| 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. |
- Gallenne, A., et al.
(författare)
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A Geometrical 1% Distance to the Short-period Binary Cepheid V1334 Cygni
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 867:2
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Tidskriftsartikel (refereegranskat)abstract
- Cepheid stars play a considerable role as extragalactic distances indicators, thanks to the simple empirical relation between their pulsation period and their luminosity. They overlap with that of secondary distance indicators, such as Type Ia supernovae, whose distance scale is tied to Cepheid luminosities. However, the period-luminosity (P-L) relation still lacks a calibration to better than 5%. Using an original combination of interferometric astrometry with optical and ultraviolet spectroscopy, we measured the geometrical distance d = 720.35 +/- 7.84 pc of the 3.33 day period Cepheid V1334 Cyg with an unprecedented accuracy of +/- 1%, providing the most accurate distance for a Cepheid. Placing this star in the P-L diagram provides an independent test of existing P-L relations. We show that the secondary star has a significant impact on the integrated magnitude, particularly at visible wavelengths. Binarity in future high-precision calibrations of the P-L relations is not negligible, at least in the short-period regime. Subtracting the companion flux leaves V1334 Cyg in marginal agreement with existing photometric-based P-L relations, indicating either an overall calibration bias or a significant intrinsic dispersion at a few percent level. Our work also enabled us to determine the dynamical masses of both components, M-1 = 4.288 +/- 0.133 M-circle dot (Cepheid) and M-2 = 4.040 +/- 0.048 M-circle dot (companion), providing the most accurate masses for a Galactic binary Cepheid system.
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| 3. |
- Wahlgren, Glenn, et al.
(författare)
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The Bismuth Abundance in the HGMN Stars chi Lupi and HR 7775 and Improved Atomic Data for Selected Transitions of BI I, BI II, and BI III
- 2001
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 551:1, s. 520-535
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution spectra of the chemically peculiar HgMn stars chi Lupiand HR 7775, obtained with the Hubble Space Telescope/Goddard HighResolution Spectrograph, are investigated for their abundance of bismuthby comparison with LTE synthetic spectrum modeling. HR 7775, previouslyknown from International Ultraviolet Explorer spectra to display stronglines of Bi II, is determined to have bismuth present at an enhancementlevel of nearly 5 orders of magnitude from the lines Bi IIlambdalambda1436, 1902 and Bi III lambda1423. The bismuthenhancement for chi Lupi is found to be near a level of 1.5 dex, andan ionization anomaly between Bi+ and Bi++ isapparent. HR 7775 abundance enhancements of the heavy elements platinum,[Pt/H]=4.7 dex, and gold, [Au/H]=3.8 dex, have also been determined. Newlaboratory measurements for wavelengths and hyperfine structure patternsof Bi I/Bi II/Bi III lines are presented, as well as the results ofcalculations for hyperfine structure constants and oscillator strengthsfor selected lines of Bi II and Bi III. Based on observations with theNASA/ESA Hubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS5-26555.
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| 4. |
- Adelman, S J, et al.
(författare)
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Heavy Element Abundances in Late-B and Early-A Stars. I. Co-Added IUE Spectra of HgMn Stars
- 2004
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Ingår i: The Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 155:1, s. 179-189
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Tidskriftsartikel (refereegranskat)abstract
- Very heavy elements (Pt, Au, Hg, Tl, and Bi) are found to be enhanced inthe atmospheres of the chemically peculiar stars of the upper mainsequence by up to a million times the solar system levels. Suchenhancements are believed to result from atmospheric dynamics (i.e.,diffusion) rather than scenarios that dredge up nuclear-processedmaterial to the surface or transfer processed material between binarycompanions. However, the theoretical framework needs to be furtherconstrained by observations beyond the realm of the spectral types forwhich such abundance enhancements are observed at optical wavelengths.The International Ultraviolet Explorer (IUE) satellite collected spectraof bright stars for which chemical peculiarities have been derived fromground-based data. For several elements the abundance enhancements haveonly been recently measured using Hubble Space Telescope data and havetherefore not yet been exploited in the IUE data. We have initiated aprogram to analyze IUE high-dispersion spectra to more fullycharacterize the pattern of very heavy element enhancement for manymercury-manganese (HgMn) stars and to potentially extend the spectralclass (effective temperature) boundaries over which these abundanceanomalies are known to exist. The abundances of very heavy elements inchemically normal B and A-type stars provide a base level that may becompared with the solar system abundances. These early spectral typestars may therefore reveal clues for galactic chemical evolution studiessince they were formed at a later epoch than the Sun in the history ofthe Galaxy. This first paper presents the motivation for the analyses tofollow, outlines our spectral co-addition technique for IUE spectra, anddiscusses the choice of model atmospheres and the synthetic spectrumprocedures, while initiating the study by highlighting the abundance ofgold in several HgMn stars.
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| 5. |
- Adelman, S. J., et al.
(författare)
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Ultraviolet Spectral Analyses of HgMn Stars
- 2001
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Ingår i: Bulletin of the American Astronomical Society. ; 33:4, s. 1328-1328
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Konferensbidrag (refereegranskat)abstract
- Almost a decade after the last observations were performed by theInternational Ultraviolet Explorer (IUE) satellite its rich archivescomprise a wealth of opportunity for the stellar astronomer, inparticular when exploring large samples of stars. We have inaugurated anexploration into the nature of chemically peculiar stars through thoseelemental abundance studies which are best carried out at UVwavelengths. The analysis of the IUE data set is benefited at this timeby improvements in data quality as instituted by IUE NEWSIPS and acoaddition procedure that we have implemented for those stars for whichmultiple spectral images exist in the IUE archives. The IUE dataanalysis is furthered by high resolution HST/GHRS and STIS spectraobtained for a few appropriate targets. The HST data allow for theproduction of spectral templates which can subsequently be applied tothe lower resolution IUE data in order to more fully understand lineblending issues. Our present studies are concentrated on thedistribution of heavy elements in the atmospheres of HgMn stars and willbe expanded to include other classes of chemical peculiarity in aneffort to understand the phenomenon of spectral line anomalies amongstars of the upper main sequence. We outline our techniques and presentabundance results for the poorly studied element gold in HgMn stars.This work was supported by a Grant from NASA's ADP Program.
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