Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production

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1 Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production Institute for Particle Physics Phenomenology 26/09/202 arxiv:.220, arxiv: Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production

2 The SHERPA event generator framework JHEP02(2009)007 Two multi-purpose Matrix Element (ME) generators AMEGIC++ JHEP02(2002)044 COMIX JHEP2(2008)039 CS subtraction EPJC53(2008)50 A Parton Shower (PS) generator CSSHOWER++ JHEP03(2008)038 A multiple interaction simulation à la Pythia AMISIC++ hep-ph/06002 A cluster fragmentation module AHADIC++ EPJC36(2004)38 A hadron and τ decay package HADRONS++ A higher order QED generator using YFS-resummation PHOTONS++ JHEP2(2008)08 Sherpa s traditional strength is the perturbative part of the event MEPS (CKKW), MC@NLO, MENLOPS, MEPS@NLO full analytic control mandatory for consistency/accuracy Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 2

3 The SHERPA event generator framework JHEP02(2009)007 Two multi-purpose Matrix Element (ME) generators AMEGIC++ JHEP02(2002)044 COMIX JHEP2(2008)039 CS subtraction EPJC53(2008)50 A Parton Shower (PS) generator CSSHOWER++ JHEP03(2008)038 A multiple interaction simulation à la Pythia AMISIC++ hep-ph/06002 A cluster fragmentation module AHADIC++ EPJC36(2004)38 A hadron and τ decay package HADRONS++ A higher order QED generator using YFS-resummation PHOTONS++ JHEP2(2008)08 Sherpa s traditional strength is the perturbative part of the event MEPS (CKKW), MC@NLO, MENLOPS, MEPS@NLO full analytic control mandatory for consistency/accuracy Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 2

4 [ O NLO+PS = dφ B(A) B (Φ B ) (A) (t 0, µ 2 Q) O(Φ B ) + + i [ dφ R R(Φ R ) i µ 2 Q t 0 (A) Di (Φ B, Φ ) dφ B(Φ B ) D (A) i (Φ R ) ] O(Φ R ) Frixione, Webber JHEP06(2002)029 (A) (t, µ 2 Q) O(Φ R ) Höche, Krauss, MS, Siegert arxiv:.220 NLO weighted Born configuration B (A) = B + Ṽ + I + dφ [D (A) D (S) ] [ use D (A) i as resummation kernels (A) (t, t t ] ) = exp dφ t D (A) /B resummation phase space limited by µ 2 Q = t max starting scale of parton shower evolution should be of the order of the hard resummation scale first implementation to allow to study µ Q uncertainty Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 3 ]

5 [ O NLO+PS = dφ B(A) B (Φ B ) (A) (t 0, µ 2 Q) O(Φ B ) + + i [ dφ R R(Φ R ) i µ 2 Q t 0 (A) Di (Φ B, Φ ) dφ B(Φ B ) D (A) i (Φ R ) ] O(Φ R ) Frixione, Webber JHEP06(2002)029 (A) (t, µ 2 Q) O(Φ R ) Höche, Krauss, MS, Siegert arxiv:.220 NLO weighted Born configuration B (A) = B + Ṽ + I + dφ [D (A) D (S) ] [ use D (A) i as resummation kernels (A) (t, t t ] ) = exp dφ t D (A) /B resummation phase space limited by µ 2 Q = t max starting scale of parton shower evolution should be of the order of the hard resummation scale first implementation to allow to study µ Q uncertainty Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 3 ]

6 [ O NLO+PS = dφ B(A) B (Φ B ) (A) (t 0, µ 2 Q) O(Φ B ) + + i [ dφ R R(Φ R ) i µ 2 Q t 0 (A) Di (Φ B, Φ ) dφ B(Φ B ) D (A) i (Φ R ) ] O(Φ R ) Frixione, Webber JHEP06(2002)029 (A) (t, µ 2 Q) O(Φ R ) Höche, Krauss, MS, Siegert arxiv:.220 every term is well defined and NLO and NLL accuracy maintained if: D (A) = i D(A) i D (A) = i D(A) i is full colour correct in soft limit contains all spin correlations in collinear limit D (A) i and D (S) i have identical parton maps conventional parton showers need to be improved for that e.g. choose D (A) i = D (S) i up to phase space constraints Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 3 ]

7 [ O NLO+PS = dφ B(A) B (Φ B ) (A) (t 0, µ 2 Q) O(Φ B ) + + i [ dφ R R(Φ R ) i µ 2 Q t 0 (A) Di (Φ B, Φ ) dφ B(Φ B ) D (A) i (Φ R ) ] O(Φ R ) Frixione, Webber JHEP06(2002)029 (A) (t, µ 2 Q) O(Φ R ) Höche, Krauss, MS, Siegert arxiv:.220 POWHEG and MC@NLO differ in choice of D (A) i and µ Q POWHEG µ 2 Q = 4 S had, D (A) i = ρ i R ρ i suitable projector on single soft-collinear singular region exponentiates process-specific non-logarithmic terms MC@NLO µ 2 Q = t max, D (A) i = B K i modify to D (A) i = f B K i for non-trivial colour structures exponentiates same as parton shower Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 3 ]

8 Short-comings of fixed-order QCD poor description in phase space regions with strongly hierarchical scales poor perturbative jet-modeling (at most two constituents) no hadronisation, MPI effects very pronounced in inclusive & dijet production jet-p turn negative in forward region unless y-dependent scale is used (e.g. H (y) T ) σ [pb] Inclusive Jet Multiplicity (R=0.4) ATLAS data Eur.Phys.J. C7 (20) 763 Sherpa NLO µf = µr = 2 HT cuts: p j > 80 GeV, p j 2 > 60 GeV Njet Bern et.al. arxiv: Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 4

9 Short-comings of fixed-order QCD poor description in phase space regions with strongly hierarchical scales poor perturbative jet-modeling (at most two constituents) no hadronisation, MPI effects very pronounced in inclusive & dijet production jet-p turn negative in forward region unless y-dependent scale is used (e.g. H (y) T ) dσ/dp [pb/gev] Transverse momentum of the leading jet (R=0.4) ATLAS data Eur.Phys.J. C7 (20) 763 Sherpa NLO µf = µr = 2 HT p (leading jet) [GeV] cuts: p j > 80 GeV, p j 2 > 60 GeV Bern et.al. arxiv: Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 4

10 Short-comings of fixed-order QCD poor description in phase space regions with strongly hierarchical scales poor perturbative jet-modeling (at most two constituents) no hadronisation, MPI effects very pronounced in inclusive & dijet production jet-p turn negative in forward region unless y-dependent scale is used (e.g. H (y) T ) dσ/dp [pb/gev] 0 5 Transverse momentum of the 2nd leading jet (R=0.4) ATLAS data Eur.Phys.J. C7 (20) 763 Sherpa NLO µf = µr = 2 HT p (2nd leading jet) [GeV] cuts: p j > 80 GeV, p j 2 > 60 GeV Bern et.al. arxiv: Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 4

11 Short-comings of fixed-order QCD poor description in phase space regions with strongly hierarchical scales poor perturbative jet-modeling (at most two constituents) no hadronisation, MPI effects very pronounced in inclusive & dijet production jet-p turn negative in forward region unless y-dependent scale is used (e.g. H (y) T ) dσ/dp [pb/gev] Transverse momentum of the 3rd leading jet (R=0.4) ATLAS data Eur.Phys.J. C7 (20) 763 Sherpa NLO µf = µr = 2 HT p (3rd leading jet) [GeV] cuts: p j > 80 GeV, p j 2 > 60 GeV Bern et.al. arxiv: Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 4

12 Describe wealth of experimental data with a single sample (LHC@7TeV) MC@NLO di-jet production: Höche, MS arxiv: µ R/F = 4 H T, µ Q = 2 p CT0 PDF (α s (m Z ) = ) hadron level calculation fully hadronised including MPI virtual MEs from BLACKHAT Giele, Glover, Kosower Nucl.Phys.B403(993) Bern et.al. arxiv: p j > 20 GeV, pj2 > 0 GeV Uncertainty estimates: µ Q variation MPI variation µ F, µ R variation µ R/F [ 2, 2] µdef R/F µ Q [ 2, 2] µ def Q MPI activity in tr. region ± 0% Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 5

13 Describe wealth of experimental data with a single sample (LHC@7TeV) MC@NLO di-jet production: Höche, MS arxiv: µ R/F = 4 H T, µ Q = 2 p CT0 PDF (α s (m Z ) = ) hadron level calculation fully hadronised including MPI virtual MEs from BLACKHAT Giele, Glover, Kosower Nucl.Phys.B403(993) Bern et.al. arxiv: p j > 20 GeV, pj2 > 0 GeV Uncertainty estimates: µ R/F [ 2, 2] µdef R/F µ Q [ 2, 2] µ def Q MPI activity in tr. region ± 0% σ [pb] Inclusive jet multiplicity (anti-kt R=0.4) µr, µf variation µ Q variation MPI variation ATLAS data Eur.Phys.J. C7 (20) 763 µr = µf = 4 HT, µ Q = 2 p Njet Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 5

14 dσ/dp [pb/gev] Jet transverse momenta (anti-kt R=0.4) ATLAS data Eur.Phys.J. C7 (20) 763 µr = µf = 4 HT, µ Q = 2 p µr, µf variation µ Q variation MPI variation st jet.4.2 Höche, MS arxiv: st jet.4.2 2nd jet th jet 0 3 3rd jet 0 2 2nd jet rd jet 4th jet p [GeV] p [GeV] Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 6

15 Scalar sum of jet transverse momenta (anti-kt R=0.4) Höche, MS arxiv: dσ/dht [pb/gev] ATLAS data Eur.Phys.J. C7 (20) 763 µr = µf = 4 HT, µ Q = 2 p µr, µf variation µ Q variation MPI variation Njet Njet 3 0 Njet 2 Njet Njet Njet HT [GeV] HT [GeV] Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 7

16 R jets over 2 jets ratio (anti-kt R=) µf, µr variation µ Q variation MPI variation CMS data Phys. Lett. B 702 (20) 336 µr = µf = 4 HT, µ Q = 2 p HT [TeV] 3-jet-over-2-jet ratio Höche, MS arxiv: determined from incl. sample 2-jet rate at NLO+NLL 3-jet rate at LO+LL common scale choices varied simultaneously at large H T large MPI uncertainties better MPI physics needed (soft QCD) similar description of related ATLAS observables Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 8

17 R jets over 2 jets ratio (anti-kt R=) µf, µr variation µ Q variation MPI variation CMS data Phys. Lett. B 702 (20) 336 µr = µf = 4 HT, µ Q = 2 p HT [TeV] 3-jet-over-2-jet ratio T ] 3 /[dσ/dh (2) T ] 2 [dσ/dh (2) Höche, MS arxiv: determined jets over 2 jets ratio for from p jets > 60 GeV (anti-kt R=0.4) incl. sample µr, µf variation 2-jet rate at NLO+NLL µ Q variation MPI variation 3-jet rate at LO+LL common scale choices ATLAS data varied simultaneously 0.2 Eur.Phys.J. C7 (20) at large H T large MPI 0 uncertainties.4.2 better MPI physics needed (soft QCD) µr = µf = 4 HT, µ Q = 2 p similar description of related ATLAS observables H (2) T [GeV] Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 8

18 dσ/dp [pb/gev] Inclusive jet transverse momenta in different rapidity ranges ATLAS data Phys. Rev. D86 (202) µr = µf = 4 HT, µ Q = 2 p µr = µf = 4 H(y) T, µ Q = 2 p µr, µf variation µ Q variation MPI variation p [GeV] Höche, MS arxiv: y < < y < 2 3 < y < < y < < y < < y < < y < p [GeV] Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 9

19 dσ/dm2 [pb/tev] Dijet invariant mass spectra in different rapidity ranges ATLAS data Phys. Rev. D86 (202) µr = µf = 4 HT, µ Q = 2 p µr = µf = 4 H(y) T, µ Q = 2 p µr, µf variation µ Q variation MPI variation 0 m2 [TeV] < y < < y < < y < < y < < y < < y < < y <.5 Höche, MS arxiv: < y <.0 y < 0 m 2 [GeV] Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 0

20 Try different scale µ R/F = 4 H(y) T with H (y) T = i jets p,i e 0.3 y boost y i with y boost = /n jets i jets y i reduces to µ R/F = 2 p e 0.3y with y = 2 y y 2 for 2 2 and captures real emission dynamics Ellis, Kunszt, Soper PRD40(989)288 better description of data at large rapidities, as expected description of most other observables worsened need proper description of forward physics (e.g. (B)FKL) < y < < y < < y < < y < < y < < y < < y <.5 Höche, MS arxiv: < y <.0 y < 0 m 2 [GeV] Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 0

21 Try different scale µ R/F = 4 H(y) T with H (y) T = i jets p,i e 0.3 y boost y i with y boost = /n jets i jets y i reduces to µ R/F = 2 p e 0.3y with y = 2 y y 2 for 2 2 and captures real emission dynamics Ellis, Kunszt, Soper PRD40(989)288 better description of data at large rapidities, as expected description of most other observables worsened need proper description of forward physics (e.g. (B)FKL) Höche, MS arxiv: st jet 2nd jet 3rd jet 4th jet p [GeV] Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 0

22 Gap Fraction Inclusive jet transverse momenta in different rapidity ranges 0 Leading dijet selection ATLAS data JHEP 09 (20) Höche, MS arxiv: GeV < p < 270 GeV 8 µr = µf = 4 HT, µ Q = 2 p µf, µr variation µ Q variation MPI variation.5 20 GeV < p < 240 GeV GeV < p < 270 GeV GeV < p < 240 GeV GeV < p < 20 GeV GeV < p < 80 GeV GeV < p < 50 GeV GeV < p < 20 GeV + 70 GeV < p < 90 GeV y.5 80 GeV < p < 20 GeV.5 50 GeV < p < 80 GeV GeV < p < 50 GeV 90 GeV < p < 20 GeV.5 70 GeV < p < 90 GeV y Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production

23 Gap Fraction Inclusive jet transverse momenta in different rapidity ranges 0 Forward-backward selection ATLAS data JHEP 09 (20) GeV < p < 270 GeV Höche, MS arxiv: µr = µf = 4 HT, µ Q = 2 p µf, µr variation µ Q variation MPI variation.5 20 GeV < p < 240 GeV GeV < p < 270 GeV GeV < p < 240 GeV GeV < p < 20 GeV GeV < p < 80 GeV GeV < p < 50 GeV GeV < p < 20 GeV + 70 GeV < p < 90 GeV y.5 80 GeV < p < 20 GeV.5 50 GeV < p < 80 GeV GeV < p < 50 GeV 90 GeV < p < 20 GeV.5 70 GeV < p < 90 GeV y Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 2

24 small- y region small uncertainty on additional jet production large- y region all uncertainties sizable GeV < p < 270 GeV Höche, MS arxiv: GeV < p < 240 GeV small- p region dominated by perturbative uncertainties large- p region non-perturbative uncertainties as large as perturbative uncertainties Reduction of theoretical uncertainty necessitates better understanding of soft QCD and nonfactorisable contributions GeV < p < 20 GeV 50 GeV < p < 80 GeV 20 GeV < p < 50 GeV 90 GeV < p < 20 GeV 70 GeV < p < 90 GeV y Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 2

25 Mean Number of Jets in Gap Inclusive jet transverse momenta in different rapidity ranges Leading dijet selection ATLAS data JHEP 09 (20) 053 µr = µf = 4 HT, µ Q = 2 p µf, µr variation µ Q variation MPI variation 4 < y < < y < < y < 3 + < y < p [GeV] < y < 5 Höche, MS arxiv: < y < 4 2 < y < 3 < y < p [GeV] Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 3

26 Mean Number of Jets in Gap Inclusive jet transverse momenta in different rapidity ranges Forward-backward selection ATLAS data JHEP 09 (20) 053 µr = µf = 4 HT, µ Q = 2 p µf, µr variation µ Q variation MPI variation 4 < y < < y < < y < 3 + < y < p [GeV] < y < 5 Höche, MS arxiv: < y < 4 2 < y < 3 < y < p [GeV] Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 4

27 de/dη [GeV] Forward energy flow in dijet events, p jets > 20 GeV CMS data JHEP (20) 48 µr = µf = 4 HT, µ Q = 2 p µf, µr variation µ Q variation MPI variation η Forward energy flow Höche, MS arxiv: energy flow in rapidity interval per event with a central back-to-back di-jet pair normalisation reduces µ R/F and µ Q dependence dominated by MPI modeling uncertainty Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 5

28 Complete estimate of theoretical uncertainties Perturbative uncertainties: unphysical scales of perturbative calculation µ F, µ R, µ Q in any fixed-order-resummation matched calculation (LOPS, NLOPS, etc.) central value fits surprisingly good given perturbative uncertainties PDF uncertainties individually through respective error sets or replica globally through PDF4LHC accord (needs individual tunes for non-perturbative physics modelling for at least every central set) Non-perturbative uncertainties: modelling uncertainties for non-perturbative physics with only little first principles basis proper: use full set of eigentunes obtainable through e.g. PROFESSOR approximate: use canonical variation of characteristic activity measure - MPI: N ch ± 0% of plateau in transverse region - hadronisation: N ch ± at LEP - intrinsic k, beam remnants,...? Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 6

29 Conclusions SHERPA s MC@NLO formulation allows full evaluation of perturbative uncertainties (µ F, µ R, µ Q ) MC@NLO can be easily combined with MEPS MENLOPS MC@NLO is a necessary input for NLO merging MEPS@NLO see Frank s talk will be included in next major release Current release: SHERPA precise theoretical calculations need to be confronted with data as differentially as possible over as large a phase space as possible to identify physics region that needs improvement Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 7

30 Thank you for your attention! Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 8

31 Dijet azimuthal decorrelation in various p lead bins Höche, MS arxiv: /σ dσ/d φ [pb] CMS data Phys. Rev. Lett. 06 (20) µr = µf = 4 HT, µ Q = 2 p µr, µf variation µ Q variation MPI variation GeV < p lead 200 GeV < p lead < 300 GeV GeV < p lead < 200 GeV 0 GeV < p lead < 40 GeV 80 GeV < p lead < 0 GeV φ φ Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 9

32 /N dn/dln(τ,c) [pb] Central transverse thrust in different leading jet p ranges.4.2 CMS data Phys. Rev. Lett. 06 (20) µr = µf = 4 HT, µ Q = 2 p µr, µf variation µ Q variation MPI variation.4.2 Höche, MS arxiv: GeV < p jet GeV < p jet GeV < p jet < 200 GeV GeV < p jet < 200 GeV GeV < p jet < 25 GeV ln(τ,c) 90 GeV < p jet < 25 GeV ln(τ,c) Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 20

33 /N dn/dln(t m,c) [pb] Central transverse thrust minor in different leading jet p ranges.4.2 CMS data Phys. Rev. Lett. 06 (20) µr = µf = 4 HT, µ Q = 2 p µr, µf variation µ Q variation MPI variation Höche, MS arxiv: GeV < p jet GeV < p jet GeV < p jet < 200 GeV GeV < p jet < 200 GeV GeV < p jet < 25 GeV ln(t m,c) 90 GeV < p jet < 25 GeV ln(t m,c) Uncertainties in NLO+PS matched calculations of inclusive jet and dijet production 2

Multijet merging at NLO

Multijet merging at NLO Multijet merging at Institute for Particle Physics Phenomenology 09/0/0 arxiv:.0, arxiv:0.588 arxiv:07.5030, arxiv:07.503 arxiv:08.85 Multijet merging at 0000 0 0 0 0 0 0 0 0 00 00000 00000 00000 00000