Proton-nucleus Interactions Research Articles

Observation of a narrow baryon resonance decaying to pK S 0 in proton-nucleus interactions at 70 GeV/c with the SVD-2 setup

SVD-2 experiment data have been analyzed to search for an exotic baryon state, the $\Theta^+$-baryon, in a $pK^0_s$ decay mode at $70 GeV/c$ on IHEP accelerator. The reaction $pA \to pK^0_s+X$ with a limited multiplicity was used in the analysis. The $pK^0_s$ invariant mass spectrum shows a resonant structure with $M=1526\pm3(stat.)\pm 3(syst.) MeV/c^2$ and $\Gamma < 24 MeV/c^2$. The statistical significance of this peak was estimated to be of $5.6 \sigma$. The mass and width of the resonance is compatible with the recently reported $\Theta^+$- baryon with positive strangeness which was predicted as an exotic pentaquark ($uudd\bar{s}$) baryon state. The total cross section for $\Theta^+$ production in pN-interactions for $X_F\ge 0$ was estimated to be $(30\div120) \mu b$ and no essential deviation from A-dependence for inelastic events $(\sim A^{0.7})$ was found.

HERA-B results on heavy flavour production in 920 GeV proton–nucleus interactions

In this report, recent results from the HERA-B experiment on heavy flavour production in proton–nucleus interactions using a 920 GeV proton beam are presented. The topics include the production of the charmonium states J/ψ, ψ′ and χc, of the D-meson states D0, D±, D*, the open beauty production cross section ( production) and the ϒ production cross section. The nuclear dependence for the differential cross sections of charmonium production is discussed. The results are mainly preliminary. The report closes with a summary of the HERA-B search for pentaquark states with strangeness, which yielded quite stringent upper limits for the production of such states in hadronic environments.

K+ PRODUCTION FROM pp AND pd INTERACTIONS

The K+-production cross section in pn collisions is an important input parameter for model calculations of K+ production in proton-nucleus and nucleus-nucleus interactions. Experimental data in the close-to-threshold region are not yet available and theoretical predictions give a wide scatter of numbers for the ratio of the total cross sections [Formula: see text]. K+ production from pd interaction has been investigated using the magnetic spectrometer ANKE at COSY-Jülich at proton beam momenta 2.65, 2.81 and 3.46 GeV/c. For the extraction of [Formula: see text] from the pd data at low beam momenta, a naive phase-space approach has been used, assuming that [Formula: see text]. Double differential cross sections and missing mass spectra for proton-kaon correlations have also been analysed. Both methods give consistent result: [Formula: see text]. During a recent beam time, experimental data have been collected at pp=3.46 GeV/c for both hydrogen and deuterium targets. A ratio [Formula: see text] has been extracted from these data.

Inclusive K+-meson production in proton-nucleus interactions

The production of K^+ mesons in pA (A = D, C, Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotron COSY-J\"ulich for beam energies T_p = 1.0 - 2.3 GeV. Double differential inclusive pC cross sections at forward angles theta < 12 degrees as well as the target-mass dependence of the K^+ momentum spectra have been measured with the ANKE spectrometer. Far below the free NN threshold at T_{NN}=1.58 GeV the spectra reveal a high degree of collectivity in the target nucleus. From the target-mass dependence of the cross sections at higher energies, the repulsive in-medium potential of K^+ mesons can be deduced. Using pN cross-section parameterisations from literature and our measured pD data we derive a cross-section ratio of sigma(pn -> K^+ X) / sigma(pp -> K^+ X) ~ (3-4).

Transverse-momentum distribution of J/ψ mesons produced in proton-nucleus and lead-lead interactions

The transverse-momentum and transverse-mass distributions of J/ψ mesons produced in proton-nucleus and lead-lead interactions at 400 GeV and 158 GeV/nucleon, respectively, were measured in the NA50 experiment. The change in these distributions with increasing centrality is studied for various interaction energies. Data obtained in the NA38 experiment for collisions of light nuclei at 200 GeV per nucleon is also used in the present analysis. Investigation of the transverse-momentum and transverse-mass distributions of J/ψ particles can provide additional information about the properties of the phase transition of ordinary nuclear matter to quark-gluon plasma.

Charmonium production and nuclear absorption in p-A interactions at 450 GeV

The production of J/ψ and ψ � charmonium states in proton-nucleus interactions has been investigated by the NA50 experiment, at the CERN SPS. High statistics data sets were collected with collisions induced by 450 GeV protons incident on Be, Al, Cu, Ag and W targets. The J/ψ and ψ � production cross-sections have been determined for each p-A system and their dependences on the nucleus size have been studied, leading to the so-called normal nuclear absorption. Comparing the two patterns we see that the nuclear absorption is stronger for the ψ � than for the J/ψ. Given the high statistics of the data samples, the xF (or rapidity) differential cross-sections of the J/ψ and ψ � states have also been studied, for each of the target nuclei.

A RICH multiplicity veto for the HERA-B experiment

We present the design and commissioning of a new multiplicity veto for the HERA-B detector, a fixed-target spectrometer originally designed to study the physics of B mesons in proton-nucleus interactions. The HERA-B trigger is a message-driven multilevel track trigger. The first level trigger (FLT) consists of custom-made electronics, and the higher trigger levels are implemented as PC farms. The multiplicity veto has been designed to reject high-multiplicity events before they enter the trigger chain. A veto signal is generated based on the comparison of the number of photons in part of the HERA-B ring-imaging Cerenkov counter (RICH) with a programmable threshold. The RICH multiplicity veto is a modular system. First the hits in 256 detector channels are summed by base sum cards (BSC), then FED sum cards (FSC) sum the subtotals of up to eight BSCs. Finally, the veto board (VB) takes the veto decision based on the sum of up to 14 FSCs. The RICH multiplicity veto has been successfully installed and commissioned in HERA-B. The measured veto efficiency is (99.9991/spl plusmn/0.0001)%, and the system is used in the routine data-taking of the HERA-B experiment.

Compilation of cross sections for proton–nucleus interactions at the HERA energy

This work compiles information concerning the total, inelastic and diffractive cross sections for proton–nucleus interactions. The values are fitted together with the expression σ= σ 0 A α , where A is the target atomic mass number. Also discussed is the amplitude of the diffractive components of the inelastic cross section.

Measurement of the [formula omitted] production cross section in 920 GeV proton-nucleus collisions

Using the HERA — B detector, the b b production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The b b production was tagged via inclusive bottom quark decays into J ψ by exploiting the longitudinal separation of J ψ → l +l − decay vertices from the primary proton-nucleus interaction. Both e + e − and μ + μ − channels have been reconstructed and the combined analysis yields the cross section σ(b b) = 32 −12 +14 ( stat) −7 +6( syst) nb/nucleon.

Measurement of the [formula omitted] production cross section in proton-nucleus collisions at HERA - B

Using the HERA - B detector, the b b production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The b b production was tagged via inclusive bottom quark decays into J/ Ψ by exploiting the longitudinal separation of J/ Ψ → l + l − decay vertices from the primary proton-nucleus interaction. Both e +e − and μ + u − channels have been reconstructed and the combined analysis yields the cross section σ (b b) = 32 +14 −12( stat) +6 −7( sys) nb/nucleon.

Measurement of the $b\overline{b}$ production cross section in 920 GeV fixed-target proton-nucleus collisions

Using the HERA-B detector, the b-bbar production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The b-bbar production was tagged via inclusive bottom quark decays into J/psi, by exploiting the longitudinal separation of J/psi->ll decay vertices from the primary proton-nucleus interaction. Both $e^+e^-$ and $\mu^+\mu^-$ channels have been reconstructed and the combined analysis yields the cross section $\sigma(b \bar b) = 32 ^{+14}_{-12} (stat) ^{+6}_{-7} (sys) nb/nucleon$.

Track finding at 10-MHz hadronic event rate

Hera-B is a fixed target experiment using a halo target inside the HERA proton ring to generate B mesons in 920 GeV proton-nucleus interactions. The first-level trigger (FLT) of the experiment has to reduce the primary 10-MHz input rate by a factor 200 in less than 10 /spl mu/s to make it acceptable to the second level trigger (SLT). The trigger strategy is based on the tracking of charged particles and on the reconstruction of their kinematic parameters. The combination of track pairs can also be used for the final decision. A parallel and pipelined set of approximately 60 dedicated boards was designed and built to perform this job. In this paper, the working principle of the system and some results obtained by analyzing the data collected during the run in the year 2000 are described.

Charged-particle multiplicity distributions in different rapidity windows in 800 GeV proton-nucleus interactions

Multiplicity distributions of charged particles produced in interactions of 800 GeV protons with emulsion nuclei in various rapidity windows are presented. The data is also analyzed separately for the forward and the backward hemispheres, for rapidity windows of different widths. It is found that the Negative Binomial Distribution (NBD) describes well the multiplicity distribution of secondary particles in various rapidity windows and also in both the hemispheres. We have compared the NBD parameters, in both the hemispheres, at 200 GeV and 360 GeV, with those at 800 GeV. The behaviour of NBD parameters in rapidity windows of different widths and for different targets has also been studied.

Charged-particle multiplicity distributions in different rapidity windows in 800 GeV proton-nucleus interactions

Charged-particle multiplicity distributions in different rapidity windows in 800 GeV proton-nucleus interactions

A dependence of the cross sections for the cumulative production of pions and protons in proton-nucleus and nucleus-nucleus interactions

The behavior of the inclusive cross sections for the cumulative production of π± mesons and protons in pA, DA, and 4HeA interactions is studied versus the atomic mass number of fragmenting nuclei. The primary-beam momenta were 4.5 GeV/c per nucleon. Secondary pions and protons were recorded with a fixed momentum of 0.5 GeV/c at an angle of 120°. Specifically, the experiment explored the fragmentation of D, He, 6Li, 7Li, C, Si, 58Ni, 64Ni, 64Zn, 114Sn, 124Sn, and Pb nuclei. The energy spectra of π+ and π− mesons and protons with momenta in the range 0.3–0.7 GeV/c (the emission angle being 120°) were measured in an 8.9-GeV/c proton beam for Ni, Zn, and Sn isotopes. The special features in the behavior of the cross sections are found and discussed, and a comparison is drawn with the results of other studies.

ANKE, a new facility for medium energy hadron physics at COSY-Jülich

ANKE is a new experimental facility for the spectroscopy of products from proton-induced reactions on internal targets. It has recently been implemented in the accelerator ring of the cooler synchrotron COSY of the Forschungszentrum Jülich (FZ-Jülich), Germany. The device consists of three dipole magnets, various target installations and dedicated detection systems. It will enable a variety of hadron-physics experiments like meson production in elementary proton–nucleon processes and studies of medium modifications in proton–nucleus interactions.

Production rates for π+ K −, pK −, and pπ− atoms in inclusive processes

The yields of π+K−, pK−, and pπ− atoms in the reaction p + Al → atom + X at energies of 24, 70, 450 GeV and emission angles of θlab=1°–6° are calculated from inclusive-production cross sections for p, π+, π−, and K−. Estimates of these hadronic-atom yields for a Ta target are also given. The inclusive-production cross sections for p, π+, π−, and K− are obtained within the Lund model of string fragmentation. The accuracy of the calculations is estimated by comparing single particle yields calculated by the Lund model and experimental yields of particles in proton-nucleus interactions.

Partial Cross Sections of Nucleus‐Nucleus Reactions

Spallation cross sections of nucleus-nucleus reactions are calculated by scaling up the proton-nucleus cross sections (with additional fitting factors) using the weak factorization property of fragment production and, with adjusted energy dependence, using the concept of nuclear participants and spectators in nuclear interactions. Special fittings are provided for charge-pickup cross sections. Separate calculations are presented for electromagnetic dissociation cross sections. Elemental and isotopic resolution is comparable to that of the proton-nucleus interactions. Also a brief discussion is presented of the total inelastic cross sections and their energy dependence.

Rapidity gaps and scaling in high energy interactions.

The rapidity gap probability is investigated in varying symmetric bin sizes in proton-nucleus interactions at 800 GeV. It shows a scaling behavior and confirms the linked pair approximation for the {ital n}-particle cumulant correlation functions to high order. A comparison of the scaled rapidity gap probability is made with the negative binomial distribution. We also interpret the rapidity gap probability in the clan production model of hadronization and reanalyze the clan parameters in its light. {copyright} {ital 1996 The American Physical Society.}

Geometrical approach for diffractive dissociation processes at high energies.

A phenomenological model for hadron diffractive dissociation is developed starting from the generalized optical theorem. The behavior of the Pomeron-hadron cross section is described by using a set of assumptions based on the current phenomenology of elastic processes and total cross section, which is compatible with the idea of Pomeron exchange as the dominant process at high energy. The obtained model is applied to describe experimental data of diffractive dissociation for the processes $\mathrm{pp}$, $\overline{p}p$, ${\ensuremath{\pi}}^{+}p$, and ${K}^{\ifmmode\pm\else\textpm\fi{}}p$. An extension of the model for diffractive dissociation of nuclei in proton-nucleus interactions is also presented.