2. CLAS12 Initial Physics Program at the JLab 12 GeV Upgrade
Volker Burkert
Jefferson Lab
Probing Strangeness in Hard Processes,
Oct. 18 – 21, Frascati, Italia
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3. Strangeness in Hard Processes, Frascati
JLab Upgrade to 12 GeV
JLab Upgrade to 6 GeV
Add new hall
CHL-2
A major focus of hadron physics with electromagnetic probes is the determination of new multi-dimensional parton distribution functions in a large kinematics range. This requires experiments at high luminosity and at sufficiently high energy. For this the existing accelerator will be equipped with accelerating superconducting RF cavities with much higher gradients. The additional 5 cryo modules will provide the same energy boost as the 20 existing ones. In addition some of the lower gradient cryo modules will be refurbished
Enhance equipment in existing halls
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4. New Capabilities in Halls A, B, & C, and a New Hall D
9 GeV tagged polarized photons and a 4 hermetic detector D
Super High Momentum Spectrometer (SHMS) at high luminosity and forward angles C B
CLAS12 high luminosity, large acceptance.
High Resolution Spectrometer (HRS) Pair, and specialized large installation experiments A
A new Hall will be constructed to house the GlueX detector, that will conduct a search for excited mesons with gluonic components, and the existing Halls will be upgraded with new equipment as well. Hall C will have an additional super high momentum spectrometer. Hall A will retain the existing spectrometers and provide space for new specialized equipment to address a variety of physics topics. Hall B will house the CLAS12 detector which is the focus of this of workshop. At 12 GeV JLab will be ideal for precision studies at large Bjorken x.
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5. Strangeness in Hard Processes, Frascati
CLAS12
Forward spectrometer
- TORUS magnet
- Forward vertex tracker
HT Cherenkov Counter
Drift chamber system
LT Cherenkov Counter
Forward ToF System
Preshower calorimeter
E.M. calorimeter
Central Detector
SOLENOID magnet
Barrel Silicon Tracker
Central Time-of-Flight
Central
Detector
Forward
Detector
Proposed equipment
- Small angle tagger
- RICH to replace LTCC
- Micromegas in CD
- Neutron detector in CD
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6. CLAS12 – Solenoid and Torus Magnets
Pions
Kaons
The Torus and Solenoid magnets provide bending power for tracking with sufficient momentum resolution to allow exclusive processes to be identified. At forward angles the Torus field provides large integral Bdl while the solenoid provides tracking at large angles over a limited radial distance.
The B-field transverse to the particle trajectory is approximately matched to the average particle momentum.
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7. CLAS12 – Design Parameters
Forward Central
Detector Detector
Angular range
Tracks 50 – – 1250
Photons –
Resolution
dp/p (%) < 5 GeV/c < 1.5 GeV/c
dq (mr) < 1 <
Df (mr) < 3 < 5
Photon detection
Energy (MeV) >
dq (mr) 1 GeV ---
Neutron detection
Neff < 0.7 (EC+PCAL) under development
Particle ID
e/p Full range ---
p/p < 5 GeV/c < 1.25 GeV/c
p/K < 2.5 GeV/c < 0.65 GeV/c
K/p < 4 GeV/c < 1.0 GeV/c
p0gg Full range ---
hgg Full range ---
L=1035cm-2s-1
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8. Strangeness in Hard Processes, Frascati
Kaon identification
CLAS12
Charged hadron identification currently relies on time-of-flight measurements and supports a strangeness program for which Kaon identification is additionally constrained, e.g. from exclusive kinematics.
Detailed studies of TMDs for strange quark contributions requires much improved Kaon identification capabilities for momentum > 2GeV/c.
A RICH detector with large momentum range and polar angle coverage would be a suitable candidate.
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9. Strangeness in Hard Processes, Frascati
CLAS12 - Institutions
Armenia:
- Yerevan Physics Institute, Yerevan, Armenia
United States of America:
- Argonne National Laboratory, Argonne, MI
- California State University, Dominguez Hills, CA
- Catholic University of America, Washington, DC
- College of William and Mary, Williamsburg, VA
- Christopher Newport University, Newport News, VA
- Fairfield University, Fairfield, CT
Florida International University, Miami, FL
Hampton University, Hampton, VA
- Idaho State University, Pocatella, ID
- James Madison University, Harrisonburg, VA
- Norfolk State University, Norfolk, VA
- Ohio University, Athens, OH
- Old Dominion University, Norfolk, VA
- Renselear Polytechnic Institute, Troy, NY
- Temple University, Philadelphia, PA
- Jefferson Lab, Newport News, VA
- University of Connecticut, Storrs, CT
- University of New Hampshire, Durham, NH
- University, of Richmond, Richmond, VA
- University of South Carolina, Columbia, SC
University of Virginia, Charlottesville, VA
France:
- Grenoble University, IN2P3, Grenoble
- Orsay University, IN2P3, Paris
- CEA Saclay, IRFU, Paris
Italy:
- INFN - Frascati, Rome
- INFN - Genoa, Genoa
- INFN - University Bari, Bari
- INFN - University Catania, Catania
- INFN - University Ferrara, Ferrara
- INFN - ISS Rome 1, Rome
- INFN - University of Rome Tor Vergata, Rome
Republic of Korea:
- Kyungpook National University, Daegu, Korea
Russian Federation:
- MSU, Skobeltsin Institute for Nuclear Physics, Moscow
- MSU, Institute for High Energy Physics, SiLab, Moscow
- Institute for Theoretical and Experimental Physics, Moscow
United Kingdom:
- Edinburgh University, Edinburgh, Scotland
- Glasgow University, Glasgow, Scotland
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10. CLAS12 - Initial Science Program
Physics Focus
Approved experiments
LOIs PAC
supported
GPD’s & Exclusive Processes 3 1
TMDs & Semi-Inclusive DIS 4
Parton Distribution Function & DIS 2
Elastic & resonance form factors
Hadronization & Color Transparency
Hadron Spectroscopy
Total # experiments and LOI’s 13 10
Requested beam time (100% efficiency)
1091 days
Approved experiments correspond to about 5 years of scheduled beam operation .
Present examples from each category
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11. Strangeness in Hard Processes, Frascati
Color transparency
CLAS12
Color Transparency is a stringent prediction of QCD: under some conditions, nuclear matter will allow the transmission of hadrons with reduced attenuation
Unexpected in a hadronic picture of strongly interacting matter, but straightforward in quark gluon basis.
Small effects observed at lower energy. Expect significant effects at higher energy.
preliminary q2
CLAS12 projected
eA→eρ0X
Q2(GeV2)
ρ0 electro-production is an ideal probe of CT as the deeply virtual photon directly couples to the ρ0 in a small size configuration.
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12. Neutron Magnetic Form Factor
CLAS12
At 12 GeV extend knowledge of magnetic structure of neutron to much shorter distances. Needed for constraints of GPDs at large t.
Does the neutron magnetic structure differ from the proton?
For Q2 < 5 GeV2 GMn deviates by less than 10% from the dipole form which also describes GMp with similar accuracy and up to much higher Q2.
CLAS12 measures GMn for all Q2≤14 GeV2 simultaneously.
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13. Neutron structure in spectator tagging
F2n/F2p ratio by tagging almost unbound neutrons using detection of low momentum protons in radial TPC.
e-D→e-psX n ps p e-
>70MeV/c
BONUS Detector
Preliminary
5 Tesla
mag. field
One of the unresolved issues in neutron structure functions studies at high Bjorken x is the correction for the nuclear binding effect in deuteron. Different corrections have resulted in vastly different results. A model-independent way is to tag the neutron by measuring the spectator proton to very low momentum using, e.g. a gas target and a low density tracking detector. Protons with momentum down to 70 MeV/c (T=2.5MeV) must be detected. The corrections for the neutron momentum in deuteron is shown in this graph. The elastic peak and the resonance structure show up clearly. The corrected ratio F2n/F2p is shown with the red points. The ratio of d-quark to u-quark distribution functions is shown here. The maximum xB is limited by the beam energy of 5.2 GeV. However, the trend is to rule out the scalar diquark model. Future experiments at the 12GeV upgrade will extend this range up to 0.9.
CLAS12
Experiment E will reach x=0.8. LOI-10-05, 10-08, received PAC support to study EMC effect by detecting nuclear fragments at 12 GeV.
First model-independent measurement of F2n/F2p and F2n
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14. Valence spin structure function
CLAS12
Valence spin structure function
Deuteron
Proton
W > 2; Q2 > 1
Accurate measurement of Q2 dependence is key for the extraction of ΔG(x)
Data: V. Dharmawardane et al. (CLAS), PLB641, 11-17, 2006
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15. Impact of QCD analysis on ΔG(x)
Precise measurement of Q2 dependence of spin structure function g1(x,Q2) gives access to gluon contributions ΔG(x) to the proton spin through QCD evolution equations.
E. Leader, A Sidorov,
D. Stamenov,
PRD75:074027,2007
The next-to-leading order fit of LSS06 shows the significant impact of the JLab data on the polarized gluon density . At x>0.2 a factor 2 to 4 reduction in the polarized gluon density uncertainty is achieved. Additional improvement at small x is due to new COMPASS data on deuterium. The sensitivity comes from the last term which is due to gluon radiation. It requires a large lever arm in Q2, which is provided by the CLAS results. The absolute density in the LSS06 NLO analysis is shown on the right side. At large the JLab data prefer a positive polarized gluon density. Overall the polarized gluon density is much smaller than what is required to explain the short fall from the polarized quark densities, opening up possible strong contributions from orbital angular excitations.
Experiment E will significantly constrain ΔG(x).
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16. Strangeness in Hard Processes, Frascati
Wigner distribution
(Quantum phase-space quark distribution in the nucleon)
X. Ji (2004)
Transverse Momentum- dependent Distributions (TMD)
3D momentum imaging of the nucleon
Generalized Parton Distributions (GPD)
(2+1)D spatial imaging of the nucleon
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17. Strangeness in Hard Processes, Frascati
Access to GPDs - Handbag Mechanism
GPDs depend on 3 variables, e.g. E(x, x, t). They probe
the quark structure at the amplitude level.
Deeply Virtual Compton Scattering (DVCS) x t
x-x
x+x
hard vertices g
x – longitudinal quark
momentum fraction
2x – longitudinal
momentum transfer xB
2-xB x =
The basic process in accessing the proton structure through exclusive processes is the “handbag” mechanism. Here shown for the DVCS process.
The important aspects is that we have hard scattering vertices here and here and the soft part is described by the GPDs. The upper and lower part factorize which allow us to probe GPDs in hard scattering processes with photons. There are 4 GPDs which depend on 3 kinematics quantities: the quark longitudinal momentum fraction x, the longitudinal momentum transfer to the quark xi and the 4-momentum transfer to the proton. What is the physical content of the GPDs ?
–t – Fourier conjugate
to transverse impact
parameter
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18. Strangeness in Hard Processes, Frascati
Deeply Virtual Exclusive Processes -
Kinematics Coverage of the 12 GeV Upgrade
H1, ZEUS
H1, ZEUS
11 GeV
27 GeV
200 GeV
11 GeV
JLab Upgrade
12 GeV
COMPASS
W = 2 GeV
HERMES
The kinematics range that can be covered in exclusive processes with high precision data is shown with this yellow area. This will be the only accelerator where the valence quark regime can be fully covered with high precision data.
Study of high xB domain
requires high luminosity
0.7
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19. A path towards extracting of GPDs 2
+ - -
+ + - =
ξ ~ xB/(2-xB)
k = t/4M2
LU ~ sin {F1H + ξ(F1+F2)H +kF2E}d ~
Polarized beam, unpolarized target:
H(ξ,t)
Kinematically suppressed
Unpolarized beam, longitudinal target:
UL ~ sin {F1H+ξ(F1+F2)(H +ξ/(1+ξ)E) -.. }d ~
Kinematically suppressed
H(ξ,t)
The most direct way of accessing GPDs is through polarization measurements. Using polarized electron beams we can measure the cross section difference for opposite electron helicities. The cross section difference depends on the 3 GPDs H, H-tilde, and E. The kinematical factors suppress the contributions of H-tilde and of E so that the beam spin asymmetry is dominated by GPD H. For longitudinally polarized target the asymmetry is dominated by H-tilde as H and E are kinematically suppressed at not too large xi giving access to H-tilde. With a transversely polarized target one has access to a combination of H and E. With these 3 measurements we are able to disentangle 3 GPDs H, E, H-tilde.
Unpolarized beam, transverse target:
UT ~ cossin(s-){k(F2H – F1E) + ….. }d
Kinematically suppressed
E(ξ,t)
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20. Strangeness in Hard Processes, Frascati
CLAS12
A path towards the extraction of GPDs
e p epg
A = Ds 2s
s+ - s-
s+ + s- =
F.X. Girod et al. (CLAS), PRL, 2008
Polarized electron beam
DsLU~sinf{F1H+..}df
The leading sin-phi term for each one of the azimuthal interference patters turns into one data point for the t-dependence at different x and Q2.
Extract H(ξ,t)
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21. Strangeness in Hard Processes, Frascati
CLAS12 - DVCS/BH Longitudinal Target Asymmetry
e p epg
Longitudinally polarized
target ~
DsUL~sinfIm{F1H+x(F1+F2)H...}df ~
Extract H(ξ,t)
Similar data can be obtained with a longitudinally polarized targets.
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22. The Promise of GPDs: 2-D & 3-D Images of the Proton
dX(x,b ) T
uX(x,b )
Target polarization
Flavor dipole
Shift depends on (x,b )
M. Burkardt ∫
d2
(2)2
ei b Eq(x, ) T
(x,b ) =
Cat scan of the
human brain
Knowing GPDs we can construct slices of the proton similar to cat scans of the human brain. A Fourier transformation of GPD H & E to impact parameter space gives 2D slices of the transverse quark distributions at fixed momentum fraction x and measures she shift of the center of gravity of up and down quarks for a transversely polarized proton.
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Strangeness in Hard Processes, Frascati 22

23. Transverse Momentum Distributions
CLAS12
TMDs are complementary to GPDs in that they allow to construct 3-D images of the nucleon in momentum space
TMDs are connected to orbital angular momentum (OAM) in the nucleon wave function – for a TMD to be non-zero OAM must be present.
TMDs can be studied in experiments measuring azimuthal angular moments in SIDIS processes.
Several proposals/LOIs to measure TMDs have been accepted/supported that require the further upgrade of CLAS12 with Kaon identification.
Transverse momentum distributions are complementary to GPDs In that they allow.. ..
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24. SIDIS and TMD Proposals
CLAS12
PAC approved: proposals and LOI’s
E : Pion SIDIS
E : Kaon SIDIS
E : Pion SIDIS
E : Kaon SIDIS
LOI : Pion SIDIS
LOI : Kaon SIDIS
Complete program on pion and Kaon TMDs
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25. SIDIS on unpolarized protons
CLAS12
In inclusive electroproduction of pions the diff. cross section has an azimuthal modulation.
dσ/dΩ = σT + εσL + εσTTcos2Φ + [ε(1+ε)]1/2σLTcosΦ
4 <Q2< 5 GeV2
E : Pion SIDIS
The cos2Φ moment of the azimuthal asymmetry gives access to the Boer-Mulders Function which measures the momentum distribution of transversely polarized quarks in unpolarized nucleons.
… the graphs shows the projected uncertainties of the x and Pt dependences of the asymmetry for different pion flavors.
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26. SIDIS on unpolarized protons
CLAS12
In inclusive electroproduction of pions the diff. cross section has an azimuthal modulation.
dσ/dΩ = σT + εσL + εσTTcos2Φ + [ε(1+ε)]1/2σLTcosΦ
4 <Q2< 5 GeV2
E : Kaon SIDIS
The cos2Φ moment of the azimuthal asymmetry gives access to the Boer-Mulders Function which measures the momentum distribution of transversely polarized quarks in unpolarized nucleons.
… the graphs shows the projected uncertainties of the x and Pt dependences of the asymmetry for different pion flavors.
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27. SIDIS in double pol. asymmetry
CLAS12
Theory: M.Anselmino et al Phys.Rev.D74:074015,2006
Data: H. Avakian et al. (CLAS), arXiv:  [hep-ex]
E : Pion SIDIS
E : Kaon SIDIS
The double polarization asymmetry is sensitive to difference in the kT distribution of quarks with spin orientation parallel and anti-parallel to proton spin.
The Pt dependence of the double polarization asymmetry is sensitive to …
CLAS12 has more sensitivity and reaches higher PT
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28. SIDIS on long. polarized target
CLAS12
SIDIS on long. polarized target
The sin2f moment gives access to the Kotzinian-Mulders function which measures the momentum distribution of transversely polarized quarks in the longitudinally polarized nucleon.
E : Pion SIDIS
E : Kaon SIDIS
The sin2f moment is sensitive to spin-orbit correlations. It is the only leading twist azimuthal moment for longitudinally polarized target.
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29. Strangeness in Hard Processes, Frascati
Summary
The Hall B upgrade has well defined physics goals of fundamental importance for the future of hadron physics, addressing in new ways the quark and gluon structure of hadrons by
accessing GPDs and TMDs
mapping the valence quark structure of nucleons with high precision
understanding hadronization processes
extending nucleon form factor measurements to short distances
hadron spectroscopy program in development
Construction of the CLAS12 base equipment is well underway. A RICH detector with large acceptance coverage will enhance significantly its physics reach.
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30. Strangeness in Hard Processes, Frascati
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31. Strangeness in Hard Processes, Frascati
Sivers effect
CLAS12
sUT ~
Sivers
LOI : Pion SIDIS
LOI : Kaon SIDIS
Probes orbital angular momentum of quarks by measuring the imaginary part of s-p-wave interference in the amplitude.
Fnally, on a transverse target the Sivers effect probes interference between different helicity states. Large effects are predicted for baryons in the target fragmentation region.
Requires non-trivial phase from the FSI + interference between different helicity states
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32. Search for cascade states
CLAS12
Search for cascade states
Kinematics for γp → K+K+Ξ-*→Ξ-π0 (Ξ-→Λπ-, Λ→ pπ-)
Fast Kaon
Slow Kaon
Two approaches:
- Direct reconstruction of Ξ+* with tracking in FST/BST of detached vertices.
- Missing mass with K+K+ detection => needs improved kaon id.
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33. Strangeness in Hard Processes, Frascati
CLAS12
Approved Experiments
Proposal
Contact Person
Physics
Energy (GeV)
PAC
days
Run Group days E
Gothe, Mokeev
N* at high Q2 11 40
120
E (a)
Sabatie
DVCS pol. beam 80 E
Avakian
ep→eπ+/-/0 X 60 E
Stoler
DVMP in π0,η prod
L/T separation
8.8
6.6 20
E (b)
DVCS pol. target
175 E
Kuhn
Long. Spin Str. E
TMD SSA
103
E (b)
Hafidi
Partonic SIDIS E
Spin-Orbit Corr. E
Color Trans. ρ0 E
Brooks
Quark Hadronizat. E
Bültman
Neutron Str. Fn. E
Gilfoyle
Neutron mag. FF 30 82
E (a) 56 E
Contalbrigo
Boer-Mulders w/ Kaons
1091 (310)
517
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