 9Be(gamma,n)8Be reaction conducted using a highly-efficient, 3He-based neutron detector and nearly-monoenergetic photon beams, covering energies from E_gamma = 1. Read More

The 48Ca({\gamma},n) cross section was measured using {\gamma}-ray beams of energies between 9.5 and 15.3 MeV generated at the Triangle Universities Nuclear Laboratory (TUNL) high-intensity {\gamma}-ray source (HI{\gamma}S). Read More

A neutron counter designed for assay of radioactive materials has been adapted for beam experiments at TUNL. The cylindrical geometry and 60% maximum efficiency make it well suited for ($\gamma,n$) cross-section measurements near the neutron emission threshold. A high precision characterization of the counter has been made using neutrons from several sources. Read More

Angular Distributions for the target spin-dependent observables A$_{0y}$, A$_{xx}$, and A$_{yy}$ have been measured using polarized proton beams at several energies between 2 and 6 MeV and a spin-exchange optical pumping polarized $^3$He target. These measurements have been included in a global phase-shift analysis following that of George and Knutson, who reported two best-fit phase-shift solutions to the previous global p+$^3$He elastic scattering database below 12 MeV. These new measurements, along with measurements of cross-section and beam-analyzing power made over a similar energy range by Fisher \textit{et al. Read More

We present new accurate measurements of the differential cross section $\sigma(\theta)$ and the proton analyzing power $A_{y}$ for proton-$^{3}$He elastic scattering at various energies. A supersonic gas jet target has been employed to obtain these low energy cross section measurements. The $\sigma(\theta)$ distributions have been measured at $E_{p}$ = 0. Read More

Recent Wilkinson Microwave Anisotropy Probe (WMAP) measurements have determined the baryon density of the Universe $\Omega_b$ with a precision of about 4%. With $\Omega_b$ tightly constrained, comparisons of Big Bang Nucleosynthesis (BBN) abundance predictions to primordial abundance observations can be made and used to test BBN models and/or to further constrain abundances of isotopes with weak observational limits. To push the limits and improve constraints on BBN models, uncertainties in key nuclear reaction rates must be minimized. Read More

A new measurement of the p-d differential cross section at Ep= 1 MeV has been performed. These new data and older data sets at energies below the deuteron breakup are compared to calculations using the two-nucleon Argonne v18 and the three-nucleon Urbana IX potentials. A quantitative estimate of the capability of these interactions to describe the data is given in terms of a chi^2 analysis. Read More

We present measurements of differential cross sections and the analyzing powers A_y, iT11, T20, T21, and T22 at E_c.m.=431. Read More

We present measurements of the analyzing powers Ay and iT11 for proton-deuteron scattering at Ecm=432 keV. Calculations using a realistic nucleon-nucleon potential (Argonne V18) are found to underpredict both analyzing powers by 40. The inclusion of the Urbana three-nucleon interaction does not significantly modify the calculated analyzing powers. Read More

The three-nucleon system is studied at energies a few hundred keV above the N-d threshold. Measurements of the tensor analyzing powers $T_{20}$ and $T_{21}$ for p-d elastic scattering at $E_{c.m. Read More