Potential for searches & measurements: an overview for discussion

Potential for searches & measurements:an overview for discussion Jonathan Butterworth UCL Boosted Boson Workshop, CERN 25/3/2014 Jon Butterworth, UCL

Potential for searches & measurements:“I apologise in advance” Jonathan Butterworth UCL Boosted Boson Workshop, CERN Jon Butterworth, UCL

The core issue… • Final stage of jet structure is “soft” non-perturbative QCD. • Formation of hadrons from gluons, 100 MeV energy scales (LQCD) • Vast phase space between quark-gluon scatter (100’s GeV, few TeV) and LQCD • Most of jet substructure can be analysedperturbatively • EWSB scale (~100 GeV) lies in this region • Jets may contain objects with EW-scale mass (W,Z,H,t,?) Jon Butterworth, UCL

Standard Model Topologies • Dibosons; especially WW/WZ/ZZ - inclusive and vector boson fusion/scattering. • Inclusive: high pTtail is where anomalous couplings might show up • VBS: Unitarity test of BEH mechanism at high diboson mass. High diboson masses  high boosts (2002, JMB, Cox, Forshawand others; recently Cui & Han 2014 (Schwartz 2011)). • In both case, low statistics at most interesting area – recover hadronic decays of the bosons

Standard Model Topologies • Top/tt • High pT tail… understand efficiencies for differential cross section measurement. • Main power is in Higgs & BSM searches (?)

Standard Model Topologies • Higgs … • H WW or ZZ decays (the “original” channel, Seymour 1994) . Boost will not come from Higgs mass. However there will be phase space where there are boosted (off-shell) hadronic decays of Ws and Zs. Any chance? • VH(H bb) (the “classic” channel? BDRS 2008) High pTis the most sensitive region in Run I. Higher boosts in Run II likely to require jet substructure.

High pT Higgs and Vector Boson (reprise) “mono”-Jet • By requiring that the Higgs and Vector Boson have a high transverse momentum, we lose a factor of ~20 in cross section • However, much of this would have failed other analysis cuts anyway • Background cross sections fall by a bigger factor (typically t-channel not s-channel) • W/Z and H are all central • Better b-tagging, better jet resolution • W/Z and H decay products collimated • Simpler topology, fewer combinatorials • Difficult for tops to fake this • Z  neutrinos becomes visible • High missing ET mH b H W u l Jon Butterworth, UCL

High pT Higgs and Vector Boson (reprise) • Note excellent Z peak for calibration • 5.9 s; potentially very competitive • bb branching information critical for extracting Higgs properties • “Measuring the Higgs sector” Lafaye, Plehn, Rauch, Zerwas, Duhrssen, arXiv:0904.3866 [hep-ph] Jon Butterworth, UCL

High pT Higgs and Vector Boson (reprise) • Pre-data! • Included trigger, ATLAS b-tagging algorithm, detailed tracking & calorimeter • Also include Wt background omitted from initial study. • Slight degradation w.r.t particle level, but still very promising Jon Butterworth, UCL

Standard Model Topologies • Higgs … • gg H (Hbb) and others. • Can we recover Hbb without the V tag? • Can we tag the hadronic V decays too?

Standard Model Topologies • Higgs … • gg H (Hbb) and others. • Can we recover Hbb without the V tag? • Can we tag the hadronic V decays too? • ttH (Plehn, Salam, Spannowsky 2010) boost of top of Higgs can be useful and needs to be dealt with.

Standard Model Topologies • Combine techniques for top and Higgs tagging to improve sensitivity to Higgs in ttH channel Jon Butterworth, UCL

Standard Model Topologies • Higgs … • Hgg … I know we’re concentrating on hadrons, but… isolation cone merging… similar issues and technologies?

BSM Topologies (all of the above?) • Especially top: Enhanced BSM production at high pT in many models • Kaluza-Klein graviton (Lillie, Randall, Wang, 2007) • t’ (Holdom, 2007) • + SUSY stuff…

Substructure in searches (boosted top, boosted W) Jon Butterworth, UCL

BSM Topologies (all of the above?) • We have new boson to boost… HH (Kribs, Martin, Roy, Spannowsky, 2009; Cooper, Konstantinidis, Lambourne, Wardrope, 2013; ATLAS-CONF-2014-005)

BSM Topologies (all of the above?) • SUSY cascades to W,Z,H (JMB, Ellis, Raklev 2007) top (Han, Katz, Son, Tweedie, 2012) • Scuffles over mass hierarchies/naturalness &c… • Models (e.g. CP violating) with low limits on hadronically decaying Higgs partners (Bhattacherjee, Chakraborty, Ghosh, Raychaudhuri, 2012)

BSM Topologies (all of the above?) • R-Parity Violating SUSY (As above + Salam 2009, and more) • from talk by Minho Son

BSM Topologies (all of the above?) • …? • … Integrated into dijet/multijet searches?

Techniques • Improve mass resolution • Dealing with pile-up, UE and soft radiation • Identifying decays • Suppressing (hard) QCD background

Jon Butterworth, UCL

MANY MORE SINCE MANY MORE SINCE Jon Butterworth, UCL

Improve mass resolution • Dealing with pile-up, UE and soft radiation

Splitting and filtering (BDRS) and ATLAS Jon Butterworth, UCL

Filtering, Trimming and PruningCMS Jon Butterworth, UCL

Shower deconstruction (Soper & Spannowsky) and ATLAS-CONF-2014-003 Jon Butterworth, UCL

Split/filter is an example of doing both • Start with Higgs candidate jet (highest pT jet in acceptance) with mass m) • Undo last stage of clustering (reduce radius to R12) J  J1, J2 • If max(m1,m2) < 2m/3 Call this a “mass drop”. This fixes the optimal radius for reconstructing the Higgs decay. Keep the jet J and call it the Higgs candidate. Else, go back to 2 • Require Y12 > 0.09 Dimensionless rejection of asymmetric QCD splitting Else reject the event • Require J1, J2 to each contain a b-tag Else reject the event Jon Butterworth, UCL

Split/filter is an example of doing both • Define Rfilt = min(0.3, Rbb/2) Make use event-by-event of the known Higgs decay radius Angular ordering means this is the characteristic radius of QCD radiation from Higgs products Stuff outside of this is likely to be underlying event and pileup. • Recluster, with Cambridge/Aachen, R = Rfilt • Take the 3 hardest subjets and combine to be the Higgs b, anti-b and leading order final state gluon radiation • Plot the mass Jon Butterworth, UCL

Improved subjet analysis Jon Butterworth, UCL

Learned since… • y cut more powerful than mass drop (identifying decay. QCD suppression rather than UE/pile up.) • Filtering, uses Higgs decay angle to optimise the zoom on “hard physics”/suppression of soft stuff. Other techniques also available, some more generic (n-subjettiness, shower deconstruction). Competition in this channel? • Dijet R = 0.4 anti kT does a pretty good job (at least at 8 TeV).

Precision jets at the highest scales • Highest transverse momentum jets; at the TeVscale

Jets at the highest scales • General agreement with NLO QCD calculations (after soft corrections) • Can comparisons be made more (or less?) precise if groomed jets are used? Significant spread in “NLO” predictions. ME/PS matching? MC tune (UE)? PDFs?

Vector bosons and (b) jets arXiv:1304.7098 arxiv:1302:2929

Limiting factors – b-tagging & gbb • CMS b/anti-b correlations • arXiv:1102.3194, JHEP 1103 (2011) 136 Princeton, J.Butterworth

Limiting factors – b-tagging & gbb • Bottom &/or charm production introduces another hard (or “semi-hard”) scale. How well is this understood? arXiv:1210.0441 Jon Butterworth, HCP

Limiting factors – b-tagging & gbb • B jet (and dijet) cross sections compared to NLO QCD arXiv:1109.6833 arXiv:1202.4617 Jon Butterworth, HCP

Limiting factors – b-tagging & gbb Good agreement with POWHEG, poorer with MC@NLO (seen by both ATLAS & CMS) arXiv:1109.6833 arXiv:1202.4617 Jon Butterworth, HCP

Limiting factors – b-tagging & gbb • Use properties of displaced decay vertices to distinguish light, c and b jets in dijet events arXiv:1210.0441 Jon Butterworth, HCP

Potential for searches & measurements: an overview for discussion