Powheg with Pythia 8 in Gauss Philip Ilten University College - PowerPoint PPT Presentation

Powheg with Pythia 8 in Gauss Philip Ilten University College Dublin Bucharest MC Workshop November 22, 2012 Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 1 / 13

Introduction Overview LO n -jet ME − PS Merging NLO ME − PS Merging ckkw(l) mlm Mc@Nlo Powheg Catani, Krauss, Mangano, Moretti, Frixione, Webber Frixione, Nason, Kuhn, Webber Piccinini, Treccani Oleari hep-ph/0109231 hep-ph/0611129 hep-ph/0402116 0709.2092 1 Calculate 1 Perform T. Sjostrand (Lauterbad) Sudakov shower and factor an all cluster jets. lines. 2 Match jets to 2 Shower, partons, reject reject if emission N p � = N jets . using factor. Solid: MC@ NLO Dashe d: HERWIG× σ N L O σ L O Dotte d: NLO Sherpa Alpgen / Herwig++ MadEvent / Pythia MadEvent / Pythia Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 2 / 13

Introduction Mc@Nlo Advantages: 1 Calculate NLO corrections to ❼ NLO variables n -body process. ❼ smooth matching with PS 2 Calculate first shower emission. ❼ large number of processes 3 Break event into NLO ME− first emission, remainder. Disadvantages: 4 Apply showers to both parts of ❼ negative weighting event. ❼ showering with Herwig(++) only pp → ( Z/γ ∗ → ) l IL ¯ pp → ( Z → ) l IL ¯ pp → ( γ ∗ → ) l IL ¯ l IL + X l IL + X l IL + X pp → ( W + → ) l + pp → ( W − → ) l − i f i ¯ IL ν IL + X IL ¯ ν IL + X pp → γ ∗ ( → P f i ) + X pp → Z 0 + X pp → W + + X pp → W − + X pp → H 0 + X pp → b ¯ pp → t ¯ b + X t + X pp → t/ ¯ pp → ¯ t + X t + X pp → t + X tW + + X tW + + X pp → tW − + X pp → tW − / ¯ pp → ¯ tH + + X tH + + X pp → tH − + X pp → tH − / ¯ pp → ¯ pp → H 0 W + + X pp → H 0 ( W + → ) l + pp → H 0 W − + X i ν i + X pp → H 0 ( W − → ) l − pp → H 0 Z + X pp → H 0 ( Z → ) l i ¯ i ¯ ν i + X l i + X pp → W + W − + X pp → Z 0 Z 0 + X pp → W + Z 0 + X pp → W − Z 0 + X Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 3 / 13

Introduction Powheg Advantages: 1 Pick largest p T emission from NLO ❼ positive weights normalized ME . ❼ separation of shower 2 Evolve shower downwards to p T scale. Disadvantages: ❼ designed for p T ordered showers Herwig++ PowhegBox pp → H pp → W pp → Z pp → HW pp → W + jet pp → Z + jet pp → ZH pp → t pp → tW pp → W gg → H pp → V V → H pp → t ¯ pp → Z pp → jet + jet t pp → W W + dijet pp → W W pp → W Z pp → ZZ pp → b ¯ bW W Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 4 / 13

Introduction PowhegBox with Pythia 8 Shower Interface Technical Interface ❼ Already done in main31.cc ❼ Experimental interface in (partially) by Richard Corke. Gauss/Gen/LbPowheg . ❼ Needs adjustment per ❼ Common structure between matrix-element. libraries. ❼ Degenerate names. p y t h i a . r e a d S t r i n g ( " S p a c e S h o w e r : → p T m a x M a t c h = 2 " ) ; ❼ Input settings from file. p y t h i a . r e a d S t r i n g ( " T i m e S h o w e r : → p T m a x M a t c h = 2 " ) ; ❼ Stores initialization in files. p y t h i a . r e a d S t r i n g ( " → M u l t i p a r t o n I n t e r a c t i o n s : → ❼ PDF from file. 2 " ) ; p T m a x M a t c h = ❼ Event passed to shower = n e w P o w h e g H o o k s ( → p o w h e g H o o k s n F i n a l , v e t o M o d e , v e t o C o u n t , through common blocks. p T h a r d M o d e , p T e m t M o d e , → e m i t t e d M o d e , ❼ Internal random number p T d e f M o d e , M P I v e t o M o d e ) → ; generation. p y t h i a . s e t U s e r H o o k s P t r ( ( U s e r H o o k s → ✯ ) p o w h e g H o o k s ) ; Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 5 / 13

Shower Interface Algorithm 1 Find p T scale during multiple interaction phase. ❼ If explicit radiation in record, set as p T scale. ❼ Otherwise set as event momentum fraction as p T scale. 2 Veto if first ISR emission above p T scale. 3 Veto if first FSR emission above p T scale. Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 6 / 13

Shower Interface Shower Hooks ❼ Interface to shower through UserHooks with 6 access points to generation process. ❼ Use doVetoMIStep to find p T scale. ❼ Use doVetoISREmission to veto ISR. ❼ Use doVetoFSREmission to veto FSR. c l a s s P o w h e g H o o k s : p u b l i c U s e r H o o k s { // Determine the p T s c a l e . b o o l c a n V e t o M I S t e p ( ) { r e t u r n t r u e ; } i n t n u m b e r V e t o M I S t e p ( ) { r e t u r n 1 ; } b o o l d o V e t o M I S t e p ( int , c o n s t E v e n t & e ) { p T v e t o = i n f o P t r − > Q F a c ( ) ; p T v e t o = p T p o w h e g = e [ 6 ] . pT ( ) ; r e t u r n f a l s e ; } // Veto both ISR and FSR e m i s s i o n s above the p T s c a l e . b o o l c a n V e t o I S R E m i s s i o n ( ) { r e t u r n t r u e ; } b o o l d o V e t o I S R E m i s s i o n ( int , c o n s t E v e n t & e ) { // Return a c c o r d i n g l y . } } ; Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 7 / 13

Shower Interface Example ❼ Veto dependent on hard process structure. ❼ Need to supply correct veto per PowhegBox matrix element. − − − − − − − − ( c o m p l e t e e v e n t ) − − − − − − − − − − − − − − − − − P Y T H I A E v e n t L i s t i n g no id n a m e s t a t u s m o t h e r s d a u g h t e r s e m 0 90 ( s y s t e m ) − 11 0 0 0 0 7000.000 7000.000 1 2212 ( p +) − 12 0 0 3 0 3500.000 0.938 2 2212 ( p +) − 12 0 0 4 0 3500.000 0.938 3 − 1 ( d b a r ) − 21 1 0 5 6 7.369 0.000 4 2 ( u ) − 21 2 0 5 6 339.234 0.000 5 24 W + 22 3 4 0 0 313.409 92.718 6 21 23 3 4 0 0 33.194 0.000 g − − − − − − − − E n d P Y T H I A E v e n t L i s t i n g − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 8 / 13

Technical Interface Gauss Package ❼ Gauss/Gen/LbPowheg ❼ cmt ❼ Based on LbPythia8 . ❼ package.sh - parses PowhegBox source # = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ❼ src/component u s e G e n e r a t o r s v ✯ G e n v ✯ → u s e p y t h i a 8 ❼ PowhegProduction - actual L C G _ G e n e r a t o r s I n t e r f a c e s production source # = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = L i b / d i j e t / ✯ . [ fF ] → l i b r a r y L b P o w h e g _ w ❼ src/Lib L i b / d i j e t / ✯ . c x x . . . ❼ GaudiRandomForPowheg - L i b / ✯ . c p p L i b → l i b r a r y L b P o w h e g L i b Pythia random numbers / ✯ . c x x c o m p o n e n t / ✯ . c p p l i b r a r y L b P o w h e g ❼ PowhegHooks - shower # = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = hooks for elements m a c r o _ a p p e n d f f l a g s " - fno - → a u t o m a t i c - f P I C - f f i x e d - line - → ❼ powheg - wrapper to l e n g t h - n o n e - fno - s e c o n d - → PowhegBox u n d e r s c o r e - O2 " ❼ <process> - Powheg ME source Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 9 / 13

Technical Interface Common Structure ❼ Ideally, different PowhegBox structure. ❼ Instead, name mangling with SED (poor-man’s lexical analyzer). ❼ Implemented in cmt/package.sh . # Convert l i b r a r y name to a l l lower case . # This needs to be done because GCC a s s i g n s the e x t e r n a l symbol names in # a l l lower case , so a l l lower case i s used f o r c o n s i s t a n c y . L I B _ L C = ❵ e c h o " ✩ { L I B } " | tr " [: u p p e r :] " " [: l o w e r :] " ❵ # Fix the i n c l u d e f i l e paths . s e d − i " s / \ ( [ [ : s p a c e : ] ] \ + i n c l u d e [ [ : s p a c e : ] ] \ + [ ✬ \ " ] \ ) [ ˆ ✬ \ " ] * \ / / \ 1 / gi " ✩ T R G D I R → / ✩ L I B _ L C / ✯ # Find a l l s u b r o u t i n e s . S U B R O U T I N E S = ❵ g r e p − − no − f i l e n a m e − − i g n o r e − c a s e − − only − m a t c h i n g " ^ [ [ : s p a c e : ] ] * → s u b r o u t i n e [ [ : s p a c e : ] ] * [ [ : a l n u m :] _ ]* " ✩ T R G D I R / ✩ L I B _ L C / ✯ | s e d ✬ s / → s u b r o u t i n e // gi ✬ ❵ # Find a l l e n t r i e s . # Find a l l f u n c t i o n s . # Find a l l common b l o c k s . # Find a l l data b l o c k s . # Mangle the names f o r a l l subroutines , f u n c t i o n s , and common b l o c k s . m a n g l e _ n a m e s ✩ E N T R I E S ✩ S U B R O U T I N E S ✩ F U N C T I O N S ✩ C O M M O N S ✩ D A T A S Ilten (UCD) Powheg with Pythia 8 in Gauss November 22, 2012 10 / 13