1. A. DJOUADI (Paris, Montpellier)
Impact of PDF
uncertainties on Higgs production at LHC (hep-ph/ )
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
S. Ferrag

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
S. Ferrag

3. 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

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

5. 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 < x < 0.7
high x quarks: < x
S. Ferrag

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).
S. Ferrag

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

8. Impact on the Higgs production: gluon fusion
LHC: smoothly oscillating (intermediate x) and increasing (high x)
~ 4-3% to 11% ( GeV)
Tevatron: increasing (high x gluons), ~ 7% to 15% ( GeV)
S. Ferrag

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
S. Ferrag

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

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.
S. Ferrag