A. Mussgiller

Azimuthal single-spin asymmetries of lepto-produced pions and charged kaons were measured on a transversely polarized hydrogen target. Evidence for a naive-T-odd, transverse-momentum-dependent parton distribution function is deduced from non-vanishing Sivers effects for pi+, pi0, and K+, K-, as well as in the difference of the pi+ and pi- cross sections.

Single-spin asymmetries for pions and charged kaons are measured in semi-inclusive deep-inelastic scattering of positrons and electrons off a transversely nuclear-polarized hydrogen target. The dependence of the cross section on the azimuthal angles of the target polarization (phi_S)and the produced hadron (phi) is found to have a substantial sin(phi+phi_S) modulation for the production of pi+, pi- and K+. This Fourier component can be interpreted in terms of non-zero transversity distribution functions and non-zero favored and disfavored Collins fragmentation functions with opposite sign. For pi0 and K- production the amplitude of this Fourier component is consistent with zero.

Multiplicities in semi-inclusive deep-inelastic scattering are presented for each charge state of \pi^\pm and K^\pm mesons. The data were collected by the HERMES experiment at the HERA storage ring using 27.6 GeV electron and positron beams incident on a hydrogen or deuterium gas target. The results are presented as a function of the kinematic quantities x_B, Q^2, z, and P_h\perp. They represent a unique data set for identified hadrons that will significantly enhance our understanding of the fragmentation of quarks into final-state hadrons in deep-inelastic scattering.

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.

A series of semi-inclusive deep-inelastic scattering measurements on deuterium, helium, neon, krypton, and xenon targets has been performed in order to study hadronization. The data were collected with the HERMES detector at the DESY laboratory using a 27.6 GeV positron or electron beam. Hadron multiplicities on nucleus A relative to those on the deuteron, R_A^h, are presented for various hadrons (\pi^+, \pi^-, \pi^0, K^+, K^-, p, and \bar{p}) as a function of the virtual-photon energy \nu, the fraction z of this energy transferred to the hadron, the photon virtuality Q^2, and the hadron transverse momentum squared p_t^2. The data reveal a systematic decrease of R_A^h with the mass number A for each hadron type h. Furthermore, R_A^h increases (decreases) with increasing values of \nu (z), increases slightly with increasing Q^2, and is almost independent of p_t^2, except at large values of p_t^2. For pions two-dimensional distributions also are presented. These indicate that the dependences of R_A^{\pi} on \nu and z can largely be described as a dependence on a single variable L_c, which is a combination of \nu and z. The dependence on L_c suggests in which kinematic conditions partonic and hadronic mechanisms may be dominant. The behaviour of R_A^{\pi} at large p_t^2 constitutes tentative evidence for a partonic energy-loss mechanism. The A-dependence of R_A^h is investigated as a function of \nu, z, and of L_c. It approximately follows an A^{\alpha} form with \alpha \approx 0.5 - 0.6.

Double-spin asymmetries in exclusive electroproduction of real photons from a transversely polarized hydrogen target are measured with respect to the product of target polarization with beam helicity and beam charge, and with respect to the product of target polarization with beam helicity alone. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe--Heitler process. They are related to the real part of the same combination of Compton form factors as that determining the previously published transverse target single-spin asymmetries through the imaginary part. The results for the double-spin asymmetries are found to be compatible with zero within the uncertainties of the measurement, and are not incompatible with the predictions of the only available GPD-based calculation.

Beam-helicity and beam-charge asymmetries in the hard exclusive leptoproduction of real photons from an unpolarised hydrogen target by a 27.6 GeV lepton beam are extracted from the HERMES data set of 2006-2007 using a missing-mass event selection technique. The asymmetry amplitudes extracted from this data set are more precise than those extracted from the earlier data set of 1996-2005 previously analysed in the same manner by HERMES. The results from the two data sets are compatible with each other. Results from these combined data sets are extracted and constitute the most precise asymmetry amplitude measurements made in the HERMES kinematic region using a missing-mass event selection technique.

The pp-->ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for ppomega production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

The exclusive electroproduction of pi+ mesons was studied with the Hermes spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off an internal hydrogen gas target. The virtual-photon cross sections were measured as a function of the Mandelstam variable t and the squared four momentum -Q^2 of the exchanged virtual photon. A model calculation based on Generalized Parton Distributions is in fair agreement with the data at low values of |t| if power corrections are included. A model calculation based on the Regge formalism gives a good description of the magnitude and the t and Q^2 dependences of the cross section.

Longitudinal double-spin asymmetries of charged hadrons with high transverse momentum $p_T$ have been measured in electroproduction using the \hermes\ detector at \hera. Processes involving gluons in the nucleon have been enhanced relative to others by selecting hadrons with $p_T$ typically above 1 GeV. In this kinematic domain the gluon polarization has been extracted in leading order making use of the model embedded in the Monte Carlo Generator \Pythia\ 6.2. The gluon polarization obtained from single inclusive hadrons in the $p_T$ range 1 GeV $< p_T <$ 2.5 GeV using a deuterium target is $\frac{\Delta g}{g}(\langle x\rangle, \langle \mu^2\rangle)=0.049\pm 0.034 (stat)\pm 0.010 (sys\textrm{-}exp)^{+0.126}_{-0.099}(sys\textrm{-}models)$ at a scale $\la\mu^2\ra=1.35~{\rm GeV}^2$ and $\langle x\rangle = 0.22$. For different final states and kinematic domains, consistent values of \DGG\ have been found within statistical uncertainties using hydrogen and deuterium targets.

Polarisation asymmetries are measured for the hard exclusive leptoproduction of real photons from a longitudinally polarised hydrogen target. These asymmetries arise from the deeply virtual Compton scattering and Bethe-Heitler processes. From the data are extracted two asymmetries in the azimuthal distribution of produced real photons about the direction of the exchanged virtual photon: $$ {\mathcal{A}_{\text{UL}}} $$ with respect to the target polarisation and $$ {\mathcal{A}_{\text{LL}}} $$ with respect to the product of the beam and target polarisations. Results for both asymmetries are compared to the predictions from a generalised parton distribution model. The sin φ and cos(0φ) amplitudes observed respectively for the $$ {\mathcal{A}_{\text{UL}}} $$ and $$ {\mathcal{A}_{\text{LL}}} $$ asymmetries are compatible with the sizeable predictions from the model. Unexpectedly, a sin(2φ) modulation in the $$ {\mathcal{A}_{\text{UL}}} $$ asymmetry with a magnitude similar to that of the sin φ modulation is observed.

The first direct measurement of the dependence on target nuclear mass of the average squared transverse momentum <pt**2> of pi+, pi-, and K+ mesons from deep-inelastic lepton scattering is obtained as a function of several kinematic variables. The data were accumulated at the HERMES experiment at DESY, in which the HERA 27.6 GeV lepton beam was scattered off several nuclear gas targets. The average squared transverse momentum was clearly observed to increase with atomic mass number. The effect increases as a function of Q**2 and x and remains constant as a function of both the virtual photon energy nu and the fractional hadron energy z, except that it vanishes as z approaches unity.

An earlier extraction from the HERMES experiment of the polarization-averaged parton distribution of strange quarks in the nucleon has been reevaluated using final data on the multiplicities of charged kaons in semi-inclusive deep-inelastic scattering obtained with a kinematically more comprehensive method of correcting for experimental effects.General features of the distribution are confirmed, but the rise at low x is less pronounced than previously reported.

A bstract The beam-helicity asymmetry in exclusive electroproduction of real photons by the longitudinally polarized Hera positron beam scattering off an unpolarized hydrogen target is measured at Hermes. The asymmetry arises from deeply virtual Compton scattering and its interference with the Bethe-Heitler process. Azimuthal amplitudes of the beam-helicity asymmetry are extracted from a data sample consisting of ep → epγ events with detection of all particles in the final state including the recoiling proton. The installation of a recoil detector, while reducing the acceptance of the experiment, allows the elimination of background from ep → eN πγ events, which was estimated to contribute an average of about 12% to the signal in previous Hermes publications. The removal of this background from the present data sample is shown to increase the magnitude of the leading asymmetry amplitude by 0 . 054 ± 0 . 016 to −0 . 328 ± 0 . 027 (stat . ) ± 0 . 045 (syst . ).

Single-spin asymmetries were investigated in inclusive electroproduction of charged pions and kaons from transversely polarized protons at the Hermes experiment. The asymmetries were studied as a function of the azimuthal angle ψ about the beam direction between the target-spin direction and the hadron production plane, the transverse hadron momentum PT relative to the direction of the incident beam, and the Feynman variable xF. The sin ψ amplitudes are positive for π+ and K+, slightly negative for π− and consistent with zero for K−, with particular PT but weak xF dependences. Especially large asymmetries are observed for two small subsamples of events, where also the scattered electron was recorded by the spectrometer.

The differential and total cross sections for kaon pair production in the $\mathit{pp}\ensuremath{\rightarrow}{\mathit{ppK}}^{+}{K}^{\ensuremath{-}}$ reaction have been measured at three beam energies of 2.65, 2.70, and 2.83 GeV using the ANKE magnetic spectrometer at the COSY-J\"ulich accelerator. These near-threshold data are separated into pairs arising from the decay of the \ensuremath{\phi}-meson and the remainder. For the non-\ensuremath{\phi} selection, the ratio of the differential cross sections in terms of the ${K}^{\ensuremath{-}}p$ and ${K}^{+}p$ invariant masses is strongly peaked toward low masses. This effect can be described quantitatively by using a simple ansatz for the ${K}^{\ensuremath{-}}p$ final state interaction, where it is seen that the data are sensitive to the magnitude of an effective ${K}^{\ensuremath{-}}p$ scattering length. When allowance is made for a small number of \ensuremath{\phi} events where the ${K}^{\ensuremath{-}}$ rescatters from the proton, the \ensuremath{\phi} region is equally well described at all three energies. A very similar phenomenon is discovered in the ratio of the cross sections as functions of the ${K}^{\ensuremath{-}}\mathit{pp}$ and ${K}^{+}\mathit{pp}$ invariant masses and the identical final state interaction model is also very successful here. The world data on the energy dependence of the non-\ensuremath{\phi} total cross section is also reproduced, except possibly for the results closest to threshold.

Azimuthal asymmetries in exclusive electroproduction of real photons are measured for the first time with respect to transverse target polarisation, providing new constraints on Generalized Parton Distributions. From the same data set on a hydrogen target, new results for the beam-charge asymmetry are also extracted with better precision than those previously reported. By comparing model calculations with measured asymmetries attributed to the interference between the deeply virtual Compton scattering and Bethe-Heitler processes, a model-dependent constraint is obtained on the total angular momenta carried by up and down quarks in the nucleon.

Exclusive electroproduction of pi+ mesons was studied by scattering 27.6 GeV positrons or electrons off a transversely polarized hydrogen target. The single-spin azimuthal asymmetry with respect to target polarization was measured as a function of the Mandelstam variable t, the Bjorken scaling variable x_B, and the virtuality Q^2 of the exchanged photon. The extracted Fourier components of the asymmetry were found to be consistent with zero, except one that was found to be large and that involves interference of contributions from longitudinal and transverse virtual photons.

Azimuthal asymmetries in exclusive electroproduction of a real photon from an unpolarized deuterium target are measured with respect to beam helicity and charge. They appear in the distribution of these photons in the azimuthal angle phi around the virtual-photon direction, relative to the lepton scattering plane. The extracted asymmetries are attributed to either the deeply virtual Compton scattering process or its interference with the Bethe-Heitler process. They are compared with earlier results on the proton target. In the measured kinematic region, the beam-charge asymmetry amplitudes and the leading amplitudes of the beam-helicity asymmetries on an unpolarized deuteron target are compatible with the results from unpolarized protons.

The quasifree $pn\ensuremath{\rightarrow}d\ensuremath{\phi}$ reaction has been studied at the Cooler Synchrotron COSY---J\"ulich, using the internal proton beam incident on a deuterium cluster-jet target and detecting a fast deuteron in coincidence with the ${K}^{+}{K}^{\ensuremath{-}}$ decay of the $\ensuremath{\phi}$ meson. The energy dependence of the total and differential cross sections are extracted for excess energies up to 80 MeV by determining the Fermi momentum of the target neutron on an event-by-event basis. Though these cross sections are consistent with $s$-wave production, the kaon angular distributions show the presence of $p$ waves at quite a low energy. Production on the neutron is found to be stronger than on the proton but not by as much as for the $\ensuremath{\eta}$ meson.

The transverse-target single-spin asymmetry for inclusive deep-inelastic scattering with effectively unpolarized electron and positron beams off a transversely polarized hydrogen target was measured, with the goal of searching for a two-photon exchange signal in the kinematic range 0.007<xB<0.9 and 0.25GeV2<Q2<20GeV2. In two separate regions Q2>1GeV2 and Q2<1GeV2, and for both electron and positron beams, the asymmetries are found to be consistent with zero within statistical and systematic uncertainties, which are of order 10−3 for the asymmetries integrated over xB.

The nuclear--mass dependence of azimuthal cross-section asymmetries with respect to charge and longitudinal polarization of the lepton beam is studied for hard exclusive electroproduction of real photons. The observed beam-charge and beam-helicity asymmetries are attributed to the interference between the Bethe-Heitler and the deeply virtual Compton scattering processes. For various nuclei, the asymmetries are extracted for both coherent and incoherent-enriched regions, which involve different (combinations of) generalized parton distributions. For both regions, the asymmetries are compared to those for a free proton, and no nuclear-mass dependence is found.

Hadron multiplicities in semi-inclusive deep-inelastic scattering were measured on neon, krypton and xenon targets relative to deuterium at an electron(positron)-beam energy of 27.6 GeV at HERMES. These ratios were determined as a function of the virtual-photon energy nu, its virtuality Q2, the fractional hadron energy z and the transverse hadron momentum with respect to the virtual-photon direction pt . Dependences were analysed separately for positively and negatively charged pions and kaons as well as protons and antiprotons in a two-dimensional representation. Compared to the one-dimensional dependences, some new features were observed. In particular, when z > 0.4 positive kaons do not show the strong monotonic rise of the multiplicity ratio with nu as exhibited by pions and negative kaons. Protons were found to behave very differently from the other hadrons.

A measurement of the virtual-photon asymmetry A_2(x,Q^2) and of the spin-structure function g_2(x,Q^2) of the proton are presented for the kinematic range 0.004 < x < 0.9 and 0.18 GeV^2 < Q^2 < 20 GeV^2. The data were collected by the HERMES experiment at the HERA storage ring at DESY while studying inclusive deep-inelastic scattering of 27.6 GeV longitudinally polarized leptons off a transversely polarized hydrogen gas target. The results are consistent with previous experimental data from CERN and SLAC. For the x-range covered, the measured integral of g_2(x) converges to the null result of the Burkhardt-Cottingham sum rule. The x^2 moment of the twist-3 contribution to g_2(x) is found to be compatible with zero.

The vector and tensor polarizations of a deuteron beam have been measured using elastic deuteron-carbon scattering at 75.6 MeV and deuteron-proton scattering at 270 MeV. After acceleration to 1170 MeV inside the COSY ring, the polarizations of the deuterons were checked by studying a variety of nuclear reactions using a cluster target at the ANKE magnet spectrometer placed at an internal target position of the storage ring. All these measurements were consistent with the absence of depolarization during acceleration and provide a number of secondary standards that can be used in subsequent experiments at the facility.

The exclusive electroproduction of ρ0 mesons was studied with the hermes spectrometer at the Desy laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target. Spin density matrix elements for this process were determined from the measured production- and decay-angle distributions of the produced ρ0 mesons. These matrix elements embody information on helicity transfer and the validity of s-channel helicity conservation in the case of a transversely polarized target. From the spin density matrix elements, the leading-twist term in the single-spin asymmetry was calculated separately for longitudinally and transversely polarized ρ0 mesons. Neglecting s-channel helicity changing matrix elements, results for the former can be compared to calculations based on generalized parton distributions, which are sensitive to the contribution of the total angular momentum of the quarks to the proton spin.

Measurements of the $\mathit{pd}\ensuremath{\rightarrow}{p}_{\text{sp}}{\mathit{dK}}^{+}{K}^{\ensuremath{-}}$ reaction, where ${p}_{\text{sp}}$ is a spectator proton, have been undertaken at the Cooler Synchrotron COSY-J\"ulich by detecting a fast deuteron in coincidence with a ${K}^{+}{K}^{\ensuremath{-}}$ pair in the ANKE facility. Although the proton beam energy was fixed, the moving target neutron allowed values of the nonresonant quasifree $\mathit{pn}\ensuremath{\rightarrow}{\mathit{dK}}^{+}{K}^{\ensuremath{-}}$ total cross section to be deduced up to an excess energy $\ensuremath{\epsilon}\ensuremath{\approx}100$ MeV. Evidence is found for the effects of ${K}^{\ensuremath{-}}d$ and $K\overline{K}$ final state interactions. The comparison of these data with those of $\mathit{pp}\ensuremath{\rightarrow}{\mathit{ppK}}^{+}{K}^{\ensuremath{-}}$ and $\mathit{pp}\ensuremath{\rightarrow}{\mathit{dK}}^{+}{\overline{K}}^{0}$ shows that all the total cross sections are very similar in magnitude.

Azimuthal asymmetries in exclusive electroproduction of a real photon from a longitudinally polarized deuterium target are measured with respect to target polarization alone and with respect to target polarization combined with beam helicity and/or beam charge. The asymmetries appear in the distribution of the real photons in the azimuthal angle ϕ around the virtual photon direction, relative to the lepton scattering plane. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe–Heitler process. The results for the beam-charge and beam-helicity asymmetries from a tensor polarized deuterium target with vanishing vector polarization are shown to be compatible with those from an unpolarized deuterium target, which is expected for incoherent scattering dominant at larger momentum transfer. Furthermore, the results for the single target-spin asymmetry and for the double-spin asymmetry are found to be compatible with the corresponding asymmetries previously measured on a hydrogen target. For coherent scattering on the deuteron at small momentum transfer to the target, these findings imply that the tensor contribution to the cross section is small. Furthermore, the tensor asymmetry is found to be compatible with zero.

Results of inclusive measurements of inelastic electron and positron scattering from unpolarized protons and deuterons at the HERMES experiment are presented. The structure functions F 2 p and F 2 d are determined using a parameterization of existing data for the longitudinal-to-transverse virtual-photon absorption cross-section ratio. The HERMES results provide data in the ranges 0.006 ≤ x ≤ 0.9 and 0.1 GeV2 ≤ Q 2 ≤ 20 GeV2, covering the transition region between the perturbative and the non-perturbative regimes of QCD in a so-far largely unexplored kinematic region. They are in agreement with existing world data in the region of overlap. The measured cross sections are used, in combination with data from other experiments, to perform fits to the photon-nucleon cross section using the functional form of the ALLM model. The deuteron-to-proton cross-section ratio is also determined.

The spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Jülich in spring 1998. An initial scientific goal is to study K+-production in pA collisions at subthreshold energies far below the free NN-threshold at Tp=1.58 GeV. This requires the identification of K+-mesons in a background of pions and protons, about 106 times more intense. In this paper the sophisticated detection system and the software procedures for kaon identification are described. With the help of TOF, energy-loss and range measurements as well as the track information from wire chambers, it is possible to measure d2σ/dΩdp for deep subthreshold K+ production at beam energies down to Tp=1.0 GeV.

Future detector systems have increasing demands on the performance of their mechanical support structures and cooling systems. Novel materials and cooling techniques are developed and continuously improved in order to fulfil these requirements. A custom thermal conductivity measurement setup is presented to measure these materials thermal conductivity. The setup consists of two heat flux meter blocks between which the samples are clamped. The setup follows the American Society for Testing and Materials standard D5470-06 and consists of two brass blocks, which act as heat flow meters. In order to minimize heat exchange between the heat flux blocks and the ambient via convection and radiation, the setup is covered with a radiation shield and measurements are carried out in a vacuum. The contribution describes the setup in detail, motivates its design aspects and highlights the commissioning and calibration procedure. The analysis method and calibration procedure are presented.

With the ANKE spectrometer at the COoler SYnchrotron COSY Juelich the mesonic structure of the nucleon will be studied in polarized proton-proton and proton-deuteron collisions. The identification and tracking of low energy protons permits using deuterium as an effective neutron target. For this purpose, modular self-triggering tracking telescopes built up by double-sided silicon strip detectors inside the accelerator ultra-high vacuum have been developed. Their basic features are /spl Delta/E/E proton identification from 2.5 $40 MeV and particle tracking over a wide dynamic range, either 2.5 MeV spectator protons or minimum ionizing particles. By the use of self-triggering read-out chips, the telescopes identify a particle passage within 100 ns and therefore allow the possibility of a fast hit pattern recognition. In combination with a read-out pitch of /spl sim/200 /spl mu/m, they provide a high rate capability. The recent development of very thick (/spl ges/5 mm) double-sided microstructured Si(Li) and very thin (/spl les/65 /spl mu/m) double-sided Si-detectors provides the use of the telescopes over a wide range of particle energies.

The pp→ppπ0 differential cross section has been measured with the ANKE spectrometer at COSY–Jülich for pion cms angles between 0° and 15.4° at a proton beam energy of 0.8 GeV. The selection of diproton pairs with an excitation energy Epp<3MeV ensures that the final pp system is dominantly in the spin-singlet S01 state. The kinematics are therefore very similar to those of pp→dπ+ but with different spin and isospin transitions. The cross sections are over two orders of magnitude smaller than those of pp→dπ+ and show a forward dip that is even stronger than that seen at lower energies. The results should provide a crucial extra test of pion production models in nucleon–nucleon collisions.

Exclusive rho^0-meson electroproduction is studied in the HERMES experiment, using a 27.6 GeV longitudinally polarized electron/positron beam and unpolarized hydrogen and deuterium targets in the kinematic region 0.5 GeV^2 < Q^2 < 7.0 GeV^2, 3.0 GeV < W < 6.3 GeV, and -t' < 0.4 GeV^2. Real and imaginary parts of the ratios of the natural-parity-exchange helicity amplitudes T_{11} (\gamma^*_T --> \rho_T), T_{01} (\gamma^*_T --> \rho_L), T_{10} (\gamma^*_L --> \rho_T), and T_{1-1} (\gamma^*_{-T} -->\rho_T) to T_{00} (\gamma^*_L --> \rho_L) are extracted from the data. For the unnatural-parity-exchange amplitude U_{11}, the ratio |U_{11}/T_{00}| is obtained. The Q^2 and t' dependences of these ratios are presented and compared with perturbative QCD predictions.

Inclusive K+ production in proton–proton collisions has been measured at a beam energy of 2.16 GeV using the COSY-ANKE magnetic spectrometer. The resulting spectrum, as well as those corresponding to K+p and K+π+ correlated pairs, can all be well described using consistent values of the total cross sections for the pp→K+pΛ, pp→K+pΣ0, and pp→K+nΣ+ reactions. While the resulting values for Λ and Σ0 production are in good agreement with world data, our value for the total Σ+ production cross section, σ(pp→K+nΣ+)=(2.5±0.6stat±0.4syst) μb at an excess energy of ε=129 MeV, could only be reconciled with other recently published data if there were a highly unusual near threshold behaviour.

A bstract A search for new top quark interactions is performed within the framework of an effective field theory using the associated production of either one or two top quarks with a Z boson in multilepton final states. The data sample corresponds to an integrated luminosity of 138 fb − 1 of proton-proton collisions at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV collected by the CMS experiment at the LHC. Five dimension-six operators modifying the electroweak interactions of the top quark are considered. Novel machine-learning techniques are used to enhance the sensitivity to effects arising from these operators. Distributions used for the signal extraction are parameterized in terms of Wilson coefficients describing the interaction strengths of the operators. All five Wilson coefficients are simultaneously fit to data and 95% confidence level intervals are computed. All results are consistent with the SM expectations.

The production of ω-mesons in the pp → ppω reaction has been investigated with the COSY-ANKE spectrometer for excess energies of 60 and 92MeV by detecting the two final protons and reconstructing their missing mass. The large physical background was subtracted using an event-by-event transformation of the proton momenta between the two energies. Differential distributions and total cross-sections were obtained after careful studies of possible systematic uncertainties in the overall ANKE acceptance. The results are compared with the predictions of theoretical models. Combined with data on the φ-meson, a more refined estimate is made of the Okubo-Zweig-Iizuka rule violation in the φ/ω production ratio.

The transverse polarization of $\mathrm{\ensuremath{\Lambda}}$ hyperons was measured in inclusive quasireal photoproduction for various target nuclei ranging from hydrogen to xenon. The data were obtained by the HERMES experiment at HERA using the 27.6 GeV lepton beam and nuclear gas targets internal to the lepton storage ring. The polarization observed is positive for light target nuclei and is compatible with zero for krypton and xenon.

The first measurement of the $pn\rightarrow d\omega$ total cross-section has been achieved at mean excess energies $Q\approx 28$ and 57 MeV by using a deuterium cluster-jet target. The momentum of the fast deuteron was measured in the ANKE spectrometer at COSY-Jülich and that of the slow “spectator” proton $(p_{\rm {sp}})$ from the $pd\rightarrow p_{\rm {sp}}d\omega$ reaction in a silicon telescope placed close to the target. The cross-sections lie above those measured for $pp\rightarrow pp\omega$ but seem to be below theoretical predictions.

The pp → ppϕ and quasi–free pn → dϕ reactions have been studied at the Cooler Synchrotron COSY–Jülich, using the internal beam and the ANKE facility. Total cross sections in the pp entrance channel have been determined at three excess energies ∊ in the range of 18.5–75.9 MeV. In case of the pn entrance channel the energy dependence of the cross section up to 80 MeV has been extracted by exploiting the intrinsic momentum of the neutron inside a deuterium target. Taken together with data for ω–production, a significant enhancement of the ϕ/ω ratio for both entrance channels of a factor 8 is found compared to predictions based on the Okubo–Zweig–Iizuka rule.

Vector and tensor analysing powers of the d→p→(pp)n (charge-exchange) and d→p→(pn)p (non-charge-exchange) breakup reactions have been measured with the ANKE spectrometer at the COSY ring at a deuteron beam energy of 1170 MeV for small momentum transfers to the low excitation energy (pp) or (pn) systems. A quantitative understanding of the values of Axx and Ayy for the charge-exchange reaction is provided by impulse approximation calculations. The data suggest that spin-flip isospin-flip transitions, which dominate the charge-exchange breakup of the deuteron, are also important in the non-charge-exchange reaction.

A measurement of the analyzing power $A_y$ of the $\vec{p}d \to (pp) + n$ reaction was carried out at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy $E_{pp} < 3$ MeV. The kinematically complete experiment made use of the ANKE spectrometer at the internal beam of COSY and a deuterium cluster--jet target. For the first time the $S$--wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at $T_p=0.8$ GeV the measured analyzing power $A_y$ vanishes, it reaches almost unity at $T_p=0.5$ GeV for neutrons scattered at $\theta_n^{c.m.}=167^\circ$. The results are compared with a model taking into account one--nucleon exchange, single scattering and $\Delta$ (1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier by us and the analyzing power at 0.8 GeV, it fails to reproduce the angular dependence of $A_y$ at 0.5 GeV.

A comprehensive collection of results on longitudinal double-spin asymmetries is presented for charged pions and kaons produced in semi-inclusive deep-inelastic scattering of electrons and positrons on the proton and deuteron, based on the full HERMES data set.The dependence of the asymmetries on hadron transverse momentum and azimuthal angle extends the sensitivity to the flavor structure of the nucleon beyond the distribution functions accessible in the collinear framework.No strong dependence on those variables is observed.In addition, the hadron charge-difference asymmetry is presented, which under certain model assumptions provides access to the helicity distributions of valence quarks.

For the final running period of HERA, a recoil detector was installed at the HERMES experiment to improve measurements of hard exclusive processes in charged-lepton nucleon scattering. Here, deeply virtual Compton scattering is of particular interest as this process provides constraints on generalised parton distributions that give access to the total angular momenta of quarks within the nucleon. The HERMES recoil detector was designed to improve the selection of exclusive events by a direct measurement of the four-momentum of the recoiling particle. It consisted of three components: two layers of double-sided silicon strip sensors inside the HERA beam vacuum, a two-barrel scintillating fibre tracker, and a photon detector. All sub-detectors were located inside a solenoidal magnetic field with a field strength of 1T. The recoil detector was installed in late 2005. After the commissioning of all components was finished in September 2006, it operated stably until the end of data taking at HERA end of June 2007. The present paper gives a brief overview of the physics processes of interest and the general detector design. The recoil detector components, their calibration, the momentum reconstruction of charged particles, and the event selection are described in detail. The paper closes with a summary of the performance of the detection system.

A telescope of three silicon detectors has been installed close to the internal target position of the ANKE spectrometer, which is situated inside the ultra-high vacuum of the COSY-Jülich light-ion storage ring. The detection and identification of slow protons and deuterons emerging from a deuterium cluster-jet target thus becomes feasible. A good measurement of the energy and angle of such a spectator proton (psp) allows one to identify a reaction as having taken place on the neutron in the target and then to determine the kinematical variables of the ion–neutron system on an event-by-event basis over a range of c.m. energies. The system has been successfully tested under laboratory conditions. By measuring the spectator proton in the pd→pspdπ0 reaction in coincidence with a fast deuteron in the ANKE Forward Detector, values of the pn→dπ0 total cross-section have been deduced. Further applications of the telescope include the determination of the luminosity and beam polarisation which are required for several experiments.

A new pixel detector for the CMS experiment was built in order to cope with the instantaneous luminosities anticipated for the Phase~I Upgrade of the LHC. The new CMS pixel detector provides four-hit tracking with a reduced material budget as well as new cooling and powering schemes. A new front-end readout chip mitigates buffering and bandwidth limitations, and allows operation at low comparator thresholds. In this paper, comprehensive test beam studies are presented, which have been conducted to verify the design and to quantify the performance of the new detector assemblies in terms of tracking efficiency and spatial resolution. Under optimal conditions, the tracking efficiency is $99.95\pm0.05\,\%$, while the intrinsic spatial resolutions are $4.80\pm0.25\,\mu \mathrm{m}$ and $7.99\pm0.21\,\mu \mathrm{m}$ along the $100\,\mu \mathrm{m}$ and $150\,\mu \mathrm{m}$ pixel pitch, respectively. The findings are compared to a detailed Monte Carlo simulation of the pixel detector and good agreement is found.

The beam-helicity asymmetry in associated electroproduction of real photons, ep → eγπN , in the Δ(1232)-resonance region is measured using the longitudinally polarized Hera positron beam and an unpolarized hydrogen target. Azimuthal Fourier amplitudes of this asymmetry are extracted separately for two channels, ep → eγπ0 p and ep → eγπ+ n, from a data set collected with a recoil detector. All asymmetry amplitudes are found to be consistent with zero.

Single-spin asymmetries were investigated in inclusive electroproduction of charged pions and kaons from transversely polarized protons at the HERMES experiment. The asymmetries were studied as a function of the azimuthal angle $ψ$ about the beam direction between the target-spin direction and the hadron production plane, the transverse hadron momentum relative to the direction of the incident beam, and the Feynman variable $x_F$. The $\sin(ψ)$ amplitudes are positive for positive pions and kaons, slightly negative for negative pions and consistent with zero for negative kaons, with particular transverse-momentum but weak $x_F$ dependences. Especially large asymmetries are observed for two small subsamples of events, where also the scattered electron was recorded by the spectrometer.

Silicon sensor based particle detectors operated in a hadronic radiation environment need to be cooled to counteract the radiation induced leakage current and to prevent thermal runaway. To achieve this most efficiently, a low thermal resistance is required between the detector modules and the cooling structures. In many cases dry thermal contacts are sufficient, but especially for a large-area contact so-called thermal interface materials (TIM), largely availably on the market in many forms, are the preferred choice. However, in the use case for detector cooling there can be many requirements, such as non-liquid phase, no heat cure, low thermal impedance, no compression force, radiation hardness, making it challenging to find a suitable TIM. One option are room temperature curing two component thermal gap fillers. The thermal test setup determines the thermal conductivity of a test sample by measuring the temperature gradient with a controlled amount of heat flow through a sample. Mechanical tests are required to qualify the structural integrity of the thermal interface under thermal stress and mechanical stress. Resembling the style of an ISO 4587 lap shear test, and an ISO 25217 mode-1 fracture test, test samples were prepared with a large 5 $\times$ 5 cm$^2$ adhesion overlap using plasma cleaned carbon fibre plates to have a surface comparable to its intended use case. After testing of unirradiated samples, they have been irradiated to 600 kGy. The measured mechanical and thermal properties are presented and the results before and after irradiation are compared.

Received 22 June 2006DOI:https://doi.org/10.1103/PhysRevLett.97.029901©2006 American Physical Society

New data on ϕ-meson production in pp collisions have been obtained at the ANKE facility of COSY-Jülich. These data will provide the energy dependence of the total cross section down to an excess energy of 19 MeV above threshold. In combination with the existing SPES-III and COSY-TOF results on ω-meson production the ϕ/ω production ratio at this low excess energy will be extracted. As an exciting new aspect an enhancement in the invariant ϕp mass spectrum is observed at a mass around 1.965 GeV/c2.

Bose–Einstein correlations of like-sign charged hadrons produced in deep-inelastic electron and positron scattering are studied in the HERMES experiment using nuclear targets of $$^1$$ H, $$^2$$ H, $$^3$$ He, $$^4$$ He, N, Ne, Kr, and Xe. A Gaussian approach is used to parametrize a two-particle correlation function determined from events with at least two charged hadrons of the same sign charge. This correlation function is compared to two different empirical distributions that do not include the Bose–Einstein correlations. One distribution is derived from unlike-sign hadron pairs, and the second is derived from mixing like-sign pairs from different events. The extraction procedure used simulations incorporating the experimental setup in order to correct the results for spectrometer acceptance effects, and was tested using the distribution of unlike-sign hadron pairs. Clear signals of Bose–Einstein correlations for all target nuclei without a significant variation with the nuclear target mass are found. Also, no evidence for a dependence on the invariant mass W of the photon-nucleon system is found when the results are compared to those of previous experiments.

Abstract As a result of the high luminosity phase of the SLHC, for CMS a tracking system with very high granularity is mandatory and the sensors will have to withstand an extreme radiation environment of up to 10 16  part/ 2 . On this basis, a new geometry with silicon short strip sensors (strixels) is proposed. To understand their performances, test geometries are developed whose parameters can be verified and optimized using simulation of semiconductor structures. We have used the TCAD-ISE (SYNOPSYS package) software in order to simulate the main electrical parameters of different strip geometries, for p-in-n-type wafers.

The CMS detector at the LHC is foreseen to experience a major upgrade in order to cope with increased radiation flux due to the high-luminosity operation phase of the accelerator. The CMS tracker will be replaced completely, introducing a new module concept in the outer part of the subsystem, which will exploit the strong magnetic field inside the CMS detector to select high transverse momentum particles locally and send the corresponding information to the triggering system thus enhancing the efficiency of the latter.In order to allow for module prototyping and production testing, an intermediate DAQ system, referred to as μDTC, was developed in the scope of this thesis. The system allows for prototype configuration, control, monitoring and read-out, and provides all the necessary infrastructure for the module qualification. This thesis describes the upgrade project with a focus on the existing module prototypes and the structure of the FPGA firmware developed for the μDTC. A sequence of test beam measurement campaigns was carried out using the aforementioned DAQ system, and the results obtained from two of them are described in detail in the text.

Large scale detectors in particle physics take many years to plan and to build. The last generation of large particle physics detectors for the energy frontier, ATLAS and CMS, have been operating for more than 10 years, and upgrades for them are now being done. Studies for the next generation of experimental facilities have been ongoing for a number of years. In this section future directions in integrated detector design are discussed, as they were visible at the time of writing this report.

The new spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Jülich. An initial scientific goal is to study K+-production in pA collisions at subthreshold energies below the free NN-threshold of T = 1.58 GeV. First measurements of double differential cross sections in p12C collisions at emission angles around 0° have been performed at T = 1.0, 1.2 and 2.0 GeV. The challenge is to identify the kaons in a huge background of pions and protons, since the signal to background ratio decreases to about 10−6 at T = 1.0 GeV. For background suppression detectors and a trigger system based on energy-loss and time-of-flight measurements have been developed. In the analysis the decay of kaons (τ = 12.4 ns) stopped in the detection system into μ+ and π+ is exploited as well as the track information from the wire chambers.

While the tracking detectors of the ATLAS and CMS experiments have shown excellent performance in Run 1 of LHC data taking, and are expected to continue to do so during LHC operation at design luminosity, both experiments will have to exchange their tracking systems when the LHC is upgraded to the high-luminosity LHC (HL-LHC) around the year 2024. The new tracking systems need to operate in an environment in which both the hit densities and the radiation damage will be about an order of magnitude higher than today. In addition, the new trackers need to contribute to the first level trigger in order to maintain a high data-taking efficiency for the interesting processes. Novel detector technologies have to be developed to meet these very challenging goals. The German groups active in the upgrades of the ATLAS and CMS tracking systems have formed a collaborative "Project on Enabling Technologies for Silicon Microstrip Tracking Detectors at the HL-LHC" (PETTL), which was supported by the Helmholtz Alliance "Physics at the Terascale" during the years 2013 and 2014. The aim of the project was to share experience and to work together on key areas of mutual interest during the R&amp;D phase of these upgrades. The project concentrated on five areas, namely exchange of experience, radiation hardness of silicon sensors, low mass system design, automated precision assembly procedures, and irradiations. This report summarizes the main achievements.

The transverse polarization of $\Lambda$ hyperons was measured in inclusive quasireal photoproduction for various target nuclei ranging from hydrogen to xenon. The data were obtained by the HERMES experiment at HERA using the 27.6 GeV lepton beam and nuclear gas targets internal to the lepton storage ring. The polarization observed is positive for light target nuclei and is compatible with zero for krypton and xenon.

Bose-Einstein correlations of like-sign charged hadrons produced in deep-inelastic electron and positron scattering are studied in the HERMES experiment using nuclear targets of $^1$H, $^2$H, $^3$He, $^4$He, N, Ne, Kr, and Xe. A Gaussian approach is used to parametrize a two-particle correlation function determined from events with at least two charged hadrons of the same sign charge. This correlation function is compared to two different empirical distributions that do not include the Bose-Einstein correlations. One distribution is derived from unlike-sign hadron pairs, and the second is derived from mixing like-sign pairs from different events. The extraction procedure used simulations incorporating the experimental setup in order to correct the results for spectrometer acceptance effects, and was tested using the distribution of unlike-sign hadron pairs. Clear signals of Bose-Einstein correlations for all target nuclei without a significant variation with the nuclear target mass are found. Also, no evidence for a dependence on the invariant mass W of the photon-nucleon system is found when the results are compared to those of previous experiments.

The CMS detector is a very complex apparatus with more than 70 million data acquisition channels. The full physics potential of CMS and the recorded data can only be exploited with precise calibration and alignment constants that have to be produced in an efficient way. The CMS Collaboration has set up an infrastructure for alignment and calibration based on dedicated skimmed data streams providing inputs which are specific to the various workflows computing these constants. A prompt calibration concept allows for the determination of the most time-dependent constants almost immediately after the data are recorded, thus following as fast as possible any change in the running conditions. The paper will introduce the basic concepts of the CMS alignment and calibration infrastructure, and present results from selected workflows.

The CMS Binary Chip (CBC) is a prototype version of the front-end read-out ASIC to be used in the silicon strip modules of the CMS outer tracking detector during the high luminosity phase of the LHC. The CBC is produced in 130 nm CMOS technology and bump-bonded to the hybrid of a double layer silicon strip module, the so-called 2S-pT module. It has 254 input channels and is designed to provide on-board trigger information to the first level trigger system of CMS, with the capability of cluster-width discrimination and high-pT track identification. In November 2013 the first 2S-pT module prototypes equipped with the CBC chips were put to test at the DESY-II test beam facility. Data were collected exploiting a beam of positrons with an energy ranging from 2 to 4 GeV. In this paper the test setup and the results are presented.

Hard exclusive processes provide access to generalized parton distributions (GPDs), which extend our description of the nucleon structure beyond the standard parton distributions. The Deeply Virtual Compton Scattering (DVCS) process provides the theoretically cleanest access to the GPDs. For the final two years of data taking, a recoil detector was installed at HERMES for the purpose of improving the ability to measure hard‐exclusive processes. In addition the recoil detector allows one to measure the individual background contributions which can be used to refine previously published results on DVCS. The progress of the ongoing data analysis is presented.

For the final running period of HERA, a Recoil Detector was installed at the HERMES experiment to improve measurements of hard exclusive processes.Here, Deeply-Virtual Compton scattering is of particular interest, as this process provides constraints on Generalized Parton Distributions that give access to the total angular momenta of quarks inside the nucleon.The HERMES Recoil Detector was designed to improve the selection of exclusive events by a direct measurement of the four-momentum of the recoiling particles.It consisted of three components: two layers of double-sided silicon sensors inside the HERA vacuum, a two-barrel scintillating fiber tracker, and a photon detector.All sub-detectors were located inside a 1 Tesla solenoidal magnetic field.The Recoil Detector was installed in late 2005.After the commissioning of all components was finished in September 2006, it was working stable until the end of data taking at HERA on June 30 of 2007.Results on the performance and calibration of the silicon detector are presented.

The present theses discusses the development, technical design and realization as well as the read-out electronics of a detection system for the identification and tracking of low energy spectator protons. With the knowledge of the four-momentum of such spectator protons it will be possible to use deuterium as an effective neutron target. Previous measurements with an early version of the detection system have already shown that this method works quite well to investigate for instance the omega or eta-meson production in proton-neutron collisions. Moreover, after the completion and installation of the polarized internal target (PIT) at ANKE, it will be even possible to engage in that field with double polarized experiments. To increase the luminosity the polarized target is equipped with an extended target cell. The described detection-system will provide the vertex reconstruction for this extended interaction region. In addition, it will act as an independent beam polarimeter at ANKE. The detection system consists of three layers of double-sided silicon strip detectors which are arranged in a telescope structure and placed inside the accelerator vacuum as close as 2 cm to the interaction region. The modular design of the electronics and the support structures for the detectors allows one to exchange detectors and electronics in a maximum flexible way. In a minimum configuration the telescope is equipped with two detectors, a thin (69 um) double-sided Silicon strip detector as a first layer and a very thick (>=5 mm) double-sided micro-structured Lithium-drifted Silicon detector as a second layer. With this arrangement it is possible to track and identify protons in a kinetic energy range from 2.5 MeV to 25 MeV. For deuterons this range for such a telescope configuration is from 4 MeV to 34 MeV$. The performance concerning the energy determination and tracking is shown based on data taken during a beam-time in November of 2003. With the existing setup an energy resolution of 120 keV for the 69 um thick first detection layer could be achieved. The proton-deuteron separation was in the order of 3.8 sigma. First results of the measurements of the analyzing powers Ay and Ayy for the reaction dp -> dp as well as Ay for the reactions dp -> (pp)n and dp -> (np)p are presented to demonstrate the possible applications of the detection-system.

The Deeply Virtual Compton Scattering (DVCS) process provides the theoretically cleanest access to the unknown generalized parton distributions (GPDs).DVCS amplitudes can be measured through the interference between the Bethe-Heitler DVCS processes via the dependence of cross-section asymmetries on the azimuthal angle.The accumulated HERMES data offers access to the four GPDs in different combinations of beam charge and helicity as well as target spin.A recent highlight has been the transverse target-spin asymmetry that provides access to the total angular momentum of quarks.In late 2005, a Recoil Detector was installed at HERMES with the purpose of greatly improving the experiment's ability to measure hard-exclusive processes during its final running period [1].

For the ANKE spectrometer at the Cooler Synchrotron COSY-Julich, a vertex detector is under development. Double-sided structured silicon-strip detectors with a thickness from 65 /spl mu/m to 5500 /spl mu/m are used in a telescope-like structure. They allow the /spl Delta/E/E-identification of low energy spectator protons and therefore the use of deuterium as an effective neutron target. As frontend chip the VA32TA2 has been selected. They are connected to both sides of the detector. Because half of them, together with their readout electronics, needs to be operated at the bias voltage of the detectors (10-1000 V), a special system for multiplexed chip readout has been developed. It provides two ADCs per detector, one per each side, and allows for the configuration of all analog voltages by DACs and control timings by programmable sequence generators.

ANKE is a second generation experimental facility at the internal beam of the accelerator COSY at the Forschungszentrum Jülich (Germany). It has recently (May 1998) been installed in the ring, commissioned and immediately after this been exploited for first experiments. Using circulating beams of protons with energies between 1.0 and 2.3 GeV, sub- and near threshold production of K+ mesons in collisions with carbon-strip targets has been investigated. The detection system of ANKE used for the first measurements is capable of detecting positively charged ejectiles in the momentum range between about 100 and 600 MeV/c. In particular, it has been optimized for K+ identification in the presence of an intense background of protons and pions. The final results of the experiments (cross sections and momentum spectra) will be used to obtain more detailed information on the subthreshold production mechanism.