Storage Ring PETRA Research Articles

Mobile dry pumping stations for PETRA III beamlines

The PETRA storage ring at DESY will be upgraded to a third generation synchrotron radiation source with 14 beamlines in the PETRA III project. Mobile pumping stations will be needed for the initial pump down of the beamlines and beamline components. They will also be provided for users to pump down their experimental chambers and include the possibility of leak detection and bake out control. Since the layout of the old pumping station design used at DORIS beamlines does not fulfil today's requirements, a new pumping station was developed. In contrast to the former design it has a dry pumping system and uses a by-pass of the turbo molecular pump for fast pump down of the attached vacuum chamber. The new control system is implemented as a binary sequential control, which runs on two CPLD-Chips (Complex Programmable Logical Device). It controls the pump down process, the bake out of the attached vacuum component, toggling of the roughing pump, and the blocking of reverse gas flow to prevent contamination of the vacuum system with particles. The pumping station is controlled via a local front panel and accessible via Ethernet for remote operation.

The High Energy Materials Science Beamline at PETRA III

The future High Energy Materials Science Beamline HEMS at the new German high brilliance synchrotron radiation storage ring PETRA III [1] will have a main energy of 120 keV, will be fully tunable in the range of 50 to 300 keV, and will be optimized for sub-micrometer focusing with Compound Refractive Lenses and Kirkpatrick-Baez Multilayer mirrors. Design and construction is the responsibility of the Research Center Geesthacht, GKSS, with approximately 70 % of the beamtime being dedicated to Materials Research, the rest reserved for “general physics” experiments covered by DESY, Hamburg. Fundamental research will encompass metallurgy, physics and chemistry. For first experiments in investigating grain-grain-interactions a dedicated 3D-microstructure-mapper will be designed. Applied research for manufacturing process optimization will benefit from the high flux in combination with ultra-fast detector systems allowing complex and highly dynamic in-situ studies of microstructural transformations. The beamline infrastructure will allow easy accommodation of large user provided equipment. Experiments targeting the industrial user community will be based on well established techniques with standardised evaluation, allowing "full service" measurements. Environments for strain mapping [2] on large structural components up to 1 t will be provided as well as automated investigations of large numbers of samples, e.g. for tomography and texture determination. The current design for the beamline (P07 in sector 5 of the future experimental hall) consists of a nearly five meter in-vacuum undulator source (U19-5) optimized for high energies, a general optics hutch, an in-house test facility and three independent experimental hutches working alternately, plus additional set-up and storage space for long-term experiments. HEMS should be operational in spring 2009 as one of the first beamlines running at PETRA III.

New fast closing shutter for the PETRA III beamlines

The conversion of the PETRA storage ring at the Deutsches Elektronen Synchrotron (DESY) to the third generation synchrotron radiation light source PETRAIII [1] poses a challenge to the design of the beamline transport system. One of these challenges is to supply 14 beamlines and experiments windowless with the extremely collimated undulator radiation from the storage ring. The windowless connection includes the risk of accidental venting of the storage ring by experiments connected to the beamlines. To stop the inrush of such an accidental venting fast closing shutter (FCS) systems with closing times in the 10msec range are mandatory. The strong radiation background in the storage ring tunnel requires the installation of all metal valves. A new small fast closing shutter with an aperture of 40mm fitting to the strong collimated undulator beams and with a closing time < 10msec was developed. The all metal sealing principle achieves leak rates smaller than 10mbarl/sec. This leak rate of the fast closing shutter combined with a standard all metal valve prevents venting of the storage ring and the beam time losses for all users. The mechanical and electronic layouts as well as first experiences with the new fast closing shutter system developed for PETRAIII are presented.

Three-dimensionalelectron momentum densities of solids

We report on the measurement of the three-dimensional electronmomentum density (EMD) of solids by means of the (γ, eγ)reaction. Fixing the reaction kinematics by a coincidencecondition, the triple-differential cross section for Comptonscattering is proportional to the EMD. The experiments wereperformed either at the wiggler beamline of the European SynchrotronRadiation Facility (ESRF) or the undulator beamline of the PETRAstorage ring at Deutsches Elektronen-Synchrotron (DESY) with photonenergies of about 150 keV. Experimental three-dimensional EMDs ofgraphite, fullerene and aluminium are compared with theoretical onesobtained from band-structure calculations like the full-potentiallinear muffin-tin orbital, augmented-plane-wave and pseudopotentialformulations. In addition, the change of the EMD caused by alloyformation has been studied in the Cu-Ni system and the results arecompared with the Korringa-Kohn-Rostoker coherent potentialapproximation.

Anisotropy of the electron momentum density of graphite studied by(γ,eγ)and(e,2e)spectroscopy

The electron momentum density (EMD) of two different modifications of graphite has been measured and the results of the measurements have been compared with theoretical calculations from three different theories: a full potential linear muffin-tin orbital, a modified augmented plane wave, and a pseudopotential calculation. Experimental results have been obtained by two different methods. The complete three-dimensional EMD is determined by inelastic photon-electron scattering, i.e., by the so-called $(\ensuremath{\gamma},e\ensuremath{\gamma})$ experiment, and by electron-electron scattering, the $(e,2e)$ experiment, cuts in the spectral electron momentum density are studied. For the $(\ensuremath{\gamma},e\ensuremath{\gamma})$ experiment 180 keV synchrotron radiation from the PETRA storage ring at the Deutsches Elektronen-Synchrotron has been used with coincident detection of the recoil electrons. The $(e,2e)$ experiments were carried out at the new $(e,2e)$ spectrometer at the Australian National University using 40 keV primary electron energy and simultaneous detection of the outgoing electrons in an equal energy sharing mode. As samples we have prepared approximately 20 nm thin self-supporting graphite foils either by thermal evaporation (TE) or by laser plasma ablation (LPA). They are thin enough to suppress in essence electron multiple scattering. Electron diffraction analysis revealed that the LPA foil contains graphitic basal planes with a random distribution of c axes, whereas the TE foil was strongly c-axis oriented in the sense that the basal planes were parallel to the foil surface. In the analysis of the results special attention was devoted to anisotropies in the EMD revealed by comparison of TE and LPA foils. The $(e,2e)$ measurements showed furthermore a strong orientation dependence of the intensity of $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ states (here we have for comparison additionally measured highly oriented pyrolytic graphite). The EMD's obtained by both techniques show anisotropies in the momentum distribution of graphite and are discussed in view of the theoretical results.

Beam-position monitors in the X-ray undulator beamline at PETRA.

At the 12 GeV storage ring PETRA, the first synchrotron radiation beamline uses a 4 m-long undulator. The beamline, with a length of 130 m between source and sample, delivers hard X-ray photons usable up to 300 keV. The photon beam has a total power of 7 kW. Combined with the high brilliance, the powerful beam is very critical for all beamline components. Copper, located at a distance of 26 m, hit by the full undulator beam, melts within 20 ms. Different monitors are described for stable, safe and reliable operation of beam and experiments.

Measurements of Emittance and Absolute Spectral Flux of the PETRA Undulator at DESY Hamburg

The first synchrotron radiation beamline using a 4 m-long undulator at the 12 GeV storage ring PETRA delivers hard X-ray photons usable up to 300 keV. The photon intensity is measured on an absolute scale in the energy range between 16 and 60 keV and compared with calculated intensities. The experimental set-up described is also used to measure the horizontal and vertical emittance of the source.

On a possibility of constructing a high-intensity, monochromatic, polarized gamma source at PETRA

A possibility of constructing a high-intensity, tunable, monochromatic, polarized γ-source at the PETRA storage ring is discussed. It is proposed to produce γ-quanta by means of Compton backscattering of laser photons on the electrons. The laser light wavelength is chosen in such a way that after the scattering the electron does not leave the separatrix. Since the probability of the scattering is rather small, energy oscillations are damped prior to the next scattering. As a result, the proposed source can operate in a “parasitic” mode not interfering with the main mode of the accelerator operation. It is proposed to install at PETRA a tunable free-electron laser operating in the 20–50 μm wavelength band with peak and average output power ∼ 10 MW and ∼ 1 kW, respectively. This will result in the intensity of the γ-source ∼ 3 × 10 12s −1 with tunable γ-quantum energy up to 60 MeV. Gamma sources with a similar principle of operation could be constructed also at other storage rings such as HERA, TRISTAN, LEP(LEP 2), ESRF, SPring-8. Such γ-sources could reveal unique possibilities for precision investigations in nuclear physics.

Influence of magnetic field errors on the spectrum of the PETRA undulator

At HASYLAB at DESY, a first undulator beamline for the storage ring PETRA is under construction. Due to the low emittance of PETRA it will deliver very brilliant radiation in the energy range from 20 to 200 keV using the 1st, 3rd and 5th harmonic of this insertion device. The brilliance of the undulator radiation is very sensitive to the magnetic field errors which deteriorate the coherence of the emitted radiation and decrease the brilliance of the harmonics. Therefore, we investigated the influence of different types of field errors on the intensities of the 1st, 3rd and 5th harmonic. The results for the PETRA undulator are presented and discussed.

A comparison of measured jet cross sections with QCD calculations fore + e − annihilation

The cross sections for 2-, 3- and 4-jet production have been determined with the JADE detector, sited on thee+e−-storage ring PETRA. Data at\(\sqrt s = 14\), 22, 35 and 44 GeV were compared to twoO(α s 2 ) QCD calculations. A first analysis was performed with uncorrected data using theO(α s 2 ) 3-jet matrix element calculation of Ellis, Ross and Terrano and the Lund String Monte Carlo program. In a second analysis the calculation of Kramer and Lampe was compared to corrected data. Both approaches gave a poor description of the data when the square of the momentum transferQ2=s was used as the scale of the running coupling constant. The description improved when the renormalization scale was adjusted to the process studied. The data ware used to fix the best renormalization scale.

Inclusive strange particle production ine + e − annihilation

We present an analysis of strange particle production frome+e− annihilation into multihadronic final states. The experiment was performed with the CELLO detector at the PETRA storage ring at DESY, the data was taken at a centre of mass energy of 35 GeV with an integrated luminosity of 86 pb−1. The particlesK S 0 ,K*± and Λ have been identified by their characteristic decays, and differential cross sections for their production have been obtained. From a comparison ofK S 0 andK*± rates the Lund vector meson suppression parameterV/(V+P) S has been determined.

A measurement of the weak axial couplings of the b- and c-quark

The forward-backward charge asymmetries of the b and c quarks are measured with the JADE detector at the e + e − storage ring PETRA at √ s = 35 GeV and 44 GeV using both electrons and muons to tag the heavy quarks. At √ s = 35 GeV, a simultaneous fit for the two asymmetries yields the result A b = −9.3 ± 5.2% (stat.) and A c = −9.6±4.0% (stat.). Combining the results of 1 parameter fits of the asymmetries at both energies gives a b = −0.72±0.34 and a c = 0.79 ± 0.40 respectively. The mixing parameter for continuum b b ̄ - production is determined to be χ = 0.24 ± 0.12 if both heavy quark coupling constants are constrained to their Standard Model values.

Search for the inclusive production ofJ/? ine + e ? collisions using PLUTO data

We have searched for the inclusive production ofJ/Ψ ine+e− hadronic events collected by the PLUTO detector at the storage ring PETRA in a range of energies from 30 to 35 GeV. The data were analyzed identifying muons in multihadronic events and looking for the decay modeJ/Ψ→μ+μ−. With no candidate found, the upper limit obtained for the total cross section is σ(e+e−→J/Ψ+X)≦12 pb (90% C.L.), using an integrated luminosity ∫dL=41.7 pb−1 at the average c.m. energy\(\sqrt s = 34.4 GeV\). Together with previous results, this rules out a model based on non-perturbative QCD production mechanisms.

A measurement of the charmed quark asymmetry ine + e ? annihilation

The charmed quark charge asymmetry has been measured at the average centre of mass energy of 35 GeV with the JADE detector at thee+e− storage ring PETRA. Charmed quarks were identified byD*± tagging using the ΔM technique.D*± mesons were reconstructed through their decay intoD0 mesons resulting in (Kπ) π and (K π π π) π final states. The measured charge asymmetryA=−0.149±0.067 is in agreement with the expectation from the electroweak interference effect in quantum flavour dynamics (QFD).

Production and decay of charmed mesions ine + e ? annihilation at $$\sqrt s &gt; 28$$

We report on a study of inclusive production ofD *± mesons ine + e − annihilation at c.m. energies between 28 and 46.8 GeV using the TASSO detector at the PETRA storage ring. A hardD *± energy spectrum is measured with a maximum nearE D *± ≃0.6E beam. The measured cross section ratio $$(\sigma _{D^{* + } } + \sigma _{D^{* - } } )/\sigma _{\mu \mu } = 1.28 \pm 0.09 \pm 0.18$$ indicates thatD * production accounts for a large fraction of the observed charm production. Two complementary methods have been used to determine the forward-backward asymmetry of charm pair production due to electroweak interference. Combining both measurements the product of the axial vector couplings of the electron and the charm quark to the weak neutral current was determined to beg A e g A c =−(0.276±0.073), in agreement with the standard model prediction of −0.25. Using a sample of reconstructedD *± mesons, the relative strength of the strong interaction coupling of thec quark compared to that of an average of all flavours is measured as αs(c)/αs(all)=0.91±0.38±0.15, consistent with the coupling constant being flavour independent. An update of ourD 0 lifetime measurement is presented, based on a considerable increase in statistics, the final result being $$\tau _{D^0 = } (4.8 \pm _{0.9 - 0.7}^{1.0 + 0.5} )10^{ - 13} s$$ .

Limits on doubly charged Higgs bosons and lepton-flavor violation.

We consider the effect of a doubly charged Higgs boson ({Delta}{sup {minus}{minus}}) on several processes. We find that the effective Hamiltonian that is normally used to interpret the results of muonium-antimuonium oscillation experiments also describes the {ital t}-channel exchange of a {Delta}{sup {minus}{minus}}. A limit on the existence of the {Delta}{sup {minus}{minus}} is extracted from the most recent muonium oscillation result. The effect of {Delta}{sup {minus}{minus}} exchange on high-energy Bhabha scattering is discussed, and a limit is extracted from the published cross sections of several experiments at the SLAC and DESY storage rings PEP and PETRA. The case of a nondiagonal coupling of the {Delta}{sup {minus}{minus}} to the charged leptons (nondiagonal in lepton flavor) is considered. A limit is extracted from the result of the most recent search for the rare decay {mu}{r arrow}3{ital e}. Finally, a coupling-independent limit is extracted from a recent measurement of the process {ital e}{sup +}e{sup {minus}}{r arrow}4 leptons at PETRA.

Experimental evidence for the non-Abelian nature of QCD from a study of multijet events produced in e+e- annihilation.

We present evidence for the non-Abelian nature of QCD from a study of multijet events produced in e+e− annihilations from √s =50 to 57 GeV in the AMY detector at the KEK storage ring TRISTAN. A comparison of the three-jet event fraction at TRISTAN to the fraction of the DESY storage ring PETRA shows that the QCD coupling strength αs decreases with increasing Q2. In addition, measurements of the angular distributions of four-jet events show evidence for the triple-gluon vertex.Received 29 December 1988DOI:https://doi.org/10.1103/PhysRevLett.62.1713©1989 American Physical Society

A measurement of the charge asymmetry of hadronic events in electron positron annihilation

The quark charge asymmetry, summed over flavours, has been measured at centre of mass energies of 35 GeV and 44 GeV using the JADE detector sited on the electron-positron storage ring PETRA. The asymmetry is found to be consistent with the expectations of the standard model at both energies and enables a measurement of the product of the axial-vector coupling constant of the electron with the axial-vector coupling constants of the quarks, assuming the moduli of these latter to be flavour independent. This gives, with reasonable assumptions concerning the effects of\(B^0 \overline {B^0 } \) mixing,aeaq=−1.09±0.18±0.23 where the first error is statistical and the second systematic.

Neutrino counting with the CELLO detector and search for supersymmetric particles

A search for single photons, produced in e +e − collisions together with particles interacting only weakly with matter, has been performed using the CELLO detector at the PETRA storage ring. We report on results from data taken at 35 GeV < √ s<46.57 GeV. An upper limit of 8.7 (90% CL) on the number of light neutrino species is set. Combining our result with published results from other e +e − experiments the number of light neutrinos is limited to N v < 4.6 at 90% CL. We also set lower limits on the masses of supersymmetric particles.

New limits from single-photon searches at e+e- colliders.

We consider the possibility of radiative pair production of millicharged matter (particles with effective electric charge epsilone where epsilon<<1) in e/sup +/e/sup -/ collisions and give constraints on the charge (epsilon) of light (< few GeV) millicharged particles from recent single-photon experiments at the SLAC and DESY e/sup +/e/sup -/ storage rings PEP and PETRA. Following a recent suggestion, we also derive limits on a possible anomalous W magnetic moment from these data.