Semi-Inclusive Kaon Electroproduction
with CLAS
M. OsipenkoPSHP 2010,
October 19, 2010,Frascati, Italy
Contribution of s-quarks
2
• Typical kinematics:
CLAS 6 GeV CLAS 6 GeV
CLAS 11 GeV CLAS 11 GeV
Q2=2.5 GeV2
z=0.5
K+
K+
K-
K-
• LO param.:GRV 94 LODSS 07 LO
• Acceptance cuts.
• K- production allows to study of s-quark contribution.
CLAS data
3
• Hadron identification – Time Of Flight system (Scintillation Counter)
cRt
h
SCSC
pst 300
cmRSC 400
cGeVmmc
Rpt
KSCh /2.2
2
22max
Resolution:Flight Distance:
Time of flight
Maximum momentum of 1
K- separation
1
222
SC
SChh R
ctpm
h+ h-+
p
K+
-Convoluted with CLAS acceptance.
TOF PID
4
P=1.7 GeV
P=1 GeVP=1 GeV
P=2 GeV
Monte Carlo GSIM describes
well TOF resolution.
Momentum dependent cuts
is applied to suppress pion
and proton contaminations.
cutcut
Energy loss in scintillator
5
• Energy loss allows to clean pion contamination at momenta Ph<0.8 GeV/c,
• Obtained after TOF cuts distributions do not exhibit large contamination,
• Distributions are slightly different from Bethe-Bloch formula + Birks quenching effect.K+ K-
+ -
Pion Contamination
6
K-K+
• Contamination remaining after all cuts (TOF,Energy loss) ranges from 10% to 20%,
• From previous measurements we know pion rate with systematic precision of 10-15%,
• The main systematic uncertainty is due to ability of Monte Carlo simulations to describe TOF resolution.
7
Kinematical Coverage of E1-6a run
K-K+ 4x105 events 2x104 events
Negative kaons:
• Lower mean z-values,
• 20 times smaller
statistics
8
Transverse momentum2 2 2 2Tp p k z
+
22 2maxT Tp p z
• Parton model predicts simple dependence of the mean transverse momentum:
• Upper limit on transverse momentum:
preliminary
curve - M.Anselmino et al., PRD71
DIS
current fragm.
9
Data vs. pQCDpreliminary
Sys.err. 15%Solid – LO DSSDashed – NLO DSSDotted – LO KretzerDot-dashed – NLO Kretzer
10
Q2-evolutionpreliminary
Sys.err. 15%Solid – LO DSSDashed – NLO DSSDotted – LO KretzerDot-dashed – NLO Kretzer
11
<cosf><Q2>=2.2 GeV2Cahn - M.Anselmino et al., PRD71, Berger – A.Brandenburg et al., PLB347
Sys.err. 2%
12
<cos2f><Q2>=2.2 GeV2Cahn - M.Anselmino et al., PRD71, Berger – A.Brandenburg et al., PLB347
Sys.err. 2%
CLAS12 projection
13
• Proposal “Studies of Boer-Mulders Asymmetry in Kaon Electroproduction with Hydrogen and Deuterium Targets” by H.Avakian et al.
• With 2 RICH sectors statistical uncertainties are of the order of 0.5% for data integrated in SIDIS,
• For large-x kinematics, the accessible f-interval is incomplete, undermining azimuthal asymmetry extraction, proposed run with inbending torus field should solve this problem.
22 4GeVM X
22 04.0 GeVpT 5.0z
22 2GeVQ
3x106 SIDIS K- H. Avakian et al. inbending outbending
14
Summary1. We measured 5-fold differential semi-inclusive electro-production
cross sections for +, -, K+ and K- in a wide kinematical range in all 5 independent variables;
2. In current fragmentation region all the data are in reasonable agreement with naïve current fragmentation pQCD calculations;
3. The measured <cosf> moments are incompatible with Cahn and Berger effects, while <cos2f> is compatible with zero in agreement with theory;
4. Projections for 12 GeV Upgrade show significant improvement in statistics and kinematic coverage.
15
BACKUP SLIDES
16
Status of Un.Semi-Inclusive in CLAS
We measured semi-inclusive electro-production cross sections for +, -, K+, K- and protons:1. + was published in PRD80 (2009),2. - in Deep Processes Working Group review (Kaftar, Harut, Marco
Contalbrigo),3. Parallel analysis of Wes Gohn is on-going, intends to extract
isospin asymmetry of pions, a cross check of the two analyses is expected, we have an agreement that - paper is published first and will not include any discussion of Boer-Mulders functions,
4. Proton is in progress: analysis note is almost ready, draft of the paper to be written,
5. K+/K- first results are obtained, analysis note and draft to be written, depends on velocity of - review,
6. Neutron analysis is foreseen, depending on status of proton analysis.
17
Semi-inclusive Kinematics( ) ( ) ( )V hq p P h p X + +
2 2Q q
~h h hp Pp Ez
q Pq
+
+
2
hT T h
p qp p p q
q
'h e
5 independent variables
Detect the scattered electron in coincidence with hadron h: e+pe'+h+X
Final state:
,h h hp E p
2 2
2 2q QxqP M
,q k k q
In OPE approximation:Four-momenta in Lab:
Initial state:
,0P M
18
Observables
5
1 2 3 42 2 2 cos cos 2T
hEd N ydxdQ dzdp d p
+ + +
H H H H
2( , , , )i i x Q z tH H
3
1 2
(2 )cos2
y f
+H
H H
Cross section is described by 4 functions of 4 variables:
Azimuthal asymmetries (moments):
4
1 2
cos 22f
+
HH H
2
4
2NxQ
beam
yE
2
2Mx
Q 2 211
4y y
2xy
2
11
+
where
coscos
n dn
d
f
J.Levelt & P.Mulders, PRD49
19
SIDIS: constant in f
22 ( ) ( )h
q q qq
H e f x D z2
2 ( , )hq q
q
H e M x z
( )qf x
Current fragmentation Target fragmentation( )h
qD z
( , )hqM x z
1 22H xH
L.Trentadue & G.Veneziano, PLB323
X.Ji et al., PRD71 J.C.Collins, PRD57Factorization proved
( )qf x( )h
h dD zdz
( ) df x
dx
20
SIDIS: f-dependence
2 21 1( , ) ( , )cos 2
( ) ( )BM T Th x p H z p
f x D z
p xP k +
2 2
22 22
2 1
1cos ~ 1 41 (1 )
n
nn T
T
k z pyny Qp
+
+ +
HH H
1.Cahn effect:
2.Berger effect:
3.Boer-Mulders function h1┴ (TMD) contribution:
D.Boer&P.Mulders, PRD57
2
( )cos ~( , , )
h
n T
n dg z p
2 2 2 2Tp p k z +
0, cos , sin ,0k k kf f
H1┴ from e+e- collisions
R.N.Cahn, PRD40
E.Berger, ZPC4
4.Higher Order pQCD corrections:2
2
(2 ) 1( )cos 12 1 (1 )
S y yQ zy
+ H.Georgi&H.Politzer, PRL40
( )h hadron wave
function
21
Q2-dependence for +
22 max2
2 min
22 max2
2 min
2
2
( , )
TTT
T
TTT
T
pppn
T Tp
n ppp
Tp
p e dp
f z
e dp
We compared our data on φ-dependent terms with EMC measurement (J.Aubert et al., PLB130) performed at significantly higher Q2:curves show Cahn effect prediction corrected for threshold effect:
<cosf>
<cos2f>
EMC(83)CLAS
x=0.24z>0.2
pT>0.2 GeV 22maxTp z
and n=1,2
Larger threshold effect predicted in: A.Konig and P.Kroll, ZPC16
22
Normalization
0Fx
2 CMhEzs
1( )tot
dD zdz
T H Hp z W z
1
0
( ) ( ) ( )e e h hh q q
q
n s D z D z dz+
+
1
0,
1( ) ( ) ( ) ( ) ( )( )
ep h hh q q q q
qqq q
n s f x D z f x D z dzf x
+
In e+e- collisions
In SIDIS, neglecting target fragmentation contribution
Hadron multiplicity:
TH
pzW
=>
Cut on xF removes part of the pT region breaking normalization of transverse momentum distribution.
=>
23
Azimuthal angle definition ,
cosh
h
k q p q
k q p q
k – initial electron 3-momentum,ph – hadron 3-momentum,q – virtual photon 3-momentum
Trentoconvention
24
pT-dependence
cos Tp
Prelim
inary
Q2=2.4 GeV2, x=0.26, z=0.23
CLAS The same pT behavior for all structure functions => trivial kinematical factors for azimuthal asymmetries <cosf> and <cos2f>
H3 contribution is negativeH4 is mostly positiveSuggest only internal transverse
motion of quarks (Cahn)?
Structure functions were separated by fitting f dependences in each separate kinematical bin.
Only bins with complete f-coverage were considered.
2cos 2 Tpf
up to pT~1 GeV
25
e- measurement1. Cherenkov Counter (CC) uniquely identify electrons up to P~3 GeV2. Electromagnetic Calorimeter (EC) separates high energy electrons
e-
-
e-
-+CC noise
26
e- inclusive1. Inclusive cross sections obtained with the same data are in good
agreement with world data.2. Little effort needed to complete the inclusive data analysis at 6 GeV
CLAS E1-6 CLAS E1-6Bodek fit Bodek fit
World World
27
Ep-elastic
28
+ measurement1. Pions are well identified by Time Of Flight (TOF) measurement in
all accessible kinematical range2. Loss of events in data and Monte Carlo (MC) simulations due to PID
cuts was checked in +n peak
all positive hadrons
selected events
+n peak
background
29
+ semi-inclusive1. New CLAS data are in agreement with previously published
measurements within given uncertainties2. Comparison also shows non-trivial pT-behavior
pT=0.07 GeV/cpT=0 or 0.1
30
+ semi-inclusive
Kinematics does not match perfectly, some extrapolations have been performed in CLAS data.
31
EMC data
EMC, PLB95
Much larger <pT2> values measured by EMC, but seen to increase
rapidly with W.
32
Parameterization dependence
CTEQ 5 LOGRV 98 LO
MRST cg LO
CTEQ 5 NLOGRV 98 NLO
MRST cg NLO
1. Very small uncertainty due to parton distribution function2. Larger uncertainty due to fragmentation function
33
ZEUS data
ZEUS, PLB481
ZEUS, PLB481
1. The same limitations as for EMC and E665
2. More detailed data sample in hep-ex/0608053 represented in different variables (pseudorapidity and minimum hadronic energy in HCM) and integrated also over neutral hadrons appears hard to compare
0.01<x<0.1180<Q2<7220 GeV2
0.2<z<1
34
EMC and E665 data
E665, PRD48
EMC, Z.Phys.C34
cos ( ) cosCT
CT T
p
n p dp n
1. The same limitations also in E665 data2. Minimum transverse momentum of hadrons is commonly used pT
C which can mask possible sign change at low pT
3. Strong xF variation is seen by EMC
Q2>4 GeV2
40<W2< 450 GeV2
Q2>3 GeV2
100<W2< 900 GeV2
35
EMC data in pT
l
yE
1 2
1( ) (2 )
1 (1 )y
f y yy
+
EMC, PLB130EMC, Z.Phys.C34
1. Summed over all charged hadrons positive and negative, no PID2. Integrated over all other variables: x, Q2, z3. Radiative corrections with Monte Carlo
2 2
1( )1 (1 )
yf yy
+
Q2>4 GeV2
40<W2< 450 GeV2
36
CLAS Acceptance 0( )
( )
DATAGEN
GSIM
N d
N d
cos cos cos cosDATA GSIM GENn n n n +
Zero-order approximation:
φ-constant term
Acceptance mixes Fourier coefficients
with different n.
37
Fourier analysis of acceptance100 harmonic expansion: CLAS acceptance is cosine-like. Even number of sectors generate mostly even functions in azimuthal distributions.
even (cos nφ) odd (sin nφ)DATA
Fourier seriesDATA
Fourier series
38
CLAS Acceptance
/ 01 1 2 2cos sin cos 2 sin 2 ...
2eff acc AA A B A B + + + + +
2, ,
0
1 ( )cosDATA GSIM DATA GSIMnI LN n d
( ) ( )LN
n nA A
, , ,0 1 2( ) cos cos 2DATA GEN DATA GEN DATA GENV V V + +
2
, , , ,0 1 2
0
01 2
1 cos cos 2
cos cos 2 ... cos2
DATA GSIM DATA GSIM DATA GSIM DATA GSIMnI V V V
A A A n d
+ +
+ + +
, , , ,1 1 2 20 1 22 2
DATA GSIM DATA GSIM DATA GSIM DATA GSIMn n n nn n
A A A AI A V V V + ++ + + +
0,1,2,...n
/1( ) ( ) ( )acc effN AL
39
CLAS Acceptance
0 2 1~DATAV H H+1 3~DATAV H
nA
2 4~DATAV H
1 1
GSIM GEN
N N N NI A V
1 1
DATA DATA
N N N NI A V
Only first 10 harmonics are significant, but 20 harmonics are kept in the analysis.
40
Three methods Comparison of the three
methods for structure function separation:
1. Fit of φ-distribution2. Moments method in zero-
order approximation3. Moments method
accounting for N=20 harmonics of CLAS acceptance
Higher harmonics are important in the extraction of φ–even observables from CLAS data
41
Pseudo-data Cross CheckPseudo-data generated in a limited kinematical area from a known model (different from that used in the reconstruction) were used to check that the two extraction procedures are able to extract correct φ-moments.
modelmodel
42
Results of Integration
22 2 0DIS
T TH p H p
Different assumptions yield slightly different results in low-z region.
Exponential pT
Exponential tNumerical pT integ.Numerical t integ.
exact formulano Eh/p|| correction
unphysical high pT tail
Correct expression for low energy: 2 max 2
222 2 2 2
0
TpTDIS
h T
h h T
H pH E dp
E m p
LO pQCD
43
Data vs. Monte Carlo
44
Semi-Inclusive Kinematical Domains
elastic peakepe’p’
resonances
• Exclusive production• Inclusive production:
• MX<1÷2 GeV - Resonance region• MX>1÷2 GeV - Deep Inelastic
Scattering (DIS)• Q2<1 GeV2 † - Non-perturbative• Q2>1 GeV2 † - Perturbative
• Current fragmentation• Target fragmentation
inelastic
0
h w,r
n
D0
epe’p’X
epe’+X
J.P.Albanese et al.,PLB144
Y CMS rapidity
45
Structure Function Separation 1 2 1 2 cos cos 2 cos 2 cos 2
hH H
ENp
+ + +
coscos
d
d
cos 2
cos 2d
d
Two methods of separation:1. fit of f-dependence2. event-by-event moments
46
pT dependences
2 22 2
0
DIST TH H p dp
2
22
2 2 0T
T
p
pTH p H e
pT dependence cannot be calculated by ordinary pQCD, only TMD-based approach will permit for a complete description of the measurement. One has to integrate the data in pT
2: