IMPORTANCE OF BUNCH-BY-BUNCH

POLARIZATION INFORMATION FOR EIC PHYSICS

E.C. Aschenauer

arXiv: 1212.1701 & 1108.1713

EIC User Meeting 20142

REQUIREMENTS TO REALIZE THE EIC PHYSICS PROGRAM

E.C. Aschenauer

Requirements from Physics:

High Luminosity ~ 1033 cm-2s-1 and higher Flexible center of mass energy Electrons and protons/light nuclei (p, He3 or D) highly polarised Wide range of nuclear beams (D to U) a wide acceptance detector with good PID (e/h and p, K, p) wide acceptance for protons from elastic reactions and neutrons from nuclear breakup

Important

EIC is a high luminosity machine >1033 cm-2s-1

such controlling systematics becomes crucial

luminosity measurement

lepton and hadron polarization measurement

EIC User Meeting 20143

g1P THE WAY TO FIND THE SPIN

E.C. Aschenauer

5 x 250 starts here

5 x 100 starts here

hep-ph:1206.6014 (M.Stratmann, R. Sassot, ECA) cross section:

pQCD scaling violations

world data

current data

w/ eRHIC data

EIC User Meeting 20144

IMPACT ON ∫DG FROM SYSTEMATIC UNCERTAINTIES

E.C. Aschenauer

Need systematics ≤ 2%

arXiv: 1206.6014

Dominant systematics:

Luminosity Measurement Relative Luminosity

needs to be controlled better then ALL~10-4 at low x

Absolut polarization measurements:electron Pe and hadron Pp

relativeluminosity

EIC User Meeting 20145

IMPACT ON CORRELATED SYSTEMATIC UNCERTAINTY IN p+p p0 ALL ON DG

E.C. Aschenauer

arXiv:1402.6296

relativeluminosity

2009: Relative Luminosity uncertainty same sizeas physics asymmetryR=1.18x10-3 + 0.21x10-3

ALL= 0.4 – 4 x 10-3

EIC User Meeting 20146

REASONS WHY POLARIZATION / CURRENT CAN VARY FROM BUNCH TO BUNCH

E.C. Aschenauer

Polarisation:Hadrons in a storage ring:source instabilitiesBeam-Beam effectsbunch-to-bunch emittance variation, Characteristic scale can be seen from AGSRHIC polarization profile variation for different bunches after accelerationleptons in a storage ring:Beam-Beam effectssource instabilities

leptons in eRHIC What is the expected fluctuation in polarisation from cathode to cathode in the gatling gun

from Jlab experience 3-5% Is there the possibility for a polarization profile for the lepton bunches

if then in the longitudinal direction can be circumvented with 352 MHz RF

Current:Hadrons & leptons in a storage ring:Variations in transfer efficiency from pre-accelerator to main ring beam-beam interaction is important, it affects the bunch lifetime during the storeleptons in eRHIC What fluctuation in bunch current for the electron do we expect

limited by Surface Charge, need to see what we obtain from prototype gun

EIC User Meeting 20147

RHIC HADRON POLARIMETRY

Polarized hydrogen Jet Polarimeter (HJet)Source of absolute polarization (normalization of other polarimeters)Slow (low rates needs looong time to get precise measurements)

Proton-Carbon Polarimeter (pC) @ RHIC and AGS Very fast main polarization monitoring toolMeasures polarization profile (polarization is higher in beam center) and lifetimeNeeds to be normalized to HJet

Local Polarimeters (in PHENIX and STAR experiments)Defines spin direction in experimental areaNeeds to be normalized to HJetAll of these systems are necessary for the

proton beam polarization measurements and monitoring

E.C. Aschenauer

EIC User Meeting 20148

RHIC HADRON POLARISATION AND BUNCH CURRENT

E.C. Aschenauer

Fill 17520 in 2013: Beginning

Fill 17520 in 2013: End

P↑

P↓

EIC User Meeting 20149

RHIC HADRON POLARISATION AND BUNCH CURRENT

E.C. Aschenauer

Fill 17571 in 2013: Beginning

Fill 17571 in 2013: End

P↑

P↓

PSTP-2013, Charlotesville, VA10

RHIC: POLARISATION-BUNCH CURRENT CORRELATION

E.C. Aschenauer

0 50 100 150 200 250 300

-0.07-0.06-0.05-0.04-0.03-0.02-0.01

00.010.020.03

Correlator vs. Energy Up Spin

B1B2Y1Y2

Energy [GeV]

Corr

elat

or

0 50 100 150 200 250 300

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

Correlator vs. Energy Down Spin

B1B2Y1Y2

Energy [GeV]

Corr

elat

or

Data from 2012-Run:

Small anti-correlationbetween polarisation andbunch current at injectionwhich washes out at collision energies

EIC User Meeting 201411

RHIC HADRON POLARISATIONAccount for beam polarization decay through fill P(t)=P0exp(-t/tp) growth of beam polarization profile R through fill pCarbon

polarimeter

x=x0

ColliderExperiments

),(),( 01011 yxIyxPP

),(),(),( 2111 yxIyxIyxPP

correlation of dP/dt to dR/dt

for all 2012 fillsat 250 GeV

Polarization lifetime has consequences for physics analysis different physics triggers mix over

fill different <P>

Result:Have achieved 6.5% uncertainty for DSA and 3.4 for

SSAwill be very challenging to reduce to 1-2%

E.C. Aschenauer

EIC User Meeting 201412 E.C. Aschenauer

POSSIBLE IMPROVEMENTS TO RHIC HADRON POLARIMETRY

H-Jet: continuously monitor molecular fraction in the H-Jet

o currently dominant systematics factor 10 lower bunch current for eRHIC precision per fill

pC-polarimeters find longer lifetime and more homogenious target material for

the pC polarimeters can we calibrate energy scale of pC closer to Ekin(C) in CNI alternative detector technology for Si-detectors to detect C smaller emittance of beam

o reduced/eliminate x-y polarisation profileo harder to measure

polarised Deuterium and He-3 polarimetry will be challenging to use CNI you need to make sure D and He-3 did not break up

local polarimetry @ eRHIC integrate a pC-polarimeter between the spin-rotators

o disappearance of asymmetry means full longitudinal polarisation

EIC User Meeting 201413

LEPTON POLARIZATION

E.C. Aschenauer

572 nm pulsed laser laser transport system: ~80m laser light polarisation measured

continuously in box #2

Multi-Photon Mode:Advantages: - eff. independent of brems. bkg and photon energy cutoff - dP/P = 0.01 in 1 min Disadvantage: - no easy monitoring of calorimeter performance

Am = (I3/2 – I1/2) / (I3/2 + I1/2) = Pe Pl Ap; Ap=0.184

Result:Have achieved 1.4% uncertainty at

HERA

Method: Compton backscattering, i.e. HERA LPOL

EIC User Meeting 201414 E.C. Aschenauer

ep

PolarimeterLaser

laser polarisationneeds to be monitored Measure Polarization at IP

overlap of bremsstrahlungs and compton photons only possible if we have number of empty p-bunches = # cathods

luminosity loss need to know polarisation is fully longitudinal

segmented Calorimeter longitudinal polarization Energy asymmetry transverse polarization component position asymmetry

Measure after / before IP need to measure at location spin is fully longitudinal or transverse

1/6 turn should rotate spin by integer number of π After IP:

does collision reduce polarization problem at ILC for eRHIC very small need to measure at location, where bremsstrahlung contribution is small

Before IP: need to find room for photon calorimeter

Want to measure both the compton photon and the scattered lepton

eRHIC LEPTON POLARIMETER

Comptonphoton

detector

# of cathods in gattling gun:

20 golden number

This guarantees that a hadron bunch collides always with

the electrons produced from one particular cathode,

avoiding/reducing significantly harmful beam-beam effect

of electron beam parameter variations on the hadrons

EIC User Meeting 201415

POLARIZATION AND LUMINOSITY COUPLING Concept: Use Bremsstrahlung ep epg as reference cross section

different methods: Bethe Heitler, QED Compton, Pair Production

Hera: reached 1-2% systematic uncertainty eRHIC BUTs:

with 1033cm-2s-1 one gets on average of 23 bremsstrahlungs photons/bunch for proton beam A-beam Z2-dependence

this will challenge single photon measurement under 0o

coupling between polarization measurement uncertainty and uncertainty achievable for lumi-measurement

no experience no polarized ep collider jet have started to calculate a with the help of Vladimir Makarenk

(NC PHEP BSU, Minsk), the CERN CLIC-QED calculations expert hopefully a is small

E.C. Aschenauer

Goals for Luminosity Measurement:

Integrated luminosity with precision δL< 1%

Measurement of relative luminosity: physics-

asymmetry/10

Fast beam monitoring for optimization of ep-

collisions and control of mid-term variations of

instantaneous luminosity

EIC User Meeting 201416 E.C. Aschenauer

SUMMARY The need for bunch by bunch polarisation information

was documented there is need to monitor not only the polarization level

but also polarization bunch current correlations the polarimeter technology needs to allow for this

information the known challenges to measure polarisation have

been discussed but EIC will be the first polarised ep collider, therefore

there might be surprising effects influencing hadron and lepton polarisation o the unknown unknowns

EIC User Meeting 201417 E.C. Aschenauer

BACKUP

EIC User Meeting 201418

LUMINOSITY MEASUREMENT: PHYSICS PROCESSES

E.C. Aschenauer

Bremsstrahlung ep egp:

Bethe-Heitler (collinear emission): very high rate of ‘zero angle’ photons and electrons, but sensitive to the details of beam optics at IP requires precise knowledge of geometrical acceptance suffers from synchrotron radiation sperature limitation pile-up

QED Compton (wide angle bremsstrahlung): lower rate, but stable and well known acceptance of central detector

Methods are complementary, different systematics

NC DIS: in (x,Q2) range where F2 is known to O(1%) for relative normalisation and mid-term yield control

HERA Concept: normally only g is measured Hera: reached 1-2% systematic uncertainty

EIC User Meeting 201419

LUMINOSITY DETECTORS zero degree calorimeter

high rate measured energy proportional to # photons subject to synchrotron radiation

alternative pair spectrometer

Vacuum

Chamber

L3

ge+/e-g e-

e+

Dipole Magnetvery thinConverter

L2L1

Segmented ECal

The calorimeters are outside of the primary synchrotron radiation fan The exit window conversion fraction reduces the overall rate The spectrometer geometry imposes a low energy cutoff in the photon spectrum, which depends on the magnitude of the dipole field and the transverse location of the calorimeters E.C. Aschenauer

EIC User Meeting 201420

REQUIREMENTS FROM PHYSICS ON IR

E.C. Aschenauer

Summarized at: https://wiki.bnl.gov/eic/index.php/IR_Design_Requirements

Hadron Beam:1. the detection of neutrons of nuclear break up in the outgoing

hadron beam direction location/acceptance of ZDC2. the detection of the scattered protons from exclusive and

diffractive reaction in the outgoing proton beam direction the detection of the spectator protons from 3He and Deuterium location/acceptance of RP; impact of crab-cavities on forward scattered protons

Lepton Beam:3. the beam element free region around the IR 4. minimize impact of detector magnetic field on lepton beam synchrotron radiation5. space for low Q2 scattered lepton detection6. space for the luminosity monitor in the outgoing lepton beam

direction7. space for lepton polarimetry

Important

EIC is a high luminosity machine 1033 cm-2s-1

such controlling systematics becomes crucial

luminosity measurement

lepton and hadron polarization measurement

EIC User Meeting 201421

eRHIC LEPTON BEAM eRHIC design is using the idea of a “Gatling” electron gun with a combiner? 20 cathodes one proton bunch collides always with electrons from one specific cathode

Important questions: What is the expected fluctuation in polarisation from cathode to cathode in the

gatling gun from Jlab experience 3-5%

What fluctuation in bunch current for the electron do we expect limited by Surface Charge, need to see what we obtain from prototype gun

Do we expect that the collision deteriorates the electron polarization. A problem discussed for ILC influences where we want to measure polarization in the ring

How much polarization loss do we expect from the source to flat top in the ERL.

Losses in the arcs have been significant at SLC

Is there the possibility for a polarization profile for the lepton bunches if then in the longitudinal direction can be circumvented with 352 MHz RF

Challenge:

Integrate Compton polarimeter into IR and Detector design

together with Luminosity monitor and low Q2-tagger

longitudinal polarization Energy asymmetry

segmented Calorimeter to measure possible transverse

polarization component position asymmetry

E.C. Aschenauer