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Measurement of F 2 and R= σ L / σ T in Nuclei at Low Q 2 Phase I. Ya Li Hampton University January 18, 2008. Outline. Physics Overview Physical Motivation and Description of Experiments E02-109/E04-001 (Jan05) Analysis Status Preliminary Results Future Plans. e(E). e’(E’). θ. Q 2. - PowerPoint PPT Presentation
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Measurement of FMeasurement of F22 and and R=R=σσLL//σσTT in Nuclei at Low Q in Nuclei at Low Q22
Phase IPhase I
Ya LiHampton University
January 18, 2008
Outline
• Physics Overview• Physical Motivation
and Description of Experiments E02-109/E04-001 (Jan05)
• Analysis Status• Preliminary Results• Future Plans
e - N scattering
2L
2T Qx, Qx,
dE'd
d
2L
2T Qx, Qx,
dE'd
d
NN
QQ22
e(Ee(E))
e’(E’e’(E’))
θθ
QQ22 - Negative - Negative squared mass squared mass of the virtual of the virtual photonphoton
MMpp - mass of the - mass of the ProtonProton
WW – invariant mass– invariant mass
One-Photon-exchange One-Photon-exchange ApproximationApproximationOne-Photon-exchange One-Photon-exchange ApproximationApproximation
12
'2
22
EMQ
MWE
p
p
12
'2
22
EMQ
MWE
p
p
Transverse Transverse virtual photon virtual photon fluxflux
1
22
2
2tan121
Q
1
22
2
2tan121
Q
Virtual photon Virtual photon polarization polarization
parameterparameter
/EE /EE
σσTT ( (σσLL) is the ) is the TransverseTransverse ((LongitudinalLongitudinal) virtual photon Cross ) virtual photon Cross SectionSection
L/T separations - Rosenbluth Method
),(2),(41
),(2)(
41 21
222
222
122
2
QxxFQxFQ
xMQxxF
MWxEdd
d p
p
),(2),(41
),(2)(
41 21
222
222
122
2
QxxFQxFQ
xMQxxF
MWxEdd
d p
p
At ε =0, F1
Diff. FL {
2L
2T Qx, Qx,
dE'd
d1
2L
2T Qx, Qx,
dE'd
d1
Reduced Reduced Cross-Cross-sectionsection
At ε =1, F2
Fit reduced cross section linearly with ε at fixed W2
and Q2 (or x, Q2) --> Need multiple beam energies.
Linear fit yields:
σσLL = Slope = Slope
σσTT = Intercept = Intercept
),(2),(41
),( 21
222
222 QxxFQxF
Q
xMQxF p
L
),(2),(41
),( 21
222
222 QxxFQxF
Q
xMQxF p
L
),(2),(),( 2
1
22
QxxFQxFQxR L
T
L
),(2),(),( 2
1
22
QxxFQxFQxR L
T
L
Physical Motivation
• Sparse data available in Resonance Region on Fundamental Separated Structure Functions in Nuclei (F1,F2,FL, R)
• Low Q2 L/T Structure Function Moments • Study Quark-Hadron Duality in
Deuteron, Neutron, and Nuclei.• Also, important input for Spin Structure
Function extraction from asymmetry measurements, RCs, etc…
Motivation from Neutrino Experiments• New generation of neutrino experiment are being built to investigate
neutrino oscillations and interactions -i.e. MinervA, mini-Boone, MINOS, , T2K
• Input for neutrino cross section models, needed for new generation of oscillation experiments around the world
• However…Neutrino Cross Sections still poorly understood
• Neutrino Oscillations Dm2 ~ E / L, requires E in few GeV range (same as JLab!)
• Global models needed linking electron and neutrino scattering data
Resonance region is a major
contribution!
Experiment Description
• E02-109: Meas. of F2 and R on Deuterium.
• E04-001: Meas. of F2 and R on Carbon, Iron, and Aluminum. Also, Hydrogen for crosschecks. (Data from this will also be used by neutrino scattering community).
• Beam Energies used were: 4.6, 3.5, 2.3, and 1.2 GeV.
• Experiments ran for ~2 weeks in Hall C of January 2005 to cover 0.05 < Q2 < 2 (GeV)2 and 0.5 <W2 < 4.25 (GeV)2.
Experiment setup and procedure
Jlab Hall C
• HMS for scattered electrons
• SOS for positrons
At fixed Ebeam, θc, scan E’ from elastic to DIS.
Repeat for each Ebeam, θc to reach a range in ε for each W2, Q2.
HMS
SOS
Kinematics' Coverage Rosenbluth Separation DataRosenbluth Separation Data• Targets: D, C, Al, Fe , and some H Targets: D, C, Al, Fe , and some H
• Final Uncertainties estimated at ~1.6 Final Uncertainties estimated at ~1.6 % pt-pt in e (2% normalization).% pt-pt in e (2% normalization).
Rosenbluth Separation DataRosenbluth Separation Data• Targets: D, C, Al, Fe , and some H Targets: D, C, Al, Fe , and some H
• Final Uncertainties estimated at ~1.6 Final Uncertainties estimated at ~1.6 % pt-pt in e (2% normalization).% pt-pt in e (2% normalization).
Low QLow Q2 2 data for data for modelingmodeling• Targets: H,D, C, Al Targets: H,D, C, Al
• Final Uncertainties estimatedFinal Uncertainties estimated at ~3 - 8% (Much larger RCs at ~3 - 8% (Much larger RCs and rates)and rates)
Low QLow Q2 2 data for data for modelingmodeling• Targets: H,D, C, Al Targets: H,D, C, Al
• Final Uncertainties estimatedFinal Uncertainties estimated at ~3 - 8% (Much larger RCs at ~3 - 8% (Much larger RCs and rates)and rates)Rosenbluth Rosenbluth
separationseparations at multi. s at multi. energiesenergies
Rosenbluth Rosenbluth separationseparations at multi. s at multi. energiesenergies
Analysis Methodology
2.36 GeV2.75 GeV
1.75 GeV2.00 GeV
HMS Momentum• Bin efficiency corrected e-
yield in p/p - (∆p/p = +/- 8%, ∆ = +/- 35 mrad)
• Subtract scaled dummy yield bin-by-bin, to remove e- background from cryogenic target Aluminium walls.
• Subtract charge-symmetric background from π0 decay via measuring e+ yields.
• Apply acceptance correction for each - bin.
• Apply radiative corrections bin-by-bin.
• Apply bin-centering correction and average over => for each bin.
Structure Function Extraction
• Rosenbluth separations at each W2 and Q2 where possible (range in ε exist to perform a good linear fit)
• A global fitting of F2 and R over the entire kinematics range.
Analysis Status Detector Calibrations Calorimeter Efficiency Cerenkov Efficiency Tracking Efficiency Trigger Efficiency Computer Dead Time Acceptance Corrections Beam Position Offsets Beam Position Stability Kinematics Offsets Beam Energy Stability Study Target Density Corrections Optics Checks Radiation Corrections Charge Symmetric Background Cross-Sections
CompletedCompletedCompletedCompletedCompletedCompletedCompleted for E’ > 1.5 GeVCompleted CompletedCompletedCompletedCompletedPreliminary Sieve SlitCompletedNearly completed inelastic ~5% and Preliminary QE
Beam and Targets Position Offsets
From geometry, we can express this as:
Tan * Z X Y/Cos Tan * Z X Y/Cos
Sin Z Cos X Y Sin Z Cos X Y
Where ∆X is the offset of the beam, ∆Z is the offset of the target relative to the pivot, and θ is the HMS angle.
Beam and Targets Position Offsets
• Comparing the beam position of the Data to the Monte Carlo for different , we’ve arrived at these offsets (mm)
Fe C H D ∆X = 0.8627 1.1837 1.0795
1.1420 Err = 0.2811 0.4530 0.3043 0.3501∆z = 2.5009 -2.0983 1.7682
1.6016 Err = 0.6245 0.4530 0.4340 0.4058
MCData Y - Y YMCData Y - Y Y
Data and MC(before position corrections)
Data and MC(after position corrections)
Beam and Targets Position Offsets
Charge Symmetric Backgrounds• Subtract off Charge
Symmetric electrons by subtracting off positron Cross-Sections. π0
γ
γ
e+
e-
e+
e-Parameterized e+ CS
eTotalCorrected eTotalCorrected
)1()( )(21
EEppe eeE )1()( )(21
EEpp
e eeE
Polynomial Fit across Theta
SOS e+ Cross-section HMS e+ Cross-section
Preliminary Cross Sections
Preliminary Cross Sections
•Model only accounts for Inelastic Cross Section
•Results do not account for Quasi-Elastic contribution
•Model does not accurately account for resonances at low Q2
Plans in the Future
• Extract position cross sections for CSB correction
• Extract QE and Inelastic cross sections• Improve on Global Fits of Data• Complete Final Cross Sections• Rosenbluth Separations• Extract Structure Functions
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