» 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 ()