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Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high pT
C. Adolph, R. Akhunzyanov, M. Alexeev, G. Alexeev, A. Amoroso, V.
Andrieux, V. Anosov, W. Augustyniak, A. Austregesilo, C. Azevedo, et al.
To cite this version:
C. Adolph, R. Akhunzyanov, M. Alexeev, G. Alexeev, A. Amoroso, et al.. Longitudinal double spin
asymmetries in single hadron quasi-real photoproduction at high pT. Modern Physics Letters B, World
Scientific Publishing, 2016, 753, pp.573 - 579. �10.1016/j.physletb.2015.12.035�. �hal-01466423�
Contents lists available atScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high p
TC. Adolph
i, R. Akhunzyanov
h, M.G. Alexeev
ab, G.D. Alexeev
h, A. Amoroso
ab,ac, V. Andrieux
v, V. Anosov
h, W. Augustyniak
ae, A. Austregesilo
q, C.D.R. Azevedo
b,
B. Badełek
af, F. Balestra
ab,ac, J. Barth
e, R. Beck
d, Y. Bedfer
v,k, J. Bernhard
n,k, K. Bicker
q,k, E.R. Bielert
k, R. Birsa
z, J. Bisplinghoff
d, M. Bodlak
s, M. Boer
v, P. Bordalo
m,2,
F. Bradamante
y,z, C. Braun
i, A. Bressan
y,z, M. Büchele
j, E. Burtin
v, W.-C. Chang
w, M. Chiosso
ab,ac, I. Choi
ad, S.-U. Chung
q,3, A. Cicuttin
aa,z, M.L. Crespo
aa,z, Q. Curiel
v, S. Dalla Torre
z, S.S. Dasgupta
g, S. Dasgupta
y,z, O.Yu. Denisov
ac,∗, L. Dhara
g,
S.V. Donskov
u, N. Doshita
ah, V. Duic
y, W. Dünnweber
4, M. Dziewiecki
ag, A. Efremov
h, P.D. Eversheim
d, W. Eyrich
i, M. Faessler
4, A. Ferrero
v, M. Finger
s, M. Finger Jr.
s, H. Fischer
j, C. Franco
m, N. du Fresne von Hohenesche
n, J.M. Friedrich
q, V. Frolov
h,k, E. Fuchey
v, F. Gautheron
c, O.P. Gavrichtchouk
h, S. Gerassimov
p,q, F. Giordano
ad, I. Gnesi
ab,ac, M. Gorzellik
j, S. Grabmüller
q, A. Grasso
ab,ac, M. Grosse Perdekamp
ad, B. Grube
q, T. Grussenmeyer
j, A. Guskov
h, F. Haas
q, D. Hahne
e, D. von Harrach
n, R. Hashimoto
ah, F.H. Heinsius
j, F. Herrmann
j, F. Hinterberger
d, N. Horikawa
r,5, N. d’Hose
v, C.-Y. Hsieh
w, S. Huber
q, S. Ishimoto
ah,6, A. Ivanov
ab,ac, Yu. Ivanshin
h, T. Iwata
ah, R. Jahn
d, V. Jary
t, R. Joosten
d, P. Jörg
j, E. Kabuß
n, B. Ketzer
d,q,
G.V. Khaustov
u, Yu.A. Khokhlov
u,7,8, Yu. Kisselev
h, F. Klein
e, K. Klimaszewski
ae, J.H. Koivuniemi
c, V.N. Kolosov
u, K. Kondo
ah, K. Königsmann
j, I. Konorov
p,q,
*
Correspondingauthors.E-mailaddresses:oleg.denisov@cern.ch(O.Yu. Denisov),gerhard.mallot@cern.ch(G.K. Mallot),claude.marchand@cea.fr(C. Marchand).
1 Deceased.
2 AlsoatInstitutoSuperiorTécnico,UniversidadedeLisboa,Lisbon,Portugal.
3 AlsoatDepartmentofPhysics,PusanNationalUniversity,Busan609-735,RepublicofKoreaandatPhysicsDepartment,BrookhavenNationalLaboratory,Upton,NY11973, USA.
4 SupportedbytheDFGclusterofexcellence‘OriginandStructureoftheUniverse’(www.universe-cluster.de).
5 AlsoatChubuUniversity,Kasugai,Aichi487-8501, Japan.
6 AlsoatKEK,1-1Oho,Tsukuba,Ibaraki305-0801, Japan.
7 AlsoatMoscowInstituteofPhysicsandTechnology,MoscowRegion,141700,Russia.
8 SupportedbyPresidentialgrantNSh-999.2014.2.
9 Presentaddress:TypesafeAB,DagHammarskjöldsväg13,75237Uppsala,Sweden.
10 Presentaddress:RWTHAachenUniversity,III.PhysikalischesInstitut,52056Aachen,Germany.
11 SupportedbytheDFGResearchTrainingGroupProgramme1102“PhysicsatHadronAccelerators”.
12 Presentaddress:UppsalaUniversity,Box516,SE-75120Uppsala,Sweden.
13 SupportedbytheGermanBundesministeriumfürBildungundForschung.
14 SupportedbyEUFP7(HadronPhysics3,GrantAgreementnumber283286).
15 SupportedbyCzechRepublicMEYSGrantLG13031.
16 SupportedbySAIL(CSR),Govt.ofIndia.
17 SupportedbyCERN-RFBRGrant12-02-91500.
18 SupportedbythePortugueseFCT–FundaçãoparaaCiênciaeTecnologia,COMPETEandQREN,GrantsCERN/FP109323/2009,116376/2010,123600/2011andCERN/FIS- NUC/0017/2015.
19 SupportedbytheMEXTandtheJSPSundertheGrantsNo.18002006,No.20540299andNo.18540281;DaikoFoundationandYamadaFoundation.
20 SupportedbytheIsraelAcademyofSciencesandHumanities.
21 SupportedbythePolishNCNGrantDEC-2011/01/M/ST2/02350.
http://dx.doi.org/10.1016/j.physletb.2015.12.035
0370-2693/©2015TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3.
574 C. Adolph et al. / Physics Letters B 753 (2016) 573–579
V.F. Konstantinov
u, A.M. Kotzinian
ab,ac, O. Kouznetsov
h, M. Krämer
q, P. Kremser
j, F. Krinner
q, Z.V. Kroumchtein
h, N. Kuchinski
h, R. Kuhn
q,9, F. Kunne
v, K. Kurek
ae, R.P. Kurjata
ag, A.A. Lednev
u, A. Lehmann
i, M. Levillain
v, S. Levorato
z, J. Lichtenstadt
x, R. Longo
ab,ac, A. Maggiora
ac, A. Magnon
v, N. Makins
ad, N. Makke
y,z, G.K. Mallot
k,∗, C. Marchand
v,∗, B. Marianski
ae, A. Martin
y,z, J. Marzec
ag, J. Matoušek
s, H. Matsuda
ah, T. Matsuda
o, G. Meshcheryakov
h, W. Meyer
c, T. Michigami
ah, Yu.V. Mikhailov
u,
Y. Miyachi
ah, P. Montuenga
ad, A. Nagaytsev
h, F. Nerling
n, D. Neyret
v, V.I. Nikolaenko
u, J. Nový
t,k, W.-D. Nowak
j, G. Nukazuka
ah, A.S. Nunes
m, A.G. Olshevsky
h, I. Orlov
h, M. Ostrick
n, D. Panzieri
a,ac, B. Parsamyan
ab,ac, S. Paul
q, J.-C. Peng
ad, F. Pereira
b,
M. Pešek
s, D.V. Peshekhonov
h, S. Platchkov
v, J. Pochodzalla
n, V.A. Polyakov
u, J. Pretz
e,10, M. Quaresma
m, C. Quintans
m, S. Ramos
m,2, C. Regali
j, G. Reicherz
c, C. Riedl
ad,
N.S. Rossiyskaya
h, D.I. Ryabchikov
u,8, A. Rychter
ag, V.D. Samoylenko
u, A. Sandacz
ae, C. Santos
z, S. Sarkar
g, I.A. Savin
h, G. Sbrizzai
y,z, P. Schiavon
y,z, K. Schmidt
j,11, H. Schmieden
e, K. Schönning
k,12, S. Schopferer
j, A. Selyunin
h, O.Yu. Shevchenko
h,1, L. Silva
m, L. Sinha
g, S. Sirtl
j, M. Slunecka
h, F. Sozzi
z, A. Srnka
f, M. Stolarski
m, M. Sulc
l, H. Suzuki
ah,5, A. Szabelski
ae, T. Szameitat
j,11, P. Sznajder
ae, S. Takekawa
ab,ac, S. Tessaro
z, F. Tessarotto
z, F. Thibaud
v, F. Tosello
ac, V. Tskhay
p, S. Uhl
q, J. Veloso
b, M. Virius
t,
T. Weisrock
n, M. Wilfert
n, J. ter Wolbeek
j,11, K. Zaremba
ag, M. Zavertyaev
p, E. Zemlyanichkina
h, M. Ziembicki
ag, A. Zink
iaUniversityofEasternPiedmont,15100Alessandria,Italy
bUniversityofAveiro,DepartmentofPhysics,3810-193Aveiro,Portugal
cUniversitätBochum,InstitutfürExperimentalphysik,44780Bochum,Germany13,14 dUniversitätBonn,Helmholtz-InstitutfürStrahlen- undKernphysik,53115Bonn,Germany13 eUniversitätBonn,PhysikalischesInstitut,53115Bonn,Germany13
fInstituteofScientificInstruments,ASCR,61264Brno,CzechRepublic13
gMatrivaniInstituteofExperimentalResearch&Education,Calcutta700030,India16 hJointInstituteforNuclearResearch,141980Dubna,Moscowregion,Russia17 iUniversitätErlangen–Nürnberg,PhysikalischesInstitut,91054Erlangen,Germany13 jUniversitätFreiburg,PhysikalischesInstitut,79104Freiburg,Germany13,14 kCERN,1211Geneva23,Switzerland
lTechnicalUniversityinLiberec,46117Liberec,CzechRepublic15 mLIP,1000-149Lisbon,Portugal18
nUniversitätMainz,InstitutfürKernphysik,55099Mainz,Germany13 oUniversityofMiyazaki,Miyazaki889-2192,Japan19
pLebedevPhysicalInstitute,119991Moscow,Russia
qTechnischeUniversitätMünchen,PhysikDepartment,85748Garching,Germany13,4 rNagoyaUniversity,464Nagoya,Japan19
sCharlesUniversityinPrague,FacultyofMathematicsandPhysics,18000Prague,CzechRepublic15 tCzechTechnicalUniversityinPrague,16636Prague,CzechRepublic15
uStateScientificCenterInstituteforHighEnergyPhysicsofNationalResearchCenter‘KurchatovInstitute’,142281Protvino,Russia vCEAIRFU/SPhNSaclay,91191Gif-sur-Yvette,France14
wAcademiaSinica,InstituteofPhysics,Taipei11529, Taiwan
xTelAvivUniversity,SchoolofPhysicsandAstronomy,69978TelAviv,Israel20 yUniversityofTrieste,DepartmentofPhysics,34127Trieste,Italy
zTriesteSectionofINFN,34127Trieste,Italy aaAbdusSalamICTP,34151Trieste,Italy
abUniversityofTurin,DepartmentofPhysics,10125Turin,Italy acTorinoSectionofINFN,10125Turin,Italy
adUniversityofIllinoisatUrbana-Champaign,DepartmentofPhysics,Urbana,IL61801-3080,USA aeNationalCentreforNuclearResearch,00-681Warsaw,Poland21
afUniversityofWarsaw,FacultyofPhysics,02-093Warsaw,Poland21
agWarsawUniversityofTechnology,InstituteofRadioelectronics,00-665Warsaw,Poland21 ahYamagataUniversity,Yamagata992-8510, Japan19
a r t i c l e i n f o a b s t ra c t
Articlehistory:
Received11September2015
Receivedinrevisedform17November2015 Accepted11December2015
Availableonline21December2015 Editor:M.Doser
Keywords:
COMPASS
Deepinelasticscattering Doublespinasymmetry
WemeasuredthelongitudinaldoublespinasymmetriesALLforsinglehadronmuoproductionoffprotons and deuteronsatphoton virtuality Q2<1 (GeV/c)2 fortransverse hadronmomenta pT intherange 1 GeV/c to4 GeV/c.They weredeterminedusingCOMPASSdata takenwithapolarisedmuonbeam of160 GeV/cor200 GeV/cimpingingonpolarised6LiDorNH3targets.Theexperimentalasymmetries arecomparedtonext-to-leadingorderpQCDcalculations,andaresensitivetothegluonpolarisationG insidethenucleonintherangeofthenucleonmomentumfractioncarriedbygluons0.05<xg<0.2.
©2015TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3.
HighpT
G
Fig. 1.Contributionstothesingle-inclusivecrosssection forquasi-realphotoproductionofahadronh intodirect (left)andresolved(right)subprocessesaccordingto Ref.[14].Theinternallinesrepresentthephotona=γ∗(left)andpartons{a,b,c}= {q,q¯,g}.Thecentralblobdescribesthehardscatteringcrosssectionσˆ.Theperipheral blobsdescribethenon-perturbativeobjects:partondistributionsofthenucleon, fbN,andofthephoton,faγ∗,andthefragmentationfunctionsoftheproducedhadron,Dhc.
1. Introduction
The spin structure of the nucleon is one of the major unre- solvedissues inhadronicphysics.While thequark spincontribu- tionto the nucleon spin, denotedas , hasbeen measured to beabout30%[1],thegluonspincontributionisstillinsufficiently constrainedaftermorethan twodecades ofintense study.Inthe frameworkofperturbativeQuantumChromodynamics(pQCD),in- clusiveDeep InelasticScattering (DIS)issensitivetogluoncontri- butionsonlythroughhigher-ordercorrectionstothecrosssection.
Thespin-averagedgluon densityg(xg),wherexg denotesthenu- cleonmomentum fraction carried by gluons, is well constrained byDISexperimentswithunpolarisedbeamandtargetbecauseof theirhighstatistics andlargekinematiccoverage. Thefewer data fromDIS experiments with polarised beam and target, however, cannot sufficientlyconstrainthegluonhelicitydistributiong(xg). Thisaffectsdirectlyourknowledgeofthecontributionofthegluon spintothespinofthenucleon,knownasG=
g(xg)dxg,and to a lesserextent that of the quarks [2]. In order tobetter con- straing(xg),one hastoresorttoprocesseswherecontributions fromgluonsappearatleadingorder,suchashadronproductionat hightransversemomentaorproductionofopencharminpolarised lepton–nucleon[3–7]orhadron–hadroninteractions[8–11].
The COMPASS collaboration hasalready investigated asymme- triesofhadronsathightransverse momenta pT,inboth the DIS andthe quasi-realphotoproductionregimes [4,6,12]. Here,trans- verse means transverse withrespect to the direction of the vir- tualphoton γ∗ thatisexchanged inthescatteringprocess.Using a Lund Monte Carlosimulation, these measurements were inter- pretedonthehadronlevel,therebysimultaneouslyextractingthe gluonhelicityonthepartonlevel.Suchananalysisisrestrictedto leadingorder(LO)inthestrongcouplingconstant αs,aspresently there exists no next-to-leading order (NLO) Monte Carlosimula- tionforleptoproduction.Duetothelimitationofneglectinggluon contributionsatNLO,suchresultscannot beusedinrecentglobal fitsatNLOofpolarisedPartonDistributionFunctions(PDFs)[13].
InthisLetter,we presenta newanalysisofCOMPASSdatafor single-inclusive hadron quasi-real photoproduction at high pT,22 which differs from our previous analysis in that all measured hadronswithinagivenpT binareincludedintheanalysis,andnot onlythehadron(s)withhighestpT.Moreover,theinterpretationof
22 Notethatalsoinclusivequasi-realphotoproductionofhadronpairscanbecon- sidered[15].
theresults isbasedona collinearpQCD framework thatwas de- velopeduptoNLO[14],thebasicconceptbeingtheapplicationof the factorisationtheoremto calculatethecross section ofsingle- inclusivehadron production. The authors ofRef. [14] discuss the sensitivityof COMPASS data to g(xg) interms ofcontributions from“direct-photon”, γ∗g→qq¯ (PhotonGluon Fusion),andfrom
“resolved-photon”subprocesses,qgandgg,wherethephotonacts as a source of partons. Similarly, they consider direct γ∗q→qg (QCD Compton) as well as resolved qq and gq subprocesses for thebackground.These contributionsto thecrosssection are rep- resented schematically in Fig. 1. In the framework of collinear fragmentation, photo-absorption on quarks, γ∗q→q,is not con- tributingtohighpT hadronproduction.
In order to gain confidence in the applicability of this pQCD framework to single-hadron production with longitudinally po- larisedbeamandtarget, an importantstepisto comparepredic- tionsofthismodeltomeasurementswithbeamandtargetunpo- larised,forwhichthePDFsarewellknown.Whilegoodagreement was found by RHIC experiments on the production of high-pT hadrons in pp collisions at √
s200 GeV [16,17], complications arisewhenhardscatteringsubprocessesareprobedinthe“thresh- old” regime, in which large logarithmic contributions from soft and collinear gluons play a significant role [18]. Such contribu- tionsbecomedominantattheCOMPASScentre-of-massenergyof
√s18 GeV.Whentakenintoaccount byatechnique knownas
“threshold resummation”at next-to-leadinglogarithm (NLL)[18], the calculations reproduce the COMPASS cross section measure- ments[19]withintheoreticaluncertainties.
In thisLetter, we analyse the quasi-realphotoproduction data collected by COMPASS from 2002 to 2011 on longitudinally po- larised deuteron and proton targets. In Sec. 2, we give a brief descriptionoftheexperimentalsetup,anddetailsonthedatase- lectioncan be foundin Sec.3.The procedure fortheasymmetry determinationisdescribedinSec.4.InSec.5,wepresentthecor- responding double spin asymmetries for single-inclusive hadron production asa function of their transverse momenta pT. These asymmetriesarecomparedtocalculationsthatwereperformedus- ingthecodeofRef.[14],whichdoesnotincludetheresummation ofthresholdlogarithms.
2. Experimentalsetup
The measurements were performed with the COMPASS setup using positive muons from the M2 beam line of the CERN SPS.
Adetaileddescription oftheexperimental setup canbe found in
