Peripheral pn production and decay angular distributions in the reaction π−p → (pn)p at 12 GeV/c incident momentum

The reaction $\text{π}{}^{\mathrm{?}}\text{p}\text{→ (}\text{p}\text{n}\text{)}\text{p}{}_{\mathrm{s}}$, where p_s is a slow proton, was measured at 12 GeV/c incident momentum with the CERN-OMEGA spectrometer. Both antiproton and proton were identified uniquely by electronics information. We obtained 1844 events with four-momentum Transfer squared in the range 0.13 ? |t| ? 0.33 GeV² and with invariant masses $\text{M(}\text{p}\text{n}\text{)}$ up to 2.5 GeV. The corresponding cross section in this t range is determined to be σ = 4 ± 0.4 μb. Extrapolating the differential cross section over the whole t range assuming dσ/dt ≈ exp(5.3t) we estimate a cross section of σ = 9.3 ± 2.0 μb. Comparison with data on $\text{π}{}^{\mathrm{?}}\text{p}\text{→ (}\text{p}\text{p}\text{)}\text{n}{}_{\mathrm{s}}$ (where n_s is a slow neutron) in the same t range shows that the $\text{(}\text{p}\text{n}\text{)}\text{p}{}_{\mathrm{s}}\text{and}\text{(}\text{p}\text{p}\text{)}\text{n}{}_{\mathrm{s}}$ cross sections have approximately the same magnitude.     

The A-dependence of J/ψ-particle inclusive distributions

The differential cross sections $\text{d}\text{σ}\text{d}\text{x}$ and $\text{d}\text{σ}\text{d}\text{p}{}_{\mathrm{t}}{}^2$ of inclusive J/ψ production by 43 GeV/c π^? off Be, Cu and W nuclei have been measured. Fitting $\text{d}\text{σ}\text{d}\text{p}{}_{\mathrm{t}}{}^2\text{～ A}{}^{\mathrm{\alpha }}\text{(p}{}_{\mathrm{t}}{}^2\text{)}$ we observed the increase of α with p_t².     

A study of the reactions π+p→ K+∑+ and K−p→π−∑+ at 10 GeV/c

For the first time, the reactions π⁺p→K⁺∑⁺ and K^?p→π^?∑⁺ have been studied in the same apparatus. This has been done at an adequately high momentum (10.1 GeV/c) to allow a check of the prediction of exchange degeneracy, that the differential cross sections should be converging at high energy. We have measured the cross section for momentum transfers t between t_min and t = ?0.3 (GeV/c)². We find that for both reactions the differential cross section shows an exponential fall, with no deviations right in to t =t_min (where some other experiments have shown a dip in the cross section). Furthermore, we find the magnitude of the differential cross sections to be closely similar at t = 0, with a ratio

$\text{R=}\text{(}\text{d}\text{σ}\text{d}\text{t)}{}_{\mathrm{t=0}}\text{(}\text{K}{}^{\mathrm{?}}\text{p}\text{→π}{}^{\mathrm{?}}\text{∑}{}^{\mathrm{+}}\text{)}\text{(}\text{d}\text{σ}\text{d}\text{t)}{}_{\mathrm{t=0}}\text{(π}{}^{\mathrm{+}}\text{p}\text{→}\text{K}{}^{\mathrm{+}}\text{∑}{}^{\mathrm{+}}$

However, the slope for the positive reaction is about 19% steeper than that for the negative reaction.     

The reactions K−p → K1− + nucleon at 3.13 and 3.3 GeV/c

Results are presented of a 12 event/μb bubble-chamber experiment; the reactions discussed in detail are $\text{K}{}^{\mathrm{?}}\text{p}\text{→}\text{K}{}^1\text{(890)}{}^{\mathrm{?}}\text{p, K}{}^1\text{(1420)}{}^{\mathrm{?}}\text{p and K}{}^1\text{(890)}{}^{\mathrm{?}}\text{Δ}{}^{\mathrm{+}}$.The K¹ (890)^?p channel is dominated by the forward peak. The suggestion of flattering at cos θ = 1 is more pronounced in $\text{(?}{}_{11}\text{+ ?}{}_{\mathrm{1?1}}\text{)}\text{d}\text{σ}\text{d}\text{t}$; which is mainly natural-parity exchange. Pseudoscalar exchange contributes to $\text{?}{}_{00}{}^{\mathrm{J}}\text{d}\text{σ}\text{d}\text{t}$; this is more sharply peaked in t. The value of $\text{(?}{}_{11}\text{? ?}{}_{\mathrm{1?1}}\text{)}\text{d}\text{σ}\text{d}\text{t}$ is somewhat larger than the upper limit from the dominant natural-parity exchange. There is significant structure in $\text{?}{}_{00}{}^{\mathrm{H}}\text{d}\text{σ}\text{d}\text{t}\text{at}\text{t ≈ ?0.6 (}\text{GeV}\text{/c)}{}^2$.The K¹ (1420)^?p channel is much more pronounced at 3.3 GeV/c than at 3.13 GeV/c, but is not markedly peripheral. The width of the K¹ (1420) in the 3.3 GeV/c data is 42 ± 12 MeV/c².The cross section for $\text{K}{}^{\mathrm{1?}}\text{Δ}{}^{\mathrm{+}}$ agrees with that expected from $\text{K}{}^{\mathrm{+}}\text{p}\text{→}\text{K}{}^1\text{Δ}$, assuming a single t-channel exchange. Our measured density matrix elements are consistent with a strong pseudoscalar exchange.     

Measurement of elastic scattering in antiproton-proton collisions at 52.8 GeV centre-of-mass energy

We measured the differential cross section for p?p and pp elastic scattering in the momentum-transfer range 0.01 <|t| < 1.0 GeV² at the CERN Intersecting Storage Rings with center-of-mass energy $\text{s}\text{= 52.8}\text{GeV}$. Fitting the differential cross section with an exponential [Aexp (bt)], we found $\text{b}\text{p}\text{p = 13.92 ± 0.59}\text{GeV}{}^{\mathrm{?2}}$ for |t| < 0.05 GeV², whilst for |t| > 0.09 GeV², $\text{b}\text{p}\text{p = 10.68 ± 0.26}\text{GeV}{}^{\mathrm{?2}}$. Using the optical theorem, we obtained for the total cross section $\text{σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{p}\text{p)= 44.86 ± 0.78}\text{mb}$ and, by integrating the differential cross section, we obtained for the total elastic cross section $\text{σ}{}_{\mathrm{<mtext>el</mtext>}}\text{(}\text{p}\text{p) = 7.89 ± 0.28}\text{mb}$. Calculations of σ_tot combining elastic-rate and total-rate measurements are also given. All of these measurements were also performed for pp scattering at the same energy, and the results for both reactions are compared.     

Upper bounds on the fine structure constant and on nucleon magnetic moments in terms of Compton scattering cross sections

We derive and compare with experimental data the bound

$\text{α??λm}{}_{\mathrm{<mtext>p</mtext>}}\text{?m}{}_{\mathrm{<mtext>p</mtext>}}\text{ν}{}^2{}_1\text{2π}{}^2\text{∫}\text{ν}{}_0\text{∞}\text{d}\text{ν′σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(ν′)}\text{(ν′}{}^2\text{+ν}{}^2{}_1\text{)}\text{+2πm}{}_{\mathrm{<mtext>p</mtext>}}\text{∫}\text{ν}{}_0\text{∞}\text{ν′}{}^2\text{d}\text{ν′σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(ν′)}\text{(ν′}{}^2\text{+ν}{}^2{}_1\text{){ν′}{}^2\text{(}\text{d}\text{σ}\text{d}\text{t)}{}_0\text{+πλ}{}^2\text{+2ν′|λ|}\text{π}\text{(}\text{d}\text{σ}\text{d}\text{t)}{}_0\text{?}\text{σ}{}^2{}_{\mathrm{<mtext>tot</mtext>}}\text{16π}\text{}}{}^{\mathrm{?1}}$

, where α is the fine-structure constant, m_p the proton mass, ν₀ the photo-pion production threshold, σ_tot and $\text{(}\text{d}\text{σ}\text{d}\text{t}\text{)}{}_0$ are the unpolarized total hadronic photo-absorption cross section on protons and the unpolarized forward differential cross section for proton Compton scattering at photon-lab energy ν′, and λ and ν₁ are any real numbers. We derive similar bounds on proton and neutron magnetic moments.     

Search for 4n IN π− double charge exchange reactions with heavy nuclei

A search for the existence of the tetraneutron has been made using the double charge exchange reaction $\text{π}{}^{\mathrm{?}}\text{+}{}^{208}\text{Pb}\text{→}{}^4\text{n + π}{}^{\mathrm{+}}\text{+}$ residuals for ⁴n production and the capture process in the same target, ${}^{208}\text{Pb}\text{+}{}^4\text{n}\text{→}{}^{212}\text{Pb}\text{+ γ}$, for the ⁴n detection. No event has been found, giving an upper limit for the product of the production cross section σ_p, the detection cross section σ_d and the ⁴n lifetime τ. Assuming 10^?18 ≦ τ ≦ 10^?9 sec it follows that σ_pσ_dτ ≦ 2.5 × 10^?65cm⁴ sec with 90 % confidence, and for $\text{τ ≧ 10}{}^{\mathrm{?9}}\text{sec}\text{, σ}{}_{\mathrm{<mtext>p</mtext>}}\text{σ}{}_{\mathrm{<mtext>d</mtext>}}\text{≦ 2.5 × 10}{}^{\mathrm{?56}}\text{cm}{}^4$ with 90 % confidence. The magnitude of this value is comparable to the experimental limit of the ⁴He(π^?, π⁺)⁴n cross section.     

Near 90° scattering in the channels K̄°p → π+Λ°, K̄°p → π+Σ° and KL°p → KS°p from 1.0 to 7.5 GeV/c

Differential cross sections for center of mass scattering angles near 90° are presented for the reactions $\text{K}\text{?}\text{°}\text{p}\text{→ π}{}^{\mathrm{+}}\text{Λ°}$, $\text{K}\text{?}\text{°}\text{p}\text{→ π}{}^{\mathrm{+}}\text{Σ°}$ and K_L°p → K_S°p in the momentum interval 1.0 to 7.5 GeV/c. The energy dependences of these cross sections are found to be equally well described by the parameterization: $\text{(}\text{d}\text{σ}\text{d}\text{Ω}\text{)}{}_{\mathrm{90°}}\text{∞ s}{}^{\mathrm{?2}}$ or $\text{(}\text{d}\text{σ}\text{d}\text{Ω}\text{)}{}_{\mathrm{90°}}\text{∞}\text{exp}\text{(? bp}{}_{\mathrm{\perp }}\text{)}$.     

Multiplicity distributions and double-scattering effects in π−d interactions at 360 GeV/c

Double-scattering effects are studied in π^?d interactions at 360 GeV/c. The partial cross sections $\text{σ}{}_{\mathrm{<mtext>N</mtext>}}\text{(π}{}^{\mathrm{?}}\text{d}\text{), σ}{}_{\mathrm{<mtext>N</mtext>}}\text{(“π}{}^{\mathrm{?}}\text{p}\text{”)}\text{and}\text{σ}{}_{\mathrm{<mtext>N</mtext>}}\text{(“π}{}^{\mathrm{?}}\text{n}\text{”)}$ are presented. The double-scattering probability per πd collision is found to be $\text{? = 0.15 ± 0.02}$. We have extracted the partial cross section X_N of the double-scattering plus interference contributions, and find that X_N obeys KNO scaling. The data are compared with various theoretical predictions.     

Measurement of the νμ and νμ nucleon charged-current total cross sections,and the ratio of νμ neutron to νμ proton charged-current total cross sections

The total ν_μ and $\text{ν}{}_{\mathrm{\mu }}$ nucleon charged-current cross sections have been measured in BEBC filled with deuterium and exposed to the wide-band neutrino and antineutrino beams at the CERN-SPS. Assuming a linear energy dependence for the cross sections, σ = aE(?_ν, we obtained the coefficients , where the quoted error is mainly systematic. The ratio of the cross sections is $\text{σ}{}_{\mathrm{<mtext>\nu </mtext><mtext>N</mtext>}}\text{/σ}{}_{\mathrm{<mtext>\nu </mtext><mtext>N</mtext>}}\text{= 0.53 ± 0.03}$.We also determined the ratio of the charged-current cross section for neutrino interactions on neutrons and protons R = σ_νn/σ_νp = 2.10 ± 0.08 (statistical) ±0.22 (sysetmatic). The dependence of R on the variables x, y and E_ν is discussed.     

A test of factorisation predictions for the fragmentation processes pp→π± at p momenta of 9.1 and 4.6 GeV/c

Relations have been derived between the invariant cross sections for various inclusive processes by assuming factorisation of the leading (pomeron) and non-leading (meson) trajectories. In this paper predictions for the invariant cross sections $\text{f(}\text{p}\text{p}\text{→π}{}^{\mathrm{\pm }}\text{)(2E}{}^1\text{/π√s)}\text{d}{}^2\text{σ/}\text{d}\text{x}\text{d}\text{p}{}^2{}_{\mathrm{\perp }}{}^2$ have been tested using data from $\text{p}\text{p}$interactions at 4.6 and 9.1 GeV/c.A large discrepancy between experiment and theory is apparent for the π^? data: in the π⁺ case the discrepancy is less marked but still present.     

Calculation of the γγ → ϱ0ϱ0 cross section at high energies

The processes with the cross sections not decreasing with energy become important at high energies. The simplest processes of this kind are γγ → V_i⁰V_j⁰ where V⁰ = ?⁰, ω, ?, ….. We calculate their cross sections in the high-energy small angle region s ? |t| ? μ². The cross section γγ → ?⁰?⁰ at high energies (s ? 10 GeV²) exceeds those of γγ → ππ, ?⁺?^? considerably. At $\text{s ? 10}{}^4\text{GeV}{}^2$ (this is the characteristic energy for the VLEPP and SLC colliders) and $\text{|t| ? 2}\text{GeV}{}^2$, the ratio $\text{(}\text{d}\text{σ/}\text{d}\text{t)(γγ → ?}{}^0\text{?}{}^0\text{)/(}\text{d}\text{σ/}\text{d}\text{t)(γγ → μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{) ? 70}$.     

Deviation from scaling in the triple-regge region of pp→ pX and fP universality

By generalizing $\text{f}\text{P}$ universality to Regge-particle “scattering” we obtain $\text{s}\text{d}\text{σ}\text{d}\text{t}\text{d}\text{M}{}^2\text{= F(}\text{s}\text{M}{}^2\text{,t)}$$\text{[1 +}\text{M}{}^{\mathrm{?1}}\text{b}{}_{\mathrm{<mtext>f</mtext>}}\text{(0)}\text{b}{}_{\mathrm{<mtext>P</mtext>}}\text{(0)}\text{]}$ for pp → pX, where b_f(t) and b_P(t) are the f and P Regge residues for, say, pp → pp. This agrees with the recent NAL data.     

Noncoplanar correlation spectra from the 2H(p, 2p)n reaction at Einc = 44.9 MeV

The differential cross section $\text{d}{}^3\text{σ/}\text{d}\text{Ω}{}_3\text{d}\text{Ω}{}_4\text{d}\text{E}{}_3$ for the ²H(p, 2p)n reaction at E_inc = 44.9 MeV is measured in noncoplanar geometry. The Amado model in general gives a good fit to the absolute cross section. The dependence of the cross section on the momentum of the undetected particle Q₅, on the scattering angle θ₃₄, as well as on the angle of the undetected particle is investigated.     

An isospin analysis of the reaction pN→NNπ from threshold to 2.90 GeV/c

We have performed an isospin analysis of single-pion production processes in antiproton-nucleon scattering from threshold to 2.90 GeV/c. Reactions used are $\text{p}\text{p}\text{→}\text{p}\text{p}\text{π}{}^0\text{,}\text{n}\text{p}\text{π}{}^{\mathrm{?}}\text{and}\text{p}\text{p}\text{→}\text{p}\text{p}\text{π}{}^{\mathrm{?}}$. Results show that σ₁, the total I=1 cross section, rises rapidly from threshold to reach a broad maximum around 2.5 GeV/c and σ₀, the I=0 cross section, rises from threshold and continues on a linearly rising trend at least up to 2.90 GeV/c. In the region of 2.9 GeV/c, σ₁ and σ₀ have comparable values, thus suggesting that considerable amount of $\text{I=}\text{1}\text{2}\text{N}\text{π}$ and $\text{N}\text{π}$ states is produced even in this low momentum region. We further determine that single pion production processes are not the source of the π₀ (2375,190) enhancement observed in the $\text{p}\text{p}$ and $\text{p}\text{d}$ total cross sections and may account for as much as 25±8% of the π₁ (2350,140) enhancement.     

Interference effects in 12C(p, γ)13N and direct capture to unbound states

Excitation functions of the capture reaction ¹²C(p, γ₀)¹³N have been obtained at θ_γ = 0° and 90° and E_p = 150–2500 keV. The results can be explained if a direct radiative capture process, E1(s and d → p), to the ground state in ¹³N is included in the analysis in addition to the two well-known resonances in this beam energy range $\text{[E}{}_{\mathrm{p}}\text{= 457(}\text{1}\text{2}{}^{\mathrm{+}}\text{)}$ and 1699 $\text{(}\text{3}\text{2}{}^{\mathrm{?}}\text{) keV]}$. The direct capture component is enhanced through interference effects with the two resonance amplitudes. From the observed direct capture cross section, a spectroscopic factor of C²S(l = 1) = 0.49 ± 0.15 has been deduced for the $\text{1}\text{2}{}^{\mathrm{?}}$ ground state in ¹³N. Excitation functions for the reaction ${}^{12}\text{C(p,γ}{}_1\text{p}{}^1\text{)}{}^{12}\text{C}$ have been obtained at θ_γ = 0° and 90° and E_p = 610–2700 keV. Away from the 1699 keV resonance the capture γ-ray yield is dominated by the direct capture process E1 (p → s) to the $\text{2366 (}\text{1}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound state. Above E_p = 1 MeV, the observed excitation functions are well reproduced by the direct capture theory to unbound states (bremsstrahlung theory). Below E_p = 1 MeV, i.e., E_p → 457 keV, the theory diverges in contrast to observation. This discrepancy is well known in bremsstrahlung theory as the “infrared problem”. From the observed direct capture cross sections at $\text{E}{}_{\mathrm{p}}\text{? 1 MeV}$, a spectroscopic factor of C²S(l = 0) = 1.02 ± 0.15 has been found for the $\text{2366 (}\text{1}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound state. A search for direct capture transitions to the $\text{3512 (}\text{3}\text{2}{}^{\mathrm{?}}\text{)}$and $\text{3547 (}\text{5}\text{2}{}^{\mathrm{+}}\text{) keV}$ unbound states resulted in upper limits of C²S(l = 1) ≦ 0.5 and C²S(l = 2) ? 1.0, respectively. The results are compared with available stripping data as well as shell-model calculations. The astrophysical aspect of the ¹²C(p, γ₀)¹³N reaction also is discussed.     

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.     

QED distributions for hard photon emission in e+e− → μ+μ−γ

The hard photon emission in e⁺e^? → μ⁺μ^?γ is investigated to order α³. Formulas for a number of distributions are obtained, when neglecting terms of order (m_e/?)² and (m_μ/?)². Both charge-even and charge-odd contributions are calculated. The total contribution to the charge asymmetry parameter

$\text{? =}\text{[}\text{d}\text{σ(θ)}\text{d}\text{O}{}_{\mathrm{\mu }}{}^{\mathrm{+}}\text{?}\text{d}\text{Oσ(π?θ)}\text{d}\text{O}{}_{\mathrm{\mu }}{}^{\mathrm{+}}\text{]}\text{[}\text{d}\text{σ(θ)}\text{d}\text{O}{}_{\mathrm{\mu }}{}^{\mathrm{+}}\text{+}\text{d}\text{σ(π ? σ)}\text{d}\text{O}{}_{\mathrm{\mu }}{}^{\mathrm{+}}\text{]}$

does not exceed 5% for the c.m.s. energy 2? = 3 GeV.     

Scale breaking in inclusive charged particle production by e+e− annihilation

The scale cross section $\text{s}\text{d}\text{σ}\text{d}\text{x}{}_{\mathrm{<mtext>p</mtext>}}$ for inclusive charged-particle production in e⁺e^? annihilation has been studied for c.m. energies W between 12.0 and 36.7 GeV. Scale breaking is observed. For x_p>0.2 the cross section decreases by ≈20% when W increases from 14 to 35 GeV. The production angular distribution was used to separate the longitudinal and transverse cross-section contributions and to determine the ratio of the structure functions $\text{m}\text{W}{}_1$ and $\text{v}\text{W}{}_2$.     

Electronic-excitation transfer collisions in flames-III: Cross sections for quenching and doublet mixing of Rb(52P32, 12) doublet by N2, O2, H2 and H2O

Weighted average quenching cross sections for the Rb(5²P) doublet by N₂ and H₂O were determined in flames with temperatures ranging from 1500 to 2500 K by measuring the fluorescence efficiency. The values found are $\text{(σ}{}_{\mathrm{qu}}\text{)}{}_{\mathrm{<mtext>N</mtext><mtext>2</mtext>}}\text{= (19±2)}\text{A}\text{?}{}^2$ and over the entire temperature range. At a temperature of 1720 K, mixing cross sections were obtained for the same doublet with N₂, H₂, O₂ and H₂O molecules. The cross sections found are: $\text{σ}{}_{21}\text{(}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{<mtext>N</mtext><mtext>2</mtext>}}\text{= (60±12)}\text{A}\text{?}{}^2$, $\text{σ}{}_{12}\text{(}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{→}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{<mtext>N</mtext><mtext>2</mtext>}}\text{= 99±20)}\text{A}\text{?}{}^2$; , $\text{(σ}{}_{21}\text{)}{}_{\mathrm{<mtext>H</mtext><mtext>2</mtext>}}\text{> 30}\text{A}\text{?}{}_2$, $\text{(σ}{}_{12}\text{)}{}_{\mathrm{<mtext>H</mtext><mtext>2</mtext>}}\text{> 50}\text{A}\text{?}{}^2\text{;}$, . The ratios σ₁₂/σ₂₁ were measured independently and were found to agree with the detailed- balance condition within 3 per cent. A critical comparison of the flame values with previous literature data on N₂-cross sections shows that both mixing and quenching cross sections are temperature dependent in the range from 300 to 2500 K.