Transverse-momentum-dependent Multiplicities of Charged Hadrons in Muon-Deuteron Deep Inelastic Scattering

A semi-inclusive measurement of charged hadron multiplicities in deep inelastic muon scattering off an isoscalar target was performed using data collected by the COMPASS Collaboration at CERN. The following kinematic domain is covered by the data: photon virtuality $Q^{2}>1$ (GeV/$c$)$^2$, invariant mass of the hadronic system $W > 5$ GeV/$c^2$, Bjorken scaling variable in the range $0.003 < x < 0.4$, fraction of the virtual photon energy carried by the hadron in the range $0.2 < z < 0.8$, square of the hadron transverse momentum with respect to the virtual photon direction in the range 0.02 (GeV/$c)^2 < P_{\rm{hT}}^{2} < 3$ (GeV/$c$)$^2$. The multiplicities are presented as a function of $P_{\rm{hT}}^{2}$ in three-dimensional bins of $x$, $Q^2$, $z$ and compared to previous semi-inclusive measurements. We explore the small-$P_{\rm{hT}}^{2}$ region, i.e. $P_{\rm{hT}}^{2} < 1$ (GeV/$c$)$^2$, where hadron transverse momenta are expected to arise from non-perturbative effects, and also the domain of larger $P_{\rm{hT}}^{2}$, where contributions from higher-order perturbative QCD are expected to dominate. The multiplicities are fitted using a single-exponential function at small $P_{\rm{hT}}^{2}$ to study the dependence of the average transverse momentum $\langle P_{\rm{hT}}^{2}\rangle$ on $x$, $Q^2$ and $z$. The power-law behaviour of the multiplicities at large $P_{\rm{hT}}^{2}$ is investigated using various functional forms. The fits describe the data reasonably well over the full measured range.Comment: 28 pages, 20 figure

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) 188]

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Light isovector resonances in π-p →π-π-π+p at 190 GeV/c

We have performed the most comprehensive resonance-model fit of π-π-π+ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction π-+p→π-π-π++precoil with a 190 GeV/c pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, 0.5<2.5 GeV/c2, and simultaneously in 11 bins of the reduced four-momentum transfer squared, 0.1<1.0 (GeV/c)2, are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with JPC=0-+, 1++, 2++, 2-+, 4++, and spin-exotic 1-+ quantum numbers. The model contains the well-known resonances π(1800), a1(1260), a2(1320), π2(1670), π2(1880), and a4(2040). In addition, it includes the disputed π1(1600), the excited states a1(1640), a2(1700), and π2(2005), as well as the resonancelike a1(1420). We measure the resonance parameters mass and width of these objects by combining the information from the PWA results obtained in the 11 t′ bins. We extract the relative branching fractions of the ρ(770)π and f2(1270)π decays of a2(1320) and a4(2040), where the former one is measured for the first time. In a novel approach, we extract the t′ dependence of the intensity of the resonances and of their phases. The t′ dependence of the intensities of most resonances differs distinctly from the t′ dependence of the nonresonant components. For the first time, we determine the t′ dependence of the phases of the production amplitudes and confirm that the production mechanism of the Pomeron exchange is common to all resonances. We have performed extensive systematic studies on the model dependence and correlations of the measured physical parameters

Measurement of P T -weighted Sivers asymmetries in leptoproduction of hadrons

The transverse spin asymmetries measured in semi-inclusive leptoproduction of hadrons, when weighted with the hadron transverse momentum PT , allow for the extraction of important transverse-momentumdependent distribution functions. In particular, the weighted Sivers asymmetries provide direct information on the Sivers function, which is a leading-twist distribution that arises from a correlation between the transverse momentum of an unpolarised quark in a transversely polarised nucleon and the spin of the nucleon. Using the high-statistics data collected by the COMPASS Collaboration in 2010 with a transversely polarised proton target, we have evaluated two types of PT -weighted Sivers asymmetries, which are both proportional to the product of the first transverse moment of the Sivers function and of the fragmentation function. The results are compared to the standard unweighted Sivers asymmetries and used to extract the first transverse moments of the Sivers distributions for u and d quark

Multiplicities of charged kaons from deep-inelastic muon scattering off an isoscalar target

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 6LiD target. They cover the kinematic domain View the MathML source in the photon virtuality, 0.0045 GeV/c2 in the invariant mass of the hadronic system. The results from the sum of the z -integrated K+ and K 12 multiplicities at high x point to a value of the non-strange quark fragmentation function larger than obtained by the earlier DSS fit

First measurement of coherent ρ0 photoproduction in ultra-peripheral Xe–Xe collisions at √sNN = 5.44 TeV

The first measurement of the coherent photoproduction of ρ0 vector mesons in ultra-peripheral Xe–Xe collisions at sNN=5.44 TeV is presented. This result, together with previous HERA γp data and γ–Pb measurements from ALICE, describes the atomic number (A) dependence of this process, which is particularly sensitive to nuclear shadowing effects and to the approach to the black-disc limit of QCD at a semi-hard scale. The cross section of the Xe+Xe→ρ0+Xe+Xe process, measured at midrapidity through the decay channel ρ0→π+π−, is found to be dσ/dy=131.5±5.6(stat.)−16.9+17.5(syst.) mb. The ratio of the continuum to resonant contributions for the production of pion pairs is also measured. In addition, the fraction of events accompanied by electromagnetic dissociation of either one or both colliding nuclei is reported. The dependence on A of cross section for the coherent ρ0 photoproduction at a centre-of-mass energy per nucleon of the γA system of WγA,n=65 GeV is found to be consistent with a power-law behaviour σ(γA→ρ0A)∝Aα with a slope α=0.96±0.02(syst.). This slope signals important shadowing effects, but it is still far from the behaviour expected in the black-disc limit.publishedVersio

Longitudinal double-spin asymmetry A1pand spin-dependent structure function g1pof the proton at small values of x and Q2

We present a precise measurement of the proton longitudinal double-spin asymmetry Ap1 and the proton spin-dependent structure function gp 1 at photon virtualities 0.006 (GeV/c)2 < Q 2 < 1 (GeV/c)2 in the Bjorken x range of 4 7 10 125 < x < 4 7 10 122. 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 Ap1 and gp1 are found to be positive. It is for the first time that spin effects are found at such low values of

A(c)(+) Production and Baryon-to-Meson Ratios in pp and p-Pb Collisions at root S-NN=5.02 TeV at the LHC

The prompt production of the charm baryon \u39bc+ and the \u39bc+/D0 production ratios were measured at midrapidity with the ALICE detector in pp and p-Pb collisions at sNN=5.02 TeV. These new measurements show a clear decrease of the \u39bc+/D0 ratio with increasing transverse momentum (pT) in both collision systems in the range 2<12 GeV/c, exhibiting similarities with the light-flavor baryon-to-meson ratios p/\u3c0 and \u39b/KS0. At low pT, predictions that include additional color-reconnection mechanisms beyond the leading-color approximation, assume the existence of additional higher-mass charm-baryon states, or include hadronization via coalescence can describe the data, while predictions driven by charm-quark fragmentation processes measured in e+e- and e-p collisions significantly underestimate the data. The results presented in this Letter provide significant evidence that the established assumption of universality (colliding-system independence) of parton-to-hadron fragmentation is not sufficient to describe charm-baryon production in hadronic collisions at LHC energies

A(c)(+) Production and Baryon-to-Meson Ratios in pp and p-Pb Collisions at root S-NN=5.02 TeV at the LHC

The prompt production of the charm baryon Λ_{c}^{+} and the Λ_{c}^{+}/D^{0} production ratios were measured at midrapidity with the ALICE detector in pp and p-Pb collisions at sqrt[s_{NN}]=5.02  TeV. These new measurements show a clear decrease of the Λ_{c}^{+}/D^{0} ratio with increasing transverse momentum (p_{T}) in both collision systems in the range 2<p_{T}<12  GeV/c, exhibiting similarities with the light-flavor baryon-to-meson ratios p/π and Λ/K_{S}^{0}. At low p_{T}, predictions that include additional color-reconnection mechanisms beyond the leading-color approximation, assume the existence of additional higher-mass charm-baryon states, or include hadronization via coalescence can describe the data, while predictions driven by charm-quark fragmentation processes measured in e^{+}e^{-} and e^{-}p collisions significantly underestimate the data. The results presented in this Letter provide significant evidence that the established assumption of universality (colliding-system independence) of parton-to-hadron fragmentation is not sufficient to describe charm-baryon production in hadronic collisions at LHC energies

Measurement of the cross section for hard exclusive π0 muoproduction on the proton

202We report on a measurement of hard exclusive π0 muoproduction on the proton by COMPASS using 160 GeV/c polarised μ+ and μ− beams of the CERN SPS impinging on a liquid hydrogen target. From the average of the measured μ+ and μ− cross sections, the virtual-photon proton cross section is determined as a function of the squared four-momentum transfer between initial and final proton in the range 0.08(GeV/c)2<|t|<0.64(GeV/c)2. The average kinematics of the measurement are 〈Q2〉=2.0(GeV/c)2, 〈ν〉=12.8GeV, 〈xBj〉=0.093 and 〈−t〉=0.256(GeV/c)2. Fitting the azimuthal dependence reveals a combined contribution by transversely and longitudinally polarised photons of (8.2±0.9stat−1.2+1.2|sys)nb/(GeV/c)2, as well as transverse-transverse and longitudinal-transverse interference contributions of (−6.1±1.3stat−0.7+0.7|sys)nb/(GeV/c)2 and (1.5±0.5stat−0.2+0.3|sys)nb/(GeV/c)2, respectively. Our results provide important input for modelling Generalised Parton Distributions. In the context of the phenomenological Goloskokov-Kroll model, the statistically significant transverse-transverse interference contribution constitutes clear experimental evidence for the chiral-odd GPD E‾T.openopenAlexeev M.G.; Alexeev G.D.; Amoroso A.; Andrieux V.; Anfimov N.V.; Anosov V.; Antoshkin A.; Augsten K.; Augustyniak W.; Azevedo C.D.R.; Badelek B.; Balestra F.; Ball M.; Barth J.; Beck R.; Bedfer Y.; Bernhard J.; Bodlak M.; Bordalo P.; Bradamante F.; Bressan A.; Buchele M.; Burtsev V.E.; Chang W.-C.; Chatterjee C.; Chiosso M.; Chumakov A.G.; Chung S.-U.; Cicuttin A.; Crespo M.L.; Dalla Torre S.; Dasgupta S.S.; Dasgupta S.; Denisov O.Y.; Dhara L.; Donskov S.V.; Doshita N.; Dreisbach C.; Dunnweber W.; Dusaev R.R.; Efremov A.; Eversheim P.D.; Faessler M.; Ferrero A.; Finger M.; Fischer H.; Franco C.; du Fresne von Hohenesche N.; Friedrich J.M.; Frolov V.; Fuchey E.; Gautheron F.; Gavrichtchouk O.P.; Gerassimov S.; Giarra J.; Gnesi I.; Gorzellik M.; Grasso A.; Gridin A.; Grosse Perdekamp M.; Grube B.; Guskov A.; Hahne D.; Hamar G.; von Harrach D.; Heitz R.; Herrmann F.; Horikawa N.; d'Hose N.; Hsieh C.-Y.; Huber S.; Ishimoto S.; Ivanov A.; Iwata T.; Jandek M.; Jary V.; Joosten R.; Jorg P.; Juraskova K.; Kabuss E.; Kaspar F.; Kerbizi A.; Ketzer B.; Khaustov G.V.; Khokhlov Y.A.; Kisselev Y.; Klein F.; Koivuniemi J.H.; Kolosov V.N.; Kondo Horikawa K.; Konorov I.; Konstantinov V.F.; Kotzinian A.M.; Kouznetsov O.M.; Kral Z.; Kramer M.; Krinner F.; Kroumchtein Z.V.; Kulinich Y.; Kunne F.; Kurek K.; Kurjata R.P.; Kveton A.; Levorato S.; Lian Y.-S.; Lichtenstadt J.; Lin P.-J.; Longo R.; Lyubovitskij V.E.; Maggiora A.; Magnon A.; Makins N.; Makke N.; Mallot G.K.; Mamon S.A.; Marianski B.; Martin A.; Marzec J.; Matousek J.; Matsuda T.; Meshcheryakov G.V.; Meyer M.; Meyer W.; Mikhailov Y.V.; Mikhasenko M.; Mitrofanov E.; Mitrofanov N.; Miyachi Y.; Moretti A.; Naim C.; Nagaytsev A.; Neyret D.; Novy J.; Nowak W.-D.; Nukazuka G.; Nunes A.S.; Olshevsky A.G.; Ostrick M.; Panzieri D.; Parsamyan B.; Paul S.; Peng J.-C.; Pereira F.; Pesek M.; Peshekhonov D.V.; Peskova M.; Pierre N.; Platchkov S.; Pochodzalla J.; Polyakov V.A.; Pretz J.; Quaresma M.; Quintans C.; Ramos S.; Regali C.; Reicherz G.; Riedl C.; Ryabchikov D.I.; Rybnikov A.; Rychter A.; Samoylenko V.D.; Sandacz A.; Sarkar S.; Savin I.A.; Sbrizzai G.; Schmieden H.; Selyunin A.; Silva L.; Sinha L.; Slunecka M.; Smolik J.; Srnka A.; Steffen D.; Stolarski M.; Subrt O.; Sulc M.; Suzuki H.; Szabelski A.; Szameitat T.; Sznajder P.; Tessaro S.; Tessarotto F.; Thiel A.; Tomsa J.; Tosello F.; Tskhay V.; Uhl S.; Vasilishin B.I.; Vauth A.; Veit B.M.; Veloso J.; Vidon A.; Virius M.; Wagner M.; Wallner S.; Wilfert M.; Zaremba K.; Zavada P.; Zavertyaev M.; Zemlyanichkina E.; Zhao Y.; Ziembicki M.Alexeev, M. G.; Alexeev, G. D.; Amoroso, A.; Andrieux, V.; Anfimov, N. V.; Anosov, V.; Antoshkin, A.; Augsten, K.; Augustyniak, W.; Azevedo, C. D. R.; Badelek, B.; Balestra, F.; Ball, M.; Barth, J.; Beck, R.; Bedfer, Y.; Bernhard, J.; Bodlak, M.; Bordalo, P.; Bradamante, F.; Bressan, A.; Buchele, M.; Burtsev, V. E.; Chang, W. -C.; Chatterjee, C.; Chiosso, M.; Chumakov, A. G.; Chung, S. -U.; Cicuttin, A.; Crespo, M. L.; Dalla Torre, S.; Dasgupta, S. S.; Dasgupta, S.; Denisov, O. Y.; Dhara, L.; Donskov, S. V.; Doshita, N.; Dreisbach, C.; Dunnweber, W.; Dusaev, R. R.; Efremov, A.; Eversheim, P. D.; Faessler, M.; Ferrero, A.; Finger, M.; Fischer, H.; Franco, C.; du Fresne von Hohenesche, N.; Friedrich, J. M.; Frolov, V.; Fuchey, E.; Gautheron, F.; Gavrichtchouk, O. P.; Gerassimov, S.; Giarra, J.; Gnesi, I.; Gorzellik, M.; Grasso, A.; Gridin, A.; Grosse Perdekamp, M.; Grube, B.; Guskov, A.; Hahne, D.; Hamar, G.; von Harrach, D.; Heitz, R.; Herrmann, F.; Horikawa, N.; D'Hose, N.; Hsieh, C. -Y.; Huber, S.; Ishimoto, S.; Ivanov, A.; Iwata, T.; Jandek, M.; Jary, V.; Joosten, R.; Jorg, P.; Juraskova, K.; Kabuss, E.; Kaspar, F.; Kerbizi, A.; Ketzer, B.; Khaustov, G. V.; Khokhlov, Y. A.; Kisselev, Y.; Klein, F.; Koivuniemi, J. H.; Kolosov, V. N.; Kondo Horikawa, K.; Konorov, I.; Konstantinov, V. F.; Kotzinian, A. M.; Kouznetsov, O. M.; Kral, Z.; Kramer, M.; Krinner, F.; Kroumchtein, Z. V.; Kulinich, Y.; Kunne, F.; Kurek, K.; Kurjata, R. P.; Kveton, A.; Levorato, S.; Lian, Y. -S.; Lichtenstadt, J.; Lin, P. -J.; Longo, R.; Lyubovitskij, V. E.; Maggiora, A.; Magnon, A.; Makins, N.; Makke, N.; Mallot, G. K.; Mamon, S. A.; Marianski, B.; Martin, A.; Marzec, J.; Matousek, J.; Matsuda, T.; Meshcheryakov, G. V.; Meyer, M.; Meyer, W.; Mikhailov, Y. V.; Mikhasenko, M.; Mitrofanov, E.; Mitrofanov, N.; Miyachi, Y.; Moretti, A.; Naim, C.; Nagaytsev, A.; Neyret, D.; Novy, J.; Nowak, W. -D.; Nukazuka, G.; Nunes, A. S.; Olshevsky, A. G.; Ostrick, M.; Panzieri, D.; Parsamyan, B.; Paul, S.; Peng, J. -C.; Pereira, F.; Pesek, M.; Peshekhonov, D. V.; Peskova, M.; Pierre, N.; Platchkov, S.; Pochodzalla, J.; Polyakov, V. A.; Pretz, J.; Quaresma, M.; Quintans, C.; Ramos, S.; Regali, C.; Reicherz, G.; Riedl, C.; Ryabchikov, D. I.; Rybnikov, A.; Rychter, A.; Samoylenko, V. D.; Sandacz, A.; Sarkar, S.; Savin, I. A.; Sbrizzai, G.; Schmieden, H.; Selyunin, A.; Silva, L.; Sinha, L.; Slunecka, M.; Smolik, J.; Srnka, A.; Steffen, D.; Stolarski, M.; Subrt, O.; Sulc, M.; Suzuki, H.; Szabelski, A.; Szameitat, T.; Sznajder, P.; Tessaro, S.; Tessarotto, F.; Thiel, A.; Tomsa, J.; Tosello, F.; Tskhay, V.; Uhl, S.; Vasilishin, B. I.; Vauth, A.; Veit, B. M.; Veloso, J.; Vidon, A.; Virius, M.; Wagner, M.; Wallner, S.; Wilfert, M.; Zaremba, K.; Zavada, P.; Zavertyaev, M.; Zemlyanichkina, E.; Zhao, Y.; Ziembicki, M