A new and detailed measurement of the cross section for hard exclusive neutral-pion muoproduction on the proton was performed in a wide kinematic region, with the photon virtuality <math altimg='si23.svg'><msup><mi>Q</mi><mn>2</mn></msup></math> ranging from 1 to 8 (GeV/ <math altimg='si134.svg'><msup><mrow><mi>c</mi><mo>)</mo></mrow><mn>2</mn></msup></math>and the Bjorken variable <math altimg='si135.svg'><msub><mi>x</mi><mrow><mrow><mi mathvariant='normal'>B</mi></mrow><mi>j</mi></mrow></msub></math> ranging from 0.02 to 0.45. The data were collected at COMPASS at CERN using 160 GeV/ <math altimg='si136.svg'><mi>c</mi></math> longitudinally polarised <math altimg='si13.svg'><msup><mi>&#956;</mi><mo>+</mo></msup></math> and <math altimg='si14.svg'><msup><mi>&#956;</mi><mo>&#8722;</mo></msup></math> beams scattering off a 2.5&#8239;m long liquid hydrogen target. From the average of the measured <math altimg='si13.svg'><msup><mi>&#956;</mi><mo>+</mo></msup></math> and <math altimg='si14.svg'><msup><mi>&#956;</mi><mo>&#8722;</mo></msup></math> cross sections, the virtual-photon&#8211;proton cross section is determined as a function of the squared four-momentum transfer between the initial and final state proton in the range 0.08 (GeV/ <math altimg='si134.svg'><msup><mrow><mi>c</mi><mo>)</mo></mrow><mn>2</mn></msup></math> <math altimg='si137.svg'><mrow><mo>&lt;</mo><mo>|</mo><mi>t</mi><mo>|</mo><mo>&lt;</mo></mrow></math> 0.64 (GeV/ <math altimg='si134.svg'><msup><mrow><mi>c</mi><mo>)</mo></mrow><mn>2</mn></msup></math>. From its angular distribution, the combined contribution of transversely and longitudinally polarised photons are determined, as well as transverse&#8211;transverse and longitudinal&#8211;transverse interference contributions. They are studied as functions of four-momentum transfer <math altimg='si18.svg'><mrow><mo>|</mo><mi>t</mi><mo>|</mo></mrow></math>, photon virtuality <math altimg='si23.svg'><msup><mi>Q</mi><mn>2</mn></msup></math> and virtual-photon energy <math altimg='si24.svg'><mi>&#957;</mi></math>. The longitudinal&#8211;transverse interference contribution is found to be compatible with zero. The significant transverse&#8211;transverse interference contribution reveals the existence of a dominant contribution by transversely polarised photons. This could provide clear experimental evidence for the chiral-odd GPD <math altimg='si138.svg'><msub><mover><mrow><mi>E</mi></mrow><mo stretchy='true'>&#8254;</mo></mover><mi>T</mi></msub></math>. In addition, the existence of a non-negligible contribution of longitudinally polarised photons is suggested by the <math altimg='si18.svg'><mrow><mo>|</mo><mi>t</mi><mo>|</mo></mrow></math>-dependence of the cross section at <math altimg='si139.svg'><mrow><msub><mi>x</mi><mrow><mrow><mi mathvariant='normal'>B</mi></mrow><mi>j</mi></mrow></msub><mo linebreak='goodbreak'>&lt;</mo></mrow></math> 0.1. Altogether, these results provide valuable input for future modelling of GPDs and thus of cross sections for exclusive pseudo-scalar meson production. Furthermore, they can be expected to facilitate the study of next-to-leading order corrections and higher-twist contributions.

G.D. Alexeev

Italy

M.G. Alexeev

C. Alice

A. Amoroso

United States

V. Andrieux

V. Anosov

Poland

K. Augsten

W. Augustyniak

Portugal

C. D R Azevedo

B. Badelek

Germany

J. Barth

R. Beck

J. Beckers

France

Y. Bedfer

Switzerland

J. Bernhard

Czechia

M. Bodlak

F. Bradamante

A. Bressan

Taiwan

W.-C Chang

C. Chatterjee

M. Chiosso

S.-U Chung

A. Cicuttin

P. M M Correia

M.L. Crespo

D. D’ago

S. Dalla Torre

India

S.S. Dasgupta

S. Dasgupta

F. Delcarro

I. Denisenko

O. Yu Denisov

M. Dehpour

S.V. Donskov

Japan

N. Doshita

Ch Dreisbach

W. Dünnweber

Armenia

R.R. Dusaev

D. Ecker

D. Eremeev

P. Faccioli

M. Faessler

M. Finger

H. Fischer

K.J. Fl

W. Florian

J.M. Friedrich

V. Frolov

L.G. Garcia Ordòñez

O.P. Gavrichtchouk

S. Gerassimov

J. Giarra

D. Giordano

M. Gorzellik

A. Grasso

A. Gridin

M. Grosse Perdekamp

B. Grube

M. Gr

A. Guskov

P. Haas

D. Von Harrach

M. Hoffmann

N. D’hose

C.-Y Hsieh

S. Ishimoto

A. Ivanov

T. Iwata

V. Jary

R. Joosten

P. Jörg

E. Kabuß

F. Kaspar

A. Kerbizi

B. Ketzer

G.V. Khaustov

F. Klein

J.H. Koivuniemi

V.N. Kolosov

K. Kondo Horikawa

I. Konorov

A. Yu Korzenev

A.M. Kotzinian

O.M. Kouznetsov

A. Koval

Z. Kral

F. Kunne

K. Kurek

R.P. Kurjata

K. Lavickova

S. Levorato

Y.-S Lian

Israel

J. Lichtenstadt

P.-J Lin

R. Longo

V.E. Lyubovitskij

A. Maggiora

N. Makke

G.K. Mallot

Measurement of the hard exclusive <math altimg='si1.svg'><msup><mi>&#960;</mi><mn>0</mn></msup></math> muoproduction cross section at COMPASS

<p>The multiplicities of positive and negative pions, kaons, and unidentified hadrons produced in deep-inelastic scattering are measured in bins of the Bjorken scaling variable <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>x</mi></math>, the relative virtual-photon energy <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>y</mi></math>, and the fraction of the virtual-photon energy transferred to the final-state hadron <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>z</mi></math>. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam of both electric charges and a liquid hydrogen target. These measurements cover the kinematic domain with photon virtuality <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>Q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>&gt;</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><mo stretchy="false">(</mo><mrow><mi>GeV</mi><mo>/</mo><mi>c</mi><msup><mrow><mo stretchy="false">)</mo></mrow><mrow><mn>2</mn></mrow></msup></mrow></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.004</mn><mo>&lt;</mo><mi>x</mi><mo>&lt;</mo><mn>0.4</mn></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.1</mn><mo>&lt;</mo><mi>y</mi><mo>&lt;</mo><mn>0.7</mn></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.2</mn><mo>&lt;</mo><mi>z</mi><mo>&lt;</mo><mn>0.85</mn></math>, in accordance with the kinematic domain used in earlier published COMPASS multiplicity measurements with an isoscalar target. The calculation of radiative corrections was improved by using the Monte Carlo generator <span class="sc">djangoh</span>, which results in up to 12% larger corrections in the low-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>x</mi></math> region.</p>

C.D.R. Azevedo

CERN

W.C. Chang

S.U. Chung

P.M.M. Correia

D. D’Ago

O. Yu. Denisov

Ch. Dreisbach

K.J. Flöthner

M. Grüner

D. von Harrach

N. d’Hose

C.Y. Hsieh

A. Khatun

A. Yu. Korzenev

Y.S. Lian

P.J. Lin

A. Maltsev

A. Martin

Multiplicities of positive and negative pions, kaons, and unidentified hadrons from deep-inelastic scattering of muons off a liquid hydrogen target

The production of vector mesons in deep inelastic scattering is an interesting yet scarcely explored channel to study the transverse spin structure of the nucleon and the spin-dependence of fragmentation. The COMPASS collaboration has performed the first measurement of the Collins and Sivers asymmetries for inclusively produced <math><msup><mrow><mi>ρ</mi></mrow><mrow><mn>0</mn></mrow></msup></math> mesons. The analysis is based on the data set collected in deep inelastic scattering in 2010 using a <math><mn>160</mn><mspace width="0.2em"></mspace><mspace width="0.2em"></mspace><mrow><mi>GeV</mi></mrow><mo>/</mo><mi>c</mi></math> <math><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup></math> beam impinging on a transversely polarized <math><mi>N</mi><msub><mrow><mi>H</mi></mrow><mrow><mn>3</mn></mrow></msub></math> target. The <math><msup><mrow><mi>ρ</mi></mrow><mrow><mn>0</mn></mrow></msup></math> mesons are selected from oppositely charged hadron pairs, and the asymmetries are extracted as a function of the Bjorken-x variable, the transverse momentum of the pair and the fraction of the energy z carried by the pair. Indications for positive Collins and Sivers asymmetries are observed.

V.E. Burtsev

A.G. Chumakov

D. D'Ago

F. Del Carro

O.Yu. Denisov

A. Efremov

C. Elia

F. Gautheron

N. Horikawa

N. d'Hose

S. Huber

M. Jandek

V.F. Konstantinov

A.M. Korzenev

F. Krinner

A. Kveton

Collins and Sivers transverse-spin asymmetries in inclusive muoproduction of Mesons

A set of measurements of azimuthal asymmetries in the production of pairs of identified hadrons in deep-inelastic scattering of muons on transversely polarised $^{6}$LiD (deuteron) and NH$_{3}$ (proton) targets is presented. All available data collected in the years 2003–2004 and 2007/2010 with the COMPASS spectrometer using a muon beam of <math><mn>160</mn><mspace width="0.25em"></mspace><mtext>GeV</mtext><mo>/</mo><mi>c</mi></math> at the CERN SPS were analysed. The asymmetries provide access to the transversity distribution functions via a fragmentation function that in principle may be independently obtained from <math><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> annihilation data. Results are presented, discussed and compared to existing measurements as well as to model predictions. Asymmetries of <math><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></math> pairs measured with the proton target as a function of the Bjorken scaling variable are sizeable in the range <math><mi>x</mi><mo>&gt;</mo><mn>0.032</mn></math>, indicating non-vanishing transversity distribution and di-hadron interference fragmentation functions. As already pointed out by several authors, the small asymmetries of <math><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></math> measured on the $^{6}$LiD target can be interpreted as indication for a cancellation of u and d-quark transversity distributions.

C. Braun

Transverse-spin-dependent azimuthal asymmetries of pion and kaon pairs produced in muon-proton and muon-deuteron semi-inclusive deep inelastic scattering

We present the study of the production of double <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> mesons using COMPASS data collected with a 190 <math><mtext>GeV</mtext><mo>/</mo><mi>c</mi></math> <math><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></math> beam scattering off NH$_{3}$, Al and W targets. Kinematic distributions of the collected double <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> events are analysed, and the double <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> production cross section is estimated for each of the COMPASS targets. The NH$_{3}$ results are compared to predictions from single- and double-parton scattering models as well as the pion intrinsic charm and the tetraquark exotic resonance hypotheses. It is demonstrated that the single parton scattering production mechanism gives the dominant contribution that is sufficient to describe the data. An upper limit on the double intrinsic charm content of the pion is evaluated. No significant signatures that could be associated with exotic tetraquarks are found in the double <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> mass spectrum.

JINR

B. Badełek

M. Ball

Russia

Estonia

P.D. Eversheim

C. Franco

S. Groote

Yu.A. Khokhlov

S. Koshkarev

Double / production in pion-nucleon scattering at COMPASS

Based on the observation of sizeable target-transverse-spin asymmetries in single-hadron and hadron-pair production in Semi-Inclusive measurements of Deep Inelastic Scattering (SIDIS), the chiral-odd transversity quark distribution functions <math><msubsup><mrow><mi>h</mi></mrow><mrow><mn>1</mn></mrow><mrow><mi>q</mi></mrow></msubsup></math> are nowadays well established. Several possible channels to access these functions were originally proposed. One candidate is the measurement of the polarisation of Λ hyperons produced in SIDIS off transversely polarised nucleons, where the transverse polarisation of the struck quark might be transferred to the final-state hyperon. In this article, we present the COMPASS results on the transversity-induced polarisation of Λ and <math><mover><mrow><mi>Λ</mi></mrow><mrow><mo>¯</mo></mrow></mover></math> hyperons produced in SIDIS off transversely polarised protons. Within the experimental uncertainties, no significant deviation from zero was observed. The results are discussed in the context of different models taking into account previous experimental results on <math><msubsup><mrow><mi>h</mi></mrow><mrow><mn>1</mn></mrow><mrow><mi>u</mi></mrow></msubsup></math> and <math><msubsup><mrow><mi>h</mi></mrow><mrow><mn>1</mn></mrow><mrow><mi>d</mi></mrow></msubsup></math>.

F. Balestra

J. Berenguer Antequera

A. Ferrero

I. Gnesi

R. Heitz

D.H. Kang

Yu. Kisselev

Y. Kulinich

Probing transversity by measuring Λ polarisation in SIDIS

In Fig. 5 on p. 311 of our Phys. Lett. B 740 (2015) 303 an adjustment by <math><msup><mrow><mn>180</mn></mrow><mrow><mo>∘</mo></mrow></msup></math> is required for the phases with respect to the <math><mi>L</mi><mo>=</mo><mn>2</mn><mo>,</mo><mi>M</mi><mo>=</mo><mn>1</mn></math> wave, of the following waves: <math><mi>L</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>3</mn><mo>,</mo><mn>5</mn></math> with <math><mi>M</mi><mo>=</mo><mn>1</mn></math>, and <math><mi>L</mi><mo>=</mo><mn>2</mn></math> with <math><mi>M</mi><mo>=</mo><mn>2</mn></math>. After this correction (Fig. 5 (corrected) below), the extracted partial waves describe the angular distribution of the <math><msup><mrow><mi>η</mi></mrow><mrow><mo>(</mo><mo>′</mo><mo>)</mo></mrow></msup></math> 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 <math><msup><mrow><mi>η</mi></mrow><mrow><mo>(</mo><mo>′</mo><mo>)</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></math> center-of-mass system and the y-axis pointing in the direction of <math><msubsup><mrow><mi>p</mi></mrow><mrow><mtext>recoil</mtext></mrow><mrow><mtext>GJ</mtext></mrow></msubsup><mo>×</mo><msubsup><mrow><mi>p</mi></mrow><mrow><mtext>beam</mtext></mrow><mrow><mtext>GJ</mtext></mrow></msubsup></math>.

C. Adolph

R. Akhunzyanov

A. Austregesilo

G. Baum

A. Berlin

K. Bicker

E.R. Bielert

J. Bieling

R. Birsa

J. Bisplinghoff

M. Boer

P. Bordalo

M. Büchele

E. Burtin

L. Capozza

Q. Curiel

V. Duic

M. Dziewiecki

W. Eyrich

N. du Fresne von Hohenesche

R. Geyer

B. Gobbo

Corrigendum to “Odd and even partial waves of And ′ In → at 191 GeV/ ” [Phys. Lett. B 740 (2015) 303–311]