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Πανεπιστήµιο Κύπρου<br />
Κ. Αλεξάνδρου<br />
Hadron Physics on the Lattice<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
Outline<br />
The Highlight of Lattice 2007- Reaching the chiral regime<br />
- Results using light dynamical fermions<br />
Twisted mass - ETMC (Cyprus, France, Germany, Italy, Netherlands, UK, Spain,<br />
Switzerland)<br />
Clover improved dynamical fermions - QCDSF/UKQCD<br />
Overlap fermions - JLQCD<br />
Hybrid approach - LHPC and Cyprus<br />
Staggered fermions:Charm Physics - HPQCD<br />
- Chiral extrapolation of lattice results<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
Lattice 2007: Highlights<br />
• Impressive progress in unquenched simulations using various<br />
fermions discretization schemes<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
ψ(n)<br />
Basics:<br />
a<br />
µ<br />
U µ (n)=e igaAµ(n)<br />
S = S G + S F Difficult to simulate --><br />
S F = ! (k)D(k,n)!(n)<br />
!O" =<br />
Lattice fermions<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
"<br />
k,n<br />
Integrate out<br />
# dUnd$ nd$ nO[U,$ ,$ ]e %S<br />
&<br />
n<br />
Z<br />
It is well known that naïve discretization of Dirac action<br />
S = d F 4 x !(x) # " ! + m%<br />
$ µ µ & !(x)<br />
' (<br />
!(x + µ)- !(x -µ)<br />
! !(x) = µ<br />
2a<br />
=<br />
90’s Det[D]=1 : quenched<br />
# dUndet[D]O[U,D %1 ]e %SG &<br />
n<br />
Z<br />
leads to 16 species<br />
A number of different discretization schemes have been developed to avoid doubling:<br />
Wilson : add a second derivative-type term --> breaks chiral symmetry for finite a<br />
Staggered: “distribute” 4-component spinor on 4 lattice sites --> still 4 times more species,<br />
take 4th root, non-locality<br />
Nielsen-Ninomiya no go theorem: impossible to have doubler-free, chirally<br />
symmetric, local, translational invariant fermion lattice action BUT…
Chiral fermions<br />
Instead of a D such that {γ 5 , D}=0 of the no-go theorem, find a D such that<br />
{γ 5 ,D}=2a D γ 5 D Ginsparg - Wilson relation<br />
Kaplan: Construction of D in 5-dimensions Domain Wall fermions<br />
Luescher 1998: realization of chiral symmetry but NO no-go theorem!<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
L 5<br />
Left-handed fermion<br />
right-handed fermion<br />
Neuberger: Construction of D in 4-dimensions but with use of sign function <br />
Overlap fermions<br />
D = 1 + !(D w )<br />
,<br />
2<br />
!(D ) = w Dw +<br />
D Dw<br />
w<br />
Equivalent formulations of chiral fermions on the lattice<br />
But still expensive to simulate despite progress in algorithms<br />
Compromise: - Use staggered sea (MILC) and domain wall valence (hybrid) - LHPC<br />
Rely on new improved algorithms<br />
- Twisted mass Wilson - ETMC<br />
- Clover improved Wilson - QCDSF, UKQCD, PACS-CS
Simulation of dynamical fermions<br />
Results from different discretization schemes must agree in the continuum<br />
limit<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Clark
Lattice 2007: Highlights<br />
Impressive progress in unquenched simulations using various<br />
fermions discretization schemes<br />
With staggered, Clover improved and Twisted mass dynamical<br />
fermions results are reported with pion mass of ~300 MeV<br />
PACS-CS reported simulations with 210 MeV pions!<br />
But no results shown yet<br />
RBC-UKQCD: Dynamical N F =2+1 domain wall simulations reaching ~300 MeV on ~3 fm<br />
volume are underway<br />
JLQCD: Dynamical overlap N F =2 and N F =2+1, m l ~m s /6, small volume (~1.8 fm)<br />
Progress in algorithms for calculating D -1 as m π physical value<br />
Deflation methods: project out lowest eigenvalues<br />
Lüscher, Wilcox, Orginos/Stathopoulos<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
Deflation methods in fermion inverters -Wilcox<br />
Solve linear system<br />
Twisted mass 20 3 x32 at κ cr<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
Lattice 2007: Highlights<br />
Impressive progress in unquenched simulations using various<br />
fermions discretization schemes<br />
With staggered, Clover improved and Twisted mass dynamical<br />
fermions results are reported with pion mass of ~300 MeV<br />
PACS-CS reported simulations with 210 MeV pions!<br />
But no results shown yet<br />
RBC-UKQCD: Dynamical N F =2+1 domain wall simulations reaching ~300 MeV on ~3 fm<br />
volume are underway<br />
JLQCD: Dynamical overlap N F =2 and N F =2+1, m l ~m s /6, small volume (~1.8 fm)<br />
Progress in algorithms for calculating D -1 as m π physical value<br />
Deflation methods: project out lowest eigenvalues<br />
Lüscher, Wilcox, Orginos/Stathopoulos<br />
Chiral extrapolations<br />
Using lattice results on f π /m π yield LECs to unprecedented accuracy<br />
Begin to address more complex observables e.g. excited states and resonances,<br />
decays, finite density<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
Chiral extrapolations<br />
Controlled extrapolations in volume, lattice spacing and quark masses: still needed<br />
for reaching the physical world<br />
Quark mass dependence of observables teaches about QCD - can not be obtained<br />
from experiment<br />
Lattice systematics are checked using predictions from χPT<br />
Chiral perturbation theory in finite volume:<br />
Correct for volume effects depending on pion mass and lattice volume<br />
Like in infinite volume<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
Pion sector<br />
Applications to pion and nucleon mass and decay constants<br />
e.g.<br />
m ! " m ! (L)<br />
m !<br />
f ! - f ! (L)<br />
f !<br />
= -<br />
= -<br />
(<br />
x<br />
$<br />
%<br />
2# Im !<br />
| ! n|!0<br />
'<br />
x<br />
#<br />
$<br />
! If "<br />
| ! n|"0<br />
(2) (#) + xIm!<br />
(2) (!) + xIf"<br />
x = m 2<br />
0<br />
0 2<br />
(4!f ) "<br />
, ! = m " | ! n | L<br />
Applied by QCDSF to correct lattice data<br />
r 0 =0.45(1)fm<br />
(4) (#)<br />
(4) (!)<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
%<br />
&<br />
&<br />
'<br />
G. Colangelo, St. Dürr and Haefeli, 2005<br />
Pion decay constant<br />
NLO continuum χPT
Twisted mass dynamical fermions<br />
Consider two degenerate flavors of quarks: Action is<br />
$<br />
( )<br />
S F = a 4 !(x) D w [U]+ m 0 + iµ" 5 # 3<br />
x<br />
!(x)<br />
Wilson Dirac operator untwisted mass<br />
Advantages: - Automatic O(a) improvement (at maximal twist)<br />
- Only one parameter to tune (zero PCAC mass at smallest µ)<br />
- No additional operator improvement<br />
Disadvantages: - explicit chiral symmetry breaking (like in all Wilson)<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Twisted mass µ<br />
τ 3 acts in flavor space<br />
- explicit breaking of flavour symmetry appears only at O(a 2 )<br />
in practice only affects π 0<br />
Physics results reported for ~300 MeV pions on spatial size of about 2.7 fm with a < 0.1fm
Pion decay constant with twisted mass fermions<br />
Simultaneous chiral fits to m π and f π<br />
r 0 =0.441(14)fm<br />
N F =2<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Extract low energy constants<br />
l ! log 3,4 " $ 2 '<br />
3,4<br />
& 2 )<br />
% m ±<br />
# (<br />
l 3 = 3.44(28), l 4 = 4.61(9)<br />
S. Necco,<br />
Lat07
ππ s-wave length a 0 0 and a0 2<br />
Leutwyler (hep-ph/0612112)<br />
ππ-scattering lengths<br />
ETMC<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
π-π scattering<br />
Lüscher’s finite volume approach:<br />
Calculate the energy levels of two particle states in a finite box<br />
!En = En - 2m = 2 p 2 2<br />
+ m - 2m<br />
n<br />
Expand ΔE 0 about p~0:<br />
with p n given by<br />
!E = - 0 4!a<br />
mL 3 1 + c (<br />
* 1<br />
)<br />
*<br />
a<br />
L + c 2<br />
" a %<br />
#<br />
$ L&<br />
'<br />
where we use particle definition for the scattering length:<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
2<br />
p cot !(p) = 1<br />
!L<br />
+<br />
-<br />
,<br />
- + O 1<br />
"<br />
L 6<br />
#<br />
$<br />
a = lim<br />
p!0<br />
%<br />
&<br />
'<br />
) !<br />
n<br />
tan"(p)<br />
p<br />
f( ! n)<br />
!<br />
n 2 " pL # &<br />
$<br />
% 2! '<br />
(<br />
Applied to I=2 two-pion system within the hybrid approach (staggered sea and domain<br />
wall fermions)<br />
m π a 0 2 =-0.0426(27)<br />
S. Beans et al. PRD73 (2006)<br />
2
More statistics<br />
mixed action χPT formula<br />
no new LECs<br />
Other applications: I=1 KK scattering<br />
π-π scattering - improved<br />
m π a 0 2 =-0.04330(42)<br />
A. Walker-Loud, arXiv:0706.3026<br />
form independent of sea quarks if valence are chiral<br />
N-N scattering - too noisy<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
Dynamical overlap, L~1.8 fm<br />
Pion form factor<br />
F ! (q 2 ) =<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
1<br />
1 " q 2 2<br />
/ m #<br />
+ d1q2 + ...<br />
F ! (q 2 ) = 1 " 1<br />
6 < r2 > q 2 + ...<br />
< r 2 1<br />
>= c " ln<br />
0 2<br />
(4!f ) ! m #<br />
%<br />
$<br />
Sh. Hashimoto<br />
2<br />
!<br />
(4!f ) ! 2<br />
&<br />
(<br />
'<br />
+ c1m 2<br />
!
4-point function: first application of the one-end trick (C. Michael):<br />
q<br />
G. Koutsou, Lat07<br />
-q<br />
Pion form factor<br />
S. Wilson Simula, ETM Collaboration<br />
one-trick for 3pt function<br />
VMD :<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
1<br />
1! q 2 2<br />
/ m "<br />
Set initial and final pion momentum to zero<br />
--> no disadvantage in applying the oneend<br />
trick
Pion form factor<br />
Comparison with experiment<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
S. Simula ,<br />
Lat07
Rho form factors<br />
decomposed into three form factors Gc (Q2 ), GM (Q2 ), GQ (Q2 )<br />
Decreasing quark mass<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Related to the ρ quadrupole<br />
moment G Q (0)=m ρ 2 Qρ<br />
Adelaide group: Q ρ non-zero --> rho-meson deformed in agreement with wave<br />
function results using 4pt functions<br />
One-end trick improves signal, application to<br />
baryons is underway<br />
G. Koutsou, Lat07<br />
Non-relativistic approx.<br />
|Ψ(y)| 2
Baryon sector<br />
Twisted mass and Staggered results<br />
Two fit parameters: m 0 =0.865(10), c 1 =-1.224(17) GeV -1 to be compared with ~-0.9<br />
GeV -1 (π-N sigma term)<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
Delta mass splitting<br />
Symmetry: u d --> Δ ++ is degenerate with Δ - and Δ + with Δ 0<br />
Check for flavour breaking by computing mass splitting between the two degenerate<br />
pairs<br />
Splitting consistent with zero in agreement with theoretical expectations that<br />
isospin breaking only large for neutral pions (~16% on finest lattice)<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007
Hybrid actions<br />
Wilson fermions<br />
Coupling constants: g A , g πNN , g πΝΔ , …<br />
Baryon structure<br />
Form factors: G A (Q 2 ), G p (Q 2 ), F 1 (Q 2 ),….<br />
Parton distribution functions: q(x), Δq(x),…<br />
Generalized parton distribution functions: H(x,ξ,Q 2 ), E(x,ξ,Q 2 ),…<br />
Masses: two-point functions <br />
Need to evaluate three-point functions: <br />
In addition:<br />
O(t, ! q) = d 3 x e !i! x. ! q<br />
"<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
#(x) $ D µ 1 µ 2 ( D ... )#(x)<br />
Four-point functions: yield detailed info on quark distribution<br />
only simple operators used up tp now - need all-to-all propagators
Nucleon axial charge<br />
Forward nucleon axial vector matrix element: < N | u! µ ! 5 u - d! µ ! 5 d | N >= g A v(p)! µ ! 5 v(p)<br />
Pleiter, Lat07<br />
Improved Wilson (QCDSF)<br />
HBχPT with Δ<br />
Hemmert et al. ,<br />
Savage & Beane<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
accurately measured<br />
no-disconnected diagrams<br />
chiral PT<br />
Finite volume dependence
Isovector form factors<br />
obtained from<br />
connected diagram<br />
Nucleon form factors<br />
Disconnected diagram not evaluated<br />
Isovector Sachs form factors:<br />
p n<br />
G = G ! G E E E<br />
p n<br />
G = G ! G M M M<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
In last couple of years<br />
better methods have<br />
become available,<br />
dilution, one-end trick,…<br />
with G E and G M given in terms of F 1 and F 2<br />
G E (q 2 ) = F 1 (q 2 ) +<br />
G M (q 2 ) = F 1 (q 2 ) + F 2 (q 2 )<br />
q 2<br />
(2m N ) 2 F 2 (q2 )<br />
Evaluation of 3pt function using the fixed<br />
sink approach --> any current to be inserted<br />
with no additional computational cost
Cyprus/MIT Collaboration, C. A.,<br />
G. Koutsou, J. W. Negele, A. Tsapalis<br />
q 2 =- Q 2<br />
Results using dynamical Wilson fermions<br />
and domain wall valence on staggered sea<br />
(from LHPC) are consistent<br />
Nucleon EM form factors<br />
F p = 2<br />
3 Fu ! 1<br />
3 Fd<br />
F n = ! 1<br />
3 Fu + 2<br />
3 Fd<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
QCDSF/UKQCD<br />
Dirac FF
Nucleon axial form factors<br />
Within the fixed sink method for 3pt function we can evaluate the nucleon matrix<br />
element of any operator with no additional computational cost<br />
A a<br />
= !" " µ µ 5<br />
2 !<br />
use axial vector current to obtain the axial form factors<br />
pseudoscalar density to obtain GπN (q2 )<br />
Pa #<br />
= !i" 5<br />
a<br />
2 !<br />
< N( ! 2<br />
3 ! " m %<br />
N<br />
p ! , s ! ) | A | N( p,s) >= i<br />
µ<br />
$<br />
# E ( p ! )E (p)<br />
'<br />
N N &<br />
2m < N( q ! p ! , s ! ) | P 3 | N( ! 2 " m %<br />
N<br />
p, s) >= $<br />
# E ( p ! )E (p)<br />
'<br />
N N &<br />
PCAC relates G A and G p to G πNN :<br />
Pion pole dominance:<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
# a<br />
1/2<br />
G (Q A 2 ) - Q2<br />
2<br />
4mN Gp (Q2 ) = 1<br />
2mN 1<br />
2m N<br />
u( !<br />
1/2<br />
)<br />
p ) G (Q A 2 )( ( + µ 5 q µ ( 5<br />
+<br />
2mN * +<br />
2<br />
f m G!NN (Q ! !<br />
2 )<br />
2 2<br />
m + Q !<br />
2<br />
f m G!NN (Q ! !<br />
2 )<br />
2 2<br />
m + Q !<br />
G (Q p 2 ) ~ 2G !NN (Q2 )f !<br />
2 2<br />
m + Q !<br />
u( p ! ) i( 5<br />
G (Q p 2 ,<br />
) .<br />
-.<br />
) 3<br />
2 u(p)<br />
/ 3<br />
Th. Korzec<br />
2 u(p)<br />
Generalized Goldberger-<br />
Treiman relation<br />
! G !NN (Q 2 )f ! = m N G A (Q 2 ) Goldberger-Treiman relation
monopole fit<br />
G A and G p<br />
monopole fit to<br />
experimental results<br />
pion pole dominance<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Results in the hybrid approach<br />
by the LPHC in agreement with<br />
dynamical Wilson results<br />
Unquenching effects large<br />
at small Q 2 in line with<br />
theoretical expectations that<br />
pion cloud effects are<br />
dominant at low Q 2<br />
Cyprus/MIT collaboration
N to Δ transition form factors<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Electromagnetic N to Δ: Write in term of Sachs form<br />
factors:<br />
< !( ! p " , s " ) | j | N( µ ! p,s) >= i 2<br />
1/2<br />
# m m &<br />
! N<br />
3<br />
%<br />
$ E ( p " )E (p)<br />
( u<br />
! N '<br />
) ( ! p " , s " )O u( )µ ! p,s)<br />
O = G (q )µ M1 2 M1<br />
)K + G (q )µ E2 2 E2<br />
)K + G (q )µ C2 2 C2<br />
)K )µ<br />
Magnetic dipole:<br />
dominant<br />
Electric<br />
quadrupole<br />
Coloumb<br />
quadrupole<br />
Axial vector N to Δ: four additional form factors, C 3 A (Q 2 ), C4 A (Q 2 ), C5 A (Q 2 ), C6 A (Q 2 )<br />
PCAC relates C5 A and C6 A to GπΝΔ :<br />
Pion pole dominance:<br />
A 2 Q<br />
C (Q ) ! 5<br />
2<br />
2<br />
mN C A 2 1<br />
(Q ) = 6<br />
2m N<br />
1<br />
m N<br />
A 2 1<br />
C (Q ) ! 6<br />
2<br />
2<br />
f m G (Q " " "N# 2 )<br />
2 2<br />
m + Q "<br />
G !N" (Q 2 )f !<br />
2 2<br />
m + Q !<br />
# G (Q !N" 2 A 2<br />
)f = 2m C (Q )<br />
! N 5<br />
Dominant: C 5 A GA<br />
C 6 A G p<br />
Generalized non-diagonal<br />
Goldberger-Treiman relation<br />
Non-diagonal Goldberger-Treiman<br />
relation
Q 2 =0.127 GeV 2<br />
Quadrupole form factors and deformation<br />
C. N. Pananicolas, Eur. Phys. J. A18 (2003)<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Quantities measured in the lab frame of<br />
the Δ are the ratios:<br />
R EM (EMR) = ! G E2 (Q2 )<br />
G M1 (Q 2 )<br />
R SM (CMR) = ! | ! q |<br />
2m "<br />
G C2 (Q 2 )<br />
G M1 (Q 2 )<br />
Precise experimental data strongly suggest<br />
deformation of Nucleon/Δ<br />
First conformation of non-zero EMR and<br />
CMR in full QCD<br />
Large pion effects
Axial N to Δ<br />
Bending seen in HBχPT<br />
with explicit Δ - Procura et al.<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
A<br />
C6 SSE to O(ε 3 ):<br />
C 5 A (Q 2 ,mπ )=a 1 +a 2 m π 2 +a3 Q 2 +loop<br />
2<br />
mN = a 4 !<br />
1<br />
2 2<br />
m + Q "<br />
$<br />
&<br />
% &<br />
2<br />
a + a m + a7Q 5 6 "<br />
2<br />
+loop(m ,c ,g ,g ,f ,#)<br />
" A A 1 "<br />
Again large unquenching<br />
effects at small Q 2<br />
'<br />
)<br />
( )
Curves refer to the quenched data<br />
G πΝ =a(1-bQ 2 /m π 2 )<br />
G πΝΔ =1.6G πΝ<br />
GTR: G πΝ =G A m N /f π<br />
G πΝN and G πΝΔ<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Q 2 -dependence for G πΝ (G πΝΔ )<br />
extracted from G A (C 5 A ) using the<br />
Goldberger-Treiman relation deviates at<br />
low Q 2<br />
Small deviations from linear Q 2 -<br />
dependence seen at very low Q 2 in the<br />
case of G πΝΔ<br />
G πΝΔ /G πΝ = 2C 5 A /GA as predicted by<br />
taking ratios of GTRs<br />
G πΝΔ /G πΝ =1.60(1)
Goldberger-Treiman Relations<br />
Deviations from GTR<br />
Improvement when using<br />
chiral fermions<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
1<br />
2m N<br />
1<br />
m N<br />
G (Q p 2 ) ! 2G !N (Q2 )f !<br />
2 2<br />
m + Q !<br />
" G !N (Q 2 )f ! = m N G A (Q 2 )<br />
A 2 1<br />
C (Q ) ! 6<br />
2<br />
G !N" (Q 2 )f !<br />
2 2<br />
m + Q !<br />
# G (Q !N" 2 A 2<br />
)f = 2m C (Q )<br />
! N 5
Four form factors: G E0 , G E2, G M1, G M3<br />
given in terms of a 1 , a 2 ,c 1 ,c 2<br />
Like for the nucleon form factors<br />
only the connected diagram is<br />
evaluated --> isovector part<br />
G E0<br />
Δ electromagnetic form factors<br />
Q 2 (GeV 2 )<br />
< !( ! p " , s " ) | j µ | !( ! p, s) >= i<br />
O #µ$ = % #$ a 1 i& µ + a 2<br />
m π =0.56 GeV<br />
m π =0.49GeV<br />
m π =0.41 GeV<br />
2m !<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
'<br />
)<br />
(<br />
( "<br />
2<br />
m !<br />
E ( " ! !<br />
p )E ( ! ! p) u ( p " , " #<br />
*<br />
p µ + p µ ) , - q# q $<br />
2<br />
+<br />
G M1<br />
2m !<br />
'<br />
)<br />
(<br />
Q 2 (GeV 2 )<br />
s )O#µ$ u $ (p,s)<br />
c 1 i& µ + c 2<br />
2m !<br />
( ! "<br />
p µ + ! p µ )<br />
m π =0.56 GeV<br />
m π =0.49 GeV<br />
m π =0.41 GeV<br />
Accurate results for the dominant form factors calculated in the quenched approximation.<br />
Unquenched evaluation is in progress - Cyprus/MIT Collaboration, C. A., Th. Korzec, Th. Leontiou J. W.<br />
Negele, A. Tsapalis<br />
*<br />
,<br />
+
Electric quadrupole Δ form factor<br />
G E2 connected to deformation of the Δ:<br />
G E2
Moments of parton distributions<br />
Parton distributions measured in deep inelastic scattering<br />
Forward matrix elements:<br />
< N(p, s) | O { µ 1 ...µ n}<br />
| N(p, s) >~ dx<br />
q<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
! x n-1 q(x)<br />
< x n > = dx x q n q(x) + (-1) n+1 1<br />
% !<br />
"<br />
q(x) #<br />
$<br />
q = q + q & '<br />
-1<br />
< x n > = dx x (q n<br />
1<br />
% (q(x) + (-1)<br />
-1<br />
n !<br />
"<br />
(q(x) #<br />
$ (q = q& - q' < x n > = dx x )q n<br />
! ! µ unpolarized moment<br />
1 ...µ n µ 1 µ µ<br />
O = q "<br />
2 ! i D ...i D n} $<br />
q #<br />
%<br />
polarized moment<br />
transversity<br />
1<br />
%<br />
-1<br />
q<br />
µµ 1 ...µ n O = q ! ! 5q<br />
5 µ i ! D µ ! µ "<br />
1 ...i D n} $<br />
#<br />
% q<br />
µ&µ 1 ...µ n O = q ! ' Tq<br />
5 µ& i ! D µ ! µ "<br />
2 ...i D n} $<br />
#<br />
% q<br />
!<br />
D = 1<br />
2 ( " D ( # Moments of parton distributions<br />
3 types of operators:<br />
D)<br />
)q(x) + (-1) n+1 !<br />
"<br />
)q(x) #<br />
$ )q = qT + q *
Moments of Generalized parton distributions<br />
Off diagonal matrix element Genelarized parton distributions<br />
$ n-1<br />
µ 1 ...µ n<br />
< N(p',s') | O<br />
{ } q<br />
| N(p,s) >= u( p ! ) &<br />
A q B<br />
Ani (t)K + Bni (t)K q<br />
&#<br />
ni<br />
ni<br />
i=0<br />
% &even<br />
GPD measured in Deep Virtual Compton Scattering<br />
p = 1<br />
p + !<br />
2 p ( ),<br />
t = #Q<br />
q = (x + ")p, q ! = (x # ")p<br />
2 = $ 2<br />
q C<br />
{ } + " C (t)K n,even ni n<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Generalized FF<br />
H n (!, t) " dx<br />
E n (!, t) " dx<br />
'<br />
) u(p)<br />
)<br />
( )<br />
1<br />
# x<br />
-1<br />
n-1 H(x, !, t)<br />
1<br />
# x<br />
-1<br />
n-1 E(x, !, t)<br />
H n (0, t) = A n0 (t) A 10 (t) = F 1 (t)<br />
E n (0, t) = B n0 (t) B 10 (t) = F 2 (t)<br />
t=0 (forward) yield moments of<br />
parton distributions<br />
GPDs
Transverse quark densities<br />
Fourier transform of form factors/GPDs gives probability<br />
Transverse quark distributions:<br />
u-d<br />
NLO: g A,0 --> g A,lat , same with f π<br />
Self consistent HBχPT<br />
LHPC<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
1<br />
dx x n-1<br />
! q(x, ! b ) = " d2 # "<br />
(2$ ) 2 ! e -i! b " . ! # !<br />
" q 2<br />
An0 (- #" )<br />
-1<br />
q(x % 1, ! b " ) & ' 2 (b " )<br />
M. Burkardt, PRD62 (2000)<br />
q(x, ! 2 d<br />
b ) = !<br />
2 " !<br />
(2# ) 2 $ e -i! b ! . ! " ! 2<br />
H(x,% = 0, -"! )<br />
as n increases slope of A n0 decreases
Total spin of quark:<br />
Spin of the nucleon:<br />
Spin structure of the nucleon<br />
J q<br />
q ( (0) ) L = J - q q 1<br />
1<br />
=<br />
2 < x > q +B20 QCDSF/UKQCD Dynamical Clover<br />
1<br />
2 = Lu+d + 1<br />
2 !" u+d + J g<br />
A20 (0)<br />
For m π ~340 MeV: J u =0.279(5) J d =-0.006(5)<br />
2 !" q<br />
L u+d =-0.007(13) ΔΣ u+d =0.558(22)<br />
In agreement with LPHC, Ph. Hägler et al., hep-lat/07054295<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
!" = ! q<br />
A (0) 10
Unpolarized<br />
d<br />
u<br />
Transverse spin density<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
q unpolarized N unpolarized<br />
N<br />
N<br />
u<br />
d
C. Alexandrou, University of Cyprus PSI, December 18th 2007
HPQCD: C. Davies et al.<br />
Charm Physics<br />
Determination of CKM matrix, Test unitarity triangle<br />
Weak decays - calculate in lattice QCD<br />
0.9 1.0 1.1 0.9 1.0 1.1<br />
Quenched<br />
Bench mark<br />
First message: Use unquenched QCD<br />
N f =2+1 dynamical<br />
staggered fermions<br />
Full QCD results show impressive agreement with<br />
experiment across the board - from light to heavy quarks<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Lattice QCD
Weak Decays and CKM matrix<br />
For charm use highly improved staggered action remove further cut off effects at<br />
α(amc )<br />
Leptonic D-meson decays:<br />
2 and (amc ) 4<br />
Semi-leptonic:<br />
in progress<br />
Lattice results versus experiment - CLEO-c<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
f Ds<br />
c<br />
d<br />
l<br />
ν<br />
f Ds /f D =1.164(11)
B-decays<br />
Use non-relativistic QCD for b-quark with m b fixed from m Υ<br />
f Bs /f Bq<br />
Log- dependence on<br />
light quark mass<br />
m q/ m s<br />
f B = 216(22) MeV,<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
f Bs<br />
f B<br />
= 1.20(3)<br />
to be compared with experiment<br />
ICHEP 06: f B =229(36)(34)MeV<br />
Semileptonic B-decays<br />
B-->πlν
Unitarity triangle<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007<br />
Using lattice input<br />
Expectation: errors on lattice results<br />
should halve in the next two years
Conclusions<br />
• Lattice QCD is entering an era where it can make significant contributions in<br />
the interpretation of current experimental results.<br />
• A valuable method for understanding hadronic phenomena<br />
Accurate results on coupling constants, Form factors, moments of<br />
generalized parton distributions are becoming available close to the chiral<br />
regime (m π ~300 MeV).<br />
More complex observables are evaluated e.g excited states,<br />
polarizabilities, scattering lengths, resonances, finite density<br />
First attempts into Nuclear Physics e.g. nuclear force<br />
• Computer technology and new algorithms will deliver 100´s of Teraflop/s in<br />
the next five years<br />
Provide dynamical gauge configurations in the chiral regime<br />
Enable the accurate evaluation of more involved matrix elements<br />
C. Alexandrou, University of Cyprus PSI, December 18th 2007