(Re)interpreting LHC new physics search results: tools and methods

16 Oct 2017, 09:00 → 18 Oct 2017, 18:45 America/Chicago

One West (WH1W) (Fermilab)

Sabine Kraml (Centre National de la Recherche Scientifique (FR)), Sezen Sekmen (Kyungpook National University (KR)), Zhen Liu (Fermilab)

The quest for new physics beyond the SM is arguably the driving topic for LHC Run2.  LHC collaborations are pursuing searches for new physics in a vast variety of channels.  Although collaborations provide various interpretations for their search results, the full understanding of these results requires a much wider interpretation scope involving all kinds of theoretical models.  This is a very active field, with close theory-experiment interaction.  In particular, development of dedicated methodologies and tools is crucial for such scale of interpretation.

Recently, a Forum was initiated to host discussions among LHC experimentalists and theorists on topics related to the BSM (re)interpretation of LHC data, and especially on the development of relevant software tools and infrastructure: 
https://twiki.cern.ch/twiki/bin/view/LHCPhysics/InterpretingLHCresults

Two meetings were held at CERN, where active discussions and concrete work on (re)interpretation methods and tools took place, with valuable contributions from the LHC experiments:

1st meeting: 15-17 June 2016: https://indico.cern.ch/event/525142

2nd meeting: 12-14 December 2016: https://indico.cern.ch/event/571190

This third meeting of the Forum will be held at Fermilab LPC, where the discussions will continue, with a special focus on the US activity in current interpretation developments.  The program will consist mainly of invited talks.  However there will also be sessions with contributed talks on interpretation studies, focusing on usage of methods and tools. 

The workshop will mainly concentrate on the following subjects.

• Re-interpretation tools: current developments, hands-on tutorials (provided enough interest)
• Re-interpretation studies (with focus on methodology)
• Machine learning methods for re-interpretation
• Statistical methods for re-interpretation, simplified likelihoods, etc.
• A dedicated common session with the Long Lived Particles WG meeting in Trieste

Chairs:
Sezen Sekmen (Kyungpook National University)
Sabine Kraml (LPSC Grenoble)
Zhen Liu (Fermilab)

Organizing committee:
JoAnne Hewett (SLAC)
Ahmed Ismail (Pittsburg U.)
Michelangelo Mangano (CERN)
David Miller (U. Chicago)
Steven Mrenna (Fermilab)
George Redlinger (BNL)
Carlos Wagner (U. Chicago)
Frank Würthwein (UCSD)

Local organization committee:
Javier Duarte (Fermilab)
Kiel Howe (Fermilab)
Şeyda İpek (Fermilab)
Nadja Strobbe (Fermilab)

LPC coordinators:
Cecilia Gerber (UIC)
Boaz Klima (Fermilab)

LPC events committee:
Gabriele Benelli (Brown U)
Ben Kreis (Fermilab)
Hannsjoerg Weber (Fermilab)

FermilabToWorkshopDinner.pdf

Floorplan.pdf

RestaurantsnearFermilab.pdf

Monday, 16 October

09:00 → 09:05 Welcome to LPC

Speaker: Cecilia Gerber (University of Illinois at Chicago (US))

09:05 → 09:15 Introduction to the workshop

Speaker: Sezen Sekmen (Kyungpook National University (KR))

SekmenReintLHCNPRWelcome171016.pdf

09:20 → 09:40 Higgs precision measurements and additional Higgs Searches

Speaker: Marcela Carena (Fermilab)

LPC-10-2017.pdf

09:45 → 10:05 Signals of nonstandard particles

Speaker: Bogdan Dobrescu (Fermilab)

ReinterpretingFermilabOct2017.pdf

10:10 → 10:30 Reinterpreting the LHC diboson searches

Searches for diboson resonances now form a major component of the ATLAS exotics and CMS B2G and (BSM) Higgs search programs. These analyses are designed to search for new massive resonances (between around 200 GeV and 4 TeV), produced directly and on threshold with very little pT, decaying into pairs of W, Z or Higgs bosons which may be highly boosted and which may decay into various combinations of hadronic and leptonic final states. Depending on kinematic and substructure selection criteria, these searches are often also sensitive to equally well motivated resonance cascades with non-trivial decay topology and possibly with fat jets resulting from boosted BSM objects in the final state. In this talk I will discuss some of the subtleties involved in recasting and reinterpreting these searches in terms of a broader class of new physics models.

Speaker: Dr Jack Collins (University of Maryland and Johns Hopkins University)

Diboson_recast.pdf

10:35 → 10:55 Review of phenomenological MSSM studies

Collider searches for supersymmetry have evolved substantially over the last several years. I review the use of the phenomenological MSSM (pMSSM) as a tool in evaluating search reach and guiding the development of experimental strategies, with a focus on recent pMSSM studies.

Speaker: Ahmed Ismail

Ismail-ReinterpretingLPC17.pdf

11:00 → 11:30 Coffee & tea break

Workshop photo at outside WH1W

11:30 → 11:50 Digging Deeper for New Physics in the LHC Data

We describe a novel, model-independent technique of "rectangular aggregations" for mining the LHC data for hints of new physics. A typical (CMS) search now has hundreds of signal regions, which can obscure potentially interesting anomalies. Applying our technique to the two CMS jets+MET SUSY searches, we identify a set of previously overlooked ∼3σ excesses. Among these, four excesses survive tests of inter- and intra-search compatibility, and two are especially interesting: they are largely overlapping between the CMS jets+MET searches and are characterized by low jet multiplicity, zero b-jets, and low MET and HT. We find a simplified model that provides an excellent fit to these two excesses and discuss all additional constraints. Based on these results, we believe the wide-spread view that the LHC data contains no interesting excesses is greatly exaggerated.

Speaker: Dr Angelo Monteux (UC Irvine)

talk_Fermilab_nooverlay.pdf

11:55 → 12:15 New Physics in Standard Model Tails

Speaker: Joshua Ruderman

JoshFermilabRecast.pdf

12:20 → 12:40 Double Gauge Boson Production and the SM EFT

Speaker: Ian Lewis (The University of Kansas)

IL_ReIntLHC.pdf

12:45 → 14:00 Lunch break

14:00 → 14:20 BSM searches in ATLAS and material provided for reinterpretation

Speaker: Matthias Danninger (University of British Columbia (CA))

Reint17_MatthiasDanninger.pdf

14:30 → 14:50 BSM searches in CMS and material provided for (re)interpretation

Speaker: Sadia Khalil (The University of Kansas (US))

Sadia_BSM_Reinterpretation_2017.pdf

15:00 → 15:15 Machinery for providing and using correlation info

Speaker: Andy Buckley (University of Glasgow (GB))

buckley-corrsmachinery.pdf

15:20 → 15:50 Discussion

Usage and limitations of simplified likelihoods, etc.

Speaker: Andrew James Whitbeck (Fermi National Accelerator Lab. (US))

reinterpretationsDiscussion_whitbeck.pdf

15:50 → 16:20 Coffee & tea break

16:20 → 17:20 Rivet and Contur tutorial

We will cover the basics of running and writing a BSM analysis code in the Rivet framework, including detector smearing functions. Statistical limits will be derived on example BSM models using the Contur toolkit.

Speakers: Andy Buckley (University of Glasgow (GB)), Jonathan Butterworth (University College London (UK))

buckley-rivettutorial.pdf

17:20 → 18:05 An Introduction to GAMBIT and ColliderBit

In this hands-on introductory tutorial, I will describe how to use the collider recast capabilities (ColliderBit) of the GAMBIT (Global and Modular BSM Inference Tool) global fitting code. We will discuss how to obtain and compile GAMBIT and the necessary external codes needed to run ColliderBit. We will then use the code to test the viability of points in the MSSM parameter space with respect to LHC and LEP constraints, and I will show how to set up a full parameter space scan. If time permits, I will demonstrate how to implement a new model into ColliderBit.

Speaker: Jonathan Cornell (McGill University)

CMSSM.yaml

ColliderBit_CMSSM_tutorial.yaml

GAMBIT_install.txt

LHCRecast_GAMBIT_tutorial.pdf

Tuesday, 17 October

09:00 → 09:20 Recent LHCb results and their implications

Speaker: Wolfgang Altmannshofer (University of Cincinnati)

altmannshofer_fermilab.pdf

09:30 → 09:50 Direct fits of Wilson coefficients using B0->K*0mu+mu- decays

The decay B0->K*0mu+mu- is a rare b->s transition and as such strongly suppressed in the Standard Model (SM), allowing for sensitive searches for New Physics contributions. A method to determine the Wilson coefficients directly from this decay is presented, which does not rely on binning the available data in the invariant di-lepton mass squared, q2. The method shows improved precision compared to the conventional approach of using q2-binned angular observables. It is furthermore shown that it will be possible to use the direct fit method with the combined Run 1 and Run 2 data sample taken by the LHCb experiment.

Speaker: Christoph Michael Langenbruch (Rheinisch Westfaelische Tech. Hoch. (DE))

langenbruch.pdf

10:00 → 10:20 SM4BSM in CMS

Speaker: Matthew Herndon (University of Wisconsin Madison (US))

ReSM_herndon_1709.pdf

10:30 → 10:50 SM4BSM in ATLAS

Speaker: Sergei Chekanov (Argonne National Laboratory (US))

NP2017_FERMILAB_Sep_2017.pdf

11:00 → 11:30 Coffee & tea break

11:30 → 12:15 CheckMATE Tutorial

I will give a short and easy tutorial into the CheckMATE program that allows models of new physics to be easily tested against the recent LHC data. CheckMATE now integrates the Monte Carlo event generation via Madgraph and Pythia 8. This allows users to go directly from a SLHA file or UFO model to the result of whether a model is allowed or not. I will show how to use CheckMATE with event files as input as well as with Madgraph and Pythia in a simple BSM setup.

Speaker: Dr Jong Soo Kim (National Institute for Theoretical Physics, School of Physics and Mandelstam Institute for Theoretical Physics, University of the Witwatersrand)

recasting_workshop_fermilab_2017.pdf

12:15 → 13:00 Hands-On SModelS: a tool to make systematic use of simplified models results

Recasting tools like CheckMate, MadAnalysis, or Rivet allow reinterpretation of LHC results by rerunning the analyses on new signal samples. SModelS works differently; it takes a candidate BSM theory that exhibits a Z2 symmetry, decomposes it into its simplified models spectrum, and confronts it with a large database of simplified models results from ATLAS and CMS SUSY searches. This procedure is much faster, though more conservative, making it a handy tool for tasks such as model surveys, classification of most important signal topologies, or the discussion of topologies missed by the current analyses.

In this tutorial, we shall learn to use the various SModelS functionalities, scrutinize concrete examples, and discuss the merits and shortcomings of this approach.

Bring your favorite model, either as an SLHA or LHE file!

Speaker: Dr Wolfgang Waltenberger (Austrian Academy of Sciences (AT))

chicago.pdf

Tutorial Files

13:00 → 14:30 Lunch break

14:30 → 15:15 CMS Open Data in Research

CMS will soon complete its public release of about half of its Run I research grade data (about 2 Pb), accompanied by corresponding MC sets and analysis software. The 7 TeV data have already been released earlier in two steps. In addition to educational applications this allows the generation of scientific papers and results by non-CMS members at the same level as for CMS members, essentially without any limitation for outsiders.
The contribution will address how the CMS data are integrated into the CERN Open Data portal, what are the procedures for data access and interpretation, and how to obtain additional information. Physics analysis and validation examples using these data will also be discussed, and feedback from the scientific community (see also contribution by J. Thaler) will be addressed. Some emphasis will be placed on aspects particularly relevant for the topics of this workshop.

Speaker: Achim Geiser (Deutsches Elektronen-Synchrotron (DE))

Discussion.pdf

ReCast17b.pdf

15:15 → 15:40 The Future is Open: Jet Substructure with CMS Public Data

I present the first ever analysis using 2010 CMS Open Data.

Speaker: Jesse Thaler (MIT)

jthaler_Fermilab2017_OpenData.pdf

15:40 → 16:00 Open Data discussion

16:00 → 16:30 Coffee & tea break

16:30 → 16:50 The Les Houches Analysis Description Accord: What it is and Why it Matters

We give a brief update on the proposal for a Les Houches Analysis Description Accord (LHADA), a formalism that is capable of describing the contents of an analysis in a standard and unambiguous way independent of any computing framework. We focus on the experiences of implementing ATLAS and CMS analyses, and on the recent developments in CutLang, an analysis framework that interprets, on the fly, keywords and commands for object selection, reconstruction and histogramming. One goal of LHADA is to speed up the analysis design process by minimizing the time devoted to compilation and programming language related debugging. CutLang can interpret complex logic statements, read and write the analysis description in XML format and also permits the use of user defined types in order to improve human readability of analysis algorithms. The ability to access different input event formats such as those from Delphes, FCC, ATLAS and CMS OpenData should be considered a bonus.

Speakers: Harry Prosper (Florida State University (US)), Gokhan Unel (University of California Irvine (US)), Sezen Sekmen (Kyungpook National University (KR))

ProsperLHADAReintLHCNP1612.pdf

17:00 → 17:20 Towards a unified interface for Reinterpretation tools

The talk will cover recent developments in Reinterpretation and Analysis Preservations within the Experiments, the status or RECAST as a generic platform for executing reinterpretation with a focus on how the phenomenology tools are integrated on an equal footing to the full experiment implementations.

Speaker: Lukas Alexander Heinrich (New York University (US))

ReinterpretationWorkshopFNAL.pdf

17:30 → 18:15 Tutorial on recasting and reinterpreting searches with MadAnalysis5

In this tutorial I will provide an introduction to MadAnalysis5 and it's functionalities. We will have a hands on tutorial on how to implement an analysis in the expert mode and obtain the results in terms of cutflows, histograms and finally obtain a limit for a particular 13 TeV CMS search.

Speaker: Dr Dipan Sengupta (Michigan State University)

Dipan_fermilab.pdf

Wednesday, 18 October

09:00 → 09:30 Reinterpretation on LLP searches (exp)

Joint session with LLP workshop in Trieste - talk given remotely from Trieste.

Speaker: Gavin Hesketh (University College London (UK))

LLP_gavin.pdf

09:30 → 10:00 Reinterpretation of LLP searches (theo.)

Joint LLP session with LLP workshop in Trieste -- talk given at Fermilab

Speaker: Jared Evans

LLP-Recasting.pdf

10:00 → 10:30 LLP discussion

10:30 → 11:00 Coffee & tea break

11:00 → 11:15 Tools and bounds on Minimal Universal Extra Dimensions

We discuss the collider phenomenology of the model of Minimal Universal Extra
Dimensions (MUED) at the Large hadron Collider (LHC). We derive analytical results for
all relevant strong pair-production processes of two level 1 Kaluza-Klein partners and use them to validate and correct the existing MUED implementation in the fortran version of the Pythia event generator. We also develop a new implementation of the model in the C++ version of Pythia. We use our implementations in conjunction with the Checkmate package to derive the LHC limits on MUED from a large number of published experimental analyses from Run 1 at the LHC.

Speaker: Ms Dipsikha Debnath (University of Florida)

DD_toolstalk.pdf

11:20 → 11:35 Coverage of the pMSSM by simplified model results

We investigate to which extent the SUSY search results published by ATLAS and CMS in the context of simplified models actually cover the more realistic scenarios of a full model. Concretely, we work within the phenomenological MSSM (pMSSM) with 19 free parameters and compare the constraints obtained from SModelSv1.1.1 with those from the ATLAS pMSSM study in arXiv:1508.06608. We find that about 40-45% of the points excluded by ATLAS escape the currently available simplified model constraints. For these points we identify the most relevant topologies which are not tested by the current simplified model results. In particular, we find that topologies with asymmetric branches, including 3-jet signatures from gluino-squark associated production, could be important for improving the current constraining power of simplified models results. Furthermore, for a better coverage of light stops and sbottoms, constraints for decays via heavier neutralinos and charginos, which subsequently decay visibly to the lightest neutralino are also needed.

Speaker: Sabine Kraml (Centre National de la Recherche Scientifique (FR))

SModelS-pMSSM-coverage-Fermilab.pdf

11:40 → 11:55 Reinterpret exotic Higgs decay H/A to ZA/ZH in the Two Higgs Doublet Model

In the Two Higgs Doublet Model (2HDM), the exotic decay modes of a heavy non-SM Higgs decaying into two light Higgses or one Higgs with one SM gauge boson offer new discovery potential for non-SM Higgses. The latest CMS experimental search for neutral resonances decaying into a Z boson and a pair of b jets or tau leptons could be interpreted as H/A to ZA/ZH. In the original experimental paper, results in the mA vs. mH place for a given value of tan(beta) near alignment limit, or in the plane of tan(beta) vs. cos(beta-alpha) for fixed values of mA and mH were given for the type-II 2HDM. We reinterpret this experimental results in both Type-I and Type-II 2HDM, and consider benchmark scenarios of non-SM Higgs spectrum, as well as representative values of tan(beta), cos(beta-alpha), and soft Z2 breaking parameter m12.

Speaker: Wei Su

fermilab_weisu.pdf

12:00 → 12:15 Simplified Limits on Resonances at the LHC

When an excess appears in LHC data, we should compare the results with broad classes of models, to get an immediate sense of which kinds of BSM theories could conceivably be relevant. Often, the new physics is likely to be an s-channel resonance. In this case, a simplified model of the resonance can translate an estimated signal cross section into bounds on the product of the dominant production and decay branching ratios. This quickly reveals whether a given class of models could possibly produce a signal of the required size at the LHC. This talk will outline a general framework and show how it operates for resonances of varying widths and with different numbers of production and decay modes. It will also discuss applications to cases of experimental interest, including resonances decaying to di-bosons, di-leptons, or di-jets. If the LHC experiments start reporting searches for BSM resonances in terms of the simplified limits variable ζ defined here, the community will home in more quickly on the models most likely to explain any observed excess.

Speaker: Kirtimaan Mohan (Michigan State University)

kirtimaan_mohan_simlim.pdf

12:20 → 13:30 Lunch break

13:30 → 13:50 Constraining Quirky Tracks with Conventional Searches

Quirks are particles that are both charged under the standard model and under a new confining group. The quirk setup assumes there are no light flavors of the new confining group so that while the theory is in a confining phase, the distance between quirk-antiquirk pairs can be macroscopic. In this work, we reinterpret existing collider limits, those from monojet and heavy stable charged particle searches, as limits on quirks. Additionally, we propose a new search in the magnetic-field-less CMS data for quirks and estimate the sensitivity. We focus on the region where the confinement scale is roughly between 1 eV and 100 eV and find mass constraints in the TeV-range, depending on the quirk's quantum numbers.

Speaker: Matthew Low

fermilabQuirksTalk.pdf

14:00 → 14:20 Setting limits on Effective Field Theories: the case of Dark Matter

The usage of Effective Field Theories (EFT) for LHC new physics searches is receiving increasing attention. It is thus important to clarify all the aspects related with the applicability of the EFT formalism in the LHC environment, where the large available energy can produce reactions that overcome the maximal range of validity, i.e. the cutoff, of the theory. We show that this does not forbid to set rigorous limits on the EFT parameter space through a modified version of the ordinary binned likelihood hypothesis test, which we design and validate. Our limit-setting strategy can be carried on in its full-fledged form by the LHC experimental collaborations, or performed externally to the collaborations, through the Simplified Likelihood approach, by relying on certain approximations. We apply it to the recent CMS mono-jet analysis and derive limits on a Dark Matter (DM) EFT model. DM is selected as a case study because the limited reach on the DM production EFT Wilson coefficient and the structure of the theory suggests that the cutoff might be dangerously low, well within the LHC reach. However our strategy can also be applied, if needed, to EFT’s parametrising the indirect effects of heavy new physics in the Electroweak and Higgs sectors.

Speaker: Mr Federico Pobbe (Università di Padova)

fermilab_18_10_17.pdf

14:30 → 14:50 Signatures for SUSY with light higgsino: from here to HL- and HE-LHC

Upgrades in HL-LHC will allow access to unexplored domains of supersymmetry.
A highly motivated example consists of supersymmetric models with light higgsinos $\sim 100-200$ GeV-- as required by naturalness-- which lead to four SUSY discovery channels arising from 1. gluino 2. stop 3. wino and 4. higgsino pair production.
Current searches for gluinos and stops within the context of simplified models are applicable since these
channels are rich in $b$-jets although now a subset of cascade decay events should contain soft dilepton pairs
arising from light higgsino-like neutralino decay. Wino pair production leads to clean same-sign dilepton$+MET$ signatures which will become increasingly important with HL-LHC. Higgsino pair production generates soft dilepton$+MET$ events which require hard initial state radiation for a trigger. A push for soft lepton identification-- with $p_T(\ell )\sim 3-20$ GeV-- greatly advances this latter channel especially in the environment of HL-LHC.
Assessing the sensitivity of HL-LHC to such scenarios and many others requires accurately extrapolating current LHC searches to the future facilities, or implementing novel searches that take into account the capabilities of the new facilities. Consequently, an effective assessment depends on the availability of sufficient input from the collaborations, such as a reliable simulation of future detectors, or information on object performance. In this talk, I will summarize a list of signatures relevant for HL-LHC, the upgrade phenomenology efforts underway, the experimental inputs that are available and further information that would be useful to make these studies more effective.

Speaker: Howard Baer (University of Oklahoma)

LHC@fnal2017.pdf

15:00 → 15:30 Coffee & tea break

15:30 → 15:50 SCYNet - Testing supersymmetric models at the LHC with neural networks

The results of direct searches for new particles at the Large Hadron Collider put the strongest constraints on many models for new physics, in particular for supersymmetric extensions of the standard model.
Calculating the profile likelihood ratio for these observables by the use of Monte Carlo methods is extremely timeconsuming and not feasible for a large number of points, as they are typically required in global fits of these models.
SCYNet is a new tool that uses neural network regression for a fast evaluation of that profile likelihood ratio. Two different approaches have been chosen to train the neural network: In the first approach, the parameters of the Lagrangian density of the 11-dimensional phenomenological MSSM are used as an input, which allows for a comparison between model predictions and measurements for any point in that model without time penalty.
In the second approach, the neural network is trained using signature related quantities, such as particle multiplicities and object energies in the experimental final states. While this approach takes a bit more computing time, it is in principle suited to be used for a wider class of new physics models. The basic features of SCYNet are described and a first evaluation of its performance with both types of neural networks is shown.

Speaker: Matthias Hamer (University of Bonn (DE))

SCYNet_17102017.pdf

16:00 → 16:20 Machine learning for interpretation

Speaker: Kyle Stuart Cranmer (New York University (US))

ML-for-reinterpretation.pdf

16:30 → 16:50 What is the machine learning?

Speaker: Tim Cohen (University of Oregon)

Cohen_MachineLearning_ReinterpretationWorkshop_Fermilab.pdf

17:00 → 17:10 Recasting analyses that use machine learning -- Case study: CMS-SUS-16-050

Quick overview of information available to recast CMS-SUS-16-050, a search for SUSY with top tagging. The top tagger is partially MVA based and code/instructions to run this top tagger is provided on the public webpage.

Speaker: Nadja Strobbe (Fermi National Accelerator Lab. (US))

RecastingCMS-SUS-16-050.pdf

17:15 → 17:45 General discussion, future plans

Speakers: Sabine Kraml (Centre National de la Recherche Scientifique (FR)), Sezen Sekmen (Kyungpook National University (KR)), Zhen Liu (Fermilab)

Fermilab-interpretation-closure.pdf