TOTEM T2 telescope

Timo Hilden

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TOTEM collaboration

• Small collaboration: 140 or participants from 9 institutes (compared to 4300 participants from 179 institutes of CMS!)

• Limited resources and manpower

• A good overview of a whole experiment

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Total cross-section

Elastic Scattering

jet

jet

Diffraction: soft (and hard with CMS)

b

Forward physics

TOTEM Physics Overview

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TOTEM

• Roman Pots: Two stations at 147 m and 220 m from the IP for measuring elastic & diffractive protons close to outgoing beam

IP5

RP147 RP220

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TOTEM • T1 and T2 - Inelastic telescopes: charged

particle and vertex reconstruction in inelastic events

IP5 T1: 3.1 < < 4.7

T2: 5.3 < < 6.5

T1 T2 5

GEM detector intro • Basic element is a 50 μm thick

polyimide foil with 5 μm copper coating on both sides perforated with 70 μm holes 140 μm from center to center

• Gas filled detector: Primary ionization is produced by ionizing the measurement gas in the drift gap. Electrons drift in electric field towards the GEM foil.

• When voltage is applied between the

copper electrodes of the foil the holes work as multiplication channels for electrons

• Exactly the same principle as in proportional chambers but in 2d, with individual holes acting as the avalanche volume

Inner hole Diameter: 50 μm

Outer hole Diameter: 70 μm

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GEM detector intro

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• Efficient ion collection at upper foil enhances rate capability.

• Multiplication can be divided into several stages to lower electric field (protection from sparking).

• Robust: good aging behavior, can withstand sustained rates up to 50 khz/mm^2.

• Large area GEMs detectors are only a fraction of the price of comparable detectors with other technologies (e.g. silicon).

• Drift speed strongly dependent on electric field and gas mixture.

• Signal spread determined by gas diffusion and gap widths.

• Quenching gas added to ensure stability and prevent sparking.

• Choice of gas a compromise between speed, diffusion, gain and safety.

• Electric field configuration defines the transparency of the foils, on the other hand affects drift speed and diffusion.

GEM detector intro

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T2 GEMs

• Triple gem design based on experience from Compass experiment.

• Compass gap configuration of 3 mm drift gap and 2 mm transport and induction gaps

• Material budget minimized in the design. Frames permaglass, copper electrodes 5 μm thick.

• Measurement gas 70 % Argon, 30 % CO2.

• The foil is divided into 4 individually powered sectors to reduce the energy and probability of a discharge between the electrodes.

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T2 GEM

• 3 mm active volume depth – 30 electrons from a mip with signal rise time jitter of ~20 ns

• Signal transport through the detector ~120 ns

• Electron cloud width at induction gap ~1mm

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Telescope design

• Each arm consists of 20 semicircular detectors arranged to form 10 planes around the beam pipe.

• Installed inside the hadronic calorimeter of CMS.

• 13,5 m from interaction point, covering η range of 5,3 – 6,5

• Services include water cooling for electronics and HV divider, gas input/output, Hv cables, power for the electronics, temperature and radiation sensors etc.

• Part of the electronics outside to protect from radiation

192° in phi/quarter

11 Beam pipe

Electronics

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• Active area is divided into 13 pad

sectors with 120 channels each. Pads are roughly 2 mm x 2 mm in the inside of the detector and 7 mm x 7 mm in the outside area

• Strips on top of pads. Strips are divided into two from the middle of the plane to reduce occupancy forming 4 strip sectors of 128 channels.

• Pads are used for triggering. The 120 pads of a single sector are divided into 8 meta-pads (5 by 3 pads) giving 8 trigger bits per sector.

Electronics

• All of TOTEM readout is based on the VFAT chip - Digital output - Programmable self triggering capability - Plenty of ”features” • Horseshoe card collects output from all 17 VFATs of

a detector

• 11th card combines data from the 10 horseshoe cards of a single tepecope arm.

• Coincidence chips on 11th card responsible for trigger output (e.g. Same meta-pad on in 4 planes out of 10)

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Electronics

• Data and trigger sent to OptoTx via lvds signal (6m cable)

• Optical link to GOH in counting room

• Capability to give trigger to CMS for common data taking in the future.

• DAQ compatible with CMS for common data taking in the future.

Assembly

• Prototypes 2004 – 2005, tested without final electronics

• Electronics 2007 – 2009. Multiple delays and a lot of debugging work done.

• 50 detectors assembled 2007 – 2009.

• Installation 2008 - 2009

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Assembly

• Extensive changes to HV distribution to enhance signal rise time.

• Mechanical modification of readout boards mostly in situ at Cern.

• New EM-shielding schema in 2008.

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Assembly 1. Sandwich

- ready made by CERN 0 h

2. Preparation of frames

- cleaning/grinding 1 h

- ultrasonic cleaning 1 h

- drying in oven 4 h

- nuvovern varnishing ½ h

- curing in oven 2 h

- HV test ½ h

3. GEM foils (3 pcs.)

- visual inspection 1 h

- optical scanning 1 h

4. Leakage current tests of the GEM foils

- 3 foils, 12 segments in total 8 h

5. Framing of the GEM foils (3pcs.)

- stretching and gluing 3 h

- curing in oven 16 h

- finishin the framed foils

6. Leakage current tests of the framed foils 8 h

7. Gluing the drift foil to the sandwich 1 h

- curing in oven 16 h

8. Assembling of the GEM stack

- gluing the three framed foils 2 h

- curing in oven 16 h

9. Leakage current tests of the GEM stack 8 h

10. Readout board

- glued to sandwich by CERN 0 h

- visual inspection 1 h

- soldering of the connectors 8 h

- capacitance measurements 4 h

- burning of the shorts 4 h ?

11. Gluing the readout board to the GEM stack 1 h

- gluing the gas adapters

- curing in oven 16 h

- removal of the central disk of the ROB

12. Sealing the GEM

- Araldite/Dow Corning 2 h

- curing in oven 16 h

13. Finishing work

- assembling of the voltage divider pcb 2 h

- assembling the HV cable 1 h

- connecting the gas connector

14. Tests 5 days

- gas leaks?

- environmental chamber, HV-tests

- electronic tests

total: 2-3 weeks

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• Leakage current measurements

• Readout channel capacitance measurement with automated system

• Foil tension samples of each framed foil

Quality control

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Quality control • Foil quality scans with image

processing techniques – measure hole size and find defects

• Gas leak testing by measuring oxygen levels down to ppm level

• Stability testing for humidity in environmental chamber

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Quality control

• Mapping of detector gain uniformity across the active area

• Full week of stability testing under irradiation

• Beam tests in Cern for full quarters

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Operation

• 3 detectors broken during 2010 run, none after that. Propably defective since manufacture.

• A lot of tuning of the system.

• Most runs with low luminosity beam. Few special optics (β* of 90 m) runs.

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Environment at 13 meters

• High charged particle flux. Total dose will eventually kill the detector (aging, materials).

• High neutron flux (esp. On Castor side). Potentially destroying the detector.

• 90% of tracks are secondaries, mostly from beam pipe and ion pumps in front of T2.

• Hot beam pipe within 1 cm of the detector.

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Limits

• Rate: T2 cannot function in full luminosity runs due to protection resistors choking the current.

• Operating in low luminosity runs / triggering on a smaller pilot bunch

Beam pipe

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• Signal speed/risetime: 2-monostable clocks (50 ns) minimum.

• Materials: breakdown of the detector due to glue disintegration: 0.7 - 1MGy

Limits

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Troubleshooting

• Noise propagated through the HV lines. HV filters installed during 2010-2011 winter shutdown.

• Water leak in minus near quarter cooling pipes. The quarter was run without cooling. Bad performance of the electronics. Fixed during 2011-2012 winter shutdown.

• Bad connection in LV line (12 Amperes) on minus near odd planes. Problems with electronics, bad noise performance. Fixed during 2011-2012 winter shutdown.

• Missing frames due to loss of synchronization between OptoTX and GOH. De-serializer required ~ms to gain sync. Fixed by firmware upgrade.

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• Digital and analog ground mixed when bonding of the VFAT hybrids. Comparator signal transmitted in readout board – crosstalk problems. Fixed by tuning chip parameters. Gain a factor of three in efficiency.

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Troubleshooting

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• First measurement of the total pp cross section at 7 TeV

• No T1 or T2

• No 147 m Roman Pots

Milestones

Milestones

• Successfully using CMS trigger, first combined data taking.

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Castor special myon trigger run Dec 2nd

CMS: 182828/161306 TOTEM: 7721/96

CMS: 182828/148273 TOTEM: 7721/4

0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

520 540 560 580 600 620 640

Rat

e[H

z]

High Voltage [uA]

Trigger Rate vs T2 HV [200ns_358b_356_336_0_24bpi15inj_IONS]

CMS Rate T2Rate T2&CMS T2ORCMS

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400

Trig

ger

Rat

io

Gain

Trigger Rate /CMS trigger rate = 1.7/1.8kHz, T2 CC=5planes, 356bs,I1I2=3.34e+12,L=2.6e+26

(PN&CMS)/CMS (PF&CMS)/CMS (MF&CMS)/CMS

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• Comparison of CMS and T2 trigger rates during the heavy ions run.

Milestones

: ALICE, ATLAS, CMS, LHCb & TOTEM-T2

7 TeV dN/d analysis @ LHC

LHCb

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Milestones

Loppukevennys

• Possible upgrade during the long shutdown

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