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R&D Proposal for an electron polarimeter, a luminosity monitor and a low Q2-tagger

RD 2013-6

E.C. Aschenauer

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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 polarisation measurement

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eRHIC-Detector Design Concept

ToRoman Pots

Upstreamlow Q2

tagger

HCAL HCAL

ECAL PWO ECAL WScinECAL W-Scintillator

RICHRICH

PID:-1<h<1: DIRC or proximity focusing Aerogel-RICH1<|h|<3: RICH Lepton-ID: -3 <h< 3: e/p 1<|h|<3: in addition Hcal response & g suppression via tracking|h|>3: ECal+Hcal response & g suppression via tracking-5<h<5: Tracking (TPC+GEM+MAPS)

DIRC/proximity RICH

h-h

E.C. Aschenauer

ToLumi

detector

e-Polarimeter where to put

before or after IR

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Example: Longitudinal Spin Structure

E.C. Aschenauer

Can DS and DG explain it all ?

Contribution to proton spin to date:Gluon: 20% (RHIC) Quarks: 30% (DIS)MISS 50% low x

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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 noweRHIC 5x100/250 GeV

dramatic reduction of uncertainties:

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• can expect ~5-10% uncertainties on ΔΣ and Δg

BUT need to control systematics

current data

w/ eRHIC data

Can we solve the spin sum rule ?

E.C. Aschenauer

total quark spin DS

gluonspin Dg

✔

✔

orbital angular momentum

can beextracted throughexclusive reactions

for details seeD. Mueller, K. KumerickiS. Fazio, and ECAarXiv:1304.0077

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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

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Luminosity Measurement: physics processes

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

requires ‘alternative’ methods for luminosity

determination

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Polarization and Luminosity Coupling Concept: Use Bremsstrahlung ep epg as reference cross section

normally only single photon counting 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), did these calculations for ZEUS and is now at CERN to work on CLIC-QED calculations

hopefully a is smallE.C.

Aschenauer

Important

need to monitor not only polarisation level but also

polarisation bunch current correlation

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Luminosity Measurement Concept: Use Bremsstrahlung ep epg as reference cross section

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

E.C. Aschenauer

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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

12E.C. Aschenauer

Detector and IR-DesignAll optimized for dedicated detectorHave +/-4.5m for main-detector p: roman pots / ZDC e: low Q2-tagger

e

eRHIC-Detector:collider detector with-4<h<4 rapidity coverageand excellent PID

p

eRHICDetector

100$-question:Can we combine low Q2-taggerlumi-monitorand compton polarimeterin one detector system?

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eRHIC Lepton Beam How to generate 50 mA of polarized electron beam? Polarized cathodes are notorious for dying fast even at mA beam currents

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 polarisation. A problem discussed for ILC influences where we want to measure polarisation in the ring

How much polarisation 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 polarisation 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 polarisation Energy asymmetry

segmented Calorimeter to measure possible

transverse polarisation component position

asymmetry

E.C. Aschenauer

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Lepton Polarization

E.C. Aschenauer

Method: Compton backscattering

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

15E.C. Aschenauer

ep

PolarimeterLaser

laser polarisationneeds to be monitored Measure Polarisation at IP

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

luminosity loss 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 polarisation? need to measure at location, where bremsstrahlung contribution is small

Before IP: need to find room for photon calorimeter

The lepton polarimeter: Location?

Summary:

all of this needs to be carefully modeled

work to integrate eRHIC IR into EICroot has started

Comptonphoton

detector

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Low Q2-taggere’-tagger:

detect low Q2 scattered electrons quasi-real photoproduction physics

possibly also detect lepton from lepton polarimeter compton scattering

design could follow the Hall-D tagger designpileup can be avoided by fine segmentation of tagger detectors

E.C. Aschenauer

e’-detector

Ee

Array of Scintillatorsvery finely spaced

might need less segmentationScintillator Calorimeter

Electron Tagger as Hall-D

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Microscope

Hodoscope support frame

Tagger strong-back

Vacuum Chamber supports

Magnet steel Vacuum chamber

Coils

Electron beam

Photon

beam

post-bre

msstra

hlungs

electrons

Hodoscope

E.C. Aschenauer

tagged scattered electrons from Bremsstrahlung from ~1 GeV to 6 GeV photon energy 6 GeV to 12 GeV

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Deliverables Luminosity:

determine a in s0(1+aPePp) through calculation develop a MC for (un)polarised bremsstrahlung in ep/eA

collisions integrate luminosity detectors into the IR-design develop detector performance requirements follow up

with detector R&D for calorimeter technology, i.e. Diamond

Polarimetry: determine performance requirements for fast and

“slow” polarisation measurement integrate polarimeter into IR-design and as close as

possible to IP simulation package of polarimeter

Low Q2-tagger: determine the detector performance requirements

can scattered leptons from bremsstrahlung be separated from low-Q2 DIS segmentation of tagger-detectors

Integrate into IR-designE.C.

Aschenauer

Goal to increase collaboration:

Will seek collaboration with Luminosity and low-Q2

tagger group from LHeC

Request:

1 postdoc position for 2 years starting in FY14

travel funding for the group 10k$ / year

19E.C. Aschenauer

BACKUP

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What needs to be covered BY THE DETECTORe’

t

(Q2)e

gL*

x+ξ x-ξ

H, H, E, E (x,ξ,t)

~~

, ,g p J/Y

p p’

Inclusive Reactions in ep/eA: Physics: Structure Fcts.: g1, F2, FL

Very good electron id find scattered lepton Momentum/energy and angular resolution of e’ critical scattered lepton kinematics

Semi-inclusive Reactions in ep/eA: Physics: TMDs, Helicity PDFs flavor separation, dihadron-corr.,… Kaon asymmetries, cross sections Excellent particle ID: p±,K±,p± separation over a wide range in h full F-coverage around g* Excellent vertex resolution Charm, Bottom identification

Exclusive Reactions in ep/eA: Physics: GPDs, proton/nucleus imaging, DVCS, excl. VM/PS prod. Exclusivity large rapidity coverage rapidity gap events ↘ reconstruction of all particles in event high resolution in t Roman potsE.C.

Aschenauer

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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

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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

Improvements of hadron polarisation measurements:

continuously monitor molecular fraction in the H-Jet

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

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eRHIC: high-luminosity IR

10 mrad crossing angle and crab-crossing High gradient (200 T/m) large aperture Nb3Sn focusing magnets Arranged free-field electron pass through the hadron triplet magnets Integration with the detector: efficient separation and registration of

low angle collision products Gentle bending of the electrons to avoid SR impact in the detector

Proton beam lattice

© D.Trbojevic, B.Parker, S. Tepikian, J. Beebe-Wang

e

p

Nb3Sn

200 T/m

G.Ambrosio et al., IPAC’10

eRHIC - Geometry high-lumi IR with β*=5 cm, l*=4.5 mand 10 mrad crossing angle 1034 cm-2 s-1

20x250

20x250

GeneratedQuad aperture limitedRP (at 20m) accepted

E.C. Aschenauer

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Integration into Machine: IR-Design

E.C. Aschenauer

space for low-Q e-tagger

Outgoing electron direction currently under detailed design detect low Q2 scattered leptons want to use the vertical bend to separate very low-Q e’ from beam-electrons can make bend faster for outgoing beam faster separation for 0.1o<Q<1o will add calorimetry after the main detector

Exclusive Reactions: Event Selection

E.C. Aschenauer

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leading protons are never in the main detector

acceptance at EIC (stage 1 and 2)

eRHIC detector acceptance

e’(Q2)

e gL*

x+ξ x-ξ

H, H, E, E (x,ξ,t)~~

g

p p’t

proton/neutron tag method

o Measurement of t o Free of p-diss backgroundo Higher MX rangeo to have high acceptance

for Roman Pots / ZDC challenging IR design

Diffractive peak

x L=p' zp z

≈1− x IP

Need for roman pot

spectrometerANDZDC

5x100 GeV 5x100 GeV20x250 GeV

t-Measurement using RP

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Accepted in“Roman Pot” at 20m

Quadrupoles

acceptance

10s from the beam-

pipe

• high‐|t| acceptance mainly limited by magnet aperture

• low‐|t| acceptance limited by beam envelop (~10σ)

• |t|‐resolution limited by– beam angular divergence ~100μrad for small |t|– uncertainties in vertex (x,y,z) and transport– ~<5-10% resolution in t (follow RP at STAR)

Simulation based on eRHIC-IR

GeneratedQuad aperture limitedRP (at 20m) accepted

20x250

E.C. Aschenauer

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Spectator proton tagging for He-3

E.C. Aschenauer

Momentum smearing mainly due to Fermi motion + Lorentz boost Angle <~3mrad (>99.9%)

after IR magnets at 20m

at 20m after IR magnets RP acceptance +10s beam clearance 90% tagging efficency

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Kinematics of Breakup Neutrons

Results from GEMINI++ for 50 GeV Au

+/-5mrad acceptance totally sufficient

Results:With an aperture of ±5 mrad we are in good shape• enough “detection” power for t > 0.025 GeV2

• below t ~ 0.02 GeV2 photon detection in very forward direction all accounted in IR designQuestion:• For some physics needed rejection power for

incoherent: ~104

Critical: ZDC efficiency

E.C. Aschenauer

29E.C. Aschenauer

ep

PolarimeterLaser

laser polarisationneeds to be monitored

Allows to measure polarisation right at IR, but only for non-colliding bunches need as many non-colliding bunches as cathods no bremsstrahlungs background

ECal: needs to be radiation hard (sees synchrotron radiation fan) possible technology diamante calorimeter ILC FCal will be used to detect compton photons

e’-tagger: detect low Q2 scattered electrons quasi-real photoproduction physics detect lepton from compton scattering

pair spectrometer: only possible high precision luminosity measurement

~ECAL

small θe’-tagger

pairspectrometer

A possible layout for all in one

Summary:

all of this needs to be carefully modeled

work to integrate eRHIC IR into EICroot has started