Complete next-to-leading order corrections for direct photon production by a polarized beam and target

Contogouris, A.P.; Kamal, B.; Merebashvili, Z.; Tkachov, F. V.

doi:10.1016/0370-2693(93)90304-z

Cited by 41 publications

(39 citation statements)

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“…The ∆a, ∆b (a, b = q,q, g) are the polarized parton densities, and the transition of parton c into the observed π 0 is described by the (spin-independent) fragmentation function D π c . We emphasize that all tools are in place now for treating the spin reactions relevant at RHIC to next-to-leading order (NLO) pQCD [13][14][15][16]. NLO corrections significantly improve the theoretical framework; it is known from experience with the unpolarized case that the corrections are indispensable in order to arrive at quantitative predictions for hadronic cross sections.…”

Section: Accessing Gluon Polarization ∆Gmentioning

confidence: 99%

QCD spin physics: Status and prospects for relativistic heavy-ion collider

Vogelsang

2004

Pramana - J Phys

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Section: Accessing Gluon Polarization ∆Gmentioning

confidence: 99%

QCD spin physics: Status and prospects for relativistic heavy-ion collider

Vogelsang

2004

Pramana - J Phys

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“…The fact that [4,6] have provided both consistent LO and NLO parton sets in all cases, enables us to more reliably study the perturbative stability of the cross sections and asymmetries. This is again a major improvement with respect to the previous studies [8,10].The quantity to be studied in prompt photon experiments with polarized beam and target is the double-spin asymmetrywhere dσ ++ (dσ +− ) denotes the cross section for the prompt photon being produced by protons with same (opposite) helicities. Two types of processes contribute to the prompt photon production cross section: the so-called 'direct' piece, where the photon is emitted via a pointlike (direct) coupling to a quark, and the fragmentation piece, in which the photon originates from the fragmentation of a final state parton.…”

mentioning

confidence: 92%

“…From the experience in the unpolarized case, the inclusion of NLO corrections is expected to be quite important 1 in order to make reliable predictions. The main shortcoming of the studies [8,10] was, however, that spin-dependent parton densities evolved only in LO had to be used at that time. Having sets of NLO polarized parton distributions available now, we can obviously put the corresponding predictions as well as the assessment of their theoretical uncertainties such as their scale dependence on a much firmer basis, which is the purpose of this paper.…”

mentioning

confidence: 99%

“…On the other hand, in the unpolarized case the fragmentation piece is known to be subdominant -even though not negligible -at fixed target energies (see, e.g., [14]). The fragmentation contribution to the polarized cross section which was omitted altogether in [8,10], will be included on a LO basis in this paper. Even though this is not strictly consistent in the framework of a NLO calculation, it is the best 'state-of-the-art' procedure and also appears reasonable in view of the fact that the K-factor K f rag ≡ σ f rag N LO /σ f rag LO for the fully inclusive fragmentation part generally turns out to be very close to unity when calculated for the unpolarized case.…”

mentioning

confidence: 99%

“…Details of this are given in the appendix. We note that we refrain from using the results of [8] for the NLO corrections to the d∆σ γ ab since it is not obvious whether the γ 5 scheme used in [8] provides a consistent regularization and can be related in any way to the HVBM prescription.Unfortunately, the NLO corrections to the polarized fragmentation subprocess cross sections d∆σ i ab (i = q,q, g) are still unknown as mentioned above. For this reason we stick to a pure LO calculation for this contribution, using the corresponding spin-dependent LO subprocess cross sections of [24] along with the respective LO sets of polarized parton distributions of [4,6], and the LO expression for α s (as entailed in (4) 2a shows the NLO predictions for the spin-dependent cross sections d∆σ/dp T dη as functions of the prompt photon's transverse momentum p T at c.m.s.…”

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Inclusive prompt photon production in polarized pp collisions at HERA-

Gordon

Vogelsang

1996

Physics Letters B

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We present a NLO study of inclusive polarized prompt photon production in a conceivable fixed target pp mode of HERA with longitudinally polarized protons at √ s = 39 GeV.We analyze the sensitivity of the corresponding double spin asymmetry to the proton's polarized gluon distribution ∆g and estimate the expected statistical precision in its determination. The main theoretical uncertainties in the predictions are examined.It has recently become possible to perform a complete and consistent study of longitudinally polarized deep-inelastic scattering (DIS) in next-to-leading order (NLO) of QCD, since the spin-dependent two-loop splitting functions, needed for the NLO evolution of the polarized parton distributions, have become available [1,2]. A first such phenomenological NLO analysis, taking into account all available experimental data on polarized DIS [3] has been presented in [4], followed by the analyses [5,6]. The studies of [4,6] have shown that present polarized DIS data are still quite far from providing accurate knowledge about the nucleon's spin-dependent sea quark and gluon distributions. This holds true, in particular, for the polarized gluon density ∆g, the x-shape of which seems to be hardly constrained at all [4,6] by the DIS data, even though a tendency towards a sizeable positive total gluon polarization, 1 0 ∆g(x, Q 2 = 4 GeV 2 )dx 1, was found [4,5,6]. Thus, there is clearly some need for independent information on ∆g. For this purpose, it seems expedient to look at processes for which ∆g enters in leading order (LO) already, rather than as a NLO correction as for the spin-dependent DIS structure function g 1 . One of such processes is inclusive large-p T prompt photon production in collisions of longitudinally polarized protons, p p → γX [7,8,9,10]. In the unpolarized case where this process has been studied in a huge number of experiments it has been an invaluable tool for pinning down the proton's unpolarized gluon distribution g(x, Q 2 ) [11,12,13,14]. Hence prompt photon production with polarized beams seems a promising source for obtaining information on ∆g.It is being discussed as one future option for HERA to polarize its 820 GeV proton beam. If this can be achieved, one could use the beam in a fixed target experiment, scattering it off an internal polarized nucleon target. This conceivable constellation, dubbed , would yield √ s ≈ 39 GeV and thus could provide information complementary to that obtained from planned similar spin physics experiments at much higher energies at the RHIC collider [16]. Theoretical predictions for polarized prompt photon production at √ s ≈ 40 GeV have been made in the past [8,10], taking into account the spin-dependent 'direct' subprocess cross sections for ab → γX (a, b = q,q, g) including their full NLO QCD corrections as calculated in [8,9]. From the experience in the unpolarized case, the inclusion of NLO corrections is expected to be quite important 1 in order to make reliable predictions. The main shortcoming of the studies [8,10] was, however...

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Aspects of χ and ψ production in polarized proton-proton collisions

Doncheski

Robinett

1994

Z. Phys. C - Particles and Fields

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Several topics of relevance to low transverse momentum ψ and χ 1,2 (cc) production in polarized proton-proton collisions are discussed. The leading O(α 3 S ) contributions to the low p T χ 1 production cross-sections via gg, qg, and qq initial states are calculated as well as the corresponding spin-spin asymmetries. We find that χ 1 production increases relative to direct ψ and χ 2 production, providing up to 25% of the observable e + e − pairs arising from ψ decays in pp collisions at √ s = 500 GeV . The spin-dependence of χ 1 production, however, is much smaller than for either direct ψ or χ 2 production and so will likely be far less useful than either process in probing the polarized gluon structure function of the proton. A subset of the O(α 3 S ) radiative corrections to χ 2 production involving initial state quarks are also performed and compared to leading order gg → χ 2 predictions.

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Complete next-to-leading order corrections for direct photon production by a polarized beam and target

Cited by 41 publications

References 15 publications

QCD spin physics: Status and prospects for relativistic heavy-ion collider

QCD spin physics: Status and prospects for relativistic heavy-ion collider

Inclusive prompt photon production in polarized pp collisions at HERA-

Aspects of χ and ψ production in polarized proton-proton collisions

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