New Qcd Results from the H1 Experiment at Hera 1. Measurement of the Proton Structure Function F L 2. Inclusive and Multi-jet Production

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Abstract

New QCD results obtained by the H1 Collaboration are summarized. These results are based on data taken in e ± p collisions at HERA I (1994-2002) and HERA II (2003-2007) corresponding to an integrated luminosity of almost 0.5 fb −1. The data were taken at an electron 1 beam energy of Ee = 27.5 GeV and proton beam energies of Ep = 820 GeV, 920 GeV, 575 GeV and 460 GeV. A direct measurement of F L , jet production and measurement of αs, production of heavy quarks and diffractive photo-production of jets are presented. The first direct measurement of the proton structure function F L (x, Q 2) performed by the H1 collaboration at HERA is presented. It is based on the measurement of the inclusive neutral current (NC) deep inelastic scattering (DIS) cross section which is given at low Q 2 by: Here x is the Bjorken variable which in the Quark Parton Model (QPM) corresponds to the fraction of the proton momentum carried by the struck quark, Q 2 is the negative four-momentum transfer squared, y = Q 2 /sx is the inelasticity and s = 4E p E e is the center of mass energy squared. The direct measurement of the proton structure function F L at HERA is based on the measurement of the reduced cross section (see Eq. 1) at the same values of x and Q 2 by varying the inelasticity y. This is achieved by changing the proton beam energy E p = 920, 575, 460 GeV while keeping the positron beam energy of E e = 27.5 GeV constant which leads to a variation of the center of mass energy. The reduced DIS cross section σ r (x, Q 2 , y) is measured in the range 12 ≤ Q 2 ≤ 800 GeV 2 and 0.00024 ≤ x ≤ 0.0015. The structure function F L is determined from linear fits to the σ r (x, Q 2 , y) as a function of y 2 /Y + using statistical and systematic uncertainties. The measurements of the structure function F L are performed as function of x and Q 2 as shown in Fig. 1. The results are in good agreement with the expectations from the perturbative QCD (pQCD) confirming a dominant gluon contribution at low x. Jet production is directly sensitive to α s and allows for a precision test …

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