Strange Quarks in the Nucleon Sea Results from Happex II Konrad A. Aniol, CSULA.
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Transcript of Strange Quarks in the Nucleon Sea Results from Happex II Konrad A. Aniol, CSULA.
For the HAPPEX Collaboration
Thomas J eff erson National Accelerator Facility – Argonne National Laboratory – CSU, Los Angeles -William and Mary – Duke – DSM/ DAPNI A/ SPhN CEA Saclay - FI U – Harvard -
I NFN, Rome - I NFN, Bari – I AE, Beij ing – I PT Kharkov - J ozef Stefan I nstitute –Kent State - MI T – NPI RAS, St. Petersburg – ODU – Rutgers - Smith College –
Syracuse – Temple – U. Blaise Pascal – U. of I llinois Urbana-Champagne –UMass, Amherst – U. of Kentucky – U. of Virginia – UST, Heifei
Strange Quarks in the Nucleon Sea
Results from Happex II
Konrad A. Aniol, CSULA
Recent Talks by the HAPPEX Collaboration
http://hallaweb.jlab.org/experiment/HAPPEX/pubsandtalks.html
APS Meeting: Parity-Violation Electron Scattering on Hydrogen and Helium and Strangeness in the Nucleon, 23 April 2006 - Paul Souder (PPT)
TJNAF Seminar: Results from the 2005 HAPPEX-II Run, 21 April 2006 - Kent Paschke (PPT)
See these talks for greater detail
Kent Paschke, University of Massachusetts
Thesis Students
Lisa Kaufman, University of Massachusetts
Bryan Moffit, College of William and Mary
Hachemi Benaoum, Syracuse University
Ryan Snyder, University of Virginia
Structure of the Nucleon is of Fundamental Interest
99.9% of baryonic matter is contained in the nucleon
Molecules = atoms, massmolecule =massatoms
Atom = (nuclei + electrons), matom=mnuclei+melectrons
Nucleus = nucleons, mnucleus Zmp+Nmn
Nucleon=quarks+gluons), mnucleon mquarks !
A hierarchy of structures
From PDG, mu is 1.5 to 4 MeV
md is 4 to 8 MeV
Proton flavor content is uud, mp 2mu + md
Example of origin of proton’s mass, PRL 74 (1071) 1995, X. Ji
Quark kinetic + potential energy = 1/3 mnucleon
Total gluon energy = 7/12 mnucleon
Quark masses = 1/12 mnucleon
Conclude – nucleon mass has significant gluon field contribution expect significant amounts of pairs to be present.
nucleon sea quarks are important components of the nucleon
How can we determine the quark content of the nucleon?
Constituent quarks are quasi-particles and become heavy fermions through the strong interactions.
g
qc
qc
A constituent u quark has spin ½ and is a dynamical system.
uc
g
uc
sdu ,,
sdu ,,
Charged-current neutrino and anti-neutrino scattering reveal the presence of strange and anti-strange quarks.
cs
The charm quarks decay semileptonically to positive muons. Muon neutrinos thus produce positive and negative muon pairs.
Likewise for muon anti-neutrinos: cs
)(
)(
Xs
Xs
Are strange sea quarks present in the nucleon?
Strange Quarks in the NucleonStrange Seameasured inN scattering
Spin polarized DISInclusive: s = -0.10 ± 0.06
uncertainties from SU(3), extrapolationSemi-inclusive: s = 0.03 ± 0.03 BUT new HERMES data determine that s = 0 !
NssN 5
NssN
NssN Strange vector FF electromagnetic structure ?
Strange massN scattering: 0-30% of nucleon mass
Strange sea is well-known, but contributions to nucleon
matrix elements are somewhat unsettled
Static nucleon properties ?
Parts of the Lagrangian responsible for neutral current scattering
photon
Z boson
Electroweak coupling of charged fundamental particles
wv QIq 23 sin2 3Iqa
Note that the fermion fields i are the same for photon or Z boson coupling. Only the coupling constants change.
I3 weak
isospin
Q electric
charge
qv vector qa a axialaxial
vectorvector
u 1/2 2/3 ½ -4/3sin2w
1/2
d -1/2 -1/3 -½ +2/3sin2w
-1/2
-1/2 -1/3 -½ +2/3sin2w
-1/2
Electroweak coupling constants
wv QIq 23 sin2 3Iqa
s
e -1/2 -1-1/2 +2sin2W
-1/2
)(22
2
AMEF
PV AAAQG
A
22ME
ZEE
E GG
GGA
22
ME
ZMM
M GG
GGA
22
22 )1(1)sin41(
2
1
ME
NCAMW
A GG
GGA
2
2
4M
Q 12 ]
2tan)1(21[
Asymmetry terms for eP or eN scattering. HAPPEX is not sensitive to the AA term for forward angle scattering
pZG ,
Flavor Separation of Nucleon Form Factors
psME
pdME
puME
pME GGGG ,
/,/
,/
,/ 3
1
3
1
3
2
sMEW
dMEW
uMEW
ZME GGGG /
2/
2/
2/ sin
3
41sin
3
41sin
3
81
Measuringnp GG ,, , cannot separate all three flavors
(assumes heavy quarks are negligible)
Adding in a measurement of
and assuming charge symmetry
nsps
nupd
ndpu
GG
GG
GG
,,
,,
,,
pZ
MEnME
pMEW
sME
pZME
nME
pMEW
dME
pZME
pMEW
uME
GGGG
GGGG
GGG
,,
,,
,,
2,
,,
,,
,,
2,
,,
,,
2,
sin41
sin42
sin43
then we can write
i
iii NqqeNG ~
Jefferson Laboratory
Polarized e-
Source
Hall A
AB
C
Continuous Electron Beam Accelerator Facility
CEBAF
Features:1. Polarized Source2. Quiet Accelerator3. Precision
Spectrometersin Hall A
The HAPPEX CollaborationCalifornia State University, Los Angeles -
Syracuse University -DSM/DAPNIA/SPhN CEA Saclay -
Thomas Jefferson National Accelerator Facility- INFN, Rome - INFN, Bari -
Massachusetts Institute of Technology - Harvard University – Temple University –
Smith College - University of Virginia - University of Massachusetts – College of William and Mary
1998-99: Q2=0.5 GeV2, 1H2004-06: Q2=0.1 GeV2, 1H, 4He 2008:Q2=0.6, 1H
HAPPEX Experiment
Target400 W transverse flow20 cm, LH220 cm, 200 psi 4He
High Resolution SpectrometerS+QQDQ 5 mstr over 4o-8o
Hall A at Jefferson Lab
Compton1.5-2% systContinuous
Møller2-3% syst
Polarimeters
Cherenkovcones
PMT
PMT
Elastic Rate:1H: 120 MHz4He: 12 MHz
High Resolution Spectrometers
100 x 600 mm
12 m dispersion sweeps away
inelastic events
Very clean separation ofelastic events by HRS optics
Overlap the elastic line above the focal plane and integrate the flux
Large dispersion and heavy shielding reduce backgrounds at the focal plane
Brass-Quartz Integrating Cerenkov Shower Calorimeter•Insensitive to background•Directional sensitivity •High-resolution•Rad hard
High-Power Cryogenic TargetNew "race track" design – 20 cm (transverse cryogen flow) CSULA design and fabrication.
20 cm 1.8% R.L. LH2
20 cm 2.2% R.L. 4He gas cell– Cold (6.6K), dense (230 psi)
Al wall thickness– 4 mils (H)– 10 mils (He)
controls
effective
analyzing
power
Tune residual
linear pol.
Slow helicityreversal
Intensity Attenuat
or(charge
Feedback)
Polarized Source
High Pe
High Q.E.
Low Apower
•Optical pumping of solid-state photocathode
•High Polarization
• Pockels cell allows rapid helicity flip
•Careful configuration to reduce beam asymmetries.
•Slow helicity reversal further to cancel beam asymmetries
4He Preliminary Results
Q2 = 0.07725 ± 0.0007 GeV2
Araw = 5.253 ppm 0.191 ppm (stat)
Raw Parity Violating Asymmetry
Helicity Window Pair Asymmetry
35 M pairs, total width ~1130 ppm
Araw correction ~ 0.12 ppm
Slug
Asym
metr
y
(pp
m)
1H Preliminary Results
Q2 = 0.1089 ± 0.0011GeV2
Araw = -1.418 ppm 0.105 ppm (stat)
Araw correction ~11 ppb
Raw Parity Violating Asymmetry
Helicity Window Pair Asymmetry
~25 M pairs, width ~540 ppm
Asym
metr
y
(pp
m)
Slug
June 2004HAPPEX-He• about 3M pairs at 1300 ppm
=> Astat ~ 0.74 ppm
June – July 2004HAPPEX-H• about 9M pairs at 620 ppm
=> Astat ~ 0.2 ppm
July-Sept 2005HAPPEX-He• about 35M pairs at 1130 ppm
=> Astat ~ 0.19 ppm
Oct – Nov 2005HAPPEX-H• about 25M pairs at 540 ppm
=> Astat ~ 0.105 ppm
HAPPEX-II
Q2=0.091 GeV2
Q2=0.099 GeV2
Q2=0.077 GeV2
Q2=0.109 GeV2
Example: The window pair statistical error is 620 ppm for 2004 HAPPEX-H.
Recent Happex Publications – 2004 runs
Phys.Rev. Lett. 96, 022003 (2006)
Parity-Violating Electron Scattering from 4He and the Strange Electric Form Factor fo the Nucleon
GEs = -0.038 0.042(stat) 0.010(syst)
Constraints on the Nucleon Strange Form Factors at Q2 0.1 GeV2
Phys. Lett. B635 (2006) 275
GEs + 0.080GM
s = 0.030 0.025(stat) 0.006(syst) 0.012(FF)
Extrapolated from G0 Q2=[0.12,0.16]
GeV2
95% c.l.
2 = 1
Theory Calculations
16. Skyrme Model - N.W. Park and H. Weigel, Nucl. Phys. A 451, 453 (1992).
17. Dispersion Relation - H.W. Hammer, U.G. Meissner, D. Drechsel, Phys. Lett. B 367, 323 (1996).
18. Dispersion Relation - H.-W. Hammer and Ramsey-Musolf, Phys. Rev. C 60, 045204 (1999).
19. Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001).
20. Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, 055204 (2002).
21. Lattice - R. Lewis et al., Phys. Rev. D 67, 013003 (2003).
22. Lattice + charge symmetry -Leinweber et al, Phys. Rev. Lett. 94, 212001 (2005) & hep-lat/0601025
18
17
16
19
21 22
HAPPEX-II 2005 Preliminary Results
A(Gs=0) = +6.37 ppm
GsE = 0.004 0.014(stat) 0.013(syst)
A(Gs=0) = -1.640 ppm 0.041 ppm
GsE + 0.088 Gs
M = 0.004 0.011(stat) 0.005(syst) 0.004(FF)
HAPPEX-4He:
HAPPEX-H: Q2 = 0.1089 ± 0.0011 (GeV/c)2 APV = -1.60 0.12 (stat) 0.05 (syst)
ppm
Q2 = 0.0772 ± 0.0007 (GeV/c)2 APV = +6.43 0.23 (stat) 0.22 (syst)
ppm
HAPPEX-II 2005 Preliminary Results Three bands:
1. Inner: Project to axis for 1-D error bar
2. Middle: 68% probability contour
3. Outer: 95% probability contour
Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account
Preliminary HAPPEX 2005
data
World data confronts theoretical predictions
Preliminary results from 2005 data
16. Skyrme Model - N.W. Park and H. Weigel, Nucl. Phys. A 451, 453 (1992).
17. Dispersion Relation - H.W. Hammer, U.G. Meissner, D. Drechsel, Phys. Lett. B 367, 323 (1996).
18. Dispersion Relation - H.-W. Hammer and Ramsey-Musolf, Phys. Rev. C 60, 045204 (1999).
19. Chiral Quark Soliton Model - A. Sliva et al., Phys. Rev. D 65, 014015 (2001).
20. Perturbative Chiral Quark Model - V. Lyubovitskij et al., Phys. Rev. C 66, 055204 (2002).
21. Lattice - R. Lewis et al., Phys. Rev. D 67, 013003 (2003).
22. Lattice + charge symmetry -Leinweber et al, Phys. Rev. Lett. 94, 212001 (2005) & hep-lat/0601025
A simple picture of GEs – Scattering from a group of
randomly oriented electric dipoles formed by the pairs. Average over cross sections and deduce <GE
S>.
beam
aa
1/3 e
-1/3 e
)sin(23
1aqG s
E
In this simple picture the dipoles would have a separation of 2a 0.014F if GE
S = 0.004.
ss
qBreit = 1.594 F-1, for HAPPEX-II data
A recent fit to the world’s data for Q2<0.3GeV2
R. D. Young et al., nucl-ex/0604010
GEs = sQ2. s = -0.06 0.41 GeV2
GMs = s. s = 0.12 0.55 0.07
Strange form factors of the proton
Includes data from SAMPLE, PVA4, G0, HAPPEX (2004)
Lattice QCD calculation of GMs
D. B. Leinweber et al., PRL 94(2005)212001
GMs = (-0.046 0.019)n
QNP06 – A. W. Thomas, HAPPEX II result plus Leinweber calculation means contribute 10 MeV or less to the nucleon’s mass.
ss
Summary
• Suggested large values at Q2~0.1 GeV2
• Ruled out
• Possible large values at Q2>0.4 GeV2
• G0 backangle, finished Spring 2007• HAPPEX-III - 2008
• Large possible cancellation at Q2~0.2 GeV2
• Very unlikely given constraint at 0.1 GeV2
• G0 back angle at low Q2 (error bar~1.5% of p) maintains sensitivity to discover GM
S
Preliminary
0.6 GeV2
G0 backward
HAPPEX-III
GMs
GEs
Preliminary
Detailed Formulae: Clean Probe of Strangeness
Inside the Nucleon
• Measurement of APV yields linear combination of GsE, G
sM
• Sensitive only to GsE
Hydrogen
4He
Parity-violating electron scattering
p
AMEF AAAQGA
24
2
~ few parts per million
For a proton:
eAA
eA
sME
nME
nV
pME
pVW
ZME
RFsGG
GGRGRG
,,,2
, )1()1)(sin41(
For 4He: GEs alone
(but only available at low Q2)
Forward angle Backward angle
eA
pMWA
ZM
pMM
ZE
pEE GGAGGAGGA '2sin41 , ,
)(2
sin2
22
nE
pE
sE
WF
PV GG
GQGA
For deuterium: enhanced GA
e sensitivity
PV Electron Scattering to Measure Weak NC Amplitudes
EMEM JQ
M lQ
24
NCV
NCA
FNCPV JgJg
GM 5
5
22
Interference with EM amplitude makes NC amplitude accessible
22
~~Z
EM
NCPV
M
Q
M
M Z0
2~LR
LRPVA