Β» Proton Polarimetry with the Hydrogen Jet Target at
RHIC in Run 2015Β«
Oleg Eyserfor the RHIC Polarimetry Group
22nd International Spin SymposiumUniversity of Illinois, Urbana-Champaign
September 26-30, 2016
Polarized Protons in RHIC 2
AGSLINAC
BOOSTER
Polarized Source
200 MeV Polarimeter
Hydrogen Jet Polarimeter
PHENIX
STAR
Siberian Snakes
Siberian Snakes
Carbon Polarimeters
RF Dipole AGS Internal Polarimeter
AGS pC Polarimeter
Strong Snake
Tune Jump Quads
Helical Partial Snake
Spin Rotators
Spin Flipper
Improvement in Beam Polarization 3
Consistent improvement in delivered luminosity and beam polarization.
Beam energies:
up to 255 GeV
Figure of merit for double helicity observables:
~β β π4
recent RHIC run 2015
π΄π =ππππππ‘ β πππππβπ‘
ππππππ‘ + πππππβπ‘
ν = π΄π β π =ππΏ β ππ ππΏ + ππ
ππ = π΅
π = π³
left
right
π π§ = Β±1
2β β π =
πβ β πβ
πβ + πβ
(proton)
(proton)(Carbon)
Polarization & Asymmetries 4
(*) perpendicular to polarization vector
(elastic scattering)
Carbon polarimeters
Two per ring
Fast measurement
πΏπ/π β 4%
Beam polarization profile
Polarization decay (time dependence)
Hydrogen jet polarimeter
Polarized target
Continuous operation
πΏπ/π β 5 β 8% per fill
normalization
5
atomic hydrogen target
proton beam100/250 GeV
Si strip detectorsβ 75 cm from interaction point
Recoil proton from elastic scattering
Independent of beam energy, species
Elastic Recoil Protons 6
Non-relativistic: ππππ =1
2ππ£2
detectorthickness
target width: ππ = 0.3 cmbunch length: ππ΅ = 1.0 ns
Detector Setup 7
INNER OUTERβ1
0 cm
12 strips3.75 mm each
75 cm
Set of eight Hamamatsu Si strip detectors
12 strips, each 3.75 mm wide, 500 ΞΌm thick
Uniform dead layer β 1.5 ΞΌm
β 0.7 cm
ππππ (MeV)
πΏ π΄π·πΆ(a.u.)
example detector
QA: Kinematics 8
Elastic proton recoil selection:
After energy and π0 calibration
ππππ π βππ < 100 MeV/π2
Ξπ‘ < 5 ns
Fit to ALL data, plotted under the distributions in each detector
Si-strips:red β central to blue β downstream
example fill
Detector Alignment 9
Magnetic holding field for target polarization changes acceptance of detectors on left and right sides
Outer correction field is adjusted for compensation
For missing proton mass:
sin π =πβ²
2 β ππ β ππ΅(2 β πΈ + 2 β ππ β ππ )
Compare with geometry ofdetector (averaged over 12 strips)
p+Au and p+Al operation had asignificant beam angle on thejet target
example detector
Missing mass:
ππππ π 2 =
πΈ +ππ β πΈβ²
ππ΅ β πβ²
2
Non-relativistic recoil:
πβ² = 2ππππ
swit
ch t
o p
+Au
swit
ch t
o p
+Alchange in STAR
rotators
fiel
d c
orr
ecti
on
ππ΅πππ = βνπ΅πππνππππππ‘
πππππππ‘
βΆ
Polarization independent background
ν =πββπβ
πβ+πβ+2βπππβ
ππ΅
ππ=
ππ΅ββππ΅
β
ππββππ
β
β·
Polarization dependent background
ν =νπππ β π β νππ
1 β πbackground fraction π = πππ/π
from Breit-Rabimeasurement
Asymmetries & Polarization 10
ν = π΄π β π
measure
Backgro
un
d
Backgro
un
dSIG
NA
L
SIGN
AL
Inclusive
Inclusive
RHIC bunch
RHIC bunch
Signal & Background I 11
Abort gaps are not aligned at polarimeter location
Use abort gaps for background and clean signal identification
beam
beam
detecto
rd
etector
Signal & Background II 12
ππππ π βππ < 50 MeV/π2
ππππ π βππ > 120 MeV/π2
Example (logarithmic z-scale)
Ξπ‘: difference of measured time-of-flight to elastic signal, π‘(ππ )
Ξππππ π : difference of missing mass to scattered proton (geometry after alignment correction)
Position of elastic proton signal is independent of energy and detector
Vertical stripes are a remnant of the spatial detector resolution
Punch through cuts are already applied
Define signal and background regions by missing mass
Signal & Background III 13
inclusive (normalized to peak)
ππππ π βππ < 50 MeV/π2
background (normalized to signal at 18 < Ξπ‘ < 25 ns)
ππππ π βππ > 120 MeV/π2
background fraction
Example (blue beam, 2 < πΈπππ < 3 MeV)
o Background in yellow abort gap (should be clean blue signal)
o Signal in blue abort gap (should be only background from yellow beam)
The normalization is same as above β only for comparison of shape and source of background
normalization
well described by normalization at 18 < Ξπ‘ < 25 ns
Background Sources 14
Example (blue beam, 3 < πΈπππ < 4 MeV) From π + π΄π’ operation
Typical bunch shape of Au-beam seen in full background, dominates earlybackground
Late background mainly from signal beam
Using signal cuts in blue abort gap:
ππππ π βππ < 50 MeV/π2
Fill-by-fill background fraction depends on conditions of both beams β important for beam polarization measurement
still excellent agreementBackground fraction π = πππ/π
Asymmetry Examples 15
From Τ¦π + π΄π’ operation
Blue beam (proton on jet target)
Clear asymmetry within Ξπ‘ = Β± 5 ns
Background asymmetry consistent with zero
Analyzing Power: π΄π( Τ¦π + π) 16
Atomic hydrogen target polarization π = 96%
Molecular component π π»2 = 3% (by mass)
Global uncertainty from target polarization not included
βπ‘-range can be extended with punch-through protons
Analyzing Power: π΄π( Τ¦π + π΄) 17
Atomic hydrogen target polarization π = 96%
Molecular component π π»2 = 3% (by mass)
Global uncertainty from target polarization not included
βπ‘-range can be extended with punch-through protons β A. Poblaguev
Longitudinal Bunch Profile: π + π 18
Full run 15 statistics: π + π
1 < ππ < 7 MeV
Comparison of inclusive and clean bunches
Beam intensity: normalized number of events
First measurement of longitudinal bunch profile
No significant longitudinal polarization profile has been found.
Longitudinal Bunch Profile: π + π΄π’ 19
Full run 15 statistics: π + π¨π
1 < ππ < 7 MeV
Comparison of inclusive and clean bunches
Beam intensity: normalized number of events
No significant effect from colliding bunches can be seen.
Final Beam Polarizations 20
Atomic hydrogen target polarization 96%π»2 content 3% (mass)
Ratio of target/beam asymmetries1 < πΈππππππ < 7 MeV (six bins)
Fit to constant
use fixed π΄π for π + π use fill by fill ratio for π + π΄
Luminosity Weighted Polarization 21
π =β« π π₯, π¦, π‘ β πΌ π₯, π¦, π‘ ππ₯ππ¦ππ‘
β« πΌ π₯, π¦, π‘ ππ₯ππ¦ππ‘
Experiments
HJET Polarimeter
Carbon Polarimeter
π =β« π π₯, π¦, π‘ β πΌπ΅ π₯, π¦, π‘ β πΌπ π₯, π¦, π‘ ππ₯ππ¦ππ‘
β« πΌπ΅ π₯, π¦, π‘ β πΌπ π₯, π¦, π‘ ππ₯ππ¦ππ‘
sweep
beam width
π = ππππ₯ β πΌ
πΌπππ₯
π
o Polarimetry at RHIC
β’ Essential input for experiments
β’ Fast feedback during collider operation
Fast polarization measurement with Carbon targets
β’ Polarization decay and transverse profile
Absolute normalization with polarized hydrogen jet target
o Analyzing power with new detectors in 2015 β improved precision and systematic studies
o New asymmetries from elastic proton-heavy-ion scattering
o Longitudinal polarization profile
o Final beam polarizations are fully background corrected
Summary 23
π π , π‘ = ππΆππ· π ππ΄ππ΅Phys. Rev. D 79, 094014 (2009)
π1 π , π‘ = +1
2+1
2π +
1
2+1
2
π2 π , π‘ = +1
2+1
2π β
1
2β1
2
π3 π , π‘ = +1
2β1
2π +
1
2β1
2
π4 π , π‘ = +1
2β1
2π β
1
2+1
2
π5 π , π‘ = +1
2+1
2π +
1
2β1
2
π΄πππ
ππ‘= β
4π
π 2Im π5
ππβ π , π‘ π+βππ π , π‘ + π5
βππβ π , π‘ π+ππ(π , π‘)
no-flip amplitude: π+ π , π‘ =1
2π1 π , π‘ +π3 π , π‘
First data from 2004 (100 GeV beam)
Elastic Proton-Proton Scattering 25
Transverse single-spin asymmetries are driven by an interference of amplitudes and can be compared to Regge theory.
26o Reconstruction
o Energy calibration
o Time of flight adjustment
o Geometry alignment
o Pedestal noise QA
o Signal selection
o Remove punch through hits
o Missing mass ππππ π βππ < 50 MeV/π2
o Time of flight Ξπ‘ < 5 ns
o Asymmetry calculation
o Inclusive and signal bunches
o Background asymmetry correction
o Beam polarization calculation
o Asymmetry ratio 1 < πΈππππππ < 7MeV
ππ =ππΌ β πππ΅1 β π
π =π΅
π + π΅
Energy Calibration 27
Calibrations are done every few days:
o Gain
o Entrance window (dead layer)
Two different Ξ±-sources
πΈπΌ πΊπ = 3.183 MeV
πΈπΌ π΄π = 5.486 MeV
Resolution of peak finding is within 1 ADC count
Stopping power for protons andπΌ-particles from NIST database:
βπΈπΌ(π΄π) = 0.72 β βπΈπΌ πΊπ
βπΈπ = 0.44 β βπΈπΌ(πΊπ) β πΈ[πππ]β0.64
example
Kinematics 28
β· β» β½ β¬
12 strips per detector
Removed peak in prompt hits at low ADC/TDC region
Using elastic p-recoil signature for time-of-flight offset determination
o Slow drift with time (detector/read-out)
o Big jumps when changing the DAQ system
example detector
Si-strips:red β central to blue β downstream
Stopped Recoil Protons 29
Slope of rise in waveform can be used to identify punch-through particles
Normalized waveform rise (4.5 < πΈ < 5.5 MeV)in each detector
Independent of DAQ system (CAMAC/VME)
Remove punch-through particles:
ππππ (MeV)
πΏ π΄π·πΆ(a.u.)
example detector
(Ξ΄ADC < β0.5) β§ (πΏπ΄π·πΆ < 8.5 β 1.5 β ππππ)
Normalized to π΄π·πΆmax
Slope πΏπ΄π·πΆ calculated in six ππ·πΆ binsaround Β½ π΄π·πΆmax
Beam Polarizations 38
Online results from 2015, no background correction included
p+Au operation p+Al operation
π΄π in Elastic Τ¦π + π Scattering 39
Noise threshold cut: 0.20 for π + π, 0.15 for π + π΄
p+A may still have some issues with high background fractions and changing beam conditions
40Summary p+AlBeam polarizations
Full run 15 statistics, p+Al
Comparison of inclusive and clean bunches
41Pedestal Noisefill 18677
channel 64(with CAMAC)
fill 19214channel 81(with VME)
ππππ‘β
ππππ‘β
solid/dashed: πππππβ /πππππ
β
The noise is mainly on one side of the detector (outside).
It changes the waveform quality (slope) for low energies and leads to asymmetric loss of events.
πππ πππβ β πππ πππ
β
(*) can use a fit for VME data, but resolution of CAMAC is too small
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