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] [Gieseke, Stephens, Webber – JHEP 0312 (2003) 045] [Plätzer, Gieseke – JHEP 1101 (2011) 024] [Bellm, Nail, Plätzer, Schichtel, Siodmok – EPJ C76 (2016) 665]

Two shower modules: angular ordered and dipole-type, both including parton shower uncertainty estimates.

[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]

Automated NLO matching and multi jet merging. Cluster hadronization model Eikonal MPI model Colour Reconnection

Shower Evolution of Heavy Quarks

[Cormier, Plätzer, Reuschle, Richardson, Webster — EPJ C79 (2019) 915] [Gieseke, Stephens, Webber – JHEP 0312 (2003) 045]

z (1 − z) ˜ q2 = −m2

e ij + m2 i

z + m2

j

1 − z − p2

⊥

z (1 − z),

Pq→qg = CF 1 − z

• 1 + z2 − 2m2

q

z˜ q2

• [Herwig++ Physics and Manual – EPJ C58 (2008) 639]

Quasi-collinear limit, ordering in angular variable Dipole shower from quasi-collinear limit,

• rdered in transverse momentum

[Plätzer, Gieseke – EPJ C72 (2012) 2187]

• Significantly improved b fragmentation

from dipole shower

• Comparable description of heavy quark
• bservables across both showers

Multi-parton Interactions

)2

] mb impact parameter b [ 2 4 A(b) [1/mb] 0.05 0.1

2

= 1.80 GeV

2

µ

2

= 0.71 GeV

2

µ

[Figure by Stefan Gieseke]

p p R1 R2 P h s

[Gieseke, Loshaj, Kirchgasser — EPJ C77 (2017) 156]

matter distribution soft & hard scatters + diffraction

[Bellm, Gieseke, Kirchgasser — arXiv:1911.13149]

colour reconnection in total six parameters, hard MPI in principle allow for HQ Key ingredients for MPI modelling in Herwig 7

Cluster Hadronization

Shower Parton Splitter Fission Decay

[Figure by Patrick Kirchgaesser]

M p ≥ qp + (m1 + m2)p,

Clusters fission if too heavy: Fission parameters different for uds, c and b, but only uds produced Lighter clusters decay into hadrons Clusters formed by splitting gluons after shower evolution Different weights for light flavours

Colour Reconnection

[Gieseke, Röhr, Siodmok — EPJ C72 (2012) 2225] [Gieseke, Kirchgaesser, Plätzer – EPJ C 78 (2018) 99]

Preconfinement assumption violated in hadronic environments: colour reconnection crucial.

2 4 6 8 10 Mcluster [GeV] 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 1/n dn/dMcl/GeV−1 after reconnection

h-type clusters i-type clusters n-type clusters

default clusters

h-type clusters i-type clusters n-type clusters

ch

ATLAS data Hw++ 2.4, µ2 = 1.0, pmin

?

= 3.0

Hw++ 2.5, MB900-CTEQ6L1 0.2 0.4 0.6 0.8 1 Charged hp?i vs. Nch at 900 GeV, track p? > 500 MeV, for Nch 1

hp?i

[GeV] 5 10 15 20 25 30 35 40 45 0.6 0.8 1 1.2 1.4 Nch MC/data

No flavour dependence!

Geometric & Baryonic Reconnection

Herwig 7 ALICE Data Herwig 7.1 default baryonic reconnection g → s¯ s splittings new model 10−3 10−2 10−1 1 K+ + K− yield in INEL pp collisions at √s = 7 TeV in |y| < 0.5.

1 2 3 4 5 6 0.6 0.8 1 1.2 1.4 pT (GeV/c) MC/Data

Herwig 7 ALICE Data Herwig 7.1 default new model 10−4 10−3 10−2 10−1 Charged Multiplicity p

(s) = 7 TeV

dN/dNch 10 20 30 40 50 60 70 0.6 0.8 1 1.2 1.4 Nch MC/Data

[Gieseke, Kirchgaesser, Plätzer – EPJ C 78 (2018) 99]

Herwig 7 ALICE Data Herwig 7.1 default baryonic reconnection g → s¯ s splittings new model 10−1 p/π in INEL pp collisions at √s = 7 TeV in |y| < 0.5.

(p + ¯

p)/(π+ + π−) 0.5 1 1.5 2 2.5 3 0.6 0.8 1 1.2 1.4 pT (GeV/c) MC/Data

New model uses geometric measure instead of ‘string length’ and introduces baryonic degrees of freedom Combination with globally enhanced strange production.

Kinematic Strange Production & Spacetime Information

¯ q

q

q

¯ s

¯ q

s Φ(s¯ s) K−/ ¯ K0 K0/K+

[Duncan, Kirchgaesser – EPJ C79 (2019) 61]

Strange production in gluon splitting and fission dependent on environment.

[Bellm, Duncan, Gieseke, Myska, Siodmok – EPJ C79 (2019) 1003]

Spacetime information in colour reconnection possibly relevant in dense environments

ws(m)2 = exp ✓−m2 m2 ◆

Open questions remain in correlations

Data Default Mass Lambda Pythia 10−1 K/π in INEL pp collisions at √s = 7 TeV in |y| < 0.5.

(K+ + K−)/(π+ + π−)

0.5 1 1.5 2 2.5 3 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 pT (GeV/c) MC/Data

More theoretical understanding

[Gieseke, Kirchgaesser, Plätzer, Siodmok – JHEP 11 (2018) 149]

Approach colour reconnection from amplitude evolution algorithms: perturbative component?

[Angeles, De Angelis, Forshaw, Plätzer, Seymour – JHEP 05 (2018) 044] [Forshaw, Holguin, Plätzer – JHEP 1908 (2019) 145]

Aτ→σ = hσ|U

• {p}, µ2, {M2

ij }

• |τi

Pτ→σ = |Aτ→σ|2 P

ρ |Aτ→ρ|2 ,

Strong support for geometric models from perturbative evolution.

−

• Herwig

analytic

Confronting hadronization models with analytic power correction models

[Hoang, Plätzer, Samitz — in progress]

More theoretical understanding

[Gieseke, Kirchgaesser, Plätzer, Siodmok – JHEP 11 (2018) 149]

Approach colour reconnection from amplitude evolution algorithms: perturbative component?

[Angeles, De Angelis, Forshaw, Plätzer, Seymour – JHEP 05 (2018) 044] [Forshaw, Holguin, Plätzer – JHEP 1908 (2019) 145]

Aτ→σ = hσ|U

• {p}, µ2, {M2

ij }

• |τi

Pτ→σ = |Aτ→σ|2 P

ρ |Aτ→ρ|2 ,

Strong support for geometric models from perturbative evolution.

−

• Herwig

analytic

Confronting hadronization models with analytic power correction models

[Hoang, Plätzer, Samitz — in progress]

More theoretical understanding

[Gieseke, Kirchgaesser, Plätzer, Siodmok – JHEP 11 (2018) 149]

Approach colour reconnection from amplitude evolution algorithms: perturbative component?

[Angeles, De Angelis, Forshaw, Plätzer, Seymour – JHEP 05 (2018) 044] [Forshaw, Holguin, Plätzer – JHEP 1908 (2019) 145]

Aτ→σ = hσ|U

• {p}, µ2, {M2

ij }

• |τi

Pτ→σ = |Aτ→σ|2 P

ρ |Aτ→ρ|2 ,

Strong support for geometric models from perturbative evolution.

−

• Herwig

analytic

Confronting hadronization models with analytic power correction models

[Hoang, Plätzer, Samitz — in progress]

Outlook

• Some first tries in heavy flavour formation within

gluon splitting, but needs kinematic feedback to only happen at relevant scales.

• Further investigations into gluon splitting and cluster

fission driven by comparison to analytic power corrections, including flavour dependence

• Study mass effects in theoretical investigations of

colour reconnection such as colour evolution.

[Kirchgaesser, Plätzer — in progress]

charm-fission default 10−5 10−4 10−3 2 4 6 8 10 12 14 16 18 20 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 Ratio

pt D yield

[Hoang, Plätzer, Samitz — in progress]

Thank you!