Mihailo Backovic

Mihailo Backovic
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Mihailo Backovic
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High Energy Physics - Phenomenology (25)
 
High Energy Physics - Experiment (15)
 
Cosmology and Nongalactic Astrophysics (3)
 
Nuclear Experiment (1)
 
Nuclear Theory (1)
 
Physics - Data Analysis; Statistics and Probability (1)
 
Physics - Physics and Society (1)
 
High Energy Astrophysical Phenomena (1)
 
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Publications Authored By Mihailo Backovic

We show that observations of solar $\gamma$-ray fluxes offer a novel probe of dark matter, in scenarios where interactions with the visible sector proceed via a long-lived mediator. As a proof of principle, we demonstrate that there exists a class of models which yield solar $\gamma$-ray lines observable with the next generation of $\gamma$-ray telescopes, while being allowed by a large variety of experimental constraints. Our results suggest that fluxes of solar $\gamma$-ray lines can be up to two orders of magnitude higher than the ones from the galactic center, and are subject to very low backgrounds. Read More

Weakly-coupled TeV-scale particles may mediate the interactions between normal matter and dark matter. If so, the LHC would produce dark matter through these mediators, leading to the familiar "mono-X" search signatures, but the mediators would also produce signals without missing momentum via the same vertices involved in their production. This document from the LHC Dark Matter Working Group suggests how to compare searches for these two types of signals in case of vector and axial-vector mediators, based on a workshop that took place on September 19/20, 2016 and subsequent discussions. Read More

LHC searches for BSM resonances in $l^+ l^-, \, jj, \, t\bar{t}, \gamma \gamma$ and $VV$ final states have so far not resulted in discovery of new physics. Current results set lower limits on mass scales of new physics resonances well into the $\mathcal{O}(1)$ TeV range, assuming that the new resonance decays dominantly to a pair of Standard Model particles. While the SM pair searches are a vital probe of possible new physics, it is important to re-examine the scope of new physics scenarios probed with such final states. Read More

Studies of dark matter lie at the interface of collider physics, astrophysics and cosmology. Constraining models featuring dark matter candidates entails the capability to provide accurate predictions for large sets of observables and compare them to a wide spectrum of data. We present a framework which, starting from a model lagrangian, allows one to consistently and systematically make predictions, as well as to confront those predictions with a multitude of experimental results. Read More

We explore the ability of the high luminosity LHC to test models which can explain the 750 GeV diphoton excess. We focus on a wide class of models where a 750 GeV singlet scalar couples to Standard Model gauge bosons and quarks, as well as dark matter. Including both gluon and photon fusion production mechanisms, we show that LHC searches in channels correlated with the diphoton signal will be able to probe wide classes of diphoton models with $\mathcal{L} \sim 3000\, \text{fb}^{-1}$ of data. Read More

Ambulance chasing is a common socio-scientific phenomenon in particle physics. I argue that despite the seeming complexity, it is possible to gain insight into both the qualitative and quantitative features of ambulance chasing dynamics. Compound-Poisson statistics suffices to accommodate the time evolution of the cumulative number of papers on a topic, where basic assumptions that the interest in the topic as well as the number of available ideas decrease with time appear to drive the time evolution. Read More

We propose a simplified model of dark matter with a scalar mediator to accommodate the di-photon excess recently observed by the ATLAS and CMS collaborations. Decays of the resonance into dark matter can easily account for a relatively large width of the scalar resonance, while the magnitude of the total width combined with the constraint on dark matter relic density lead to sharp predictions on the parameters of the Dark Sector. Under the assumption of a rather large width, the model predicts a signal consistent with ~300 GeV dark matter particle in channels with large missing energy. Read More

We present the updated version of MadDM, a new dark matter tool based on MadGraph5_aMC@NLO framework. New version includes direct detection capability in addition to relic abundance computation. In this article, we provide short description of the implementation of relevant effective operators and validations against existing results in literature. Read More

Weakly interacting dark matter particles can be pair-produced at colliders and detected through signatures featuring missing energy in association with either QCD/EW radiation or heavy quarks. In order to constrain the mass and the couplings to standard model particles, accurate and precise predictions for production cross sections and distributions are of prime importance. In this work, we consider various simplified models with s-channel mediators. Read More

Searches for fermionic top partners at the TeV scale will bring forward a new final state kinematic regime and event topologies, where Run I search strategies will inevitably fail. We propose concrete search strategies for singly produced charge 2/3 fermionic top partners ($T'$) adequate for LHC Run II. Our analysis spans over all of the $T'$ decay modes ($i. Read More

2015Jul
Authors: Daniel Abercrombie, Nural Akchurin, Ece Akilli, Juan Alcaraz Maestre, Brandon Allen, Barbara Alvarez Gonzalez, Jeremy Andrea, Alexandre Arbey, Georges Azuelos, Patrizia Azzi, Mihailo Backović, Yang Bai, Swagato Banerjee, James Beacham, Alexander Belyaev, Antonio Boveia, Amelia Jean Brennan, Oliver Buchmueller, Matthew R. Buckley, Giorgio Busoni, Michael Buttignol, Giacomo Cacciapaglia, Regina Caputo, Linda Carpenter, Nuno Filipe Castro, Guillelmo Gomez Ceballos, Yangyang Cheng, John Paul Chou, Arely Cortes Gonzalez, Chris Cowden, Francesco D'Eramo, Annapaola De Cosa, Michele De Gruttola, Albert De Roeck, Andrea De Simone, Aldo Deandrea, Zeynep Demiragli, Anthony DiFranzo, Caterina Doglioni, Tristan du Pree, Robin Erbacher, Johannes Erdmann, Cora Fischer, Henning Flaecher, Patrick J. Fox, Benjamin Fuks, Marie-Helene Genest, Bhawna Gomber, Andreas Goudelis, Johanna Gramling, John Gunion, Kristian Hahn, Ulrich Haisch, Roni Harnik, Philip C. Harris, Kerstin Hoepfner, Siew Yan Hoh, Dylan George Hsu, Shih-Chieh Hsu, Yutaro Iiyama, Valerio Ippolito, Thomas Jacques, Xiangyang Ju, Felix Kahlhoefer, Alexis Kalogeropoulos, Laser Seymour Kaplan, Lashkar Kashif, Valentin V. Khoze, Raman Khurana, Khristian Kotov, Dmytro Kovalskyi, Suchita Kulkarni, Shuichi Kunori, Viktor Kutzner, Hyun Min Lee, Sung-Won Lee, Seng Pei Liew, Tongyan Lin, Steven Lowette, Romain Madar, Sarah Malik, Fabio Maltoni, Mario Martinez Perez, Olivier Mattelaer, Kentarou Mawatari, Christopher McCabe, Théo Megy, Enrico Morgante, Stephen Mrenna, Siddharth M. Narayanan, Andy Nelson, Sérgio F. Novaes, Klaas Ole Padeken, Priscilla Pani, Michele Papucci, Manfred Paulini, Christoph Paus, Jacopo Pazzini, Björn Penning, Michael E. Peskin, Deborah Pinna, Massimiliano Procura, Shamona F. Qazi, Davide Racco, Emanuele Re, Antonio Riotto, Thomas G. Rizzo, Rainer Roehrig, David Salek, Arturo Sanchez Pineda, Subir Sarkar, Alexander Schmidt, Steven Randolph Schramm, William Shepherd, Gurpreet Singh, Livia Soffi, Norraphat Srimanobhas, Kevin Sung, Tim M. P. Tait, Timothee Theveneaux-Pelzer, Marc Thomas, Mia Tosi, Daniele Trocino, Sonaina Undleeb, Alessandro Vichi, Fuquan Wang, Lian-Tao Wang, Ren-Jie Wang, Nikola Whallon, Steven Worm, Mengqing Wu, Sau Lan Wu, Hongtao Yang, Yong Yang, Shin-Shan Yu, Bryan Zaldivar, Marco Zanetti, Zhiqing Zhang, Alberto Zucchetta

This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations. Read More

Supersymmetric extensions of the Standard Model with highly mixed squark flavours beyond minimal flavour violation provide interesting scenarios of new physics, which have so far received limited attention. We propose a calculable realization of such scenarios in models of gauge mediation augmented with an extra interaction between the messengers and the up type squark. We compute the supersymmetric spectrum and analyze the flavour physics constraints on such models. Read More

We propose a strategy for new physics searches in channels which contain a boosted $Z$ boson in the final state. Our proposal exploits the previously overlooked advantages of boosted $Z\rightarrow \nu \bar{\nu}$ topologies, where collimated neutrinos result in signals with large missing energy. We illustrate the advantage of this channel in a case study of singly produced TeV scale charge 2/3 fermionic top partners ($T'$) which decay to $t+Z$. Read More

Many searches for physics beyond the Standard Model at the Large Hadron Collider (LHC) rely on top tagging algorithms, which discriminate between boosted hadronic top quarks and the much more common jets initiated by light quarks and gluons. We note that the hadronic calorimeter (HCAL) effectively takes a "digital image" of each jet, with pixel intensities given by energy deposits in individual HCAL cells. Viewed in this way, top tagging becomes a canonical pattern recognition problem. Read More

We propose a new search strategy for quark partners which decay into a boosted Higgs and a light quark. As an example, we consider phenomenologically viable right handed up-type quark partners of mass $\sim 1$ TeV in composite pseudo-Nambu-Goldstone-boson Higgs models within the context of flavorful naturalness. Our results show that $S/B > 1$ and signal significance of $\sim 7\sigma$ is achievable at $\sqrt{s} = 14$ TeV LHC with 35 $fb^{-1}$ of integrated luminosity, sufficient to claim discovery of a new particle. Read More

We propose a new search strategy for heavy top partners at the early stages of the LHC run-II, based on lepton-jet final states. Our results show that final states containing a boosted massive jet and a hard lepton, in addition to a top quark and possibly a forward jet, offer a new window to both detecting and measuring top partners of mass $\sim 2$ TeV. Our resulting signal significance is comparable or superior to the same sign di-lepton channels for top partner masses heavier than roughly 1 TeV. Read More

We present a procedure for tagging boosted semi-leptonic $t\bar t$ events based on the Template Overlap Method. We introduce a new formulation of the template overlap function for leptonically decaying boosted tops and show that it can be used to compensate for the loss of background rejection due to reduction of b-tagging efficiency at high $p_T$. A study of asymmetric top pair production due to higher order effects shows that our approach improves the resolution of the truth level kinematic distributions. Read More

The framework of a warped extra dimension with the Standard Model (SM) fields propagating in it is a very well-motivated extension of the SM since it can address both the Planck-weak and flavor hierarchy problems of the SM. We consider signals at the 14 and 33 TeV large hadron collider (LHC) resulting from the direct production of the new particles in this framework, i.e. Read More

We show that the Template Overlap Method can improve the signal to background ratio of boosted $H\to b \bar b$ events produced in association with a leptonically decaying $W$. We introduce several improvements on the previous formulations of the template method. Varying three-particle template subcones increases the rejection power against the backgrounds, while sequential template generation ensures an efficient coverage in template phase space. Read More

TemplateTagger is a C++ package for jet substructure analysis with Template Overlap Method. The code operates with arbitrary models within fixed-order perturbation theory and arbitrary kinematics. Specialized template generation classes allow the user to implement any model for a decay of a boosted heavy object. Read More

Several arguments suggest parity violation may be observable in high energy strong interactions. We introduce new analysis tools for describing the azimuthal dependence of multi-particle distributions, or "azimuthal flow." Analysis uses the representations of the orthogonal group O(2) and dihedral groups $D_{N}$ necessary to define parity correctly in two dimensions. Read More

We find new and universal relations for the properties of dark matter particles consistent with standard relic abundances. Analysis is based on first characterizing the $s$-channel resonant annihilation process in great detail, keeping track of all velocity-dependence, the presence of multiple scales and treating each physical regime above, below, and close to thresholds separately. The resonant regime as well as extension to include non-resonant processes are then reduced to analytic formulas and inequalities that describe the full range of multi-dimensional numerical work. Read More

We find model-independent upper limits on rates of dark matter annihilation in galactic halos. The Born approximation generally fails, while exotic threshold enhancements akin to "Sommerfeld factors" also turn out to be baseless The most efficient annihilation mechanism involves perturbatively small decay widths that have largely been ignored. Widths that are very small compared to TeV mass scales suffice to effectively saturate unitarity bounds on annihilation rates. Read More