14310220
Probing quantum gravity effects in black holes at LHC
We study modifications of the Hawking emission in the evaporation of miniature black holes possibly produced in accelerators when their mass approaches the fundamental scale of gravity, set to 1TeV according to some extra dimension models. Back-reaction and quantum gravity corrections are modelled by employing modified relations between the black hole mass and temperature. We release the assumption that black holes explode at 1TeV or leave a remnant, and let them evaporate to much smaller masses. We have implemented such modified decay processes into an existing micro-black hole event generator, performing a study of the decay products in order to search for phenomenological evidence of quantum gravity effects.
121570479
Compatibility and possible implications of the experimental results on solar neutrinos
Abstract The effect of varying the assumed value of the cross-section for the proton-proton fusion weak reaction of the solar cycle on the solar neutrino problem is discussed. It is shown that an increase of about 20% of the relevant astrophysical factor fields compatibility (within the present experimental accuracy) of the available results with theory and among themselves.
110639465
The LHCb Run Control
LHCb has designed and implemented an integrated Experiment Control System. The Control System uses the same concepts and the same tools to control and monitor all parts of the experiment: the Data Acquisition System, the Timing and the Trigger Systems, the High Level Trigger Farm, the Detector Control System, the Experiment's Infrastructure and the interaction with the CERN Technical Services and the Accelerator. LHCb's Run Control, the main interface used by the experiment's operator, provides access in a hierarchical, coherent and homogeneous manner to all areas of the experiment and to all its sub-detectors. It allows for automated (or manual) configuration and control, including error recovery, of the full experiment in its different running modes. Different instances of the same Run Control interface are used by the various sub-detectors for their stand-alone activities: test runs, calibration runs, etc. The architecture and the tools used to build the control system, the guidelines and components provided to the developers, as well as the first experience with the usage of the Run Control will be presented
202714087
The HERA-B electromagnetic pre-trigger and its possible adaptations to the LHC-B Level-0 calorimeter trigger
In this document the pretrigger system developed for the electromagnetic calorimeter of the HERA-B experiment is described, showing some possible implementations of this system to perform the LHC-B Level-0 Trigger for the Electron and Hadron Trigger Algorithms.
7213389
DIRAC - Distributed Infrastructure with Remote Agent Control
This paper describes DIRAC, the LHCb Monte Carlo production system. DIRAC has a client/server architecture based on: Compute elements distributed among the collaborating institutes; Databases for production management, bookkeeping (the metadata catalogue) and software configuration; Monitoring and cataloguing services for updating and accessing the databases. Locally installed software agents implemented in Python monitor the local batch queue, interrogate the production database for any outstanding production requests using the XML-RPC protocol and initiate the job submission. The agent checks and, if necessary, installs any required software automatically. After the job has processed the events, the agent transfers the output data and updates the metadata catalogue. DIRAC has been successfully installed at 18 collaborating institutes, including the DataGRID, and has been used in recent Physics Data Challenges. In the near to medium term future we must use a mixed environment with different types of grid middleware or no middleware. We describe how this flexibility has been achieved and how ubiquitously available grid middleware would improve DIRAC.
126243169
The selection crate for the L0 calorimeter trigger
14357002
Effects of primordial chemistry on the cosmic microwave background
Context. Previous works have demonstrated that the generation of secondary CMB anisotropies due to the molecular optical depth is likely too small to be observed. In this paper, we examine additional ways in which primordial chemistry and the dark ages might influence the CMB. Aims. We seek a detailed understanding of the formation of molecules in the postrecombination universe and their interactions with the CMB. We present a detailed and updated chemical network and an overview of the interactions of molecules with the CMB. Methods. We calculate the evolution of primordial chemistry in a homogeneous universe and determine the optical depth due to line absorption, photoionization and photodissociation, and estimate the resulting changes in the CMB temperature and its power spectrum. Corrections for stimulated and spontaneous emission are taken into account. Results. The most promising results are obtained for the negative hydrogen ion $\mathrm{H}^-$ and the $\mathrm{HeH}^+$  molecule. The free-free process of $\mathrm{H}^-$  yields a relative change in the CMB temperature of up to 2$\times$10 -11 , and leads to a frequency-dependent change in the power spectrum of the order 10 -7 at 30 GHz. With a change of the order 10 -10 in the power spectrum, our result for the bound-free process of $\mathrm{H}^-$ is significantly below a previous suggestion. $\mathrm{HeH}^+$ efficiently scatters CMB photons and smears out primordial fluctuations, leading to a change in the power spectrum of the order 10 -8 . Conclusions. We demonstrate that primordial chemistry does not alter the CMB during the dark ages of the universe at the significance level of current CMB experiments. We determine and quantify the essential effects that may contribute to changes in the CMB and leave an imprint from the dark ages, thus constituting a potential probe of the early universe.
18590
The Chemistry of the early universe
The process of molecule formation in the primor- dial gas is considered in the framework of Friedmann cosmo- logical models from redshift z =1 0 4 to z =0 . First, a com- prehensive analysis of 87 gas phase reaction rates (both col- lisional and radiative) relevant in the physical environment of the expanding universe is presented and critically discussed. On this basis, calculations are carried out of the abundance of 21 molecular species as function of redshift, for different values of the cosmological parameters 0, and H0, evaluating con- sistently the molecular heating and cooling due to H2 ,H D and LiH molecules. One of the major improvements of this work is the use of a better treatment of H recombination that leads to a reduction of a factor 2-3 in the abundance of electrons and H + at freeze-out, with respect to previous studies. The lower residual ionization has a negative effect on the chemistry of the primordial gas in which electrons and protons act as cat- alysts in the formation of the first molecules. We find that in the standard model (h =0 :67, 10 =4 :5, 0 =1 and (D/H) =4 :3 10 5 ), the residual fractional ionization at z =1 is (e= H) =3 :0210 4 , and the main molecular species fractional abundances (H2= H) =1 :1 10 6 , (HD=H 2 )=1 :1 10 3 , (HeH + = H) =6 :2 10 13 , (LiH + = H) =9 :4 10 18 and (LiH=LiH + )=7 :6 10 3 . We devise a reduced chemical network that reproduces with excellent accuracy the numerical results of the complete model and allows to follow the chemical compositions and the thermal properties of a primordial gas in the presence of an external radiation field. Finally, we provide accurate cooling functions of H2, HD and LiH in a wide range of density and temperature that can be conveniently used in a variety of cosmological applications.
10085260
Mean Field Magnetohydrodynamics of Accretion Disks
We consider the accretion process in a disk with magnetic fields that are dragged in from the interstellar medium by gravitational collapse. Two diffusive processes are at work in the system: (1) viscous torques exerted by turbulent and magnetic stresses, and (2) resistive redistribution of mass with respect to the magnetic flux arising from the imperfect conduction of current. In steady state, self-consistency between the two rates of drift requires that a relationship exists between the coefficients of turbulent viscosity and turbulent resistivity. Ignoring any interactions with a stellar magnetosphere, we solve the steady-state equations for a magnetized disk under the gravitational attraction of a mass point and threaded by an amount of magnetic flux consistent with calculations of magnetized gravitational collapse in star formation. Our model mean field equations have an exact analytical solution that corresponds to magnetically diluted Keplerian rotation about the central mass point. The solution yields the strength of the magnetic field and the surface density as functions of radial position in the disk and their connection with the departure from pure Keplerian rotation in representative cases. We compare the predictions of the theory with the available observations concerning T Tauri stars, FU Orionis stars, and low- and high-mass protostars. Finally, we speculate on the physical causes for high and low states of the accretion disks that surround young stellar objects. One of the more important results of this study is the physical derivation of analytic expressions for the turbulent viscosity and turbulent resistivity.
18962006
ENHANCED PRODUCTION OF BARIUM IN LOW-MASS STARS: EVIDENCE FROM OPEN CLUSTERS
We report the discovery of a trend of increasing barium abundance with decreasing age for a large sample of Galactic open clusters. The observed pattern of [Ba/Fe] versus age can be reproduced with a Galactic chemical evolution model only assuming a higher Ba yield from the s-process in low-mass stars than the average one suggested by parameterized models of neutron-capture nucleosynthesis. We show that this is possible in a scenario where the efficiency of the extra-mixing processes producing the neutron source 13C is anticorrelated with the initial mass, with a larger efficiency for lower masses. This is similar to the known trend of extended mixing episodes acting in H-rich layers and might suggest a common physical mechanism.
119089633
3He in Planetary Nebulae: A Challenge to Stellar Evolution Models
The discrepancy between the observed abundances of 3He in the interstellar medium and those predicted by stellar and Galactic chemical evolution remains largely unexplained. In this paper, we attempt to shed some light on this unsolved problem by presenting a quantitative comparison of the 3He abundances recently measured in six planetary nebulae (IC 289, NGC 3242, NGC 6543, NGC 6720, NGC 7009, NGC 7662) with the corresponding predictions of stellar evolution theory. The determination of the mass of the planetary nebulae progenitors allows us to dismiss, with a good degree of confidence, the hypothesis that the abundance of 3He in the envelopes of all low-mass stars (M 2.5 M?) is strongly reduced with respect to the standard theoretical values by some mixing mechanism acting in the latest phases of stellar evolution. The abundance versus mass correlation, with allowance made for the limitation of the sample, is in fact found to be fully consistent with the classical prediction of stellar evolution. We examine the implications of this result on the Galactic evolution of 3He with the help of a series of models with standard and nonstandard (i.e.,3He-depleted) nucleosynthesis prescriptions in varying percentages of low-mass stars. The results are found to be consistent with the abundances determined in the presolar material and in the local interstellar medium only if the vast majority of low-mass stars (more than 70%-80%) follow nonstandard prescriptions. This implies that either the sample of planetary nebulae under examination is highly biased and therefore not representative of the whole population of low-mass stars, or the solution to the 3He problem lies elsewhere.