Workshop on Parton Radiation & Fragmentation: Summary of Detector Requirements MC Interplay with EW, H, Jet Algorithms Constraints & Tuning BSM @ FCC-ee Jet Substructure Jet Calibrations Precision Legacy for FCC-hh Hadronisation Perturbative QCD Colour Reconnections Event Shapes Particle Correlations AlphaS Extractions Particle Spectra QCD Fragmentation Heavy Quarks Resummation Functions P. Skands (Monash U.) & D. d’Enterria (CERN) 2 nd mini-workshop on FCC-ee detector requirements, Nov 23 2016
Disclaimer • For many, this was their “first take” on FCC-ee ๏ Fresh set of people thinking about the possibilities, but few came with prepared studies → Few explicitly quantitative statements about detector requirements ๏ Several themes emphasised repeatedly • Particle Identification (particle spectra, correlations) ๏ Fragmentation Functions, Hadronisation Models (Jet composition ⟷ particle flow) ๏ Genuine non-perturbative effects revealed at scales ~ Λ QCD ~ few hundred MeV Gigi says 3 hits down to 30-40 MeV ๏ Important to resolve soft tracks down to |p| ~ 70 MeV = m π /2 ๏ Good π /K down to |p| ~ 100 MeV? (LEP had x K measurements down to |p K | ~ 250 MeV) Probably not realistic for protons. ๏ Leading-Particle (x → 1) studies: hard protons, Kaons, pions? ( → fake rates) Use tracks, K0S, Lambda, … ๏ + MC constraints & tuning, Colour Reconnections, Baryon and Strangeness Correlations, Bose-Einstein ( π ,K) and Fermi-Dirac (p, Λ ) correlations, … ๏ Note: Fermi-Dirac radius puzzle . Fermi-Dirac correlations at LEP across multiple experiments & for both protons and Lambda → 0.1 fm << r p W. Metzger • Calo resolutions (& thresholds) ๏ Neutrals: Jet charge (colour reconnection constraints) , gluon (vs q) jet discrimination ๏ Heavy-quark dead-cone effect: θ ~ m/E ~ 0.1 for b quarks, 0.03 for c quarks (at m Z ) 2 P e t e r S k a n d s M o n a s h U n i v e r s i t y
Fragmentation Functions ๏ A. Vossen (FF overview) + + - - World Data (Sel.) for e World Data (Sel.) for e e e ± ± +X Production +X Production → → π π Precision of theory and experiment big ) 13 S s 10 L D 9 1 advantage à Complementary to pp SIDIS G e V FCC-ee? ( 1 12 × 0 c( 12 ) 10 D E L ¡ Evolution P H I × 9 1 G 11 e 10 V ( /dz 5 × ¡ Transverse momentum dependence in h+Jet 1 10 A × 0 L E ) P H 9 10 1 G 10 e Fragmentation V ( 3 × 9 1 0 × ) σ 9 T A ¡ Gluon FFs 10 S d S O 3 4 G e V , 4 4 G tot.had. ¡ Smaller mass effects at low z e V 8 ( 10 7 × 7 1 0 × Evolution ) T P C Scaling 2 9 ¡ Flavor separation (polarization?) G e 7 V 10 ( 2 × 1 6 0 × ) Flavor structure for FFs of Hyperons and other σ 6 10 1/ t h i s hadrons that are difficult to reconstruct in pp m e a s . 5 , B 10 e l l e 1 1 G C e and SIDIS L V E ( O 0 1 × . 0 0 4 G ) e 4 V 10 ( 3 0 × 0 0 ) Heavy Quark FFs – Also from H decay? A R G 3 U S 10 9 G e V , 1 V 7 : 0 G Larger multiplicities: Parity violating FF < e V ( 1 2 5 × 10 0 ) Local strong parity violating effects (next…) R o n a n e t a 10 l . 3 G e V ( 1 × ) 1 Repeatedly 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Particle ID z emphasised gluon FF poorly constrained: Belle has FCC-ee like statistics at 10 GeV Higher ee energy (than Z → bbg , ZH( → gg): High-z binning determined by Belle) → reach in z good b-tagging high-|p| track reco determined by reach in Gigi says 1% all the way up to x=1 low-|p| track reco High-N ch performance S. Moch (& others): field now moving towards NNLO accuracy: per-cent level errors (or better) 3 P e t e r S k a n d s M o n a s h U n i v e r s i t y
Parton Showers ๏ P. Richardson (overview talk) In general good agreement for event shapes, jet rates etc. The description of meson spectra was generally good. However in all simulations baryon production has issues. At LEP II interest in colour reconnection between the W decay products and Bose-Einstein correlations. • Multi-jet events: kicked off matrix-element matching & merging ๏ → State of the art at LHC: multi-jet NLO merging For the first time in many years more work on the accuracy of the parton-shower algorithms. • Needed as we go to higher accuracy for the matrix elements. (Precision) Jet 1 / N c ( Pl¨ odahl JHEP 1207 (2012) 042 ), ( Nagy, Soper, JHEP 1507 (2015) 119 ) Substructure atzer, Sj¨ → Resolution! Subleading logs ( Li, Skands, arXiv:1611.00013 ) This is the area where there is probably the greatest potential for improvement. If we can consistently improve the logarithmic accuracy. 4 P e t e r S k a n d s M o n a s h U n i v e r s i t y
Quarks and Gluons G. Soyez, K. Hamacher, G. Rauco, S. Tokar, Y. Sakaki ๏ Handles to split degeneracies • H → gg vs Z → qq ๏ Rely on good H → gg vs H → bb separation; mandated by Higgs studies requirements anyway? • Z → bbg vs Z → qq(g) ๏ g in one hemisphere recoils against two b-jets in other hemisphere: b tagging • Vary jet radius: small-R → calo resolution ๏ (R ~ 0.1 also useful for jet substructure) Octet neutralisation? (zero- • Vary E CM range : below m Z : radiative events → charge gluon jet with forward boosted rapidity gaps) → neutrals Colour reconnections, glueballs, … ๏ (also useful for FFs & general scaling studies); Scaling is slow , logarithmic → large lever arm Leading baryons in g jets? Hamacher (discriminates between string/ cluster models) • mitigate systematics/resolution by unfolding, control using E-dependence high-E baryons - measurements mass-plots of resonances incl. (!) neutrals - check baryons + resonances ( ∆ 0 , ++ , Λ , Λ (1520) , . . . ) Experimentally: need some particle id., high resolution e.m. calorimetry 5 P e t e r S k a n d s M o n a s h U n i v e r s i t y
Colour Reconnections & Correlations T. Sjostrand, W. Metzger, S. Kluth, C. Bierlich ๏ At LEP 2: hot topic (by QCD standards) : ’string drag’ effect on W mass • Can turn around at FCC-ee; use semi-leptonic events to measure Sjostrand m W → use m W as constraint in fully hadronic WW to measure CR • Non-zero effect convincingly demonstrated at LEP, but without much detailed (differential) information No-CR excluded at 99.5% CL. ๏ Has become even hotter topic at LHC • Much more colour flowing around; expect larger effects ๏ <pT> increases with N ch (known since long) ๏ ALICE @ ICHEP 2016: strangeness increases with N ch • It appears jet universality is under heavy attack. Fundamental to our understanding (and modelling) of hadronisation Low-momentum ๏ Many follow-up studies now underway at LHC. (identified) particles in high-multiplicity Z ๏ High-stats EE needed to tell the other side of story and WW events 6 P e t e r S k a n d s M o n a s h U n i v e r s i t y
(Another reason to measure CR) T. Sjostrand Is the 125 GeV Higgs a pure CP -even state? Any odd admixture? For LHC and future e + e − (& µ + µ − ?) colliders to probe. One possibility is H 0 → W + W − → q 1 q 2 q 3 q 4 . Angular correlations put limits on odd admixture. q q jet axis q q jet axis q q But: colour reconnection ⇒ shifted jet directions ⇒ shifted angular correlations. 7 P e t e r S k a n d s M o n a s h U n i v e r s i t y
Details of Hadronisation ๏ E.g.: how “local” is it? Fundamental property of hadronisation models • Baryon number, Strangeness, Spin, correlations between successive-rank hadrons (is it “screwy”? S. Todorova) Matevosyan: quark spin in hadronisation • Particle ID is crucial ● Particle production in MCs important for precision modelling – Should pay attention to LEP MC modeling tests ● Both OPAL measurements stat. limited Kluth on baryon correlations – ~4·10 6 hadronic Z decays – Would reach OPAL systematics at 10 8 Z decays ● LC detectors: – Particle ID, mom. resolution, displaced vertices :) – Low momentum particles? Run with scaled B-field on Z peak and WW threshold? 8 P e t e r S k a n d s M o n a s h U n i v e r s i t y
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