1. Studies of Strange Sea Distribution Functions using Kaons with CLAS12
@ Jlab
Fatiha Benmokhtar
Duquesne University, Pittsburgh, PA, USA
Baryons 2016, Tallahassee, FL, USA
F. Benmokhtar, Baryons 2016 1

2. Flavor contributions to the Nucleon Spin
valence
« sea= virtual pairs »
Our interest is on getting all the flavors! But Special interest on the strange sea.
- Why the strangeness  because of its impact on calculations of short distance processes at high energies.
F. Benmokhtar, Baryons 2016

3. -p elastic scattering
World Data on S
Polarized deep-inelastic inclusive scattering
(SMC)
-p elastic scattering
(E734 BNL)
Polarized Semi-Inclusive DIS (HERMES)
* 5 flavor tagging
* Isoscalar method-> published (2008) then reviewed and
published (2014), slightly positive
COMPASS: sidis m-NH3 (2010)  compatible with zero.
ATLAS results (2012) suggest that at small x the strangeness contribution can be substantially larger than assumed.
So far, the results vary widely and the uncertainties are big
“Strange quark polarization puzzle”
F. Benmokhtar, Baryons 2016

4. Semi Inclusive DIS Sidis Selection: Hadron Selection:  = E-E’
x = Q2 /(2M  )
y =  /E
W2 = M2 - 2M  - Q2
Q2 = 4EE’sin2(θ/2)
Hadron Selection:
z = Eh / 
xF = 2 |p||| / W
F. Benmokhtar, Baryons 2016

5. Measurement of Δq in Semi-Inclusive DIS
Select PDFs : q -(x) or q +(x) by changing the orientation of target nucleon spin or helicity of incident lepton beam
- Pqh Purity is a conditional probability that a hadron of type h observed in the final state is originated from a struck quark of flavor q in case of unpolarized beam/target.
- Dqh is a measure of the probability that a quark of flavor q will fragment into a hadron of type h = fragmentation function

6. Isoscalar extraction of ΔS:
Measure (inclusive) asymmetry A1,d and (sidis) kaon asymmetries A1(K++K-)
Extract isoscalar combinations of ΔQ(x) and ΔS(x)
Inclusive purities from PDFs
(CTEQ6, MRST, GRV…)
Kaon purities can be computed from the Kaon multiplicities and the pdfs.
F. Benmokhtar, Baryons 2016

7. Kaon Purities Fit parameters Measure Multiplicities
- Using charge symmetry
Fit parameters
Measure
Multiplicities
F. Benmokhtar, Baryons 2016

8. E12‐09‐007 CLAS12 – Jefferson Lab (A-):
(H. Avakian, F. Benmokhtar, A. EL Alaoui, K. Hafidi & M. Mirazita)
Goal: Measurements of pions and kaons multiplicities and longitudinal double spin asymmetries using SIDIS off hydrogen and deuterium targets. Extract all the flavors!
F. Benmokhtar, Baryons 2016

9. Flavor decomposition E12‐09‐007 CLAS12 : Flavor Decomposition
Unpolarized Measurements
Polarized Measurements
Proton
Deuteron
Deuteron
Proton
Measure Multiplicities
(π+, π-, π0, K+, K-, Ks0)
Measure Multiplicities
(π+ + π-, K+ + K-, Ks0)
Measure Asymmetries
(e-, π+ + π-, K+ + K-, Ks0)
Measure Asymmetries
(e-, π+, π-, π0, K+, K-, Ks0)
Isoscalar Method
Extract shape of
Extract
*Extraction of Δu − Δd to test whether or not the light sea is symmetrically polarized
Flavor Decomposition 9
F. Benmokhtar, Baryons 2016
Extract

10. Jefferson Lab CLAS12 @ 11GeV
Wide detector and physics acceptance (current/target fragmentation)
High beam polarization 85%
High target polarization 85%
NH3,ND3 targets
Track resolutions:
p (GeV/c) p p2
 (mr) < 1
(mr) < 3
Lumi > 1035cm-1s-1
F. Benmokhtar, Baryons 2016

11. A RICH detector is under construction!
Replace one or two LTTC with a Ring Imaging CHerenkov
GeV/c 1 2 3 4 5 6 7 8 9 10
p/K
p/p
K/p
e/p
TOF
HTCC
EC/PCAL
LTCC
RICH
A RICH detector is under construction!
LTCC
RICH
HTCC
LTCC
RICH
LTCC
F. Benmokhtar, Baryons 2016

12. CLAS12 RICH detector
F. Benmokhtar, Baryons 2016

13. RICH Collaboration
F. Benmokhtar, Baryons 2016

14. Expected precision (Strangeness)
Corrections
F. Benmokhtar, Baryons 2016

15. Conclusion: promise of considerable improvement in statistics and the understanding of the strange sea and other flavors contributions to the Nucleon spin. - More flavor separation plots on backup Thanks!
F. Benmokhtar, Baryons 2016

16. Projections – Deuteron unpolarized data
K+ + K-
HERMES:
0.2 < z < 0.8 & integrated over Q2
CLAS12:
1.3 < Q2 < 1.6 GeV2 & 0.5 < z <0.6
4. < Q2 < 5. GeV2 & 0.5 < z <0.6
Ks0
F. Benmokhtar, Baryons 2016 16

17. Projections – Isoscalar Method
K+ + K-
Ks0
F. Benmokhtar, Baryons 2016

18. Projections – Flavor decomposition (1) - 10% systematics on asymmetries
F. Benmokhtar, Baryons 2016

19. Projections – Flavor decomposition (2) - 10% systematics on asymmetries
F. Benmokhtar, Baryons 2016

20. E12‐09‐007 update Kawtar Hafidi 1
Goal: Measurements of pions and kaons multiplicities and longitudinal double spin asymmetries using SIDIS off hydrogen and deuterium targets. The experiment will use the CLAS12 spectrometer to detect the scattered electron and the produced hadron in coincidence
■ Extraction of the individual contributions of quarks and anti-quarks
to the nucleon spin using the 5-flavor decomposition method. In
addition, the isoscalar method will be used to obtain the strange sea
contribution
■ Extraction of the unpolarized strange sea shape 0.05<x<0.7, 1<Q^2<9 GeV^2, 0.4<z<0.7
■ Multiplicity data will provide more constraints to improve the existing fragmentation functions parameterizations
■ Extraction of Δu − Δd to test whether or not the light sea is symmetrically polarized
The success of this program relies on the combination of the highly polarized 11 GeV electron beam, the high luminosity and the large acceptance offered by CLAS12. The use of a RICH detector is
mandatory for the improvement of particle identification
Spokespersons: K. Hafidi, H. Avakian, F. Benmokhtar, A. EL Alaoui, M. Mirazita
F. Benmokhtar, Baryons 2016 20
F. Benmokhtar, DNP meeting 2015

21. Backup slides
F. Benmokhtar, Baryons 2016

22. Jlab 12 GeV experiment:
E : A. Avakian, F. Benmokhtar, K. Hafidi, A. El-Alaoui and M. Mirazita
F. Benmokhtar, Baryons 2016

23. - Cherenkov angle distributions for 8GeV/c pions tagged by the CERN T9 gas Cherenkov compared with those of kaons and protons.
F. Benmokhtar, Baryons 2016

24. Isoscalar extraction of ΔS
Need a longitudinally polarized deuterium target
- strange quark in proton and neutron identical
- fragmentation simplifies
Assumptions:
- isospin symmetry between proton and neutron
- charge-conjugation invariance in fragmentation
Extraction from data of:
- inclusive A1d(x,Q2) and kaon A1dK(x,Q2) double spin asymmetries
- kaon multiplicities
F. Benmokhtar, Baryons 2016

25. F. Benmokhtar, Baryons 2016

26. ΔS from SIDIS 1- Five flavor decomposition (Δq)
2-Isoscalar extraction of ΔS
F. Benmokhtar, Baryons 2016

27. Strange Quark Contribution to the Nucleon Properties (in brief)
Mass:
Hyp ->
-N ->
 0 to 30 % with big
theoretical uncertainties…
Longitudinal Momentum:
-Study the spectral functions q(x),
From unpol DI -Nucleon scattering (NuTeV)
. For x <  Difficult to connect with
ordinary observable
Electromagnetic Form Factors: Parity violation experiments: G0, HAPPEX, PVA4.
 Small
F. Benmokhtar, Baryons 2016

28. Kaon Multiplicities Fit parameters Measure Multiplicities
- Using charge symmetry
Fit parameters
Measure
Multiplicities
F. Benmokhtar, Baryons 2016

29. Quark helicities contribution to the nucleon spin
Inclusive DIS
Semi-Inclusive DIS
ΔΣ = 0.2 – 0.25 at Q2= 1 GeV2 MS-Bar scheme
Δu is large and positive
Δd is negative and smaller
ΔS ≈ ± 0.01
Δu is large and positive
Δd is negative and smaller
ΔS ≈ 0 and slightly positive
Assumptions:
SU(3) flavor symmetry in hyperon decay
Flavor symmetric sea
Quark and anti-quarks of the same flavor can
not be distinguished
The strange sea can only be separated in terms
of first x-moments
Need a good knowledge of fragmentation
functions
The exploitation of the method suffers
from “u-quark dominance”
Kawtar Hafidi SIDIS CLAS Probing strangeness in hard processes /19/2010
F. Benmokhtar, Baryons 2016

30. A RICH detector with CLAS12
For forward scattered particles(θ<13deg) with momenta p ~3–8 GeV/c, a proximity imaging method with thin (2cm) aerogel and direct Cherenkov light detection will be used.
- For larger incident particle angles of 13<θ<35 and intermediate momenta of p~3–6 GeV/c, the Cherenkov light will be focused by a spherical mirror, undergo two further passes through the thin radiator material and a reflection from planar mirrors before detection.
F. Benmokhtar, Baryons 2016

31. Phys. Rev. D 89, 097101 – Published 30 May 2014
HERMES 2014
HERMES 2008
Phys. Rev. D 89, – Published 30 May 2014
ATLAS Phys. Rev. Lett. 109, – Published 5 July 2012
F. Benmokhtar, Baryons 2016