We review what can (and cannot) be learned if dark matter is detected in one or more experiments, emphasizing the importance of combining LHC data with direct, astrophysical and cosmological probes of dark matter. We briefly review the conventional picture of a thermally produced WIMP relic density and its connection with theories of electroweak symmetry breaking. We then discuss both experimental and theoretical reasons why one might generically expect this picture to fail. If this is the case, we argue that a combined effort bringing together all types of data -- combined with explicitly constructed theoretical models -- will be the only way to achieve a complete understanding of the dark matter in our universe and become confident that any candidate actually provides the relic density.
Using an artificial neutral network we explore the parameter space of supergravity grand unified models consistent with the combined Fermilab E989 and Brookhaven E821 data on $(g-2)_μ$. The analysis indicates that the region favored by the data is the one generated by gluino-driven radiative breaking of the electroweak symmetry. This region naturally leads to a split sparticle spectrum with light sleptons and weakinos but heavy squarks, with the stau and the chargino as the lightest charged particles. We show that if the entire deviation from the standard model $(g-2)_μ$ arises from supersymme…
Fluid dynamical description of elementary particle collisions has a long history dating back to the works of Landau and Fermi. Nevertheless, it is during the last 10-15 years when fluid dynamics has become the standard tool to describe the evolution of matter created in ultrarelativistic heavy ion collisions. In this review I briefly describe the hydrodynamical models, what we have learned when analyzing the RHIC and LHC data using these models, and what the latest developments and challenges are.
Since recent RHIC data and the development of new theories for small x physics, a new interest appeared for forward physics. At LHC, a correct description of multiple parton interactions will be crucial to understand all the results. On the other hand, forward particle production and multiple interactions are the key points of air shower development. That's why air shower measurements done by precise experiments like KASCADE can help to understand high energy interactions, using hadronic models which are able to reproduce both accelerator and air shower data. In the framework of the EPOS model…
This Report summarizes the results of the activities in 2014 of the Standard Model Working Group within the workshop "What Next" of INFN. We present a framework, general questions, and some indications of possible answers on the main issue for Standard Model physics in the LHC era and in view of possible future accelerators.
Recently CMS and ATLAS announced that they had measured the Higgs boson parity. Here we note that their approach can determine this parity only under the additional assumption that this particle has a definite parity. If parity conservation is violated in the Higgs sector, the parity of observed "Higgs" boson does not exist. The approach used in the mentioned experiments does not allow to observe such opportunity. In this sense titles of mentioned CMS and ATLAS publications are misleading.
The first evidence of new strong interactions may be a sufficiently massive fourth family observed at the LHC. The fourth family masses, of the leptons in particular, are constrained by the electroweak precision data, and this leads to signatures at the LHC that may imply early discovery. We study the implications of this discovery from a bottom-up perspective, where effective 4-fermion operators model the dominant effects of the new dynamics. We identify simple approximate symmetries of these operators that may be required for realistic masses of the third and fourth families. The large top m…
Deeply-inelastic scattering (DIS) stands to enter a golden age with the prospect of precision programs at the Electron-Ion Collider (EIC) and Large Hadron-electron Collider (LHeC). While these programs will be of considerable importance to resolving longstanding issues in (non)perturbative QCD as well as hadronic and nuclear structure, they will also have valuable implications for a wider range of physics at the Energy and Intensity Frontiers, including at the High-Luminosity LHC (HL-LHC) and future $νA$ facilities. In this plenary contribution, we highlight a number of salient examples of the…
Topical phenomena in high-energy physics related to collision experiments of heavy nuclei ("Little Bang") and early universe cosmology ("Big Bang") involve far-from-equilibrium dynamics described by quantum field theory. One example concerns the role of plasma instabilities for the process of thermalization in heavy-ion collisions. The reheating of the early universe after inflation may exhibit rather similar phenomena following a tachyonic or parametric resonance instability. Certain universal aspects associated to nonthermal fixed points even quantitatively agree, and considering these pheno…
We investigate the implications for supersymmetry from an assumed absence of any signal in the first period of LHC data taking at 7 TeV center-of-mass energy and with 1 to 7 fb^(-1) of integrated luminosity. We consider the zero-lepton plus four jets and missing transverse energy signature, and perform a combined fit of low-energy measurements, the dark matter relic density constraint and potential LHC exclusions within a minimal supergravity model. A non-observation of supersymmetry in the first period of LHC data taking would still allow for an acceptable description of low-energy data and t…
We explain what features of string theory can be tested at the LHC. We review the present bounds on the string mass and on extra gauge bosons as well as the prospects for the upcoming experiments.
The existing data appears to provide hints of an underlying high scale theory. These arise from the gauge coupling unification, from the smallness of the neutrino masses, and via a non-vanishing muon anomaly. An overview of high scale models is given with a view to possible tests at the Large Hadron Collider. Specifically we discuss here some generic approaches to deciphering their signatures. We also consider an out of the box possibility of a four generation model where the fourth generation is a mirror generation rather than a sequential generation. Such a scenario can lead to some remarkab…
We present an overview of what we learned so far from low-energy flavour observables, concerning physics beyond the Standard Model, and what we could still learn from further studies in flavour physics in the next few years.
The W b anti-b, Z b anti-b and t anti-t b anti-b production at LHC are irreducible backgrounds for possible observability of the Standard Model (SM) and Minimal Supersymmetric Standard Model (MSSM) light Higgs boson respectively in the associated WH, ZH and t anti-t H production followed by the H -> b anti-b decay. We present a comparison of the background estimates as obtained with (a) complete massive matrix element implemented in AcerMC Monte Carlo generator and (b) PYTHIA implementation of the inclusive W, Z, and t anti-t production, followed by the parton showering mechanism. Both approac…
This proceeding explores some of the questions that connect the LHC and neutrino experiments: What is the origin of mass? What is the meaning of flavor? Is there direct evidence of new forces or particles? The neutrino program investigating these questions is large and diverse. The strategy here, to narrow the discussion, is to focus on relatively new ideas for experiments that may be less known within the LHC community.
What is the Higgs boson telling us? What else is there, maybe supersymmetry and/or dark matter? How do we find it? These are now the big questions in collider physics that I discuss in this talk, from a personal point of view.
High P_T observables associated with hard pQCD processes are regarded as tomographic probes of the medium created in ultrarelativistic heavy-ion collisions. Unfortunately, tomography is unexpectedly complicated in practice due to model uncertainties and the highly averaged nature of many observables. However, a systematic comparison study demanding a simultaneous description of many observables within the same framework is sufficiently powerful to rule out a large fraction of conjectured models about the physics mechanism of parton-medium interaction. From this study, it can be inferred that t…
We find out the connection between the unintegrated gluon distribution at low intrinsic transverse momenta and the inclusive spectrum of the hadrons produced in pp collision at LHC energies in the mid-rapidity region and low hadron transverse momenta. The parameters of this distribution are found from the best description of the LHC data. Its application to the analysis of ep deep inelastic scattering allows us to obtain the results which reasonable describe the H1 and ZEUS data on the structure functions at low x. The connection between the soft processes at LHC and small-x physics at HERA is…
Consider the day when an invariant mass peak, roughly compatible with "the Higgs", begins to emerge, say at the LHC, ... and may you see that day. There will be a difference between discovery and scrutiny. The latter would involve an effort to ascertain what it is, or is not, that has been found. It turns out that the two concepts are linked: Scrutiny will naturally result in deeper knowledge - is this what you were all looking for? - but may also speed up discovery.
We discuss the limitations to the use of the effective field theory approach to study dark matter at the LHC. We introduce and study a few quantities, some of them independent of the ultraviolet completion of the dark matter theory, which quantify the error made when using effective operators to describe processes with very high momentum transfer. Our criteria indicate up to what cutoff energy scale, and with what precision, the effective description is valid, depending on the dark matter mass and couplings.
What kind of New Physics, if any, we expect to discover at the LHC? I will try to address this formidable question by re-formulating it as follows: is the breaking of the electroweak symmetry strong or weak ?
Motivated by the upcoming Higgs analyzes we investigate the importance of the complementarity of the Higgs boson chase on the low mass WIMP search in direct detection experiments and the gamma-ray emission from the Galactic Center measured by the Fermi-LAT telescope in the context of the $SU(3)_c\otimes SU(3)_L\otimes U(1)_N$. We obtain the relic abundance, thermal cross section, the WIMP-nucleon cross section in the low mass regime and network them with the branching ratios of the Higgs boson in the model. We conclude that the Higgs boson search has a profound connection to the dark matter pr…
The success of the first few years of LHC operations at CERN, and the expectation of more to come as the LHC performance improves, are already leading to discussions of what should be next for both proton-proton and electron-positron colliders. In this discussion I see too much theoretical desperation caused by the so far unsuccessful hunt for what is beyond the Standard Model, and too little of the necessary interaction of the accelerator, experimenter, and theory communities necessary for a scientific and engineering success. Here, I give my impressions of the problem, its possible solution,…
A U(1)' or Z' is generic in many scenarios of physics beyond the Standard Model, such as string theory compactifications, GUTs, extra-dimensions, compositeness, dynamical electroweak symmetry breaking, dark-sector models, etc. We study the potential of probing a TeV-scale Z' with electroweak couplings in future experiments. In particular, we focus on two scenarios: (1) If a Z' is discovered at the LHC, what is the potential of measuring its mass and width and to distinguish between benchmark models utilizing various observables, especially asymmetries, at a high luminosity LHC and the ILC. (2)…
In nucleus-nucleus collisions at the Relativistic Heavy Ion Collider (RHIC), one generically observes a strong medium-induced suppression of high-pT hadron production. This suppression is accounted for in models which assume a significant medium-induced radiative energy loss of high-pT parent partons produced in the collision. How can we further test the microscopic dynamics conjectured to underly this abundant high-pT phenomenon? What can we learn about the dynamics of parton fragmentation, and what can we learn about the properties of the medium which modifies it ? Given that inelastic parto…
We consider an extension of the MSSM with an added vectorlike top partner. Our aim is to revisit to what extent such an extension can raise the Higgs boson mass through radiative corrections and help ameliorate the MSSM hierarchy problem, and to specify what experimental probes at the LHC will find or exclude this possibility during the high-luminosity phase. Direct detection, precision electroweak and precision Higgs analyses are all commissioned to this end. To achieve the $ 125 \, \textrm{GeV} \ $ Higgs boson mass, we find that superpartner masses can be reduced by a factor of more than thr…
These lectures give an overview of aspects of missing E_T signatures from new physics at the LHC, along with their important connection to dark matter physics. Mostly, I will concentrate on supersymmetric (SUSY) sources of missing E_T, but will also mention Little Higgs models with T-parity (LHT) and universal extra dimensions (UED) models with KK-parity. Lecture 1 covers SUSY basics, model building and spectra computation. Lecture 2 addresses sparticle production and decay mechanisms at hadron colliders and event generation. Lecture 3 covers SUSY signatures at LHC, along with LHT and UED sign…
The Large Hadron Collider is shown to have great scope for a light charged Higgs discovery, in the context of the CP-violating type-I two Higgs doublet model. This scenario with similar masses of $H^\pm$ and W was suggested by the puzzling departure from charged current lepton universality found in the LEP data. With the lightest neutral Higgs mass set to 125 GeV, the charged-neutral Higgs associated production mechanism can cause a significant excess in the $τνb \bar{b}$ events over a vast range of tan beta as long as the Higgs mixing pattern avoids a few limiting cases. Thanks to the low $H^…
These lectures on Higgs boson collider searches were presented at TASI 2006. I first review the Standard Model searches: what LEP did, prospects for Tevatron searches, the program planned for LHC, and some of the possibilities at a future ILC. I then cover in-depth what comes after a candidate discovery at LHC: the various measurements one has to make to determine exactly what the Higgs sector is. Finally, I discuss the MSSM extension to the Higgs sector.
The effect of 2010 and 2011 LHC data are discussed in connection to the potential for the direct detection of supersymmetric dark matter. The impact of the recent XENON100 results are contrasted to these predictions.
Weak scale supersymmetry (SUSY) remains a compelling extension of the Standard Model because it stabilizes the quantum corrections to the Higgs and W, Z boson masses. In natural SUSY models these corrections are, by definition, never much larger than the corresponding masses. Natural SUSY models all have an upper limit on the gluino mass, too high to lead to observable signals even at the high luminosity LHC. However, in models with gaugino mass unification, the wino is sufficiently light that supersymmetry discovery is possible in other channels over the entire natural SUSY parameter space wi…
In this talk I review the New Physics reach of semileptonic beta decay experiments, and their interplay with LHC searches. Assuming the new particles are heavy enough we can use an Effective Field Theory approach to analyze the LHC searches, what allows us to perform a direct and model-independent comparison with low-energy experiments.
We discuss the connection between the understanding of TeV scale physics to be found at the LHC and a high energy e+e- linear collider, using Higgs physics, low energy supersymmetry, and the top quark sector as examples.
In anticipation of data from the Large Hadron Collider (LHC) and the potential discovery of supersymmetry, in this work we seek an answer to the following: What are the chances that supersymmetry will be found at the LHC? Will the LHC data be enough to discover a given supersymmetric model? And what other measurements can assist the LHC establish the presence of supersymmetry? As a step toward answering these general questions, we calculate the odds of the next-to-minimal version of the popular supergravity motivated model (NmSuGra) being discovered at the LHC to be 4:3 (57 %). We also demonst…
The search for the heavy charged Higgs (mH+ > mtop) has been mainly based on the off-shell top pair production process. However, resonance production in s-channel single top events is an important channel to search for this particle. In a previous work, it was shown that this process, i.e., qq' -> H+ -> tb + h.c., can lead to comparable results to what is already obtained from LHC searches through gb -> tH- process. What was obtained was, however, based on diagonal Yukawa couplings between incoming quarks assuming cs as the main incoming pair due to the CKM matrix element being close to unity.…
Naively, the LHC Higgs boson looks like a Standard Model Higgs boson, with no guidance to physics beyond the Standard Model, as has often been remarked. The data show that what was discovered is the true Higgs boson. If one includes the full information available, experimental and theoretical, there are actually four significant clues implied by data. They point toward a supersymmetric two-doublet decoupling theory, and a hierarchy problem solution via TeV scale supersymmetry. That in turn suggests an underlying compactified string/M theory with a de Sitter vacuum, so we can be confident that …
One item on the agenda of future colliders is certain to be the Higgs boson. What is it trying to tell us? The primary objective of any future collider must surely be to identify physics beyond the Standard Model, and supersymmetry is one of the most studied options. it Is supersymmetry waiting for us and, if so, can LHC Run 2 find it? The big surprise from the initial 13-TeV LHC data has been the appearance of a possible signal for a new boson X with a mass ~750 GeV. What are the prospects for future colliders if the X(750) exists? One of the most intriguing possibilities in electroweak physi…
In this contribution to the volume "From My Vast Repertoire -- The Legacy of Guido Altarelli" I discuss selected topics of Standard Model (SM) physics at the LHC and their connection to the work of Guido Altarelli. An overarching connection is given by Guido's fundamental contributions to our understanding of the strong force, parton distribution functions and their evolution, and techniques to calculate theoretical predictions through perturbative Quantum Chromodynamics. The increasingly precise LHC measurements of diverse processes can be confronted with SM predictions relying on these found…
What has the LHC told us about the electroweakino sector of the Minimal Supersymmetric Standard Model?
Nanjing Normal University（南京师范大学）；Monash University（蒙纳士大学）；University of Glasgow（格拉斯哥大学）；University College London（伦敦大学学院）；University of Oslo（奥斯陆大学）；Xi’an Jiaotong-Liverpool University（西交利物浦大学）；Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；European Organisation for the Exploitation of Meteorological Satellites（欧洲气象卫星应用组织）；CERN（欧洲核子研究中心）；Gridsight（网格视野）
The CDF PYTHIA 6.2 Tune DW predictions of the LHC underlying event (UE) data at 900 GeV and 7 TeV are examined in detail. The behavior of the UE at the LHC is roughly what we expected. The new LHC PYTHIA 6.4 Tune Z1 does an even better job describing the UE data at 900 GeV and 7 TeV. However, the modeling of "min-bias" at the LHC (i.e. the overall inelastic cross section) is a very different story. No model describes all the features of "min-bias" collisions at 900 GeV and 7 TeV.
In this article, we show that making global fits of string theory model parameters to data is an interesting mechanism for probing, mapping and forecasting connections of the theory to real world physics. We considered a large volume scenario (LVS) with D3-branes matter fields and supersymmetry breaking. A global fit of the parameters to low energy data shows that the set of LVS models are associated with light gluinos which are quasi-degenerate with the neutralinos and charginos they can promptly decay into and thus possibly hidden to current LHC gluino search strategies.
Effective field theory (EFT) formulations of dark matter interactions have proven to be a convenient and popular way to quantify LHC bounds on dark matter. However, some of the non-renormalizable EFT operators considered do not respect the gauge symmetries of the Standard Model. We carefully discuss under what circumstances such operators can arise, and outline potential issues in their interpretation and application.
We discuss the current status of LHC physics from the perspective of precision theory predictions for the attendant QCD and EW higher order corrections. We focus on the interplay between the available data and the predictions for these data viewed in the context of the establishment of baselines for what is needed to exploit fully the discovery potential of the existing LHC data and the data expected by the end of the second LHC run (i.e., 300fb$^{-1}$). We conclude that significant improvement in the currently used theoretical predictions will be mandatory. Possible strategies to achieve such…
We discuss results of the CMS collaboration on the sensitivity of the LHC to $W$ boson polarisation in the process $pp\to W^\pm + jet \to e^\pm jet+\not\!\!P_T$ using the $L_P$ variable directly connected to $θ^*$ angle of the outgoing lepton in the rest frame of the decaying $W$. We have shown that for a given $L_P$, interference between different polarizations of the $W$-boson is not negligible, and needs to be taken into account when considering the differential cross-section with respect to $L_P$. The $L_P$ variable suggested by CMS collaboration is highly suitable variable to study LHC se…
Once supersymmetry is found at the LHC, the question arises what are the fundamental parameters of the Lagrangian. The answer to this question should thereby not be biased by assumptions on high-scale models. SFitter is a tool designed for this task. Taking LHC (and possibly ILC) data as input it scans the TeV-scale MSSM parameter space using its new weighted Markov chain technique. Using this scan it determines a list of best-fitting parameter points. Additionally a log-likelihood map is calculated, which can be reduced to lower-dimensional Frequentist's profile likelihoods or Bayesian probab…
We confront the most common version of the CP-conserving 2HDM with LHC data, taking into account all previously available experimental data. We also discuss the scenario where the 125 GeV Higgs discovered at the LHC is the lightest neutral scalar of a particular CP-violating 2HDM. In this scenario we focus on what data can already tell us about the amount of mixing between CP-even and CP-odd states.
The CDF PYTHIA 6.2 Tune DW predictions for the behavior of the LHC underlying event (UE) data at 900 GeV and 7 TeV are examined in detail. The behavior of the UE at the LHC is roughly what we expected. The LHC PYTHIA 6.4 Tune Z1 does an excellent job describing the UE data at 900 GeV and 7 TeV. Both Tune DW and Tune Z1 describe fairly well the Drell-Yan UE data at 1.96 TeV and 7 TeV. No model describes all the features of "min-bias" (MB) collisions at 900 GeV and 7 TeV.
Top-Antitop Production and Decay at Threshold at the LHC in QCD Perturbation Theory
INFN, Sezione di Milano-Bicocca（意大利国家核物理研究所米兰比可卡分部）；Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano-Bicocca（米兰比可卡大学G. Occhialini物理系）
While the LHC takes on the challenge of experimentally exploring the electroweak symmetry breaking sector, it is not only interesting but also crucial to explore alternatives to the Standard Model scenario with an elementary scalar Higgs boson. The idea of electroweak symmetry breaking by some new strong dynamics is discussed. A simple, general and self-consistent low energy effective description of Higgsless models is introduced. This effective theory is studied from the point of view of prolonging perturbative unitarity of WW scattering by spin-1 resonances originating from the strongly inte…
In the absence of a Higgs boson, the perturbative description of the Standard Model ceases to make sense above a TeV. Heavy spin-1 fields coupled to W and Z bosons can extend the validity of the theory up to higher scales. We carefully identify regions of parameter space where a minimal addition - a single spin-1 custodial SU(2) triplet resonance - allows one to retain perturbative control in all channels. Elastic scattering of longitudinal W and Z bosons alone seems to permit a very large cut-off beyond the Naive Dimensional Analysis expectation. We find however that including scattering of t…
Tremendous ongoing theory efforts are dedicated to developing new methods for QCD calculations. Qualitative rather than incremental advances are needed to fully exploit data still to be collected at the LHC. The maximally supersymmetric Yang-Mills theory (${\mathcal N}=4$ sYM) shares with QCD the gluon sector, which contains the most complicated Feynman graphs, but at the same time has many special properties, and is believed to be solvable exactly. It is natural to ask what we can learn from advances in ${\mathcal N}=4$ sYM for addressing difficult problems in QCD. With this in mind, we revie…
The top asymmetries measured at the Tevatron, and the discrepancy in the di-photon Higgs rate under investigation at the LHC represent two possible hints of physics beyond the Standard Model (SM). In this paper we address the possibility to explain and relate both these experimental anomalies with the help of an extra scalar doublet in addition to the SM particle spectrum. The connection is provided by the constraints that the electroweak precision tests impose on the oblique S and T parameters. As a result, considering the semi-leptonic single top production in the tW-channel at the LHC, our …
In a very short time the experiments at the LHC have collected a large amount of data that can be used to study minimum bias (MB) collisions and the underlying event (UE) in great detail. The CDF PYTHIA 6.2 Tune DW predictions for the LHC UE data at 900 GeV and 7 TeV are examined in detail. The behavior of the UE at the LHC is roughly what we expected. The LHC PYTHIA 6.4 Tune Z1 does an excellent job describing the LHC UE data. The modeling of MB (i.e. the overall inelastic cross section) is more complicated because one must include a model of diffraction. The ability of PYTHIA Tune DW and Tun…
Many techniques exist to reconstruct New Physics masses from LHC data, though these tend to either require high luminosity O(100) fb^-1, or an accurate measurement of missing transverse energy (MET) which may not be available in the early running of the LHC. Since in popular models such as SUSY a fairly sharp, triangular dilepton invariant mass spectrum can emerge already at low luminosity O(1) fb^-1, a Decay Kinematics (DK) technique can be used on events near the dilepton mass endpoint to estimate squark, slepton, and neutralino masses without relying on MET. With the first 2 fb^-1 of 7 TeV …
We investigate what new physics signatures the LHC can discover in the 2009-2010 run, beyond the expected sensitivity of the Tevatron data by 2010. We construct "supermodels", for which the LHC sensitivity even with only 10 inverse picobarn is greater than that of the Tevatron with 10 inverse femtobarn. The simplest supermodels involve s-channel resonances in the quark-antiquark and especially in the quark-quark channels. We concentrate on easily visible final states with small standard model backgrounds, and find that there are simple searches, besides those for Z' states, which could discove…
We found the parameterization of the unintegrated gluon distribution from the best description of the LHC data on the inclusive spectra of hadrons produced in $pp$ collisions at the mid-rapidity region and small transverse momenta. It is different from the one obtained within perturbative QCD only at low intrinsic transverse momenta $k_t$. The application of this distribution to analysis of the $e-p$ DIS allows us to get the results which do not contradict the H1 and ZEUS data on the structure functions at low $x$. So, the connection between the soft processes at LHC and low-$x$ physics at HER…
The purpose of this review is to investigate what kind of physics can be extracted at the LHC, assuming a discovery is made in events with missing transverse momentum, as generically expected in supersymmetry (SUSY) with R-parity conservation. To set the scene, we first discuss the collider phenomenology of the six possible electroweakino benchmark scenarios, as they provide valuable insight into what one might be facing at the LHC. We review the existing methods for mass reconstruction from measured kinematic endpoints in the distributions of suitable variables, e.g., the invariant masses of …
In recent years, the LHCb collaboration has published results on the measurement of several observables associated to semileptonic $b \to s$ transitions. Interestingly, various deviations from their expected values in the Standard Model have been found, including some tantalizing hints pointing towards the violation of Lepton Flavor Universality. We discuss New Physics models that address these anomalies and explore their possible connection to the dark matter of the Universe.
