Semi-inclusive deep inelastic scattering at small-x

We study the semi-inclusive hadron production in deep inelastic scattering at small-x. A transverse-momentum-dependent factorization is found consistent with the results calculated in the small-x approaches, such as the color-dipole framework and the color glass condensate, in the appropriate kinematic region at the lowest order. The transverse-momentum-dependent quark distribution can be studied in this process as a probe for the small-x saturation physics. Especially, the ratio of quark distributions as a function of transverse momentum at different x   demonstrates strong dependence on the saturation scale. The Q²$Q^2$ dependence of the same ratio is also studied by applying the Collins–Soper–Sterman resummation method.     

Hadronic jets with a large Q⊥ lepton pair trigger

We propose to observe hadron jets in correlation with large Q⊥ transverse momentum lepton pairs. This would allow to test the theoretical idea that the large transverse momentum of the pair is mainly produced through a scattering subprocess $\text{a}\text{+}\text{b}\text{→}\text{c}\text{+γ}{}^1$. The quantum number content of these jets is a specific signature of the subprocess, especially of those involved in perturbative QCD.     

Features of diffractive scattering and the nature of the N1(1400) observed in NN→N(Nπ) reactions at 5.7 GeV/c

The results for the diffractive scattering contribution ($\text{F}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^0$) obtained in a cross channel isospin analysis of the $\text{N}\text{N}\text{→}\text{N}\text{(}\text{N}\text{π)}$ reactions at 5.7 GeV/c are compared with those obtained for other ZN → Z′(Nπ) reactions where Z stands for N, π and the carbon nucleus. The dependence of the diffractive scattering on the mass M_πN and the momentum transfer t seems very weakly related to the nature of Z and the incident momentum.A comparison between amplitudes of the isospin exchange I_ex = 0 and I_ex = 1 leading to $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ production shows that $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1492)}$ and $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1670)}$ are produced essentialy through I_ex = 1.     

Study of the Kππ system produced in K−p → KππN reactions at 14.3 GeV/c

We have studied the $\text{K}\text{ππ}$ system in the 14.3 GeV/c reactions K^?p → K^?π⁺π^?p, $\text{K}{}^{\mathrm{?}}\text{p}\text{→}\text{K}{}^0\text{π}{}^{\mathrm{?}}\text{π}{}^0\text{and}\text{K}{}^{\mathrm{?}}\text{p}\text{→}\text{K}{}^0\text{π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{n}$. The data have been obtained from a 500 000 picture exposure of the CERN 2m HBC. The first two final states are dominated by Q-production in the Kππ system; there is also an L-signal at M (Kππ) ～ 1.75 GeV. The reaction cross sections are compared to K^?p data at other energies. We discuss the Kππ mass dependence of the diffractive production slope. Evidence is presented for a Q^?p versus Q⁺p differential cross section cross-over around |t| = 0.17 GeV². A t-channel isospin analysis for the $\text{KN}\text{→}\text{K}\text{1(890)π}\text{N}$ channels in the Q-region shows that the I = 1 exchange amplitude is $\text{? 10\%}$ of the dominant I = 0 exchange amplitude. The Kππ decay distributions indicate a predominant J^P = 1⁺ state in the Q-region, and an important J^P = 2^? contribution in the L-region. We find neither s-channel nor t-channel helicity conservation at the meson vertex in the Q- or L-regions. The Kπ angular correlation moments within the Kππ diffractive system are characteristic of Kπ elastic scattering, suggesting a π-exchange Deck-type production mechanism. There is evidence for a Kf⁰ and κπ contribution (where κ is the J^P(Kπ) = 0⁺ state) to the diffractive Kππ system. A fit to the $\text{K}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{and}\text{K}{}^0\text{π}{}^{\mathrm{?}}\text{π}{}^0$ Dalitz-plot distributions for the Q-re gion indicates that the ratio of $\text{K}\text{?}\text{to K}{}^1\text{π}$ decay amplitudes decreases with increasing Kππ mass.     

Absorptive parts of the hadron-nucleus amplitude and multiparticle production on nuclei

The process of the hadron-nucleus interaction is considered in the framework of Glauber theory. A two-channel model is used for inelastic shadow corrections due to low-mass diffractive jets. It is shown that inelastic hadron-nucleus cross sections are connected with the cuts of a number of hadron-nucleon blobs in the elastic scattering amplitude. The relations derived between contributions to the absorptive part of the amplitude from cuts of different kinds satisfy the Abramovsky-Gribov-Kancheli rules up to a factor which is determined by the ratio of the inelastic and total hadron-nucleon cross sections. The inclusive spectrum in the central region is proportional to $\text{A}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$. The average charged multiplicity increases with A slower than $\text{A}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ due to energy conservation. The results obtained are in good agreement with experimental data on the average multiplicities and distributions of charged particles.     

Doubly charmed exotic mesons: A gift of nature?

We study doubly charmed exotic states by solving the scattering problem of two D   mesons. Our results point to the existence of a stable isoscalar doubly charmed meson with quantum numbers (I)JP=(0)¹⁺$(I)J^P=(0)1^{+}$. We perform a thorough comparison to the results obtained within the hyperspherical harmonic formalism. Such exotic states could be measured at LHC and RHIC. Their experimental observation would, for the first time, confirm the contribution of multiquark structures to hadron spectroscopy.     

Rotation-vibration analysis of the Coriolis-coupled ν5g, ν6g, ν8g and ν9 bands of H2CCO

Medium resolution infrared grating spectra of gaseous ketene, H₂CCO were recorded between 1000 and 400 cm^?1, both at instrument temperature (40°C) and with cooling (?40°C). Interferometric Fourier spectra were also measured at ?70°C with resolution 0.22 cm^?1 between 450 and 330 cm^?1. The K structure of the fundamentals ν₅, ν₆, ν₈, and ν₉ was assigned. These fundamentals are coupled by a-axis Coriolis interactions. These couplings were analysed on the symmetric top basis for setting up the perturbation matrix and by utilizing the K-dependent Coriolis shifts of levels. A preliminary analysis of the Coriolis intensity anomalies was also undertaken.Band center values from combination differences are $\text{ν}{}_5{}^0\text{= 587.30 (27)}$ and $\text{ν}{}_6{}^0\text{= 528.36 (39)}\text{cm}{}^{\mathrm{?1}}$. Synthetic spectra indicate the band origins of ν₈ and ν₉ to be close to 977.8 and 439.0 cm^?1, respectively. Estimates of Coriolis coupling constants obtained from synthetic spectra are $\text{ζ}{}_{58}{}^{\mathrm{a}}\text{= + 0.33 (5)}$, $\text{ζ}{}_{68}{}^{\mathrm{a}}\text{= + 0.714 (20)}$, $\text{ζ}{}_{59}{}^{\mathrm{a}}\text{= ? 0.774 (20)}$, and $\text{ζ}{}_{69}{}^{\mathrm{a}}\text{= ? 0.30 (2)}$. Approximate ratios of unperturbed vibrational transition moments obtained from spectral simulations are $\text{M}{}_8{}^0\text{:±iM}{}_5{}^0\text{:±iM}{}_6{}^0\text{:M}{}_9{}^0\text{≈ +2:?9:+10:+0.5}$.     

Electromagnetic effects in the production of dimuons at large transverse momentum

The effects of single-photon corrections to the simple Drell-Yan mechanism $\text{(}\text{q}\text{q}\text{→ γ}{}^1\text{→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{)}$ are studied for massive dimuons at large transverse momentum in the processes $\text{π}{}^{\mathrm{?}}\text{p}\text{→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{X and}\text{p}\text{p}\text{→ μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{X}$. It is found that single-photon emission by the muons constitutes an important correction to the effects of single-gluon emission by the quarks for very massive (M_μμ² ? m_μ²) muon pairs.Interference of the amplitude for photon emission from the muons with that for radiation from the quarks generates an asymmetry in the muon angular distribution. The forward-backward asymmetry is studied in detail as a function of pair mass and transverse momentum.     

Ambiguity of multipole analysis and new amplitudes of the γp → nπ+ process

A multipole analysis of the γp → nπ⁺ process using new data on the angular distributions of the polarized photon asymmetry has been made. At present the difference between the phase of the resonance amplitude $\text{M}{}_{\mathrm{1+}}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and the corresponding πN scattering phase shift is found to be ?2.5° ± 1.1°. The problem of the ambiguous solutions of a system of equations with respect to the multipole amplitude has been discussed.     

Low momentum transfer theorem for two photon exchange in lepton hadron scattering

The two photon exchange contribution to lepton-hadron scattering is considered. Under the assumptions of Lorentz covariance, gauge invariance, unitarity and analyticity, we prove a low momentum transfer theorem for the relevant amplitudes. Fixed energy dispersion relations tell us that their nonanalytic part, in the neighbourhood of t = 0, is given by the contribution of the two photon cut in the t-channel. The t-channel absorptive parts are obtained from unitarity. Their calculation has as input the two amplitudes corresponding to Compton scattering on the hadron with a pole contribution, and the continuum controlled at low t by the electromagnetic polarizabilities. By means of the dispersion integral, one proves the expansion $\text{k}{}_1\text{(s)+k}{}_2\text{(s)}\text{?t}\text{+k}{}_3\text{(s)t}\text{log}\text{(?t)+O(t)}$ for the continuum contribution, where k₁(s) is the only unknown. Explicit expressions are obtained for the pole contribution as M → ∞, where M is the hadron mass, and for the continuum when (?t) <Λ and (?t) < 4m², where m is the muon mass and Λ is a characteristic parameter of the hadron structure.     

Eikonal contributions to ultra high energy neutrino–nucleon cross sections in low scale gravity models

We calculate low scale gravity effects on the cross section for neutrino–nucleon scattering at center of mass energies up to the Greisen–Zatsepin–Kuzmin (GZK) scale, in the eikonal approximation. We compare the cases of an infinitely thin brane embedded in n=5$n=5$ compactified extra-dimensions, and of a brane with a physical tension MS=1 TeV$M_S=1\text{TeV}$ and MS=10 TeV$M_S=10\text{TeV}$. The extra dimensional Planck scale MD$M_D$ is set at ¹⁰³ GeV${10}^3\text{GeV}$ and 2×¹⁰³ GeV$2\times {10}^3\text{GeV}$. We also compare our calculations with neutral current standard model calculations in the same energy range, and compare the thin brane eikonal cross section to its saddle point approximation. New physics effects enhance the cross section by orders of magnitude on average. They are quite sensitive to MS$M_S$ and MD$M_D$ choices, though much less sensitive to n.     

e+e− annihilation into hadrons and the nature of the hadronic fixpoint

It is shown that the experimental behaviour of the ratio $\text{R =}\text{σ(}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→}\text{hadrons}\text{)}\text{σ(}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→ >}{}^{\mathrm{+}}\text{>}{}^{\mathrm{?}}\text{)}$ has a natural explanation if hadron interactions at short distances are described by an infrared stable fixpoint of the renormalization group. Experimental estimates of the limiting value of R, the 90% saturation point and of the anomalous dimension dθ of the trace of the energy momentum tensor are given.     

Proton-proton inelastic scattering at 0.5 TeV

We have measured at 500 GeV the cross section $\text{d}{}^2\text{σ}\text{dt dM}{}_{\mathrm{X}}{}^2$ for the inclusive reaction p + p → + X. We determine the mass spectrum of the diffractive peak to be $\text{1}\text{M}{}^{\mathrm{3.8\pm 0.2}}$ and the scaling part of the cross section to be dσ/dM_X² = (15.7±1.1)/smb/GeV².     

Spin-parity analysis of the nπ+ system produced in the reaction π+p → π+π+n at 16GeV/c

A spin-parity analysis of the nπ⁺ system produced in the reaction π⁺p → π⁺π⁺n at 16 MeV/c has shown apart from the mass enhancements associated with the known resonances Δ⁺(1238), N¹(1520) and N¹(1688) there is an enhancement peaked at M(nπ⁺) ? 1.35 GeV, ∑0.2 GeV wide. For masses below M(nπ⁺) ? 1.35 GeV this enhancement is predominantly due to $\text{J}{}^{\mathrm{P}}\text{=}\text{1}\text{2}{}^{\mathrm{?}}$ states, predominate. The presence of $\text{J}{}^{\mathrm{P}}\text{=}\text{1}\text{2}{}^{\mathrm{?}}$ states indicates that the rule ΔP = (?1)^ΔJ is strongly violated in the diffractive process N → Nπ, and hence it cannot be considered a specific characteristic of all diffractive processes.     

Twist-three fragmentation function contribution to the single spin asymmetry in pp collisions

We study the twist-three fragmentation function contribution to the single transverse spin asymmetries in inclusive hadron production in pp   collisions, p^↑p→h+X$p^{\uparrow }p\to h+X$. In particular, we calculate the associated derivative terms which dominate the spin asymmetries in these processes. With certain parameterizations for the twist-three fragmentation function, we estimate its contribution to the single spin asymmetry of π⁰${\pi }^0$ production at RHIC energy. We find that the contribution is sizable and might be responsible for the big difference between the asymmetries in η   and π⁰${\pi }^0$ productions observed by the STAR collaboration at RHIC.     

Some observations on the differential cross-sections for pp → K−K+

We present Legendre coefficients from fits to the differential cross-sections for $\text{p}\text{p→ K}{}^{\mathrm{?}}\text{K}{}^{\mathrm{+}}$ in the momentum range 0.8 to 2.4 GeV/c. The s-dependence of the cross-sections at small angles is examined for evidence of Reggeized baryon exchange, and a fit made to this channel and backward K⁺p elastic scattering. Comparisons are made with $\text{p}\text{p→ π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}$.     

Could saturation effects be visible in a future electron–ion collider?

We expect to observe parton saturation in a future electron–ion collider. In this Letter we discuss this expectation in more detail considering two different models which are in good agreement with the existing experimental data on nuclear structure functions. In particular, we study the predictions of saturation effects in electron–ion collisions at high energies, using a generalization for nuclear targets of the b-CGC model, which describes the ep HERA quite well. We estimate the total, longitudinal and charm structure functions in the dipole picture and compare them with the predictions obtained using collinear factorization and modern sets of nuclear parton distributions. Our results show that inclusive observables are not very useful in the search for saturation effects. In the small x region they are very difficult to disentangle from the predictions of the collinear approaches. This happens mainly because of the large uncertainties in the determination of the nuclear parton distribution functions. On the other hand, our results indicate that the contribution of diffractive processes to the total cross section is about 20% at large A   and small Q²$Q^2$, allowing for a detailed study of diffractive observables. The study of diffractive processes becomes essential to observe parton saturation.     

Off-diagonal generalized vector dominance and inelastic ep scattering

By also taking into account off-diagonal contributions to the virtual forward Compton amplitude, scaling in ep scattering is obtained from scaling of the total cross section for e⁺e^? annihilation into hadrons. The parameter which sets the scale for the q² dependence in ep scattering is calculated to be $\text{m}{}^2\text{? 0.61 m}{}_{\mathrm{?}}{}^2\text{? 0.36}\text{GeV}{}^2$.     

Elastic scattering slope and total cross section relations

The empirical equality of $\text{B}{}^2\text{σ}{}_{\mathrm{<mtext>t</mtext>}}$ is noted, for the pomeron terms in NN, πN, KN, ?N, ωN, and φN scattering, where B is the elastic slope parameter and σ_t is the total cross section. This ratio increases slowly with energy, but remains the same in all channels. This is equivalent to a relation between the diffractive interaction radii and opacities; the opacity scales with the square of the radius. We conjecture that this systematics extends to ψN scattering. We contrast $\text{B}{}^2\text{σ}{}_{\mathrm{<mtext>t</mtext>}}$ universaility with the slope predictions of an f-coupled pomeron model. Some other predictions of the f-dominance hypothesis are tested against data.