Heavy Quarks in Herwig 7 Simon Pltzer Particle Physics University - PowerPoint PPT Presentation

Heavy Quarks in Herwig 7 Simon Plätzer Particle Physics — University of Vienna at the Heavy Flavour Hadronization Workshop CERN | 3 March 2020

Herwig 7 Overview [Herwig collaboration – Eur.Phys.J. C76 (2016) 665] Two shower modules: angular ordered and dipole-type, [Gieseke, Stephens, Webber – JHEP 0312 (2003) 045] [Plätzer, Gieseke – JHEP 1101 (2011) 024] both including parton shower uncertainty estimates. [Bellm, Nail, Plätzer, Schichtel, Siodmok – EPJ C76 (2016) 665] Automated NLO matching and multi jet merging. [Plätzer –- with Bellm, Wilcock, Rauch, Reuschle, 2011 – 2015] [Plätzer, Gieseke – EPJ C72 (2012) 2187] [Plätzer — JHEP 1308 (2013) 114] [Bellm, Gieseke, Plätzer — EPJ C78 (2018) 244] Cluster hadronization model Eikonal MPI model Colour Reconnection

Shower Evolution of Heavy Quarks [Gieseke, Stephens, Webber – JHEP 0312 (2003) 045] Quasi-collinear limit, ordering in angular variable [Herwig++ Physics and Manual – EPJ C58 (2008) 639] z + m 2 � � ij + m 2 p 2 q 2 = − m 2 1 + z 2 − 2 m 2 j C F i ⊥ z (1 − z ) ˜ z (1 − z ) , q 1 − z − e P q → qg = 1 − z z ˜ q 2 � Dipole shower from quasi-collinear limit, ordered in transverse momentum [Plätzer, Gieseke – EPJ C72 (2012) 2187] [Cormier, Plätzer, Reuschle, Richardson, Webster — EPJ C79 (2019) 915] • Significantly improved b fragmentation from dipole shower • Comparable description of heavy quark observables across both showers

Multi-parton Interactions Key ingredients for MPI modelling in Herwig 7 A(b) [1/mb] 2 2 = 1.80 GeV µ 0.1 2 2 = 0.71 GeV µ soft & hard scatters 0.05 + diffraction ) 2 R 1 p 0 2 4 impact parameter b [ mb ] P s h [Figure by Stefan Gieseke] matter distribution colour reconnection p R 2 [Gieseke, Loshaj, Kirchgasser — EPJ C77 (2017) 156] in total six parameters, hard MPI in principle allow for HQ [Bellm, Gieseke, Kirchgasser — arXiv:1911.13149]

Cluster Hadronization Clusters formed by Fission Parton Splitter Decay Shower splitting gluons after shower evolution Different weights for light flavours Clusters fission if too heavy: M p ≥ q p + ( m 1 + m 2 ) p , Fission parameters different for uds, c and b, but only uds produced Lighter clusters decay into hadrons [Figure by Patrick Kirchgaesser]

Colour Reconnection Preconfinement assumption violated in hadronic environments: colour reconnection crucial. ch 1 /n d n/ d M cl / GeV − 1 Charged h p ? i vs. N ch at 900 GeV, track p ? > 500 MeV, for N ch � 1 [GeV] default clusters 0 . 35 1 h -type clusters h p ? i 0 . 30 i -type clusters 0 . 8 n -type clusters 0 . 25 0 . 6 after reconnection 0 . 20 ATLAS data 0 . 4 Hw++ 2 . 4 , µ 2 = 1.0, p min h -type clusters = 3.0 ? Hw++ 2 . 5 , MB 900 -CTEQ 6 L 1 0 . 15 i -type clusters 0 . 2 n -type clusters 0 . 10 0 1 . 4 1 . 2 MC/data 0 . 05 1 0 . 8 0 . 00 0 2 4 6 8 10 0 . 6 5 10 15 20 25 30 35 40 45 M cluster [GeV] N ch No flavour dependence! [Gieseke, Röhr, Siodmok — EPJ C72 (2012) 2225] [Gieseke, Kirchgaesser, Plätzer – EPJ C 78 (2018) 99]

Geometric & Baryonic Reconnection New model uses geometric measure p ( s ) = 7 TeV Charged Multiplicity K + + K − yield in INEL pp collisions at √ s = 7 TeV in | y | < 0.5. d N /d N ch 10 − 1 d p T d y ( c /GeV) 1 instead of ‘string length’ and introduces ALICE Data ALICE Data Herwig 7 . 1 default Herwig 7 . 1 default new model baryonic reconnection 10 − 1 d 2 N 10 − 2 baryonic degrees of freedom g → s ¯ s splittings N inel new model 1 10 − 2 10 − 3 10 − 3 Herwig 7 Herwig 7 10 − 4 1 . 4 1 . 4 MC/Data 1 . 2 MC/Data 1 . 2 1 1 0 . 8 0 . 8 0 . 6 0 . 6 1 2 3 4 5 6 10 20 30 40 50 60 70 p T (GeV/ c ) N ch p/ π in INEL pp collisions at √ s = 7 TeV in | y | < 0.5. p ) / ( π + + π − ) ( p + ¯ Combination with 10 − 1 ALICE Data Herwig 7 . 1 default globally enhanced baryonic reconnection g → s ¯ s splittings Herwig 7 new model strange production. 1 . 4 MC/Data 1 . 2 1 0 . 8 0 . 6 0 . 5 1 1 . 5 2 2 . 5 3 p T (GeV/ c ) [Gieseke, Kirchgaesser, Plätzer – EPJ C 78 (2018) 99]

Kinematic Strange Production & Spacetime Information Strange production in gluon splitting Spacetime information in colour and fission dependent on environment. reconnection possibly relevant in [Duncan, Kirchgaesser – EPJ C79 (2019) 61] dense environments ✓ − m 2 ◆ w s ( m ) 2 = exp 0 m 2 K / π in INEL pp collisions at √ s = 7 TeV in | y | < 0.5. ( K + + K − ) / ( π + + π − ) Data 10 − 1 Default Mass Lambda K 0 /K + Pythia 1 . 4 q 1 . 3 MC/Data 1 . 2 ¯ s q 1 . 1 Φ (s¯ s) 1 0 . 9 0 . 8 0 . 7 q ¯ s 0 . 6 0 . 5 0 . 5 1 1 . 5 2 2 . 5 3 K 0 K − / ¯ q ¯ p T (GeV/ c ) [Bellm, Duncan, Gieseke, Myska, Siodmok – EPJ C79 (2019) 1003] Open questions remain in correlations

More theoretical understanding Approach colour reconnection from amplitude Confronting hadronization models with evolution algorithms: perturbative component? analytic power correction models [Angeles, De Angelis, Forshaw, Plätzer, Seymour – JHEP 05 (2018) 044] [Forshaw, Holguin, Plätzer – JHEP 1908 (2019) 145] Herwig { p } , µ 2 , { M 2 � � A τ → σ = h σ | U ij } | τ i |A τ → σ | 2 P τ → σ = ρ |A τ → ρ | 2 , P � − Strong support for geometric models from perturbative evolution. analytic [Gieseke, Kirchgaesser, Plätzer, Siodmok – JHEP 11 (2018) 149] [Hoang, Plätzer, Samitz — in progress]

More theoretical understanding Approach colour reconnection from amplitude Confronting hadronization models with evolution algorithms: perturbative component? analytic power correction models [Angeles, De Angelis, Forshaw, Plätzer, Seymour – JHEP 05 (2018) 044] [Forshaw, Holguin, Plätzer – JHEP 1908 (2019) 145] Herwig { p } , µ 2 , { M 2 � � A τ → σ = h σ | U ij } | τ i |A τ → σ | 2 P τ → σ = ρ |A τ → ρ | 2 , P � − Strong support for geometric models from perturbative evolution. analytic [Gieseke, Kirchgaesser, Plätzer, Siodmok – JHEP 11 (2018) 149] [Hoang, Plätzer, Samitz — in progress]

More theoretical understanding Approach colour reconnection from amplitude Confronting hadronization models with evolution algorithms: perturbative component? analytic power correction models [Angeles, De Angelis, Forshaw, Plätzer, Seymour – JHEP 05 (2018) 044] [Forshaw, Holguin, Plätzer – JHEP 1908 (2019) 145] Herwig { p } , µ 2 , { M 2 � � A τ → σ = h σ | U ij } | τ i |A τ → σ | 2 P τ → σ = ρ |A τ → ρ | 2 , P � − Strong support for geometric models from perturbative evolution. analytic [Gieseke, Kirchgaesser, Plätzer, Siodmok – JHEP 11 (2018) 149] [Hoang, Plätzer, Samitz — in progress]

Outlook • Some first tries in heavy flavour formation within D yield gluon splitting, but needs kinematic feedback to only charm-fission happen at relevant scales. default [Kirchgaesser, Plätzer — in progress] 10 − 3 • Further investigations into gluon splitting and cluster 10 − 4 fission driven by comparison to analytic power 10 − 5 corrections, including flavour dependence 1 . 4 1 . 3 [Hoang, Plätzer, Samitz — in progress] 1 . 2 1 . 1 Ratio 1 0 . 9 • Study mass effects in theoretical investigations of 0 . 8 0 . 7 0 . 6 0 . 5 colour reconnection such as colour evolution. 2 4 10 12 14 20 8 18 6 16 p t

Thank you!