941 research outputs found
Flux Modulations seen by the Muon Veto of the GERDA Experiment
The GERDA experiment at LNGS of INFN is equipped with an active muon veto.
The main part of the system is a water Cherenkov veto with 66~PMTs in the water
tank surrounding the GERDA cryostat. The muon flux recorded by this veto shows
a seasonal modulation. Two effects have been identified which are caused by
secondary muons from the CNGS neutrino beam (2.2 %) and a temperature
modulation of the atmosphere (1.4 %). A mean cosmic muon rate of /(sm) was found in good agreement with other experiments at
LNGS at a depth of 3500~meter water equivalent.Comment: 7 pages, 6 figure
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Challenges in QCD matter physics --The scientific programme of the Compressed Baryonic Matter experiment at FAIR
Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sNN= 2.7--4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (μB> 500 MeV), effects of chiral symmetry, and the equation of state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2024, in the context of the worldwide efforts to explore high-density QCD matter
Background free search for neutrinoless double beta decay with GERDA Phase II
The Standard Model of particle physics cannot explain the dominance of matter
over anti-matter in our Universe. In many model extensions this is a very
natural consequence of neutrinos being their own anti-particles (Majorana
particles) which implies that a lepton number violating radioactive decay named
neutrinoless double beta () decay should exist. The detection
of this extremely rare hypothetical process requires utmost suppression of any
kind of backgrounds.
The GERDA collaboration searches for decay of Ge
(^{76}\rm{Ge} \rightarrow\,^{76}\rm{Se} + 2e^-) by operating bare detectors
made from germanium with enriched Ge fraction in liquid argon. Here, we
report on first data of GERDA Phase II. A background level of
cts/(keVkgyr) has been achieved which is the world-best if
weighted by the narrow energy-signal region of germanium detectors. Combining
Phase I and II data we find no signal and deduce a new lower limit for the
half-life of yr at 90 % C.L. Our sensitivity of
yr is competitive with the one of experiments with
significantly larger isotope mass.
GERDA is the first experiment that will be background-free
up to its design exposure. This progress relies on a novel active veto system,
the superior germanium detector energy resolution and the improved background
recognition of our new detectors. The unique discovery potential of an
essentially background-free search for decay motivates a
larger germanium experiment with higher sensitivity.Comment: 14 pages, 9 figures, 1 table; ; data, figures and images available at
http://www.mpi-hd.mpg/gerda/publi
Limits on uranium and thorium bulk content in GERDA Phase I detectors
Internal contaminations of U, U and Th in the bulk of
high purity germanium detectors are potential backgrounds for experiments
searching for neutrinoless double beta decay of Ge. The data from GERDA
Phase~I have been analyzed for alpha events from the decay chain of these
contaminations by looking for full decay chains and for time correlations
between successive decays in the same detector. No candidate events for a full
chain have been found. Upper limits on the activities in the range of a few
nBq/kg for Ra, Ac and Th, the long-lived daughter
nuclides of U, U and Th, respectively, have been
derived. With these upper limits a background index in the energy region of
interest from Ra and Th contamination is estimated which
satisfies the prerequisites of a future ton scale germanium double beta decay
experiment.Comment: 2 figures, 7 page
Results on decay with emission of two neutrinos or Majorons in Ge from GERDA Phase I
A search for neutrinoless decay processes accompanied with
Majoron emission has been performed using data collected during Phase I of the
GERmanium Detector Array (GERDA) experiment at the Laboratori Nazionali del
Gran Sasso of INFN (Italy). Processes with spectral indices n = 1, 2, 3, 7 were
searched for. No signals were found and lower limits of the order of 10
yr on their half-lives were derived, yielding substantially improved results
compared to previous experiments with Ge. A new result for the half-life
of the neutrino-accompanied decay of Ge with significantly
reduced uncertainties is also given, resulting in yr.Comment: 3 Figure
decay of Ge into excited states with GERDA Phase I
Two neutrino double beta decay of Ge to excited states of Se
has been studied using data from Phase I of the GERDA experiment. An array
composed of up to 14 germanium detectors including detectors that have been
isotopically enriched in Ge was deployed in liquid argon. The analysis
of various possible transitions to excited final states is based on coincidence
events between pairs of detectors where a de-excitation ray is
detected in one detector and the two electrons in the other.
No signal has been observed and an event counting profile likelihood analysis
has been used to determine Frequentist 90\,\% C.L. bounds for three
transitions: : 1.6 yr,
: 3.7 yr and : 2.3 yr. These bounds are more
than two orders of magnitude larger than those reported previously. Bayesian
90\,\% credibility bounds were extracted and used to exclude several models for
the transition
QM/MM description of newly selected catalytic bioscavengers against organophosphorus compounds revealed reactivation stimulus mediated by histidine residue in the acyl-binding loop
© 2018 Zlobin, Mokrushina, Terekhov, Zalevsky, Bobik, Stepanova, Aliseychik, Kartseva, Panteleev, Golovin, Belogurov, Gabibov and Smirnov. Butyrylcholinesterase (BChE) is considered as an efficient stoichiometric antidote against organophosphorus (OP) poisons. Recently we utilized combination of calculations and ultrahigh-throughput screening (uHTS) to select BChE variants capable of catalytic destruction of OP pesticide paraoxon. The purpose of this study was to elucidate the molecular mechanism underlying enzymatic hydrolysis of paraoxon by BChE variants using hybrid quantum mechanical/molecular mechanical (QM/MM) calculations. Detailed analysis of accomplished QM/MM runs revealed that histidine residues introduced into the acyl-binding loop are always located in close proximity with aspartate residue at position 70. Histidine residue acts as general base thus leading to attacking water molecule activation and subsequent SN2 inline hydrolysis resulting in BChE reactivation. This combination resembles canonical catalytic triad found in active centers of various proteases. Carboxyl group activates histidine residue by altering its pKa, which in turn promotes the activation of water molecule in terms of its nucleophilicity. Observed re-protonation of catalytic serine residue at position 198 from histidine residue at position 438 recovers initial configuration of the enzyme's active center, facilitating next catalytic cycle. We therefore suggest that utilization of uHTS platform in combination with deciphering of molecular mechanisms by QM/MM calculations may significantly improve our knowledge of enzyme function, propose new strategies for enzyme design and open new horizons in generation of catalytic bioscavengers against OP poisons
Limit on the Radiative Neutrinoless Double Electron Capture of Ar from GERDA Phase I
Neutrinoless double electron capture is a process that, if detected, would
give evidence of lepton number violation and the Majorana nature of neutrinos.
A search for neutrinoless double electron capture of Ar has been
performed with germanium detectors installed in liquid argon using data from
Phase I of the GERmanium Detector Array (GERDA) experiment at the Gran Sasso
Laboratory of INFN, Italy. No signal was observed and an experimental lower
limit on the half-life of the radiative neutrinoless double electron capture of
Ar was established: 3.6 10 yr at 90 % C.I.Comment: 7 pages, 3 figure
The background in the neutrinoless double beta decay experiment GERDA
The GERmanium Detector Array (GERDA) experiment at the Gran Sasso underground
laboratory (LNGS) of INFN is searching for neutrinoless double beta decay of
76Ge. The signature of the signal is a monoenergetic peak at 2039 keV, the
Q-value of the decay, Q_bb. To avoid bias in the signal search, the present
analysis does not consider all those events, that fall in a 40 keV wide region
centered around Q_bb. The main parameters needed for the neutrinoless double
beta decay analysis are described. A background model was developed to describe
the observed energy spectrum. The model contains several contributions, that
are expected on the basis of material screening or that are established by the
observation of characteristic structures in the energy spectrum. The model
predicts a flat energy spectrum for the blinding window around Q_bb with a
background index ranging from 17.6 to 23.8*10^{-3} counts/(keV kg yr). A part
of the data not considered before has been used to test if the predictions of
the background model are consistent. The observed number of events in this
energy region is consistent with the background model. The background at Q-bb
is dominated by close sources, mainly due to 42K, 214Bi, 228Th, 60Co and alpha
emitting isotopes from the 226Ra decay chain. The individual fractions depend
on the assumed locations of the contaminants. It is shown, that after removal
of the known gamma peaks, the energy spectrum can be fitted in an energy range
of 200 kev around Q_bb with a constant background. This gives a background
index consistent with the full model and uncertainties of the same size
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