Light Stop Searches at the LHC in Events with two b-Jets and Missing Energy

We propose a new method to discover light top squarks (stops) in the co-annihilation region at the Large Hadron Collider (LHC). The bino-like neutralino is the lightest supersymmetric particle (LSP) and the lighter stop is the next-to-LSP. Such scenarios can be consistent with electroweak baryogenesis and also with dark matter constraints. We consider the production of two stops in association with two b-quarks, including pure QCD as well as mixed electroweak-QCD contributions. The stops decay into a charm quark and the LSP. For a higgsino-like light chargino the electroweak contributions can exceed the pure QCD prediction. We show the size of the electroweak contributions as a function of the stop mass and present the LHC discovery reach in the stop-neutralino mass plane.Comment: 12 pages, 10 figure

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

Constraints on supersymmetry with light third family from LHC data

We present a re-interpretation of the recent ATLAS limits on supersymmetry in channels with jets (with and without b-tags) and missing energy, in the context of light third family squarks, while the first two squark families are inaccessible at the 7 TeV run of the Large Hadron Collider (LHC). In contrast to interpretations in terms of the high-scale based constrained minimal supersymmetric standard model (CMSSM), we primarily use the low-scale parametrisation of the phenomenological MSSM (pMSSM), and translate the limits in terms of physical masses of the third family squarks. Side by side, we also investigate the limits in terms of high-scale scalar non-universality, both with and without low-mass sleptons. Our conclusion is that the limits based on 0-lepton channels are not altered by the mass-scale of sleptons, and can be considered more or less model-independent.Comment: 20 pages, 8 figures, 2 tables. Version published in JHE

Stop the Top Background of the Stop Search

The main background for the supersymmetric stop direct production search comes from Standard Model ttbar events. For the single-lepton search channel, we introduce a few kinematic variables to further suppress this background by focusing on its dileptonic and semileptonic topologies. All are defined to have end points in the background, but not signal distributions. They can substantially improve the stop signal significance and mass reach when combined with traditional kinematic variables such as the total missing transverse energy. Among them, our variable M^W_T2 has the best overall performance because it uses all available kinematic information, including the on-shell mass of both W's. We see 20%-30% improvement on the discovery significance and estimate that the 8 TeV LHC run with 20 fb-1 of data would be able to reach an exclusion limit of 650-700 GeV for direct stop production, as long as the stop decays dominantly to the top quark and a light stable neutralino. Most of the mass range required for the supersymmetric solution of the naturalness problem in the standard scenario can be covered.Comment: 16 pages, 5 figure

Momentum asymmetries as CP violating observables

Three body decays can exhibit CP violation that arises from interfering diagrams with different orderings of the final state particles. We construct several momentum asymmetry observables that are accessible in a hadron collider environment where some of the final state particles are not reconstructed and not all the kinematic information can be extracted. We discuss the complications that arise from the different possible production mechanisms of the decaying particle. Examples involving heavy neutralino decays in supersymmetric theories and heavy Majorana neutrino decays in Type-I seesaw models are examined.Comment: 20 pages, 9 figures. Clarifying comments and one reference added, matches published versio

BTK inhibition sensitizes acute lymphoblastic leukemia to asparaginase by suppressing the amino acid response pathway

Asparaginase (ASNase) therapy has been a mainstay of acute lymphoblastic leukemia (ALL) protocols for decades and shows promise in the treatment of a variety of other cancers. To improve the efficacy of ASNase treatment, we used a CRISPR/Cas9-based screen to identify actionable signaling intermediates that improve the response to ASNase. Both genetic inactivation of Bruton’s tyrosine kinase (BTK) and pharmacological inhibition by the BTK inhibitor ibrutinib strongly synergize with ASNase by inhibiting the amino acid response pathway, a mechanism involving c-Myc–mediated suppression of GCN2 activity. This synthetic lethal interaction was observed in 90% of patient-derived xenografts, regardless of the genomic subtype. Moreover, ibrutinib substantially improved ASNase treatment response in a murine PDX model. Hence, ibrutinib may be used to enhance the clinical efficacy of ASNase in ALL. This trial was registered at www.clinicaltrials.gov as # NCT02884453

Light Stop Decay in the MSSM with Minimal Flavour Violation

In supersymmetric scenarios with a light stop particle $\tilde{t}_1$ and a small mass difference to the lightest supersymmetric particle (LSP) assumed to be the lightest neutralino, the flavour changing neutral current decay $\tilde{t}_1 \to c \tilde{\chi}_1^0$ can be the dominant decay channel and can exceed the four-body stop decay for certain parameter values. In the framework of Minimal Flavour Violation (MFV) this decay is CKM-suppressed, thus inducing long stop lifetimes. Stop decay length measurements at the LHC can then be exploited to test models with minimal flavour breaking through Standard Model Yukawa couplings. The decay width has been given some time ago by an approximate formula, which takes into account the leading logarithms of the MFV scale. In this paper we calculate the exact one-loop decay width in the framework of MFV. The comparison with the approximate result exhibits deviations of the order of 10% for large MFV scales due to the neglected non-logarithmic terms in the approximate decay formula. The difference in the branching ratios is negligible. The large logarithms have to be resummed. The resummation is performed by the solution of the renormalization group equations. The comparison of the exact one-loop result and the tree level flavour changing neutral current decay, which incorporates the resummed logarithms, demonstrates that the resummation effects are important and should be taken into account.Comment: 29 page

SUSY parameter determination at the LHC using cross sections and kinematic edges

We study the determination of supersymmetric parameters at the LHC from a global fit including cross sections and edges of kinematic distributions. For illustration, we focus on a minimal supergravity scenario and discuss how well it can be constrained at the LHC operating at 7 and 14 TeV collision energy, respectively. We find that the inclusion of cross sections greatly improves the accuracy of the SUSY parameter determination, and allows to reliably extract model parameters even in the initial phase of LHC data taking with 7 TeV collision energy and 1/fb integrated luminosity. Moreover, cross section information may be essential to study more general scenarios, such as those with non-universal gaugino masses, and distinguish them from minimal, universal, models.Comment: 22 pages, 8 figure

Hadronic production of squark-squark pairs: The electroweak contributions

We compute the electroweak (EW) contributions to squark--squark pair production processes at the LHC within the framework of the Minimal Supersymmetric Standard Model (MSSM). Both tree-level EW contributions, of O(alpha_s alpha + alpha^2), and next-to-leading order (NLO) EW corrections, of O(alpha_s^2 alpha), are calculated. Depending on the flavor and chirality of the produced quarks, many interferences between EW-mediated and QCD-mediated diagrams give non-zero contributions at tree-level and NLO. We discuss the computational techniques and present an extensive numerical analysis for inclusive squark--squark production as well as for subsets and single processes. While the tree-level EW contributions to the integrated cross sections can reach the 20% level, the NLO EW corrections typically lower the LO prediction by a few percent.Comment: 36 pages, 18 figure