Photon Production In Pp Collisions Research Articles

Isolated photon production in pp collisions at forward rapidities and high multiplicity events

Isolated photon production in pp collisions at forward rapidities and high multiplicity events

Color entanglement like effect in collinear twist-3 factorization

We study color entanglement effect for T-odd cases in collinear twist-3 factorization. As an example, we compute the transverse single spin asymmetry for direct photon production in pp collisions in pure collinear twist-3 approach. By analyzing the gauge link structure of the collinear gluon distribution on unpolarized target side, we demonstrate how color entanglement effect arises in the presence of the additional gluon attachment from polarized projectile. The result is consistent with that obtained from a hybrid approach calculation.

Predictions for the Isolated Prompt Photon Production at the LHC ats= 13 TeV

The prompt photon production in hadronic collisions has a long history of providing information on the substructure of hadrons and testing the perturbative techniques of QCD. Some valuable information about the parton densities in the nucleon and nuclei, especially of the gluon, can also be achieved by analysing the measurements of the prompt photon production cross section whether inclusively or in association with heavy quarks or jets. In this work, we present predictions for the inclusive isolated prompt photon production in pp collisions at center-of-mass energy of 13 TeV using various modern PDF sets. The calculations are presented as a function of both photon transverse energyETγand pseudorapidityηγfor the ATLAS kinematic coverage. We also study in detail the theoretical uncertainty in the cross sections due to the variation of the renormalization, factorization, and fragmentation scales. Moreover, we introduce and calculate the ratios of photon momenta for different rapidity regions and study the impact of various input PDFs on such quantity.

Partonic transverse momenta in non-relativistic hyper-central quark potential models

We investigate the impact of three-body forces on the transverse-momentum distribution of partons inside the proton. This is achieved by considering the three-body problem in a class of hyper-central quark potential models. Solving the corresponding Schrödinger equation, we determine the quark wave function in the proton and with appropriate transformations and projections we find the transverse-momentum distribution of a single quark. In each case the parameters of the quark potentials are adjusted in order to sufficiently describe observable properties of the proton. Using a factorization ansatz, we incorporate the obtained transverse-momentum distribution in a perturbative QCD scheme for the calculation of the cross-section for prompt photon production in pp collisions. A large set of experimental data is fitted using as a single free parameter the mean partonic transverse momentum. The dependence of 〈k T〉 on the collision characteristics (initial energy and transverse momentum of the final photon) is much smoother when compared with similar results found in the literature using a Gaussian distribution for the partonic transverse momenta. Within the considered class of hyper-central quark potentials the one with the weaker dependence on the hyper-radius is preferred for the description of the data since it leads to the smoothest mean partonic transverse-momentum profile. We have repeated all the calculations using a two-body potential of the same form as the optimal (within the considered class) hyper-central potential in order to check if the presence of three-body forces is supported by the experimental data. Our analysis indicates that three-body forces influence significantly the form of the parton transverse-momentum distribution and consequently lead to an improved description of the considered data.

Direct photons at forward rapidities in high-energy pp collisions

We investigate direct photon production in pp collisions at the energies of RHIC, CDF and LHC, at different rapidities employing various color-dipole models. The cross section peaks at forward rapidities due to the Abelian dynamics of photon radiation. This opens new opportunities for measurement of direct photons at forward rapidities, where the background from radiative hadronic decays is strongly suppressed. Our model calculations show that photon production is sensitive to the gluon saturation effects, and strongly depends on the value of the anomalous dimension.

Study of new scaling of direct photon production in pp collisions at high energies using MC simulation

The new scaling, z-scailing, of prompt proton production in pp collisions at high energies is studied: The scaling function H( z) is expressed via the inclusive cross section of photon production Ed 3 σ/ dq 3 and the multiplicity density of charged particles ρ( s) at pseudorapidity η = 0. Monte Carlo (MC) simulation based on the PYTHIA code is used to calculate the cross section and to study the scaling. The MC technique used to construct the scaling function is described. The H( z) dependence on the scaling variable z, the center-of-mass energy √ s at a produced angle of θ = 90 is investigated. The predictions of the Ed 3 σ/ dq 3 dependence on transverse momentum q⊥ at a colliding energy of √ s = 0.5, 5.0 and 14.0 TeV are made. The obtained results are compared with the experimental data and can be of interest for future experiments at RHIC (BNL), LHC (CERN), HERA (DESY) and Tevatron (Batavia).

Measurement of single spin asymmetry for direct photon production in pp collisions at 200 GeV/c

The single spin asymmetry for inclusive direct-photon production has been measured using a polarized proton beam of 200 GeV/c with an unpolarized proton target at −0.15 < xf < 0.15 and 2.5 < pt < 3.1 GeV/c at Fermilab. The data on the cross section for pp → γX at 2.5 < pt < 3.8 GeV/c are also provided. The measurement was done using lead-glass calorimeters and photon detectors which surrounded the fiducial area of the calorimeters. Background rejection has been done using these surrounding photon detectors. The cross section obtained is consistent with the results of previous measurements assuming a nuclear dependence of A 1.0. The single spin asymmetry, A N , for the direct-photon production is consistent with zero within experimental uncertainty.

Direct photon production at the CERN ISR

A measurement of direct photon production in pp collisions at a center of mass energy ∝ s=63 GeV is reported. Arrays of lead-glass calorimeters and multiwire proportional chambers were used as photon detectors. Data are presented in the transverse momentum range from 4.5 to 10 GeV/ c and compared with QCD predictions. The event structure of this sample is compared with that of a set dominated by high transverse momentum π O ́ ' s .

Direct photon production beyond leading log approximation—q+q→γ+q+q contribution

Theq+q→γ+q+q contribution (for incoming quarks of equal and different flavours) to the next-to-leading correction for the direct photon production inpp collisions is calculated, analyzed in terms of double moments and compared with the data. The dimensional regularization method is used and the final state Bremsstrahlung infinities are regularized by an angular cut-off. The correction is found to be 30–40% of the Born contribution providing a better description of the data.

High-p T direct photon production inpp collisions

Direct photon and neutral-pion production have been measured inpp collisions at the CERN ISR for 30<\(\sqrt s \)<63 GeV and transverse momenta up to 12 GeV/c. The direct photon signal relative to neutral-pion production increases withpT and shows little\(\sqrt s \)-dependence. Results are reported from a variety of running conditions, and details are given on the method of analysis and on the evaluation of systematic errors for the inclusive cross-section of single-photon and neutral-pion production.

An analysis of intermediate transverse momentum pion and photon production inpp collisions through a QCD resummation mechanism

We propose a resummation of QCD radiative corrections in large transverse momentum hadronic processes, based on the introduction of an infrared cut-off, linked to the confinement radius. An analysis of the inclusive reactionspp → π0X andpp → γX and of γ/π0 ratio is presented.

High transverse momentum pion and photon production in pp collisions at ISR energies

High transverse momentum ( p T) production of pions and prompt photons in proton-proton collisions is studied in a QCD model including “higher twist” contributions parametrized by constituent interchange model. QCD scaling violations are included and comparisons are made with ISR data on invariant cross sections and the γ π 0 ratio. Studies of the away-side jet and charge angular distributions are proposed in order to isolate the various subprocesses contributing to high p T production, in particular that involving the trigluon coupling of QCD.

A measurement of direct photon production at large pT at the CERN ISR

We have measured direct photon production in pp collisions at the CERN intersecting storage rings for c.m. energies 31 < √ s < 63 GeV and transverse momenta up to 9GeV/ c, using segmented lead/liquid-argon calorimeters. The ratio of direct photon to π 0 production is significantly larger than zero, starting at p T ≈ 4 GeV/ c and increasing to values of about 0.4 at 9GeV/ c. No significant √s dependence is seen.

Direct production of high pT single photons in pp collisions at the CERN ISR

Single photon production in pp collisions at 30 < √ s < 62 GeV has been measured with liquid-argon-lead calorimeters at the CERN ISR. This process remains approximately constant with increasing √ s. For fixed √ s, the single photon to π 0 ratio increases strongly with increase in p T . The γ π 0 ratio is about 0.2 for p T above 4.5 GeV/c.

Comparison of direct photon production in pp collisions at [formula omitted] and 53.2 GeV

We present data obtained at the ISR, on the determination of the ratio R = γ π 0 at s = 30.6 GeV and we compare the results with our previous measurement at s = 53.2 GeV. The ratio R = γ π 0 integrated over the interval 0.1 ⩽ χ T ⩽ 0.2 is (1.6 ± 0.5) × 10 −2 and we obtain an indication of a universal χ T dependence.

Single direct photon production in pp collisions at √ s = 53.2 GeV in the pt interval 2.3 to 5.7 GeV/ c

We report the results of an experiment made at the CERN ISR to investigate the possible diret production of single photons in pp collisions at √ s = 53.2 GeV at 90° and in the p t interval 2.3 to 5.7 GeV/ c. The value of the ratio R = n γ / n π 0 is compatible with zero for low p t ⪅ 3 GeV/ c but, in spite of the large error, shows a trend to increase for larger p t.