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GHP06, Nashville, TN 23 Oct 2006PowerPoint Presentation

GHP06, Nashville, TN 23 Oct 2006

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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

Overview

- Nuclear structure functions and EMC effects
- Review of measurements
- Limitations in the data

- JLab E03-103
- Status of the analysis
- Preliminary results and future plans

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 xBj
- Shadowing : x<0.1
- Anti-shadowing: 0.1<x<0.3
- EMC effect x>0.3

- Size of the effect varies with A

E139 (Fe)EMC (Cu)BCDMS (Fe)

EMC effect: Large x region

- SLAC E139
- Most precise data for large x region
- Nuclei from A=4 to 197

- Conclusions
- Independent of Q2
- 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

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.

- Most models could provide an EMC-like effect

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

Benhar, Pandharipande, and Sick, Phys. Lett. B469, 19 (1999)

- 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

EMC effect: Importance of 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
- Smaller nuclear structure uncertainties

- Sensitive to A-dependence
- Scaling EMC effect with <r> very different from A

- Data lower quality
- Lower precision for 4He
- No data at large x for 3He

EMC effect: JLab E03-103

- JLab E03-103: JA and D. Gaskell, spokespersons, Jason Seely and Aji Daniel – thesis students
- Measured structure function for 1H, 2H, 3He, 4He, Be, C, Al, Cu, and Au
- High density 3,4He cryotargets allow improved statistics and systematics compared to SLAC E139

- Lower Q2 allows access to large-x region, but only for W2<4 GeV2

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

EMC effect: Scaling at lower Q2, W2- Measurement is not entirely in usual DIS region (W2>4 GeV2)
- DIS-scaling behavior has been observed to extend to lower Q2, W2 in nuclei
- Yields resonance region EMC ratios identical to DIS results
- Can be understood as consequence of quark-hadron duality
- E03-103 data at higher Q2, with precise measurement of Q2 dependence

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)

E03-103: Experimental details

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

- Larger p- contamination
- Large charge-symmetric background
- Larger Coulomb distortion corrections

Ratio of e+ to e- production

E03-103: Analysis status

- 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 sn/sp)

E03-103: Carbon EMC ratio

Preliminary results, 12C/2H ratio compared to SLAC and EMC

E03-103: Carbon EMC ratio

- Data taken for 12C and 2H at ten Q2 setting
- Measure Q2 dependence of the nuclear structure functions
- Verify Q2 independence of the EMC ratios

- Extracted EMC ratio for Carbon for the five highest Q2 settings

21435

Data show no indication of Q2 dependence, even at the lowest values of Q2, W2 shown

E03-103: Helium-4 EMC ratio

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

E03-103: Comparison of Carbon and Helium-4

Preliminary results, 4He/2H and12C/2H ratios

12C/4He ratio compared to previous 12C EMC ratios

4He

12C

E03-103: Comparison of Carbon and Helium-412C much heavier than 4He, but has similar average density

Preliminary results for 4He/2H and12C/2H ratios favor density-dependent EMC effect

E03-103: Helium-3 EMC ratio

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

E03-103: Helium-3 EMC ratio

- Bad news:
- Large correction (5-20%) to extract isoscalar ratio
- SLAC, NMC fits to sn/sp yield corrections that differ by 2-4% for x<0.6; difference changes sign at large x

- Good news:
- 197Au correction is roughly equal but has opposite sign; constrain combination of sn/sp and A-dependence of EMC[Working on Coulomb corrections, and checks on radiative corrections for heavy nuclei]
- 3He/(2H+1H) ratio less sensitive to neutron cross section

Summary, and more to come…

- Preliminary results from E03-103
- EMC effect nearly identical for 4He and 12C
- Indications of a large EMC effect in 3He
- Ratios independent of Q2 down to quite low Q2 values

- Results on the way
- More reliable 3He isoscalar ratios, ratios to proton+deuteron
- EMC ratios for Be, C, Al, Cu, Au – emphasis on large x region
- Absolute cross sections for 1H, 2H, 3He, 4He
- Test models of sn/sp + nuclear effects in few-body nuclei
- E02-019: absolute cross sections for x>1 for 2H, 3He, 4He

- More detailed, quantitative studies of the Q2 dependence
- Structure functions
- Ratios

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(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

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 x=0.65, there is a large gap between JLab, SLAC data, but there are indications of scaling up to x=0.75

- Our data fill in the gap up to x¼0.75, show indications of scaling up to x¼0.9

EMC ratios as a function ofxand x

- EMC ratios vs x and x
- Small differencefor x<.4
- SLAC E139 and JLab E03-103 have similar range in Q2, nearly identical difference between x, x

JLab E03-103

SLAC E139

Isoscalar corrections: 3He and 197Au

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

Nuclear Structure: High Momentum Nucleons

- Short-range structure in nuclei [E02-019 (Arrington)]
- Inclusive quasielastic scattering from nuclei at x>1
- Study distribution of extremely high momentum nucleons (>1 GeV/c) in 2H, 3He, 4He, 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 n-A interactions in supernovae, in neutrino oscillation experiments, and in q13 measurements

- Ran in 2004, data analysis in progress

Projected 3He uncertainties

HERMES

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 3He and 4He

[E03-103 (Arrington)]

- Allows reliable few-body calculations of binding
- Test A dependence and x dependence for very light nuclei
- First 3He data above x=0.4, factor of two improvement for 4He

Properties of Bound Nucleons: EMC effect

- Preliminary results: A- and x-dependence
- SLAC E139: Can scale with ln(A) or <rA>
- New data suggest it scales with density
- Also indicates identical x-dependence for 4He and 12C

x=0.6

4He

12C

PRELIMINARY

(statistical errors)

x=0.6

4He

PRELIMINARY

(statistical errors)

<rA>

Properties of Bound Nucleons: JLab @ 12 GeV

Three proposals for PAC30

- EMC effect
- Map out A-dependence at large x (test binding calculations)
- Precise measurements in anti-shadowing region

- DIS from 3He and 3H
- Ratio of 3H/3He provides measurements of sn/sp and d(x)/u(x), without uncertainty associated with nuclear effects
- Combine with precise 3He/2H 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

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