A. DJOUADI (Paris, Montpellier) Impact of PDF uncertainties on Higgs production at LHC (hep-ph/0310209) Samir FERRAG University of OSLO A. DJOUADI (Paris, Montpellier) Introduction: Higgs production PDF uncertainties (MRST, CTEQ6 and Alekhin) Uncertainties behaviour: quarks and gluon components Impact on the Higgs production and comparison CERN, Mar 26-27 2004 S. Ferrag

Standard Model Higgs production NLO cross section of 4 Higgs production processes: NLO program were not 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 S. Ferrag

Uncertainties from PDFs: Alekhin MRST2001 and CTEQ6 Alekhin, MRST and CTEQ6 sets and their error PDF sets are implemented and used in the previous codes. Alekhin fit is performed by minimizing a c2 functional containing covariance matrix and using NPDF=14 PDF parameters and aS MRST and CTEQ6 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 Xi Pt(GeV) 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 uncertainty band limits Alekhin, MRST and CTEQ6 uncertainties are compared and results are expressed with CTEQ6 S. Ferrag

PDF comparison: normalized to CTEQ6 set Higgs mass range: 100-1000 GeV Range of interest Alekhin (anti)quarks are the highest S. Ferrag

Uncertainties behaviour: up quark low x quark intermediate x quark low x intermediate x quark High x quark 3 ranges, low x quarks: x < few 10-3 intermediate x : few 10 -3 < x < 0.7 high x quarks: 0.7 < x S. Ferrag

Uncertainties behaviour: gluons 0.3 High x gluon High x gluon 2 ranges, high x gluons: 0.3 < x other gluons: x < 0.3. Different range limits (compared to quarks). S. Ferrag

NLO Higgs cross sections at hadron colliders 0.1 pb limit, LHC, gg and Hqq : Mhiggs in 100 - 1000 GeV ttH and HW : Mhiggs in 100 - 200 GeV Tevatron, gg and HW : Mhiggs in 100 - 200 GeV S. Ferrag

Impact on the Higgs production: gluon fusion 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) S. Ferrag

Impact on the Higgs production: WH LHC: constant (intermediate x quarks), ~ 4% Tevatron: increasing (intermediate x + high x quarks), ~ 5% to 7% Higher central values for Alekhin ~12% LHC and 8% Tevatron S. Ferrag

Impact on the Higgs production: Hqq and ttH Hqq: constant (intermediate x quarks), ~ 4% (100-1000 GeV) Htt : top pair, smoothly increasing ~ 5% to 7% (100-200GeV) (intermediate x quarks + high x gluons) Higher and decreasing Alekhin central values: (+14% to +6% in Hqq ) (+ 7% in Htt) S. Ferrag

Conclusion Only experimental uncertainties are spread into PDF uncertaities. Theoritical uncertainties, choice of data and difference in traitement of experimental uncertainties are seen as dispersion between different sets predictions. Alekhin intermediate x (anti)quarks are the most important. Uncertainties du to PDFs are ~ 5 to 10 % in Higgs production. CTEQ6 uncertainties are 2 times larger than MRST ones: number of parameters (quadratic summation) different quantity Dc2 DCTEQ6 > DAlekhin > DMRST High x gluons uncertainties are more important then high x quarks ones. S. Ferrag