• Energy Research

Abstract Measurements of differential cross sections are presented for inclusive isolated-photon production in pp collisions at a centre-of-mass energy of 13 TeV provided by the LHC and using 139 fb−1 of data recorded by the ATLAS experiment. The cross sections are measured as functions of the photon transverse energy in different regions of photon pseudorapidity. The photons are required to be isolated by means of a fixed-cone method with two different cone radii. The dependence of the inclusive-photon production on the photon isolation is investigated by measuring the fiducial cross sections as functions of the isolation-cone radius and the ratios of the differential cross sections with different radii in different regions of photon pseudorapidity. The results presented in this paper constitute an improvement with respect to those published by ATLAS earlier: the measurements are provided for different isolation radii and with a more granular segmentation in photon pseudorapidity that can be exploited in improving the determination of the proton parton distribution functions. These improvements provide a more in-depth test of the theoretical predictions. Next-to-leading-order QCD predictions from JETPHOX and SHERPA and next-to-next-to-leading-order QCD predictions from NNLOJET are compared to the measurements, using several parameterisations of the proton parton distribution functions. The measured cross sections are well described by the fixed-order QCD predictions within the experimental and theoretical uncertainties in most of the investigated phase-space region.

A bstract Se realiza una búsqueda de nuevos fenómenos en eventos con un chorro de alta energía y gran momento transversal faltante utilizando datos de colisiones protón-protón a $ \sqrt{s}=7 $ TeV con el experimento ATLAS en el Gran Colisionador de Hadrones. Se exploran cuatro regiones cinemáticas utilizando un conjunto de datos correspondiente a una luminosidad integrada de 4.7 fb −1 . No se observa un exceso de eventos más allá de las expectativas de los procesos del Modelo Estándar, y se establecen límites en las grandes dimensiones adicionales y la producción de pares de partículas de materia oscura. A bstract A search for new phenomena in events with a high energy jet and large missing transverse momentum is performed using data from proton-proton collisions at $ \sqrt{s}=7 $ TeV with the ATLAS experiment at the Large Hadron Collider. Quatre régions cinématiques sont explorées à l'aide d'un ensemble de données correspondant à une luminosité intégrée de 4,7 fb −1 . Aucun excès d'événements au-delà des attentes des processus du modèle standard n'est observé, et des limites sont fixées pour les grandes dimensions supplémentaires et la production de paires de particules de matière noire. A bstract A search for new phenomena in events with a high-energy jet and large missing transverse momentum is performed using data from proton-proton collisions at $ \sqrt{s}=7 $ TeV with the ATLAS experiment at the Large Hadron Collider. Four kinematic regions are explored using a dataset corresponding to an integrated luminosity of 4.7 fb −1 . No excess of events beyond expectations from Standard Model processes is observed, and limits are set on large extra dimensions and the pair production of dark matter particles. ملخص يتم إجراء البحث عن ظواهر جديدة في الأحداث ذات النفاثة عالية الطاقة والزخم العرضي الكبير المفقود باستخدام بيانات من تصادمات البروتون والبروتون عند $\sqrt{s}=7 $ TeV مع تجربة أطلس في مصادم الهدرونات الكبير. يتم استكشاف أربع مناطق حركية باستخدام مجموعة بيانات تتوافق مع لمعان متكامل قدره 4.7 fb −1 . لم يتم ملاحظة أي زيادة في الأحداث تتجاوز التوقعات من عمليات النموذج القياسي، ويتم تعيين الحدود على أبعاد إضافية كبيرة وإنتاج زوج من جزيئات المادة المظلمة.

AbstractThis paper presents a measurement of b-jet production in Pb+Pb and pp collisions at $$\sqrt{s_{_\text {NN}}}=5.02$$ s NN = 5.02  TeV with the ATLAS detector at the LHC. The measurement uses 260 $$\text {pb}^{-1}$$ pb - 1 of pp collisions collected in 2017 and 1.4 $$\text {nb}^{-1}$$ nb - 1 of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti-$$k_{t}$$ k t algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters $$R= 0.2$$ R = 0.2 and $$R= 0.4$$ R = 0.4 , and only $$R= 0.2$$ R = 0.2 jets are used in Pb+Pb collisions. For comparison, inclusive $$R= 0.2$$ R = 0.2 jets are also measured using 1.7 $$\text {nb}^{-1}$$ nb - 1 of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, $$R_\text {AA}$$ R AA , is calculated for both b-jets and inclusive jets with $$R= 0.2$$ R = 0.2 over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet $$R_\text {AA}$$ R AA to inclusive jet $$R_\text {AA}$$ R AA is also presented and suggests that the $$R_\text {AA}$$ R AA for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.

Abstract A search for new phenomena has been performed in final states with at least one isolated high-momentum photon, jets and missing transverse momentum in proton–proton collisions at a centre-of-mass energy of $$ \sqrt{s} $$ s = 13 TeV. The data, collected by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb−1. The experimental results are interpreted in a supersymmetric model in which pair-produced gluinos decay into neutralinos, which in turn decay into a gravitino, at least one photon, and jets. No significant deviations from the predictions of the Standard Model are observed. Upper limits are set on the visible cross section due to physics beyond the Standard Model, and lower limits are set on the masses of the gluinos and neutralinos, all at 95% confidence level. Visible cross sections greater than 0.022 fb are excluded and pair-produced gluinos with masses up to 2200 GeV are excluded for most of the NLSP masses investigated.