RHIC SPIN:recent progress and future prospects

1
RHIC SPIN recent progress and future prospects

• Alessandro Bravar

CERN 5th August 04
2
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

3
Proton Spin puzzle
The Spin of the nucleon made of pñ ½ ½ D?
DG Lq Lg D? Du Dd Ds ? Spin of
Quarks DG ? Spin of Gluons Lq, Lg
? Orbital angular momentum

Naïve expectations quarks carry all the nucleon
spin Þ DS 1 (0.6) but EMC (89) D?
0.12 0.09 0.014 Þ Ds -0.19 0.03
0.05 DS consisten with 0 Þ Spin crisis Ds lt
0 generated by axial anomaly Þ large DG gt 0 (pQCD
origin) non perturbative origin also possible,
but more difficult curiosity existence of
proton spin first deduce from specific heats of H2
4
Program
Short term - Run-2
Short term - Run-3 - Run-6 200 GeV
Long term - Rare Probes 500 GeV

Transverse AN
Longitudinal AL
Single Spin
Longitudinal ALL
Transverse ATT
Double Spin
STAR spin program requires charged particle
tracking and identification of electrons, pions,
photons and jets
5
Hadron Hadron Collisions
po
factorization
D(z)
P1
S1
P2
S2
universality of f(x), s , D(z)
6
Spin Asymmetries
ALL Double Longitudinal Spin asymmetry
ALParity Violation
ATT Transversity
ANTwist-3
7
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 Snake
LINAC
BOOSTER
AGS inelastic polarimeter
AGS
Pol. Proton Source
AGS pC CNI polarimeter
Rf Dipoles
200 MeV polarimeter
Strong Snake
8
The RHIC Experiments

polarimeters
pp2pp
BRAHMS
STAR
9
Spin Running in RHIC
Luminosity and Polarization Development

• 2001-2 Run-2 (53 weeks)
• Transverse beam polarization P15
• Luminosity 5x1029 s-1cm-2
• Integrated luminosity at STAR 0.15 pb-1
• 2003 Run-3 (53 weeks)
• Transverse and Longitudinal
  beam polarization of 25
• Luminosity 2x1030 s-1cm-2
• Integrated luminosity at STAR

Rotators Off transverse polarization
On longitudinal polarization
Transverse Run-3 Longitudinal
Run-3 0.5 pb-1 0.4
pb-1

• 2004 Run-4 (6 weeks)
• - machine commissioning polarization
• luminosity development
• - P gt 40 in both rings at RHIC flattop
• - L gt 6x1030 s-1cm-2 achieved

Integrated luminosity ( nb -1)
2 16 16
30
Timedays
10
A typical RHIC store
measured beam polarization
intesntiy luminosity
I 40 1011 protons
Pbeam 40
L 4 1030 cm-2 s-1
Pbeam 40
11
RHIC Polarization Run 04
Jet data taking dedicated
non-dedicated
online results
Data Points Black 24GeV Color 100GeV
Change in Si dead layer parameters
little loss or none at the ramp
switch to horizontal target
Polarization
Days from April 1st
Polarization
Days from April 1st
being analyzed right now
12
Detector

13
Detector New Elements
EMC (Half) Barrel
Magnet
Time Projection Chamber
BBC East
BBC West
Forward Pion Detectors
PSD SMD PbGlass
EndCap EMC
West East
14
TPC Event

STAR pp, ?s 200 GeV
Head-on HI collision
di-jet event in pp
15
STAR Beam-Beam Counters

• Fast, segmented scintillators (small tiles only)
  serve many purposes
• Minimum Bias Trigger Sensitive to 50 of
  total cross section
• Absolute Luminosity Van der Meer scan
• Relative Luminosity Fast scalers,
  updated every beam crossing
• Local Polarimeter Transverse Spin
  Asymmetries (left right)

1. Polarized Yellow beam
2. Polarized Blue beam

Top
Interaction Vertex
Left
Right

Bottom
BBC East
3.3lthlt 5.0
BBC West
16
Spin Asymmetry Measurements
Single Transverse Double
Longitudinal
relative luminosities
Statistical significance
beam polarization

• Require concurrent measurements of
• magnitude of beam polarization, P1(2)
  RHIC
  polarimeters
• direction of polarization vector at interaction
  point
• relative luminosity of bunch crossings with
  different
• spin directions
  STAR
  (PHOENIX)
• spin dependent yields of process of interest
  Ni and Nij

17
Relative Luminosity Measurements

• Precision of relative luminosity monitoring
  critical for ALL 1 dALL/ALL 5 Þ
  dR/R10-3
• Luminosity BBC coincidence rate (large cross
  section of 27 mb)
• RHIC stores up to 120 bunches per ring -
  different bunches injected with different spin
  orientation
• 
  - collision luminosity can
  vary with spin combination

Relative Luminosity R L / L-
abort gaps (beam-gas
background)
R 1 and time dependent!
1.0
beam-1 beam-2
05/16/03
05/30/03
bunch crossing
Time Run Number
Relative luminosities uncertainties d Rstat
10-4 10-3 and dRsyst lt 10-3 Next use the
spin flipper to reverse beam polarization
several times during one store Þ R 1
18
Spin Rotators and Longitudinal Polar.
local polarimeter
azimuthal asymmetry for forward neutrons AN
10 sensitive on transverse beam polarization
Spin rotators OFF Vertical polarization Spin
rotators ON correct current ! Only longitudinal
polarization !
19
DG from Inclusive Jets
STAR pp, ?s200 GeV

• Mixture of gg / gq / qq scatterings
• sensitive to gluon polarization
• large -section high statistics with low L
• STAR reconstructs jets via TPC pT for charged
  hadrons
• EMC ET for EM showers

05 projections
L 7 pb-1 and PB 40
Dg 0 Dg gmax Dg -gmax Dg gstd
ETjet GeV
20
- - - p0 -section _at_ mid rapidity
-section result consistent with NLO pQCD
calculations over 8 orders of magnitude favors a
larger gluon-to-pion FF p0 production at
mid-rapidity better understood than direct-g
? however pure collinear kinematics intrinsic kT
and fragmentation pT 0 ! gluon radiation and
Sudakov effects ? important confirmation of
theoretical foundations for spin program ?
21
First ALL measurement from
p p p0 X, h 0
pQCD NLO predictions based on GRSV polarized PDFs
negative ALL difficult to accommodate in the
framework of pQCD !
scale uncertainty of 65 not included
03 data
22
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
23
Forward ?0 Production s AN
PRL 92, 171801 (2004)
p? p ? ?0 X

• pQCD calculations consistent with measured
  large-? p0 cross sections
• Large transverse single-spin effects observed
  for ?s 200 GeV pp collisions
• Collins effect ? transversity Sivers
  effect ? orbital angular momentum
• Additional measurements required to disentangle
  contributions

24
Spin Dynamics
Spin Precession in Laboratory Frame (Thomas
1927, Bargmann, Michel, Telegdi 1959) dS/dt
- (e/gm) (Gg1)B? (1G) B? ? S Gg
1.91 E Lorentz Force dv/dt - (e/gm)
B? ? v For pure vertical
field Spin rotates Gg times faster than motion,
nsp Gg Spin depolarization resonances due to
transverse magnetic fields Imperfection
resonance (magnet errors and misalignments,
closed orbit errors, ) Gg nsp n Intrinsic
resonance (vertical focusing fields -
quadrupoles, finite beam emittance, ) Gg nsp
Pn ny
B?
v
25
AGS Polarization during acceleration
each point 50 MeV step

raw asymmetry AN PB
depolarizing resonances intrinsic Gg
imperfection Gg n
12n
36-n
36n
Gg 1.91 Ebeam
48-n
red line simulation of polarization losses
assuming constant AN
26
Imperfection Resonances Gg n
partial snake (AGS) imperfection resoance
Gg n
Gg n 1/2
1
d
d
S
d
2
2d
if snake sufficiently strong (5 enough in AGS)
spin is fully flipped when crossing an
imperfection resonance with no polarization
loss for Gg ¹ n, spin oscillates around stable
direction, which is tilted from the vertical
3
3d
d
27
Intrinsic Resonances Gg nP n
betatron oscillation of frequency n if spin
precession in phase with betatron oscillation
Gg n when crossing the quadrupole depolarizing
kicks d add Þ depolarizing resonance condition
quadrupole
S
N
d
2d
S
N
to be in phase with betatron oscillation over a
closed orbit spin must precess n n times in a
periodic accelerator spin in phase with
betatron oscillation when crossing same
quadrupole in consecutive FODO section if Gg nP
n Polarization losses reduced / avoided by
forcing a full spin reversal (flip) using an RF
dipole
FODO section
Q
Q
AGS
Q
Q
28
Siberian Snake Operation

• Partial Snake (AGS)
• rotate around beam direction
• compensate for imperfections
• use an RF dipole to compensate
• for intrinsic resonances
• Full Snake (with 2 rotators - RHIC)
• rotate around two orthogonal
• axes in the accelerator plane
• (i.e. x and y comp. separately)
• compensate for imperfections
• and intrinsic resonances

beam trajectory and spin orientation when
crossing a siberian snake
29
New Helical Snake in AGS
helical snake decouples horizontal and vertical
motions (not the case for the solenoidal snake
used until now)
substantial improvement of polarization in
AGS PBEAM 45 at extraction, sometime
exceeding 50 a stronger superconducting helical
snake for next run expect PBEAM 70 after 2 3
years of operation
30
Polarimetry Impact on Spin Physics
Physics Asymmetries
Single Spin Asymmetries
Double Spin Asymmetries
measurements

• measured spin asymmetries normalized by PB to
  extract Physics Spin Observables
• RHIC Spin Program requires DPbeam / Pbeam 0.05
• normalization Þ scale uncertainty
• polarimetric process with large s and known AN
• pC elastic scattering in CNI region, AN almost
  calculable, but small 1 2
• fast measurements
• requires absolute calibration polarized gas jet
  target

31
Elastic pC pC scattering at low t
0.005 lt t lt 0.05 (GeV/c)2
scattered proton

polarized beam
t (pout pin)2 lt 0 Tkin 2 MC
Carbon target
recoil
recoil Carbon

• AN from interference of hadronic spin non-flip
• and ElectroMagnetic spin-flip amplitudes
• - hadronic spin-flip
• Polarimetry
• - almost calculable, measured to 30 _at_ 21.7
  GeV
• - small AN 1- 2 Þ requires large
  statistics gt 107
• - large cross section
• - weak beam momentum dependence (p gt 20 GeV/c)
  ?
• Absolute calibration
• - use a polarized H gas-jet target
• - exploit symmetry in elastic pp scattering
  ANbeam (t ) - ANtarget (t )
• PB - PT . eNB / eNT

pC Analyzing Power
E950_at_BNL p 21.7 GeV/c
32
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
33
RHIC pC Polarimeters
beam direction
inside RHIC ring _at_IP12
Ultra thin Carbon ribbon Target (3.5mg/cm2 ,10mm)
1
6
5
2
Si strip detectors (ToF, EC)
3
4
30cm
RHIC 2 rings
similar setup in AGS ring

• 2 72 channels read out with Wave Form
  Digitizers
• very large statistics per measurement ( 20 106
  events) detailed analysis
• bunch by bunch analysis
• channel by channel (each channel is an
  independent polarimeter)
• 45o detectors sensitive to vertical and radial
  components of Pbeam
• unphysical asymmetries

34
Performance
TOF, ns
Typical mass reconstruction
Tkin ½ MR(dist/ToF)2 non-relativistic kinematics
MR 11 GeV sM 1 GeV
Carbon
Prompts
Alpha
Alpha C aX
Carbon
Prompts
EC, keV
MR, GeV

• Very clean data
• Event selection select events in the Carbon
  band (banana)
• Good separation of C ions from prompts may allow
  going to very high t values
• Low ?2 of sequential measurements stable
  operation
• No beam intensity dependence up to 1012 p /
  bunch

35
Si Detector and Energy Loss
at t -0.005 (GeV/c)2, Energy of recoil Carbon
Ekin few 100 keV ( Ekin -t / 2MC ) range in
Silicon, only fraction of micrometer substantial
fraction of Carbon energy lost in dead layer
(entrance window) correct Ekin for energy loss
energy scale error important to minimize energy
losses in dead layer of detector
p implants 150 nm deep
charge collection Al electrodes
active area 24 x 12 mm2 thickness 400 m 12 2 mm
wide DC coupled strips
n type Si wafer
n implants and Al backplane
top view of Si strip
36
DAQ and WFD
Wave Form Digitizer peak sensing ADC, CFD,
common to the pC and JET DAQ system
ADC 3140 MHz
synchronized to accelerator clocks bunch -ing Þ
start TDC
online analysis of waveform performed between
consecutive bunch -ing Þ PH, tot Q, t.o.f
FPGA
Dt 2 ns DE lt 50 keV
onboard memory
DAQ PC
20 106 events in 20 seconds Þ deadtimeless DAQ
system can accept, analyze, and store 1 event /
each bunch -ing
37
pC raw asymmetry at 24.3 GeV

e PB AN
preliminary
calculated over several t bins
ANth from a fit to E950 data at 21.7 GeV over
similar t range L. Trueman hep-ph/0305085
normalization region
áANñ 1.12 0.009 lt t lt 0.022 (GeV/c)2
PB 0
recoil Carbon energy (keV)
Similar procedure in RHIC
38
RHIC polarization profile

• Polarization
• Beam Intensity
• H Scan --horizontal scan with vertical target
• V Scan vertical scan with horizontal target

• large polarization profile in vertical direction
  (small profile in horizontal)
• observed position dependent fluctuation in
  polarization measurements
• an issue for calibration the JET integrates
  over the full beam profile
• the pC CNI polarimeter measures the beam
  center

39
The Absolute pp Polarimeter
JET in the IR
Polarized Hydrogen Gas Jet Target intensity
1017 atoms / s thickness 1012 H / cm2
polarization 93 no depolarization
from beam wake fields Silicon recoil
spectrometer Measure ANpp in pp elastic
scattering in the CNI region to DAN lt 10-3
accuracy transfer target to beam
polarization PBeam - PTarget e Beam / e
Target Initially (2004) measure PBeam to 10
40
The Atomic H Beam Source
Hyperfine state (1), (2), (3), (4)
H2 dissociator

separation magnets (sextupoles)
(1), (2)
RF transitions
focusing magnets (sextupoles)
Pz (1), (4) (SFT ON (2)?(4)) Pz- (2), (3)
(WFT ON (1)?(3)) Pzo (1), (2), (3), (4)
(SFT WFT ON )
recoil detectors

• record beam intensity
• 1012 H / cm2
• 100 eff. RF transitions
• focusing high intensity
• B-R polarimeter

Breit-Rabi polarimeter
holding field magnet
41
JET target polarization
Target polarization cycle / - / 0 500 / 500 /
50 sec (600 / 600 / 60 cycle 1 cycle 0.83
sec) polarization to be scaled down due to a 3
H2 background Ptarget 93 2 -3 (current
understanding)
42
The Road to Pbeam with the JET target

• Requires several independent measurements
• 0 JET target polarization Ptarget (Breit-Rabi
  polarimeter)
• 1 AN for elastic pp in CNI region AN - 1 /
  Ptarget eN
• 2 Pbeam 1 / AN eN
• 1 2 can be combined in a single measurement
  Pbeam / Ptarget - eN / eN
• self calibration works for elastic scattering
  only
• 3 CALIBRATION ANpC for pC CNI polarimeter in
  covered kinematical range
• ANpC 1 / Pbeam eN
• (1 ) 2 3 measured simultaneously with several
  insertions of carbon target
• 4 BEAM POLARIZATION Pbeam 1 / ANpC eN to
  experiments
• at each step pick-up some measurement errors

expected precision
transfer calibration measurement
43
Recoil spectrometer
ANbeam (t ) - ANtarget (t ) for elastic
scattering only! Pbeam - Ptarget . eNbeam /
eNtarget
6 Si detectors covering blue beam MEASURE
energy (res. lt 50 keV) time of
flight (res. lt 2 ns) scattering angle (res.
5 mrad) of recoil protons from pp pp elastic
scattering

• HAVE design
• azimuthal coverage
• one Si layer only
• smaller energy range
• reduced bckgrnd rejection power

44
pp elastic data collected
ToF vs EREC correlation Tkin ½ MR(dist/ToF)2
recoil protons elastic pp ? pp scattering
JET Profile measured selecting pp elastic events
FWHM 6 mm As designed
D ToF lt 7.5 ns
background 118 cts. subtracted
Number of elastic pp events
CNI peak AN 1 lt E REC lt 2 MeV
? source calibration
Hor. pos. of Jet 10000 cts. 2.5 mm
prompt events and beam gas

• recoil protons unambiguously identified !
• 100 GeV 700,000 events at the peak of AN
  100 hours
• ( 2 106 total useful pp elastic events)
• 24 GeV 120,000 events at the peak of AN
  17 hours
• ( 4 105 total useful pp elastic events)

45
Energy - Position correlations
EREC µ q2 (i.e. position2)

recoil energy (MeV)
fully absorbed protons
position (x)
missing mass squared
punch through protons
FWHM 0.1 GeV2
number of events (a. u.)
inelastic threshold
DMX2
TDC vs ADC individual channels
MX2 GeV2
elastic pp events clearly identified !
46
Event selections
Strip distribution for energy interval 1250
1750 keV
signal
background
Si 2
Si 6
visually implement the energy / angle correlation
in selecting elastic pp events typically, for
each energy bin, select 3 to 4 strips per
detector future replace this selection with a
selection on MX Background only from selected
channels not from whole detector (4 5 smaller
!) Total Backgrounds lt 8 , a source lt 4,
Physics Background lt 4
47
ONLINE polarization Results
ONLINE º statistical errors only no
background corrections no systematic
studies no false asymmetries studies partial
run selection
data divided into 3 energy energy bins

an example 750 lt EREC lt 1750 keV
Target average over beam polarization Beam
average over target polarization
target asymmetry
blue beam with alternating bunch polarizations
?? ?? ?? good uniformity from run to
run (stable JET polarization) JET polarization
reversed each 5 min.
1 run 1 hour
beam asymmetry

• Pbeam 36.9 1.9
• Pbeam (pC CNI) ñ 38.1
• No major surprises ?
• (statistical errors only !)

48
Summary and outlook accelerator

• RHIC Spin Program well under way
• Successfully demonstrated accelaration, storage,
  and collisions of polarized protons up to 100 GeV
• All accelerator components for spin in place and
  commissioned
• Expect cold snake in AGS next year (last missing
  piece)
• Substantial progress has been made in improving
  PBeam
• PBeam 40 in both rings
• almost no loss during acceleration in RHIC
• Luminosity 1 pb-1 / week (equivalent) achieved
• Polarimetry fast and reliable, lt 30 sec.
  measurement time
• steady progress in understanding and addressing
  systematic issues
• JET target operated beautifully in 2004,
  absolute calibration under way
• High Polarization (PBeam 70) and Luminosity
  (several pb-1 / week)
• in a few years

49
Summary and Outlook experiments

• All spin experiments work beautifully
• Major 1st generation upgrades (almost)
  completed for Spin Physics
• New Spin Physics results already extracted from
  the first p p collisions in 2002 and 2003
• Plan for a long (10 weeks) Spin Run in 05
• L 10 pb-1 with PBeam gt 40
• DG from inclusive JET and p0 production
• Long term plan
  
  (continuous effort for luminosity and
  polarization development needed)
• Measurements with rare probes ALL(? jet),
  ALPV(W) and transversity
  via mid-rapidity jet fragmentation