<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>

G.D. Alexeev

Italy

M.G. Alexeev

C. Alice

A. Amoroso

United States

V. Andrieux

V. Anosov

Czechia

K. Augsten

Poland

W. Augustyniak

Portugal

C.D.R. Azevedo

B. Badelek

Germany

J. Barth

R. Beck

J. Beckers

France

Y. Bedfer

CERN

J. Bernhard

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

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. Flöthner

W. Florian

J.M. Friedrich

V. Frolov

L.G. Garcia Ordòñez

O.P. Gavrichtchouk

S. Gerassimov

J. Giarra

D. Giordano

A. Grasso

A. Gridin

M. Grosse Perdekamp

B. Grube

M. Grüner

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

E. Kabuß

F. Kaspar

A. Kerbizi

B. Ketzer

A. Khatun

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

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

M. Gorzellik

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

S. Goertz

S. Grabmüller

T. Grussenmeyer

F. Haas

D. Hahne

R. Hashimoto

F.H. Heinsius

F. Herrmann

F. Hinterberger

Ch. Höppner

Yu. Ivanshin

R. Jahn

P. Jasinski

P. Jörg

K. Klimaszewski

K. Kondo

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

Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured by the HERMES experiment at DESY on proton and deuteron targets, and by the COMPASS experiment using the CERN SPS muon beam and a $^{6}$LiD target. In both cases, the amplitudes of the <math><mi>cos</mi><mo>⁡</mo><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>h</mi></mrow></msub></math> and <math><mi>cos</mi><mo>⁡</mo><mn>2</mn><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>h</mi></mrow></msub></math> modulations show strong kinematic dependences for both positive and negative hadrons. It has been known since some time that the measured final-state hadrons in those SIDIS experiments receive a contribution from exclusive diffractive production of vector mesons, particularly important at large values of z, the fraction of the virtual photon energy carried by the hadron. In previous measurements of azimuthal asymmetries this contribution was not taken into account, because it was not known that it could distort the azimuthal modulations. Presently, a method to evaluate the contribution of the exclusive reactions to the azimuthal asymmetries measured by COMPASS has been developed. The subtraction of this contribution results in a better understanding of the kinematic effects, and the remaining non-zero <math><mi>cos</mi><mo>⁡</mo><mn>2</mn><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>h</mi></mrow></msub></math> modulation gives indication for a non-zero Boer-Mulders effect.

J. Agarwala

N.V. Anfimov

Contribution of exclusive diffractive processes to the measured azimuthal asymmetries in SIDIS