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PDF uncertainties in Higgs production at hadron colliders

PDF uncertainties in Higgs production at hadron colliders. S. Ferrag LPNHE , Paris A. Djouadi CERN and LPMT , Montpellier. Introduction: Higgs production PDF uncertainties (MRST and CTEQ6) Uncertainties behaviour: quarks and gluon components Impact on the Higgs production

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PDF uncertainties in Higgs production at hadron colliders

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  1. PDF uncertainties in Higgs production at hadron colliders S. Ferrag LPNHE, Paris A. Djouadi CERN and LPMT, Montpellier • Introduction: Higgs production • PDF uncertainties (MRST and CTEQ6) • Uncertainties behaviour: quarks and gluon components • Impact on the Higgs production • Conclusion Monte Carlo workshop July 23rd 2003

  2. Introduction: Standard Model Higgs production • NLO cross section of 4 Higgs production processes: T. Han et al, Phys Lett B273 (1990). A. Djouadi et al Phys Rev D62 (2000) 14004 T. Han et al Phys Rev Lett 69 (1992) 3274 M. Spira et al Nucl Phys B453 (1995) 17 NLO program not yet public * * choose scale where NLO = LO and use NLO PDF with LO cross section • Used programs: V2HV, VV2H, Higlu and HQQ http://mspira.home.cern.ch/mspira/proglist.html

  3. Uncertainties from PDFs: MRST2001 and CTEQ6 • MRST and CTEQ6 sets and their error PDFs sets are used. • Schemes based on the Hessian matrix method. • PDFs (nominal sets and error sets) are built as follow: • - fit data with NPDF parameters and built nominal PDFs , CTEQ6M and MRST2001C: • NPDF=20 in CTEQ6, NPDF=15 in MRST • - Increase the global c2 by Dc2 and get the error matrix • Dc2 =100 in CTEQ6, Dc2 =50 in MRST • - Diagonalization of the matrix error to obtain 2NPDF eigenvector parameters • - excursion, up and down, for every eigenvector. 2NPDF sets of parameters • - for each set of new parameters, built an error PDF (2NPDF PDFs) X0 • Construction of the cross section uncertainties band: Si: error PDF X(Si): error PDF dependant cross section X0: predicted cross section (computed with nominal PDFs ) DXi + =Xi-X0 if Xi > X0 and DXi-- =X0-Xi if Xi < X0 Quadratic summation to get uncertainties band limits Xi Pt(GeV)

  4. Uncertainties behaviour: up quark low x quark intermediate x quark intermediate x quark High x quark low x • 3 ranges: low x, intermediate x and high x quarks.

  5. Uncertainties behaviour: down quark intermediate x quark low x quark low x High x intermediate x quark • 3 ranges: low x, intermediate x and high x quarks.

  6. Uncertainties behaviour: gluons 0.3 High x gluon High x gluon • 2 ranges: high x gluons and others. • Different range limits.

  7. Higgs cross sections at hadron colliders

  8. Impact on the Higgs production: gg to H LHC: smoothly oscillating (intermediate x) and increasing (high x) ~ 4-3% to 11% (100-1000 GeV) Tevatron: increasing (high x gluons), ~ 7% to 15% (100-200 GeV)

  9. Impact on the Higgs production: qqbar to WH LHC: constant (intermediate x quarks), ~ 4% Tevatron: increasing (intermediate x + high x quarks), ~ 5% to 7%

  10. Impact on the Higgs production: VBF and ttH LHC VBF: constant (intermediate x quarks), ~ 4% (100-1000GeV) Htt : top pair, smoothly increasing ~ 5% to 7% (100-200GeV) (intermediate x quarks + high x gluons)

  11. Conclusion • CTEQ6 uncertainties are 2 times larger than MRST ones: • number of parameters (quadratic summation) • different quantity Dc2 • High x gluons uncertainties are more important then high x quarks • To do: compare with Alekhin sets

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