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Recent Topics of Particle Physics

Tuesdays 12:15 in Seminar Room P1-01-306.

Date Speaker Title
Upcoming Sessions Winter Term 2017/18
Please note:   This seminar is taking place on Mondays, starting 16:15 (room: CP-O3-123)
20.11.2017 Dr. Andrea Thamm (CERN, Genf) Collider Probes of Axion-like Particles

I will show that the study of rare Higgs decays in the high-luminosity run of the LHC can probe axions and axion-like particles (ALPs) in a wide range of parameter space, which is otherwise inaccessible to experimental searches.  If the ALP decays predominantly into photons, our strategy covers the current "gap" in the mass range between 1 MeV and 60 GeV down to a photon-axion coupling as small as 10^-6 TeV.  An ALP in this parameter range can explain the anomalous magnetic moment of the muon and is consistent with electroweak precision tests.  In our analysis we consider the most general effective Lagrangian for a spin-0 particle protected by a shift symmetry, motivated by many extensions of the Standard Model with a spontaneously broken global symmetry.

Sessions Winter Term 2016/17
23.01.2017 Dr. Rainer Wanke (Universität Mainz) Precision Kaon Physics and More: NA63 at the CERN SPS
Kaon physics has been one of the key building blocks of the Standard Model and continues to play a fundamental role complementary to the direct searches for New Physics.  The ulta-rare decays K^+ -> pi^+nu nubar and K_L -> pi^0 nu nubar are among the most sensitive probes of physics beyond the SM.  The detection of these decay modes is challenging because the branching ratios are predicted by the SM to be of order 10^-10 and the two neutrinos cannot be observed.  The NA62 experiment at CERN has now started data-taking and aims to collect a total of about 100 events for a precise measurement of the K^+ -> pi^+ nu nubar branching fraction.  The seminar will focus on both the current NA62 K^+ -> pi^+ nu nubar run and on future plans for searches for lepton-flavour violating decays and hidden particles as axions, dark photons, and heavy neutral leptons.
 Sessions Summer Term 2016
NEW: Please note that this seminar is taking place on Mondays now, starting 16:15 (CP-03-123)
11.07.2016 Prof. Ulrich Wiedner (Ruhr-Universität Bochum) Tetra-Quarks und Co.
Das Standardmodell der Teilchenphysik ist äußerst erfolgreich in der Beschreibung der fundamentalen Teilchen und ihrer Wechselwirkungen.  Sobald man allerdings Quarks und Gluonen zu Hadronen wie dem Proton oder Mesonen kombiniert, kann man die Wechselwirkung nicht mehr störungstheoretisch behandeln, unser Verständnis beginnt zu schwinden, und neue Phänomene tauchen auf. Die Hadronenphysik im nicht-perturbativen Bereich gehört zu den letzten unverstandenen Puzzlesteinen des Standardmodells der Kern- und Teilchenphysik.  Sie umfasst dabei ein breites Spektrum an Themen - von der Struktur der Hadronen über die Spektroskopie von Quark- und Gluonzuständen bis hin zu hadronischen Wechselwirkungen.  Experimentell benutzt man Elektronen, Photonen, Protonen, Antiprotonen, Myonen, Pionen und Kaonen an verschiedenen Forschungszentren weltweit.  Der Vortrag gibt einen Einblick in die überraschenden neuerdings erzielten Ergebnisse in der Spektroskopie und zeigt die Perspektiven für die Zukunft auf.
27.06.2016 Prof. Nico Serra (Univ. Zürich) Angular analysis of rare B-decays at LHCb
The Flavour Changing Neutral Current transitions b -> s l l are sensitive probe of physics beyond the Standard Model.  In particular, decays of the type B -> h l l allow to access a large number of observables via angular analyses, increasing the sensitivity to new physics.  Some measurements of these observables by the LHCb collaboration show tensions with respect to Standard Model predictions an are attracting significant attention in the flavour physics community.  I will review the status of B -> h l l measurements, focusing in particular on angular analyses.  I will also discuss present limitations and future prospects.
30.05.2016 Dr. Anna Nelles (Univ. of California, Irvine, USA) Radio-Detektion von Neutrinos im Ross-Schelfeis der Antarktis

Um Neutrinos der höchsten Energien (cosmogenic neutrinos) zu detektieren, werden aller Voraussicht nach noch größere Detektoren benötigt als bisher in Betrieb sind.  Das ARIANNA Experiment hat es sich zum Ziel gesetzt, die Möglichkeiten der Messung des Radiosignals von Neutrinoschauern im Eis zu erkunden.  Durch die Wahl des Ross-Schelfeises kombiniert ARIANNA die Vorteile der langen Abschwächungslänge von Radiosignalen im Eis mit der kosteneffizienten Installation von Antennen auf anstatt im Eis.  Ende 2014 wurde die erste Phase von ARIANNA installiert, und wir können nun auf mehr als ein Jahr Erfahrung zurückblicken.  Ich werde zunächst einen Einstieg in die theoretischen Konzepte der Radioemission on Teilchenschauern geben, um mich danach, mit einem einem besonderen Fokus auf ARIANNA, auf die experimentellen Erfahrungen der Neutrinodetektion zu konzentrieren.  Darüber hinaus werde ich die Brücke zur Radiodetektion von Luftschauern schlagen und darauf eingehen, inwieweit dieser Hintergrund eine Rolle für Neutrinoexperimente spielt.

09.05.2016 Dr. Felix Yu (Univ. Mainz) Phenomenology of Enhanced Light Quark Yukawa Couplings
I discuss phenomenological consequences in collider physics of the Higgs boson arising from enhanced down, up, strange, and charm Yukawa couplings.  I highlight a possible induced modification of the charge asymmetry in W^+ h versus W^- h production as a result of large, enhanced Yukawa couplings.  This motivates a collider study of the same-sign lepton final state, pp -->W^pm h --> l^pm nu l^pm nu jj, which can serve as a Standard Model discovery scenario for the W^pm h production mode with 100 fb^{-1} luminosity.  We find the prospects of this final state as a probe of nonstandard Yukawa couplings, however, are diminished unless the Higgs couplings to vector bosons are increased beyond the SM expectation or the extra increase in the Higgs width from the enhanced Yukawas is simultaneously mitigated.  I also briefly discuss the concomitant effects of new s-channel Higgs production from enhanced light quark Yukawa couplings.
                                                                                                                            Sessions Winter Term 2015/16
26.01.2016 Prof. Stefan Dittmaier (Univ. Freiburg) Electroweak gauge bosons at the LHC

The Drell-Yan-like production of W and Z bosons, pp -> W/Z -> 2leptons, is one of the most prominent classes of "standard-candle" processes at the LHC.  These processes represent powerful tools for detector and luminosity calibration, deliver important information on parton distribution functions, and allow for high-precision measurements in the resonance regions, inlcuding measurements of the effective weak mixing angle and the W-boson mass.

On the theory side, the Drell-Yan-like production of W or Z bosons is one of the best understood and most precisely predicted processes.  In this talk, salient features of the underlying precision calculations are reviewed, with an emphasis on electroweak corrections.  In particular, the structure and results of a recent calculation of mixed QCD-EW corrections at the next-to-next-to-leading order are outlined.

12.01.2016 Dr. Fady Bishara (Univ. of Oxford) Bo to K-star gamma with converted photons
We re-examine the possibility to measure the photon polarization in B\to K^*\gamma decays in which the photon converts to a lepton pair in the field of a nucleus.  We show that interference between the B\to(K^*\to K\pi)\gamma decay and the \gamma N\to\ell^+\ell^-N conversion permits both the ratio and relative weak phase between the left- and right-handed photon amplitudes to be probed by an angular observable constructed from the final state dilepton, kaon and pion kinematics.  To enhance the sensitivity to these interference effects, we develop special kinematic cuts that enhance the statistical power of this technique.  We then demonstrate the efficacy of these cuts on a sample of events generated with a dedicated Monte Carlo code.
01.12.2015 Conor Fitzpatrick (EPFL Lausanne) Pinning down the Standard Model with the CKM angle gamma
Measurements of the unitary angles probe the nature of our universe through CP violation, but is it standard model?  Only one angle, gamma, can be determined uniquely at tree level, making it the standard against which new physics in the flavor sector must be compared.  In this seminar I will summarize LHCb measurements of gamma and future prospects.
24.11.2015 Prof. Dr. Bernd Kniehl (Universität Hamburg) Heavy-quarkonium theory in the LHC era
We review the present landscape of heavy-quarkonium theory, its tests by worldwide collider and fixed-target experiments, and the future perspectives offered by the LHC.  Special emphasis is placed on the effective quantum field theory of nonrelativistic QCD (NRQCD), endowed with the factorization theorem conjured by Bodwin, Braaten, and Lepage, which arguably constitutes the most probable candidate theory at the present time.  Being impressively consolidated at the next-to-leading order by the world's data on unpolarized J/psi production, NRQCD factorization has now reached the crossroads because the predicted universality of the long-distance matrix elements is challenged by recent measurements of J/psi polarization and eta_c yield.

Sessions Winter Term 2011/12

29.11.2011 Dr. B.S. Wonsak (OPERA, DESY Hamburg) The OPERA Neutrino Velocity Measurement
OPERA is a long-baseline neutrino oscillation experiment designed to find tau neutrinos appearing in a pure muon neutrino beam.  Recently a measurement of the flight-time of the neutrinos between the CNGS at CERN and the OPERA detector at the LNGS has been performed.  It was found that the neutrinos arrive at the detector significantly earlier in time than expected if travelling at the speed of light.  In this talk the main aspects of this measurement will be presented.  This includes timing and geo-desy issues as well as the analysis.  An update concerning results with a fine structured time distribution of the beam is given.
Sessions Summer Term 2011
12.07.2011 Prof. Dr. Achim Stahl (RWTH Aachen) Neutrino Oscillations: Past, Present, and Future
After a quick review of the current experimental situation on neutrino oscillations, I will focus on the newest experiments. A new generation of reactor neutrino experiments is just starting and T2K has published its first results. I will discuss these results and sketch a possible future experiment (LENA) in Europe
28.06.2011 Prof. Rohini Godbole (CHEP, Indian Inst. of Science, Bangalore) Appraisal of Higgs mass bounds from the Tevatron searches
In this talk I will give a critical appraisal of the mass bounds for the Higgs in the SM and BSSM obtained from the Tevatron.
21.06.2011 Dr. Yvonne Wong (RWTH Aachen) Clustering dark energy
The apparent accelerated expansion of the universe seems to require the introduction of a dark energy component in the energy budget of the universe. However, the exact nature of this dark energy is still very poorly known. One possibility is that the dark energy can cluster in dark matter halos, if it has a sound speed much smaller than the speed of light. In this talk I report on a recent work on how to incorporate clustering dark energy into the spherical collapse model, a simple model used to investigate structure formation.
14.06.2011 Dr. Markus Diehl (DESY) When protons collide: multi-parton interactions at the LHC
When protons collide at high energy, several parton collisions in a single event can produce high mass or high transverse momenta in the final state. Such multi-parton interactions play an important role for the structure of final states at LHC. I discuss basics and recent theoretical progress made in their theoretical description, such as the space-time structure of multiple interactions, their power behavior, spin and color correlations, interference terms and scale evolution. Outstanding theoretical problems are highlighted as well.
10.05.2011 Prof. Dr. Gautam Bhattacharyya (SAHA Institute of Nuclear Physics, Kolkata) R-parity violation: Flavor-LHC interplay
With just two R-parity violating couplings, we can correlate several channels like D meson decays, lepton flavor violating tau decays, muon anomalous magnetic moment, etc. Simultaneous observations of these processes at a rate much above their Standard Model predictions can give us sufficient hints to look for specific signatures of R-parity violation at LHC. We show that we can identify some unmistakable signals of such New Physics even in the early (7 TeV) runs of LHC.
Previous Sessions 2010
06.07.2010 Dr. Thilo Michel (Universität Erlangen) Neutrinophysik und medizinische Röntgenbildgebung mit zählenden Pixeldetektoren
29.06.2010 Prof. Tom Weiler (Vanderbilt Univ., Nashville, TN, USA The LHC and its Detector as Portals for Time Travel
If nature is whimsical enough to offer us (i) extra dimensions, (ii) a warped metric, and (iii) higgs singlets - all possibilities - then these higgses may travel backwards in time. This time travel means that particles produced in the future can appear as events at the LHC now. The logic behind this possible acausality will be explained.
15.06.2010 Dr. Jürgen Rohrwild (RWTH Aachen) Can a large CP violating phase in B_s mixing be explained by a fourth family?
B_s mixing is - from the perspective of the four generation "Standard Model" - a rather peculiar phenomenon. On the one hand, constraints from flavour and electroweak observables restrict the parameter space of the model strong enough to reveal some of its signatures in the B_s mixing. On the other hand, some of standard theory assumptions that enter the measurement of the phase phi_s and the CKM angle beta_s (via B to J/psi Phi) receive modifications in the four generation scenario. I will discuss the current bounds on the model as well as its implications for B_s mixing focussing on phi_s and beta_s.
11.05.2010 Dr. Teresa Marrodan Undagoitia (ETH Zürich) Direct dark matter search using liquid xenon detectors
During the last years, liquid noble gases have proven a great potential as detector medium for dark matter searchs. Among them, xenon has the advantage of combining a high WIMP (Weakly Interacting Massive Particle) sensitivity with an excellent self-shielding capability for background reduction. A common technique, which has been demonstrated, e.g. by the XENON10 experiment, is to employ a two-phase TPC (Time Projection Chamber), where the produced light and charge is detected by PMTs. XENON100 is a 65kg active volume detector placed at the Gran Sasso underground laboratory in Italy. Currently, the detector is taking dark matter data. Due to its low-radioactivity materials (designed for 10mDRU) and its large mass, it would be able to reach a sensitivity for the WIMP-nucleus cross section of 2x10^-45cm2 at 100GeV WIMP mass. After an introduction to dark matter and its detection possibilities, the status and first results of the XENON100 experiment will be presented. The current status of other liquid xenon experiments will be also reviewed.

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Nur Atar
Group Secretary
Tel.: 0231 755-3572