e.c. aschenauer varenna, july 2011 1. how do the partons form the spin of protons varenna, july 2011...

Varenna, July 2011 1

LECTURE IVWHAT DO WE REALLY

MEASUREE.C. Aschenauer

How do the partons form the spin of protons


SqDq

DG

Lg

SqLq

dq1Tf

SqDq

DG

Lg

SqLq dq1Tf

Is the proton looking like this?

“Helicity sum rule”

12h= P, 12 |J QCD

z |P, 12 = 12q

∑ Sqz+Sg

z+ Lqz

q∑ +Lg

z

total u+d+squark spin

angular momentum

gluonspin Where do we stand

solving the “spin puzzle” ?

E.C. Aschenauer


Probing the Proton Structure

EM interaction Photon

Sensitive to electric charge2

Insensitive to color charge

Strong interaction Gluon

Sensitive to color charge Insensitive to flavor

Weak interaction Weak Boson

Sensitive to weak charge ~ flavor Insensitive to color

E.C. Aschenauer

Main Underlying Processes in DIS

4Varenna, July 2011E.C. Aschenauer

Q2

q

g

q

g qg + + +

„Soft“ & Hard VMD:Elastic, diffractive,

non-diffractive minimum bias

Splitting of qq

hard QCD 22

if scattered lepton in detector

kinematics is knownxBj and Q2

can calculate parton kinematics

for DIS xBj = xparton Scale: pt or mq

x of parton is not known unfolding

very much like pp

Scale: Q2 pt can be big

+


Underlying processes in pp

E.C. Aschenauer

gqgq

qqqq

gggg

Mid-rapidity pp p0X dominated by gggg and gqgq

p0

p0

p0

g

g

ECAL

~

δq

q

δq

q

~

δq

q

δg

g

~

δg

g

δg

gkinematics is unknown

Scale: pT

parton kinematics needs to be unfolded in theo.

calculation

Forward-rapidity pp p0X dominated by gqgq

=3.3, s=200 GeV


Predictive power of pQCD

Hard Scattering Process

P2

x2P2

P1

x1P1

s

σ qg→ qg

D

q

π 0

(z )

X

q(x1)

g(x2)

“Hard” (high-energy) probes have predictable rates given:Partonic hard scattering rates (calculable in pQCD)Parton distribution functions (need experimental input)Fragmentation functions (need experimental input)

Universal non-perturbative functions

E.C. Aschenauer

DIS pQCD e+e-? σ (pp → π 0 X ) ~q(x

1) ⊗ g(x

2) ⊗ )σ qg→ qg (

)s) ⊗ D

q

π 0

(z )


Correlation pT – x and √s

E.C. Aschenauer

2-2.5 GeV/c4-5 GeV/c9-12 GeV/c

2-2.5 GeV/c4-5 GeV/c9-12 GeV/c

low pT low x scale uncertainty

high √s low x forward rapidity low x

x ~2pT

se−y


The Gluon Polarization

E.C. Aschenauer

unpolarised cross sections nicely reproduced in NLO pQCD

in NLO

RHIC: many sub-processes with a dominant gluon contribution

high-pT jet, pion, heavy quark, …


Does QCD work: Cross Sectionss=62 GeV (PRD79, 012003) s=200 GeV (PRD76, 051106) s=500 GeV (Preliminary)

Data compared to NLO pQCD calculations: s=62 GeV calculations may need inclusion of NLL (effects of threshold logarithms) s=200 and 500 GeV: NLO agrees with data within ~30% Input to qcd fits of gluon fragmentation functions DSS √s=200 GeV Jet Cross Sections agree with data in ~20%

E.C. Aschenauer

PRL 97, 152302


versus

Detected particle momentum

Proton spin

vector

Two-spin helicity asymmetry:

Can be large in pQCD hard scatter.

Stat. Unc. ~ (P12P2

2 L dt )1/2 One-spin helicity asym. AL violates parity if non-vanishing, but can be large in weak processes like W prod’n.

N++/L++ N+/L+N++/L++ + N+/L+

1P1P2

ALL

Single-spin transverse asym.

where () are defined with respect to reaction plane, is suppressed by chiral symmetry in pQCD hard scatter, but can occur via non-pert. aspects of initial and final-state spin dynamics.

N/L N/L1P1

AN N/L + N/L

Stat. Unc. ~ (P12 L

dt )1/2

versus

What We Measure

E.C. Aschenauer


Δg from inclusive DIS and polarized pp

E.C. Aschenauer

Scaling violations of g1

(Q2-dependence) give indirect access to the gluon distribution via DGLAP evolution. RHIC polarized pp collisions at midrapidity directly involve gluons

Rule out large DG for 0.05 < x < 0.2

dg1

d log(Q2 )~ −Δg(x,Q2 )

Current knowledge on Dg

constrained x-range still very limited

RHIC

DIS

EIC

DIS


Much more data

E.C. Aschenauer

STAR


Dq: W Production Basics

u 　　

d

Since W is maximally parity violating W’s couple only to one parton helicitylarge Δu and Δd result in large asymmetries.

No Fragmentation !

W+/ − μ+/ − / e+/ −

ν

μ / e/ ν

ν / e

ud → W +

du → W −

AL

W+

=σ↑ −σ↓

σ↑ + σ↓~

Δd (x1)u(x

2) −Δu(x

1)d (x

2)

d (x2)u(x

1) + d (x

1)u(x

2)

Similar expression for W- to get Δ and Δd…

u

E.C. Aschenauer

14

de Florian, Vogelsang

expectations for ALe in pp collisions

Varenna, July 2011

t large u large

strong sensitivity to Δu

t large u large

limited sensitivity to ΔdE.C. Aschenauer

15

RHIC: can detect only decay leptons; lepton rapidity most suited observable

• strong correlation with x1,2

allows for flavor separation for 0.07 < x < 0.04

RHIC: AL for W bosons

Varenna, July 2011

x

1,2~

MW

se±η / 2

Δχ2 = 2% uncertainty bands of DSSV analysis

Δχ2 = 2% uncertainty bands with RHIC data

de Florian, Vogelsang, arXiv:1003.4533

E.C. Aschenauer

ALW: First proof of principle


STAR

Need much

more

statis

tics (

300pb-1 ) t

o

compete

with

SIDIS

doubled statis

tics i

n 2011

E.C. Aschenauer


ALW: Future Possibilities

Can we increase p-beam energy? 325 GeV: factor 2 in sW

access to lower x for Dg(x)

Increased beam-energy and polarized He-3 beam full flavor separation

ALW:

pp

@ 5

00 G

eV

ALW

: H

e3-p

@ 4

32 G

eV

phase 2 of pp2pp@STAR can separate scattering on n or p

E.C. Aschenauer

Quantum phase-space tomography of the nucleon

3D picture in momentum space 3D picture in coordinate space transverse momentum generalized parton distributions dependent distributions exclusive reaction like DVCS


Polarized p d-quarku-quark Polarized p

Join the real 3D experience !!

TMDs GPDs

Wigner DistributionW(x,r,kt)

d3 r

d 2ktdz

E.C. Aschenauer

More insights to the proton - TMDs

Varenna, July 2011

Unpolarized distribution function q(x), G(x)

Helicity distribution function Dq(x), DG(x)

Transversity distribution function dq(x)

kr⊥q

Correlation between and rs⊥

q

kr⊥q

Correlation between and rS⊥

N

Correlation between and rs⊥

q rS⊥

N

Sivers distribution function

f1T⊥

Boer-Mulders distribution function

h1⊥

Single Spin Asymmetries

beyond collinear pictureExplore spin orbit correlations

peculiarities of f^1T

chiral even naïve T-odd DFrelated to parton orbital

angular momentumviolates naïve universality of

PDFsQCD-prediction: f^1T,DY = -f^1T,DIS

19E.C. Aschenauer

Processes to study Single Spin Asymmetries

Varenna, July 2011

γ*

u,d,s

p,K

polarized SIDISdqf, f^1Tpolarized pp scattering

? dqf, f^1T?

u,d,s,g

u,d,s,g

p,K,gjet

20

polarized DYf^1T

u,d,s

g*

e+/m+

e-/m-

u, d , s

E.C. Aschenauer

u 　　 d

W+/ −

μ+ / − / e+ / −

ν

μ / e/ ν

ν / e

polarized W-prod.f^1T


Single Transverse Spin Asymmetries Fermilab E-704 reported

Large Asymmetries AN Could be explained as

Transversity x Spin-dep. fragmentation (Collins effect),

Intrinsic-kT imbalance (Sivers effect) , or

Twist-3 (Qiu-Sterman, Koike)

Or combination of above

Left Right

E.C. Aschenauer

pp → πX at s =19. 4GeV


Transverse single-spin asymmetries

E.C. Aschenauer

ANL ZGSs=4.9 GeV

BNL AGSs=6.6 GeV

FNAL s=19.4 GeV

BRAHMS@RHIC s=62.4 GeV

left

right

p0

Big single spin asymmetries in pp !!

Naive pQCD (in a collinear picture) predicts AN ~ asmq/sqrt(s) ~ 0

What is the underlying process?Sivers or Twist-3 or Collins or ..

Do they survive at high √s ?Is pt dependence as expected from p-QCD?


Transverse Polarization Effects @ RHIC

E.C. Aschenauer

Left

-Right

Phys. Rev. Lett. 101 (2008) 222001 midrapidity: maybe gluon Sivers????


What is seen at RHIC

E.C. Aschenauer

No strong dependence on s from 19.4 to 200 GeV Spread probably due to different acceptance in pseudorapidity and/or pT xF ~ <z>Pjet/PL ~ x : shape induced by shape of Collins/Sivers Sign also consistent with Sivers and/or Transversity x Collins

need other observables to disentangle underlying processesDo we understand the theory


Azimuthal angles and asymmetries

E.C. Aschenauer

(φ−φS)angle of hadron relative to initial quark spin (Sivers)

(φ+φS) angle of hadron relative to final quark spin (Collins)

1T1 Df Sivers

11 Hh Collins

SIDIS allows to study subprocesses individuallyat RHIC we can unfortunately not define the 2 planesOnly idea is to define a reaction plane in pp like in AA


How to disentangle Sivers and Transversity

E.C. Aschenauer

Processes Universality vs non-universality: Semi-Inclusive deep inelastic scattering ✔ Drell-Yan ✔ e+/e- annihilation ✔ p + p h1 + h2 + X ! ! arXiv:1102.4569

✔

TMD PDF is not just non-universal,it is ill-defined at the operator level ! work has started to fix this problems

Watch out for sign flips !

BUT

zx

y

Colliding beams

proton spin

parton kTx

Sivers:AN for direct photonsAN for jetsAN for dijetsAN for WsAN for heavy flavour gluon Sivers

Transversity:AN for angular modulation of p in around jet axisInterference fragmentation function


STAR: Upcoming physics topics

Forward Meson SpectrometerWith projectionGoal = 20 pb-1

Final = ~ 27.4 pb-1

~137%

Calorimeter High TowerWith projectionGoal = 20 pb-1

Final = ~ 22.2 pb-1

~111%

Sampled Luminosity for STAR FY11 pp 500 Transverse data set

Nice data set to studyAN – jet: Sivers fct.AN for single lepton from W+/-:Sign change in Sivers fct. compared to SIDISAN

for dijets: Sivers fct. via back to back imbalance of 2 jets

W+e++X

W-e-+XE.C. Aschenauer


What do we know: Twist-3 vs. TMD

QLQCD QT/PT <<<<QT/PT

Collinear/twist-3

Q,QT>>LQCD

pT~Q

Transversemomentumdependent

Q>>QT>=LQCD

Q>>pT

Intermediate QT

Q>>QT/pT>>LQCD

Sivers fct.Efremov, Teryaev;

Qiu, Sterman

DIS: attractiveFSI

Drell-Yan: repulsiveISI

QCD:

SiversDIS = - SiversDY

critical test for our understanding of TMD’s and TMD factorization

E.C. Aschenauer


• latest twist: “sign mismatch”

1st kT moment of Sivers fct and twist-3 analogue related at operator level

Kang, Qiu, Vogelsang, Yuan

Boer, Mulders, Pijlman;Ji, Qiu,, Vogelsang, Yuan

both sides have been extracted from data

find: similar magnitude ✓but wrong sign ✖

inconsistency in formalism?

possible resolutions: (1) data constrain Sivers fct only at low kT; function has a node

(2) analysis of Tq,F neglects possible final-state contributions to AN

phenomenological studies with more flexible Sivers fct. under wayKang, Prokudin

need data for AN which are insensitive to fragmentation: photons, jets, DY

• on the bright side: recent progress on evolution for Sivers fct Kang, Xiao, Yuan

crucial for consistent phenomenology – properly related experiments at different scales

from sign changes to sign mismatches

gT

q,F(x, x) =− d 2∫ k

⊥

| k⊥|2

Mf1T

⊥q (x, k⊥

2 )SI DI S

E.C. Aschenauer

30

New Global Fit

Varenna, July 2011

Parameterization:

f

1T

⊥q ~ xα

q (1 −x )β

q (1 −ηqx )shape ala DSSV node if ηq>0

Data-Input: HERMES and COMPASS SIDIS & STAR p0

Impact on DY AN

Anselmino et al. 2009A. Prokudin, Z.-B. Kang

need to measure DY xf < 0.3

E.C. Aschenauer


u,d,s

g*

e+/m+

e-/m-

u, d , s

DRELL-YAN

or how to suppress backgrounds by a factor of 1000 and more

Comments…

partonic luminosities increase with s

net result is that DY grows with s largest s probes lowest x

Consider large-xF DY at s=500 GeV

Collision Energy Dependence of Drell Yan Production

32

qq→ γ * has σ ~ 1/ s

x ~2pT

se−y xf =x1 −x2

M 2 =x1x2s x2 ~M 2 / (xF s)

Varenna, July 2011E.C. Aschenauer

Kang & Qiu PRD 81 (2010) 054020

Prediction of AN using TMDs Sivers fct based on fit to HERMES & COMPASS


Backgrounds to DY production

E.C. Aschenauer

Most dominat background sources QCD 22 Heavy flavour photon conversion in material All charged particle pairs between J/ and Hadron suppression 103-104 needed at 500 GeV

Drell Yan signal reduced in 200 GeV forward

200 GeV 500 GeV


Heavy flavor contributions

E.C. Aschenauer

More low mass heavy flavor in forward directions

Charm & bottom contributions increase with minv

Comparison at minv < 3 GeV/c2 needs more studies See previous slide Smaller energy cut


QCD jet background

E.C. Aschenauer

Drell Yan signal 3 – 10 GeV/c2

Energy cut E1,2 > 2 GeV

Forward rapidities Effectively no

background left Statistically limited Drell Yan

for minv < 3 GeV/c2 not physical (PYTHIA settings)


ANDY @ IP-2

E.C. Aschenauer

Idea: have DY feasibility test at IP-2

staged measurements over 3 years

re-use as much detector equipment as possible to finish till summer 2014 Measurement:

why IP-2 transverse polarization measure parallel to

√s = 500 GeV W-program h > 3, M>4 GeV

0.1<xf<0.3 optimizes

Signal / Background & DY rate measure dAN

DY ~0.015 for ∫ L~100 pb-1

Proposal approved June 2011 BNL PAC

Final configuration 2013


arXiv:1103.1591 jet AN measurements are required to clarify signs of quark/gluon correlators related to Sivers functions.

from p+pp

“old” Sivers function

“new” Sivers function

s=200 GeV

Run11 Goal: AN for jets With ~10 pb-1 & P=0.50 ANDY run11 can measure AN(Jet).

Determine whether AN(jet) is non-0 isa requirement for AN(DY) sign-flip measurement

E.C. Aschenauer


Conclusions

E.C. Aschenauer

Many new avenues for further important

measurements and theoretical developments

we have just explored the tip of the iceberg

you are here

Lq,g

Ds

Dg

Dutot, Ddtot

Du, Dd

spin sum rule

Thank you for your attention

TMDs

Finish your PhDs and

join us as postdocsto unravel the puzzle around

kt in PDFs


BACKUP


Measuring TMDs

E.C. Aschenauer

Measure AN for identified hadrons in pp and pHe3

flavor separation test of current extractions of u and d PDFs

planed upgrade of pp2pp @ STAR can tag the scattering occurred on the p or n


AN in 3He-proton collisions Sivers fcts. for u and d quarks opposite in sign and slightly larger for d quarks

Z. Kang @ 2010 Iowa RSC meeting

• u <-> d isospin rotation leads to different signs for AN for protons and neutrons

• asymmetries for neutrons are larger (due to electric charges)

expectations for Drell Yan

proton

neutron

expectations for AN (pions)

• similar effect for π± (π0 unchanged)

this time computed within twist-3 formalism here, effect due to favored/unfavored fragmentation

caveat:does not yet includepossibility of nodesin Sivers function

3He: helpful input for understanding

of transverse spin phenomena

The long term future future of pp@RHIC

To do it well we need detector upgrades

E.C. Aschenauer


what do we mean by “Direct”….

p0

Prompt“Fragmentati

on”much better

called internal

bremsstrahlung

Induced

EM & Weak Decay

proton – proton:

g

Fragmentation

Au – Au or d-Au

Thermal Radiation

QGP / Hadron Gas

De-excitationfor excited states

(1) (2) (3) (4) (5)

(6)

E.C. Aschenauer


What is in Pythia 6.4 Processes included which would fall under prompt (1)

14: qqbar gg 18: qqbar gg (19: qqbar gZ0 20: qqbar gW+ 29: qg qg 114: gg gg 115: gg gg (106: gg J/Psi g 116: gg Z0 g )

initial and final internal bremsstrahlung (g and g) (3) Pythia manual section 2.2

Process 3 and 4 are for sure not in pythia

I’m still checking 5

the decay of resonances like the p0 is of course in pythia

E.C. Aschenauer


GRSV curves and data with cone radius R= 0.7 and -0.7 < < 0.9

ALL systematics

(x 10 -3)

Reconstruction + Trigger Bias

[-1,+3] (pT dep)

Non-longitudinal Polarization

~ 0.03 (pT dep)

Relative Luminosity

0.94

Backgrounds 1st bin ~ 0.5Else ~ 0.1

pT systematic 6.7%

STAR

Inclusive Jet Asymmetry at s=200 GeV

E.C. Aschenauer

STAR: Large acceptance Jets have been primary probe Not subject to uncertainties

on fragmentation functions, but need to handle complexities of jet reconstruction

Helicity asymmetry measurement

e+


Detector Developments: PHENIX

E.C. Aschenauer

Move from a 4 armdetector to a more standard high energy detector


Detector Developments: STAR

E.C. Aschenauer

Forward instrumentation optimized for p+A and transverse spin physicsCharged-particle trackinge/h and g/p0 discriminationBaryon/meson separation

Discussions on a bigger forward upgrade ongoing eSTAR


Additional info on Jets

E.C. Aschenauer

x1= 1

s(p

t3

eη3 + p

t4

eη4 )

x2= 1

s(p

t3

e−η3 + p

t4

e−η4 )

M = x1x

2s

η3+ η

4= ln

x1

x2

Di-jet Kinematics:


Coincidence Transverse Spin Measurements Should Unravel Transversity, Collins, Sivers Effects

Study transversity by exploiting chiral-odd fragment’n “analyzing powers” (Collins or interference frag. fcns.) calibrated at BELLE

Search for spin-dependent transverse motion preferences inside proton via predicted leading-twist spin-dependent deviation from back-to-back alignment of di-jet axes study unique to RHIC spin

p

p

q

g

Jets with 2 hadrons detected

+

+ …

p

p q

q

parton kT

p spin

Predictions from Boer & Vogelsang for various gluon Sivers models

AN

Unravel the underlying process for AN

E.C. Aschenauer


At qg q vertex:

½ + 1 ½ q and g have opposite spin projections (g can’t have proj’n zero along its momentum dir’n!), same helicitiesÞ aLL = +1 at all *; |M|2 1/cos2(

*/2)Þ Dominates for in incident q

direction!

^

At qq vertex: szq flips!

At qgq vertex: exchanged q and g must have opposite spin projections!

So, incident q and g must have same sign spin proj’ns opposite helicities Þ aLL = -1 at all *; |M|2 cos2( */2)

Þ vanishes for in incident q direction, contributes equally with first diagram for opposite q

^

Bottom line: aLL varies from 0 to 1 as * goes from 0 to 180° and ( *) strongly increases!

^

Spin Correlation for QCD Compton Scattering

E.C. Aschenauer


<z>

<xq>

<xg>

NLO pQCD

Jaeger,Stratmann,Vogelsang,Kretzer

T

B

N S

Pb-glass arrays

STAR Forward Pion Detectors Permit Study of Hadron Prod’n @

High Rapidity

High-energy 0 in this region are

predominantly high-z fragments from asymmetric q-g

scattering @ moderate pT

E.C. Aschenauer

pp → π 0 ; η

π= 3. 8; s = 200GeV

Star: Forward Physics program


add electromagnetic calorimetry at forward rapidity access low and high x x ~

2pT

se−y

2003: FPD: 3.3 < < 4.1TPC: -1.0 < < 1.0BEC: -1.0 < h < 1.0

TPC: -1.0 < < 1.0BEC: -1.0 < h < 1.0

2008: FMS: 2.5 < < 4.1

E.C. Aschenauer


Deep Inelastic Scattering

E.C. Aschenauer

( , )E k( ', ')E k

q

Important kinematic variables:

cross section:

DF FF2

~'

Ld

d dEWμ

νν

μσ

W μν =−gμνF1 −

pμ pν

νF2 +

iνε μνλσqλsσ g1 +

i

ν 2ε μνλσqλ (p⋅qsσ −s⋅qpσ )g2

−rμνb1 +

16(sμν + tμν +uμν )b2 +

12(sμν −uμν )b3 +

12(sμν −tμν )b4

Spin 1

'E Eν 2

2

Qx

Mv

hEz

ν

Photon:

Hadron:

Quark:

2tp

Fixed target:

Q2 =−q2 =−(k−k')2 =4EE'sin2Θ2

'E Eν

hEz

ν

Photon:

Hadron:

Quark:

2tp

Collider:

Q2 =−q2 =−(k−k')2 =2EeEe'(1+cosΘe)

x =Q2

sy


truncated moment (“RHIC pp region”)

bottom line:

RHIC pp data clearly needed (current DIS+SIDIS data alone do not constrain Δg)

new (SI)DIS data do not change much for Δg trend for positive Δg at large x (as before)

truncated moment (“high x”)

Δg and the relevance of RHIC data

E.C. Aschenauer

STAR forward detectors

54

≈ 6 Lint spaghetti calorimeter10cm x 10cm x 120 cm “cells”

DX shell R ~ 60cm

Proposed FHC(for jet & lambda)

FMSIn open position

x~50cm from beam

FTPC (to be removed next year)

Varenna, July 2011

No space for FHC near beamNo space in front of FMS neither

E.C. Aschenauer


Much more data

E.C. Aschenauer

Phys. Rev. D 79, 012003 : √s = 62.4 GeV

Direct photon

η ALL : Phys. Rev. D 83, 032001

DY Signal

56

Everything h>2

FMS closed(FHC cannot be placed dueto DX magnet)

FMS open (x=50cm)+ FHC (x=60cm)

pythia6.222, p+p @ √s=500DY process, 4M events/6.7E-05mb ~ 60/pbe+/e- energy>10GeV & h>2xF>0.1 (25GeV)4GeV < invariant mass < 10GeV

Inv Mass E pT

14799 events

6512 events

1436 events(1/5 from closed)

Varenna, July 2011E.C. Aschenauer

e.c. aschenauer varenna, july 2011 1. how do the partons form the spin of protons varenna, july 2011...

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