Impact of PDF uncertainties on Higgs production at LHC (hep-ph/0310209)

1. 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

2. 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

3. X0 Xi Pt(GeV) 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) • 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

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

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

6. 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).

7. 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

8. 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)

9. 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

10. 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)

11. 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.