Heavy Flavour Hadronisation in Pythia Peter Skands (Monash - PowerPoint PPT Presentation

Heavy Flavour Hadronisation in Pythia Peter Skands (Monash University) 1. Heavy-Flavour Hadronisation in the Lund Model 2. Constraints 3. From ee to pp 4. New Theory Models in Pythia 5. Some Suggestions for New Measurements 6. Multiply heavy hadrons? VINCIA VINCIA Heavy-Flavour Hadronization in pp & HI Collisions, CERN, March 2020

Reminder: Fragmentation Models ๏ Hard process (e.g., dijets) ➤ hard factorisation scale Q UV ~ p Tjet ๏ Parton Showers: perturbative bremsstrahlung down to Q IR ~ 1 GeV ๏ Hadronisation: confinement (+ hadron decays) at Q HAD ~ Q IR u ( ~ p ⊥ 0 , p + ) shower Q UV ⇡ + ( ~ p ⊥ 1 , z 1 p + ) Q IR p ⊥ 0 − ~ · · · d ¯ d Perturbative K 0 ( ~ p ⊥ 2 , z 2 (1 − z 1 ) p + ) p ⊥ 1 − ~ main parameter α s Different “tunes” use Non-Perturbative s ¯ s different α seff (m Z ) values Fragmentation Function (at Q HAD ) Monash : 0.1365 ... A14: 0.129 + flavour / p T / … parameters, hadron decay tables ๏ Spectrum = combination of α s choice & non-perturbative parameters 2 Peter Skands Monash U.

<latexit sha1_base64="aAal5nrmGpvCXvPlbYJdVuONyw=">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</latexit> Flavour Composition in the Lund Model ๏ Starting point: isolated string in 1+1 dimensions • Tension κ ~ 1 GeV/fm ~ 0.2 GeV 2 m q m q Schwinger Tunneling • String breaks by Schwinger mechanism ! t t M • ➜ Suppression of strange − m 2 q + p 2 n a i o s ⊥ p s l d e exp n s quarks (and diquarks) s e e s n s κ e d l p s s o a i n M x t ➜ StringFlav:probStoUD = 0.217 ๏ + Spin-splitting in hadron multiplets V/P ≠ 3 ρ / π StringFlav:mesonUDvector = 0.50 D*/D StringFlav:mesonCvector = 0.88 K*/K StringFlav:mesonSvector = 0.55 B*/B StringFlav:mesonBvector = 2.2 Note: model parameters are for primary hadrons ≠ measured ratios (feed-down) ๏ 3 Peter Skands Monash U.

<latexit sha1_base64="aAal5nrmGpvCXvPlbYJdVuONyw=">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</latexit> Flavour Composition in the Lund Model ๏ Starting point: isolated string in 1+1 dimensions • Tension κ ~ 1 GeV/fm ~ 0.2 GeV 2 m q m q Schwinger Tunneling • String breaks by Schwinger mechanism ! t t M • ➜ Suppression of strange − m 2 q + p 2 n a i o s ⊥ p s l d e exp n s quarks (and diquarks) s e e s n s κ e d l p s s o a i n M x t ➜ StringFlav:probStoUD = 0.217 ๏ + Spin-splitting in hadron multiplets V/P ≠ 3 ρ / π StringFlav:mesonUDvector = 0.50 D*/D StringFlav:mesonCvector = 0.88 K*/K StringFlav:mesonSvector = 0.55 B*/B StringFlav:mesonBvector = 2.2 Note: model parameters are for primary hadrons ≠ measured ratios (feed-down) ๏ ๏ arXiv:1404.5630 Rookie Mistake: for D*/D in the Monash tune I took the D and D* rates from separate sources ➤ wrong ratio Thanks to D. Bardhan Should be higher ~ 1.25 - 1.5 to agree with measured values for pointing to this 4 Peter Skands Monash U.

<latexit sha1_base64="oCsGDCyEfHJKje51M5XeY3UoRIY=">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</latexit> <latexit sha1_base64="aAal5nrmGpvCXvPlbYJdVuONyw=">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</latexit> Heavy-Flavour Endpoint Quarks ๏ Same starting point as for massless endpoints • Tension κ ~ 1 GeV/fm ~ 0.2 GeV 2 m q m q m Q Schwinger m Q Tunneling • String breaks by Schwinger mechanism ! Massive endpoint Massive endpoint t • ➜ Suppression of strange − m 2 q + p 2 ⊥ exp quarks (and diquarks) κ x ➜ StringFlav:probStoUD = 0.217 ! • Same parameters govern D s /D, B s /B, Λ c /D, Λ b /B ➜ Interesting to check if D s /D, B s /B affected in same way in same environments where we see strangeness enhancements in light-quark sector: multiplicity dependence ๏ Massive endpoints have v < c ➜ smaller string space-time area : • ➜ Modified (“Lund-Bowler”) FF: ! − b m 2 (1 − z ) a ⊥ ,h with r b ~r c ~1 Q exp ๏ z 1 + r Q b m 2 z (Note: Peterson etc strictly speaking • incompatible with causality in string picture) • StringZ:rFactB = 0.855 • 5 Peter Skands Monash U.

Constraints : B Spectra ๏ Main constraint: x B spectra of weakly decaying B hadrons in Z decays 91.2 GeV Z q q 91.2 GeV Z q q → → B f(x) dx weak weak x (DELPHI) x (moments) 1/N dN/dx B B 10 DELPHI LEP (combined) 1 N-1 Monash (r 0.855) Monash (r 0.855) ≡ ≡ B B x Monash (r 1) Monash (r 1) → → ∫ B B 4C 4C Vincia Vincia 1 1 − 10 Spectrum Moments 1 − 10 Pythia 8.301 Pythia 8.301 Data from Eur.Phys.J. C71 (2011) 1557 Data from Eur. Phys. J. C71 (2011) 1557 − 2 10 1.4 1.2 Theory/Data Theory/Data 1.2 1.1 1 1 0.8 0.9 0.6 0.8 0 0.2 0.4 0.6 0.8 1 5 10 15 20 x Mellin Moment N ๏ for details see arXiv:1404.5630 (section 2.3) 6 Peter Skands Monash U.

+ B-tagged Event Shapes & Jet Rates ๏ IR safe: sensitive to α s and b mass effects in shower + hadronisation 3-jet rate (b/udsc) Jet Broadening (b) 91.2 GeV Z q q → 3 91.2 GeV Z q q → 10 R3bl W R3bl Wide Jet Broadening (b) /dB Delphi L3 σ 2 d 10 Monash (r 0.855) ≡ Monash (r ≡ 0.855) 1.1 σ B B Monash (r 1) 1/ Monash r 1 → ≡ B B 4C 4C 10 Vincia Vincia 1 1 1 − 10 2 − 10 0.9 Pythia 8.301 Pythia 8.301 Data from Phys.Rept. 399 (2004) 71 Data from Eur.Phys.J.C46(2006)569 3 − 10 1.4 1.1 Theory/Data Theory/Data 1.2 1.05 1 1 0.8 0.95 0.6 0.9 0 0.1 0.2 0.3 0 0.02 0.04 B (b) y Durham k T 3-jet resolution y 23 W 23 ๏ for details see arXiv:1404.5630 (section 2.3) 7 Peter Skands Monash U.

LHC: Top Decays ➤ In-situ controlled B-Jet Sample? ๏ Yesterday: 25th anniversary of the top quark discovery March 2nd 1995 t → bW provides a clean high-statistics reference sample, with a well- defined initial b-quark energy (in top CM) very similar to Z → bb. Compare B FF(x) and B hadron flavour ratios to those for inclusive b-jets, incl. any dependence on UE level (measured away from the top jets) Note: finite top width ➜ “collective effects” may be suppressed in top (“early” vs “late” resonance decays) 8 Peter Skands Monash U.

Some Comments on b fragmentation “tuning” ๏ Note: Monash uses “large" TimeShower:alphaSvalue = 0.1365 • Regarded at least in part as making up for NLO K-factor for ee → 3 jets (baseline Pythia only accurate to LO for 3 jets). • Consistent with 3-flavour Λ QCD ~ 0.35 GeV (since we use 1-loop running) ๏ Not guaranteed to be universal. • LHC studies tend to prefer lower effective values of α s • E.g., A14 uses TimeShower:alphaSvalue = 0.129 (could be reinterpreted via CMW to MSbar alphaS(mZ) ~ 0.12 so consistent with world average.) • (but I would then also change to 2-loop running to preserve Λ QCD value) ๏ E.g., a lower α s ➜ less perturbative radiation ➜ harder x b (Q IR ) • ➜ Would need to retune non-perturbative parameters (e.g., r b ) at LEP • Problem: most LEP measurements are inclusive (including 3-jet events) ➜ Would need 3-jet NLO merging to ensure correct 3-jet admixture. ๏ 9 Peter Skands Monash U.