# Presentation: 161186

## Experimental aspectsof the RHIC spinprogram 

## Outline 

- Introduction

- Outline

- Future prospects (STAR / PHENIX)

- Polarized proton collider RHIC

- The STAR detector

- First results              (STAR / PHENIX)

- The PHENIX detector

## RHIC Spin program (e.g. ΔG) 

- RHIC Spin program (e.g. ΔG)

- Fundamental question: How is the proton spin  made up?

-  Where is the spin of the proton then?

- Need: New generation of experiments to explore the spin structure of the proton: polarized proton collisions at RHIC which allows to access directly G in polarized pp collisions!

- At present: G is only poorly constrained from scaling violations in fixed target DIS experiments

-  SMC result: Fraction of proton spin carried by quarks is small:

-  SMC QCD-fit:

- B. Adeva et al., SMC Collaboration, Phys. Rev. D58 (1998) 112002.

- RHIC spin program:

- Spin structure of the proton (gluon polarization, flavor decomposition, transverse spin dynamics and transversity)
- Spin dependence of fundamental interactions
- Spin dependence of fragmentation
- Spin dependence in elastic polarized pp collisions

- Unique multi-year program which has just started...!
- Explore various aspects of the spin structure and dynamics of the proton in a new domain:

- Introduction

## Introduction

-  Measurement of asymmetries (A): Principal approach to study spin effects

-  Ultimately at RHIC, any combination of beam polarization (longitudinal (+/-) /transverse (/)) is possible, which allows to access different aspects of the proton spin structure

-  Study helicity distribution functions, e.g. gluon polarization: G!

- Double longitudinal-spin asymmetry:

- Single longitudinal-spin asymmetry:

-  Study parity violation effects and flavor decomposition!

## Introduction

- Collins: include intrinsic transverse component, k, in final state (transversity)
- Qiu and Sterman (Initial-state twist-3)/Koike (final-state twist-3)

- Asymmetries

- Double transverse-spin asymmetry:

-  Study transverse dependent distribution functions e.g. in jet production or Drell-Yan production (Transversity δq  Last unmeasured leading twist distribution function)!

- Single transverse-spin asymmetry:

-  Study transverse spin effects:

## Introduction

- Experimental aspects on asymmetry measurements at RHIC: AN

- Measurement of AN for forward π0 production at STAR:

- Asymmetry:

- Determination of AN requires three measurements:

- Spin dependent event yield:  N()
- Relative luminosity: R=L/L (Essential for longitudinal asymmetry measurements!)
- Beam polarization: P

- AN : DIFFERENCE over SUM – In general quite small  Require therefore:

- Statistical precision
- Control of systematic effects

- Left detector (L)

- Right detector (R)

- P: Beam
- polarization
- (up)

- Target

## Polarized proton collider RHIC

- Overview of RHIC polarized pp collider complex

- Siberian Snakes

- BRAHMS & PP2PP

- RHIC pC Polarimeters

- STAR

**AGS**

**LINAC**

**BOOSTER**

- Spin Rotators

- Partial Siberian Snake

- 200 MeV Polarimeter

- Rf Dipole

- AGS Nylon and pC Polarimeters

- Strong AGS Snake (2004)

- Helical Partial Siberian Snake (2004)

- Spin Rotators

- Spin flipper

- PHENIX

- PHOBOS

- Siberian Snakes

- Pol. H- source
- 500 A, 300 s

- Lmax = 2 x 1032 cm-2s-1

- 70% Beam Polarization

- 50 < √s < 500 GeV

## Polarized proton collider RHIC

- Achievements in FY02:

- Beam energy: 100 GeV
- Inst. luminosity:  5 • 1029 s-1 cm-2
- Integrated luminosity:  0.3pb-1
- Bunch crossing time: 213ns
- Polarization:  0.2 (transverse)
- First transverse spin result (AN)!

- 0

- 50

- 100

- 150

- 200

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- 350

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**Days into run (from 12/20/01)**

**Integrated luminosity at STAR IR (nb****-1****)**

**Trans. polarization: FY02**

**Blue**** and ****Yellow**** Beam polarization (RHIC CNI) FY02**

## Polarized proton collider RHIC

- Achievements in FY03:

- Beam energy: 100 GeV
- Inst. luminosity:  6 • 1030 s-1 cm-2
- Integrated luminosity:  0.5 pb-1 (transverse)  0.4 pb-1  (longitudinal)
- Bunch crossing time: 213ns
- Polarization:  0.3 (transverse and longitudinal)
- First longitudinal spin result (ALL)!

**Integrated luminosity at STAR IR (nb****-1****)**

**Days in May 2003**

**Trans. polarization: FY03**

**Long. polarization: FY03**

**Blue**** and ****Yellow**** Beam polarization (RHIC CNI) FY03**

- RHIC/AGS CNI polarimeters

- Beam
- direction

- 1

- 3

- 4

- 5

- 6

- 2

- 30cm

-  2 rings

- Silicon strip detectors

- Very thin carbon ribbon target (5g/cm2  25 mm) in the RHIC beam
- Measure scattered recoil carbon at θLab~ 90o  with Ecarbon= 0.1 - 1 MeV (silicon strip detectors)
- Measure E and TOF to identify recoil carbon ions, determine 4-momentum (-t) and determine left-right/up-down asymmetries
- Readout system based on wave-form digitizer (WFD) board to allow high counting rates (~0.5 MHz)

- Arrival time (ns)

- Carbon

- pC CNI elastic scattering (-t=0.008-0.025GeV/c2):
-  Detect recoil carbon

- RHIC

- Very thin ribbon target

- ADC counts

- Absolute polarization measurement using an internal polarized hydrogen gas jet target ( 10% normalization uncertainty on G requires knowledge of beam polarization to ±5%): Calibrate fast RHIC CNI polarimeter!
- Polarimeter process: Elastic pp scattering at very low t in the CNI region (0.001<|t|<0.02GeV/c2)
- Measure recoil proton in elastic pp scattering using silicon strip recoil detectors
- Properties of polarized hydrogen gas jet target:
- Polarization: ~90%
- Density: 5·1011 p/cm3
- Target polarization measurement: Breit-Rabi polarimeter
- Transfer target polarization to beam polarization using self-calibration method: AN for
- 	are identical in magnitude:
- Goal: 10% accuracy on beam polarization in 2004 with final goal of 5% in 2005

- Polarized proton collider RHIC

- RHIC polarized gas-jet target

## Polarized proton collider RHIC

- Siberian snake and spin rotator magnets successfully commissioned
- Fast polarimeters in AGS/RHIC demonstrated to work
- Spin transfer AGS to RHIC demonstrated to work

- Commissioning status:

- Installation and commissioning of AGS partial snake magnets
- Commissioning of polarized gas jet target ( Absolute polarization measurement!)
- Commissioning of 250GeV ramp
- Adequate time for commissioning and luminosity development...!

- RHIC SPIN effort is in the beginning of its multi-year program!

- Overview of commissioning status

-  5 % helical snake build at Tokana Industries funded by RIKEN (Just arrived at BNL!). Installation: Jan. 2004!

-  30% s.c. helical snake build at SMD (AIP)
- Installation: Oct. 2004!

- Warm snake avoids polarization mismatch at AGS injection and extraction
- Cold strong snake eliminates all depolarizing resonances in AGS

## Overview 

- Upgrade program of the STAR experiment for the first polarized proton collisions (FY02/FY03):
-  Beam-Beam Counter (BBC): (2 < || < 5)
- Relative luminosity measurement
- Rejection of beam-gas event in pp collisions
- Minimum bias trigger
- Beam tuning to make collisions at STAR
- Luminosity monitor
-  Forward-Pion Detector (FPD) (3 <  < 4)
- Electromagnetic calorimeter system: Prototype setup (FY02) of 3 Pb-glass arrays and 1 Pb-scintillator calorimeter east side for FY02
- Upgrade in FY03: Pb-glass arrays                    (FPD WEST/FPD EAST)
- Energy and shower profile measurement (0  )
- Event yield for Forward 0 production
- Commissioning of EM-calorimeter modules and trigger (Barrel: -1 <  < 1 & Endcap: 1.09 <  < 2)
- Commissioning of spin scaler system

- ~7.5m

- ~7.5m

- BBC  West

- BBC  East

- FPD West

- FPD East

- ~7.5m

- The STAR detector

## The STAR detector

- STAR Beam-Beam Counter (BBC)

- 1 cm thick scintillator
- 4 optical fibres for light collection
-  15 photoelectron/MIP

- Inner annulus: inner (outer) diameter 9.6cm (48cm) of 18 pixels (3.3 < |η| < 5.0)
- Outer annulus: inner (outer) diameter 38cm (193cm) of 18 pixels (2.0 < |η| < 3.3)

- Hexagonal scintillator array structure at 3.5m from IP:

- Singe scintillator tile:

## FPD upgrade for FY03 run 

- Pb-glass

- Physics motivation:
- AN measurement for
- Tuning of STAR spin rotator (Local polarimeter)
- Gluon density in heavy nuclei (low x)

- Acceptance:
- Forward rapidity: 3 < η < 4
- High xF: xF > 0.2
- Moderate pT: 1 < pT < 4 GeV

- 7 X 7 matrix

- 7 X 7 matrix

- 5 X 5 matrix

- 5 X 5 matrix

- The STAR detector

## STAR calorimeter system: Barrel  

- The STAR detector

## STAR calorimeter system: Endcap  

- The STAR detector

## First results (STAR)

- Polarization pattern at STAR:    Spin Up        Spin Down          Unpolarized

**Bunch Crossing**

**Luminosity         BBC E•W counts**

- STAR BBC luminosity monitoring

- Abort gaps  beam-gas background!

## BBC asymmetries: Used for STAR spin rotator tuning during FY03 run  

- 3.3<|η|< 5.0 (small tiles only)** **

- BBC East Left-Right asymmetry (vertical)

- BBC East Top-Bottom asymmetry(radial)

-            Yellow beam** **

- Rotator
- commissioning

- RHIC CNI
- polarimeter

-                  Transverse                    Longitudinal** **

- Spin manipulation around IR’s:
- Stable spin direction at RHIC is vertical
- Spin Rotater brings spin to almost radial orientation
- D0/DX magnet causes spin precession
- Longitudinal at IR
- DX/D0/Spin Rotater put spin back to vertical** **

- First results (STAR)

- Days since 05/01/03

- Radial & vertical pol. < 3%!

- Raw asymmetry

- Raw asymmetry

## First measurement of AN for forward π0 production at RHIC  

- AN is found to increase with energy similar to E704 result (s = 20 GeV (10 X smaller than at RHIC), 0.5 < pT < 2.0 GeV)
- This behavior is also seen by several models which predict non-zero AN values

- Sivers: include intrinsic transverse component, k, in initial state (orbital momentum) (before scattering takes place)
- Collins: include intrinsic transverse component, k, in final state (transversity) (after scattering took place)
- Qiu and Sterman (Initial-state twist-3)/Koike (final-state twist-3): more “complicated QCD calculations” (higher-twist, multi-parton correlations)

- Several approaches beyond the basic “naive QCD calculations” yield non-zero AN values at RHIC energies:

- First results (STAR)

- STAR collaboration, hep-ex/0310058, submitted to Phys. Rev. Lett.

- Forward π0 production cross-section in comparison to NLO calculations

- Measured forward π0 production cross-section in comparison to NLO pQCD calculations
- NLO pQCD calculations:
- CTEQ6M parton distribution function
- Two sets of fragmentation functions:
- Kniehl-Kramer-Pötter (KKP)
- Kretzer
- Measured results fall in-between two NLO pQCD which reflect uncertainties in the underlying fragmentation functions

- STAR collaboration, hep-ex/0310058, submitted to Phys. Rev. Lett.

## RHIC forward π0 production cross-section in comparison to lower energy data  

- RHIC forward π0 production cross-section in comparison to lower energy data

- Bourelly and Soffer (hep-ph/0311110): Comparison of forward π0 production to pQCD NLO calculations
- Comparison illustrates that agreement of measured cross-sections to pQCD NLO calculations for forward π0 production improves with increasing center-of-mass energy, i.e. from fixed-target to RHI

- Inclusive jet production (FY03)

- First results (STAR)

- First longitudinal data sample will allow to have a first look at ALL for inclusive jet production
- Condition:
- Average polarization: 0.25
- Integrated luminosity: 400nb-1
- Cone-jet algorithm
- Trigger:
- High-tower trigger (700k recon. jets): Single tower energy threshold above ~2.4GeV
- Jet patch trigger (250k recon. jets): Jet patch (η X Φ = 1 X 1) energy threshold ET>5GeV
- Expected stat. precision on AL L (EMC+TPC)

- ALL Pythia simulation incl. trigger and jet reconstruction  efficiencies

- More data needed!

## The PHENIX detector

- Overview

- Minimum Bias trigger and Relative Luminosity:
- Beam-Beam Counter (BBC): 3.0<||<3.9, =2

- Main concept of PHENIX:
- High rate and granularity
- Good mass resolution and particle ID
- Commissioning of spin scaler system and relative luminosity monitor for first polarized pp run
- Reconstruction of π0 mesons and high pT photon trigger:
- EMCal: ||<0.38, =,                     granularity  = 0.010.01

## Relative luminosity measurement: PHENIX BBC and ZDC 

- Relative luminosity measurement: PHENIX BBC and ZDC

- Both, Beam-Beam Counter (BBC) and Zero-Degree calorimeters (ZDC) are used in the relative luminosity measurement
- Achieved relative luminosity precision R=2.510-4
- Pessimistic estimation limited by ZDC statistics (30 times less than BBC statistics used in Rel. Lum. measurements)
- ALL of BBC relative to ZDC consistent with 0 (< 0.2%)
- Strong indication that both ALLs are zero (Very different kinematical regions, different physics signals)

- BBC

- ZDC

## The PHENIX detector

- Dx magnet

- Zero Degree Calorimeter (ZDC): Tungsten-fiber sandwich calorimeter

- SMD

- Shower-Max. Detector (SMD):  Plastic scintillator strips (0.5cm x 3)
- 	10 and 15 cm long
- 	7 x 1.5cm columns
- 	8 x 1.5cm rows
- 	Readout: Hamamatsu MAPMT

- PHENIX local polarimeter upgrade: ZDC-SMD

- ~1800cm

- 10cm

- (±2mrad)

- Blue beam

**Yellow beam**

- ZDC asymmetries: Used for PHENIX spin rotator tuning during FY03 run

- BLUE

- YELLOW

- BLUE

- YELLOW

- Transverse polarization (Maximum at ±π/2):

- Transverse-radial polarization (Maximum at 0): Wrong rotator wiring!

- Azimuthal angle

- Azimuthal angle

- Azimuthal angle

- Azimuthal angle

- Raw asymmetry / P

- Raw asymmetry / P

- Raw asymmetry / P

- Raw asymmetry / P

- Longitudinal polarization (ZER0):

##   PHENIX 0 production cross section

Data covers over 8 orders of magnitude
pT = 1 – 13 GeV/c
based on combining minimum bias trigger and EMCal trigger data

NLO pQCD calculation is consistent with data
CTEQ5M PDF + PKK FF
with a scale variation:  = pT/2 and  2pT

Confidence in understanding subprocesses
Solid basis for future polarized pp asymmetry measurements

- Data covers over 8 orders of magnitude
*p**T* = 1 – 13 GeV/*c*
- based on combining minimum bias trigger and EMCal trigger data
- NLO pQCD calculation is consistent with data
- CTEQ5M PDF + PKK FF
- with a scale variation:  = pT/2 and  2pT
- Confidence in understanding subprocesses
- Solid basis for future polarized pp asymmetry measurements

- Normalization error of
- 30% is not included!

- First results (PHENIX)

- PHENIX collaboration, hep-ex/0304038, accepted for publ. in Phys. Rev. Lett.

## First measurement of ALL at RHIC for inclusive π0 production  

- First measurement of ALL at RHIC for inclusive π0 production

- Polarization scaling error P/P ~30% is not included:
- Enters ALL in quadrature
- Analyzing power AN(100 GeV) = AN(22GeV) is assumed
- P/P* *~ 30%: combined stat. and sys. error for AN(22GeV) (AGS E950)
- Relative luminosity contribution to 0 ALL error is < 0.2%
- pT smearing correction is not included

- More data needed!

| pT
GeV/c | 
(rbck) |  | 
(Background subtracted) |
| --- | --- | --- | --- |
| 1-2 | -0.0280.012 (45%) | -0.0060.014 | -0.0460.025 |
| 2-3 | -0.0220.015 (17%) | -0.0350.027 | -0.0190.019 |
| 3-4 | -0.0020.033 (7%) | 0.0940.092 | -0.0090.036 |
| 4-5 | -0.0230.074 (5%) | 0.380.24 | -0.0450.079 |

- Luminosity: 0.215 pb-1, Average polarization: 26%

## Prospects on constraining ΔG in RUN4/RUN5   

- Future prospects

- ALL Pythia simulation including trigger and jet reconstruction efficiencies
- Inclusive jet production (STAR)

- ALL NLO pQCD calculation
- Inclusive pion production (PHENIX)

## Future prospects

- Simulated ALL at two different RHIC center-of-mass energies::

- Combined data sample at 200 GeV and 500 GeV is essential to minimize extrapolation errors in determining ΔG:

- Ultimately: Global analysis of various ΔG!

- Accuracy: 0.5

- Multi year program at RHIC which requires:
- High luminosity
- High polarization
- s = 200 / 500GeV

## Heavy Flavor production: PHENIX VTX upgrade 

- Future prospects

- Heavy Flavor production: PHENIX VTX upgrade

- Measurement of Gluon polarization by Heavy flavor production
- c, b  e,  + displaced vertex
- B  displaced J/
- D  Kat high pt
- VTX measurement of displaced vertex
- Improved S/B  higher sensitivity to G(x)
- Broader *x* coverage
- Also: Aid in recoil jet reconstruction (charged tracks) in photon-jet events

- VTX increases the x coverage of G(x) measurement!

**1.2<|********|<****2.4**

**|********|<****1.2**

## W production: Flavor dependence 

- W production: Flavor dependence

- W± production in pp collisions probes flavor structure of QCD sea analogous to deep-inelastic scattering
- Polarized proton beams allow the measurement of (the expected large) parity violation in W± production
- Forward e () detection (PHENIX muon system -  STAR forward tracking upgrade needed!) gives direct access to probe the underlying quark (anti-quark) polarization which is dominated at RHIC by u/d quarks (Asymmetric partonic collisions!)

- Future prospects

## Summary and Outlook 

- RHIC Spin program at BNL
- First successful polarized proton collisions ever at RHIC (transverse and longitudinal)
- Successful upgrade and commissioning of various new STAR/PHENIX components for the first polarized proton run at RHIC
- First measurement of AN for forward π0 production at STAR and AN for forward neutron production at PHENIX (and PHENIX-IP12)
- First measurement of ALL (Inclusive pion production - PHENIX) and STAR analysis for inclusive jets in preparation
- Unique opportunity to explore the spin structure and dynamics of the proton in a new unexplored regime at RHIC over the next years:
- Transverse spin dynamics and transversity
- Gluon polarization
- Short-term: PHENIX (Pion production) and STAR (Inclusive jet production)
- Long-term: Prompt photons and heavy quark production
- Flavor decomposition (W production)
- This requires various accelerator, polarimeter and detector components to be completed and upgraded! (High polarization and luminosity  Frequent pp running and development crucial!)

## Overview 

- Overview

- BRAHMS proposal (DOE review 2003):
- Measure AN for pp  π + X at s=200 GeV, ηπ~3.9

*       *π+ measurements               π- measurements

- Rate estimates
- assume
-  L ~ 1.5 b-1s-1

| xF | pT(GeV/c) | Counts/h | xF | pT(GeV/c) | Counts/h
 |
| --- | --- | --- | --- | --- | --- |
| 0.21 | 1.0 | 6454 | 0.21 | 1.0 | 5296 |
| 0.25 | 1.4 | 1068 | 0.25 | 1.4 | 807 |
| 0.30 | 1.9 | 163 | 0.30 | 1.9 | 91 |
| 0.35 | 2.5 | 24 | 0.35 | 2.5 | 12 |

## Overview  

- pp2pp program - Backup

- Overview

- Measurement of small-angle pp elastic scattering at
- 50  s  500 GeV;
- 4 x 10-4  t  1.3 (GeV/c)2
- using silicon strip detectors in Roman Pots

- 			2002            2003
- p+ intensity / beam	0.5•1012   	1.9•1012
- p+ polarization	0.24 	0.37
- Beam tune β*	10 m            10 m
- Beam momentum	100 GeV    	100 GeV
- Elastic events	300,000    	3 Million
- Expected statistical errors (on single data point):
- δAN 		0.025            0.005
- δb			1.60              0.35
- Improvement of systematic error due to:
- Measurement of local angle with Roman Pot station set added in 2003
- Beam tune measurement

- First measurement of exponential slope parameter b of the diffractive in elastic pp scattering at RHIC at √s = 200GeV:
- b=16.3 ± 1.6 (stat.) ± 0.9 (sys.) (GeV/c)-2

## The PHENIX detector - Backup

- Local polarimeter development at IP12  PHENIX test setup

## The PHENIX detector - Backup

- Asymmetry results (IP12)

- Characteristic  dependence as expected for a transverse polarized beam!
- Successful measurement of forward neutron production
- Large asymmetry provides good figure-of-merit for local PHENIX polarimetry
- Physics origin of large analyzing powers not understood

- <AN> = -0.108 ± 0.009

- Define different Left/Right slices in Φ and
- calculate asymmetry  as function of Φ using:

## Polarized proton collider RHIC - Backup

- Luminosity growth and running time at other collider facilities

- Adequate time for commissiong and luminosity development at the level of 14 weeks (CAD RHIC collider projections) is reasonable in comparison to other collider facilities!

- RHIC

- Tevatron

- LEP

- HERA