We consider the leading order result for polarized leptoproduction, putting emphasis on transvers... more We consider the leading order result for polarized leptoproduction, putting emphasis on transverse momentum dependent effects appearing in azimuthal asymmetries. Measurements of weighted cross sections enable extraction of the distribution of transversely polarized quarks. We focus on the distribution in a longitudinally polarized hadron and estimate the expected asymmetries in leptoproduction.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 9, 2022
We report the first measurements of deep inelastic scattering spin-dependent azimuthal asymmetrie... more We report the first measurements of deep inelastic scattering spin-dependent azimuthal asymmetries in back-to-back dihadron electroproduction, where two hadrons are produced in opposite hemispheres along the z-axis in the center-of-mass frame, with the first hadron produced in the current-fragmentation region and the second in the target-fragmentation region. The data were taken with longitudinally polarized electron beams of 10.2 and 10.6 GeV incident on an unpolarized liquid-hydrogen target using the CLAS12 spectrometer at Jefferson Lab. Observed non-zero sin ∆φ modulations in ep → e pπ + X events, where ∆φ is the difference of the azimuthal angles of the proton and pion in the virtual photon and target nucleon center-of-mass frame, indicate that correlations between the spin and transverse momenta of hadrons produced in the target-and current-fragmentation regions may be significant. The measured beam-spin asymmetries provide a first access in dihadron production to a previously unobserved leading-twist spin-and transversemomentum-dependent fracture function. The fracture functions describe the hadronization of the target remnant after the hard scattering of a virtual photon off a quark in the target particle and provide a new avenue for studying nucleonic structure and hadronization.
We report on a measurement of hard exclusive π 0 muoproduction on the proton by COMPASS using 160... more We report on a measurement of hard exclusive π 0 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 Q 2 = 2.0 (GeV/c) 2 , ν = 12.8 GeV, x B j = 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 ± 0.9 stat + 1.2 − 1.2 sys) nb/(GeV/c) 2 , as well as transverse-transverse and longitudinal-transverse interference contributions of (−6.1 ± 1.3 stat + 0.7 − 0.7 sys) nb/(GeV/c) 2 and (1.5 ± 0.5 stat + 0.3 − 0.2 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 transversetransverse interference contribution constitutes clear experimental evidence for the chiral-odd GPD E T .
It is shown that the evaluation of the expectation value (EV) of topological charge density over ... more It is shown that the evaluation of the expectation value (EV) of topological charge density over $\theta$-vacuum is reduced to investigation of the Chern-Simons term EV. An equation for this quantity is established and solved. EV of the topological charge density at an arbitrary $\theta$ occurs equal to zero and, as a consequence, topological susceptibility of both QCD and pure Yang-Mills vacua defined in a Wick sense is equal to zero, whereas when defined in a Dyson sense it differs from zero by the quantity proportional to the respective condensate of the chromomagnetic field. Thus, the usual Wittten-Veneziano formula for the $\eta^{'}$ meson mass is modified.
The inclusive double-spin asymmetry, A p 1 , has been measured at COMPASS in deepinelastic polari... more The inclusive double-spin asymmetry, A p 1 , has been measured at COMPASS in deepinelastic polarised muon scattering off a large polarised NH 3 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 p 1 (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 N S 1 (x, Q 2). The isovector quark density, ∆q 3 (x, Q 2), is evaluated from a NLO QCD fit of g N S 1. The first moment of ∆q 3 is in good agreement with the value predicted by the Bjorken sum rule and corresponds to a ratio of the axial and vector coupling constants |g A /g V | = 1.28±0.07(stat.)±0.10(syst.).
Spin asymmetries for events with high p T hadrons in DIS and an evaluation of the gluon polarizat... more Spin asymmetries for events with high p T hadrons in DIS and an evaluation of the gluon polarization In remembrance of Vernon W. Hughes, initiator of the SMC experiment and spokesman of the collaboration, who passed away on March 25, 2003 and to whom this article is dedicated.
New possibilities arising from the availability at GSI of antiproton beams, possibly polarised, a... more New possibilities arising from the availability at GSI of antiproton beams, possibly polarised, are discussed. The investigation of the nucleon structure can be boosted by accessing in Drell-Yan processes experimental asymmetries related to cross-sections in which the parton distribution functions (PDF) only appear, without any contribution from fragmentation functions; such processes are not affected by the chiral suppression of the transversity function h1(x). Spin asymmetries in hyperon production and Single Spin Asymmetries are discussed as well, together with further items like electric and magnetic nucleonic form factors and open charm production. Counting rates estimations
Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaon... more 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.
Foundation and Yamada Foundation. Supported by the DFG cluster of excellence 'Origin and Structur... more Foundation and Yamada Foundation. Supported by the DFG cluster of excellence 'Origin and Structure of the Universe' (www.universe-cluster.de).
C ER N {PH {EP/2009{008 9 A pri l2009 K eywords:C O M PA SS;doubl e-spi n asym m etry;hel i ci ty... more C ER N {PH {EP/2009{008 9 A pri l2009 K eywords:C O M PA SS;doubl e-spi n asym m etry;hel i ci ty densi ty;parton di stri buti on functi on; avourseparati on anal ysi s;pol ari sed D IS and SID IS reacti ons;charged kaon asym m etry
The longitudinal polarisation transfer from muons to Λ andΛ hyperons, D Λ(Λ) LL , has been studie... more The longitudinal polarisation transfer from muons to Λ andΛ hyperons, D Λ(Λ) LL , has been studied in deepinelastic scattering off an unpolarised isoscalar target at the COMPASS experiment at CERN. The spin transfers to Λ andΛ produced in the current fragmentation region exhibit different behaviours as a function of x and x F. The measured x and x F dependences of D Λ LL are compatible with zero, while DΛ LL tends to increase with x F , reaching values of 0.4-0.5. The resulting average values are D Λ LL = −0.012 ± 0.047 ± 0.024 and DΛ LL = 0.249 ± 0.056 ± 0.049. These results are discussed in the frame of recent model calculations.
We present an update of a previous global analysis of the experimental data on azimuthal asymmetr... more We present an update of a previous global analysis of the experimental data on azimuthal asymmetries in semiinclusive deep inelastic scattering (SIDIS), from the HERMES and COMPASS Collaborations, and in e + e − → h1h2X processes, from the Belle Collaboration. Compared to the first extraction, a more precise determination of the Collins fragmentation function and the transversity distribution function for u and d quarks is obtained.
We present a precise measurement of the proton longitudinal double-spin asymmetry A p 1 and the p... more We present a precise measurement of the proton longitudinal double-spin asymmetry A p 1 and the proton spin-dependent structure function g p 1 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 p 1 and g p 1 are found to be positive. It is for the first time that spin effects are found at such low values of x.
Eight proton transverse-spin azimuthal asymmetries are extracted in four regions of the photon vi... more Eight proton transverse-spin azimuthal asymmetries are extracted in four regions of the photon virtuality Q 2 from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muonnucleon scattering. These Q 2 regions correspond to the four regions of the di-muon mass Q 2 used in the ongoing analyses of the COMPASS Drell-Yan measurements, which allows for a future direct comparison of the nucleon transverse-momentum-dependent parton distribution functions extracted from these two alternative measurements. In addition, for the azimuthal asymmetries induced by the Sivers transverse-momentum-dependent parton distribution function various two-dimensional kinematic dependences are presented. The integrated Sivers asymmetries are found to be positive with an accuracy that appears to be sufficient to test the sign change of the Sivers function predicted by Quantum Chromodynamics.
Multiplicities of charged pions and unidentified charged hadrons from deep-inelastic scattering o... more Multiplicities of charged pions and unidentified charged hadrons from deep-inelastic scattering of muons off an isoscalar target The COMPASS Collaboration
The COMPASS experiment at the CERN SPS has studied the diffractive dissociation of negative pions... more The COMPASS experiment at the CERN SPS has studied the diffractive dissociation of negative pions into the À À þ final state using a 190 GeV=c pion beam hitting a lead target. A partial wave analysis has been performed on a sample of 420 000 events taken at values of the squared 4-momentum transfer t 0 between 0.1 and 1 GeV 2 =c 2. The well-known resonances a 1 ð1260Þ, a 2 ð1320Þ, and 2 ð1670Þ are clearly observed. In addition, the data show a significant natural-parity exchange production of a resonance with spin-exotic quantum numbers J PC ¼ 1 Àþ at 1:66 GeV=c 2 decaying to. The resonant nature of this wave is evident from the mass-dependent phase differences to the J PC ¼ 2 Àþ and 1 þþ waves. From a mass-dependent fit a resonance mass of ð1660 AE 10 þ0 À64 Þ MeV=c 2 and a width of ð269 AE 21 þ42 À64 Þ MeV=c 2 are deduced, with an intensity of ð1:7 AE 0:2Þ% of the total intensity.
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Papers by Aram Kotzinian