FIT (Fast Interaction Trigger) detector development for ALICE experiment at LHC (CREN)

•Institute for Nuclear Research (INR RAS)•National Research Nuclear University (MEPhI)•NATIONAL RESEARCH CENTRE "KURCHATOV INSTITUTE"•University of Jyväskylä

Finogeev Dmitry, On behalf of the FIT collaboration

Plan report

ALICE experiment upgradeT0 & FIT detectorsTest measurements at T10 PS CERNDigitizer data processing algorithmsDifferent radiators comparisonCFD test: LP Filters, dynamic rangeConclusions

ALICE at LHC, CERN •ALICE, CERN LHC dedicated to the study of strongly interacting matter, in particular the properties of the Quark-Gluon Plasma (QGP).•Upgrade goal:• excellent tracking performance, in particular at

low momenta• efficient secondary vertex reconstruction• improve the particle identification• upgraded experimental setup for capabilities to

allow an inspection of Pb-Pb collisions at an interaction rate of 50 kHz and for P-P collisions rate will be 200kHz (up to 1MHz)

• signal-to-background ratio requiring a high statistics measurement

•Crucial parts of the upgrade are the development and implementation of a significantly improved inner tracking system (ITS), the replacement of the TPC readout chambers with GEMs, a general upgrade of the trigger detectors (e.g. V0, T0) and of all readout electronics, and a new system integrating DAQ, High-Level Trigger and offline computing. [1]

T0 detectorInteraction time for TOF detector for particles identificationMonitoring beam luminosity at ALICE for pp interactionsEvent plane determination

VETO for ultra-peripheral collisions

Interaction triggers based on centrality and vertex determination to reject pile-up and background events:

Vertex minimum bias trigger multiplicity trigger beam-gas event rejection collision time for TOF [2]

T0

Reasons for T0 upgrade

•Increasing detector acceptance for “minimum bias” trigger generation in pp collisions.•Possibility operation at interaction rate 40kHz, after-pulses at T0 PMTs do not allow to registries events at high rate.•Time resolution better than 50ps•Installation capability with MFT (Muon Forward Tracker)•Improve Amplitude resolution in wide dynamic range for determine the density of charged particles and reaction plane, centrality selection.[3]

•24+28 MCPs = 1460cm2

V0

T0

V0+

T0+

FIT consist of T0+ & V0+

•12 + 12 PMTs = 75cm2

T0 vs FIT

T0 FIT

•PMT-187: photocathode diameter 20mm, length 45mm with quartz gain •Cherenkov radiator: diameter 20 mm, length 20mm

•Planacon MCP-PMT XP-85012 53x53mm2, 4 channels + common output•Cherenkov radiator 53x53mm2 divided by 4, isolated one from each other•Life time: 100 mC/cm2 (gain X0,9)

Test of the MCP & analog front-end electronic and cabling system for FIT detector at beam T10 PS, CERN.

Test purposes:Measure MCP time resolutionCompare different radiator configurationsDetermine LP filters influenceMeasure dynamic range of front-end electronic for amplitude signals MCP1

MCP2

XY

beam

Connection sheme

Test setupSTART trigger based on T0 PMT-187, trigger resolution 24ps

Cable system proposed for FIT detector: 5.5 m of 3 mm UHF cables + 40 m of 10 mm low-loss UHF cables.The losses in the cable system are ~25% of the pulse amplitude, time resolution contribution: 6ps.

beam

Digitizer data processing algorithms

•16+1 Channels 12bit 5GS/s•The DC offset is adjustable via a 16-bit DAC in the range ±1V•1024 storage cells per channels (200 ns recorded time per event) •200ps per time channel

Mod. DT5742 Desktop Waveform Digitizer

Signals Analyzing

Analyzing algorithm provide for each event:Calculation for analysis:•Linear TIME•TIME by fittingsimulating real triggering:•Leading-Edge Timing •Constant-Fraction Timing

Also determined:Peak start, stop, front_stop, back_start time defined by A/10 from zero level and top point, max amplitude, top point time, signal level for logic signal, charge for amplitude signal.

Signal front is fitted by two function: polinomial^1 and polynomial^3

•Polynomial ^3 looks much better, but in practice it has a very low efficiency, less than 1% of all events have a good fit pol^3 function•Does not improve the time resolution

High Frequency filter

by Blackman function:

•Improve the time resolution up to 2ps for polinomial^1 fitting

Digitizer jitter dependence from signal amplitude by high rate generator (generator jitter 5ps)

0 100 200 300 400 500 600 700 8000

5

10

15

20

25

30

35

40

Time resolution, ps vs ampl, mV

sigma, ps vs ampl, mV

Digitizer time resolution 16ps up to 75mV

Time-amplitude correction

Time-amplitude correction may grant 2ps time resolution improvement

Comparison of different radiators fragmentation: •Best result for #1 (31ps)•Backward show same result (32ps)

Amplitude, mV

LPF 300MHz & 400MHz influence

LPF 400MHz (top)LPF 300MHz (bot)

With out LPF

Tightening signals fronts LP Filters decrease time resolution by 10ps

Time – Amplitude dependenceamplifier X10, attenuator X 0.25

Amplifier overloaded at amplitudes more than 220mV

= 690mV

= 210mV

Conclusions:

MCP time resolution 30ps with 4 pieces radiator that allow use less voltage of power supply and increase time of life of MCPDividing radiator more than by 4 pieces do not increase time resolutionPosition backward to beam does not decrease time resolution that permits turn FIT detector back to iteration point, background contribution decrease the life time of MCP in that case.The dynamic range of the tested electronics is less than planned.The next iteration of the FIT input electronics, including this improvements, gating circuit and Q-T converter, similar to the one using now in T0 must be built for the tests in the ALICE cavern with current TOF readout

Thank you for your attention,

and FIT collaboration!

References

[1] ALICE Upgrades EPJ Web of Conferences 60, DOI: 10.1051/epjconf/201360[2] CERN-LHCC-2013-019 / ALICE-TDR-015 26/06/2015[3] Fit report 24 October 2012 T. Karavicheva