Proton-nucleon Interactions Research Articles

Constraints on exotic spin-velocity-dependent interactions

Experimental searches for exotic spin-dependent forces are attracting a lot of attention because they allow to test theoretical extensions to the standard model. Here, we report an experimental search for possible exotic spin-dependent force, specifically spin-and-velocity-dependent forces, by using a K-Rb-21Ne co-magnetometer and a tungsten ring featuring a high nucleon density. Taking advantage of the high sensitivity of the co-magnetometer, the pseudomagnetic field from this exotic force is measured to be ≤7 aT. This sets limits on coupling constants for the neutron-nucleon and proton-nucleon interactions in the range of ≥0.1 m (mediator boson mass ≤2 μeV). The coupling constant limits are established to be |{g}_{V}^{n}|,le ,8.2times 1{0}^{-11} and |{g}_{V}^{p}|,le ,3.7times 1{0}^{-10}, which are more than one order of magnitude tighter than astronomical and cosmological limits on the coupling between the new gauge boson such as Z’ and standard model particles.

FPGA-based trigger system for the Fermilab SeaQuest experimentz

The SeaQuest experiment (Fermilab E906) detects pairs of energetic μ+ and μ− produced in 120GeV/c proton–nucleon interactions in a high rate environment. The trigger system consists of several arrays of scintillator hodoscopes and a set of field-programmable gate array (FPGA) based VMEbus modules. Signals from up to 96 channels of hodoscope are digitized by each FPGA with a 1-ns resolution using the time-to-digital convertor (TDC) firmware. The delay of the TDC output can be adjusted channel-by-channel in 1-ns step and then re-aligned with the beam RF clock. The hit pattern on the hodoscope planes is then examined against pre-determined trigger matrices to identify candidate muon tracks. Information on the candidate tracks is sent to the 2nd-level FPGA-based track correlator to find candidate di-muon events. The design and implementation of the FPGA-based trigger system for SeaQuest experiment are presented.

Spin observables in proton-deuteron scattering and T-invariance test

The total cross section for the interaction of transversely polarized protons ppy and deuterons that have a tensor polarization Pxz provides a null-test signal of T-invariance violation under the condition of P invariance. The relevant experiment is planned by the PAX Collaboration at the COSY accelerator with protons accelerated to the energy of 135 MeV. A modified Glauber theory is used here to calculate the differential spin observables Ay, Cy,y, Cxz,y, Cz,x, and Cx,z and the differential and total cross sections for proton-deuteron scattering in the case of T-even P-even proton-nucleon interactions. This makes it possible to estimate background conditions of the planned experiment.

Nonrelativistic description of nucleon-nucleus scattering

Within the three-dimensional semiclassical approximation, an analytic expression is obtained for the amplitude of proton-nucleus scattering at intermediate energies of incident protons. The method for deriving this amplitude is based on the use of the high-energy approximation with distorted waves. In view of the short-range character of proton-nucleon interaction, the process of proton-nucleus scattering is represented as a series of single scattering events occurring on each individual nucleon. With the aid of the proposed mathematical formalism, a recursion relation is derived that makes it possible to express the nuclear form factor obtained within the distorted-wave method in terms of the sum of an infinite Born series. Parameters that characterize the distributions of protons and neutrons in the spherical nuclei 40Ca, 48Ca, 90Zr, and 208Pb and which include the width of the surface layer of nucleons and the root-meansquare radii of the proton-, neutron-, and nucleon-density distributions are determined from an analysis of the measured cross sections for the elastic scattering of 1-GeV protons, a modified Fermi function being employed for the nucleon-density distribution.

The fast control system for HERA-B

The HERA-B experiment is dedicated to measure CP-violation in decays of neutral B-mesons. The B-mesons are produced in a nearly overwhelming background of inelastic proton-nucleon interactions. To reconstruct a sufficient number of B-decays the experiment has to be operated with multiple interactions at a 10 MHz event rate. A granularity of 540,000 channels is required. The challenge for the DAQ system is deadtimeless readout. This requires unprecedented speed of storing and labeling the data. A 50 kHz first level trigger rate needs a fast distribution of accepted-event identifiers. Ambitious plans for drift time measurements require a high precision time reference for the front end electronics. A fast control system has been developed to fulfil these requirements. The system consists of a VME-accessible mother unit with trigger and command processing logic, a two-stage signal distribution system and one individually configurable daughter module with timing adjustment capabilities in each of more than 200 front end electronics crates.

Study of the OZI selection rule in hadronic processes

In the experiments with LEPTON-F and SPHINX spectrometers the pion-induced charged exchange reactions π- + p → ϕ + n and π- + p → ω + n at Pπ-=32.5 GeV, as well as proton-induced diffractive reactions p + N → [pϕ] + N and p + N → [pω] + N at E p =70 GeV were studied. The comparison of the cross-sections for ϕ and ω-production in these reactions is used for testing the OZI selection rule in hadronic processes. It has been demonstrated that in pion reactions the ratio of the yields of ϕ and ω-mesons R(ϕ/ω) = (3 ± 1) · 10−3 is in a good agreement with naive quark model prediction based on the mixing in vector meson nonet and on the OZI rule (R(ϕ/ω)ozi = tg 2Δθ V − 4 · 10−3). At the same time in proton reactions the effective ratio of ϕ and ω yields is ∼ (4 ÷ 7) · 10-2, i.e. a strong violation of the OZI rule is observed in proton-nucleon interactions. This violation can be in favor of possible existence of some exotic ss̅ component in the quark structure of protons.

First level trigger for HERA-B

HERA-B aims to measure CP violation in the B meson system. A high rate of B mesons is obtained from 820 GeV fixed target proton-nucleon interactions. Together with the B mesons, a 6 orders of magnitude larger background of minimum bias interactions is produced. A highly selective and efficient trigger system has been designed to acquire a sufficient amount of signal decays. It is able to find and reconstruct lepton and hadron tracks. The trigger decision is based on the momenta and masses of track pairs, and mainly aims at J ψ → ℓ +ℓ − signatures. A parallel and pipelined system of approximately 100 processors has been worked out to perform this job. It provides 3 orders of magnitude background suppression at an efficiency of 50% for the main physics channel.

Negative binomial distributions in different pseudorapidity windows in 800 GeV proton-nucleon interactions

Experimental results on multiplicity distributions for full phase space and in different pesudorapidity windows of charged secondary particles produced in proton-nucleon collisions at 800 GeV are presented and discussed. It is found that all these multiplicity distributions are well described by negative binomial distributions. We interpret our results on the basis of clan model. The bin size dependence of multiplicity distribution of charged secondary particles in proton-nucleon interactions is analysed in terms of multifractals. The values of generalised dimensions obtained from fitted distributions show a good agreement with those obtained from the data.

η Production by proton-nucleon and proton-nucleus interactions from 800 MeV to 1.5 GeV

η Production by proton-nucleon and proton-nucleus interactions from 800 MeV to 1.5 GeV

Scaling of cluster parameters in interactions of 800 GeV protons with emulsion nuclei

The energy independence of cluster parameters in 800 GeV proton-nucleon and proton-nucleus interaction has been investigated and the results have been compared with those at lower primary energies.

Continuum yields from 12C(p,p′) at incident proton energies of 90 and 200 MeV

The inclusive reaction 12C(p,p') at incident proton energies of 90 MeV and 200 MeV is investigated to determine whether the continuum spectra can be described in terms of a simple quasifree knockout model. Reasonable agreement is obtained at 200 MeV, irrespective of our choice of approximation to the half-shell proton-nucleon interaction. At 90 MeV, however, only the initial-energy prescription gives acceptable theoretical results. Realistic spectroscopic factors are extracted from the data, which further support the assumption that the quasifree knockout mechanism is an important component of the reaction leading to protons scattered into the continuum.

Effective interaction analysis of 500 MeV (p

A nonrelativistic distorted wave Born approximation analysis, using a phenomenological effective proton-nucleon interaction to generate both optical and transition potentials, is made of new 500 MeV (p\ensuremath{\rightarrow},p') data for excitation of low-lying states in $^{40}\mathrm{Ca}$, $^{48}\mathrm{Ca}$, $^{90}\mathrm{Zr}$, and $^{208}\mathrm{Pb}$. The data, differential cross section and analyzing power angular distributions for 5\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.\mathrm{\ensuremath{\le}}30\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}$, are well described using this effective interaction. Calculations using the impulse approximation to generate the optical and transition potentials do not adequately describe the data. As a further test of the 500 MeV empirical effective interaction, model-dependent neutron transition densities are deduced for excitations which are expected to be purely isoscalar, such as the first ${3}^{\mathrm{\ensuremath{-}}}$ states of $^{40}\mathrm{Ca}$ and $^{208}\mathrm{Pb}$. These are found to be qualitatively similar in strength and overall shape to the renormalized (\ifmmode\times\else\texttimes\fi{}N/Z) model-independent proton densities determined from analysis of (e,e') data. Model-dependent neutron transition densities are also deduced for other excitations and are in reasonable agreement with results of analyses of other hadron plus nucleus scattering data. These results indicate that the 500 MeV isoscalar effective interaction is better than the free proton-nucleon scattering amplitudes (impulse approximation) as a starting point for analysis of (p,p') data aimed at detailed extraction of neutron transition densities and other nuclear structure information.

Observation of double phi-meson production in 400-GeV/c proton-nucleon interactions.

The production of phi-meson pairs has been observed in 400-GeV/c proton-nucleon interactions at the Fermilab multiparticle spectrometer in the inclusive reaction pN..-->..phiphi+X, where each phi decays to a K/sup +/K/sup -/ pair. A fast (200 nsec)= high-level processor was used to selectively trigger on events containing two pairs of oppositely charged kaons having low invariant masses. The experimental apparatus and trigger processor are described. The cross section for phiphi production and an upper limit for eta/sub c/ production are presented.

A Measurement of the Total Charm Cross Section in 200 and 360 GeV/c pN Interactions Using a Holographic Bubble Chamber

We present results from the first holographic bubble chamber experiment. Using topological information on the events observed in the heavy liquid bubble chamber HOBC, we have determined a total charm pair production cross section of (24.6-8.3+12.0) μb and (3.9-1.9+2.5) μb in 360 GeV/c and 200 GeV/c proton-nucleon interactions respectively. For these estimates we assumed a linear dependence of the charm cross section on the atomic number A.

Experimental study of proton-emulsion nuclei interactions at high energy

Proton-emulsion nuclei interactions at 200 and 400 GeV have been studied. The results on the energy dependence of and /D, multiplicity scaling, multiplicity density scaling in the central region, integral angular distribution, rapidity dispersion and maximum rapidity gap are presented and compared with those of proton-nucleon interactions at the corresponding energies.

Nucleon fragmentation into baryons in proton-nucleon interactions at 19 GeV/c compared with some quark-parton model predictions

We present some new data on baryon production in pn interactions at 19 G-eV/c obtained in a bubble chamber experiment. We determine the longitudinal-momentum spectradσ/dx of the baryon in the reactions pn → pF+X, pn→ pB+X, pn →ΔF++(1232) + X and pn → → ΔB++(1232) + X, where F(B) labels the forward (backward) cm. hemisphere. The spectra of pf and pb are also given when the effects of diffraction and Δ++(1232) resonance production are subtracted. These data, together with dσ/dx of pp→Λ0+X at the same beam momentum, are compared with the predictions of some quark-parton models. Particle multiplicities of nucleons, Δ++(1232) and hyperons are found to be incompatible with the probabilistic quark model of Van Hove.

On mean number of collisions in high energy hadron-nucleus interaction

Properties of the mean number of collisionsvpA have been discussed in some detail. It was shown that the standard parametrization (2) should be taken with a proper care if a wide range of nuclei is considered. Moreover, we have seen that any serious approach to the very high energy collisions cannot avoid an inclusion of an energy dependence of the parametersv1v2. It reflects primarily the energy dependence of the proton-nucleon inelastic (and total) cross sections. On the other hand, it appears that these parameters are rather insensitive to the details of the proton-nucleon interaction and of the nuclear wave function.

Study of multiparticle rapidity clustering in hadronic interaction at 70 GeV/c

This paper presents a study of multiparticle rapidity clustering in proton–nucleon interaction at 70 GeV/c using the generalized rapidity-gap method. The observed rapidity-gap distribution has been compared with those from a model of uncorrelated particle production. A clear indication of cluster production was observed.

Rapidity-Gap Correlation in Proton-Nucleus Interactions at 200 and 400 GeV/c

The results on the rapidity-gap correlations in proton-nucleus interactions at 200 and 400 GeV/c in nuclear emulsion are presented and compared with proton-nucleon interactions at the same energies. Some striking differences between the results in the two types of interactions have been observed and examined on the basis of existing models.

Forward and backward multiplicities in high-energy proton-nucleus and proton-nucleon collisions

Multiplicities of charged particles produced in the forward and backward hemispheres are investigated for proton-nucleus and proton-nucleon collisions in the range from 20 to 400 GeV/c. Weak, but growing with incident beam momentum, forward-backward multiplicity correlations are observed which cannot be reduced to the inelastic diffraction. These correlations are more pronounced in proton-nucleus than proton-nucleon interactions.