New measurements of the EMC effect in few-body nuclei John Arrington, Physics Division, Argonne Second meeting of the APS Topical Group on Hadron Physics. GHP06, Nashville, TN 23 Oct 2006. Overview. Nuclear structure functions and EMC effects Review of measurements Limitations in the data
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New measurements of the EMC effect in few-body nuclei John Arrington, Physics Division, ArgonneSecond meeting of the APS Topical Group on Hadron Physics
GHP06, Nashville, TN
23 Oct 2006
E139 (Fe)EMC (Cu)BCDMS (Fe)
Benhar, Pandharipande, and Sick, Phys. Lett. B469, 19 (1999)
SLAC fit to heavy nuclei (scaled to 3He)
3He and 4He calculations by Pandharipande and Benhar
HERMES dataE03103 projected uncertainty
Q2¼ 4 GeV2
1.3 < W2 < 2.8 GeV2
B.W.Filippone, et al., PRC45:1582 (1992) JA, et al., PRC64:014602 (2001)
W.Melnitchouk, R. Ent, and C. Keppel, Phys. Rept. 406:127 (2005)
JA, et al., PRC73:035205 (2006)
Main improvement over SLAC due to improved He targets:
JLab E03-103
0.5-0.7%
0.4%
1.0%
SLAC E139
1.0-1.2%
1.4%
2.1%
Source of uncertainty
Statistics
*Density fluctuations
Absolute density
*- sizeof correction is 8% at 4 uA vs. 4% at 80 uA
Main drawback is lower beam energy
Requires larger scattering angle to reach same Q2
Ratio of e+ to e- production
Preliminary results, 12C/2H ratio compared to SLAC and EMC
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Data show no indication of Q2 dependence, even at the lowest values of Q2, W2 shown
Preliminary results, 4He/2H ratio compared to SLAC
Results consistent with SLAC fit to A=12 (using A-dependent fit)
Consistent with density-dependent fit to A=4
Preliminary results, 4He/2H and12C/2H ratios
12C/4He ratio compared to previous 12C EMC ratios
4He
12C
12C much heavier than 4He, but has similar average density
Preliminary results for 4He/2H and12C/2H ratios favor density-dependent EMC effect
Preliminary results, 3He EMC ratio compared to HERMES
Blue is uncorrected 3He/2H ratio
Green includes correction for proton excess in 3He (isoscalar EMC ratio)
Larger EMC effect than most models
Different x-dependence than calculations, heavier nuclei
Might suggest larger EMC effect than expected for deuterium
However, result isvery sensitive to isoscalar correction
F2(x,Q2) consistent with QCD evolution in Q2 for low x values (x<0.5)
Huge scaling violations at large x (especially for x>1)
F2(x,Q2) consistent with QCD evolution in Q2 to much larger x values
Scaling violations are mostly the “target-mass” corrections (plus a clear contribution from the QE peak)
Nearly independent of A
JLab E03-103
SLAC E139
Projected 3He uncertainties
HERMES
[E03-103 (Arrington)]
x=0.6
4He
12C
PRELIMINARY
(statistical errors)
x=0.6
4He
PRELIMINARY
(statistical errors)
<rA>
Three proposals for PAC30