Hadronic showers transfer a relevant amount of their energy to electromagnetic subshowers. We show that the generation of "secondary" dark photons in these subshowers is significant and typically ...dominates the production at low dark photon masses. The resulting dark photons are however substantially less energetic than the ones originating from mesons decay. We illustrate this point both semianalytically and through Monte Carlo simulations. Existing limits on vector-mediator scenarios for light dark matter are updated with the inclusion of the new production processes.
Medium-energy electron beam-dump experiments provide an intense source of secondary muons. These particles can be used to search for muon-coupling light dark scalars that may explain the (g − 2)μ ...anomaly. We applied this idea to the SLAC E137 experiment deriving new exclusion limits and evaluated the expected sensitivity for the planned Jefferson Lab BDX experiment (in case of a null result report). The calculation is based on numerical simulations that include a realistic description of secondary muons generation in the dump, dark scalar production, propagation, and decay, and, finally, the decay product (electrons, positrons, or photons) interaction with the detector. For both experiments, exclusion limits were extended to cover a broader area in the scalar-to-muon coupling vs scalar mass parameter space. This study demonstrates that electron beam-dump experiments have an enhanced sensitivity to new physics in processes that are usually studied using proton beams.
A novel mechanism to produce and detect light dark matter in experiments making use of GeV electrons (and positrons) impinging on a thick target (beam dump) is proposed. The positron-rich environment ...produced by the electromagnetic shower allows us to produce an A^{'} via nonresonant (e^{+}+e^{-}→γ+A^{'}) and resonant (e^{+}+e^{-}→A^{'}) annihilation on atomic electrons. The latter mechanism, for some selected kinematics, results in a larger sensitivity with respect to limits derived by the commonly used A^{'}-strahlung. This idea, applied to beam-dump experiments and active beam-dump experiments, pushes down the current limits by an order of magnitude.
High-energy positron annihilation is a viable mechanism to produce dark photons (A′). This reaction plays a significant role in beam-dump experiments using multi-GeV electron beams on thick targets ...by enhancing the sensitivity to A′ production. The positrons produced by the electromagnetic shower can produce an A′ via nonresonant (e++e−→γ+A′) and resonant (e++e−→A′) annihilation on atomic electrons. For visible decays, the contribution of resonant annihilation results in a larger sensitivity with respect to limits derived by the commonly used A′-strahlung in certain kinematic regions. When included in the evaluation of the E137 beam-dump experiment reach, positron annihilation pushes the current limit on ϵ downwards by a factor of 2 in the range 33 MeV/c2<mA′<120 MeV/c2.
The Jefferson Laboratory community recently joined the dark sector search program with different, complementary efforts: APEX, HPS, DarkLight, and BDX. These fixed-target, electron-beam experiments ...are designed to search for Dark Matter in the mass range 10 MeV/c2 - 1 GeV/c2, the so-called "light Dark Matter" region. Each experiment is optimized to look for a specific light Dark Matter signal signature. In this paper, after a brief introduction to the light Dark Matter hypothesis, I present the four experiments, describing their scientific goal, the measurement setup, and the obtained or expected results.
This systematic review aimed to examine whether the incidence of osteonecrosis differed between patients who have dental extractions before or after radiotherapy (RT). The reported incidence of ...osteoradionecrosis (ORN) of the jaws following RT to the head and neck varies widely in the literature. Currently, for patients with head and neck cancer there are no universally accepted guidelines on the optimal timing of dental surgery relative to RT to minimise incident ORN. A literature review was conducted using the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) criteria. A search of PubMed, EMBASE, Evidence-Based Medicine, and Web of Science databases targeted literature published up to and including 10 April 2020. Two independent reviewers assessed studies for eligibility against inclusion criteria. An assessment of bias was conducted for each of the included studies and relevant data extracted. A meta-analysis was undertaken using the statistical methods described. Twenty-four of 708 studies were included. They were heterogeneous and included a wide variation of RT methods, head and neck malignancies, and comorbidities. While some concluded that the incidence of ORN was dependent on the timing of dental extractions in relation to RT, with regard to the risk of its development, others reported additional factors such as age, comorbidities, extent of surgical resection, and dose and field of radiation, as more important predictors than timing. In many there was consistent lack of detail around the timing of dental procedures in relation to the delivery of RT. From 21 studies including 36,294 patients, of whom 14,389 had extractions before RT, the pooled incidence of ORN was 5.5% (95% CI: 2.1% to 10.1%). Significant heterogeneity was found in Cochran’s Q-test (p<0.001) and Higgins I2=98.0%. From 21 studies including 37,805 patients, of whom 6030 had extractions after RT, the pooled incidence of ORN was 5.3% (95% CI: 2.9% to 8.2%). Significant heterogeneity was found in Cochran’s Q-test (p<0.001) and Higgins I2=80.0%. There was no statistically significant difference between these two groups (random-effects model Q=0.12, p=0.73). Large, longitudinal studies with a priori-specified methods are needed to identify, recruit, and prospectively follow patients with head and neck cancer for the onset of ORN after dental surgery. This will allow clinical guidelines to be established to assist clinicians to plan treatment when extractions are indicated in patients undergoing RT to the head and neck.
This paper describes the design and performance of a compact detector, BDX-MINI, that incorporates all features of a concept that optimized the detection of light dark matter in the MeV-GeV mass ...range produced by electrons in a beam dump. It represents a reduced version of the future BDX experiment expected to run at JLAB. BDX-MINI was exposed to penetrating particles produced by a 2.176 GeV electron beam incident on the beam dump of Hall A at Jefferson Lab. The detector consists of 30.5 kg of PbWO
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crystals with sufficient material following the beam dump to eliminate all known particles except neutrinos. The crystals are read out using silicon photomultipliers. Completely surrounding the detector are a passive layer of tungsten and two active scintillator veto systems, which are also read out using silicon photomultipliers. The design was validated and the performance of the robust detector was shown to be stable during a six month period during which the detector was operated with minimal access.
The large number of diseases occurring when desmosome constituents are impaired provides striking evidence for the key role of desmosomes in maintaining tissue integrity. A detailed understanding of ...the molecular alterations causing desmosomal dysfunction has, in turn, underpinned the development of novel diagnostic tools. This has salient clinical implications for dentists and oral medicine practitioners because the majority of desmosomal diseases affect the oral cavity. In the present article, we review the autoimmune, infectious, genetic, and neoplastic diseases that target the desmosome, with particular emphasis on clinical manifestations, diagnostic pathways, and relevant laboratory investigations.
We study tensor meson photoproduction outside of the resonance region, at beam energies of a few GeVs. We build a model based on Regge theory that includes the leading vector and axial exchanges. We ...consider two determinations of the unknown helicity couplings and fit to the recent a2 photoproduction data from CLAS. Both choices give a similar description of the a2 cross section but result in different predictions for the parity asymmetries and the f2 photoproduction cross section. We conclude that new measurements of f2 photoproduction in the forward region are needed to pin down the correct production mechanism. We also extend our predictions to the 8.5 GeV beam energy, where current experiments are running.
The interrelationship between malignant epithelium and the underlying stroma is of fundamental importance in tumour development and progression. In the present study, we used cancer-associated ...fibroblasts (CAFs) derived from genetically unstable oral squamous cell carcinomas (GU-OSCC), tumours that are characterized by the loss of genes such as TP53 and p16
and with extensive loss of heterozygosity, together with CAFs from their more genetically stable (GS) counterparts that have wild-type TP53 and p16
and minimal loss of heterozygosity (GS-OSCC). Using a systems biology approach to interpret the genome-wide transcriptional profile of the CAFs, we show that transforming growth factor-β (TGF-β) family members not only had biological relevance in silico but also distinguished GU-OSCC-derived CAFs from GS-OSCC CAFs and fibroblasts from normal oral mucosa. In view of the close association between TGF-β family members, we examined the expression of TGF-β1 and TGF-β2 in the different fibroblast subtypes and showed increased levels of active TGF-β1 and TGF-β2 in CAFs from GU-OSCC. CAFs from GU-OSCC, but not GS-OSCC or normal fibroblasts, induced epithelial-mesenchymal transition and down-regulated a broad spectrum of cell adhesion molecules resulting in epithelial dis-cohesion and invasion of target keratinocytes in vitro in a TGF-β-dependent manner. The results demonstrate that the TGF-β family of cytokines secreted by CAFs derived from genotype-specific oral cancer (GU-OSCC) promote, at least in part, the malignant phenotype by weakening intercellular epithelial adhesion.
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