Nuclear and Particle Physics coming seminars
Academic year 2007-2008

We illustrate the impact of one-loop perturbative corrections due to electroweak interactions onto the production of cross section of jets and heavy quarks at TeVatron and the Large Hadron Collider.

In the search of new physics at the LHC, understanding jets in backgrounds and signals will be of primary importance. Two methods are used to simulate the jet activity in collision processes: parton shower generators such as Pythia or Herwig, which accurately simulate jets which are close in phase space, and matrix element generators such as MadEvent and AlpGen, which give a good description of widely separated jets. In order to get complete simulations which can be used for experimental studies, the two approaches must be combined (matched) without double counting. I will discuss different methods for this matching, and show examples of the effects on both signal processes (SUSY particle production) and backgrounds (top pair production and weak boson production) using MadEvent and Pythia.

It may look premature to talk about LHC upgrade before the LHC has been completed and first physics results indicate the direction of physics in the TeV range. However, the time scale for the upgrade project is very long which necessitate early preparation. Future physics program will be reviewed based on different upgrade scenarios of the LHC machine for higher luminosity and energy. In particular the program if no Higgs is found at LHC will push the capability of the machine and detector to the limit. The LHC upgrade will have big impact on the ATLAS detector with the Inner Detector, closest to the interaction point, suffering most from the increased radiation. The technological challenges and possible solutions to them will be presented.

The standard model of fundamental interactions is remarkably successful, but it leaves an unfinished agenda. Several major questions seem ripe for exploration in the near future. I anticipate that the coming decade will be a Golden Age of discovery in fundamental physics.

The recent accumulation of experimental evidence for neutrino oscillations (the ability for a neutrino to periodically appear under different aspects along its journey) suggests that neutrinos do have non-zero masses. I have discussed the neutrino oscillations and masses in a docent lecture, given in September. In this seminar, I will again review basic phenomenological aspects of neutrino oscillations and discuss some experimental results in a more in-depth and interactive way than in the docent lecture, including some of the "director's cuts".

Chiral perturbation theory is the effective field theory of the strong interactions at low energies. It is based on the approximate chiral SU(3)_L X SU(3)_R symmetry of QCD and is quite successfull in the description of the interactions between light mesons and baryons. In some instances, however, the strict perturbative framework of chiral perturbation theory can be restricted to small energy ranges and it certainly fails in the vicinity of resonances. In this respect, the combination of chiral effective field theory with non-perturbative methods has proven useful as I will demonstrate in my talk. On the one hand, it is the implementation of the Bethe-Salpeter equation which leads to a successful description both of Kbar N physics as well as eta, eta' decays. On the other hand, these are lattice simulations of light nuclei in chiral effective field theory -- a novel and promising approach to nuclear physics.

The feasibility study for a possible future linear collider named CLIC (Compact Linear Collider) will be presented. CLIC is based on the Two Beams concept. It is composed of a Main Beam Linac to accelerate particles coupled with a Drive Beam Linac, which provides the RF power for the acceleration. CLIC is based on normal conducting structures (100 MV/m and 12 GHz) and therefore it is the only linear collider able to reach the multi-TeV energy range. The present design is for colliding electrons and positrons at 3 TeV centre of mass energy.

Nevertheless several key issues remain to be demonstrated for this technology. An R&D program is going on at CERN with a CLIC Tests Facility (CTF3). In this seminar, we will present the status and the results already obtained in this test facility and the perspective for the future.

A first CLIC workshop took place at CERN in October 2007, where new parameters were discussed. The main highlights will be reported. One goal, today, is to write a CLIC Conceptual Design Report for 2010. It would contribute to a decision to build a possible future linear collider at a time when the Physics community will have the first results from the LHC.

The Large Area Telescope (LAT), one of two instruments on the Gamma-ray Large Area Space Telescope (GLAST) mission, scheduled for launch by NASA in 2007, is an imaging, wide field-of-view, high-energy gamma-ray telescope, covering the approximate energy range from 20 MeV to more than 300 GeV. Annihilation of Weakly Interacting Massive Particles, predicted in many extensionsof the Standard Model of Particle Physics, may give rise to a signal in gamma-ray spectra from many cosmic sources. In my talk I will discuss the GLAST-LAT instrument, the status of the mission and the searches for Dark Matter currently being prepared within the GLAST collaboration

For several decades, production of light pseudoscalar mesons (π, η, η’, K) have been studied all over the world, resulting in a continuously increasing understanding of the long- and intermediate-range part of the nucleon-nucleon interaction. Studies of the vector mesons (ω, φ, ρ), which dominate the nucleon-nucleon interactions at short distances, have been rarer, mainly due to experimental difficulties. Since the seventies, a few attempts have been made to measure ω production in for example πp -> nω and pd -> 3He ω, but the results are debated and poorly understood. Furthermore, the correctness of the data interpretation has been questioned and the need of more data have been stressed by several theoreticians.

New CELSIUS/WASA data on pd -> 3He ω, taken near the kinematic threshold, are currently being analysed. In this talk, I will briefly discuss what we can learn from studying ω production, before I introduce you to the WASA detector setup. The preliminary results will be shown and compared to theoretical calculations, performed by K.P. Khemchandani (see seminar from March 2007) using a two-step model.

Left-right symmetry is a generic feature of a large class of models beyond the Standard Model of particle physics. Such a framework is the natural setting for the seesaw mechanism, which is one of the most promising solutions to the problem of why neutrinos have so small masses. In addition, the seesaw mechanism has the attractive feature of a built-in mechanism for generating the baryon asymmetry of the universe (BAU) through the baryogenesis via leptogenesis mechanism. Thus, this framework can simultaneously solve two very distinct problems and provides a bridge between cosmology and particle physics. We study theoretical and phenomenological aspects of a class of left-right symmetric seesaw models in the context of neutrino masses and leptogenesis and investigate the extent to which these models can be consistent with experimental observations.

Future neutrino oscillation experiments may give us new information on physics beyond the Standard Model. We briefly review the standard framework and current status of neutrino oscillations before looking at possible manifestations of "non-standard effects". In particular, some focus will be put on non-standard interactions (NSI) with matter and their impact on future neutrino oscillation experiments. If time allows, a brief account on the impact of neutrino oscillations on indirect WIMP searches will also be given.

The Gesellschaft für Schwerionenforschung (GSI) facility in Darmstadt, Germany, will be upgraded to accommodate a new generation of physics experiments. The future accelerator facility will be called FAIR and one of the experiments at the site will be PANDA, which aims at performing hadron physics investigations by colliding anti-protons with protons. The licentiate thesis treats three topics related to PANDA. The first is energy resolution studies of a 3x3-matrix of PWO crystals, the second light yield uniformity studies of PWO crystals and the third reconstruction of the Lambdabar-polarisation in the PANDA experiment.

External examiner: Thomas Nilsson (Chalmers)

One of the most promising approaches to determine the energy spectrum and composition of cosmic rays with energies above 1 PeV is the measurement of the number of electrons and muons produced in EAS. Therefore EAS simulations using electromagnetic and hadronic interaction models are necessary. These simulations show uncertainties which are mainly related to hadronic interaction models.

In this talk, I will present how the reliability of EAS simulations can be improved by investigating the role of hadronic interactions for muon production. The importance of low energy interactions is studied and it is argued that current fixed target experiments can help to reduce uncertainties in the low energy range. This is demonstrated by analyzing data of the CERN fixed target experiment HARP on proton and pion interactions with a carbon target and by comparing the obtained production spectra with model predictions.

The simulation studies of the relevant energies and phase space regions of hadronic interactions in EAS form the basis on the cosmic ray part of a proposal for a new fixed target experiment. Early 2007 the proposal was accepted by CERN and the new NA61 experiment started its pilot run in autumn of 2007. One of the next data taking will be p+C collisions at 30 GeV/c.

After the discovery by Belle the X(3872) has very quickly been confirmed by numerous other experiments. Since then, the same experiments have delivered many experimental clues, as to how this state can be understood. Reviewing most of these properties, the possible spin configurations can be reduced and some conclusions regarding the nature of the X(3872) can be made.

The HESR-ring of the future FAIR-facility in Germany will include both electron cooling and stochastic cooling in order to achieve the demanding beam parameters required by the PANDA experiment. The high-energy electron cooler will cool antiprotons in the energy range 0.8 GeV to 8 GeV. The design is based on an electrostatic accelerator and shall not exclude a further upgrade to the full energy of HESR, 14.1 GeV. In this talk I will give an introduction to FAIR and HESR, present the electron cooler design and recent prototype tests.

In the beginning of 2007, the Norweigan Ministry of Petroleum and Energy appointed an international expert committee with a mandate to establish a solid knowledge base concerning both opportunities and risks related to the use of thorium for long-term energy production. The report "Thorium as an energy source - Opportunities for Norway" has just been presented to the Minister and to the Press. The energy resources in minable thorium are huge and correspond approximately to 200 times the energy in Norweigan oil resources extracted so far and additional reserves. Key technologies for the energy generation are reactors of the IV generation and for the waste incineration, ADS accelerator driven systems. In the seminar more details will be given of the thorium fuel cycle, the different nuclear reactor types, radiation protection, non-proliferation and economical aspects.

The five-dimensional Bulk Randall-Sundrum model, where all Standard Model particles except the Higgs are free to propagate in the bulk, predicts the existence of Kaluza-Klein (KK) modes of the gluon with a large branching into top-antitop pairs. This scenario has very interesting collider implications. While some of the studies have focussed on graviton production, the interesting signal for this scenario is the production of KK gauge bosons and, for the LHC in particular, the production of KK gluons. I will discuss first the production of the lowest KK gluon mode at the Tevatron energy, and then the production of KK gluons in association with a ttbar pair at the LHC.

A very interesting possibility for generating the observed neutrino masses and mixings is to use R-parity violation in supersymmetry. In contrast to the conventional see-saw mechanism this model uses TeV scale physics in order to explain the neutrino data. Therefore, it can be tested at the upcomming LHC experiment. I will concentrate on bilinear R-parity violating models and show that indeed the LHC can either falsify or prove that this model is the mechanism behind the neutrino masses.

The heaviest fragments, recoils, have been studied in proton and deuteron induced 28Si reactions and proton-20Ne reactions at 100-300 MeV per nucleon. Inclusive charge and angular distributions and coincidences between He nuclei and recoils have been compared to two theoretical models, Dubna Cascade Model and JAERI Quantum Molecular Dynamics. The overall agreement was good for the reactions with 28Si, however the angular distributions of He fragments could not be reproduced.

For the 20Ne reactions the recoil angular distributions were only reproduced for large angles. There was a significant underestimation at small angles and low recoil charge. α-clustering in the bombarding nucleus is a possible explanation for the deviations. In the 100 MeV per nucleon reactions all assumptions of the models may not be valid and the agreement was worst for these reactions.

In proton-natXe reactions intermediate mass fragments have been studied from 200 to 1400 MeV. Slow ramping was used to scan the energy. Charge distributions and a caloric curve have been compared to Cascade Fragmentation Evaporation Model. Charge distributions showed good agreement for fragments with Z less than 8 but the heavier fragments were underestimated.

Reactions at relativistic energies in inverse kinematics provide clean informations on the nucleon distributions inside nuclei and unbound resonances. Few body systems and their ground and continuum state constituent correlations will be presented and discussed in conjunction with different reaction mechanisms. Conclusions on the properties of the exotic nuclear systems will be drawn. I'd like to outline and compare ongoing and future experiments at the GSI&FAIR facility.

The future International Linear Collider (ILC) and Compact Linear Collider (CLIC) are intended for precision measurements of phenomena discovered at the Large Hadron Collider (LHC) and also for the discovery of new physics. In order to offer optimal conditions for such experiments, the new colliders must produce very-high-luminosity collisions at energies in the TeV regime.

Emittance growth caused by imperfections in the main linacs is one of the factors limiting the luminosity of CLIC and ILC. In this thesis, various emittance preservation and luminosity tuning techniques have been tested and developed in order to meet the challenging luminosity requirements.

Beam-based alignment was shown to be insufficient for reduction of emittance growth. Emittance tuning bumps provide an additional powerful preservation tool. After initial studies of tuning bumps designed to treat certain imperfections, a general strategy for design of optimised bumps was developed. The new bumps are optimal both in terms of emittance reduction performance and convergence speed. They were clearly faster than previous bumps and reduced emittance growth by nearly two orders of magnitude both for CLIC and ILC.

Time-dependent imperfections such as ground motion and magnet vibrations also limit the performance of the colliders. This type of imperfections was studied in detail, and a new feedback system for optimal reduction of emittance growth was developed and shown to be approximately ten times more efficient than standard trajectory feedbacks.

The emittance tuning bumps require fast and accurate diagnostics. The possibility of measuring emittance using a wide laserwire was introduced and simulated with promising results. While luminosity cannot be directly measured fast enough, it was shown that a beamstrahlung tuning signal could be used for efficient optimisation of a number of collision parameters using tuning bumps in the Final Focus System.

Complete simulations of CLIC emittance tuning bumps, including static and dynamic imperfections and realistic tuning and emittance measurement procedures, showed that an emittance growth six times lower than that required may be obtained using these methods.

A future linear collider has been proposed to explore the TeV scale in detail via the collisions of electrons and positrons. This will require both high energy beams and also unprecedented luminosities, which in turn will require very high performance beam diagnostics devices, both for fault finding and also for performance monitoring during luminosity runs. The "Laser-wire" is a system that can scan across the electron beams using a finely-focussed beam of laser light, where the electron profile can be inferred by counting the rate of Compton events as function of relative position of electron and laser beams. The principle of the device will be described and recent results from laser-wire systems at the test facilities at PETRA (DESY) and ATF (KEK) will be reported. In addition preliminary results of simulations of the signal extraction at a realistic linear collider layout will be presented.

Neutrino-less double beta decay is permitted if the neutrino is its own anti-particle and possesses non-zero mass. The existence of this decay mode, at any finite rate, establishes lepton number violation and provides a measure of the neutrino “effective mass”. No convincing evidence for the 0- mode exists, at present. New efforts to exploit active target masses at the 100+ kg scale, some with liquid xenon, are underway. Meanwhile, a search for direct detection of WIMPs, also using liquid xenon, has reached a similar target mass scale. With two high-risk goals, but similarities in technique, why haven’t groups combined their efforts? I offer a quick review of these two experimental paths with xenon, noting some parallels and divergences. By starting with the goal of optimized energy resolution, I arrive at the conclusion that high-pressure xenon gas appears to offer a single detector concept with uncompromised capabilities for both searches; as discovered decades ago, but rather neglected in high energy physics, the methodology to obtain the optimal energy resolution is electroluminescence.

During operation of heavy ion accelerators a significant pressure rise has been observed when the intensity of the high energy beam was increased. The cause for this pressure rise is ion induced desorption, which is the result when beam ions collide with residual gas molecules in the accelerator, whereby they undergo charge exchange. Since the change in charge state will affect the bending radius of the particles after they have passed a bending magnet, they will not follow the required trajectory but instead collide with the vacuum chamber wall and gas are released. For the Future GSI project FAIR (Facility for Antiproton and Ion Research) there is a need to upgrade the SIS18 synchrotron in order to meet the requirements of the increased intensity. The aim of this work was to measure the desorption yields, η, (released molecules per incident ion) from materials commonly used in accelerators: 316LN stainless steel, Cu, Etched Cu, gold coated Cu, Ta and TiZrV coated stainless steel with argon and uranium beams at the energies 5-100 MeV/u. The measurements were performed at GSI and at The Svedberg Laboratory where a new dedicated teststand was built. It was found that the desorption yield scales with the electronic energy loss to the second power, decreasing for increasing impact energy above the Bragg Maximum. A feasibility study on the possibility to use laser refractometry to improve the accuracy of a specific throughput system was performed. The result was an improvement by up to 3 orders of magnitude, depending on pressure range.

The D0 and CDF experiments at the Tevatron have recorded about 3fb?1 data each from collisions of proton-antiprotons. This large data set allows high sensitivity searches for Higgs bosons. Extensions of the Standard Model predict several Higgs bosons, neutral and charged. The latest preliminary results of the searches for Higgs bosons in the Standard Model and beyond are reported. The expected sensitivity increase with additional luminosity is briefly discussed.

The interesting but difficult phenomenology of supersymmetric models at the LHC and ILC demands a corresponding complexity and maturity from simulation tools. This includes multi-particle final states, reducible and irreducible backgrounds, spin correlations, real emission of photons and gluons, virtual corrections etc. Most of these topics are included in the multi-particle Monte Carlo (MC) Event generators Madgraph, WHIZARD and Sherpa. A comparison of these codes is shown, with a special focus on the new release of WHIZARD. I show examples for the necessity of considering full matrix elements with all off-shell effects and interferences for multi-particle final states in supersymmetric models and give a status report on ongoing projects for simulations of SUSY processes at the LHC with these codes, including all of the abovementioned corrections.

The phenomenological implications of the theory of strong interactions, QCD, are not yet understood from first principles. E.g., the observed spectrum of mesonic excitations may be very rich containing, besides the conventional $\bar qq$ mesons, also hybrids (states with gluonic exciations), 4-quark states, or hadronic molecules (bound states of two hadrons). If we want to learn anything about the mechanisms of how QCD forms hadrons, it is important to develop methods that allow one to distinguish amongst the mentioned possibilities. In the talk I will present a method applicable to scalar resonances located close to a threshold, that allows one to quantify the molecular component of the state. The method will then be applied to better understand the nature of some scalar mesons discovered recently, namely X(3872) and Y(4660).

A search for a diffuse flux of cosmic neutrinos with energies in excess of 10**14 eV was performed using two years of AMANDA-II data, collected in 2003 and 2004. A 20% evenly distributed sub-sample of experimental data was used to verify the detector description and the analysis cuts. A very good agreement between this 20% sample and the background simulations was observed. The analysis was optimised for discovery, to a relatively low price in limit setting power. The background estimate for the livetime of the examined 80% sample is 0.035 ± 68% events with an additional 41% systematical uncertainty.

The total neutrino flux needed for a 5σ discovery to be made with 50% probability was estimated to 3.4 ∙ 10-7 E-2 GeV s-1 sr-1 cm-2 equally distributed over the three flavours, taking statistical and systematic uncertainties in the background expectation and the signal efficiency into account. No experimental events survived the final discriminator cut. Hence, no ultra-high energy neutrino candidates were found in the examined sample. A 90% upper limit is placed on the total ultra-high energy neutrino flux at 2.8 ∙ 10-7 E-2 GeV s-1 sr-1 cm-2, taking both systematical and statistical uncertainties into account. The energy range in which 90% of the simulated E-2 signal is contained is 2.94 ∙ 10**14 eV to 1.54 ∙ 10**18 eV (central interval), assuming an equal distribution over the neutrino flavours at the Earth. The final acceptance is distributed as 48% electron neutrinos, 27% muon neutrinos, and 25% tau neutrinos.

A set of models for the production of neutrinos in active galactic nuclei that predict spectra deviating from E-2 was excluded.

The reaction dd → 4Heππ has been measured exclusively for the first time. The measurements were performed at Td = 712 MeV and Td = 1029 MeV, with the WASA detector assembly at CELSIUS (Uppsala-Sweden). The aim was to investigate a long standing puzzle, the so called ABC effect. This is a peculiar feature of double pion production in light nuclei collisions. In addition to confirming previous experimental observations in this regard, our results also reveal a strong angular dependence of the pions in the overall center of mass system as well as non-isotropic angular distribution of the low mass enhancement in the ππ invariant mass. The results are qualitatively reproduced by a theoretical model, according to which, the ABC effect is described as a result of kinematical enhancement in the independent production of the pion pairs from two parallel and independent NN → dπ reactions.

ANTARES is the largest neutrino detector currently operating in the Northern hemisphere. The detector is located at the bottom of the Mediterranean Sea, 40 km off the coast of Toulon, France. Since May 29th, 2008, the detector is in its final configuration of twelve lines equipped with photomultipliers to detect the Cherenkov light of neutrino induced muons. The first five lines of the detector have been working continuously since about one year. The performance of the detector with these five lines and first neutrino candidates will be presented. Together with two other pilot projects for neutrino astronomy in the Mediterranean Sea a consortium has been established to build KM3NeT, a future cubic kilometre scale neutrino telescope. The status of the KM3NeT design study will be presented.

The PAX collaboration has proposed an experimental program with polarized antiprotons at the new "Facility for Antiproton and Ion Research" (FAIR), to be built at GSI (Darmstadt, Germany) during the next decade. The physics case for experiments with polarized antiprotons is outstanding and covers e.g.: (i) the investigation of nucleon spin structure ("transversity") via the Drell-Yan process, (ii) measurements of electromagnetic form factors in the time-like region, and (iii) double-polarized proton-antiproton hard scattering. There are, however, major technological challenges to be met in order to produce polarized antiprotons - foremost is the question of how to polarize antiprotons effectively. In my talk, I will discuss the ideas of how to achieve this goal and what is currently done as preparatory tests and measurements at COSY-Jülich and elsewhere.