Study of H γγ at NLO and NNLO

Transcription

1 Study of H γγ at NLO and NNLO G. Dissertori A. Holzner, F. Stöckli ETH Zürich Apr 13, 2005

2 Introduction Recently obtained : Higgs production (via gluon fusion) at NNLO (QCD), fully differential Anastasiou, Melnikov, Petriello, hep-ph/ At the moment available decay : H γγ Possible to obtain differential information on Higgs momentum, as well as of decay products Possible to apply cuts on final state and compute acceptances at NNLO! Comparison to other calculations (at lower order)? G. Dissertori CMS Physics Week, FNAL, Apr 05 2

3 The Process gg H γγ Large higher order corrections: σ(nnlo, inclusive) = LO ( ) NLO : exact up to one additional parton radiated in the initial state MCatNLO : exact up to NLO, but contains also logs (soft and collinear partons) up to all orders (structure of jets via parton shower) H NNLO : exact up to two additional partons radiated in the initial state Note : NLO and NNLO in Heavy-Top-Mass limit! (ok to 2-3% for light Higgs) G. Dissertori CMS Physics Week, FNAL, Apr 05 3

4 Goal of this study Apply selection criteria as close to exp. reality as possible Compare NLO, MCatNLO and NNLO predictions Study theoretical systematic uncertainties Compare distributions of signal (beyond NLO) and irreducible background G. Dissertori CMS Physics Week, FNAL, Apr 05 4

5 Programs employed Pure NLO and NNLO: FEHiP (hep-ph/ ) MCatNLO: Version 2.31, by S. Frixione and B. Webber Very user-friendly setup and interface by A. Holzner DiPHOX (for γγ production at NLO) Version 1.2, by Binoth et al. Basic parameters: proton-proton collisions at 14 TeV M top = 175 GeV. G. Dissertori CMS Physics Week, FNAL, Apr 05 5

6 Our (acceptance) cuts Photon p T Leading photon Second photon > 40 GeV > 25 GeV Isolation E T < 15 GeV in cone around photon, R=0.4 Photon rapidity η < 2.5 G. Dissertori CMS Physics Week, FNAL, Apr 05 6

7 Inclusive and accepted cross sections Cross section / Branching ratio inclusive accepted (= after cuts) Acceptance vs M H G. Dissertori CMS Physics Week, FNAL, Apr 05 7

8 Numbers : Inclusive / accepted cross sections : MCatNLO vs NNLO 2 % 3.8 % 1.6 % Cross sections (inc, acc) within 2-5% Acceptance within 0.5-6% G. Dissertori CMS Physics Week, FNAL, Apr 05 8

9 Scale dependencies After cuts G. Dissertori CMS Physics Week, FNAL, Apr 05 9

10 Scale dependencies : MCatNLO Cross sections (inc, acc) within 22-50%! But : Acceptance within 0.2-2%! G. Dissertori CMS Physics Week, FNAL, Apr 05 10

11 PDF dependencies (µ=m H /2) 15 % 2 % 9 % 0.5 % 1.7 % 5 % Higher order corrections reduced after cuts MRST - CTEQ NLO within 2 % G. Dissertori CMS Physics Week, FNAL, Apr 05 11

12 Distributions : PDF comparisons Average photon p T photon rapidity difference G. Dissertori CMS Physics Week, FNAL, Apr 05 12

13 Distributions : PDF comparisons Average photon p T photon rapidity difference G. Dissertori CMS Physics Week, FNAL, Apr 05 13

14 Distributions : MCatNLO vs NNLO Average photon p T photon rapidity difference G. Dissertori CMS Physics Week, FNAL, Apr 05 14

15 Distributions MCatNLO (Signal) vs Background (DiPHOX) Average photon p T photon rapidity difference G. Dissertori CMS Physics Week, FNAL, Apr 05 15

16 Comparison to irreducible background MCatNLO DiPHOX (µ = M H /2) Note : efficiency taken as in Bern et al. (Phys.Rev.D66:074018,2002 / hep-ph/ ) Mass window : ±2 x 0.65% M H = 3.12 GeV G. Dissertori CMS Physics Week, FNAL, Apr 05 16

17 Conclusions New NNLO calculations for Higgs production, which allow to study effect of cuts Comparison to MCatNLO : good agreement within 5 % for integrated cross sections and acceptance Distributions : Beware, inclusive K-factors would not give correct scaling Variables such as average photon p T could have discriminating power G. Dissertori CMS Physics Week, FNAL, Apr 05 17

18 Acknowledgements Babis Anastasiou For providing most of the NNLO results, the program FEHiP and many many stimulating discussions S. Frixione For answering questions about MCatNLO G. Dissertori CMS Physics Week, FNAL, Apr 05 18

19 Mass dependence of NNLO results, for two scale choices G. Dissertori CMS Physics Week, FNAL, Apr 05 19

20 Integrated Higgs p T G. Dissertori CMS Physics Week, FNAL, Apr 05 20

21 DiPHOX scale dependence G. Dissertori CMS Physics Week, FNAL, Apr 05 21