next up previous
Next: heavy quark production Up: Measurements of Gluon Previous: Measurements of Gluon

high-pT prompt photon production

One of the promising methods to probe the gluon helicity distribution is the asymmetry measurement for prompt photon production with high transverse momentum. In pp collisions, the production is dominated by the gluon Compton graph ( 90%) and annihilation graph ( 10%) shown in Figure 2. Thus, the cross section is quite sensitive to the gluon distribution in the proton.

  
Figure 2: Dominant contributions to high- prompt photon production in pp collisions, (a) gluon Compton and (b) annihilation processes.

If the polarization of anti-quark is small (this can be checked in our measurement as discussed in the next section), the asymmetry is also dominated by the gluon Compton, and allows simple representation of the longitudinal spin asymmetrygif

where , represents the partonic asymmetry for gluon Compton process [8]. By using the knowledge on the quark helicity distributions, the gluon helicity distribution will be extracted from the measured asymmetries.

The yield of the prompt photon production has been estimated with PYTHIA [9], one of the widely used QCD event generators and summarized in Table 2 and Table 3. Assuming that overall contribution of is about 0.2, the sensitivity of the measurement of the gluon helicity distribution has been evaluated and also listed in the tables. A typical error of the measurement will be 3-20% at 0.1<x<0.3 in pp collisions at GeV, and 1-5% at 0.05<x<0.1 in pp collisions at GeV.

  
Table 2: Expected yield for prompt photon production at =200 GeV and expected sensitivities for gluon helicity distribution.

  
Table 3: Expected yield for prompt photon production at =500 GeV and expected sensitivities for gluon helicity distribution.




next up previous
Next: heavy quark production Up: Measurements of Gluon Previous: Measurements of Gluon

Naohito Saito
July 3, 1996