» Absolute Polarimetry of Proton Beams at RHIC« Oleg Eyser for the RHIC Polarimetry Group International Workshop on Polarized Sources, Targets and Polarimetry Ruhr-Universität, Bochum September 14-18, 2015
Dec 14, 2015
» Absolute Polarimetry of Proton Beams at RHIC«
Oleg Eyserfor the RHIC Polarimetry Group
International Workshop on Polarized Sources, Targets and Polarimetry
Ruhr-Universität, Bochum
September 14-18, 2015
2The Relativistic Heavy Ion Collider
RHIC
NSLS-II
at Brookhaven National Laboratory
3Polarized Protons in RHIC
AGSLINACBOOSTER
Polarized Source
200 MeV Polarimeter
Hydrogen Jet Polarimeter
PHENIXSTAR
Siberian Snakes
Siberian Snakes
Carbon Polarimeters
RF Dipole AGS Internal Polarimeter
AGS pC Polarimeter
Strong Snake
Tune Jump QuadsHelical Partial Snake
Spin Rotators
Spin Flipper
→ Talk by A. Zelenski’s
4Improvement in Beam Polarization
Consistent improvement in delivered luminosity and beam polarization.
Beam energies:
up to 255 GeV
Figure of merit for double helicity measurements:
recent run 2015
5
𝐴𝑁=𝑑𝜎 𝑙𝑒𝑓𝑡−𝑑𝜎 h𝑟𝑖𝑔 𝑡
𝑑𝜎 𝑙𝑒𝑓𝑡+𝑑𝜎 h𝑟𝑖𝑔 𝑡
𝜀=𝐴𝑁 ∙𝑃=𝑁 𝐿−𝑁𝑅
𝑁 𝐿+𝑁𝑅
𝒔𝒛=𝑵
𝒑=𝑳
left
right
scattering plane
𝑠𝑧=±12ℏ⇒𝑃=𝑛
↑−𝑛↓
𝑛↑+𝑛↓
(proton)
(proton)(Carbon)
Polarization & Asymmetries
(*) perpendicular to polarization vector
(elastic scattering)
6
𝜑 (𝑠 ,𝑡 )= ⟨𝜆𝐶 𝜆𝐷|𝜑|𝜆𝐴 𝜆𝐵 ⟩ Phys. Rev. D 79, 094014 (2009)
no-flip amplitude:
First data from 2004 (100 GeV beam)
Elastic Proton-Proton Scattering
Transverse single-spin asymmetries are driven by an interference of amplitudes and can be compared to Regge theory.
7
atomic hydrogen target
proton beam100/250 GeV
Si strip detectors from interaction point
Recoil proton from elastic scattering
Independent of beam energy, species
Elastic Recoil Protonsscattered proton
Non-relativistic:
detectorthickness
target width: bunch length:
Carbon polarimetersTwo per ringFast measurement
Beam polarization profilePolarization decay (time dependence)
Hydrogen jet polarimeterPolarized targetContinuous operation per fill
beam
normalization
8
→ Talk by G. Webb
9Detector Setup
INNER OUTER
≈10 cm
12 strips3.75 mm each
75 cm
Set of eight Hamamatsu Si strip detectors12 strips, each wide, thickUniform dead layer
≈ 0.7 cm
10Energy CalibrationCalibrations are done every few days:o Gaino Entrance window (dead layer)
Two different α-sources
Resolution of peak finding is within 1 ADC count
Stopping power for protons and-particles from NIST database:
example
11Kinematics❷ ❻ ❽ ⓬
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 – central to blue – downstream
12Stopped Recoil Protons
Slope of rise in waveform can be used to identify punch-through particles
Normalized waveform rise ()in each detector
Independent of DAQ system (CAMAC/VME)
Remove punch-through particles:
𝑇 𝑘𝑖𝑛(MeV)
𝛿𝐴𝐷𝐶(a.u.)
example detector
(δADC<−0.5)∧(𝛿𝐴𝐷𝐶<8.5−1.5∗𝑇𝑘𝑖𝑛)
Normalized to
Slope calculated in six binsaround
→Talk by A. Poblaguev
13Detector AlignmentMagnetic holding field for target polarization changes acceptance of detectors on left and right sides
Outer correction field for compensation
For missing proton mass:
Compare with geometry ofdetector averaged 12 strips
p+Au and p+Al operation had asignificant beam angle on thejet target
example detector
Missing mass:
Non-relativistic recoil:
switc
h to
p+A
u
switc
h to
p+A
lchange in STAR rotators
field
cor
recti
on
14QA: KinematicsElastic proton recoil selection:
Fit to ALL data, plotted under the distributions in each detector
Si-strips:red – central to blue – downstream
example fill
15
𝑃 𝐵𝑒𝑎𝑚=−𝜀𝐵𝑒𝑎𝑚𝜀𝑇𝑎𝑟𝑔𝑒𝑡
𝑃𝑇𝑎𝑟𝑔𝑒𝑡
❶Polarization independent background
⇒
❷Polarization dependent background
background fraction
from Breit-Rabimeasurement
Asymmetries & Polarization
𝜀=𝐴𝑁 ∙𝑃
measure
16Background
BackgroundSIG
NAL
SIGNAL
Inclusive
Inclusive
RHIC bunch
RHIC bunch
Signal & Background IAbort gaps are not aligned at 12 o’clock
Use abort gaps for background and clean signal identification
17Signal & Background IIExample (logarithmic z-scale)
: difference of time-of-flight to elastic signal (in geometry)
: difference of missing mass to scattered proton (in 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
18Signal & Background III
inclusive (normalized to peak)
background (normalized to signal at )
background fraction
Example (blue beam, )
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 only for comparison of shape and source of background
normalization
well described by normalization at
19Background SourcesExample (blue beam, ) From operation
Typical bunch shape of Au-beam seen in full background, dominates early background
Late background mainly from signal beam
Using signal cuts in blue abort gap:
Fill-by-fill background fraction depends on conditions of both beams important for beam polarization measurement
still excellent agreementBackground fraction
20Asymmetry Examples
From operation
Blue beam (proton on jet target)
Clear asymmetry within
Background asymmetry consistent with zero
21Correlated BackgroundInelastic background: expected to be polarization independent (or small compared to signal)Elastic background: opposite beam can affect low energy signalo jet target size o would have opposite sign for target polarization, no effect on beam polarizationo consistent with zero
Increased asymmetries have been observed at low energies, attributed to parts of the blue-side detectors (masked out)Possibly due to correlated background that suppresses the signal in one polarization state
22Analyzing Power:
Atomic hydrogen polarization
Molecular component (by mass)
Global uncertainty from target polarization not included
-range can be extended with punch-through protons
PRELIMINARY
23Analyzing Power:
PRELIMINARY
Atomic hydrogen polarization
Molecular component (by mass)
Global uncertainty from target polarization not included
-range can be extended with punch-through protons
24Beam PolarizationsOnline results from 2015, no background correction included
p+Au operation p+Al operation
25
o Polarimetry at RHIC• Essential input for experiments
• Fast feedback during collider operation
Fast polarization measurement with Carbon targets
Absolute normalization with polarized hydrogen jet target
o Analyzing power with new detectors in 2015 improved precision
o New asymmetries from elastic proton-heavy-ion scattering
o Determination of beam polarizations with background correction expected soon
Summary
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Background Normalization ()
Background Fraction ()