April 20, 2023 Valencia Workshop

Very Forward Region Instrumentation

Wolfgang Lohmann, DESY

Basic functions:

- Hermeticity to small polar angles

- Fast and precise Luminosity measuremt

- Shielding of the inner detectors-

April 20, 2023 LDC meeting

20mrad DID

Shielding function

20mrad solenoid

Due to the small bunch size

x~100nm, y~5 nmand the large bunch

charge, N x 1010/bunch,

beamstrahlung becomes important

lots of e+e- pairs

Current design

IP

VTX

FTD

300 cm

L* = 4m

Bhabha ScatteringLumiCal 26 < < 82 mrad

Beampipe

Head-on or small X-angle

BeamCal 4 < < 28 mrad

PhotoCal downstream(100 < < 400 rad

Precise Luminosity Measurement, LumiCal

Goal: <10-3 Precision

Gauge Process:

• Technology: Si-W Sandwich Calorimeter

• MC Simulations

e+e- e+e- ()

Optimisation of Shape and Segmentation,Key Requirements on the

Design

Physics Case: Giga-Z , Two Fermion Cross Sections at High Energy, e+e- W+W-

LumCal bgr

Bhabha

N NL

Inner Radius of Cal.: < 4 μm

Distance between Cals.: < 100 μm

Radial beam position: < 0.6 mm

Requirements on Alignment

and mechanical Precision(MC simulations, BHLUMI)

LumiCal

LumiCalIP

Requirements on the Mechanical Design

< 4 μm

< 0.6 mm

Mechanical frame: Decouple sensor support from absorber support structure

Sensor carriers

Absorber carriers

Technology

Si/W sandwich calorimeter, simulations at advanced level.No hardware devolepment up to now.

Comparison head-on, 2, 20 mrad

Centered around the outgoing beam

Centered around the detector axis

Radial beam shift: 400m

For a 20 mrad design LumiCal MUST be centered around the outgoing

beam-pipe!

)]}ln()([,0max{T

ibeami E

EEconstW

i

ii

W

WXX

Constant value))(_( radmean genrec

))(( rad

value of the constant

0.11e-3 rad

0.13e-3 rad

30 layers 15 rings

20rings

10ring

s

4 layers

15 layers

11 layers

10rings

Performance Simulations for e+e- e+e-()Event selection: acceptance, energy balance, azimuthal and angular symmetry.

Simulation: Bhwide(Bhabha)+CIRCE(Beamstrahlung)+beamspread

•More in the talks by Halina Abramowicz

Beamstrahlung pair background

using serpentine field

0.E+00

1.E+09

2.E+09

3.E+09

4.E+09

5.E+09

6.E+09

8 9 10 11 12 13 14 15 16

R min (cm)

Nm

ber

of

Bh

abh

a ev

ets

per

yea

r

0

500

1000

1500

2000

2500

3000

3500

Bac

kgro

un

d (

GeV

)

Events per year

Background (GeV)

250 GeV

Number of Bhabha events as a function of the innerRadius of LumiCal

Background from beamstrahlung

Background in the LumiCal :(500 GeV, TDR)Zero or small X-angle: negligible20 mrad X-angle: 3-5 TeV

background

• 15000 e+e- per BX 10 – 20 TeV

(10 MGy per year)

• e+e- Pairs from Beamstrahlung are deflected into the BeamCal

GeV

Zero (or 2 mrad) crossing

angle

20 mradCrossing

angle

BeamCal

Background in the BeamCal :(500 Gev, TDR)Zero or small X-angle: 30 TeV/BX20 mrad X-angle: 60 TeV/BX

• Radiation hard sensors needed

Detection of High Energy Electrons and Photons (Detector Hermeticity)

√s = 500 GeVSingle Electrons of 50, 100 and 250 GeV, detection efficiency as a function of R (‘high background region’)

Detection efficiency as a function of the pad-size

Message: Electrons can be

detected!

Red – high BGblue – low BG

QuantityNominal Value

Precision

x 553 nm 4.8nm

y 5.0 nm 0.1 nm

z 300 m 11.5 m

y 0 2.0nm

Beam Parameter Determination with BeamCal

PRELIMINARY!

20 mrad crossing angle

total energyfirst radial momentangular spreadL/R, U/D F/B asymmetries

Also simultaneous determination of several beam parameter is feasible, but: Correlations!Analysis in preparation

Observables

Fast Lumi estimate and feedback for beam steering

nominal setting(550 nm x 5 nm)

>100mIP

L/R, U/D F/B asymmetriesof energy in the angulartails

QuantityNominal Value

Precision

x 553 nm 4.2 nm

z 300 m 7.5 m

y 0 0.2 nm

Heavy gas ionisation Calorimeter

and with PhotoCalPhotons from Beamstrahlung

Heavy crystalsW-Diamond sandwich

sensorSpace for electronics

Technologies for the BeamCal:

•Radiation Hard

•Fast

•Compact

Sensor prototyping, Crystals

Light Yield from direct coupling

Similar results for lead glassCrystals (Cerenkov light !)

and using a fibre

~ 15 %

Compared with GEANT4Simulation, good agreement

Sensor prototyping, Diamonds

ADC

Diamond (+ PA)

Scint.+PMT&

signal gate

May,August/2004 test beams

CERN PS Hadron beam – 3,5 GeV

2 operation modes:

Slow extraction ~105-106 / s

fast extraction ~105-107 / ~10ns (Wide range intensities)

Diamond samples (CVD):

- Freiburg

- GPI (Moscow)

- Element6

Pm1&2

Pads

Linearity Studies with High Intensities

(PS fast beam extraction)105 particles/10 ns

Response to mip

Diamond Sensor Performance

Particle flux, N/cm2/10ns

Univ. of Colorado, Boulder, AGH Univ., INP & Jagiell.

Univ. Cracow,JINR, Dubna,

NCPHEP, Minsk,FZU, Prague,

IHEP, Protvino,TAU, Tel Aviv,DESY, Zeuthen

look to our web-page: http//www.zeuthen-desy.de/LC/FCAL

We would be happy to welcome youto fight together!

Summary• Many (and promising) results in

simulations/design studies • Concept for a Luminometer for small crossing angle is advanced, 20 mrad needs a different design – work to be done • compact and fine segmented calorimeters necessary, needs R&D

• Prototype tests mandatory

Remark:

• The instrumentation of the forward region is relatively independent of the detector concept,

• Mechanics design just started, needs effort

• radiation hard sensors for the inner calorimeter – needs R&D

• no electronics concept so far