0000000000105964
AUTHOR
M. Krämer
showing 50 related works from this author
K− over K+ multiplicity ratio for kaons produced in DIS with a large fraction of the virtual-photon energy
2018
The K$^{-}$ over K$^{+}$ multiplicity ratio is measured in deep-inelastic scattering, for the first time for kaons carrying a large fraction $z$ of the virtual-photon energy. The data were obtained by the COMPASS collaboration using a 160 GeV muon beam and an isoscalar $^6$LiD target. The regime of deep-inelastic scattering is ensured by requiring $Q^2>1$ (GeV/$c)^2$ for the photon virtuality and $W>5$ GeV/$c^2$ for the invariant mass of the produced hadronic system. Kaons are identified in the momentum range from 12 GeV/$c$ to 40 GeV/$c$, thereby restricting the range in Bjorken-$x$ to $0.010.75$. For very large values of $z$, $i.e.$ $z>0.8$, we observe the kaon multiplicity ratio to fall …
The impact of mineral dust on cloud formation during the Saharan dust event in April 2014 over Europe
2018
A regional modeling study on the impact of desert dust on cloud formation is presented for a major Saharan dust outbreak over Europe from 2 to 5 April 2014. The dust event coincided with an extensive and dense cirrus cloud layer, suggesting an influence of dust on atmospheric ice nucleation. Using interactive simulation with the regional dust model COSMO-MUSCAT, we investigate cloud and precipitation representation in the model and test the sensitivity of cloud parameters to dust–cloud and dust–radiation interactions of the simulated dust plume. We evaluate model results with ground-based and spaceborne remote sensing measurements of aerosol and cloud properties, as well as the in situ meas…
A microphysics guide to cirrus clouds - Part 1: Cirrus types
2016
Abstract. The microphysical and radiative properties of cirrus clouds continue to be beyond understanding and thus still represent one of the largest uncertainties in the prediction of the Earth's climate (IPCC, 2013). Our study aims to provide a guide to cirrus microphysics, which is compiled from an extensive set of model simulations, covering the broad range of atmospheric conditions for cirrus formation and evolution. The model results are portrayed in the same parameter space as field measurements, i.e., in the Ice Water Content-Temperature (IWC-T) parameter space. We validate this cirrus analysis approach by evaluating cirrus data sets from 17 aircraft campaigns, conducted in the last…
Polarization effects in exclusive semi-leptonic Λc and Λb charm and bottom baryon decays
1992
Abstract We discuss polarization effects in semi-leptonic decays of polarized and unpolarized heavy Λ-type baryons into heavy and into light Λ-type baryons. We use the non-leptonic decay of the daughter baryon and the leptonic decay of the Woff-shell into a lepton pair as polarization analyzers to analyze the polarization of the daughter baryon and the Woff-shell. Technically this is done by writing down joint angular decay distributions. We calculate the values of the various asymmetry parameters that characterize the angular dependence of the angular decay distributions where we use the predictions of the heavy quark effective theory (HQET) supplemented by simple ansatze for the q2-depend…
Search for exclusive photoproduction ofZc±(3900) at COMPASS
2015
A search for the exclusive production of the Z(c)(+/-)(3900) hadron by virtual photons has been performed in the channel Z(c)(+/-)(3900). J/Psi pi(+/-). The data cover the range from 7GeV to 19GeV in the centre-of- mass energy of the photon-nucleon system. The full set of the COMPASS data set collected with a muon beam between 2002 and 2011 has been used. An upper limit for the ratio BR(Z(c)(+/-)(3900)-> J/Psi pi(+/-)) x sigma(gamma N) -> Z(c)(+/-)(3900) N/sigma gamma N -> J/Psi N 3.7 x10(-3) has been established at the confidence level of90%. (C) 2015 The Authors. Published by Elsevier B.V.
Out-of-plane emission of nuclear matter in Au+Au collisions between 100 and 800 AMeV
1997
We present new experimental results concerning the azimuthal distributions of proton-likes, light and intermediate mass fragments at midrapidity for Au(100-800 AMeV)+Au collisions measured with the FOPI phase-I detector at GSI in Darmstadt. The azimuthal distributions are investigated as a function of the collision centrality, the incident energy, the fragment charge and transverse momentum. The azimuthal anisotropy is maximum for impact parameters around 7 fm. Intermediate mass fragments present a stronger out-of-plane emission signal than light fragments and a saturation is reached for Z greater than or equal to 4. The azimuthal anisotropy increases with the fragment transverse momentum a…
First measurement of the Sivers asymmetry for gluons using SIDIS data
2017
The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. It was extracted from measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it turned out to be non-zero for quarks. In this letter the evaluation of the Sivers asymmetry for gluons in the same process is presented. The analysis method is based on a Monte Carlo simulation that includes three hard processes: photon-gluon fusion, QCD Compton scattering and leading-order virtual-photon absorption process. The Sivers asymmetries of the three processes are simul…
Positrons and Electrons Emitted in Elastic and Dissipative Heavy Ion Collisions
1987
The main research line of the Tori group is the study of the reaction dynamics of dissipative collisions between heavy ions ia positron and electron spectroscopy. The last five years since the Lahnstein-Conference1 are marked for our group by the installation of a new experimental device for detecting positrons and electrons emitted in these collisions, the so-called Tori spectrometer2. The first part of this report is devoted therefore to describe the main characteristics of this apparatus.
Interplay among transversity induced asymmetries in hadron leptoproduction
2015
In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the dif…
Spin alignment and violation of the OZI rule in exclusive ω and ϕ production in pp collisions
2014
Exclusive production of the isoscalar vector mesons $\omega$ and $\phi$ is measured with a 190 GeV$/c$ proton beam impinging on a liquid hydrogen target. Cross section ratios are determined in three intervals of the Feynman variable $x_{F}$ of the fast proton. A significant violation of the OZI rule is found, confirming earlier findings. Its kinematic dependence on $x_{F}$ and on the invariant mass $M_{p\mathrm{V}}$ of the system formed by fast proton $p_\mathrm{fast}$ and vector meson $V$ is discussed in terms of diffractive production of $p_\mathrm{fast}V$ resonances in competition with central production. The measurement of the spin density matrix element $\rho_{00}$ of the vector mesons…
Transverse spin effects in hadron-pair production from semi-inclusive deep inelastic scattering
2012
First measurements of azimuthal asymmetries in hadron-pair production in deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron) and NH_3 (proton) targets are presented. The data were taken in the years 2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c at the CERN SPS. The asymmetries provide access to the transversity distribution functions, without involving the Collins effect as in single hadron production. The sizeable asymmetries measured on the NH_ target indicate non-vanishing u-quark transversity and two-hadron interference fragmentation functions. The small asymmetries measured on the ^6LiD target can be interpreted as indication …
Comparison of aircraft measurements during GoAmazon2014/5 and ACRIDICON-CHUVA
2019
Abstract. The indirect effect of atmospheric aerosol particles on the Earth's radiation balance remains one of the most uncertain components affecting climate change throughout the industrial period. The large uncertainty is partly due to the incomplete understanding of aerosol–cloud interactions. One objective of the GoAmazon2014/5 and the ACRIDICON (Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems)-CHUVA (Cloud Processes of the Main Precipitation Systems in Brazil) projects was to understand the influence of emissions from the tropical megacity of Manaus (Brazil) on the surrounding atmospheric environment of the rainforest and to investiga…
Sivers asymmetry extracted in SIDIS at the hard scales of the Drell-Yan process at COMPASS
2017
Proton transverse-spin azimuthal asymmetries are extracted from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon-nucleon scattering in those four regions of the photon virtuality $Q^2$, which correspond to the four regions of the di-muon mass $\sqrt{Q^2}$ used in the ongoing analysis of the COMPASS Drell-Yan measurements. This allows for a future direct comparison of the nucleon transverse-momentum-dependent parton distribution functions extracted from these two alternative measurements. Various two-dimensional kinematic dependences are presented for the azimuthal asymmetries induced by the Sivers transverse-momentum-dependent parton distribution function. The inte…
Implementation of a comprehensive ice crystal formation parameterization for cirrus and mixed-phase clouds in the EMAC model (based on MESSy 2.53)
2018
A comprehensive ice nucleation parameterization has been implemented in the global chemistry-climate model EMAC to improve the representation of ice crystal number concentrations (ICNCs). The parameterization of Barahona and Nenes (2009, hereafter BN09) allows for the treatment of ice nucleation taking into account the competition for water vapour between homogeneous and heterogeneous nucleation in cirrus clouds. Furthermore, the influence of chemically heterogeneous, polydisperse aerosols is considered by applying one of the multiple ice nucleating particle parameterizations which are included in BN09 to compute the heterogeneously formed ice crystals. BN09 has been modified in order to co…
In situ observation of new particle formation (NPF) in the tropical tropopause layer of the 2017 Asian monsoon anticyclone - Part 2: NPF inside ice c…
2021
From 27 July to 10 August 2017, the airborne StratoClim mission took place in Kathmandu, Nepal, where eight mission flights were conducted with the M-55 Geophysica up to altitudes of 20 km. New particle formation (NPF) was identified by the abundant presence of nucleation-mode aerosols, with particle diameters dp smaller than 15 nm, which were in-situ-detected by means of condensation nuclei (CN) counter techniques. NPF fields in clear skies as well as in the presence of cloud ice particles (dp > 3 µm) were encountered at upper troposphere–lowermost stratosphere (UTLS) levels and within the Asian monsoon anticyclone (AMA). NPF-generated nucleation-mode particles in elevated concentration…
The spin structure functiong1pof the proton and a test of the Bjorken sum rule
2016
New results for the double spin asymmetry A(1)(p) and the proton longitudinal spin structure function g(1)(p) are presented. They were obtained by the COMPASS Collaboration using polarised 200 GeV muons scattered off a longitudinally polarised NH3 target. The data were collected in 2011 and complement those recorded in 2007 at 160 GeV, in particular at lower values of x. They improve the statistical precision of g(1)(p)(x) by about a factor of two in the region x less than or similar to 0.02. A next-to-leading order QCD fit to the g(1) world data is performed. It leads to a new determination of the quark spin contribution to the nucleon spin, Delta Sigma, ranging from 0.26 to 0.36, and to a…
Longitudinal double-spin asymmetry A1p and spin-dependent structure function g1p of the proton at small values of x and Q2
2018
Abstract We present a precise measurement of the proton longitudinal double-spin asymmetry A 1 p and the proton spin-dependent structure function g 1 p at photon virtualities 0.006 ( GeV / c ) 2 Q 2 1 ( GeV / c ) 2 in the Bjorken x range of 4 × 10 − 5 x 4 × 10 − 2 . The results are based on data collected by the COMPASS Collaboration at CERN using muon beam energies of 160 GeV and 200 GeV . The statistical precision is more than tenfold better than that of the previous measurement in this region. In the whole range of x , the measured values of A 1 p and g 1 p are found to be positive. It is for the first time that spin effects are found at such low values of x .
Multiplicities of charged pions and charged hadrons from deep-inelastic scattering of muons off an isoscalar target
2017
Multiplicities of charged pions and charged hadrons produced in deep-inelastic scattering were measured in three-dimensional bins of the Bjorken scaling variable x , the relative virtual-photon energy y and the relative hadron energy z . Data were obtained by the COMPASS Collaboration using a 160GeV muon beam and an isoscalar target ( 6 LiD). They cover the kinematic domain in the photon virtuality Q2>1(GeV/c)2 , 0.004 1(GeV/c$)^2$, $0.004 < x < 0.4$, $0.2 < z < 0.85$ and $0.1 < y < 0.7$. In addition, a leading-order pQCD analysis was performed using the pion multiplicity results to extract quark fragmentation functions.
Aircraft-based observations of isoprene-epoxydiol-derived secondary organic aerosol (IEPOX-SOA) in the tropical upper troposphere over the Amazon reg…
2018
During the ACRIDICON-CHUVA field project (September–October 2014; based in Manaus, Brazil) aircraft-based in situ measurements of aerosol chemical composition were conducted in the tropical troposphere over the Amazon using the High Altitude and Long Range Research Aircraft (HALO), covering altitudes from the boundary layer (BL) height up to 14.4 km. The submicron non-refractory aerosol was characterized by flash-vaporization/electron impact-ionization aerosol particle mass spectrometry. The results show that significant secondary organic aerosol (SOA) formation by isoprene oxidation products occurs in the upper troposphere (UT), leading to increased organic aerosol mass concentratio…
Estimates of the Nuclear Time Delay in Dissipative U + U and U + Cm Collisions Derived from the Shape of Positron andδ-Ray Spectra
1983
Positron and delta-ray spectra have been measured in coincidence with quasielastic scattered particles and fission fragments from the bombardment of Pd, U, and Cm targets with U beams of energies between 5.9 and 8.4 MeV/u. For collisions leading to a fission reaction, the atomic positron and delta-ray spectra fall off more steeply at high energies than expected from calculations based on pure Rutherford trajectories. A quantitative analysis of this effect is in accord with a nuclear contact time of about 10/sup -21/ s.
Evidence for molecular-cluster states in222Th
1983
The groundstate and a negative parity band of222Th have been observed in the208Pb (180, 4n)222Th reaction by conversion electron and γ-ray spectroscopy identifying the evaporation residues in a recoil separator. The de-excitation pattern is characterized by strong El transitions interconnecting the levels of alternating parity. The yrast levels may be interpreted as a molecularcluster band.
Exclusive muoproduction on transversely polarised protons and deuterons
2012
The transverse target spin azimuthal asymmetry A(UT)(sin(phi-phi s)) in hard exclusive production of rho(0) mesons was measured at COMPASS by scattering 160 GeV/c muons off transversely polarised protons and deuterons. The measured asymmetry is sensitive to the nucleon helicity-flip generalised parton distributions E-q, which are related to the orbital angular momentum of quarks in the nucleon. The Q(2), x-B-j and p(T)(2) dependence of A(UT)(sin(phi-phi s)) is presented in a wide kinematic range: 1 (GeV/c)(2) < Q(2) < 10 (GeV/c)(2), 0.003 < xB(j) < 0.3 and 0.05 (GeV/c)(2) < p(T)(2) < 0.5 (GeV/c)(2) for protons or 0.10 (GeV/c)(2) < p(T)(2) < 0.5 (GeV/c)(2) for deuterons. Results for deuteron…
Corrigendum to “Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section” [Phys. Lett. B 793 (…
2019
Physics letters / B B 800, 135129 (2020). doi:10.1016/j.physletb.2019.135129
Illustration of microphysical processes in Amazonian deep convective clouds in the gamma phase space: introduction and potential applications
2017
Abstract. The behavior of tropical clouds remains a major open scientific question, resulting in poor representation by models. One challenge is to realistically reproduce cloud droplet size distributions (DSDs) and their evolution over time and space. Many applications, not limited to models, use the gamma function to represent DSDs. However, even though the statistical characteristics of the gamma parameters have been widely studied, there is almost no study dedicated to understanding the phase space of this function and the associated physics. This phase space can be defined by the three parameters that define the DSD intercept, shape, and curvature. Gamma phase space may provide a commo…
Measurement of the cross section for hard exclusive π0 muoproduction on the proton
2020
Physics letters / B B805, 135454 (2020). doi:10.1016/j.physletb.2020.135454
Observation of a New Narrow Axial-Vector Mesona1(1420)
2015
The COMPASS Collaboration at CERN has measured diffractive dissociation of 190 GeV/c pions into the π(-)π(-)π(+) final state using a stationary hydrogen target. A partial-wave analysis (PWA) was performed in bins of 3π mass and four-momentum transfer using the isobar model and the so far largest PWA model consisting of 88 waves. A narrow peak is observed in the f0(980)π channel with spin, parity and C-parity quantum numbers J(PC)=1(++). We present a resonance-model study of a subset of the spin-density matrix selecting 3π states with J(PC)=2(++) and 4(++) decaying into ρ(770)π and with J(PC)=1(++) decaying into f0(980)π. We identify a new a1 meson with mass (1414(-13)(+15)) MeV/c2 and wid…
New analysis of ηπ tensor resonances measured at the COMPASS experiment
2018
We present a new amplitude analysis of the $\eta\pi$ $D$-wave in $\pi^- p\to \eta\pi^- p$ measured by COMPASS. Employing an analytical model based on the principles of the relativistic $S$-matrix, we find two resonances that can be identified with the $a_2(1320)$ and the excited $a_2^\prime(1700)$, and perform a comprehensive analysis of their pole positions. For the mass and width of the $a_2$ we find $M=(1307 \pm 1 \pm 6)$~MeV and $\Gamma=(112 \pm 1 \pm 8)$~MeV, and for the excited state $a_2^\prime$ we obtain $M=(1720 \pm 10 \pm 60)$~MeV and $\Gamma=(280\pm 10 \pm 70)$~MeV, respectively.
Cluster Formation during Expansion of Hot and Compressed Nuclear Matter Produced in Central Collisions of Au on Au at 250AMeV
1995
Complete distributions of the light and intermediate mass fragments ({ital Z}=1--6) produced within the polar angular range 1{sup {circ}}{le}{Theta}{sub lab}{le}30{sup {circ}} in highly central collisions of 250{ital A} MeV Au+Au are presented. The results of this measurement and a model analysis are used to study the expansion and clustering of the hot and compressed transient state formed in central collisions of such a heavy system. The influence of the initial conditions on the final observables is discussed.
The COMPASS Setup for Physics with Hadron Beams
2015
The main characteristics of the COMPASS experimental setup for physics with hadron beams are described. This setup was designed to perform exclusive measurements of processes with several charged and/or neutral particles in the final state. Making use of a large part of the apparatus that was previously built for spin structure studies with a muon beam, it also features a new target system as well as new or upgraded detectors. The hadron setup is able to operate at the high incident hadron flux available at CERN. It is characterised by large angular and momentum coverages, large and nearly flat acceptances, and good two and three-particle mass resolutions. In 2008 and 2009 it was successful…
The spin-dependent structure function of the proton g1p and a test of the Bjorken sum rule
2010
Abstract The inclusive double-spin asymmetry, A 1 p , has been measured at COMPASS in deep-inelastic polarised muon scattering off a large polarised NH3 target. The data, collected in the year 2007, cover the range Q 2 > 1 ( GeV / c ) 2 , 0.004 x 0.7 and improve the statistical precision of g 1 p ( x ) by a factor of two in the region x 0.02 . The new proton asymmetries are combined with those previously published for the deuteron to extract the non-singlet spin-dependent structure function g 1 NS ( x , Q 2 ) . The isovector quark density, Δ q 3 ( x , Q 2 ) , is evaluated from a NLO QCD fit of g 1 NS . The first moment of Δ q 3 is in good agreement with the value predicted by the Bjorken su…
The ATAL within the 2017 Asian Monsoon Anticyclone: Microphysical aerosol properties derived from aircraft-borne in situ measurements
2021
The Asian summer monsoon is an effective pathway for aerosol particles and precursors from the planetary boundary layer over Central, South, and East Asia into the upper troposphere and lower stratosphere. An enhancement of aerosol particles within the Asian monsoon anticyclone (AMA), called the Asian tropopause aerosol layer (ATAL), has been observed by satellites. We discuss airborne in situ and remote sensing observations of aerosol microphysical properties conducted during the 2017 StratoClim field campaign within the AMA region. The aerosol particle measurements aboard the high-altitude research aircraft M55 Geophysica (maximum altitude reached of about 20.5 km) were conducted with a m…
Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high $p_T$
2015
We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$\it c$ to 4 GeV/$\it c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$\it c$ or 200 GeV/$\it c$ impinging on polarised $\mathrm{{}^6LiD}$ or $\mathrm{NH_3}$ targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation $\Delta G$ inside the nucleon in the range of the nucleon momentum fraction carried by gluons $0.05 < x_g < 0.2$. We measured the longi…
Flavour Separation of Helicity Distributions from Deep Inelastic Muon-Deuteron Scattering
2009
We present a LO evaluation of helicity densities of valence, \Delta u_v+\Delta d_v, non-strange sea, \Delta\bar{u}+\Delta\bar{d}, and strange quarks, \Delta s (assumed to be equal to \Delta\bar{s}). They have been obtained from the inclusive asymmetry A_{3,d} and the semi-inclusive asymmetries A^{\pi+}_{1,d}, A^{\pi-}_{1,d}, A^{K+}_{1,d}, A^{K-}_{1,d} measured in polarised deep inelastic muon-deuteron scattering. The full deuteron statistics of COMPASS (years 2002-2004 and 2006) has been used. The data cover the range Q^2 > 1 (GeV/c)^2 and 0.004<x<0.3. Both non-strange densities are found to be in a good agreement with previous measurements. The distribution of \Delta s(x) is compatible wit…
Sideward flow in Au + Au collisions at 400 A.MeV
1995
Abstract We present new experimental data obtained with the FOPI detector at SIS, for the Au + Au heavy-ion collisions at 400 A MeV incident energy. The sideward flow, determined from a method without reaction-plane reconstruction, and the nuclear stopping are studied as a function of the centrality of the collisions. In order to study the nuclear in-medium effects, which act on the NN cross sections and potential and hence on experimental observables like the nuclear-matter flow and stopping, these results are compared with the predictions of two different QMD versions. The first one offers a fully microscopic calculation of the cross sections and potential in the G-matrix formalism and na…
Erratum to: Hadron transverse momentum distributions in muon deep inelastic scattering at 160 GeV/ $$c$$ c
2015
Author(s): Adolph, C; Alekseev, MG; Alexakhin, VY; Alexandrov, Y; Alexeev, GD; Amoroso, A; Andrieux, V; Austregesilo, A; Badelek, B; Balestra, F; Barth, J; Baum, G; Bedfer, Y; Berlin, A; Bernhard, J; Bertini, R; Bicker, K; Bieling, J; Birsa, R; Bisplinghoff, J; Boer, M; Bordalo, P; Bradamante, F; Braun, C; Bravar, A; Bressan, A; Buchele, M; Burtin, E; Capozza, L; Chiosso, M; Chung, SU; Cicuttin, A; Crespo, ML; Dalla Torre, S; Dasgupta, SS; Dasgupta, S; Denisov, OY; Donskov, SV; Doshita, N; Duic, V; Dunnweber, W; Dziewiecki, M; Efremov, A; Elia, C; Eversheim, PD; Eyrich, W; Faessler, M; Ferrero, A; Filin, A; Finger, M; Finger Jr, M; Fischer, H; Franco, C; du Fresne von Hohenesche, N; Friedri…
New investigations on homogeneous ice nucleation: the effects of water activity and water saturation formulations
2022
Laboratory measurements at the AIDA cloud chamber and airborne in-situ observations suggest that the homogeneous freezing thresholds at low temperatures are possibly higher than expected from the so-called “Koop-line”. This finding is of importance, because the ice onset relative humidity affects the cirrus cloud coverage and, at the very low temperatures of the tropical tropopause layer, together with the number of ice crystals also the transport of water vapor into the stratosphere. Both, the appearance of cirrus clouds and the amount of stratospheric water feed back to the radiative budget of the atmosphere. In order to explore the enhanced ice onset humidities, we re-examine…
A highly-segmented ΔE-time-of-flight wall as forward detector of the 4π-system for charged particles at the SIS/ESR accelerator
1993
Abstract At the SIS/ESR accelerator facility at GSI in Darmstadt the 4π-detector system FOPI is under construction at present. It is designed for the investigation of central collisions of heavy ions in the energy range up to 2 A GeV. As phase I of this detector a forward wall has been built and used in various experiments. It comprizes a total number of 764 scintillators with an additional shell of 188 thin ΔE -detectors in front of it and covers the full azimuth of the polar angles from 1° to 30°. The velocity and the nuclear charge of the fragments are determined by a combined time-of-flight and ΔE measurement.
Study of Σ(1385) and Ξ(1321) hyperon and antihyperon production in deep inelastic muon scattering
2013
Large samples of \Lambda, \Sigma(1385) and \Xi(1321) hyperons produced in deep-inelastic muon scattering off a ^6LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of \Sigma(1385)^+, \Sigma(1385)^-, \bar{\Sigma}(1385)^-, \bar{\Sigma}(1385)^+, \Xi(1321)^-, and \bar{\Xi}(1321)^+ hyperons decaying into \Lambda(\bar{\Lambda})\pi were measured. The heavy hyperon to \Lambda and heavy antihyperon to \bar{\Lambda} yield ratios were found to be in the range 3.8% to 5.6% with a relative uncertainty of about 10%. They were used to tune the parameters relevant for strange particle production of the LEPTO Monte Carlo generator.
Thermodynamic correction of particle concentrations measured by underwing probes on fast flying aircraft
2016
Abstract. Particle concentration measurements with underwing probes on aircraft are impacted by air compression upstream of the instrument body as a function of flight velocity. In particular for fast-flying aircraft the necessity arises to account for compression of the air sample volume. Hence, a correction procedure is needed to invert measured particle number concentrations to ambient conditions that is commonly applicable for different instruments to gain comparable results. In the compression region where the detection of particles occurs (i.e. under factual measurement conditions), pressure and temperature of the air sample are increased compared to ambient (undisturbed) conditions i…
Microphysical properties of synoptic scale polar stratospheric clouds: in situ measurements of unexpectedly large HNO&lt;sub&gt;3&lt;/sub…
2014
Abstract. In January 2010 and December 2011 synoptic scale PSC fields were probed during seven flights of the high altitude research aircraft M-55 Geophysica within the RECONCILE (Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interaction.) and the ESSenCe (ESSenCe: ESA Sounder Campaign) projects. Particle size distributions in a diameter range between 0.46 μm and 40 μm were recorded simultaneously by up to four different optical in situ instruments. Three of these particle instruments are based on the detection of forward scattered light by single particles. The fourth instrument is a grey scale optical array…
Evidence for collective expansion in light-particle emission following Au+Au collisions at 100, 150 and 250 A·MeV
1995
Abstract Light-particle emission from Au+Au collisions has been studied in the bombarding-energy range 100–250 A ·MeV, using ΔE − E R telescopes in coincidence with the FOPI detector in its phase I configuration. Center-of-mass energy spectra have been measured for Z = 1,2 isotopes emitted in central collisions at CM polar angles between 60° and 90°. Evidence for a collective expansion is reported, on the basis of the mean kinetic energies of hydrogen isotopes. Comparison is presented with statistical calculations (WIX code). For CM kinetic energy spectra, fair agreement is found between data and a recently developed transport model.
Multiplicities of charged kaons from deep-inelastic muon scattering off an isoscalar target
2017
Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y, and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off an isoscalar 6 LiD target. They cover the kinematic domain 1 (GeV/c)2 < Q2 < 60 (GeV/c)^2 in the photon virtuality, 0.004 < x < 0.4, 0.1 < y < 0.7, 0.20 < z < 0.85, and W > 5 GeV/c^2 in the invariant mass of the hadronic system. The results from the sum of the z-integrated K+ and K- mu…
Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons
2015
Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise.
Positron-Electron Angular Correlations in Heavy Ion Collisions
1987
Recent measurements of positrons in coincidence with electrons emitted in U+Th collisions near the Coulomb barrier show sharp line structures in the sum and difference energy spectra of the two leptons (ref. 1). A possible method to clarify the origin of these lines is to study the angular correlation of the leptons. In this short contribution we want to report on a positron-electron coincidence test measurement performed with the TORI spectrometer. This apparatus offers the possibility to measure positrons in coincidence with electrons emitted into the same and opposite hemisphere as well.
Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin
2018
Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by 1 or 2 orders of magnitude. The measurements were made during the German–Brazilian cooperative aircraft campaign ACRIDICON–CHUVA, where ACRIDICON stands for Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems and CHUVA is the acronym for Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM …
Measurement of azimuthal hadron asymmetries in semi-inclusive deep inelastic scattering off unpolarised nucleons
2014
Spin-averaged asymmetries in the azimuthal distributions of positive and negative hadrons produced in deep inelastic scattering were measured using the CERN SPS muon beam at $160$ GeV/c and a $^6$LiD target. The amplitudes of the three azimuthal modulations $\cos\phi_h$, $\cos2\phi_h$ and $\sin\phi_h$ were obtained binning the data separately in each of the relevant kinematic variables $x$, $z$ or $p_T^{\,h}$ and binning in a three-dimensional grid of these three variables. The amplitudes of the $\cos \phi_h$ and $\cos 2\phi_h$ modulations show strong kinematic dependencies both for positive and negative hadrons.
Measurement of the Collins and Sivers asymmetries on transversely polarised protons
2010
The Collins and Sivers asymmetries for charged hadrons produced in deeply inelastic scattering on transversely polarised protons have been extracted from the data collected in 2007 with the CERN SPS muon beam tuned at 160 GeV/c. At large values of the Bjorken x variable non-zero Collins asymmetries are observed both for positive and negative hadrons while the Sivers asymmetry for positive hadrons is slightly positive over almost all the measured x range. These results nicely support the present theoretical interpretation of these asymmetries, in terms of leading-twist quark distribution and fragmentation functions.
Corrigendum to “Odd and even partial waves of ηπ− and η′π− in π−p → η(′)π−p at 191 GeV/c” [Phys. Lett. B 740 (2015) 303–311]
2020
Abstract In Fig. 5 on p. 311 of our Phys. Lett. B 740 (2015) 303 an adjustment by 180 ∘ is required for the phases with respect to the L = 2 , M = 1 wave, of the following waves: L = 1 , 3 , 5 with M = 1 , and L = 2 with M = 2 . After this correction (Fig. 5 (corrected) below), the extracted partial waves describe the angular distribution of the η ( ′ ) in the Gottfried-Jackson (GJ) frame, using Eq. (4) with implicit Condon-Shortley phase convention. The other results of our paper are not affected. The right-handed GJ coordinate system was defined by the z-axis pointing in the direction of the beam in the η ( ′ ) π − center-of-mass system and the y-axis pointing in the direction of p recoil…
Final COMPASS results on the deuteron spin-dependent structure functiong1dand the Bjorken sum rule
2017
Final results are presented from the inclusive measurement of deep-inelastic polarised-muon scattering on longitudinally polarised deuterons using a 6 LiD target. The data were taken at 160 GeV beam energy and the results are shown for the kinematic range 1(GeV/c)2 4GeV/c2 in the mass of the hadronic final state. The deuteron double-spin asymmetry A1d and the deuteron longitudinal-spin structure function g1d are presented in bins of x and Q2 . Towards lowest accessible values of x , g1d decreases and becomes consistent with zero within uncertainties. The presented final g1d values together with the recently published final g1p values of COMPASS are used to again evaluate the Bjorken sum rul…
Thermodynamic correction of particle concentrations measured by underwing probes on fast-flying aircraft
2016
Particle concentration measurements with underwing probes on aircraft are impacted by air compression upstream of the instrument body as a function of flight velocity. In particular, for fast-flying aircraft the necessity arises to account for compression of the air sample volume. Hence, a correction procedure is needed to invert measured particle number concentrations to ambient conditions that is commonly applicable to different instruments to gain comparable results. In the compression region where the detection of particles occurs (i.e. under factual measurement conditions), pressure and temperature of the air sample are increased compared to ambient (undisturbed) conditions in certain …