The PADME beam line Monte Carlo simulation Bossi, F.; Branchini, P.; Buonomo, B. ...
The journal of high energy physics,
09/2022, Letnik:
2022, Številka:
9
Journal Article
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bstract
The PADME experiment at the DAΦNE Beam-Test Facility (BTF) of the INFN Laboratory of Frascati is designed to search for invisible decays of dark sector particles produced in ...electron-positron annihilation events with a positron beam and a thin fixed target, by measuring the missing mass of single-photon final states. The presence of backgrounds originating from beam halo particles can significantly reduce the sensitivity of the experiment. To thoroughly understand the origin of the beam background contribution, a detailed G
eant
4-based Monte Carlo simulation has been developed, containing a full description of the detector together with the beam line and its optical elements. This simulation allows the full interactions of each particle to be described, both during beam line transport and during detection, a possibility which represents an innovative way to obtain reliable background predictions.
Abstract
A control and data acquisition software operating a TimePix3 sensor array from Advacam is described. A method for characterizing the positron beam used in the PADME Experiment is proposed ...and preliminary results obtained from data taking during the Fall 2022 are presented.
Electrolyte additions are used to control the functionality of a nanostructured oxide. Dopant ions affect the size and shape of deposit crystallites and modify the host structure. Such ions can be ...incorporated into the deposit or form a separate oxide phase. The manganese dioxide family of polymorphs with ion-molecular sieve properties represents the additional possibilities of “template” effects of dopant ions on the phase composition, heterovalent substitution in the cationic sublattice, changes in morphology and alteration of nanocrystallite size during electrocrystallisation. The effects of electrolyte doping in electrodeposited, non-stoichiometric manganese dioxide (NH4+, Li+ and Co2+), chromium oxide-based films (Co2+, Li+) were investigated. The structural characteristics and morphology were studied for all the obtained nanocomposites and deposits were evaluated as highly crystalline cathode materials cathodes, having high cyclability, in Li batteries.
The improved functionality of the electrodeposited nanomaterials was correlated to structural changes. Hollandite and pyrolusite electrodeposition pathways were proposed, based on symmetry principles of phase transitions.
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•Electrolyte doping for powdered MnO2 and CrxOy thin films have advantages vs conventional electrodeposition;•Hollandite and pyrolusite formation pathways can be derived from symmetry principles of phase transitions;•Semi-amorphous, isostructural series of ramsdellite-heterogenite like products at heavy Co + Li doping was established.•Cyclability of Co-doped CrxOy thin film coatings in Li batteries is demonstrated.
Human papillomavirus (HPV) is linked with a subset of head and neck squamous cell carcinomas (HNSCC). HPV-positive HNSCCs show a better prognosis than HPV-negative HNSCCs, which may be explained by ...sensitivity of the HPV-positive HNSCCs to ionizing radiation (IR). Although the molecular mechanism behind sensitivity to IR in HPV-positive HNSCCs is unresolved, DNA damage response (DDR) might be a significant determinant of IR sensitivity. An important player in the DDR, SMG-1 (suppressor with morphogenetic effect on genitalia), is a potential tumor suppressor and may therefore be deregulated in cancer. No studies have yet been conducted linking defects in SMG-1 expression with cancer. We investigated whether deregulation of SMG-1 could be responsible for defects in the DDR in oropharyngeal HNSCC.
Expression and promoter methylation status of SMG-1 were investigated in HNSCCs. To identify a functional link between HPV infection and SMG-1, we transfected the HPV-negative cells with an E6/E7 expression construct. SMG-1 short hairpin RNAs were expressed in HPV-negative cells to estimate survival upon IR.
Forced E6/E7 expression in HPV-negative cells resulted in SMG-1 promoter hypermethylation and decreased SMG-1 expression. Due to promoter hypermethylation, HPV-positive HNSCC cells and tumors express SMG-1 at lower levels than HPV-negative SCCs. Depletion of SMG-1 in HPV-negative HNSCC cells resulted in increased radiation sensitivity, whereas SMG-1 overexpression protected HPV-positive tumor cells from irradiation.
Levels of SMG-1 expression negatively correlated with HPV status in cancer cell lines and tumors. Diminished SMG-1 expression may contribute to the enhanced response to therapy exhibited by HPV-positive HNSCCs.
High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5 μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in ...particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1 Å are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ∼8 μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic InxAl1-xAs buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded InxAl1-xAs MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6 μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T = 10–300 K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As4/III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3 × 107 cm−2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300 nm, the extremely low surface roughness with the RMS value of 1.6–2.4 nm, measured by AFM, as well as rather high 3.5 μm-PL intensity at temperatures up to 300 K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform.
CHL1 gene (also known as CALL) on 3p26.3 encodes a one-pass trans-membrane cell adhesion molecule (CAM). Previously CAMs of this type, including L1, were shown to be involved in cancer growth and ...metastasis.
We used Clontech Cancer Profiling Arrays (19 different types of cancers, 395 samples) to analyze expression of the CHL1 gene. The results were further validated by RT-qPCR for breast, renal and lung cancer. Cancer Profiling Arrays revealed differential expression of the gene: down-regulation/silencing in a majority of primary tumors and up-regulation associated with invasive/metastatic growth. Frequent down-regulation (>40% of cases) was detected in 11 types of cancer (breast, kidney, rectum, colon, thyroid, stomach, skin, small intestine, bladder, vulva and pancreatic cancer) and frequent up-regulation (>40% of cases)--in 5 types (lung, ovary, uterus, liver and trachea) of cancer. Using real-time quantitative PCR (RT-qPCR) we found that CHL1 expression was decreased in 61% of breast, 60% of lung, 87% of clear cell and 89% papillary renal cancer specimens (P<0.03 for all the cases). There was a higher frequency of CHL1 mRNA decrease in lung squamous cell carcinoma compared to adenocarcinoma (81% vs. 38%, P = 0.02) without association with tumor progression.
Our results suggested that CHL1 is involved in the development of different human cancers. Initially, during the primary tumor growth CHL1 could act as a putative tumor suppressor and is silenced to facilitate in situ tumor growth for 11 cancer types. We also suggested that re-expression of the gene on the edge of tumor mass might promote local invasive growth and enable further metastatic spread in ovary, colon and breast cancer. Our data also supported the role of CHL1 as a potentially novel specific biomarker in the early pathogenesis of two major histological types of renal cancer.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Effect of In nanoparticles on electrical properties of InN MBE layers depends on growth modes.•Three-step growth comprising MBE, MEE, and DERI modes minimizes the metallic In amount.•In ...nanoparticles dominate the InN transport parameters even at minimum In amount of 3.8%.
Influence of the molecular beam epitaxy (MBE) growth conditions on the electrical properties of the InN epilayers in terms of minimization of the effect of spontaneously formed In nanoparticles was studied. A three-step growth sequence was used, including direct MBE growth of an InN nucleation layer, migration enhanced epitaxy (MEE) of an InN buffer layer, and In-rich MBE growth of the main InN layer, utilizing the droplet elimination by radical-beam irradiation (DERI) technique. The three-step growth regime was found to lead to decreasing the relative amount of In nanoparticles to 4.8% and 3.8% in In-rich and near-stoichiometric conditions, respectively, whereas the transport properties are better for the In-rich growth. Further reduction of the metallic indium inclusions in the InN films, while keeping simultaneously satisfactory transport parameters, is hardly possible due to fundamental processes of InN thermal decomposition and formation of the nitrogen vacancy conglomerates in the InN matrix. The In inclusions are shown to dominate the electrical conductivity of the InN films even at their minimum amount.
We report on pseudomorphic MBE growth of CdTe/Zn(Mg)(Se)Te quantum dot (QD) structures on InAs(100) substrates and studies of their structural and optical properties. The QDs were fabricated by using ...a thermal activation technique comprising deposition of a strained CdTe 2D layer, covering it with amorphous Te, followed by fast thermal desorption of the Te layer, which results in a 2D-3D RHEED pattern transition. The QDs exhibit the surface density as low as ~1010cm−2. The influence of MBE growth parameters and the structure design on photoluminescence properties of the QDs are discussed. Single QD photoluminescence was observed at T=8K from the 200-nm-wide mesa-structures made of the CdTe QD structures, and the antibunching effect with g(2)(0)=0.16±0.04 was demonstrated. The peculiarities of MBE growth of ZnTe/MgTe/MgSe short-period superlattices nearly lattice-matched to InAs, which could serve as wide gap barriers for efficient electron and hole confinement in the CdTe/Zn(Mg)(Se)Te QDs, are also described.
•CdTe/Zn(Mg)(Se)Te QD structures lattice-matched to InAs were grown by MBE.•CdTe/ZnTe QDs formed by thermal activation technique demonstrate antibunching effect.•MBE growth of ZnTe/MgTe/MgSe short-period superlattices pseudomorphic to InAs is reported.
Abstract
During 2022 data taking (Run III) PADME searched for a resonant production and a visible decay of the X17 particle into e
+
e
-
. A precise knowledge within 1% uncertainty of the number of ...positrons was required for the observation. To that purpose, an array of 2 × 6 Timepix3 (total of 512 × 1536 pixels) hybrid pixel detectors operated in data-streaming mode with ToA resolution of 1.56 ns for every pixel was employed. Two methods for data acquisition were developed. A frame-based method, integrating the number of hits for each individual pixel for a predefined period of time served for monitoring the beam conditions and to provide a rough estimation of the beam distribution and number of positrons. A data streaming mode exploiting the nanosecond time resolution of Timepix3 detector was used for precise characterization of the transverse beam profile and the distribution of the incident positrons within each bunch of ∼ 200 ns duration.
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