The QCD factorization theorem provides us with a framework where distinct parameters can be indepen- dently studied in order to interpret the experimental re- sults. Prominent among them we find the parton distri- bution functions which correspond to the momentum dis- tributions of partons inside a proton. The extraction of the parton distribution function from experimental data and theoretical approach is a complicated task [1, 5]. The uncertainties grow with diminishing x$_{B}$ and are generally very much larger for gluons than for quarks. At the LHC (Large Hadron Collider) energies, the gluons will play an important role to understand the new physics. Some QCD analysis of parton distribution has been done [1]. At this energies, one will be able to explore regions of small x$_{B}$ as shown in Table I for minimum bias events. In order to describe the recoil and sphericity variables and their behavior as function of the parton distribu- tion function of the gluon used, we generated a sample of PYTHIA 6.214 minimum bias events [6]. The generation incorporates some parameters proposed as ATLAS tune , based on reference [7]. This tuning parameters were fixed to describe the experimental minimum bias data of UA5 and CDF experiments. The pseudorapidity and trans- verse momenta distribution were the first variables fitted in this tuning. Setting from these fits after that, predic- tion of the properties of minimum bias and underlying event at LHC energy were scaled. We have used this version of PYTHIA to implant two different parton distribution functions: ZEUS2005 [8] and CTEQ5L [9]. The latter PDF was extracted from a global analysis to several experimental data while the former is extracted only from HERA data. Plotting the ratio of the two gluon distribution as we have done in Fig. 1, we see that at different energies and Q values they differ substantially, the lowest values of x showing the largest difference. In Fig. 2 we show in the top panel the mean multi- plicity variation with the sphericity variable obtained at central pseudorapidity. We observe an interesting depen- dence on the PDF used: the mean multiplicity at high x -5 10 -4 10 -3 10 -2 10 -1 10 ) 2 (x,Q CTEQ )/xf 2 (x,Q ZEUS xf 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4  = 200 GeV ) s = 6.3 GeV (   = 900 GeV ) s = 20.0 GeV (   = 10 TeV ) s = 142.1 GeV (  sphericities is much higher for the CTEQ5L PDF than for the ZEUS one. The phenomenon is the most accen- tuated in the case of the 10 TeV collisions where the x$_{B}$ value reached is also the smallest. The bottom part of Fig. 2 illustrates this fact, it shows the behavior of the ratio of the mean multiplicities for the three cases as a function of sphericity. The studies displayed here are within the reach of all the LHC experiments, though we have done the simula- tion for the case of a relatively small acceptance detec- tor which has the capability to detect low charged par- ticle momenta. We consider only primary tracks within | η | ≤ 0 . 9 and p$_{t}$ ≥ 0 . 5 GeV / c defined according to refer- ence [10]. In this context they are the particles produced in the collision, including products of strong and electro- magnetic decays, but excluding feed-down products from strange weak decays and particles produced in secondary interactions. In Fig. 3 we show the ratio of the sphericity distri- butions obtained for the three energies. One observes that in all cases the difference between the two PDF’s increases with growing spherificity but much more so in the case of the 10 TeV simulations. This is due to the smaller x$_{B}$ in that case, where the differences between the two PDF’s are the largest. The strong slope in case of 10 TeV data demonstrate the sensitivity of the approach. Next, the recoil variable is computed according to Eq. 2, the results are shown in Fig. 5 where a charac- teristic behavior of the ratio of the mean R values is ob- served for the 3 energies. Namely, The ZEUS PDF has a larger momentum inbalance than CTEQ5L. We explain the feature by the fact that, due to the smaller rise of the gluon PDF in ZEUS one is confronted with an emission of particles resulting from collisions of partons of differ- ent momenta, while in the case of the more peaky gluon 2 FIG. 1: Ratio of the gluon contributions for the ZEUS and CTEQ5L parton distribution functions, the ratio is shown for different Q values corresponding to the mean Q values obtained from the simulations at 0.2, 0.9 and 10 TeV, respec- tively III. THE PARTON DISTRIBUTION FUNCTIONS IV. RESULTS ON EVENT SHAPE VARIABLES AND PDF OF GLUONS √ s x B Collider 200 GeV ∼ $^{5}$× 10 − 3 RHIC 900 GeV ∼ 10 − 3 TEVATRON/LHC 10 TeV 10 − 4 LHC TABLE I: The x B values for low p t production at different en- ergies. The evaluation was done at central rapidity, assuming p t = 500 MeV/c.