-
K. Ackerstaff,
A. Airapetian,
I. Akushevich,
N. Akopov,
M. Amarian,
E.C. Aschenauer,
R. Avakian,
H. Avakian,
A. Avetisian,
B. Bains, [......],
M.C. Vetterli,
E. Volk,
W. Wander,
T.P. Welch,
S.E. Williamson,
T. Wise,
T. Wolfel,
K. Zapfe-Duren,
G. Zograbian,
R. Zurmuhle
[show abstract]
[hide abstract]
ABSTRACT: Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function g1 n(x,Q 2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target. The data cover the kinematic range 0.023<x<0.6 and 1(GeV/c) 2<Q 2<15(GeV/c) 2. The integral ∫0.023 0.6g1 n(x)dx evaluated at a fixed Q 2 of 2.5(GeV/c) 2 is −0.034±0.013(stat.)±0.005(syst.). Assuming Regge behavior at low x, the first moment Γ1 n=∫0 1g1 n(x)dx is −0.037±0.013(stat.)±0.005(syst.)±0.006(extrapol.).
Physics Letters B 02/2013; 404(3-4):383-389. · 3.95 Impact Factor
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K. Ackerstaff,
A. Airapetian,
N. Akopov,
I. Akushevich,
M. Amarian,
E.C. Aschenauer,
H. Avakian,
R. Avakian,
A. Avetisian,
B. Bains, [......],
M.G. Vincter,
J. Visser,
E. Volk,
W. Wander,
J. Wendland,
S.E. Williamson,
T. Wise,
K. Woller,
S. Yoneyama,
H. Zohrabian
[show abstract]
[hide abstract]
ABSTRACT: Cross section ratios for deep-inelastic scattering from 14N and 3He with respect to 2H have been measured by the HERMES experiment at DESY using a 27.5 GeV positron beam. The data cover a range in the Bjorken scaling variable x between 0.013 and 0.65, while the negative squared four-momentum transfer Q^2 varies from 0.5 to 15 GeV^2. The data are compared to measurements performed by NMC, E665, and SLAC on 4He and 12C, and are found to be different for x < 0.06 and Q^2 < 1.5 GeV^2. The observed difference is attributed to an A-dependence of the ratio R = sigma_L / sigma_T of longitudinal to transverse deep-inelastic scattering cross sections at low x and low Q^2.
Physics Letters B 02/2013; 475:386-394. · 3.95 Impact Factor
-
A. Airapetian,
N. Akopov,
Z. Akopov,
M Amarian,
V.V. Ammosov,
A Andrus,
E.C. Aschenauer,
W. Augustyniak,
R. Avakian,
A. Avetissian, [......],
J Volmer,
C. Weiskopf,
J Wendland,
J. Wilbert,
G. Smit,
Y Ye,
Z Ye,
S. Yen,
B. Zihlmann,
P. Zupranski
[show abstract]
[hide abstract]
ABSTRACT: Hard exclusive electroproduction of pi(+) pi(-) pairs off hydrogen and deuterium targets has been studied by the HERMES experiment at DESY Legendre moments (P-1) and (P-3) of the angular distributions of pi(+) mesons in the center-of-mass frame of the pair have been measured for the first time. Their dependence on the pi(+) pi(-) invariant mass can be understood as being due to the interference between relative P-wave (isovector) and S-, D-wave (isoscalar) states of the two pions. The increase in magnitude of (P-1) as Bjorken x increases is interpreted in the framework of generalized parton distributions as an enhancement of flavour non-singlet qq exchange for larger values of x, which leads to a sizable admixture of isoscalar and isovector pion pairs. In addition, the interference between P-wave and D-wave states separately for transverse and longitudinal pion pairs has been studied. The data indicate that in the f(2)(1270) region at [Q(2)] = 3 GeV2 higher-twist effects can be as large as the leading-twist longitudinal component.
Phys.Lett.B599:212-222,2004. 02/2013;
-
J. Brack,
B. Delgado,
J. Dhooghe,
J. Felde,
B. Gookin,
S. Grullon,
J. R. Klein,
R. Knapik,
A. LaTorre,
S. Seibert,
K. Shapiro,
R. Svoboda,
L. Ware,
R. Van Berg
[show abstract]
[hide abstract]
ABSTRACT: Future large water Cherenkov and scintillator detectors have been proposed
for measurements of long baseline neutrino oscillations, proton decay,
supernova and solar neutrinos. To ensure cost-effectiveness and optimize
scientific reach, one of the critical requirements for such detectors are
large-area, high performance photomultiplier tubes (PMTs). One candidate for
such a device is the Hamamatsu R11780, a 12" PMT that is available in both
standard and high quantum efficiency versions. Measurements of the single
photoelectron response characteristics, relative efficiencies of the standard
and high quantum efficiency versions, a preliminary measurement of the absolute
quantum efficiency of the standard quantum efficiency version, and a
two-dimensional scan of the relative efficiency across the photocathode surface
are presented in this paper. All single photoelectron investigations were made
using a Cherenkov light source at room temperature at a gain of 1*10^7. These
results show that the R11780 PMT is a excellent candidate for such large
optical detectors, including the peak-to-valley ratios greater than 2, transit
time spreads around 1.3 ns, and late-pulsing probabilities less than 5%.
10/2012;
-
P. Abreu,
M. Aglietta,
M. Ahlers,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J. Allen,
P. Allison,
A. Almela, [......],
J. Zhou,
Y. Zhu,
M. Zimbres Silva,
M. Ziolkowski,
D. Charrier,
L. Denis,
G. Hilgers,
L. Mohrmann,
B. Philipps,
O. Seeger
[show abstract]
[hide abstract]
ABSTRACT: The Pierre Auger Observatory is exploring the potential of the radio
detection technique to study extensive air showers induced by ultra-high energy
cosmic rays. The Auger Engineering Radio Array (AERA) addresses both
technological and scientific aspects of the radio technique. A first phase of
AERA has been operating since September 2010 with detector stations observing
radio signals at frequencies between 30 and 80 MHz. In this paper we present
comparative studies to identify and optimize the antenna design for the final
configuration of AERA consisting of 160 individual radio detector stations. The
transient nature of the air shower signal requires a detailed description of
the antenna sensor. As the ultra-wideband reception of pulses is not widely
discussed in antenna literature, we review the relevant antenna characteristics
and enhance theoretical considerations towards the impulse response of antennas
including polarization effects and multiple signal reflections. On the basis of
the vector effective length we study the transient response characteristics of
three candidate antennas in the time domain. Observing the variation of the
continuous galactic background intensity we rank the antennas with respect to
the noise level added to the galactic signal.
09/2012;
-
The Pierre Auger Collaboration,
P. Abreu,
M. Aglietta,
M. Ahlers,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J. Allen,
P. Allison, [......],
B. Zamorano Garcia,
E. Zas,
D. Zavrtanik,
M. Zavrtanik,
I. Zaw,
A. Zepeda,
J. Zhou,
Y. Zhu,
M. Zimbres Silva,
M. Ziolkowski
[show abstract]
[hide abstract]
ABSTRACT: The Pierre Auger Observatory is a facility built to detect air showers
produced by cosmic rays above 10^17 eV. During clear nights with a low
illuminated moon fraction, the UV fluorescence light produced by air showers is
recorded by optical telescopes at the Observatory. To correct the observations
for variations in atmospheric conditions, atmospheric monitoring is performed
at regular intervals ranging from several minutes (for cloud identification) to
several hours (for aerosol conditions) to several days (for vertical profiles
of temperature, pressure, and humidity). In 2009, the monitoring program was
upgraded to allow for additional targeted measurements of atmospheric
conditions shortly after the detection of air showers of special interest,
e.g., showers produced by very high-energy cosmic rays or showers with atypical
longitudinal profiles. The former events are of particular importance for the
determination of the energy scale of the Observatory, and the latter are
characteristic of unusual air shower physics or exotic primary particle types.
The purpose of targeted (or "rapid") monitoring is to improve the resolution of
the atmospheric measurements for such events. In this paper, we report on the
implementation of the rapid monitoring program and its current status. The
rapid monitoring data have been analyzed and applied to the reconstruction of
air showers of high interest, and indicate that the air fluorescence
measurements affected by clouds and aerosols are effectively corrected using
measurements from the regular atmospheric monitoring program. We find that the
rapid monitoring program has potential for supporting dedicated physics
analyses beyond the standard event reconstruction.
08/2012;
-
The Pierre Auger Collaboration,
P. Abreu,
M. Aglietta,
M. Ahlers,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J. Allen,
P. Allison, [......],
A. Yushkov,
B. Zamorano,
E. Zas,
D. Zavrtanik,
M. Zavrtanik,
I. Zaw,
A. Zepeda,
Y. Zhu,
M. Zimbres Silva,
M. Ziolkowski
[show abstract]
[hide abstract]
ABSTRACT: The Surface Detector of the Pierre Auger Observatory is sensitive to
neutrinos of all flavours above 0.1 EeV. These interact through charged and
neutral currents in the atmosphere giving rise to extensive air showers. When
interacting deeply in the atmosphere at nearly horizontal incidence, neutrinos
can be distinguished from regular hadronic cosmic rays by the broad time
structure of their shower signals in the water-Cherenkov detectors. In this
paper we present for the first time an analysis based on down-going neutrinos.
We describe the search procedure, the possible sources of background, the
method to compute the exposure and the associated systematic uncertainties. No
candidate neutrinos have been found in data collected from 1 January 2004 to 31
May 2010. Assuming an E^-2 differential energy spectrum the limit on the single
flavour neutrino is (E^2 * dN/dE) < 1.74x10^-7 GeV cm^-2 s^-1 sr^-1 at 90% C.L.
in the energy range 1x10^17 eV < E < 1x10^20 eV.
02/2012;
-
The Pierre Auger Collaboration,
P. Abreu,
M. Aglietta,
M. Ahlers,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J. Allen,
P. Allison, [......],
A. Yushkov,
B. Zamorano,
E. Zas,
D. Zavrtanik,
M. Zavrtanik,
I. Zaw,
A. Zepeda,
Y. Zhu,
M. Zimbres Silva,
M. Ziolkowski
[show abstract]
[hide abstract]
ABSTRACT: Atmospheric conditions at the site of a cosmic ray observatory must be known
for reconstructing observed extensive air showers. The Global Data Assimilation
System (GDAS) is a global atmospheric model predicated on meteorological
measurements and numerical weather predictions. GDAS provides
altitude-dependent profiles of the main state variables of the atmosphere like
temperature, pressure, and humidity. The original data and their application to
the air shower reconstruction of the Pierre Auger Observatory are described. By
comparisons with radiosonde and weather station measurements obtained on-site
in Malarg\"ue and averaged monthly models, the utility of the GDAS data is
shown.
01/2012;
-
The Pierre Auger Collaboration,
P Abreu,
M Aglietta,
M Ahlers,
E J Ahn,
I F M Albuquerque,
D Allard,
I Allekotte,
J Allen,
P Allison, [......],
Zamorano B Garcia,
E Zas,
D Zavrtanik,
M Zavrtanik,
I Zaw,
A Zepeda,
J Zhou,
Y Zhu,
Zimbres M Silva,
M Ziolkowski
[show abstract]
[hide abstract]
ABSTRACT: The surface detector array of the Pierre Auger Observatory can detect neutrinos with energy E ν between 10 17 eV and 10 20 eV from point-like sources across the sky south of +55° and north of –65° declinations. A search has been performed for highly inclined extensive air showers produced by the interaction of neutrinos of all flavors in the atmosphere (downward-going neutrinos), and by the decay of tau leptons originating from tau neutrino interactions in Earth's crust (Earth-skimming neutrinos). No candidate neutrinos have been found in data up to 2010 May 31. This corresponds to an equivalent exposure of ~3.5 years of a full surface detector array for the Earth-skimming channel and ~2 years for the downward-going channel. An improved upper limit on the diffuse flux of tau neutrinos has been derived. Upper limits on the neutrino flux from point-like sources have been derived as a function of the source declination. Assuming a differential neutrino flux k PS · E –2 ν from a point-like source, 90% confidence level upper limits for k PS at the level of ##IMG## [http://ej.iop.org/icons/Entities/ap.gif] ≈ 5 × 10 –7 and 2.5 × 10 –6 GeV cm –2 s –1 have been obtained over a broad range of declinations from the searches for Earth-skimming and downward-going neutrinos, respectively.
The Astrophysical Journal Letters. 01/2012; 755(1):L4.
-
P Abreu,
M Aglietta,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J Allen,
P. Allison,
J. Alvarez Castillo,
J. Alvarez-Muñiz, [......],
G. Yuan,
A. Yushkov,
B. Zamorano,
E. Zas,
D Zavrtanik,
M. Zavrtanik,
I Zaw,
A. Zepeda,
M. Zimbres-Silva,
M Ziolkowski
[show abstract]
[hide abstract]
ABSTRACT: We present a comprehensive study of the influence of the geomagnetic field on
the energy estimation of extensive air showers with a zenith angle smaller than
$60^\circ$, detected at the Pierre Auger Observatory. The geomagnetic field
induces an azimuthal modulation of the estimated energy of cosmic rays up to
the ~2% level at large zenith angles. We present a method to account for this
modulation of the reconstructed energy. We analyse the effect of the modulation
on large scale anisotropy searches in the arrival direction distributions of
cosmic rays. At a given energy, the geomagnetic effect is shown to induce a
pseudo-dipolar pattern at the percent level in the declination distribution
that needs to be accounted for.
11/2011;
-
J. Abraham,
P Abreu,
M Aglietta,
C Aguirre,
E. J. Ahn,
D. Allard,
I. Allekotte,
J Allen,
J. Alvarez-Muñiz,
M. Ambrosio, [......],
T Yamamoto,
P. Younk,
G. Yuan,
A. Yushkov,
E. Zas,
D Zavrtanik,
M. Zavrtanik,
I Zaw,
A. Zepeda,
M Ziolkowski
[show abstract]
[hide abstract]
ABSTRACT: The surface detector array of the Pierre Auger Observatory consists of 1600
water-Cherenkov detectors, for the study of extensive air showers (EAS)
generated by ultra-high-energy cosmic rays. We describe the trigger hierarchy,
from the identification of candidate showers at the level of a single detector,
amongst a large background (mainly random single cosmic ray muons), up to the
selection of real events and the rejection of random coincidences. Such trigger
makes the surface detector array fully efficient for the detection of EAS with
energy above $3\times 10^{18}$ eV, for all zenith angles between 0$^\circ$ and
60$^\circ$, independently of the position of the impact point and of the mass
of the primary particle. In these range of energies and angles, the exposure of
the surface array can be determined purely on the basis of the geometrical
acceptance.
11/2011;
-
The Pierre Auger Collaboration,
P Abreu,
M Aglietta,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J Allen,
P. Allison,
J. Alvarez Castillo, [......],
G. Yuan,
A. Yushkov,
B. Zamorano,
E. Zas,
D Zavrtanik,
M. Zavrtanik,
I Zaw,
A. Zepeda,
M. Zimbres-Silva,
M Ziolkowski
[show abstract]
[hide abstract]
ABSTRACT: In this paper we introduce the concept of Lateral Trigger Probability (LTP)
function, i.e., the probability for an extensive air shower (EAS) to trigger an
individual detector of a ground based array as a function of distance to the
shower axis, taking into account energy, mass and direction of the primary
cosmic ray. We apply this concept to the surface array of the Pierre Auger
Observatory consisting of a 1.5 km spaced grid of about 1600 water Cherenkov
stations. Using Monte Carlo simulations of ultra-high energy showers the LTP
functions are derived for energies in the range between 10^{17} and 10^{19} eV
and zenith angles up to 65 degs. A parametrization combining a step function
with an exponential is found to reproduce them very well in the considered
range of energies and zenith angles. The LTP functions can also be obtained
from data using events simultaneously observed by the fluorescence and the
surface detector of the Pierre Auger Observatory (hybrid events). We validate
the Monte-Carlo results showing how LTP functions from data are in good
agreement with simulations.
11/2011;
-
The Pierre Auger Collaboration,
P Abreu,
M Aglietta,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J Allen,
P. Allison,
J. Alvarez Castillo, [......],
G. Yuan,
A. Yushkov,
B. Zamorano,
E. Zas,
D Zavrtanik,
M. Zavrtanik,
I Zaw,
A. Zepeda,
M. Zimbres-Silva,
M Ziolkowski
[show abstract]
[hide abstract]
ABSTRACT: We present the results of an analysis of data recorded at the Pierre Auger
Observatory in which we search for groups of directionally-aligned events (or
`multiplets') which exhibit a correlation between arrival direction and the
inverse of the energy. These signatures are expected from sets of events coming
from the same source after having been deflected by intervening coherent
magnetic fields. The observation of several events from the same source would
open the possibility to accurately reconstruct the position of the source and
also measure the integral of the component of the magnetic field orthogonal to
the trajectory of the cosmic rays. We describe the largest multiplets found and
compute the probability that they appeared by chance from an isotropic
distribution. We find no statistically significant evidence for the presence of
multiplets arising from magnetic deflections in the present data.
11/2011;
-
The LBNE Collaboration,
T. Akiri,
D. Allspach,
M. Andrews,
K Arisaka,
E. Arrieta-Diaz,
M. Artuso,
X Bai,
B. Balantekin,
B. Baller, [......],
W. Willis,
R J Wilson,
L. Winslow,
J Ye,
M Yeh,
B Yu,
G. Zeller,
C Zhang,
E Zimmerman,
R. Zwaska
[show abstract]
[hide abstract]
ABSTRACT: In early 2010, the Long-Baseline Neutrino Experiment (LBNE) science
collaboration initiated a study to investigate the physics potential of the
experiment with a broad set of different beam, near- and far-detector
configurations. Nine initial topics were identified as scientific areas that
motivate construction of a long-baseline neutrino experiment with a very large
far detector. We summarize the scientific justification for each topic and the
estimated performance for a set of far detector reference configurations. We
report also on a study of optimized beam parameters and the physics capability
of proposed Near Detector configurations. This document was presented to the
collaboration in fall 2010 and updated with minor modifications in early 2011.
10/2011;
-
The Pierre Auger Collaboration,
P Abreu,
M Aglietta,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J Allen,
P. Allison,
J. Alvarez Castillo, [......],
G. Yuan,
A. Yushkov,
B. Zamorano,
E. Zas,
D Zavrtanik,
M. Zavrtnik,
I Zaw,
A. Zepeda,
M. Zimbres-Silva,
M Ziolkowski
07/2011;
-
The Pierre Auger Collaboration,
P Abreu,
M Aglietta,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J Allen,
P. Allison,
J. Alvarez Castillo, [......],
G. Yuan,
A. Yushkov,
B. Zamorano,
E. Zas,
D Zavrtanik,
M. Zavrtnik,
I Zaw,
A. Zepeda,
M. Zimbres-Silva,
M Ziolkowski
07/2011;
-
The Pierre Auger Collaboration,
P Abreu,
M Aglietta,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J Allen,
P. Allison,
J. Alvarez Castillo, [......],
G. Yuan,
A. Yushkov,
B. Zamorano,
E. Zas,
D Zavrtanik,
M. Zavrtnik,
I Zaw,
A. Zepeda,
M. Zimbres-Silva,
M Ziolkowski
07/2011;
-
The Pierre Auger Collaboration,
P Abreu,
M Aglietta,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J Allen,
P. Allison,
J. Alvarez Castillo, [......],
G. Yuan,
A. Yushkov,
B. Zamorano,
E. Zas,
D Zavrtanik,
M. Zavrtnik,
I Zaw,
A. Zepeda,
M. Zimbres-Silva,
M Ziolkowski
[show abstract]
[hide abstract]
ABSTRACT: Studies of the composition of the highest energy cosmic rays with the Pierre
Auger Observatory, including examination of hadronic physics effects on the
structure of extensive air showers.
07/2011;
-
The Pierre Auger Collaboration,
P Abreu,
M Aglietta,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J Allen,
P. Allison,
J. Alvarez Castillo, [......],
G. Yuan,
A. Yushkov,
B. Zamorano,
E. Zas,
D Zavrtanik,
M. Zavrtnik,
I Zaw,
A. Zepeda,
M. Zimbres-Silva,
M Ziolkowski
07/2011;
-
The Pierre Auger Collaboration,
P. Abreu,
M. Aglietta,
E. J. Ahn,
I. F. M. Albuquerque,
D. Allard,
I. Allekotte,
J. Allen,
P. Allison,
J. Alvarez Castillo, [......],
G. Yuan,
A. Yushkov,
B. Zamorano,
E. Zas,
D. Zavrtanik,
M. Zavrtnik,
I. Zaw,
A. Zepeda,
M. Zimbres-Silva,
M. Ziolkowski
06/2011;
