Pp Annihilation Research Articles

Highlights in the hadron electromagnetic structure

In frame of a general view of proton electromagnetic form factors, two recent findings related to reanalyses of data are presented. Recent experiments in the scattering and in the annihilation region provided us with more precise data and/or extending the kinematical region, allowing a deeper analysis and a common view of these fundamental quantities. We will discuss two issues: the discrepancy between the form factors extracted from unpolarized and polarized ep elastic scattering experiments, in connection with the commonly used dipole parametrization; peculiar oscillations in e + e − → pp ( γ ) annihilation cross section, that become periodical when plotted as a function of the 3-momentum of the relative motion of the final proton and antiproton, after subtraction of a smooth function.

A Large GEM-TPC Prototype Detector for anda

The PANDA spectrometer will be a state of the art universal detector for strong interaction studies at the High-Energy Storage Ring (HESR) in the future international Facility for Anti-proton and Ion Research (FAIR) at GSI, Darmstadt. The detector is designed to take advantage of the extraordinary physics potential which will be available utilizing high intensity, phase space cooled anti-proton beams. This facility will provide a cooled anti-proton beam −2 with momenta of 1.5-15 GeV/c, a maximal luminosity of 2×10 32 cms −1 that translates into 2×10 7 pp annihilations per second. A GEM based Time Projection Chamber (TPC) was one of the central tracker candidates for the PANDA experiment. To check the feasibility of such a detector system, a large prototype GEM-TPC was built and tested inside the FOPI Spectrometer at GSI. A set of three Gas Electron Multiplier (GEM) foils were used as amplification stage instead of Multi Wire Proportional Chambers. In this report, the design, construction, characterization of the prototype-detector system will be discussed in detail along with the results of recent beam tests.

Results of a search for thehc(P11)state of charmonium in theηcγandJ/ψπ0decay modes

We report evidence for the h{sub c} state of charmonium in its {eta}{sub c}{gamma} decay mode and lack of evidence in the J/{psi}{pi}{sup 0} mode. We studied these channels in pp annihilations near the center of gravity of the {sup 3}P{sub J} states, where the h{sub c} was reported in the J/{psi}{pi}{sup 0} mode by E760, our previous experiment, at 3526.2{+-}0.15{+-}0.2 MeV, with {gamma}{sub R}{<=}1 MeV. We observe an event excess in the {eta}{sub c}{gamma} mode near 3526 MeV. Testing the null hypothesis of a linearly varying background cross section against the alternate hypothesis that includes a resonance near 3526 MeV, we reject the null hypothesis with P{approx}0.001. The resonance mass is 3525.8{+-}0.2{+-}0.2 MeV and the resonance width {<=}1 MeV. We estimate 10.0{+-}3.5<{gamma}{sub pp}B{sub {eta}{sub c}}{sub {gamma}}<12.0{+-}4.5 eV, corresponding to fixed values 0.5<{gamma}{sub R}<1.0 MeV. We find no event excess within the search region in the J/{psi}{pi}{sup 0} mode.

Effects of supersymmetricCPphases on chargino-pair production via the Drell-Yan process at the CERN LHC

We compute the rates for pp annihilation into chargino-pairs via Drell-Yan process taking into account the effects of supersymmetric soft phases, at proton-proton collider. In particular, the phase of the µ parameter gains direct accessibility via the production of dissimilar charginos. The phases of the trilinear soft masses do not have a significant effect on the cross sections.

Study of charmonium states formed in [formula omitted] annihilations: results from Fermilab E835

The resonant formation of charmonium states in pp annihilations has been studied at Fermilab by the E835 experiment. We present new, preliminary results concerning the χ 0, χ 2 and η c states, as well as new measurements of the proton magnetic form factor in the timelike region at high-momentum transfer.

Interference study of the chi c0(13P0) in the reaction -pp-->pi0pi0.

Fermilab experiment E835 has observed (-)pp annihilation production of the charmonium state chi(c0) and its subsequent decay into pi(0)pi(0). Although the resonant amplitude is an order of magnitude smaller than that of the nonresonant continuum production of pi(0)pi(0), an enhanced interference signal is evident. A partial wave expansion is used to extract physics parameters. The amplitudes J=0 and 2, of comparable strength, dominate the expansion. Both are accessed by L=1 in the entrance (-)pp channel. The product of the input and output branching fractions is determined to be B((-)pp-->chi(c0))xB(chi(c0)-->pi(0)pi(0))=(5.09+/-0.81+/-0.25)x10(-7).

Proton-antiproton annihilation into 6γ and 7γ

Preliminary results on ωπ 0 π 0 and ωηπ 0 in pp anihilation at rest [1] and on pp annihilation in flight into ηηπ 0 [2] are briefly described. In ωηπ 0 there is evidence for 1 +− and 1 −− mesons decaying to ωη. In ηηπ 0 at 900 MeV/c the f 0(1500) meson decaying into ηη is strongly produced, while the f J (1710) is not observed.

Formula omitted] annihilation at two different target densities

The OBELIX spectrometer (installed at the Low Energy Antiproton Ring of CERN) has taken data on the NN annihilation in liquid hydrogen and in gaseous hydrogen at 3bar. The results of the spin-parity analysis on the pp annihilation into four charged pions at this two target densities are here briefly described.

High precision charmonium spectroscopy in [formula omitted] annihilations

Fermilab experiment E835 studies the direct formation of charmonium states in proton-antiproton annihilations, obtained by intersecting the p beam of the Fermilab Antiproton Accumulator with an internal hydrogen jet target. In this paper we report the preliminary results from the 1996/1997 run, in particular about η c mass and width, search for η′ c and first observation of the χ 0 state in pp annihilations.

Coupled-channel analysis of πππ and [formula omitted] final states from [formula omitted] annihilation at rest in hydrogen targets at three densities

The spin-parity analysis of the reactions pp → π +π −π 0,K +K −π 0,K ±K 0π ∓ is performed in the context of an approach which solves the problems connected to the complexity of K + K − π 0 dynamics and to the number of partial waves involved in pp annihilation at rest. The preliminary results are presented.

Formula omitted] annihilation cross sections at low energy

New measurements of the pp annihilation cross section have been performed with the OBELIX apparatus between 37 and 70 MeV/c. From previous samples of data it was already clear that the 1 p behaviour for the annihilation cross section is drastically modified at very low momenta, due to the Coulomb interaction. However, at the lowest measured momentum (43.6 MeV/c), the annihilation cross section was unexpectedly high; this evidence suggested a more accurate investigation of this region. Furthermore, measurements of annihilation cross section have been performed with p impinging on D 2 and 4He targets.

Resonances formed by [formula omitted] and decaying into π0π0η for masses 1960 t0 2410 MeV

Data on pp annihilation in flight into π 0 π 0 η are presented for nine beam momenta 600 t0 1940 MeV/c. The strongest four intermediate states are found to be f 2(1270) η, a 2(1320) π, ση and a 0(980) π. Partial wave analysis is performed mainly to look for resonances formed by pp and decaying into π 0 π 0 η through these intermediate states. There is evidence for the following s-channel I = 0 resonances: two 4 ++ resonances with mass and width ( M, Γ) at (2044, 208) MeV and (2320±30, 220±30) MeV; three 2 ++ resonances at (2020±50, 200±70) MeV, (2240±40, 170±50) MeV and (2370±50, 320±50) MeV; two 3 ++ resonances at (2000±40, 250±40) MeV and (2280±30, 210±30) MeV; a 1 ++ resonance at (2340±40, 340±40) MeV; and two 2 −+ resonances at (2040±40, 190±40) MeV and (2300±40, 270±40) MeV.

Present status of charmonium spectroscopy in pp annihilations

Fermilab E835 Collaboration is committed to complete the study of the charmonium spectrum by means of pp annihilations, obtained by intersecting the Fermilab Antiprotn Accumulator with an internal hydrogen jet target. In this paper we report the preliminary results from the 1996/1997 fixed target run, particularly about η c mass and width, search for η′ c and first observation of the X 0 state in pp annihilations.

Meson spectroscopy with very low momentum antiprotons

The OBELIX spectrometer, studying at the Low Energy Antiproton Ring (LEAR) of CERN the NN annihilation, has collected annihilation data with very low momentum p(≈ 50MeV/c). The results of the spin-parity analysis on the pp annihilation into four and five pions are briefly described.

Results of CPLEAR

The CPLEAR experiment uses tagged K 0 and K 0 produced in pp annihilation at rest to measure CP-, T- and CPT-violation parameters in the neutral kaon system. The results of these measurements and some implications are reported.

Study of antiproton nucleon annihilations at rest into five pions

The Crystal Barrel Experiment at LEAR allows the detection of charged particles and photons with almost 4 π angular coverage, respectively. Here we present a study of pp annihilation and pd annihilation at rest into five-pion final states ( pp →5 π 0 , pp → π + π − 3 π 0 , pd → π − 4 π 0 p and pd → π + 2 π − 2 π 0 p). These reactions are well suited to look for four pion decays of scalar and vector mesons. Previous experiments on pn →2 π + 3 π − [3], np →3 π + 2 π − [4], and pp → + π - 3 π 0 [5] established the dominance of the production of a scalar isoscalar resonance with a mass of about 1370 MeV and a width of about 350 MeV. The ƒ 0 (1370) was found to have a sizeable decay branching ratio into σσ and ρρ . We show, in an analysis of the reaction pp →5 π 0 , that there is indeed a scalar resonance decaying into 4 π 0 , but this resonance can be identified with the ƒ 0 (1500), a new resonance, observed by the Crystal Barrel Collaboration in the decay modes π 0 π 0 , ηη and ηη ′. In the 5 π 0 final state we found evidence for the ƒ 0 (1500) decay to σσ and π (1300) π . A preliminary result of a combined analysis of the four five-pion data sets mentioned above confirms the existence of the ƒ 0 (1500) in the data and shows that the σσ decay of the ƒ 0 (1500) is more important than its decay to ρρ .

A search for axial vectors in [formula omitted] annihilations at rest in gaseous hydrogen at NTP

The study of the K ± K miss 0 π ∓ π + π − channel (7016 events), from pp annihilations in a gaseous hydrogen target at NTP, with the OBELIX spectrometer at LEAR (CERN), is presented. A spin-parity analysis provides evidence for two axial vectors, one in the low K Kπ mass region, the well established f 1(1285), decaying to a 0(980) π, the second, the 1 ++ component of the old puzzling E l , the f 1(1420), decaying mainly to K ∗ K , seen for the first time in pp annihilation at rest. The analysis confirms the dominant production of the pseudoscalar η(1405), decaying mainly to (Kπ) S K , and the existence of a second pseudoscalar in the same mass region, the η(1460), decaying mainly to K ∗ K .

Formula omitted]p low energy parameters from annihilation cross section data

The recent experimental data obtained by the OBELIX group on total pp annihilation cross section are analysed; the low energy spin averaged parameters of the pp scattering amplitude (the imaginary parts of the S-wave scattering length and P-wave scattering volume) are extracted from the data. Their values are found to be equal to Im a sc = −0.69 ± 0.01 (stat) ± 0.03 (sys) fm, Im A sc = −0.76 ± 0.05 (stat) ± 0.04 (sys) fm 3. The results are in very good agreement with existing atomic data.

Observation of f0(1500) decay into KLKL

The f 0(1500) is observed in its K K decay mode in an amplitude analysis of high statistics data in pp annihilation at rest into π 0 K L K L . The mass and width is found to be ( m, Γ) = (1515 ± 20, 105 ± 15) MeV. A comparison of the decay rate into 2 π 0 shows that this state cannot be dominantly s s . The f′ 2(1525) has been observed for the first time in pp annihilation and its production rate is consistent with the expectation from the OZI rule.

S- and P-state annihilation in p interactions at rest

Two body branching ratios for pp annihilation at rest are used to calculate the fraction of P-state annihilation as a function of target density. In the presence of Stark mixing it is necessary to take into account an enhancement of annihilations from fine structure states over that expected from a statistical population. The enhancement factors are obtained using an atomic cascade calculation which fits available pp atom X-ray measurements.