1

Future of Transverse Spin at

RSC Meeting, Ames, Iowa, May 15th

Anselm Vossen

2

• What contributes most of the visible mass in the universe?

– Not Higgs: The QCD interaction!

• SPIN is fundamental quantity:What role does it play in strong interactions?

Interesting transverse spin effects help us understand QCD

Transverse Spin allows to probe Matrix elements via Interference

RHIC is the only place with polarized proton collisions in the foreseeable future

Test Factorization Explore role of soft interactions How and why is pp->hadrons

different from SIDIS & DY

Motivation for Transverse Spin PhysicsMotivation for Transverse Spin Physics

3

Still not understood…

• Several orders of magnitude in sqrt(s)• Several theoretical frameworks…• Effects strong in forward direction• Valence quark effect in parton picture

A N(%

)

4

Next decadal Plan: Full Forward Spectrometer• Coverage in 2 < < 4 (2o < < 30o)• Needs Open Geometry

• replace current central detector with a new one covering || =< 1

• replace South muon arm by a endcap spectrometer able to do all the physics on the next slides

60cm

2T Solenoid

Silicon TrackerVTX + 1 layer

Silicon TrackerFVTX

1.2 < < 2.7 8o < < 37o

North Muon Arm

68cm

IP

80cm

145cm

5

Subsystems

• Charged Particle Tracking• RICH allows PID up to high momenta: Flavor decomposition• EM Cal: Neutral particles • HCAL: Hadrons and jet reconstruction• Dedicated Magnet?• Jets!

Tracking

6

Mechanisms for AN (An Outline)• Spin dependent quark distributions

– TMD picture: Sivers– Collinear Picture: Twist3 pdfs→Tests of Factorization

• Spin dependent Fragmentation– Collins Effect– Interference Fragmentation Function

• Flavor separation for all of the above

• More forward physics– Charm AN

– Lambda– …

M. Boglione at DIS09

7

Collinear, Unpolarized Factorization is valid in the forward region

8

Spin Dependent Quark Distributions

• Twist 3

– One hard scale (pt)

• Sivers TMD + soft gluon interaction

• One hard, one soft scale• TMD factorization not proven for pp->hX (counterexample)• DY should work

twist-3PRD 74, 114013

ST

P

xP

9Shape like Hermes Sivers measurement

In SIDIS turnover seems to be at around 1 GeV in pT

Scale Dependence

PheniXAN in MPC:

TurnaroundAt pT~ 3GeV??

10

Sivers in Different Configurations

• Open Questions– Factorization: Does it break, how much?– How does PP compare to DY and DIS (Kinematics similar)

DIS: attractive Drell-Yan: repulsive Proton-Proton ?

(Werner Vogelsang)

11

Flavor Decomposition can answer differences between pp and SIDIS

• Role of Strange Quarks• Additional interesting Channels

– Vector Mesons

12

Sivers Channels

• Crucial: Jet Measurements to get initial parton kinematics

• Back To Back Jets

• Photon-Jet

• Possible Correlations– Forward – Forward– Forward – Central– Forward – Backward (isolated photons in

MPC)

13

Kinematic Coverage of New Arm• Min Energy of 20GeV (inclusive pions)• One jet forward, EJet>20GeV, One jet in central arm

xF

PT

xF

PT

Q2

pT Q2

pTPythia, Tune100, sqrt(s)=200GeV, only hard processes, all units in GeV

14

Compass observed possible W dependence

• One mechanism to explain Discrepancy to HERMES• More Input required

W in DIS: Mass of hadronic systempp equivalent:

1 2s x x s

15

Kinematics

Q2

Q2

xBj

xBj

COMPASS

HERMES

Jets

Inclusive Pions

16

• W is not large• Jet energy > 20GeV• W can be reconstructed in di-jet events->Test of COMPASS observation

xF

Jets

Inclusive pions

WW

WInclusive pions

W

xF

xF

17

Shape of Expected Sivers Asymmetries

• Gauss around 0.3, width 0.4, Amp. 0.3

• Not taking into account the partial cancellation between u and d

ASivPT

18

With FVTX: Measure F, D type Sivers and Tri-Gluon Functions

model trigluon correlation functions

using ordinary unpolarized gluon

distribution function : A rough estimate

PRD 78,114013quark-gluon negligible

T(f) = T(d) = 0

T(f) = T(d)

T(f) = -T(d)

trigluon

Charm AN with FVTX:Vast improvement

19

Spin Dependent Fragmentation

• Needs one reconstructed jet

• Coupling to transversity

• Collins effect (also Twist3 analogues)

• Interference Fragmentation Function

20

Chiral odd FFs

+

_

+

1h

_

+

_1H

Collins effect

q

N

: Collins FF

21

The Collins effect in the Artru fragmentation model

π+ picks up L=1 tocompensate for thepair S=1 and is emittedto the right.

String breaks anda dd-pair with spin-1 is inserted.

A simple model to illustrate that spin-orbital angular momentum coupling can lead to left right asymmetries in spin-dependent fragmentation:

In Artru Model: favored (ie u) and disfavored (ie u) Collins function naturally of opposite sign

Jet direction

22

Observables: Azimuthal Asymmetries of Hadrons around Jet Axis

pT

Tests Transversity at high x, high z– High x: Tensor Charge

Connection to Lattice

• Again: what does u, d quark

sign difference mean for us? ACol

pt

z

Mean z: 0.64

PT

23

Chiral odd FFs

+

_

+ _

+ q

N

_

Lz-1Lz

1H

Interference Fragmentation Function

( )

1h

24

Advantages of IFF• Independent Measurement

• Favorable in pp: no Sivers

• Transverse momentum is integrated– Collinear factorization

– No assumption about kt in evolution– Universal function– Evolution known, collinear scheme can be used – Directly applicable to semi-inclusive DIS and pp

• First experimental results from HERMES, COMPASS, PHENIX

25

IFF as Measured by BELLE

Charm contributions unaccounted RHIC could shed light on flavor composition etc…

MInv

Invariant mass in new Arm

26

Combined Analysis: Extract Transversity Distributions

Transversity, δq(x)Tensor Charge

Lattice QCD: Tensor Charge

Factorization + Universality ?!

Theo

rySIDIS

~ δq(x) x CFF(z)~ δq(x) x IFF(z)

e+e-

~ CFF(z1) x CFF(z2)~ IFF(z1) x IFF(z2)

pp jets

~ G(x1) x δq(x2) x CFF(z)

pp h+ + h- + X~ G(x1) x δq(x2) x IFF(z)

pp l+ + l- + X~ δq(x1) x δq(x2)

27

AN for He3

• Predictions by Umberto D’Alesio, with DSS FF• Sign Flip due to isospin

Measurement would test Universality, moderate & high x for u, d quarks

28

First Measurement of Forward Lambda’s

• Lambda Kinematics with , proton in Forward Arm

pt

xf

pt

29

Summary: What we will learn from Proton Proton

• Transverse Spin essential!• Test QCD• Measure Sivers, Collins & IFF

– Asymmetries expected to be large in forward direction– Cancellation between different flavors still unclear

• Asymmetries should be smaller than SIDIS, but AN large

• Color charges in initial and final states– Factorization– TMD, Collinear– Attractive, repulsive forces (color ‘anti-color’)

• Transversity at high X (should be faster than JLab..)• Lambdas• Local Parity Violation, other TMDs…• RHIC is the only place… for a long time!!

….and finally we will understand An and can lay it to its well deserved rest..

30

31

Backup

32

33

DCAR Shape• μ decay from D, B and hadrons have different DCAR shapes in a given

μ pT bin.• DCAR shape also depends on the parent particle and the decay μ pT.

Distributions are normalized according to PHENIX cross sections.

• Single particle shapes can be evaluated using MC.

• They can be fitted together to the merged event shape, to get B, D and BG contributions.

34

c and b Separation -- Results

Limitations:

Same pT spectra for B and D and same background sample are used in training sample and mixed sample.

Systematic error need to be quantified.

With 10 pb-1 statisticsWith achieved statistics

35

36

37

DCAR

);00

0(*0

)00

0(*0

22

22

recopyrecopx

recopyrecoy

recopyrecopx

recopxrecoxDCAR

DCAR = impact parameter projected onto μ pT.

38

Collins Fragmentation at Belle

• First extraction of transversity quark distribution

Together with HERMES, COMPASSFirst, still model dependent transversity Extraction :

Alexei Prokudin, DIS2008, update of Anselmino et al: hep-ex 0701006

Belle 547 fb-1 data set (Phys.Rev.D78:032011,2008.)

39

vs Invariant Mass of the Pair

sinUTA

First measurement of IFF in pp

beijing

40

Comparison to theory predictions

Leading order, experimental results might contain effects from gluon radiation not contained in the model

Mass dependence : Magnitude at low masses comparable, high masses significantly larger (some contribution possibly from charm )

Z dependence : Rising behavior steeper

However: Theory contains parameters based on HERMES data.

Initial model description by Bacchetta,Checcopieri, Mukherjee, Radici : Phys.Rev.D79:034029,2009.

41

Subprocess contributions (MC)

41

8x8 m1 m2 binning

charged B(<5%, mostly at higher mass)Neutral B (<2%)charm( 20-60%, mostly at highest masses)uds (main contribution)

Charm Asymmetries in simulated data consistent with zero!To be checked with charm enhanced sample

Data not corrected for Charm contributions

42

• Simulations: ~ 10(nb)-1

43

Other

• Lambda

• Local P viol

44

45

vs invariant mass of the pairsin

UTA

Added statistics from 2008 running NEWNo significant asymmetries seen at mid-rapidity.

46

Di-Hadron SSA in SIDIS

(both on proton target, sign convention different)

47

Motivation: Transversity Quark Distributions δq(x) fromTransverse Single Spin Asymmetries in Semi Inclusive Deep Inelastic Scattering

Collins- and IFF- asymmetriesin semi-inclusive deep inelastic scattering (SIDIS) and pp measure

~ δq(x) x CFF(z)

combined analysis with CFF from e+e- annihilation

Example: COMPASS results for Collins Asymmetries on proton target (see talk by H. Wollny)

4848

Definition of Vectors and Angles

1 2

1 2

1 2

p+p c.m.s. = lab frame

, : momenta of protons

, : momenta of hadrons

( ) / 2

: proton spin orientation

A B

h h

C h h

C h h

B

P P

P P

P P P

R P P

S

""""""""""""""""""""""""""""

""""""""""""""""""""""""""""

""""""""""""""""""""""""""""""""""""""""""

""""""""""""""""""""""""""""""""""""""""""

""""""""""""""

1hP""""""""""""""

2hP""""""""""""""

100 GeVAP""""""""""""""

100 GeVBP""""""""""""""

CP""""""""""""""

BS""""""""""""""

pp hhX

1 2hadron plane: ,

scattering plane: ,

h h

C B

P P

P P

""""""""""""""""""""""""""""

"""""""""""""""""""""""""""" : from scattering plane

to hadron planeR : from polarization vector

to scattering plane S

Bacchetta and Radici, PRD70, 094032 (2004)

2 CR""""""""""""""

49

50

51

52

53

54

55

What plots?

• X1, x2

• Eta, x1 (or greater x1)

• eta, pt

• X1, pt

• Collins, eta & (tagged) (eta, pt??)

56

57

Outline

• Jets sivers, photons,• Wernder, daniel back to back sivers (quark

sivers sehr grosse x) • Transversity > x ->Tensor charge• Collins in jets• DY• Lambda

• ip2

58

PRD 74, 114013 (2006) twist-3

59

60

Collins Fragmentation at Belle

• First extraction of transversity quark distribution

Together with HERMES, COMPASSFirst, still model dependent transversity Extraction :

Alexei Prokudin, DIS2008, update of Anselmino et al: hep-ex 0701006

Belle 547 fb-1 data set (Phys.Rev.D78:032011,2008.)

61

Collins Extraction of Transversity: model dependence from Transverse

Momentum Dependences!

),(

)(),(

)sin()sin(),()(

),(

22

,122

pzDdy

dkxqkddde

pzHdy

dkxqkddde

AhqhS

qq

hShqSqhS

qq

CollinsUT

Anselmino, Boglione, D’Alesio,Kotzinian, Murgia, Prokudin, TurkPhys. Rev. D75:05032,2007

k┴ transverse quark momentum in nucleonp┴ transverse hadron momentum in fragmentation

transv

ersity

Collin

s FF

hadron FFquark pdf

The transverse momentum dependencies are unknown anddifficult to obtain experimentally!

62

Transversity Quark Distribution

• Why is this so difficult to measure?

–

63

Handbag Diagrams

γγ**

u,d,u,d,ss

ee--

Optical Theorem:

=-m(forward scattering)

+

+ +

+

64

Transversity is Chiral Odd

_

+1h

_

+↑

↑ ↑

↑ ↓

↑ ↑

↓ _

• Helicity base: chiral odd

Need chiral odd partner => Fragmentation function

Difference in densities for ↑, ↓ quarks in ↑ nucleon

• Transversity base:

65

QED and QCD interactions (and SM weak interactions) conserve

helicity:

Cannot measure h1 inclusively

_

+1h

_

+

QED, QCD Preserve Helicity

•Helicity base: chiral odd

Need chiral odd partner => Fragmentation function

66

Chiral odd FFs

+

_

+

1h

_

+

_1H

Collins effect

q

N

: Collins FF

67

68

Kinematics

Put pics at 200 and 500 Gev here…

69

Xf

W W

pt

70

xF

W

W

71

in PT & Q2

• Min Energy of 20GeV (incl. pions)

Q2

pT

72

Jet KinematicsOne jet forward, EJet>20GeV, One jet in central arm

pT