We study open-charm hadrons production in pp and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV using an improved multiphase transport (AMPT) model. Specifically, we show the transverse-momentum spectra and nuclear modification factors <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>R</mi><mi>AA</mi></msub></math> of <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>D</mi><mn>0</mn></msup></math> mesons and <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi mathvariant="normal">Λ</mi><mrow><mi>c</mi></mrow><mo>+</mo></msubsup></math> baryons, as well as the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Λ</mi><mrow><mi>c</mi></mrow><mo>+</mo></msubsup><mo>/</mo><msup><mi>D</mi><mn>0</mn></msup></mrow></math> ratio in pp and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions. The results obtained from the AMPT model simulations are compared with the STAR experimental data and found to be consistent. We further investigate the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Λ</mi><mrow><mi>c</mi></mrow><mo>+</mo></msubsup><mo>/</mo><msup><mi>D</mi><mn>0</mn></msup></mrow></math> ratio by evaluating contributions from coalescence, fragmentation, and the combined <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>coalescence</mi><mo>+</mo><mi>fragmentation</mi></mrow></math> mechanisms, and we find that fragmentation alone underestimates the pronounced enhancement in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> relative to pp at low and intermediate <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub></math>, whereas the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>coalescence</mi><mo>+</mo><mi>fragmentation</mi></mrow></math> mechanism reproduces the observed trend significantly better. These results indicate that coalescence plays a key role in charm-baryon productions and helps constrain the relative importance of different hadronization mechanisms in the ultrarelativistic nuclear collisions.

China

Bijun Fan

Shusu Shi

Chao Zhang

Liang Zheng

Open charm production and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msubsup><mi mathvariant="normal">Λ</mi><mrow><mi>c</mi></mrow><mo>+</mo></msubsup><mo>/</mo><msup><mi>D</mi><mn>0</mn></msup></mrow></math> ratio in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>Au</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions at <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn><mo> </mo><mi>GeV</mi></mrow></math>

We present measurements of the total and differential cross sections for near-threshold <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> photoproduction obtained with the CLAS12 detector at the Thomas Jefferson National Accelerator Facility. The results are based on data collected during the fall 2018 and spring 2019 running periods, using electron beams with energies of 10.6 and 10.2 GeV, respectively, scattered off a liquid-hydrogen target. Near-threshold <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> photoproduction offers a unique sensitivity to the strong interaction in the nonperturbative regime of quantum chromodynamics (QCD). The energy dependence of the cross section constrains the underlying <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> production mechanisms, including multigluon exchange and potential baryonic excitations. Additionally, the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>t</mi></math> dependence of the differential cross section can be related to the transverse spatial distribution of gluons in the proton, providing critical input for theoretical descriptions of the gluonic structure of the proton. An interpretation of the results in terms of the gluon content of the proton is presented, providing new experimental constraints on QCD-inspired models of the proton structure and the role of gluonic degrees of freedom in hadronic mass generation.

France

P. Chatagnon

United States

V. Kubarovsky

R. Paremuzyan

S. Stepanyan

M. Tenorio

United Kingdom

R. Tyson

A.G. Acar

P. Achenbach

J.S. Alvarado

M.J. Amaryan

W.R. Armstrong

H. Avakian

N.A. Baltzell

Italy

L. Barion

M. Bashkanov

M. Battaglieri

F. Benmokhtar

A. Bianconi

A.S. Biselli

S. Boiarinov

M. Bondi

F. Bossù

Germany

K.-Th. Brinkmann

W.J. Briscoe

S. Bueltmann

V.D. Burkert

T. Cao

D.S. Carman

A. Celentano

H. Chinchay

G. Ciullo

P.L. Cole

A. D'Angelo

Armenia

N. Dashyan

M. Defurne

R. De Vita

A. Deur

S. Diehl

C. Dilks

C. Djalali

M. Dugger

R. Dupré

H. Egiyan

M. Ehrhart

Chile

A. El Alaoui

L. El Fassi

L. Elouadrhiri

M. Farooq

S. Fegan

R.F. Ferguson

I.P. Fernando

E. Ferrand

A. Filippi

C. Fogler

K. Gates

G.P. Gilfoyle

D.I. Glazier

R.W. Gothe

Y. Gotra

B. Gualtieri

K. Hafidi

H. Hakobyan

F. Hauenstein

T.B. Hayward

D. Heddle

M. Hoballah

D. Holmberg

M. Holtrop

C.E. Hyde

Y. Ilieva

D.G. Ireland

Russia

E.L. Isupov

South Korea

H.S. Jo

K. Joo

T. Kageya

M. Kerr

A. Kim

H.T. Klest

V. Klimenko

Israel

I. Korover

A. Kripko

S.E. Kuhn

L. Lanza

S. Lee

P. Lenisa

X. Li

D. Marchand

D. Martiryan

V. Mascagna

B. McKinnon

A. Mehta

R.G. Milner

T. Mineeva

M. Mirazita

V.I. Mokeev

E.F. Molina Cardenas

C. Munoz Camacho

P. Nadel-Turonski

K. Neupane

D. Nguyen

Measurement of the near-threshold <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> photoproduction cross section with the CLAS12 experiment

The Dalitz decay <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mn>0</mn></msup><mo>→</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mi>γ</mi></mrow></math> has been measured with the highest statistical accuracy obtained so far in the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>γ</mi><mi>p</mi><mo>→</mo><msup><mi>π</mi><mn>0</mn></msup><mi>p</mi></mrow></math> reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value of the slope parameter for the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>π</mi><mn>0</mn></msup></math> electromagnetic transition form factor, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi>a</mi><mi>π</mi></msub><mo>=</mo><mn>0.0315</mn><mo>±</mo><mn>0</mn><mo>.</mo><msub><mn>0026</mn><mi>stat</mi></msub><mo>±</mo><mn>0</mn><mo>.</mo><msub><mn>0010</mn><mi>syst</mi></msub></mrow></math>, is obtained from the analysis of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>2.4</mn><mo>×</mo><msup><mn>10</mn><mn>6</mn></msup></mrow></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mn>0</mn></msup><mo>→</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mi>γ</mi></mrow></math> observed decays. Within experimental uncertainties, it is in agreement with existing measurements and theoretical calculations, with its own uncertainty being smaller than previous results based on the analysis of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mn>0</mn></msup><mo>→</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mi>γ</mi></mrow></math> decays.

S. Prakhov

L. Heijkenskjöld

Switzerland

S. Abt

P. Adlarson

F. Afzal

Canada

Z. Ahmed

K. Altangerel

J.R.M. Annand

R. Beck

M. Biroth

JINR

N.S. Borisov

A. Braghieri

F. Cividini

C. Collicott

S. Costanza

A. Denig

M. Dieterle

A.S. Dolzhikov

E.J. Downie

P. Drexler

S. Gardner

D. Ghosal

I. Gorodnov

W. Gradl

M. Günther

G.M. Gurevich

D. Hornidge

G.M. Huber

A. Käser

V.L. Kashevarov

S.J.D. Kay

Croatia

M. Korolija

B. Krusche

A. Lazarev

K. Livingston

S. Lutterer

I.J.D. MacGregor

D.M. Manley

P.P. Martel

R. Miskimen

M. Mocanu

E. Mornacchi

C. Mullen

A. Neganov

A. Neiser

M. Ostrick

P.B. Otte

D. Paudyal

P. Pedroni

A. Powell

E. Rickert

T. Rostomyan

V. Sokhoyan

K. Spieker

O. Steffen

I.I. Strakovsky

Th. Strub

I. Supek

M. Thiel

A. Thomas

Yu. A. Usov

S. Wagner

D.P. Watts

D. Werthmüller

J. Wettig

M. Wolfes

N. Zachariou

New high-statistics measurement of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mn>0</mn></msup><mo>→</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mi>γ</mi></mrow></math> Dalitz decay at the Mainz Microtron

The quality of recent Short-Range Correlations/Color-Transparency (SRC/CT) Collaboration <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> photoproduction data off a <math xmlns="http://www.w3.org/1998/Math/MathML"><mmultiscripts><mi>He</mi><mprescripts></mprescripts><none></none><mn>4</mn></mmultiscripts></math> target from Hall D at Jefferson Laboratory, combined with the feasibility of measuring the reaction close to the free-nucleon energy threshold, opens the door to using incoherent <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> photoproduction to explore a variety of interesting physics aspects. An example is the estimation of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi><mspace width="4pt"></mspace><mi>p</mi></mrow></math> scattering length <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mo>|</mo></mrow><msub><mi>α</mi><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi><mspace width="4pt"></mspace><mi>p</mi></mrow></msub><mrow><mo>|</mo></mrow></mrow></math> on the bound proton, obtained using the vector meson dominance model. The new experiment E12–25–002, conducted by the SRC/CT Collaboration, was recently approved in Hall D with the GlueX spectrometer, which will significantly enhance the number of reconstructed <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> mesons. Using a plane-wave theoretical model to generate quasidata, we estimated that the experiment could achieve a result of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mo>|</mo></mrow><msub><mi>α</mi><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi><mspace width="4pt"></mspace><mi>p</mi></mrow></msub><mrow><mo>|</mo><mo>=</mo><mn>3.08</mn><mo>±</mo><mn>0.45</mn><mspace width="4pt"></mspace><mi>mfm</mi></mrow></mrow></math>. This value can be compared to an extraction based on the free proton data from the GlueX Collaboration, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mrow><mo>|</mo></mrow><msub><mi>α</mi><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi><mspace width="4pt"></mspace><mi>p</mi></mrow></msub><mrow><mo>|</mo><mo>=</mo><mn>3.08</mn><mo>±</mo><mn>0.55</mn><mspace width="4pt"></mspace><mi>mfm</mi></mrow></mrow></math>. A comparison between the two would provide an opportunity to evaluate the effects of medium modification in light nuclei.

Igor I. Strakovsky

William J. Briscoe

Japan

Philipp Gubler

Jackson R. Pybus

Axel Schmidt

Alexander Somov

<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math>-meson–nucleon scattering length from threshold photoproduction on light nuclei