update to 29/11/2012

Transcription

1 pp H + n jets with SHERPA update to 29/11/2012 S. Höche, F. Krauss, G. Luisoni, M. Schönherr, F. Siegert Institute for Particle Physics Phenomenology 20/12/2012 pp H + n jets with SHERPA update to 29/11/2012 1

2 Multijet merging at NLO extension of CKKW-type multijet merging to NLO accuracy Lavesson, Lönnblad JHEP12(2008)070 Höche, Krauss, MS, Siegert arxiv: Gehrmann, Höche, Krauss, MS, Siegert arxiv: implement resummation of parton shower through Sudakov weights, remove overlap of O(α s ) terms with NLO calculation through modified vetoed truncated shower construct inclusive sample where the first few jet multiplicities are calculated at NLO (supplemented by higher multiplicities at LO) while resumming the hierarchy of the emission scales of each individual jet up to a resummation scale (starting scale of the parton shower) - scales need to be set according to parton shower histories to retain parton shower resummation properties α s (µ 2 def )n+k = α s (µ 0 ) n k i=1 α s (t i ) pp H + n jets with SHERPA update to 29/11/2012 2

3 Multijet merging at NLO extension of CKKW-type multijet merging to NLO accuracy Lavesson, Lönnblad JHEP12(2008)070 Höche, Krauss, MS, Siegert arxiv: Gehrmann, Höche, Krauss, MS, Siegert arxiv: implement resummation of parton shower through Sudakov weights, remove overlap of O(α s ) terms with NLO calculation through modified vetoed truncated shower construct inclusive sample where the first few jet multiplicities are calculated at NLO (supplemented by higher multiplicities at LO) while resumming the hierarchy of the emission scales of each individual jet up to a resummation scale (starting scale of the parton shower) - scales need to be set according to parton shower histories to retain parton shower resummation properties α s (µ 2 def )n+k = α s (µ 0 ) n k i=1 α s (t i ) pp H + n jets with SHERPA update to 29/11/2012 2

4 Plan for YR3 Setup: pp H+ jets (ggf) purely perturbative calculation (no hadronisation, MPI, etc.) 0,1,2 NLO, 3(4) LO here still only NLO Q cut = 20 GeV, N max = 3 customary perturbative scale variations µ R/F [ 1 2, 2] µ def µ Q [ 1 2, 2] m h variation of merging parameter Q cut {20, 30, 50} GeV and max. ME multi N max {1, 2, 3} inclusive calculation scales of each jet-multiplicity subsample not independent dσ/dp [pb/gev] Higgs boson transverse momentum Sherpa MEPS@NLO µf, µr [ 1 2,2] µ def µ Q [ 1 2, 2]m h p (H) [GeV] inclusive cross section σ = pb µ R/F -, µ Q -, Q cut -, N max var. N max large due to inclusion of new initial states pp H + n jets with SHERPA update to 29/11/2012 3

5 Variation of Q cut inclusive observables VBF-like topologies dσ/dp [pb/gev] 10 1 Higgs boson transverse momentum dσ/dy [pb] Rapidity of leading jet (VBF cuts) p (H) [GeV] y(j1) very small residual Q cut dependence, formally of O( 1 α N sl 2 3 ) C 2 mismatch of terms in PS and NLO ME pp H + n jets with SHERPA update to 29/11/2012 4

6 Variation of Q cut dσ/d φ [pb] two-jet selection Azumuthal separation of the two leading jets (njet 2) φ(j1, j2) dσ/d φ [pb] VBF selection Azumuthal separation of the two leading jets (VBF cuts) φ(j1, j2) with Q cut = 50 GeV significant fraction of events produced at below Q cut 1st jet produced at LO by pp H MC@NLO 2nd jet produced by PS on top of pp H MC@NLO PS produces uncorrelated emissions in soft-collinear approximation pp H + n jets with SHERPA update to 29/11/2012 5

7 Variation of Q cut y of 3rd jet (njet 2) two-jet selection y of 3rd jet (VBF cuts) VBF selection dσ/dy [pb] dσ/dy [pb] y with Q cut = 50 GeV significant fraction of events produced at below Q cut 1st jet produced at LO by pp H MC@NLO 2nd jet produced by PS on top of pp H MC@NLO 3rd jet produced by PS on top of pp H MC@NLO PS produces uncorrelated emissions in soft-collinear approximation y pp H + n jets with SHERPA update to 29/11/2012 6

8 Preliminary results large uncertainties due to Q cut only when substantial number of events in selection have hard well-separated jets but fall below Q cut this test the ability of the PS to describe hard well-separated jets if it were able to so, multijet merging would not be relevant VBF-topologies are currently only described at LO move to NLO NLO description of multileg final states (in ME region) and resummation of scale hierarchies at the same time needed for multiscale processes Plans for YR3 NLO, LO (pp H + 2jets virtual from GOSAM) full theoretical uncertainty estimate (perturbative & non-perturbative) pp H + n jets with SHERPA update to 29/11/2012 7

9 Thank you for your attention! pp H + n jets with SHERPA update to 29/11/2012 8