arXiv subjects

R. Seidl

Publications and source records attributed to R. Seidl.

26 records · Page 2Linked to original sources

arXiv2013

Precision measurement of charged pion and kaon differential cross sections in electron-positron annihilation at Q = 10.52 GeV

Measurements of inclusive differential cross sections for charged pion and kaon production in electron-positron annihilation have been carried out at a center-of-mass energy of Q = 10.52 GeV. The measurements were performed with the Belle detector at the KEKB electron-positron collider using a data sample containing 113 million e+e- -> qqbar events, where q={u,d,s,c}. We present charge-integrated differential cross sections dσ_h+-/dz for h+- = pi+-, K+- as a function of the relative hadron energy z = 2*E_h / sqrt{s} from 0.2 to 0.98. The combined statistical and systematic uncertainties for pi+- (K+-) are 4% (4%) at z ~ 0.6 and 15% (24%) at z ~ 0.9. The cross sections are the first measurements of the z-dependence of pion and kaon production for z > 0.7 as well as the first precision cross section measurements at a center-of-mass energy far below the Z^0 resonance used by the experiments at LEP and SLC.

hep-ex↗

arXiv2012

Excess flux stability fingerprints in the I_c(B)-T_c(B) phase boundary of superconducting thin films with quasiperiodic microtopology

We experimentally investigate the magnetic field $B$ dependence of the critical current I_c and the transition temperature T_c, i.e. the I_c(B)-T_c(B) phase boundary, of superconducting niobium thin films patterned with periodic and quasiperiodic antidot arrays on the submicron scale. For this purpose we monitor current-voltage characteristics at different values of B and T. We investigate samples with antidots positioned at the vertices of two different tilings with quasiperiodic symmetry, namely the Shield Tiling and the Tuebingen Triangle Tiling. For reference we investigate a sample with a triangular antidot lattice. We find modulations of the phase boundary for both quasiperiodic tilings, which were predicted by numerical simulations but not observed in experiments yet. The particularity of these commensurability effects is that they correspond to excess flux densities, which are slightly higher than the matching flux. The observed matching effects can be explained by quasiperiodic caging of interstitial vortices and/or the formation of symmetry induced giant vortices.

cond-mat.supr-con↗

arXiv2011

Observation of transverse polarization asymmetries of charged pion pairs in e+e- annihilation near sqrt s=10.58 GeV

The interference fragmentation function translates the fragmentation of a quark with a transverse projection of the spin into an azimuthal asymmetry of two final-state hadrons. In e+e- annihilation the product of two interference fragmentation functions is measured. We report nonzero asymmetries for pairs of charge-ordered pi+pi- pairs, which indicate a significant interference fragmentation function in this channel. The results are obtained from a 672 fb-1 data sample that contains 711 \times 106 pi+pi- pairs and was collected at and near the ?(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e+e- collider.

hep-ex↗

arXiv2008

Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs in e+e- Annihilation at \sqrt{s} = 10.58 GeV

The Collins effect connects transverse quark spin with a measurable azimuthal asymmetry in the yield of hadronic fragments around the quark's momentum vector. Using two different reconstruction methods we measure statistically significant azimuthal asymmetries for charged pion pairs in e+e- annihilation at center-of-mass energies of 10.52 GeV and 10.58 GeV, which can be attributed to the fragmentation of primordial quarks with transverse spin components. The measurement was performed using a dataset of 547 fb^{-1} collected by the Belle detector at KEKB improving the statistics of the previously published results by nearly a factor of 20.

hep-ex↗

arXiv2008

Parton fragmentation in the vacuum and in the medium

We present the mini-proceedings of the workshop on ``Parton fragmentation in the vacuum and in the medium'' held at the European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*, Trento) in February 2008. The workshop gathered both theorists and experimentalists to discuss the current status of investigations of quark and gluon fragmentation into hadrons at different accelerator facilities (LEP, B-factories, JLab, HERA, RHIC, and Tevatron) as well as preparations for extension of these studies at the LHC. The main physics topics covered were: (i) light-quark and gluon fragmentation in the vacuum including theoretical (global fits analyses and MLLA) and experimental (data from e+e-, p-p, e-p collisions) aspects, (ii) strange and heavy-quark fragmentation, (iii) parton fragmentation in cold QCD matter (nuclear DIS), and (iv) medium-modified fragmentation in hot and dense QCD matter (high-energy nucleus-nucleus collisions). These mini-proceedings consist of an introduction and short summaries of the talks presented at the meeting.

hep-ph↗

arXiv2006

Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs in e+e- Annihilation at Belle

The Collins effect connects transverse quark spin with a measurable azimuthal dependence in the yield of hadronic fragments around the quark's momentum vector. Using two different reconstruction methods we observe statistically significant azimuthal asymmetries for charged pion pairs in e+e- annihilation at a center-of-mass energy of 10.52 GeV, which can be attributed to a transverse polarization of the primordial quarks. The measurement was performed using a sample of 79 million hadronic events collected with the Belle detector.

hep-ex↗

arXiv2006

Spin dependent fragmentation function at Belle

The measurement of the so far unknown chiral-odd quark transverse spin distribution in either semi-inclusive DIS (SIDIS) or inclusive measurements in pp collisions at RHIC has an additional chiral-odd fragmentation function appearing in the cross section. These chiral-odd fragmentation functions (FF) can for example be the so-called Collins FF or the Interference FF. HERMES has given a first hint that these FFs are nonzero, however in order to measure the transversity one needs these FFs to be precisely known. We have used 29.0 fb$^{-1}$ of data collected by the Belle experiment at the KEKB $e^+e^-$ collider to measure azimuthal asymmetries for different charge combinations of pion pairs and thus access the Collins FF.

hep-ex↗

arXiv2004

Transverse Spin Physics at HERMES

Single-spin asymmetries in semi-inclusive pion production are measured by the HERMES experiment for the first time, with a transversely polarised hydrogen target. Two different sine-dependencies are extracted which can be related to the quark distributions transversity h_1(x) and the Sivers function f_1T^perp(x).

hep-ex↗