S. Ferrag

Impact of PDF uncertainties on Higgs

production at LHC (hep-ph/0310209) Samir FERRAG

University of OSLOA. DJOUADI (Paris, Montpellier)

CERN, Mar 26-27 2004

– Introduction: Higgs production– PDF uncertainties (MRST, CTEQ6 and Alekhin)– Uncertainties behaviour: quarks and gluon components– Impact on the Higgs production and comparison

S. Ferrag

Standard Model Higgs production

• NLO cross section of 4 Higgs production processes:

**, Httqqgg

Hgg

qqHVVqq

HVqq

• Used programs: V2HV, VV2H, Higlu and HQQ

http://mspira.home.cern.ch/mspira/proglist.html

* * choose scale where NLO = LO and use NLO PDF with LO cross section

NLO program were not public

S. Ferrag

Uncertainties from PDFs: Alekhin MRST2001 and CTEQ6

X0

Xi

Pt(GeV)

• 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 2 functional containing covariance matrix and using NPDF=14 PDF parameters and S

• 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 by and get the error matrix =100 in CTEQ6, =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)

Si: error PDF X(Si): error PDF dependant cross section

X0: predicted cross section (computed with nominal PDFs )

Xi + =Xi-X0 if Xi > X0 and Xi

-- =X0-Xi if Xi < X0

Quadratic summation to get uncertainty band limits

• Construction of the cross section uncertainties band:

• Alekhin, MRST and CTEQ6 uncertainties are compared and results are expressed with CTEQ6

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PDF comparison: normalized to CTEQ6 set

• Range of interest• Alekhin (anti)quarks are the highest

• Higgs mass range: 100-1000 GeV

S. Ferrag

Uncertainties behaviour: up quark

High x quarkintermediate x quarkintermediate x quarklow 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

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0.3

Uncertainties behaviour: gluons

High x gluonHigh 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 GeVTevatron, 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

• CTEQ6 > Alekhin > MRST

• High x gluons uncertainties are more important then high x quarks ones.