Nucleon Spin Structure...RHIC polarimetry (I) Measurement of degree of polarization • Elastic p-p Coulomb Nuclear Interference (CNI) measures absolute polarization employing a polarized

Nucleon Spin StructureLongitudinal Spin of the Proton

HUGS Summer SchoolJefferson National Laboratory

June 1-3, 2011 Lecture 4 of 6

Thursday, June 2, 2011

6/2/2011Abhay Deshpande, Nucleon Spin Lectures 4 of 6 at HUGS 2011

Introduction & Overview (II)

• Lecture 4 & Lecture 5– Relativistic Heavy Ion Collider as a Polarized Collider– Comments experimental techniques– Review of results– Principle limitations

• Lecture 6: Future studies in nucleon spin– Review of all experimental limitations– Non-Longitudinal spin structure of the proton– Status and possibilities at an Electron Ion Collider (EIC)

2Thursday, June 2, 2011


Complementary techniques

Photons colorless: forced to interact at NLO with gluons

Can’t distinguish between quarks and anti-quarks either

Why not use polarized quarks and gluons abundantly available in protons as probes ?



The RHIC Spin Program



The RHIC Spin Program• Direct determination of polarized gluon distribution via

multiple probes ( π0/+/-, γ, c-cbar,… production) – Double longitudinal helicity asymmetry: ALL









• Direct determination of anti-quark polarization using production and parity violating decay of W+/- – Single longitudinal spin asymmetry: AL











• Systematic study of transverse spin phenomena– Single transverse spin collisions – Possible connections: Orbital Angular Momentum (OAM)?



The probes and techniques at RHIC



RHIC as a Polarized Proton Collider

6

BRAHMS

STAR

PHENIX

AGS

LINACBOOSTER

Pol. H-‐ Source

Spin Rotators(longitudinal polarizaBon)

Siberian Snakes

200 MeV Polarimeter

Internal Polarimeter

pC PolarimetersAbsolute Polarimeter (H↑ jet)

pC Polarimeter10-‐25% Helical ParBal Siberian Snake

5.9% Helical ParBal Siberian Snake

PHOBOS

Spin Rotators(longitudinal polarizaBon)

Spin flipper

Siberian Snakes

Without Siberian snakes: νsp = Gγ = 1.79 E/m → ~1000 depolarizing resonancesWith Siberian snakes (local 180¡ spin rotators): νsp = ½ → no first order resonancesTwo parBal Siberian snakes (11¡ and 27¡ spin rotators) in AGS



Siberian Snakes

7

Ø AGS Siberian Snakes: variable twist helical dipoles, 1.5 T (RT) and 3 T (SC), 2.6 m long

Ø RHIC Siberian Snakes: 4 SC helical dipoles, 4 T, each 2.4 m long and full 360° twist

2.6 m 2.6 m

RIKEN

RIKEN

RIKEN RIKEN

DOE

Courtesy of A. LuccioThursday, June 2, 2011


Polarized Collider Development

8

Parameter Unit 2002 2003 2004 2005 2006 Design

No. of bunches -- 55 55 56 106 111 111

bunch intensity 1011 0.7 0.7 0.7 0.9 1.4 2.0

store energy GeV 100 100 100 100 100 100250

β* m 3 1 1 1 1 1

peak luminosity 1030cm-2s-1 2 6 6 10 35 80

average luminosity 1030cm-2s-1 1 4 4 6 20 60

Collision points -- 4 4 4 3 2 2

average polarization, store % 15 35 46 47 60 70



Since 2006: more data, 200 and 500 GeV

9

Run (End Year) √s (GEV) L recorded(pb-‐1)

PolarizaBon FOM (P4*L)

Run 06 200 7.5 57% 0.79Run 06 62.4 0.08 48% 0.0042Run 09 200 16 57% 1.5Run 09 500 14 39% 0.21Run 11 500 25 45 1.03



Polarization at 100 GeV



A typical store at 100 GeV

11

19:00 21:00 23:00 01:00 03:00

20

40

60

0

50

0

0

10

20

PolarizaB

on [%

]Luminosity

[103

0 cm

-‐2 s-‐

1 ]Proton

s [10

11]

Start of collisionsStart of acceleraBon ramp

60 % polarizaBon

100

150

30

CollimaBon complete



RHIC beam polarimetry

How do we know the proton beams are polarized?Polarimetry had to be developed

How do we know that they are longitudinally polarized?Stable direction of spins in the storage ring is vertical, spin rotator magnets rotate them. How do we know they are doing their job?



RHIC polarimetry (I)Measurement of degree of polarization

• Elastic p-p Coulomb Nuclear Interference (CNI) measures absolute polarization employing a polarized Hydrogen-Jet (as target)

• Elastic p-Carbon CNI polarimeter monitors the degree of polarization with multiple measurements during fills

• Both together succeeded in getting an uncertainty in the polarization measurement of +/- 4.7%


6/2/2011Abhay Deshpande, Nucleon Spin Lectures 4 of 6 at HUGS 2011 14

Beam polarization measurement (1)

• Use single spin asymmetry in elastic scattering of p-p and p-Carbon – Coulomb Nuclear

Interference (CNI) kinematics

Top viewLeft

Right

For a known/understood scakering process, measure the single spin asymmetry and calculate the beam polarizaBon.



RHIC Absolute Polarization

• Calculation by Shwinger 1946

• Unknown spin-flip amplitude

• Now found to be zero

Very forward scattering

ElasBc p-‐p scakering single spin asymmetry as a funcBon of momentum transfer t

PLB 638 (2006) 450GeV

QED Spin Flip

RHIC-‐AGS Best Thesis Award 2006, Hiromi Okada



RHIC polarimetry (I)

Determination and monitoring of spin vector direction in the interaction region

• Employs (accidentally discovered in 2002) single transverse spin asymmetry in “forward” neutron production

• “Local Polarimeters”: at PHENIX, now at STAR as well



PHENIX* Local Polarimeter

(±2mrad)

～1800cm

10cm

PHENIX Collision Point

Blue beam Yellow beam

*Now also STAR




(±2mrad)

～1800cm

10cm



Blue Yellow

Blue Yellow

*Now also STAR




(±2mrad)

～1800cm

10cm



Blue Yellow

Blue Yellow

PL/P > 0.99 blue & yellow

*Now also STAR



Measured Asymmetry During Longitudinal Running

<PT/P>=10±2(%)<PL/P> =99.48±0.12±0.02(%)

LR χ2/NDF = 88.1/97p0 = -0.00323±0.00059

LR

UD χ2/NDF = 82.5/97p0 = 0.00423±0.00057

XF>0 XF>0

XF<0 XF<0

χ2/NDF = 119.3/97p0 = 0.00056±0.00063

UD χ2/NDF = 81.7/97p0 = -0.00026±0.00056

Fill NumberFill Number

<PT/P>=14±2(%)<PL/P>=98.94±0.21±0.04(%)




<PT/P>=10±2(%)<PL/P> =99.48±0.12±0.02(%)

LR χ2/NDF = 88.1/97p0 = -0.00323±0.00059

LR

UD χ2/NDF = 82.5/97p0 = 0.00423±0.00057

XF>0 XF>0

XF<0 XF<0

χ2/NDF = 119.3/97p0 = 0.00056±0.00063

UD χ2/NDF = 81.7/97p0 = -0.00026±0.00056


<PT/P>=14±2(%)<PL/P>=98.94±0.21±0.04(%)

• Measurement of remaining transverse component à spin pakern is correct




<PT/P>=10±2(%)<PL/P> =99.48±0.12±0.02(%)

LR χ2/NDF = 88.1/97p0 = -0.00323±0.00059

LR

UD χ2/NDF = 82.5/97p0 = 0.00423±0.00057

XF>0 XF>0

XF<0 XF<0

χ2/NDF = 119.3/97p0 = 0.00056±0.00063

UD χ2/NDF = 81.7/97p0 = -0.00026±0.00056


<PT/P>=14±2(%)<PL/P>=98.94±0.21±0.04(%)

Developed in Run-5, now routine operation

• Measurement of remaining transverse component à spin pakern is correct



ΔG MEASUREMENTS



PHENIX Detector at RHIC• Design philosophy:

– High resolution limited acceptance– High rate capability DAQ– Excellent triggers for rare events

• Central arm– Tracking: Drift chambers, pad

chambers, time expansion chamber– Superb EM Calorimetry PbGl, PbSc ΔφxΔη~0.01 x 0.01 π0 to 2γ resolved up to 25 GeV pT– Particle Identification: RICH, TOF

• Forward Muon Arms:– Muon tracker, muon identifiers

• Global detectors:– Beam beam collision (BBC) counter,

Zero Degree Calorimeters (ZDCs)• Online monitoring, calibration and

production



STAR Detector at RHIC

• Design Philosophy:•Maximize acceptance• lower resolution

•Subsystems:• φ = 2π acceptance in EM calorimetry

Barrel and EndCapTotal: -1 < η < 2

• Time Projection Chamber• Separate Forward pion detector • Silicon vertex tracker• Beam-Beam Counters• Zero Degree Calorimeter



Measuring ALL

(N) Yield (R) Relative Luminosity(P) Polarization

ü Bunch spin configuration alternates every 106 ns ü Data for all bunch spin configurations are collected at the same time⇒ Possibility for false asymmetries are greatly reduced



Measuring ALL

(N) Yield (R) Relative Luminosity(P) Polarization

ü Bunch spin configuration alternates every 106 ns ü Data for all bunch spin configurations are collected at the same time⇒ Possibility for false asymmetries are greatly reduced

Exquisite control over false asymmetries due to ultra fast rotaBons of the target and probe spin.



Hadron-Hadron Collisions: Observables• Do not know the initial energy,

orientation about the incoming partons

• A hadron created in the collision:– Measure its Transverse

momentum with a solenoid-al magnetic field: pT (GeV/c)

– Angle with respect to the beam direction θ leads to psudorapidity:

23

θ



Calibration of our probes…



Calibration of our probes…• Measurement of a cross section involves:

– Detailed understanding of the luminosity– Detailed understanding of the detector









• Comparison of the data with theory: if they agree:– Theoretical framework applicable in this kinematic

regime– Double spin asymmetries can be interpreted in terms of

polarized gluon distributions





• Comparison of the data with theory: if they agree:– Theoretical framework applicable in this kinematic

regime– Double spin asymmetries can be interpreted in terms of

polarized gluon distributions

• An extremely important check: Imperative for all measurements we publish



Un-polarized π0 Cross Section: 200 GeV CM

|η|<0.35

STAR: π0 high rapidity (forward)PRL 97, 152302

PHENIX: π0 mid-‐rapidity (central)hep-‐ex-‐0704.3599



Un-polarized π0 Cross Section: 200 GeV CM

Good agreement between NLO pQCD calculaXons and dataComparison fails at lower energies

|η|<0.35

STAR: π0 high rapidity (forward)PRL 97, 152302

PHENIX: π0 mid-‐rapidity (central)hep-‐ex-‐0704.3599



Unpol. Cross Section in ppPHENIX: pp→γ X

PRL 98, 012002STAR: pp→jet XPRL 97, 252001



Unpol. Cross Section in ppPHENIX: pp→γ X

PRL 98, 012002STAR: pp→jet XPRL 97, 252001

Excellent agreement between NLO pQCD calculaXons and data



Accessing ΔG in p+p Collisions at RHIC

• If Δf = Δq, then we have this from pDIS• So roughly, we have

where the coefficients a, b and c depend on final state observable and event kinematics (η,pT).

+-‐ = ++

++=

From ep (&pp)(HERA mostly)

NLO pQCDFrom e+e-(& SIDIS,pp)






+-‐ = ++

++=






• If Δf = Δq, then we have this from pDIS

+-‐ = ++

++=







+-‐ = ++

++=







+-‐ = ++

++=







+-‐ = ++

++=








+-‐ = ++

++=





2005, 2006 Run Data Sets Analyzed

• 2005 • 2006 Preliminary

• 2005: PRD76, 05116• 2006: arXiv:0810.0694 (PRL)

28

GRSV: NLO Fit to the polarized DIS data to extract polarized gluon distribuBonPRD63, 094005 (2001)



1st step: truly global NLO QCD fit• D. deFlorian et al, PRL 101, 072001 (2008)• Includes PHENIX Inclusive π0 at 200 and 62 GeV and

STAR inclusive Jets at 200 GeV along with world’s polarized DIS data sets à Resulting ΔG is small, with large uncertainties



ΔG(x) @ Q2=10 GeV2

• Global analysis: DIS, SIDIS, RHIC-Spin

• Uncertainly on ΔG large: Need more low-x measurements!

de Florian, Sassot, Stratmann & Vogelsang

Present



What about the anti-quark polarization?

• DIS probe (γ*) doesn’t distinguish q from qbar– Has to take measure semi-inclusive (π, K production)– Uncertainties in fragmentation functions

• High energy p-p collisions enable probing q,qbar through W+/- production –> Plan at RHIC



Many others… luminosity deprived…




32

STAR neutral pions: central rapidity




32


STAR neutral pions: forward rapidity




32



PHENIX charged pions: central rapidity




32




PHENIX η: central rapidity




32





PHENIX Direct Photon: central rapidity




32





PHENIX Direct Photon: central rapidity

A large luminosity increaseHave occurred since 2009.Many new probes of ΔG are

expected to be available for futuremeasurements…. Stay tuned.



Principle Limitations




• Overlapping x for pT bins




• Overlapping x for pT bins• Need more exclusive

measurements (Luminosity)– γ-Jet (PHENIX VTX upgrade)






33

present (π0)x-range√s = 200 GeV

Extend to lower x at √s = 500 GeV






• Limited x-range

33








• Limited x-range• Need to widen it…

Higher and lower Center of Mass OperationPHENIX measured at 62 GeV CM

33





Summary & Outlook



Summary & Outlook• RHIC Spin program has come of age; it has provided many

important clues toward solving the nucleon spin puzzle









• Measurements of ΔG ongoing: Indicate little contribution to nucleon spin from the kinematic region accessed so far– Different center of mass energies & kinematics needs to

be explored.





• Measurements of ΔG ongoing: Indicate little contribution to nucleon spin from the kinematic region accessed so far– Different center of mass energies & kinematics needs to

be explored.

• Focus of RHIC Spin program moving to W physics and a systematic study of transverse spin phenomena


Documents

Nucleon Spin Structure...RHIC polarimetry (I) Measurement of degree of polarization • Elastic p-p Coulomb Nuclear Interference (CNI) measures absolute polarization employing a polarized