RHIC SPIN: un update

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RHIC SPIN un update

• Alessandro Bravar

COMPASS June 12, 03
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Physics _at_ RHIC

• Study of QCD in extreme conditions
• heavy ion physics - hot and dense limit
• spin physics - high Q2 with spin d.o.f.
• Heavy Ion Physics
• search for a new state of matter
• the Quark Gluon Plasma
• characterize its properties
• Spin Physics
• elucidate the spin structure of the nucleon
• search for physics beyond standard model

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Spin Physics _at_ RHIC

• Collide Polarized Protons
• to study
• Spin Structure of the Nucleon
• Gluon polarization DG
• Quark polarizations Du and Dd
• Transversity Distributions dq
• Spin Dependence of Fundamental Interactions
• Parity Violating Interactions
• Physics Beyond Standard Model
• Elastic pp Scattering

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Spin Asymmetries
ALParity Violation
ALL Double Longitudinal Spin asymmetry
ATT Transversity
gives access to quark and gluon helicity
distributions
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Hadron - Hadron Collisions
factorization Emitting Partons f(x) Hard
interaction of partons s Parton fragment into
hadron D(z) Universality of f(x), s , D(z)

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pp2pp
BRAHMS
polarimeters

STAR
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RHIC The Polarized Collider
70 Polarization Lmax 2 ? 1032 s-1cm-2 50 lt
Ös lt 500 GeV
RHIC pC CNI polarimeters

absolute pH polarimeter
BRAHMS PP2PP
PHOBOS
Siberian Snakes
RHIC
PHENIX
STAR
Siberian Snakes
Spin Rotators
Partial Siberian Snake
LINAC
BOOSTER
AGS inelastic polarimeter
AGS
Pol. Proton Source
AGS pC CNI polarimeter
200 MeV polarimeter
Rf Dipoles
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Spin Dynamics

• Precession Equation in Laboratory Frame
• (Thomas 1927, Bargmann, Michel, Telegdi 1959)
• dS/dt - (e/gm) (Gg1)B? (1G) B? ? S
  Gg 1.91 E
• Lorentz Force equation
• dv/dt - (e/gm) B?
  ? v
• For pure vertical fieldSpin rotates Gg times
  faster than motion, nsp Gg
• For spin manipulationAt low energy, use
  longitudinal fieldsAt high energy, use
  transverse fields

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Depolarizing Spin Resonances
Spin tune Number of 360 degree spin rotations
per turn Depolarizing resonance
condition Number of spin rotations per turn
Number of spin kicks per turn Imperfection
resonance (magnet errors and misalignments,
closed orbit errors) Gg nsp n Intrinsic
resonance (vertical focusing fields, finite beam
emittance) Gg nsp Pn ny P
Superperiodicity AGS 12 ny Betatron tune
AGS 8.75
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Siberian Snake Operation

• Partial Snake
• rotate around beam direction
• (by 5 degrees)
• compensate for imperfections
• Full Snake (with 2 rotators)
• Rotate around two orthogonal
• axes in the accelerator plane
• (i.e. x and y comp. separately)
• compensate for imperfections
• and intrinsic resonances

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Siberian Snake
Beam Trajectory while rotating Spin Direction
3D image of snake

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AGS Polarization vs Energy (2003)
intrinsic resonances

• Full spin flip at all imperfection resonances
  using partial Siberian solenoidal snake
• Full spin flip at strong intrinsic resonances
  using rf AC dipole
• Remaining polarization loss from coupling and
  weak intrinsic resonances
• Almost 2 improvement (on avarage) compared to
  2002 run
• Consistently measured polarization of 45 also
  reached 50 on occasions
• Small emittance beam of 10 p with scraping
  intensity 6 x 1010 p / bunch
• Add a warm helical snake (run 04)
• To avoid all depolarization build a strong
  superconductinb helical Siberian snake snake
  (2005-2006)

Extraction to RHIC Gg 46.5
2.6 GeV
24.3 GeV
Gg 1.91 Ebeam
imperfection resonances every integers
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AGS Polarization during acceleration
each point 50 MeV step

raw asymmetry AN PB
depolarizing resonances intrinsic Gg
imperfection Gg n
Gg 1.91 Ebeam
12n
36-n
36n
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RHIC Polarization from Run 03
Blue at injection
Blue at flattop
not well known (for now)
Yellow at injection

• polarization on average
• at injection
• Blue 40
• Yellow 40
• at flattop
• Blue 25-35
• Yellow 20-30
• being analyzed right now

Yellow at flattop
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A Polarized Proton Store in RHIC
from STAR Luminosity Monitors
2003-05-15 Fill 3714
BBC MinBias
(Pol)
Background Blue beam Background Yellow beam
0.5
Polarization
0.4
0.3
0.2
L 2 x 1030 cm-2 s-1 0.2 pb-1 /day
0.1
0.0
0600 0700 0800 0900
1000 1100 1200 1300

Time (Hours)
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Systematics in RHIC
different spin combination every bunch
crossing 55 bunches (planned 110) Blue
Yellow Spin flip and
recogging
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OPPIS High Intensity H- Source
KEK OPPIS upgraded at Triumph 70 80
polarization 15 1011 protons / pulse at the
source (500 mA, 300 ms) 6 1011 protons/pulse at
end of LINAC

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The RHIC Magnets
Blue and Yellow Rings

Siberian Snake
4 super conducting helical dipoles 4 Tesla, 2.4
m long
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Prompt Photon Production

• Gluon Compton dominates
• Small Background from Annihilation
• No fragmentation contribution at LO

å
D
2
)
(
x
q
e
2
i
i
D
)
(
x
g
g

Ä
Ä

1
i
)
(
q
gq
a
A
å
LL
LL
2
)
(
)
(
x
q
e
x
g
2
1
i
i
i
A1
large quark polarization for x gt 0.2
large analyzing power
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Prompt Photon Production 2
Golden Channel _at_ RHIC

Comparison at cross section level direct
observable
xgluon reconstructed using away side
jet inclusive integrate over xgluon
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Jet Production

• Mixture of gg / gq / qq scatterings
• sensitive to gluon polarization
• very high statistics

Vogelsang et al.
same diagrams for inclusive hadron production
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DG Expectations from 03 Run
First attempt at Gluon Polarization
measurement STAR inclusive jet
PHOENIX inclusive hadron Projections for L 3
pb-1 and PB 50
Y. Goto
W. Vogelsang
inclusive jet production
inclusive hadron production
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Unpolarized g(x)

• Large uncertainties due to intrinsic kT
• RHIC pp can fix it !

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Detector

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Detector New Elements
EMC (Half) Barrel
Magnet
Time Projection Chamber
BBC East
BBC West
Forward Pion Detectors
PSD SMD PbGlass
EndCap EMC (1/3)
West East
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TPC Event

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STAR Beam-Beam Counters

• Fast, highly-segmented scintillation counters
  (small tiles only) serve many purposes in STAR
• Minimum Bias Trigger Sensitive to 50 of
  total cross section
• Absolute Luminosity Van der Meer
  scan
• Relative Luminosity Fast scalers, updated
  every beam crossing
• Measurement of Transverse e.g., for BBC
  East, sort data by Yellow beam
• Asymmetries polarization, sum Blue beam
  polarizations

Top
Interaction Vertex
Left
Right

Bottom
BBC East
3.3lthlt 5.0
BBC West
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Forward ?0 Detector (FPD) at
FPD West
BBC West
BBC East
FPD East
Next run
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Analyzing Power
p? p ? ?0 X

• Theory predictions at pT1.5 GeV/c
• Collins effect
• Anselmino, et al., private communication
• Sivers effect
• Anselmino, et al., private communication
• Twist 3 effect
• Qiu and Sterman, private communication

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Differential Cross Section
The data are in fair agreement with NLO pQCD
calculation...
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PHENIX Detector System

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PHENIX event

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Polarimetry Impact on Spin Physics
Physics Asymmetries
Single Spin Asymmetries
Double Spin Asymmetries

• In any Spin asymmetry measurement, the raw
  asymmetries have to be normalized by the beam(s)
  polarization to obtain the Physics Spin
  Observables (AN, ALL , etc.)
• Elastic pC Scattering in CNI (Coulomb Nuclear
  Interference) region adopted as polarimeter for
  its fast and reliable measurement performance
• Need of absoulte calibration via Elastic pp
  Scattering in CNI region using a polarized gas
  jet target (planned for run 04)

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Elastic pC pC scattering at low t

recoil

• 1. AN from interference of spin non-flip and spin
  flip amplitudes
• Þ spin dependence of interaction
• Þ hadronic spin flip (spin-coupling of Pomeron)
• RHIC Polarimetry
• - almost calculable
• - sizeable AN 1 (requires large statistics gt
  107)
• - large cross section
• - weak beam momentum dependence (p gt 20 GeV/c)

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AN from where does it come?

• Ahadronic ACoulomb2 ( P g2 )
• around t -10-3 (GeV/c)2 Ahadronic ACoulomb Þ
  INTERFERENCE
• CNI Coulomb Nuclear Interference
• unpolarized Þ clearly visible in the cross
  section ds/dt (charge)
• polarized Þ left right asymmetry AN
  (magnetic moment)

µ(m-1)p µÖspphad
QED Þ calculable, expect AN ¹ 0 up to
4.5 QCD Þ unpredictable, need direct
measurement
B. Kopeliovich L.Trueman
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Elastic pp pC ds / dt AN

r5pC 0.088 0.058 -i 0.161
0.226 µ Fshad / Im F0had
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Polarimeter Setup in the AGS Ring
ultra-thin Carbon ribbon (target) 5 ?g/cm2 600 mm
wide

right
left
25 cm
beam direction
p
p
Si strip detectors 12 vertical strips
beam
12 mm
24 mm
similar setups in RHIC for each beam
read-out with waveform digitizers CFD and ADC
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Event Selection

• recoil carbons detected with Si detectors
• identified via ToF vs Enery correlation
• position vs energy correlation spoiled by
  multiple scattering in target
• very high event rate
• events acquired with deadtime free
• wave-form digitizers

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Time of Flight vs. Energy i.e.

does not pass the cuts
event selection
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pC raw asymmetry at 24.7 GeV/c
PB 37 42

preliminary
e PB AN
calculated over several t bins
ANth from a fit to E950 data at similar energy
and t range L. Trueman hep-ph/0305085
áANñ 1.12 0.009 lt t lt 0.022 (GeV/c)2
normalization region
PB 0
each measurement 5 min for next run 1 min
recoil Carbon energy (keV)
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AN pC pC at 24.7 GeV/c

• only statistical errors shown
• normalization error (i.e. PB)
• 25 (relative)
• systematic error
• (background, pileup, etc.)
• lt 20 (relative)
• fit to E950 data
• L. Trueman hep-ph/0305085
• similar behavior E950 Þ
• substantial hadronic spin-flip
• confirmed
• (no time yet to fit these data)

AN ()
preliminary
recoil Carbon energy (keV)
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AN pC pC at 3.7 6.8 GeV/c

only statistical errors are shown normalization
errors 10 (at 3.7) 15 (at 6.8)
25 (at 24.7) systematic error lt 20
CNI peak 4
p 3.7 GeV/c
AN ()
preliminary
PB 73
p 6.8 GeV/c
CNI
PB 65
p 24.7 GeV/c
PB 40
recoil Carbon energy (keV)
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AN pC pC at 100 GeV/c (RHIC)

for normalization assume AN (24 GeV/c) AN (100
GeV/c) i.e. no energy dependence 0.009 lt t lt
0.022 (GeV/c)2 very similar shape of the t
dependence at 24 and 100 GeV/c Þ suggestive of
very small energy dependence for AN between 24
and 100 GeV/c systematic error for RHIC data lt
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preliminary
AN ()
CNI
blue beam yellow beam AGS
recoil Carbon energy (keV)
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The RHIC Absolute Polarimeter

• RHIC Spin Program requires DPbeam / Pbeam lt 0.05
• Polarimetric process with large s and known AN
• pp elastic scattering in CNI region
• Current knowledge on AN to poor
• Measure AN to required accuracy DAN lt 10-3
• with unpolarized beam and polarized target
• then measure Pbeam using this AN with
• polarized beam and unpolarized target
• or Transfer target pol. to beam polarization
• i.e. measure the ratio of spin asymmetries with
• beam and target polarized
• Target polarized gas jet
• low density and almost pointlike
• very high polarization (gt90)

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The Polarized Gas-Jet Target
beam

RF transitions
atomic beam source
Breit-Rabi Polarimeter (not shown)
separation magnets (sextupoles)
focusing magnets (sextupoles)
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Next pp, pp and pp with a Polarized Gas Jet
Target

• Polarized Hydrogen Gas Jet Target
• thickness of 5 1011 p/cm2
• polarization gt 90
• Silicon recoil detectors
• Rate 125 Hz for 0.001 lt t lt 0.02 (GeV/c)2
• Measure ANpp in pp elastic scattering
• in the CNI region to a 3 accuracy
• Transfer ANpp to the pC polarimeters (ANpC)
• Expected accuracy on PB of 6 with
• calibrated pC CNI polarimeters
• Install for the 04 run
• Initially measure PB to 10

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Conclusions

• Successfully demonstrated acceleration, storage,
  and collisions of polarized protons up to 100
  GeV no fundamental problems anticipated going to
  250 GeV
• All spin experiments work beautifully
• New spin physics results already extracted from
  the first p p collisions in 2002
• Commissioning STAR and PHENIX spin rotators has
  permitted first longitudinal double spin
  measurements in just completed 2003 run
• Substantial progress has been made in improving
  beam polarization on average PB 25 35
• Luminosity 1 pb-1 / week, total several pb-1
• Polarimetry fast and reliable, need absolute
  calibration