Early LHC Research Articles

Abstract 407: The Efficacy and Frequency of Early Left Heart Catheterization After Out of Hospital Cardiac Arrest Over That Last Decade

Background: The efficacy of early coronary intervention after return of spontaneous circulation (ROSC) from out of hospital cardiac arrest, (OHCA) is debated. A recent review of the Wayne County, (Mi) CARES dataset from 2014-18 noted that early LHC maintained the strongest correlation to survival to discharge with good neurological outcome, for all-cause OHCA. Though the overall rate of LHC remained relatively stable, there was a sizable reduction in early LHC and a comparable increase in late LHC in those with CPC 1 and 2 at discharge [ 12 ] Our objective is to utilize the national CARES data to analyze the effect of early LHC on survival with good neurological outcome and to describe the frequency and timing of LHC in OHCA. Methods: This observational study included patients enrolled in the national CARES registry from 2013-21. For the outcome of LHC by year, chi square analysis was performed. Outcome was cerebral performance category, (CPC) (good <3 vs. poor > 3) at hospital discharge. A propensity score (PS) model was constructed using variables predictive of LHC and good outcome to determine probability of LHC. The PS was then used in an inverse weighted random effects logistic regression model to determine the independent effect of early LHC on outcome. Results: 132,758 individual cases were identified. Median age was 60.3 years (s.d. 16.6), 61.8% were male. Early coronary angiography was performed in 26,999 (20.3%) patients. Patients who underwent early angiography often had shockable rhythms (78.% vs 34%), suffered the OHCA in a public location (36.9% vs 26.1%%), and were witnessed cardiac arrests (80% vs 48%). For the full model the odds ratio for a good outcome after early LHC was 2.54 (95% CI 2.36 - 2.73). Only initial shockable rhythm was more predictive of a good outcome with an OR of 3.9. The proportion undergoing early catheterization declined from 27.6 % to 17.3% from 2013 to 2021; p < 0.0001), though the overall catheterization rate remained the same. Conclusion: In patients with OHCA, early left heart catheterization retains a strong association with good neurological outcome at hospital discharge. The use of early left heart catheterization has declined significantly over the last 9 years.

Hadronic Interactions Studies at the LHC

The deficit of muons in the simulation of extensive air showers is a long-standing problem and the origin of large uncertainties in the reconstruction of the mass of the high-energy primary cosmic rays. Hadronic interaction models re-tuned after early LHC data have a more consistent description of the muon content among them but still disagree with the data. Furthermore, some inconsistencies are also visible in the electromagnetic component. Ten years after the first LHC-tuned model release, much more detailed data are available both from LHC, SPS and hybrid air shower measurements, allowing for the understanding of some deficiencies in the model which could lead to a change in both Xmax and the muon production by air showers. A better treatment of the core-corona approach according to LHC data has important consequences on the muon production while an update of diffraction and nuclear fragmentation is changing the Xmax distribution. An updated version of EPOS LHC will be presented addressing the main issues of this model.

Measuring charged particle multiplicity with early ATLAS public data

We study 100 images of early LHC collisions that were recorded by the ATLAS experiment and made public for outreach purposes, and extract the charged particle multiplicity as a function of momentum for proton–proton collisions at a centre-of-mass energy of 7 TeV. As these collisions have already been pre-processed by the ATLAS Collaboration, the particle tracks are visible, but are available to the public only in the form of low-resolution bitmaps. We describe two separate image processing methods, one based on the industry-standard OpenCV library and C++, another based on self-developed algorithms in Python. We present our analysis of the transverse momentum and azimuthal angle distributions of the particles, in agreement with the literature.

Enhanced rates for diphoton resonances in the MSSM

We propose a simple mechanism for copiously producing heavy Higgs bosons with enhanced decay rates to two photons at the LHC, within the context of the Minimal Supersymmetric extension of the Standard Model (MSSM). In the CP-conserving limit of the theory, such a diphoton resonance may be identified with the heavier CP-even $H$ boson, whose gluon-fusion production and decay into two photons are enhanced by loops of the lightest supersymmetric partner of the top quark $\tilde{t}_1$ when its mass $m_{\tilde{t}_1}$ happens to be near the $\tilde{t}^*_1\tilde{t}_1$ threshold, i.e.~for $m_{\tilde{t}_1}\!\simeq \!\frac12 M_H$. The scenario requires a relatively low supersymmetry-breaking scale $M_S\stackrel{<}{{}_\sim} 1$ TeV, but large values of the higgsino mass parameter, $\mu \stackrel{>}{{}_\sim} 1$ TeV, that lead to a strong $H \tilde{t}^*_1 \tilde{t}_1$ coupling. Such parameters can accommodate the observed mass and standard-like couplings of the 125 GeV $h$ boson in the MSSM, while satisfying all other constraints from the LHC and dark matter searches. Additional enhancement to the diphoton rate could be provided by Coulombic QCD corrections and, to a lesser extent, by resonant contributions due to $\tilde{t}_1^* \tilde{t}_1$ bound states. To discuss the characteristic features of such a scenario, we consider as an illustrative example the case of a diphoton resonance with a mass of approximately 750 GeV, for which an excess was observed in the early LHC 13 TeV data and which later turned out to be simply a statistical fluctuation.

The design and performance of the ATLAS Inner Detector trigger for Run 2

The design and performance of the ATLAS Inner Detector (ID) trigger algorithms running online on the High Level Trigger (HLT) computing cluster with the early LHC Run 2 data are discussed. During the LHC shutdown from 2013 to 2015, the HLT farm was redesigned to run in a single HLT stage, rather than in two stages (Level 2 and Event Filter) as was used in Run 1. This allowed for a redesign of the HLT ID tracking algorithm, which aims to satisfy the challenging demands of the higher collision energy of the LHC in Run 2 and is essential for tracking of different charged particles in the ATLAS detector. The detailed performance of the tracking algorithms with the initial Run 2 data is discussed for electrons, muons and other charged particles. Comparison with the Run 1 strategy is made and demonstrates the superior performance of the strategy adopted for Run 2.

Minimal model of a diphoton resonance: Production without gluon couplings

We consider the phenomenology of a resonance that couples to photons but not gluons, and estimate its production rate at the LHC from photon-photon fusion in elastic pp scattering using the effective photon and narrow width approximations. The rate is sensitive only to the mass, the spin, the total width of the resonance, and its branching fraction to photons. Production cross sections of 5-10 fb at 13 TeV can be easily accommodated for a 750 GeV resonance with partial photon width of 15 GeV. This provides the minimal explanation of the reported diphoton anomaly in the early LHC Run II data.

750 GeV composite axion as the LHC diphoton resonance

We propose that the 750 GeV resonance, presumably observed in the early LHC Run 2 data, could be a heavy composite axion that results from condensation of a hypothetical quark in a high-colour representation of conventional QCD. The model, motivated by a recently proposed solution to the strong CP problem, is very economical and is essentially defined by the properties of the additional quark - its colour charge, hypercharge and mass. The axion mass and its coupling to two photons (via axial anomaly) can be computed in terms of these parameters. The axion is predominantly produced via photon fusion ($\gamma\gamma \to {\cal A}$) which is followed by $ Z $ vector boson fusion and associated production at the LHC. We find that the total diphoton cross section of the axion can be fitted with the observed excess. Combining the requirement on the cross-section, such that it reproduces the diphoton excess events, with the bounds on the total width ($\Gamma_{tot} \leqslant 45$ GeV), we obtain the effective coupling in the range $1.6\times 10^{-4}$ GeV$^{-1}\gtrsim C_{{\cal A}} \gtrsim 6.5\times 10^{-5}$ GeV$^{-1}$. Within this window of allowed couplings the model favours a narrow width resonance and $ y_{Q}^2 \sim \mathcal{O}(10)$. In addition, we observe that the associated production $q\bar{q} \to {\cal A}\gamma\to \gamma\gamma\gamma$ can potentially produce a sizeable number of three photon events at future LHC and $ e^{+} e^{-} $ colliders. However, the rare decay $Z\to\mathcal{A}^*\gamma \to \gamma\gamma\gamma$ is found to be too small to be probed at the LHC.

Dark Matter benchmark models for early LHC Run-2 Searches: Report of the ATLAS/CMS Dark Matter Forum

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.

Gravity mediation retrofitted

Most discussion of metastable dynamical supersymmetry breaking (MDSB) has focussed on low energy breaking, as in gauge mediation. It is of interest to consider possible implications for intermediate scale breaking ("gravity mediation"), especially as the early LHC results suggest the possibility that supersymmetry, if broken at relatively low energies, might be tuned. A somewhat high scale for susy breaking could ameliorate the usual flavor problems of gravity mediation, resolve the question of cosmological moduli, and account for a Higgs with mass well above $M_Z$. We study MDSB in gravity mediation, especially retrofitted models in which discrete $R$ symmetries play an important role, considering questions including implications of symmetries for $B$ and $A$ terms, and the genericity of split supersymmetry.

Search for the signal of monotop production at the early LHC

We investigate the potential of the early LHC to discover the signal of monotops, which can be decay products of some resonances in models such as R-parity violating SUSY or SU(5), etc. We show how to constrain the parameter space of the models by the present data of $Z$ boson hadronic decay branching ratio, $K^0-\bar{K^0}$ mixing and dijet productions at the LHC. Then, we study the various cuts imposed on the events, reconstructed from the hadronic final states, to suppress backgrounds and increase the significance in detail. And we find that in the hadronic mode the information from the missing transverse energy and reconstructed resonance mass distributions can be used to specify the masses of the resonance and the missing particle. Finally, we study the sensitivities to the parameters at the LHC with $\sqrt{s}$=7 TeV and an integrated luminosity of $1 {\rm fb}^{-1}$ in detail. Our results show that the early LHC may detect this signal at 5$\sigma$ level for some regions of the parameter space allowed by the current data.

General neutralino NLSPs at the early LHC

Gauge mediated supersymmetry breaking (GMSB) is a theoretically well-motivated framework with rich and varied collider phenomenology. In this paper, we study the Tevatron limits and LHC discovery potential for a wide class of GMSB scenarios in which the next-to-lightest superpartner (NLSP) is a promptly-decaying neutralino. These scenarios give rise to signatures involving hard photons, W ’s, Z’s, jets and/or higgses, plus missing energy. In order to characterize these signatures, we define a small number of minimal spectra, in the context of General Gauge Mediation, which are parameterized by the mass of the NLSP and the gluino. Using these minimal spectra, we determine the most promising discovery channels for general neutralino NLSPs. We find that the 2010 dataset can already cover new ground with strong production for all NLSP types. With the upcoming 2011-2012 dataset, we find that the LHC will also have sensitivity to direct electroweak production of neutralino NLSPs.

Measurements of the production, decay and properties of the top quark: a review

With the full Tevatron Run II and early LHC data samples, the opportunity for furthering our understanding of the properties of the top quark has never been more promising. Although the current knowledge of the top quark comes largely from Tevatron measurements, the experiments at the LHC are poised to probe top-quark production and decay in unprecedented regimes. Although no current top quark measurements conclusively contradict predictions from the standard model, the precision of most measurements remains statistically limited. Additionally, some measurements, most notably A FB in top quark pair production, show tantalizing hints of beyond-the-Standard-Model dynamics. The top quark sample is growing rapidly at the LHC, with initial results now public. This review examines the current status of top quark measurements in the particular light of searching for evidence of new physics, either through direct searches for beyond the standard model phenomena or indirectly via precise measurements of standard model top quark properties.

Dark matter and imaging air Cherenkov arrays

The CTA will mean a significant increase of the potential for dark matter detection, compared to present-day detectors like MAGIC, HESS and VERITAS. In particular, if – as it might be indicated from early LHC results – the dark matter sector is heavy, perhaps in the TeV mass range, imaging air Cherenkov arrays have a good opportunity to detect γ-rays from dark matter annihilation in the galactic halo, the galactic center, dwarf galaxies, or galaxy clusters. A review of the present situation is given and a few of the “miracles” that may enhance chances for detection in CTA are discussed, such as Sommerfeld enhancement and internal bremsstrahlung radiation. A few templates for dark matter are studied, and the importance of the acceptance of the detector at low energies is pointed out. Finally, the idea of a complement to CTA in the form of a high-altitude, low energy threshold dedicated dark matter array, DMA, is discussed.

Discriminating minimal SUGRA and minimal gauge mediation models at the early LHC

Among various supersymmetric (SUSY) standard models, the gravity mediation model with a neutralino LSP and the gauge mediation model with a very light gravitino are attractive from the cosmological view point. These models have different scales of SUSY breaking and their underlying physics in high energy is quite different. However, if the sparticles' decay into the gravitino is prompt in the latter case, their collider signatures can be similar: multiple jets and missing transverse momentum. In this paper, we study the discrimination between these models in minimal cases at the LHC based on the method using the significance variables in several different modes and show the discrimination is possible at a very early stage after the discovery.

Implications on the minimal universal extra dimension model from the early LHC data onℓ+E̸Tsignal

Recently, the ATLAS and CMS collaborations reported their search for a new heavy gauge boson ${W}^{\ensuremath{'}}$ with one lepton plus missing transverse momentum. We find that ${W}^{(2)}$, the second Kaluza-Klein (KK) state of the $W$ boson in the minimal universal extra dimension (mUED) model, can be a good candidate for this signal, as its branching ratio into $\ensuremath{\ell}\ensuremath{\nu}$ is sizable. Moreover, nearly degenerate KK mass spectra in the mUED model yield generically very soft standard model particles accompanying ${W}^{(2)}$ from the subsequent decays of the second KK quarks and gluons. In a hadron collider, this indirect ${W}^{(2)}$ production is difficult to distinguish from the ${W}^{(2)}$ single production. The involved strong interactions make it more important than the single production. The early LHC data on $\ensuremath{\ell}+{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}$ signal for $1.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ integrated luminosity is shown insufficient to limit our model. However, the results show that the present LHC $5.6\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ data can cover most of the reasonable parameter space of the mUED model.

Implementation of the type III seesaw model in FeynRules/MadGraph and prospects for discovery with early LHC data

We discuss the implementation of the "minimal" type III seesaw model, i.e. with one fermionic triplet, in FeynRules/MadGraph. This is the first step in order to realize a real study of LHC data recorded in the LHC detectors. With this goal in mind, we comment on the possibility of discovering this kind of new physics at the LHC running at 7 TeV with a luminosity of few fb^-1.

A two-tiered correlation of dark matter with missing transverse energy: reconstructing the lightest supersymmetric particle mass at the LHC

We suggest that non-trivial correlations between the dark matter particle mass and collider based probes of missing transverse energy H_T^miss may facilitate a two tiered approach to the initial discovery of supersymmetry and the subsequent reconstruction of the LSP mass at the LHC. These correlations are demonstrated via extensive Monte Carlo simulation of seventeen benchmark models, each sampled at five distinct LHC center-of-mass beam energies, spanning the parameter space of No-Scale F-SU(5).This construction is defined in turn by the union of the Flipped SU(5) Grand Unified Theory, two pairs of hypothetical TeV scale vector-like supersymmetric multiplets with origins in F-theory, and the dynamically established boundary conditions of No-Scale Supergravity. In addition, we consider a control sample comprised of a standard minimal Supergravity benchmark point. Led by a striking similarity between the H_T^miss distribution and the familiar power spectrum of a black body radiator at various temperatures, we implement a broad empirical fit of our simulation against a Poisson distribution ansatz. We advance the resulting fit as a theoretical blueprint for deducing the mass of the LSP, utilizing only the missing transverse energy in a statistical sampling of >= 9 jet events. Cumulative uncertainties central to the method subsist at a satisfactory 12-15% level. The fact that supersymmetric particle spectrum of No-Scale F-SU(5) has thrived the withering onslaught of early LHC data that is steadily decimating the Constrained Minimal Supersymmetric Standard Model and minimal Supergravity parameter spaces is a prime motivation for augmenting more conventional LSP search methodologies with the presently proposed alternative.

Theory of Heavy Quark Energy Loss

We briefly review some of the models and theoretical schemes established to describe heavy quark quenching in ultrarelativistic heavy ions collisions. Some lessons are derived from RHIC and early LHC data, especially as for the contraints they impose on those models.

Searching for light higgsinos with b-jets and missing leptons

Abstract A recently proposed class of supersymmetric models predicts rather light and nearly mass-degenerate higgsinos, while the other superparticles are significantly heavier. In this paper we study the early LHC phenomenology of a benchmark model of this kind. If the squarks and gluinos, and in particular the lighter stop, are still light enough to be within reach, then evidence for our model can be found in hadronic SUSY searches. Moreover, with dedicated searches it will be possible to distinguish the light higgsino model from generic SUSY models with a bino LSP. Search channels with b-jets and with isolated leptons play a crucial role for model discrimination.

Early LHC bound on the [formula omitted] boson mass in the nonuniversal gauge interaction model

We study the phenomenology of the heavy charged gauge boson and obtain the lower bounds on its mass with the early LHC data at 7 TeV center-of-mass energy in the nonuniversal gauge interaction model, in which the electroweak SU(2) gauge group depends upon the fermion family. We found that the direct bound with the early data of the LHC is already better than the indirect bound on the mass of the W′ boson.