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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

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