Detection of Superparticles Beyond the Standard Model

This Phd thesis deals with supersymmetric particles within the context of astroparticle and collider physics. The first part is about the detection of UHE cosmic particles; it based on the use of the matter of Earth and Moon as detector volume, where in the case of UHE neutralino LSPs the Earth acts in addition as a filter against the background of UHE neutrinos. We present the solutions of the transport equations regarding UHE neutralino LSP and neutrino fluxes; these solutions are given for processes where the total cross section is dominated by t- or s- channel scattering. The last section of the first part provides the final formulas for the calculation of event rates with respect to the Earth, including the background of UHE neutrinos, and the Moon. Here, we are taking into account the energy loss of tau leptons in matter, before they decay back into neutrinos. We then find detectable event rates in experiments of several teratons scale, like a future satellite experiment as EUSO or OWL only if the following conditions are satisfied: the lightest neutralino must be a higgsino, rather than a bino; the X particle must decay via a mode which results in a large ratio of neutralino LSP and proton flux; the X particle mass must be rather close to its lower bound ; the experiment must be able to detect Cerenkov light. The second part deals with electroweak contributions, being the result of neutralinos and chargino exchange in the t- and/or u-channel as well as electroweak gauge bosons in the s-channel, to squark pair production at the CERN LHC. The reason for the partly sizable electroweak contributions is the interference between electroweak and QCD interactions. These contributions are most important for two final state SU(2) doublet (L-type) squarks; if one has at least one SU(2) singlet (R-type) squark, the change of the total cross sections decreases to only a few percent. We found that higher squark masses give rise to higher relative electroweak contributions and a larger change of the total cross section, respectively. In case of two produced SU(2) doublet squarks this change can be a increase or reduction of the cross section by more than 50% if we consider: heavy squarks with masses of about 2 TeV, a scenario without gaugino mass unification and a absolute value of the SU(2) gaugino soft breaking mass near the squark mass. Electroweak contributions can change the cross section for the production of two SU(2) doublet squarks by more than 30% in the case of scenarios with gaugino mass unification, if the squark masses are again near 2 TeV. Furthermore, the electroweak contributions peak at small transverse momentum of the produced squark, so it is not possible to subsume them in a constant k-factor. </p

The Passage of Ultrarelativistic Neutralinos through the Matter of the Moon

I consider the prospect to use the outer layer of the Moon as a detector volume for ultra-high energy (UHE) neutrino fluxes and the flux of the lightest neutralino which I assume is the lightest supersymmetric particle (LSP). For this purpose, I calculate the event rates of these fluxes for top-down scenarios. I show that a suitable experiment for the detection of radio waves might be able to detect sufficient event rates after a measurement period of one year.Comment: 3 pages, 1 figure, to appear in the proceedings of 16th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY08), Seoul, Korea, June 16-21 200

Prospects for Indirect Detection of Sneutrino Dark Matter with IceCube

We investigate the prospects for indirect detection of right-handed sneutrino dark matter at the IceCube neutrino telescope in a $U(1)_{B-L}$ extension of the MSSM. The capture and annihilation of sneutrinos inside the Sun reach equilibrium, and the flux of produced neutrinos is governed by the sneutrino-proton elastic scattering cross section, which has an upper bound of $8 \times 10^{-9}$ pb from the $Z^{\prime}$ mass limits in the $B-L$ model. Despite the absence of any spin-dependent contribution, the muon event rates predicted by this model can be detected at IceCube since sneutrinos mainly annihilate into leptonic final states by virtue of the fermion $B-L$ charges. These subsequently decay to neutrinos with 100% efficiency. The Earth muon event rates are too small to be detected for the standard halo model irrespective of an enhanced sneutrino annihilation cross section that can explain the recent PAMELA data. For modified velocity distributions, the Earth muon events increase substantially and can be greater than the IceCube detection threshold of 12 events $\mathrm{km}^{-2}$ $\mathrm{yr}^{-1}$. However, this only leads to a mild increase of about 30% for the Sun muon events. The number of muon events from the Sun can be as large as roughly 100 events $\mathrm{km}^{-2}$ $\mathrm{yr}^{-1}$ for this model.Comment: 13 pages, 9 figures, replaced to match the published version, only minor changes: addition of one reference in section 5, correction of two typo

Rapidity Gap Events for Squark Pair Production at the LHC

The exchange of electroweak gauginos in the $t-$ or $u-$channel allows squark pair production at hadron colliders without color exchange between the squarks. This can give rise to events where little or no energy is deposited in the detector between the squark decay products. We discuss the potential for detection of such rapidity gap events at the Large Hadron Collider (LHC). We present an analysis with full event simulation using PYTHIA as well as Herwig++, but without detector simulation. We analyze the transverse energy deposited between the jets from squark decay, as well as the probability of finding a third jet in between the two hardest jets. For the mSUGRA benchmark point SPS1a we find statistically significant evidence for a color singlet exchange contribution.Comment: 4 pages, 2 figures. To be published in the proceedings of SUSY09, Northeastern University, Boston, M

Electroweak Contributions to Squark Pair Production at the LHC

In this paper we compute electroweak contributions to the production of squark pairs at hadron colliders. These include the exchange of electroweak gauge bosons in the s-channel as well as electroweak gaugino exchange in the t- and/or u-channel. In many cases these can interfere with the dominant QCD contributions. As a result, we find sizable contributions to the production of two SU(2) doublet squarks. At the LHC, they amount to 10 to 20% for typical mSUGRA (or CMSSM) scenarios, but in more general scenarios they can vary between -40 and +55%, depending on size and sign of the SU(2) gaugino mass. The electroweak contribution to the total squark pair production rate at the LHC is about 3.5 times smaller.Comment: 28 pages, 9 figure

Signals of Very High Energy Neutralinos in Future Cosmic Ray Detectors

``Top--down'' models explain the observation of ultra high energy cosmic rays (UHECR; E \gsim 5 \cdot 10^{19} eV) through the decay of very massive, long--lived ``$X$ particles''. If superparticles with masses near a TeV exist, $X$ decays also lead to a significant flux of very energetic neutralinos, assumed to be the (stable or long--lived) lightest superparticles. There is a range of energies where neutrinos get absorbed in the Earth, but neutralinos can still traverse it. These neutralinos could in principle be detected. We calculate the detection rate in planned experiments such as OWL and EUSO. For bino--like neutralinos, which have been considered previously, we find detection rates below 1 event per Teraton of target and year in all cases; often the rates are much smaller. In contrast, if the neutralino is higgsino--like, more than ten events per year per Teraton might be observed, if the mass of the $X$ particle is near its lower bound of $\sim 10^{12}$ GeV.Comment: 14 pages, 2 figure

Rapidity Gap Events in Squark Pair Production at the LHC

The exchange of electroweak gauginos in the $t-$ or $u-$channel allows squark pair production at hadron colliders without color exchange between the squarks. This can give rise to events where little or no energy is deposited in the detector between the squark decay products. We discuss the potential for detection of such rapidity gap events at the Large Hadron Collider (LHC). Our numerical analysis is divided into two parts. First, we evaluate in a simplified framework the rapidity gap signal at the parton level. The second part covers an analysis with full event simulation using PYTHIA as well as Herwig++, but without detector simulation. We analyze the transverse energy deposited between the jets from squark decay, as well as the probability of finding a third jet in between the two hardest jets. For the mSUGRA benchmark point SPS1a we find statistically significant evidence for a color singlet exchange contribution. The systematical differences between current versions of PYTHIA and HERWIG++ are larger than the physical effect from color singlet exchange; however, these systematic differences could be reduced by tuning both Monte Carlo generators on normal QCD di--jet data.Comment: 23 pages, 10 figure

Functional analysis of structural variants in single cells using Strand-seq

Somatic structural variants (SVs) are widespread in cancer, but their impact on disease evolution is understudied due to a lack of methods to directly characterize their functional consequences. We present a computational method, scNOVA, which uses Strand-seq to perform haplotype-aware integration of SV discovery and molecular phenotyping in single cells by using nucleosome occupancy to infer gene expression as a readout. Application to leukemias and cell lines identifies local effects of copy-balanced rearrangements on gene deregulation, and consequences of SVs on aberrant signaling pathways in subclones. We discovered distinct SV subclones with dysregulated Wnt signaling in a chronic lymphocytic leukemia patient. We further uncovered the consequences of subclonal chromothripsis in T cell acute lymphoblastic leukemia, which revealed c-Myb activation, enrichment of a primitive cell state and informed successful targeting of the subclone in cell culture, using a Notch inhibitor. By directly linking SVs to their functional effects, scNOVA enables systematic single-cell multiomic studies of structural variation in heterogeneous cell populations