New Results on the EMC Effect at Large x in Light to Heavy Nuclei Patricia Solvignon Argonne National Laboratory For the E03-103 Collaboration Good afternoon. I am going to present today new results from Jlab experiment E03-103 on the EMC effects in light to heavy nuclei with an emphasis at large x. The spokepeople of this experiment are John Arrington and Dave Gaskell and the graduate students are Aji Daniel and Jason Seely who graduated last year. spokespersons: J. Arrington and D. Gaskell graduate students: A. Daniel and J. Seely Hall C Summer Workshop August 9-10, 2007

Nuclear structure functions and the EMC effect Nuclear structure: A  Z.p + N.n Effects found in several experiments at CERN, SLAC, DESY Same x-dependence in all nuclei Shadowing: x<0.1 Anti-shadowing: 0.1<x<0.3 EMC effect: x>0.3 The size of the effect is a function of A In early 80’s, it was discovered that in the nuclear structure, the cross section is not simply the sum over its constituents protons and neutrons. This discovery was called the “EMC effect” from the name of the collaboration that first made the observation. Morever, the quark distribution in nuclei has a strong x-dependence which is the same for all nuclei with the shadowing region at x<0.1, the anti-shadowing region for x between 0.1 and 0.3 and the EMC effect region at x>0.3. It was also found that the size of the effect depends on the atomic number A. E139 (Fe) EMC (Cu) BCDMS (Fe)

Mapping the EMC Effect Models should include conventional effects: Fermi motion and binding dominate at high x Binding also affects quark distribution at all x Then more “exotic” explanations may be added if these effects are not enough to describe the data like: Nuclear pions Multiquark clusters Dynamical rescaling Theoretical activities have since then tried to map out the EMC effect. It seems that most the ideas converge on common requirements which are that models should include fermi motion and binding because these effects dominate at high x. Binding effects also extend to all x. Then, if the Fermi motion-binding contribution are not enough to reproduce the data, more exotic explanations can be added like nuclear pions, multiquark clusters, dynamical rescaling. (read blue sentence) For exemple, here a plot from Benhar et al comparing their calculation to SLAC and EMC data. It can be seen that the model including nuclear pions does reproduce well the data in the for x between 0.2 and 0.75. Many of these models can reproduce the large x region but failed in other x-regions or for other data (Drell-Yan) or didn’t include conventional effects. Benhar, Pandharipande, and Sick Phys. Lett. B410, 79 (1997)

EMC effect in few-body nuclei Calculations predict different x-dependence for 3He and 4He Different models predict different x-dependence Some models predict different shapes for 3He and 4He Spectral functions are easier to calculate for light nuclei Data lower quality Lower precision for 4He No data at large x for 3He For few-body nuclei, the models disagree on the x-dependence and the shape of the EMC effect. The world data for light nuclei have a low precision or are missing in the large x as for 3He.

Existing EMC Data SLAC E139 most extensive and precise data set for x>0.2 A/D for A=4 to 197 4He, 9Be, 12C, 27Al, 40Ca, 56Fe, 108Ag, and 197Au Size at fixed x varies with A, but shape is nearly constant E03-103 will improve with Higher precision data for 4He Addition of 3He data Precision data at large x and on heavy nuclei  Lowering Q2 to reach high x region

Quark-hadron duality I. Niculescu et al., PRL85:1182 (2000) First observed by Bloom and Gilman in the 1970’s on F2: Scaling curve seen at high Q2 is an accurate average over the resonance region at lower Q2 To access the large x region, one needs a Q2 of above 18GeV2. But the phenomenom of quark-hadron duality may be of great help to access this region by lowering our W2 cut on the data to be included.

Quark-hadron duality J. Arrington, et al., PRC73:035205 (2006) First observed by Bloom and Gilman in the 1970’s on F2: Scaling curve seen at high Q2 is an accurate average over the resonance region at lower Q2 To access the large x region, one needs a Q2 of above 18GeV2. But the phenomenom of quark-hadron duality may be of great help to access this region by lowering our W2 cut on the data to be included. In nuclei, the averaging is in part done by the Fermi motion.

EMC effect: Scaling at lower Q2, W2 JLab E89-008: Q2 ~ 4 GeV2 1.3<W2<2.8 GeV2 data in the resonance region E03-103 data at higher Q2, with precise measurement of Q2-measurement J. Arrington, et al., PRC73:035205 (2006)

JLab Experiment E03-103 Ran in Hall C at Jlab Summer and Fall 2004 (w/E02-019  x>1) A(e,e’) at 5.77 GeV Targets: H, 2H, 3He, 4He, Be, C, Al, Cu, Au 10 angles to measure Q2-dependence All targets at large angles: 40, 46 and 50. C and D data at all angles to verify precise scaling and our extraction of the EMC ratio is Q2-dependence.

JLab Experiment E03-103 Ran in Hall C at Jlab Summer and Fall 2004 (w/E02-019  x>1) A(e,e’) at 5.77 GeV Targets: H, 2H, 3He, 4He, Be, C, Al, Cu, Au 10 angles to measure Q2-dependence All targets at large angles: 40, 46 and 50. C and D data at all angles to verify precise scaling and our extraction of the EMC ratio is Q2-dependence. E89-008 coverage

E03-103: Experimental details Main improvement over SLAC due to improved 4He targets: Source of uncertainty Statistics *Density fluctuations Absolute density SLAC E139 1.0-1.2% 1.4% 2.1% JLab E03-103 0.5-0.7% 0.4% 1.0% (1.5% for 3He) * - size of correction is 8% at 4 uA vs. 4% at 80 uA SLAC: high power pulsed beam, gas target? JLAB: much higher density: (cryo not gas target), raster, heat compensation system

E03-103: Experimental details Main improvement over SLAC due to improved 4He targets: Source of uncertainty Statistics *Density fluctuations Absolute density SLAC E139 1.0-1.2% 1.4% 2.1% JLab E03-103 0.5-0.7% 0.4% 1.0% (1.5% for 3He) * - size of 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 Larger - contamination Large charge-symmetric background Larger Coulomb distortion corrections Ratio of e+ to e- production Ratio of e+ to e- production Say something about e+/e-: worse case and we can compare with ratio at lower angle

E03-103: Analysis status Analysis is in the final stage Cut off at x=2 Analysis is in the final stage Cross section extraction Calibrations, efficiency corrections, background subtraction completed Finalizing model-dependence in radiative corrections, bin centering, etc… Investigating Coulomb distortion corrections (heavy nuclei) EMC Ratios: Isoscalar EMC correction (requires n/p) Investigating the rules of n/p ratio at large x (x>0.6-0.65)

E03-103: Carbon EMC ratio and Q2-dependence Preliminary

E03-103: Carbon EMC ratio and Q2-dependence Preliminary

E03-103: Carbon EMC ratio and Q2-dependence Preliminary

E03-103:Comparison of Carbon and 4He Nuclear dependence of cross sections Preliminary

E03-103: Preliminary 3He EMC ratio Large correction for proton excess Preliminary

E03-103: Preliminary 3He EMC ratio Large correction for proton excess Preliminary Significant EMC effect Different shape at large x than for the heavier nuclei Calculations underestimate the effect

Coulomb distortions on heavy nuclei Initial (scattered) electrons are accelerated (decelerated) in Coulomb field of nucleus with Z protons Not accounted for in typical radiative corrections Usually, not a large effect at high energy machines – not true at JLab (6 GeV!) E03-103 uses modified Effective Momentum Approximation (EMA) Aste and Trautmann, Eur, Phys. J. A26, 167-178(2005)

E03-103: EMC effect in heavy nuclei E03-103 data corrected for coulomb distortion Scale errors: 1.2-2% Preliminary

E03-103: EMC effect in heavy nuclei E03-103 data corrected for coulomb distortion Preliminary observation: Large and low x cross-overs A-independent Preliminary

EMC effect in heavy nuclei Corrected for coulomb distortion E03-103 data corrected for coulomb distortion Preliminary observation: Large and low x cross-overs A-independent Good agreement with the SLAC data for Fe Preliminary

EMC effect in heavy nuclei Corrected for coulomb distortion E03-103 data corrected for coulomb distortion Preliminary observation: Large and low x cross-overs A-independent Good agreement with the SLAC data for Fe and Au About 1% correction for coulomb distortions in SLAC data Preliminary

A or (A) dependence of the EMC effect ? Good agreement between E03-103 and SLAC E139 data after Coulomb corrections. Preliminary E03-103 results confirm A and density dependence of the EMC effect. x = 0.6 E03-103 data with CC SLAC data with CC Density dependence is tricky: we don’t really know how to calculate it, especially for 3He. Adding heavy nuclei data doesn’t bring much, but the light nuclei constrain a lot more fits. Preliminary

A or (A) dependence of the EMC effect ? Good agreement between E03-103 and SLAC E139 data after Coulomb corrections. Preliminary E03-103 results confirm A and density dependence of the EMC effect. x = 0.6 E03-103 data with CC SLAC data (no CC) Preliminary

Summary JLab E03-103 provides: Precision nuclear structure ratios for light nuclei Access to large x EMC region for 3He  197Au Preliminary observations: Scaling of the structure function ratios for W<2GeV down to low Q2 Carbon and 4He have the same EMC effect Large EMC effect in 3He Similar large x shape of the structure function ratios for A>3 More to come: Absolute cross sections for 1H, 2H, 3He and 4He: test models of n/p and nuclear effects in few-body nuclei Quantitative studies of the Q2-dependence in structure functions and their ratios

Extra slides

Isoscalar Corrections SLAC param. (1-0.8x) CTEQ NMC fit Isoscalar correction applied to data Au 3He

Scaling of the nuclear structure functions 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(,Q2) consistent with QCD evolution in Q2 to much larger  values Scaling violations are mostly the “target-mass” corrections (plus a clear contribution from the QE peak)  Nearly independent of A

E03-103: Charge-symmetry background Ratio of e+ to e- production =40o

E03-103: Charge-symmetry background Ratio of e+ to e- production =40o =50o

Scaling of the nuclear structure functions Low Q2 JLab data (from E89-008, 4 GeV) are consistent with extrapolated structure function from high Q2 SLAC data [ fixed dln(F2)/dln(Q2) ] Above =0.65, there is a large gap between JLab, SLAC data, but there are indications of scaling up to =0.75

Scaling of the nuclear structure functions Low Q2 JLab data (from E89-008, 4 GeV) are consistent with extrapolated structure function from high Q2 SLAC data [ fixed dln(F2)/dln(Q2) ] Above =0.65, there is a large gap between JLab, SLAC data, but there are indications of scaling up to =0.75 Our data fill in the gap up to ~0.75, show indications of scaling up to ~0.9