Integration of GRACE and PYTHIA Shigeru ODAKA High Energy - PowerPoint PPT Presentation

Integration of GRACE and PYTHIA Shigeru ODAKA High Energy Accelerator Research Organization (KEK) E-mail: shigeru.odaka@kek.jp S. Odaka, ACAT2000, Fermilab 1

Collaboration between Atlas-Japan and Minami-Tateya to develop event generators for hadron collider experiments : LHC ( pp ) and Tevatron ( ) pp Atlas-Japan K. Sato, S. Tsuno (Tsukuba U.) S. Odaka (KEK) Minami-Tateya J. Fujimoto, T. Ishikawa, Y. Kurihara (KEK) S. Odaka, ACAT2000, Fermilab 2

GRACE by the Minami-Tateya group Automatic generation of Feynman diagrams and FORTRAN codes for calculating the cross sections based on their amplitudes including cross-section integration and event generation tools BASES/SPRING ⇒ general-purpose event-generator generation framework powerful for multi-body production processes e.g., grc4f for LEP2 S. Odaka, ACAT2000, Fermilab 3

GRACE for hadron collisions Multi-particle productions will become more important at future (higher energy) hadron colliders; multiple heavy-particle ( W/Z , top, H ) production, cascade decay of SUSY particles ) → + → + 0 e.g., pp ( or pp bbH X bbbb X 5 (9) processes and 144 (240) diagrams However, GRACE deals with hard scattering only PYTHIA GRACE → need to add Parton Distribution Function ( PDF ) and QCD evolution ( parton radiation) ⇒ connection to a general-purpose event generator e.g., PYTHIA , ISAJET , HERWIG S. Odaka, ACAT2000, Fermilab 4

How to connect ? parameters Interfacing using data files flexible and portable . . . . . . . . . easier to code . . . . . . . . . GRACE I/F . . . . . . . . . I/F PYTHIA . . . . . . . . . used in GRAPE ( GRACE+PYTHIA for ep interactions) Hard-scattering CompHEP+PYTHIA event data parameters Embedding PYTHIA easy to handle in event generation I/F (PYUPEV) one-step generation hard GRACE scattering our choice S. Odaka, ACAT2000, Fermilab 5

Kinematics ( x x , ) uniform random 1 2 and momenta of produced numbers particles Choice of variables and mapping to the random numbers τ ≡ ≡ x two methods were developed 1 x x , y ln 1 1 2 2 x 2 and singularity -oriented choice for produced particles Functional mapping by users Grid mapping by BASES may be more efficient, if skillful detailed tuning is not required final sampling by PYTHIA event generation by SPRING S. Odaka, ACAT2000, Fermilab 6

PYUPEV Initialization stage to be called by PYUPIN ・ calculation of “total” cross section for every “process ” using BASES → SIGMAX Event generation stage ・ choose one of the “processes ” ・ determine a set of random numbers ・ read the BASES output ・ convert them to kinematic variables according to ・ event generation by SPRING the chosen “kinematics ” → ・ SIGEV = SIGMAX calculate the differential cross section i.e., no rejection using the GRACE output code → SIGEV = PDF * differential cross section * Jacobian ・ set the color flow (automatic) ・ Lorentz boost (event sampling using SIGEV/SIGMAX in PYTHIA ) S. Odaka, ACAT2000, Fermilab 7

Processes tested → γ + pp ( or pp ) q X 2/3-body → + → µν + Wg X g X → + → µν + HW X bb X 4-body → + → µν + bb W X bb X ( QCD ) → + → + Hbb X bbbb X 4-body → + bbbb X (under development) ( QCD ) S. Odaka, ACAT2000, Fermilab 8

Performance (example) ± → + = ≥ pp gW X at s 14 TeV, p ( ) g 5 GeV T User-defined BASES/ PYTHIA kinematics SPRING ISUB=16 Total cross section 63.36 ± 0.20 63.43 ± 0.13 63.17 ± 0.20 (nb) Generation 19 35 19 efficiency (%) CPU time for 12.5 20.3 4.6 100 k events (min) Linux PC (Pentium II, 300 MHz) CKM-diagonal diagrams only Without parton radiation and hadronization/decay (another 45 min. needed for them) S. Odaka, ACAT2000, Fermilab 9

→ + → + s = 2 pp Hbb X bbbb X at TeV Sum Pt (Mh = 80, 120, 160 GeV) arbitrary unit 0.09 Sum Pt Distribution 0.08 Mh = 80 GeV � = 4.161 MeV tot 0.07 COMPHEP : = 6.083 fb � GRA CE : = 6.006 fb � 0.06 Mh = 120 GeV � = 6.537 MeV 0.05 tot COMPHEP : = 1.002 fb � GRA CE : = 0.9892 fb 0.04 � Mh = 160 GeV 0.03 � = 60.677 MeV tot COMPHEP : = 0.3561 fb � 0.02 GRA CE : = 0.3565 fb � preliminary 0.01 0 0 50 100 150 200 250 300 350 SumPt(GeV) S. Odaka, ACAT2000, Fermilab 10

Possible improvements • Multi-process BASES / SPRING • Automatic generation of hand-written codes • Variable mass and coupling (reduction of the “processes” and built-in implementation of the CKM matrix) S. Odaka, ACAT2000, Fermilab 11

Summary • We have established a technique for embedding the GRACE output codes into PYTHIA . • This is a powerful tool for developing event generators for multi-body production processes in high-energy hadron collisions . • Some “improvements” are planned to make the development easier. S. Odaka, ACAT2000, Fermilab 12