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

2 Overview Nuclear structure functions and EMC effects –Review of measurements –Limitations in the data JLab E –Status of the analysis –Preliminary results and future plans

3 Nuclear structure functions and the EMC effect Structure functions related to nuclear quark distributions –Non-trivial nuclear dependence (“EMC effect”) observed by EMC, BCDMS, SLAC experiments –Much larger than effect expected from Fermi motion –Significant (20+%) deviations between heavy nuclei and deuterium Universal dependence on x Bj –Shadowing:x<0.1 –Anti-shadowing:0.1<x<0.3 –EMC effectx>0.3 Size of the effect varies with A E139 (Fe) EMC (Cu) BCDMS (Fe)

4 EMC effect: Large x region SLAC E139 –Most precise data for large x region –Nuclei from A=4 to 197 Conclusions –Independent of Q 2 –Universal x-dependence (shape) for all A –Magnitude varies with A Scales with ave. density Scales with A Limitations –Poor precision at large x –Limited data for low A

5 EMC effect: Easy to explain (too easy?) Many “exotic” explanations –Fermi motion insufficient –Dynamical rescaling, nuclear pions, multi-quark clusters, medium modification to nucleon structure, etc… More careful treatment of “conventional” effects –Reexamination of binding effects –Effects of nucleon correlations Unique explanation? –Most models could provide an EMC-like effect Some could explain only part of the observed effect Many appeared inconsistent with other measurements such as Drell-Yan or limits on medium modification Others fully explained the data without any contribution from binding.

6 EMC effect: Conventional vs. exotic More systematic understanding necessary –Fermi motion and binding are clearly important, and must be included in any evaluation of “exotic” effects –A reliable binding calculation will tell us if we’re need a new explanation for THIS or THIS –Binding calculations must be evaluated against high-x data, which is dominated by Fermi motion and binding –Current data is limited at large x, where one can evaluate binding models, and low-A, where uncertainties due to nuclear structure are smallest Benhar, Pandharipande, and Sick, Phys. Lett. B469, 19 (1999)

7 EMC effect: Importance of few-body nuclei Calculations predict different x-dependence for 3 He and 4 He –Different models predict different x-dependence –Some models predict different shapes for 3 He and 4 He –Smaller nuclear structure uncertainties Sensitive to A-dependence –Scaling EMC effect with very different from A Data lower quality –Lower precision for 4 He –No data at large x for 3 He

8 EMC effect: JLab E He and 4 He calculations by Pandharipande and Benhar SLAC fit to heavy nuclei (scaled to 3He) HERMES data E03103 projected uncertainty –Lower Q 2 allows access to large-x region, but only for W 2 <4 GeV 2 JLab E03-103: JA and D. Gaskell, spokespersons, Jason Seely and Aji Daniel – thesis students –Measured structure function for 1 H, 2 H, 3 He, 4 He, Be, C, Al, Cu, and Au –High density 3,4 He cryotargets allow improved statistics and systematics compared to SLAC E139

9 EMC effect: Scaling at lower Q 2, W 2 Measurement is not entirely in usual DIS region (W 2 >4 GeV 2 ) –DIS-scaling behavior has been observed to extend to lower Q 2, W 2 in nuclei –Yields resonance region EMC ratios identical to DIS results –Can be understood as consequence of quark-hadron duality –E data at higher Q 2, with precise measurement of Q 2 dependence JA, et al., PRC73: (2006) B.W.Filippone, et al., PRC45:1582 (1992) JA, et al., PRC64: (2001) W.Melnitchouk, R. Ent, and C. Keppel, Phys. Rept. 406:127 (2005) Q 2 ¼ 4 GeV < W 2 < 2.8 GeV 2

10 E03-103: Experimental details Source of uncertainty Statistics *Density fluctuations Absolute density * - size of correction is 8% at 4 uA vs. 4% at 80 uA SLAC E % 1.4% 2.1% JLab E % 0.4% 1.0% Main improvement over SLAC due to improved He targets: Requires larger scattering angle to reach same Q 2  Larger   contamination  Large charge-symmetric background  Larger Coulomb distortion corrections Main drawback is lower beam energy Ratio of e+ to e- production

11 Ran in Hall C at Jefferson Lab, summer/fall of 2004 (EMC and x>1) 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 ) E03-103: Analysis status

12 E03-103: Carbon EMC ratio Preliminary results, 12 C/ 2 H ratio compared to SLAC and EMC

13 E03-103: Carbon EMC ratio Data taken for 12 C and 2 H at ten Q 2 setting –Measure Q 2 dependence of the nuclear structure functions –Verify Q 2 independence of the EMC ratios Extracted EMC ratio for Carbon for the five highest Q 2 settings Data show no indication of Q 2 dependence, even at the lowest values of Q 2, W 2 shown

14 E03-103: Helium-4 EMC ratio Preliminary results, 4 He/ 2 H ratio compared to SLAC Results consistent with SLAC fit to A=12 (using A-dependent fit) Consistent with density-dependent fit to A=4

15 E03-103: Comparison of Carbon and Helium-4 Preliminary results, 4 He/ 2 H and 12 C/ 2 H ratios 12 C/ 4 He ratio compared to previous 12 C EMC ratios

16 E03-103: Comparison of Carbon and Helium-4 12 C much heavier than 4 He, but has similar average density Preliminary results for 4 He/ 2 H and 12 C/ 2 H ratios favor density- dependent EMC effect 4 He 12 C

17 E03-103: Helium-3 EMC ratio Preliminary results, 3 He EMC ratio compared to HERMES Blue is uncorrected 3 He/ 2 H ratio Green includes correction for proton excess in 3 He (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 is very sensitive to isoscalar correction

18 E03-103: Helium-3 EMC ratio Good news: – 197 Au correction is roughly equal but has opposite sign; constrain combination of  n /  p and A- dependence of EMC [Working on Coulomb corrections, and checks on radiative corrections for heavy nuclei] – 3 He/( 2 H+ 1 H) ratio less sensitive to neutron cross section Bad news: –Large correction (5-20%) to extract isoscalar ratio –SLAC, NMC fits to  n /  p yield corrections that differ by 2-4% for x<0.6; difference changes sign at large x

19 Summary, and more to come… Preliminary results from E –EMC effect nearly identical for 4 He and 12 C –Indications of a large EMC effect in 3 He –Ratios independent of Q 2 down to quite low Q 2 values Results on the way –More reliable 3 He isoscalar ratios, ratios to proton+deuteron –EMC ratios for Be, C, Al, Cu, Au – emphasis on large x region –Absolute cross sections for 1 H, 2 H, 3 He, 4 He Test models of  n /  p + nuclear effects in few-body nuclei E02-019: absolute cross sections for x>1 for 2 H, 3 He, 4 He –More detailed, quantitative studies of the Q 2 dependence Structure functions Ratios

20 Scaling of the nuclear structure functions F 2 (x,Q 2 ) consistent with QCD evolution in Q 2 for low x values (x<0.5) Huge scaling violations at large x (especially for x>1) F 2 ( ,Q 2 ) consistent with QCD evolution in Q 2 to much larger  values Scaling violations are mostly the “target-mass” corrections (plus a clear contribution from the QE peak)  Nearly independent of A

21 Scaling of the nuclear structure functions Low Q 2 JLab data (from E89-008, 4 GeV) are consistent with extrapolated structure function from high Q 2 SLAC data [ fixed dln(F 2 )/dln(Q 2 ) ] 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  ¼0.75, show indications of scaling up to  ¼0.9

22 EMC ratios as a function of x and  EMC ratios vs x and  –Small difference for x<.4 –SLAC E139 and JLab E have similar range in Q 2, nearly identical difference between x,  SLAC E139 JLab E03-103

23 Isoscalar corrections: 3 He and 197 Au F2n/F2p from SLAC, CTEQ, NMC (bottom) Correction to 3He (top right) and 197Au (bottom right)

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25 Nuclear Structure: High Momentum Nucleons Short-range structure in nuclei [E (Arrington)] –Inclusive quasielastic scattering from nuclei at x>1 –Study distribution of extremely high momentum nucleons (>1 GeV/c) in 2 H, 3 He, 4 He, and heavy nuclei –Goal is to understand high-momentum components and map out strength of Short Range Correlations (SRCs) in nuclei Important part of nuclear structure, relevant to topics in nuclear and particle physics: neutron star structure, medium modification in sub- threshold hadron production, and -A interactions in supernovae, in neutrino oscillation experiments, and in  13 measurements –Ran in 2004, data analysis in progress

26 Properties of Bound Nucleons: EMC effect Medium modification: The EMC effect –Clear observation of nuclear (density) dependence in parton distributions –Still no consensus on the cause of the effect Binding is important at all x values, but may also require modification to internal structure of the nucleon EMC effect in 3 He and 4 He [E (Arrington)] –Allows reliable few-body calculations of binding –Test A dependence and x dependence for very light nuclei –First 3 He data above x=0.4, factor of two improvement for 4 He Projected 3 He uncertainties HERMES

27 12 C Properties of Bound Nucleons: EMC effect Preliminary results: A- and x-dependence –SLAC E139: Can scale with ln(A) or –New data suggest it scales with density –Also indicates identical x-dependence for 4 He and 12 C PRELIMINARY (statistical errors) PRELIMINARY (statistical errors) x=0.6 4 He 

28 Properties of Bound Nucleons: 12 GeV EMC effect –Map out A-dependence at large x (test binding calculations) –Precise measurements in anti-shadowing region DIS from 3 He and 3 H –Ratio of 3 H/ 3 He provides measurements of  n /  p and d(x)/u(x), without uncertainty associated with nuclear effects –Combine with precise 3 He/ 2 H ratio to extract isoscalar EMC effect for A=3 Inclusive scattering from nuclei at x>1 –At 6 GeV, dominated by QE scattering, map out distribution of high-p nucleons –At 12 GeV, begin to probe quark distributions at x>1 Three proposals for PAC30