CMS physics technical design report : Addendum on high density QCD with heavy ions

Peer reviewe

An embedding technique to determine ττ backgrounds in proton-proton collision data

An embedding technique is presented to estimate standard model tau tau backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed mu mu events and replaced with simulated tau leptons with the same kinematic properties. In this way, a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed. The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at root s = 13 TeV corresponding to an integrated luminosity of 41.5 fb(-1).Peer reviewe

Measurement of the Z y production cross section in pp collisions at 8 TeV and search for anomalous triple gauge boson couplings

The cross section for the production of Z γ in proton-proton collisions at 8 TeV is measured based on data collected by the CMS experiment at the LHC corresponding to an integrated luminosity of 19.5 fb −1 . Events with an oppositely-charged pair of muons or electrons together with an isolated photon are selected. The differential cross section as a function of the photon transverse momentum is measured inclusively and exclusively, where the exclusive selection applies a veto on central jets. The observed cross sections are compatible with the expectations of next-to-next-to-leading-order quantum chromodynamics. Limits on anomalous triple gauge couplings of ZZ γ and Z γγ are set that improve on previous experimental results obtained with the charged lepton decay modes of the Z boson

Performance of missing transverse momentum reconstruction in proton-proton collisions at root s=13 TeV using the CMS detector

The performance of missing transverse momentum ((p) over right arrow (miss)(T)) reconstruction algorithms for the CMS experiment is presented, using proton-proton collisions at a center-of-mass energy of 13 TeV, collected at the CERN LHC in 2016. The data sample corresponds to an integrated luminosity of 35.9 fb(-1). The results include measurements of the scale and resolution of (p) over right arrow (miss)(T), and detailed studies of events identified with anomalous (p) over right arrow (miss)(T). The performance is presented of a (p) over right arrow (miss)(T) reconstruction algorithm that mitigates the effects of multiple proton-proton interactions, using the "pileup per particle identification" method. The performance is shown of an algorithm used to estimate the compatibility of the reconstructed (p) over right arrow (miss)(T) with the hypothesis that it originates from resolution effects.Peer reviewe

Timing and Spatial Distribution of Loess inXinjiang, NW China

Central Asia is one of the most significant loess regions on Earth, with an important role in understanding Quaternary climate and environmental change. However, in contrast to the widely investigated loess deposits in the Chinese Loess Plateau, the Central Asian loess– paleosol sequences are still insufficiently known and poorly understood. Through field investigation and review of the previous literature, the authors have investigated the distribution, thickness and age of the Xinjiang loess, and analyzed factors that control these parameters in the Xinjiang in northwest China, Central Asia. The loess sediments cover river terraces, low uplands, the margins of deserts and the slopes of the Tianshan Mountains and Kunlun Mountains and are also present in the Ili Basin. The thickness of the Xinjiang loess deposits varies from several meters to 670 m. The variation trend of the sand fraction (>63 μm) grain-size contour can indicate the local major wind directions, so we conclude that the NW and NE winds are the main wind directions in the North and South Xinjiang, and the westerly wind mainly transport dust into the Ili basin. We consider persistent drying, adequate regional wind energy and well-developed river terraces to be the main factors controlling the distribution, thickness and formation age of the Xinjiang loess. The well-outcropped loess sections have mainly developed since the middle Pleistocene in Xinjiang, reflecting the appearance of the persistent drying and the present air circulation system. However, the oldest loess deposits are as old as the beginning of the Pliocene in the Tarim Basin, which suggests that earlier aridification occurred in the Tarim Basin rather than in the Ili Basin and the Junggar Basin

Greater health risk in wet season than in dry season in the Yellow River of the Lanzhou region

The Yellow River flows through Lanzhou city and is the only drinking water source for 3.6 million residents. Yet, little is known regarding the safety and quality of the Yellow River for resident consumption. To address this knowledge-gap, water samples were collected from different sites within this section during the dry and wet seasons. Physico-chemical parameters and microbial community metrics were analyzed to assess the health risk associated with this Chinese mother river. Water quality of the river was better during the dry season (March–April) than in the wet season (September–October). Fifteen conventional physico-chemical and biological indices, such as NH3-N, NO2−-N, total nitrate (TN), five day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), volatile phenol (VP), and coliform abundances, generally exceeded acceptable standards. The average abundance of coliforms was 2.8 times that of acceptable standards in the dry season and 4.6 times the standards in the wet season. The concentration of the toxic metal As was more than two times than that of the national standard in waters from the wet season. Microbial community analysis also indicated that community diversity and species richness were positively correlated with the concentrations of several physico-chemical parameters. The results indicate that As and Cr6+ pose potential risk for human health through consumption by residents. Further, the results indicated that human activities are the main causes of water pollution, and that long-term strict monitoring should be conducted to ensure the safety of drinking water consumption and the health of the environment

Comparison between luminescence and radiocarbon dating of lateQuaternary loess from the Ili Basin in Central Asia

Dust depositions are critical archives for understanding interior aridification and westerly climatic changes in Central Asia. Accurate and reliable dating of loess is very important for interpreting and correlating environmental records. There remains a disparity between luminescence ages and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia. In this study, we establish a closely spaced quartz optically stimulated luminescence (OSL) chronology for the 20.5-m-thick Nilka loess section in the Ili Basin. Based on OSL ages, two intervals of higher mass accumulation rate occurred at 49&ndash;43&nbsp;ka and 24&ndash;14&nbsp;ka. We further compare these OSL ages with 23 accelerator mass spectrometry (AMS) 14C ages of bulk organic matter. The results indicate that the OSL and radiocarbon ages agree well for ages younger than ca. 25 14C cal&nbsp;ka&nbsp;BP. However, beyond 30&nbsp;cal&nbsp;ka&nbsp;BP, there is no consistent increase in AMS 14C age with depth, while the OSL ages continue to increase. These differences confirm the observation that the AMS 14C ages obtained using conventional acid&ndash;base&ndash;acid (ABA) pretreatment are severely underestimated in other terrestrial deposits in Central Asia, which could be due to 2&ndash;4% modern carbon contamination. However, OSL dating is applicable for constructing an accurate chronology beyond 30&nbsp;cal&nbsp;ka&nbsp;BP. We suggest caution when interpreting paleoenvironmental changes based on radiocarbon ages older than 25&nbsp;cal&nbsp;ka&nbsp;BP.</p

Geoconservation and geotourism in Luochuan Loess National Geopark, China

The Chinese Loess Plateau (CLP) is the largest area of loess deposits in the world. Loess sediments in the CLP have high scientific value for global climate change research and are also important resources for tourism, especially science-based tourism. Unfortunately, loess conservation and geotourism do not attract much attention from the general public in China. This study briefly introduces the history of geoconservation and geotourism in China and uses Luochuan Loess National Geopark (LLNG) as an example to review problems with the development of geotourism and geoconservation. The main problems identified are inadequate measures to protect the loess geoheritage, a conflict between ecological restoration and scientific observation, ineffective interpretation of geological features for visitors, a lack of an engaging way to exhibit the materials in the Loess Museum and insufficient financial support. We propose new strategies for the sustainable development of LLNG, such as improving infrastructure, improving management actions, planting grass rather than trees for ecological restoration, popularizing science and increasing its practical use, developing a modern geological museum, and integrating the park into a global network of geological parks.</p

Evolution of aerosol chemistry in Xi'an, inland China, during the dust storm period of 2013-Part 1: Sources, chemical forms and formation mechanisms of nitrate and sulfate

A total suspended particulate (TSP) sample was collected hourly in Xi&#39;an, an inland megacity of China near the Loess Plateau, during a dust storm event of 2013 (9 March 18: 00-12 March 10: 00 LT), along with a size-resolved aerosol sampling and an online measurement of PM2.5. The TSP and size-resolved samples were determined for elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC) and nitrogen (WSON), inorganic ions and elements to investigate chemistry evolution of dust particles. Hourly concentrations of Cl-, NO3-, SO42-, Na+ and Ca2+ in the TSP samples reached up to 34, 12, 180, 72 and 28 mu g m(-3), respectively, when dust peak arrived over Xi&#39;an. Chemical compositions of the TSP samples showed that during the whole observation period NH4+ and NO3- were linearly correlated with each other (r(2) = 0.76) with a molar ratio of 1 : 1, while SO42- and Cl- were well correlated with Na+, Ca2+, Mg2+ and K+ (r(2) &gt; 0.85). Size distributions of NH4+ and NO3- presented a same pattern, which dominated in the coarse mode (&gt;2.1 mu m) during the event and predominated in the fine mode (&lt;2.1 mu m) during the non-event. SO42- and Cl- also dominated in the coarse mode during the event hours, but both exhibited two equivalent peaks in both the fine and the coarse modes during the non-event, due to the fine-mode accumulations of secondarily produced SO42- and biomass-burning-emitted Cl- and the coarse-mode enrichments of urban soil-derived SO42- and Cl-. Linear fit regression analysis further indicated that SO42- and Cl- in the dust samples possibly exist as Na2SO4, CaSO4 and NaCl, which directly originated from Gobi desert surface soil, while NH4+ and NO3- in the dust samples exist as NH4NO3. We propose a mechanism to explain these observations in which aqueous phase of dust particle surface is formed via uptake of water vapor by hygroscopic salts such as Na2SO4 and NaCl, followed by heterogeneous formation of nitrate on the liquid phase and subsequent absorption of ammonia. Our data indicate that 54 +/- 20% and 60 +/- 23% of NH4+ and NO3- during the dust period were secondarily produced via this pathway, with the remaining derived from the Gobi desert and Loess Plateau, while SO42- in the event almost entirely originated from the desert regions. Such cases are different from those in the East Asian continental outflow region, where during Asia dust storm events SO42- is secondarily produced and concentrates in sub-micrometer particles as (NH4)(2)SO4 and/or NH4HSO4. To the best of our knowledge, the current work for the first time revealed an infant state of the East Asian dust ageing process in the regions near the source, which is helpful for researchers to understand the panorama of East Asian dust ageing process from the desert area to the downwind region.</p