Results from TOTEM

The TOTEM experiment at the CERN LHC is focussed on the measurement of the elastic proton-proton scattering, the total pp cross-section, and all kinds of diffractive phenomena. Detectors housed in “Roman Pots” which can be moved close to the outgoing proton beams allow to trigger on elastic and diffractive protons and to determine their parameters like the momentum loss and the transverse momentum transfer. In addition, charged particle detectors in the forward regions detect almost all inelastic events. Together with the CMS detector, a large solid angle is covered enabling precise studies of Min. Bias as well as Single Diffractive and Double Pomeron Interactions. The results will considerably help the interpretation of the Cosmic Ray Showers at highest energies and will give insight into the proton structure and the QCD theory of strong interactions. TOTEM measured the elastic pp- scattering over a large range of t (the squared momentum transfer) from 10-3 – 4 GeV2. Noneof the considered models could yield a satisfactory fit over the complete range. However, the exponential slope at low |t|-values and the position of the diffractiveminimum are well within the extrapolation from lower energies. The total pp cross-section has been determined in different ways from the extrapolation of the elasticscattering to t=0 (optical point) and the inelastic rate: (i) From the elastic scattering using the optical theorem and the CMS, (ii) luminosity independently, usingthe inelastic rate, elastic scattering and the optical theorem, (iii)ρ independently, by using elastic scattering, inelastic rate and the CMS luminosity. The results for the total crosssection obtained from the different methods are in excellent agreement with each other. First studies of the data on diffractive phenomena havebeen performed by correlating the momentum loss of the forward protons with the topology of the particle flux. The data look very promising and further studies will follow. Since the conference, data have also been taken with specialized optics to reach even lower |t|-values. A determination of the ρ value is now in reach.The TOTEM results and the ways how they have been obtained are described in the publications [1–8] listed below

FELIX, a full acceptance detector for the CERN LHC

Plans for FELIX, a full acceptance detector for the future CERN Large Hadron Collider (LHC), are described. The physics goals include detailed studies of the strong interactions (QCD), the forward energy flow and diffractive processes (Pomeron interactions), electroweak rapidity gaps, and elastic scattering. The precise measurement of particle production at a centre-of-mass energy of 14 TeV, well above the cosmic ray ``knee", will be fundamental for the interpretation of the highest energy cosmic ray events and may clarify some of the anomalies indicated by some cosmic ray experiments. The magnetic architecture and some of the design issues are briefly reviewed

A stochastical model for periodic domain structuring in ferroelectric crystals

A stochastical description is applied in order to understand how ferroelectric structures can be formed. The predictions are compared with experimental data of the so-called electrical fixing: Domains are patterned in photorefractive lithium niobate crystals by the combination of light-induced space-charge fields with externally applied electrical fields. In terms of our stochastical model the probability for domain nucleation is modulated according to the sum of external and internal fields. The model describes the shape of the domain pattern as well as the effective degree of modulation

Holographic grating formation in silver nanoparticle suspensions

Thermal gratings are recorded in silver nanoparticle suspensions by nanosecond pulsed holography. Initial transients in diffraction efficiency demonstrate competing effects in grating formation. The grating's final decay is consistent with the suspension's thermal conductivity

Model simulation of seasonal growth of Fucus vesiculosus in its benthic community

Numerical models are a suitable tool to quantify impacts of predicted climate change on complex ecosystems but are rarely used to study effects on benthic macroalgal communities. Fucus vesiculosus L. is a habitat-forming macroalga in the Baltic Sea and alarming shifts from the perennial Fucus community to annual filamentous algae are reported. We developed a box model able to simulate the seasonal growth of the Baltic Fucus-grazer-epiphyte system. This required the implementation of two state variables for Fucus biomass in units of carbon (C) and nitrogen (N). Model equations describe relevant physiological and ecological processes, such as storage of C and N assimilates by Fucus, shading effects of epiphytes or grazing by herbivores on both Fucus and epiphytes, but with species-specific rates and preferences. Parametrizations of the model equations and required initial conditions were based on measured parameters and process rates in the near-natural Kiel Outdoor Benthocosm (KOB) experiments during the Biological Impacts of Ocean Acidification project. To validate the model, we compared simulation results with observations in the KOB experiment that lasted from April 2013 until March 2014 under ambient and climate-change scenarios, that is, increased atmospheric temperature and partial pressure of carbon dioxide. The model reproduced the magnitude and seasonal cycles of Fucus growth and other processes in the KOBs over 1 yr under different scenarios. Now having established the Fucus model, it will be possible to better highlight the actual threat of climate change to the Fucus community in the shallow nearshore waters of the Baltic Sea

Modelling the Seasonal Growth of the Brown Seaweed Fucus Vesiculosus in the Kiel Outdoor Benthocosms

Warming and acidification of the oceans as a consequence of increasing CO2-concentrations occur globally. In mesocosm experiments, the single and combined impact of elevated seawater temperature and pCO2 (1,100 ppm) on the brown alga Fucus vesiculosus together with its ssociated community (epiphytes and mesograzers) was studied in four consecutive experiments (from April 2013 to April 2014). Based on these experiments, a numerical boxmodel simulating the seasonal growth of F. vesiculosus in the Kiel Outdoor Benthocosms (KOBs) was developed. Nitrogen and carbon cycling in the KOBs were considered and relevant physiological and ecological processes were implemented. To run simulations under present and global change scenarios (e.g. warming, ocean acidification) the model was forced with atmospheric and hydrographic data of the Kiel fjord. DIN and DIC concentration in the water and Fucus growth as carbon and nitrogen increase were explicitly modelled. For instance, the following processes were implemented: (1) Storage of carbon and nitrogen assimilates by Fucus, leading to a temporal decoupling of assimilation and growth. (2) Shading effects of epiphytes. (3) Grazing by Idotea, Gammarus and Littorina on both Fucus and epiphytes, but with species-specific rates and preferences. At present, the model is a suitable scientific tool capable of integrating our knowledge about macroalgal processes, their growth and productivity in coastal areas. It further facilitates the communication of complex knowledge to lay persons. Ultimately, the development of a predictive model, which can be coupled to a 3D-high resolution western Baltic Sea model, is anticipated. This will allow observations on the consequences of global change for the wellbeing and distribution of F. vesiculosus in the western Baltic Sea. Understanding responses of macroalgae and of the associated community is important because changing global temperatures and elevated CO2 may affect the ecological role of Fucus as primary producer, carbon sink, water purifier, and ecosystem engineer in the coastal ecosystem of the Baltic Sea

Holographic grating formation in a colloidal suspension of silver nanoparticles

Holographic gratings are recorded in colloidal suspensions of silver nanoparticles by utilizing interfering nanosecond pulses. The diffraction efficiency is measured with continuous-wave light. An instantaneous response together with a transient grating are observed: the nanoparticles absorb the pump light and heat up. Heat is transferred to the solvent, and a delayed thermal grating appears. The final decay time constant of this grating depends quadratically on the period length and has a typical value of 1 µs for grating spacings of several micrometers

Cosmic multi-muon events observed in the underground CERN-LEP tunnel with the ALEPH experiment

Multimuon events have been recorded with the ALEPH-detector, located 140 m underground, in parallel with e$^+$e$^-$ data taking. Benefitting from the high spatial and momentum resolution of the ALEPH tracking chambers narrowly spaced muons in high multiplicity bundles could be analysed. The bulk of the data can be successfully described by standard production phenomena. The multiplicity distribution favors, though not with very high significance, a chemical composition which changes from light to heavier elements with increasing energy around the ``knee". The five highest multiplicity events, with up to 150 muons within an area of $\sim$ 8 m$^2$, occur with a frequency which is almost an order of magnitude above the simulation. To establish a possible effect, more of these events should be recorded with a larger area detector