April 20, 2023 MDI WS SLAC

Electron Detection in the Very Forward Region

V. Drugakov, W. Lohmann

Motivation Talk given by Philip Detection of Electrons and

Photons at very low angle – extend hermiticity (Important for Searches, radiative events, calibrations)

Geometry

•Fast Beam Diagnostics

•Shielding of the inner Detector

IP

VTX

LumiCal BeamCal

FTD

L* = 4m

300 cm

LumiCal: 26 < < 82 mradBeamCal: 4 < < 28 mrad

So far for zero crossing angle

The Challenge

e+ e-

• 15000 e+e- per BX 10 – 20 TeV

• 10 MGy per year Rad. hard sensors

Technologies: Diamond-W Sandwich

Scintillator Crystals

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

GeV

CalorimeterSmall Molière radius (1cm)High granularity (1/2 cm)Longitudinal segmentation

(30 x 1 X0)

sensorSpace for electronics

Depositions from a

high energy

electron

Signal(+background) event

Electron (Photon) Reconstruction

– using beamstrahlung depositions of 10 (random) bunch crossings, the average background deposition and its rms in each pad is determined – Taking a ‘signal’ (electron + background) event, this average background deposition is subtracted in each pad

– Remaining depositions larger than 5x the rms are kept. Chains of such pads in the region of the expected shower maximum are searched for – Adjacent chains are grouped to a shower and the energy and position is estimated.

√s = 500 GeVSingle Electrons of 50, 100 and 250 GeV in the region of large background

Comparison SamplingHeavy Crystal

Comparison 500 GeV - 1TeV

Reconstruction efficiencies

Efficiency less then

90%

Minsk-Desy

‘blind’ regions

√s = 500 GeV

√s = 1000 GeV

Includes seismic motions, Delay of Beam Feedback System, Lumi

Optimisation etc.(G. White)

Efficiency to identify energetic electrons and photons(E > 200 GeV)

Fake rate

√s = 500 GeV

Realistic beam simulation(Input from G. White)

Electron Fake RateBeamstrahlung tails (> 50 GeV): ~ 1%Background Fluctuations (> 50 GeV): ~ 1%Radiative Bhabha Events

Not yet studied:Incompletely reconstructedBhabha’s – potentially a large fraction

(Study done by A. Elagin)

Summary Using a Compact Fine Segmented Calorimeter electrons and photonscan be detected to palar angles of about 5 mrad with reasonableEfficincy up to 1 TeV cm energyElectrons with energies near the beam energy can be detected with very high efficiency in regions with low depositions from beamstrahlungand still with high efficiency in regions largely affected by beamstrahlung (Similar results also obtained by T. Maruyama) The fake rate due to Beamstrahlung is at % level (even for realistic beam simulation)

The Bhabha process needs more studies

Future – development of a more realistic design of the calorimeter

200 GeV ElectronsEfficiency less then

90%

Pile up effects

250 GeV e-BG

Si Layers

Pair Background 250 GeV Electron

Ebg + Eelectron - <Ebg>

Dep

osit

ed E

nerg

y (a

rb. U

nits

)

SLAC ECFA - Durham2004

Electron detection with crossing angle

CollaborationHigh precision design