NLO WG 2002 (KEK) shigeru.odaka@kek.jp - - PowerPoint PPT Presentation

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NLO WG 2002 (KEK) shigeru.odaka@kek.jp 1 2002 12 24 WS, GR@PPA generators (LO) S. Tsuno (U. of Tsukuba) GR@PPA_4b Official release in Apr. 2002 (version

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SLIDE 1

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 1

NLO WG 報告

尾高 茂

2002 年

(KEK)

shigeru.odaka@kek.jp

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SLIDE 2

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 2

GR@PPA generators (LO)

  • S. Tsuno (U. of Tsukuba)
  • GR@PPA_4b

– Official release in Apr. 2002 (version 1.06) http://atlas.kek.jp/physics/nlo-wg/grappa.html – A paper was submitted to CPC (hep-ph/0204222; KEK Preprint 2002-7).

  • GR@PPA_all

– Many other generators are added. – Not well tested yet, especially at the LHC condition.

  • Others

– Generators for W + jets (up to 4 jets) are being developed.

W ff bb Wbb Zbb W ff cc Wcc Zcc bb Wbbbb tt ( ) , , , ( ) , , , , , → →

+ −

τ τ (6 body)

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SLIDE 3

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 3

10 10 2 10 3 50 100 150 200

Et (GeV/c) number of events 1st b jet

1 10 10 2 10 3

  • 4
  • 2

2 4

η number of events 1st b jet

1 10 10 2 10 3 20 40 60 80 100

Et (GeV/c) number of events 4th b jet

1 10 10 2 10 3

  • 4
  • 2

2 4

η number of events 4th b jet

solid: GR@PPA_4b, dashed: PYTHIA

Result:

GR@PPA_4b: (348 ± 3) pb PYTHIA: (447 ±12) pb PYTHIA ≈ 1.3 × GR@PPA_4b

Event selection:

4 b-jets with ET ≥ 15 GeV ∆R≥ 0.4 for all b-jet pairs ET ≥ 50 GeV for leading 2 b-jets

PYTHIA:

QCD 2-jet (MSEL = 1)

Detector:

Active detector in |η| ≤ 4.5 b-quark tag in |η| ≤ 2.5

GR@PPA_4b vs PYTHIA

for QCD 4-b production

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SLIDE 4

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 4

250 500 750 1000 1250 1500 1750 2000 2250 0.5 1 1.5 2 2.5 3

∆φ number of events non-leading two b-jets

PYTHIA GR@PPA_4b gg gg → in PYTHIA

Origin of PYTHIA events

~ 50% gg gg → gb gb → ~ 35% gg qq bb bb bb ( ) → → + ~ 10%

Consistent with the result in: Richter-Was and Froidevaux, Z. Phys. C 76, 665 (1997) and our Feb-2002 result. Additional b’s from the final-state PS. Additional b’s from the initial-state PS.

Note: PYTHIA ≈ 70×GR@PPA_4b in CPU-time. Comparable results under a reasonable detection condition, if the QCD 2-jet subset (MSEL = 1) is chosen in PYTHIA. PYTHIA events are dominated by gg → gg and gb → gb interactions. The contribution of b-pair producing processes is small (~10%).

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SLIDE 5

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 5

NLL-jet

  • NLL-PS

– All branching functions are ready (Sugiura and Tanaka at Rikkyo U.). – A preliminary coding with a temporary kinematics implementation has been tested (Tanaka).

  • X-deterministic forward evolution PS

– A new method of the initial-state PS with a forward Q2 evolution (Y. Kurihara, hep- ph/0207214). – The final x is fixed before determining x values at intermediate branches. – A good efficiency can be achieved. – The idea has been tested for LL evolution. Monte Carlo implementation (parton shower) of the next-to-leading logarithmic

  • rder QCD evolution in the initial state

u u

0.0001 0.001 0.01 0.1 1 0.001 0.01 0.1 1 dN/dx1 x1 Q^2=10^3 GeV^2 LLA NLL ’OUTG01.DAT’

u quark distribution at Q2 = 103 GeV2

Input: GRV98 at Q02 = 1 GeV2 Histograms: GRV98 at Q2 = 103 GeV2

CTEQ5L : GeV Q m Q

b

100 = ⇒ =

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SLIDE 6

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 6

NLO event generator

  • One-loop corrections (only 3-points yet)

are already in the CHANEL library.

  • Modified LL-subtraction method to solve

the double counting problem in ME and PS. – Numerical subtraction of LL terms from ME – A maximum pT of the radiation (= factorisation scale) has to be introduced to reproduce the actual implementation of PS and PDF. – Y. Kurihara, hep-ph/0207214.

  • Modified BASES/SPRING to handle

negative-weight events. – The weight of generated events = ±1. – The fraction of negative-weight events is very small after the LL subtraction.. Gluon-pT in the DY process

s kT

µ µ

+ − ≥

≥ 40 1 GeV, GeV ∗ → ⊗

+ −

: ( PS qq µ µ )

  • : (

PS PS

sub

qq

LL

→ ⊗

[ ] +

⊗

[ ]

+ − −

µ µ σ ) ˜ hist : ( from PS rejected) qq g g →

+ −

µ µ

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SLIDE 7

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 7

NLO Drell-Yan

QED only

  • Test and demonstration of the

ideas

– Kurihara et al., hep/ph- 0212216 – NLO calculation and event generation in the framework of GRACE – Numerical modified LL subtraction – X-deterministic forward evolution LL-PS

  • Smooth transition from a PS-

dominated small ET region to a ME-dominated large ET region

Solid: non-rad. (mod. LL included) ⊗ PS Dashed: rad. (mod. LL subtracted) ⊗ PS Star: NLO (= non-rad. ⊗ PS + rad. ⊗ PS) Dot-dashed: rad. ⊗ PDF (naive) sµ µ

+ − ≥ 10 GeV

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SLIDE 8

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 8

ME-PS matching

double-counting problem

  • A serious problem when

– Colored parton(s) in the final-state

  • f ME, and

– ET(jet) < µF

  • For example:

– NLO – W/Z + jet(s) – t-pair + jet(s) – H + jet(s)

  • Being seriously discussed at Tevatron

– “MC Tuning WS” – Next meeting on Jan. 14 at Durham (England)

  • Various possible solutions have been

proposed.

q2 = q02 > q12 > ... > qn2 ... Q2 = Q02 < Q12 < ... < Qn2 q2 = Q2 = 0

ME

...

PS/PDF

W µF pT(W) "W" ⊗ PS "W + jet" ⊗ PS "W + jet": Q ∼ µF

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SLIDE 9

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 9

Possible solutions

  • (Modified) Log-term subtraction

– Kurihara, hep-ph/0207214 – Subtract Log terms from ME, and add non-radiative process + PS, instead – Theoretically well defined, but hard to implement in multi-jet cases – Perhaps, a similar method in MC@NLO (Frixione and Webber, hep/ph-0204244)

  • Hard-PS rejection

– Mangano at the last “MC Tuning WS” on Nov. 16 @ FNAL – Require a matching between ME partons and observed jets -> reject mismatched events – Easy to implement, but theoretical basis is not clear

  • Extended CKKW method

– Mrenna at the last “MC Tuning WS” on Nov. 16 @ FNAL – CKKW (Catani, Kraus, Kuhn and Webber, hep/ph-0109231) for multi-jet Z decays – Generate events of a large jet multiplicity, applying PS with a small µF -> merge the jets and correct the event weight using the Sudakov suppression factor – Theoretically well defined, but need to generate multi-jet events

  • (Simple) phase-space slicing

– Simple and well defined, but hard to avoid discontinuity

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SLIDE 10

年 2002 月 12 日 アトラス日本 24 物理分科会 WS, 10

2003 年カレンダー

  • 月

2 日 17 日：

  • 21

ATLAS Week (CERN)

  • 月

5 日 21 日：

  • 25

アテネ ATLAS Physics WS ( )

  • 月

5 日 27 月

  • 6

日： 6

Physics at TeV Colliders WS

(Les Houches, France)

– http://wwwlapp.in2p3.fr/conferences/LesHouches/Houches2003/

  • 月

6 日 23 日：

  • 27

ATLAS Week (CERN)

  • 月

7 日 7 月

  • 8

日： 2 LHC Monte Carlo WS (CERN)

– http://lhc-monte-carlo.web.cern.ch/lhc-monte-carlo/workshop.html

  • 月

9 日 13 日：

  • 19

プラハ ATLAS Week ( )