| 1. |
- Alimena, Juliette, et al.
(författare)
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Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider
- 2020
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Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 47:9
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Tidskriftsartikel (refereegranskat)abstract
- Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments-as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER-to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the high-luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity 'dark showers', highlighting opportunities for expanding the LHC reach for these signals.
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| 2. |
- Buchhave, Lars A., et al.
(författare)
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An abundance of small exoplanets around stars with a wide range of metallicities
- 2012
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 486:7403, s. 375-377
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Tidskriftsartikel (refereegranskat)abstract
- The abundance of heavy elements (metallicity) in the photospheres of stars similar to the Sun provides a 'fossil' record of the chemical composition of the initial protoplanetary disk. Metal-rich stars are much more likely to harbour gas giant planets(1-4), supporting the model that planets form by accumulation of dust and ice particles(5). Recent ground-based surveys suggest that this correlation is weakened for Neptunian-sized planets(4,6-9). However, how the relationship between size and metallicity extends into the regime of terrestrial-sized exoplanets is unknown. Here we report spectroscopic metallicities of the host stars of 226 small exoplanet candidates discovered by NASA's Kepler mission(10), including objects that are comparable in size to the terrestrial planets in the Solar System. We find that planets with radii less than four Earth radii form around host stars with a wide range of metallicities (but on average a metallicity close to that of the Sun), whereas large planets preferentially form around stars with higher metallicities. This observation suggests that terrestrial planets may be widespread in the disk of the Galaxy, with no special requirement of enhanced metallicity for their formation.
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| 3. |
- Smith, Nathan, et al.
(författare)
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Kinematics and Ultraviolet to Infrared Morphology of the Inner Homunculus of η Carinae
- 2004
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 605:1, s. 405-424
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Tidskriftsartikel (refereegranskat)abstract
- We present the first ultraviolet and optical images of η Car and itscircumstellar Homunculus nebula, obtained with the Advanced Camera forSurveys/High Resolution Camera (ACS/HRC) on board the Hubble SpaceTelescope (HST). Compared to those at visual wavelengths, UV imagesreveal excess emission 0.1"-0.6" from the central source along the minoraxis that may emanate from the outer parts of η Car's nonsphericalstellar wind, which dominates the UV flux from η Car. The UVemission fills the cavity inside a dust torus measured from infrared(IR) data; within 0.2" of the star the UV emission projects a morphologyreminiscent of the IR torus, but it is a factor of 10 smaller. This``little torus'' seen in the UV may be related to the ``LittleHomunculus'' discovered recently, signifying recurrent mass ejectionswith the same geometry. Finally, we reexamine the kinematics of nebularcondensations near the star (Weigelt objects C and D) in HST images andspectra obtained over the past decade. We measure heliocentricvelocities slower than previous estimates, and from proper motions wederive an ejection date of 1908+/-12 yr, assuming linear motion.However, because of radiative acceleration, these objects may have beenejected earlier-perhaps during the 1890 outburst of η Car.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
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