24,726 research outputs found
Status and recent dark matter search results from the PandaX experiment
No full textThe PandaX project is a staged xenon-based deep underground experiment at the China Jin-Ping Underground Laboratory. The first phase experiment, PandaX-I, a 120 kg dark matter detector using the dual phase xenon time projection chamber (TPC) technology was completed in 2014 with a 5480.1 kg-day exposure. Recently, the commissioning run of the second phase of the experiment, PandaX-II, was completed with a 30619.1 kg-day exposure. We report the status of the PandaX experiment, and then present the dark matter search results from both runs
Search for lepton portal dark matter in the PandaX-4T experiment
No full textWe report a search for a lepton-portal dark matter model, where dark matter couples to a charged lepton in the standard model. This simplified model naturally leads to photon-mediated dark matter interactions with nuclei, making it suitable for direct dark matter detection experiments. Matching to the framework of non-relativistic effective field theory for dark matter, we report the first sensitive search for this model using data from the PandaX-4T commissioning run. Our results yield strong constraints on Dirac fermion dark matter but relatively weaker constraints on Majorana dark matter due to the suppression of effective photon interactions. These constraints complement those obtained from the collider and indirect detection experiments
Search for light dark matter with ionization signals in the PandaX-4T Experiment
No full textWe report the search results of light dark matter through its interactions
with shell electrons and nuclei, using the commissioning data from the
PandaX-4T liquid xenon detector. Low energy events are selected to have an
ionization-only signal between 60 to 200 photoelectrons, corresponding to a
mean nuclear recoil energy from 0.77 to 2.54 keV and electronic recoil energy
from 0.07 to 0.23 keV. With an effective exposure of 0.55 tonneyear, we
set the most stringent limits within a mass range from 40 to 10
for point-like dark matter-electron interaction, 100 MeV/c
to 10 GeV/c for dark matter-electron interaction via a light mediator, and
3.2 to 4 for dark matter-nucleon spin-independent interaction.
For DM interaction with electrons, our limits are closing in on the parameter
space predicted by the freeze-in and freeze-out mechanisms in the early
Universe.Comment: 5 pages, 8 figur
The Structure of Scientific Collaboration Networks in Scientometrics
No full textThe structure of scientific collaboration networks in scientometrics was investigated at the level of individuals by using bibliographic data of all papers published in the international journal Scientometrics retrieved from the Science Citation Index (SCI) during 1978 to 2004. Combined analysis of social network analysis (SNA), co-occurrence analysis, cluster analysis and frequency analysis of words was explored to reveal: (1) The microstructure of the collaboration network on scientists’ aspects of scientometrics; (2) The major collaborative fields of the collaborative sub-networks; (3) The collaborative center of the collaboration network in scientometrics
Searches on Weakly Interacting Massive Particles and sub-MeV Fermionic Dark Matter in PandaX-II and PandaX-4T
No full textThe nature of dark matter is a crucial problem for both cosmology and particle physics. The weakly interactive massive particle (WIMP) is one of the top dark matter candidates searched for decades because of the so-called `WIMP-miracle'. Dual phase liquid xenon time projection chambers (LXeTPCs) have led the most sensitive searches on the GeV-scale spin-independent WIMP-nucleus scattering cross section for years because of the strong background suppression and scalability. With 3.7 tonne liquid xenon in the sensitive region of the LXeTPC, the Particle AND Astrophysical Xenon (PandaX) collaboration is now running PandaX-4T experiment at the B2 Hall of China Jinping Underground Laboratory after the PandaX-II experiment. The strongest limit back to the release time was published with the 0.63 tonneyear exposure on the standard thermal WIMP search with a lowest excluded cross section (90\% C.L.) of ~cm at a dark matter mass of 40~GeV/c.
In this thesis, I discuss research and developments correlated to PandaX experiments. I present the whole procedure of Rb/Kr calibration in the PandaX-II detector from sources production with 3.4/20~MeV protons bombardment on natural krypton to the data analysis after injection into the PandaX-II detector, which becomes crucial for the increasingly larger detectors. With the Kr events, I present the developments on the horizontal position construction algorithms in PandaX-II, which is important to fully take advantage of the self-shielding ability of xenon, determining the fiducial volume directly related to the exposure. Moreover, I discuss the procedure of the profile likelihood ratio analysis to set the limits and sensitivities, where probability distribution functions are prepared with reweighting Monte Carlo to handle the systematic uncertainties in the detector response modeling more robustly. The methodology is applied on the spin-independent WIMP search to prove consistency with the template morphing method. Then, I conduct a search on electronic absorption of sub-MeV fermionic dark matter which shares similarities with sterile neutrino dark matter. Such dark matter with a 60~keV/c mass can explain the low-energy ER excess reported by XENON1T collaboration, but is only marginally allowed by our constraints
Collaboration in Iranian Scientific Publications
No full textThis study looks at international collaboration in Iranian scientific publications through the ISI Science Citation Index® (SCI) for the years 1995-1999, inclusive. These results are compared to and contrasted with the earlier findings for the periods covering 1985-1994 (Osareh & Wilson 2000). The results of Iran's increasing productivity over a 15-year period are presented. Iran doubled its output in the first two five-year periods and increased 2.8-fold from the second to the third five-year period. The rise in Iran's scientific publication output is due mainly to factors such as the ending of the war, better economic conditions, recent changes in the Iranian government's policy, basic changes in the political environment brought about by the Reformers, expansion of the Iranian presses for national publications, and the recent return of a large number of students trained overseas through government scholarships. External changes also account for the increased productivity, e.g., the acceptance of three Iranian source journals by the SCI, increased access to international databases through the Internet and better electronic communication facilities for international collaboration. One of the most important and significant factors that caused this dramatic rise seems to be the government's research policies in the last few years. Since 1999, the Iran Science, Research and Technology Ministry, has encouraged researchers to publish their non-Farsi language articles in highly ranked international scientific journals, for example, by giving prizes to researchers who publish their articles in ISI-ranked journals
The methodological status of co-authorship networks
No full textA powerful strategy within the study of collaboration
in science is to posit that co-authorship patterns
represent social networks.
It is prerequisite to an application of Social
Network Analysis (SNA) to define the network
entities. A network analysis of the inter-institutional
collaboration in COLLNET on the basis
of co-authorships was conducted. The study reveals
that it is crucial whether the co-authorship
itself is seen as an author's relational property or
as a social event that brings the authors together.
The former possibility is represented by a onemode
network in which each author can be related
to each other author. Quite distinct from
that are two-mode networks, the latter approach.
They consist of two single data sets in which relations
are only possible between different sets.
Different modes of representations require
different network approaches. One is that co-authorship
networks are seen as one-mode networks,
which has the advantage of the application
of a variety of measures. In contrast, twomode
networks, the other option, cannot be analysed
by standard techniques but its distinctive
features demand a new conceptualisation of
measures. In conclusion, the two-mode perspective
is more promising because it allows a dual
perspective on collaboration in science which includes
researchers as well as their scientific output
Probing Spin-Independent WIMP-Nucleon Interactions with the PandaX-I Detector.
No full textA dark matter relic density remaining from the Big Bang is believed to be permeating our Universe in the form of dark matter particles. It is likely that these relics could be detected in Earth-based experiments, prompting a prolonged search effort by experimental groups looking for the mysterious particle. Recent dark matter searches have received much attention due to several possible positive direct detection results, with reports putting the dark matter mass near 10 GeV/c^2. This has motivated other direct detection experiments to focus their efforts in the low mass region which has resulted in several competing null results.
The PandaX-I detector, located at China JinPing Laboratory in Sichuan Province, China, is a dual-phase liquid xenon time projection chamber with three-dimensional position reconstruction capabilities. The high light yield design allows for a low energy threshold and sizable xenon mass, targeting the low mass WIMP-nucleon cross-section region of parameter space. The detector was designed, constructed, and operated by the international Particle and Astrophysical Xenon (PandaX) collaboration with the goal of probing the alluring low WIMP mass cross-section parameter space.
This dissertation outlines the operation of the deep underground, low background PandaX-I detector utilized for a rare event dark matter search. I discuss dark matter interactions rates in terrestrial detectors and the properties of liquid xenon as a suitable dark matter target. A detailed discussion of the dark matter WIMP search with liquid xenon based detectors is given, including the design, background simulation, construction and operation of the MiX (Michigan Xenon) development detector and the large scale PandaX-I (Particle and Astrophysical Xenon) detector. Finally, I discuss the outcome resulting from a dark matter search analysis of the first 17.4 live-days in the PandaX-I 37 kg fiducial volume. With this effort, the PandaX collaboration provided a deep probe of the low WIMP mass parameter space, excluding the aforementioned low mass dark matter signal reports.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111341/1/isospin_1.pd
Co-authorship Network of Scientometrics Research Collaboration
No full textThis paper examines the co-authorship network in the field of scientometrics using social network analysis techniques with the aim of developing an understanding of research collaboration in this scientific community. Using co-authorship data from 3125 articles published in the journal Scientometrics with a time span of more than three decades (1980-2012), we construct an evolving co-authorship network and calculate three centrality measures (closeness, betweenness, and degree) for 3024 authors, 1207 institutions, 68 countries and 22 academic fields in this network. This paper also discusses the usability of centrality measures in author ranking, and suggests that centrality measures can be useful indicators for impact analysis. Findings revealed that scientometrics was not dominated by a couple of key researchers as quite a significant number of popular researchers were identified. The United States occupies the topmost position in all measures except for degree centrality. The most active, central and collaborative academic discipline in scientometrics is Information & Library Science
Study of background from accidental coincidence signals in the PandaX-II experiment
No full textThe PandaX-II experiment employed a 580kg liquid xenon detector to search for
the interactions between dark matter particles and the target xenon atoms. The
accidental coincidences of isolated signals result in a dangerous background
which mimic the signature of the dark matter. We performed a detailed study on
the accidental coincidence background in PandaX-II, including the possible
origin of the isolated signals, the background level and corresponding
background suppression method. With a boosted-decision-tree algorithm, the
accidental coincidence background is reduced by 70% in the dark matter signal
region, thus the sensitivity of dark matter search at PandaX-II is improved.Comment: 20 pages, 12 figures in main text and 5 figures in the appendix.
Accepted by Chinese Physics
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