Upload
hedwig-bryant
View
36
Download
0
Embed Size (px)
DESCRIPTION
The Nucleons Went Two By Two: Short Range Correlations in Nuclei. Larry Weinstein Old Dominion University. Theory Overview What are Correlations? How big are they? np vs pp pairs Summary. Quarks and Nuclear Physics 2009. Comprehensive Theory Overview. Nuclear Theory - circa 2000. - PowerPoint PPT Presentation
Citation preview
L. Weinstein, Gordon 2004 1
The Nucleons Went Two By Two: Short Range
Correlations in NucleiLarry WeinsteinOld Dominion University
• Theory Overview• What are Correlations?• How big are they?• np vs pp pairs• Summary
Quarks and Nuclear Physics 2009
Nuclear Theory - circa 2000
Nuclear Theory - today: 1, 2, 3, … 12, … many
Comprehensive Theory Overview
High momentum tails: k > kF Calculable for few-body nuclei, nuclear matter. Dominated by two-nucleon short range correlationsPoorly understood part of nuclear structureNN potential models not applicable at p > 350 MeV/c
Uncertainty in SR interaction leads to uncertainty at k>>kf, even for simplest systems
3
Short Range Correlations (SRCs)
Looking for quarks in the nucleus is like looking for the mafia in Sicily. Everyone knows they are there, but evidence is hard to find.
Deuteron
Carbon
NM k > 250 MeV/c25% of nucleons60% of KE
k < 250 MeV/c75% of nucleons40% of KE
p (GeV/c)
n(p
) (G
eV/c
)-3
0.80.2
Two nucleon short range correlations (NN-SRC)
1.7 fm~1.0 fm
0 = 0.16 fm-3
NN-SRC ~ 50
Studying NN-SRC concerns:• High momentum part of the nuclear wave function• Short distance behavior of nucleons - overlapping??• Cold dense nuclear matter• Neutron Stars
Average Two Nucleon Properties in the Nuclear Ground StateResponsible for the high momentum part of of the Nuclear WF
Two-body currents are not Correlations
Cor
rela
tion
sC
urre
nts Two body currents
strongly enhance the effects of correlations
MEC IC
What are correlations?
Why are Correlations Interesting?
Responsible for high momentum part of Nuclear WF
Momentum (1/fm) Momentum (1/fm)
Ciofi degli Atti, PRC 53 (1996) 1689
Correlations
p-15Nbreakup
ContinuumContinuum
p-dbreakup CorrM
omen
tum
Den
sity
Correlations are Universal: A(e,e’)
Frankfurt et al, PRC48 2451 (1993)
Egiyan et al., PRL 96, 082501 (2006)
α2N ≈20%α3N ≈1%
Scaling (flat ratios) indicates a common momentum distribution.1 < x < 1.5: dominated by different mean field n(k)1.5 < x < 2: dominated by 2N SRCx > 2.3: dominated by 3N SRC
Rat
io o
f (e
,e’)
C
ross
sec
tion
s
12C/3He
56Fe/3He
4He/3He
Ratios to 3He (3/A)
21
Q2 > 1.4 GeV2
xB
What are Correlations?Average Two Nucleon Properties in the Nuclear Ground State
Not Two-Body Currents
An Experimentalist’s Definition:• A high momentum nucleon whose
momentum is balanced by one other nucleon• NN Pair with
• Large Relative Momentum• Small Total Momentum
• Whatever a theorist says it is
12C(p,ppn) EVA/BNL
cos
Large neutron momentum p opposite nSmall neutron momentum p isotropicHigh momentum nucleons are paired Tang et al, PRL 90, 042301 (2003)
p
pp
n
12C
Pmiss = 300, 400, 500 MeV/c
e
e’
*n or p p
P =
300
-600
MeV
/c
Ee = 4.627 GeV
Ee’ = 3.724 GeV
50.40
19.50
40.1 ,35.8 ,32.00p
p ~ 1.4 GeV/c
Knockout the proton, look for its partner nucleon
JLab Hall A C(e,e’pN)Q2 = 2 GeV2
xB = Q2/2m = 1.2Pmiss = 300-600 MeV/c
R. Subedi et al., Science, 2008
9.5 ± 2 % R. Shneor et al.,
PRL 99, 072501 (2007)
Missing momentum [MeV/c]
edextrapolat )',(
)',(12
12
peeC
ppeeC
BNL Experiment
measurement was 92%
+8-18
edextrapolat )',(
)',(12
12
peeC
pneeC96 ± 23 %
Yie
ld R
ati
o [
%]
Yie
ld R
ati
o [
%]
pp/pN = 5%Since the electroncan hit eitherproton
High momentum protons have partners
pn
pp
(proton initial momentum)
CLAS3He(e,e’p
p)Detect 2 protons,reconstruct the neutron
Huge electron acceptance
<Q2> ~ 0.8
<Q2> ~ 1.8
Select peaksin Dalitz plot
Pair has back-to-back peak!
3He(e,e’pp)n nucleon energy balance: p > 250 MeV/c
pn pair
Cut on leading nucleon perpendicular momentum
I don’t want to get involved:spectator correlated pairs
4.7 GeVleading ppn pair
Isotropic!Smallforwardmomentum(describedby theory)
2 GeV
cos(neutron q angle)
2 GeV
pn pair2 GeV
pn pair4.7 GeV
Similar momentum distributions•Relative•Totalpn:pp ratio ~ 4
Results: 2.2 GeV (Q2≈0.8 GeV2)4.7 GeV (Q2≈1.5 GeV2)4.7 GeV scaled by 5.3 4.7 GeV
5.3
2 GeV
Golak 2.2
Golak 4.7 5.3
pn pairs pn pairs
pp pairspp pairs+ =1-Body
Theory (Golak)•Describes 2 GeV OK
•Prel too low•Too low at 4.7 GeV
pp to pn compariso
n
<Q2>(GeV2)
pn to pp ratio
Hall A / BNL
2 / ?? 18
CLAS 1-2 4
Contradiction???
Subedi et al, Science (2008)
Relative
np/2N
pp/2N
12C
BNL Hall A
HALL A Hall A
The s-wave momentum distribution has a minimumThe np minimum is filled in by strong tensor correlations
pn
pp
Ciofi degli Atti, Alvioli;
Schiavilla, Wiringa, Pieper, Carlson
Sargsian, Abrahamyan, Strikman, Frankfurt
3He3He
V18 Bonn
np np
pp pp
Pair relative momentum
3He8Be
Why is np/pp so dominant at prel=300-500 MeV/c?
4000 1000
pp to pn resolution:pp/pn ratio increases with pair total
momentum Ptot
Hall A: small Ptot less ppCLAS: large Ptot more pp
Larger Ptot pp pair wave fn minimum fills in
300 < Prelative < 500 MeV/cTensorCorrelations!
Hall A / BNL
CLAS
Correlations and Neutron Stars
‘Classical’ neutron star: fermi gases of e, p and nLow temperature almost filled fermi spheres limited ability of pn decays (Urca process)
Correlations high momentum tail and holes in the fermi spheres
Why does this matter?
Cooling should be dominated by the Urca process:
Correlations-caused holes in the proton fermi sphere should enhance this process by large factors and speed neutron star cooling.
L. Frankfurt, PANIC 2008
Summary of results1. Short Range Correlations (SRC) are universal (same
momentum distribution in all nuclei) • Probabilities range from 5% (d) to 25% (Fe)
2. Correlated nucleons have their momentum balanced by only one other nucleon• When that nucleon is knocked out, its partner is also
emitted 3. pn pairs dominate (at 300 < prel < 500 MeV/c)
• Tensor correlations• At large pair cm momentum, pn and pp pairs are equal
4. We have measured pair relative and total momentum distributions by hitting the third nucleon in 3He and measuring the spectator correlated pairs
Future: extend measurements to larger relative momentum to study central correlations and access higher densities
See quark effects??