The ZEUS Micro Vertex Detector Roberto Carlin INFN – University of Padova for the ZEUS MVD Group Vertex 2002 Workshop Kailua-Kona, Hawaii 4-8 November

The The ZEUSZEUS Micro Vertex Detector Micro Vertex Detector

Roberto CarlinINFN – University of

Padovafor the ZEUS MVD Group

Vertex 2002 WorkshopKailua-Kona, Hawaii4-8 November 2002

ZEUS MVD Group: Bonn Univ., DESY-Hamburg, DESY-Zeuthen, Hamburg Univ., KEK-Japan, NIKHEF, Oxford Univ., Padova, Torino, Bologna, Firenze Univ. and INFN, UCL.

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R.Carlin: Status of the ZEUS Micro Vertex DetectorR.Carlin: Status of the ZEUS Micro Vertex DetectorVertex 2002 – Kona, HawaiiVertex 2002 – Kona, Hawaii

Outlook:

• The structure of Zeus MVD

• Status of MVD, dead channels and some reason for that

• Cosmic rays runs and alignment

• Backgrounds, noise in the detector

• First measurements with e-p events

• Irradiation of MVD and how to cope with it

This is what we were expecting last year, but things went differently:• Hera startup difficult with very high

radiation backgrounds• A short lumi run is starting in November, we

will need a 3 months shutdown (spring ?) to get things really under control

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• Readout with analogue chip (HELIX3.0, Heidelberg+Nikhef) built with AMS 0.8 CMOS technology

• Only preamp, analog pipeline and drivers on chip

• LVDS Clock and Control drivers 6m far on special patch boxes

• ADCs 30m far on the MVD racks !• Special care on cabling, signal

handling, grounding, shielding…

120 m

Si detectors and FE readoutSi detectors and FE readout• n-doped silicon wafers (300 m

thickness) with p+ implantations (12 or 14 m wide), HAMAMATSU PH. K.K.

• 512 readout AC coupled channels in the barrel, 480 in the wheels

• Using the capacitive charge sharing, the analogue readout of one strip every 6 allows a good resolution (<20 m) despite the readout pitch of 120 m

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•Five modules are mounted on a carbon fiber support structure to form a ladder.

•The Si planes, Hybrids and Cabling are located on the 3 planes of the ladder

•30 ladders, in 3 planes, are positioned around the elliptical beam pipe in the MVD barrel detector

Modules in the BARRELModules in the BARREL

•Two single side sensors are glued and bonded to gold strips plated on Upilex flex foils, and finally to a FE hybrid

•Two planes are glued together to form a module with x-y readout

64 mm

125 mm

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•The forward wheels have detector differently shaped (trapezoidal with two different sizes to accommodate the beam pipe)

•Two layers of single side Si detectors, same pitch and construction as in the barrel, strips cross at an angle of 26°

•Same electronics and connectivity as in the barrel

And in the forward WHEELSAnd in the forward WHEELS

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The forward section:The forward section:• 4 wheels 4 wheels • each one composed by each one composed by

2 layers of 14 Si 2 layers of 14 Si detectorsdetectors

• Total of 112 hybrids, Total of 112 hybrids, >50k channels >50k channels

The barrel section:The barrel section:• 30 ladders 30 ladders • each one composed of 5 each one composed of 5

modules of 4 Si modules of 4 Si detectorsdetectors

• Total of 300 hybrids, Total of 300 hybrids, >150k channels >150k channels

The read section:The read section:• Cooling pipes and Cooling pipes and

manifolds manifolds • Distribution of FE, slow Distribution of FE, slow

control and alignment control and alignment cablescables

Overall structure and inventoryOverall structure and inventory

One half of the entire MVDAll cables in a Faraday All cables in a Faraday

cagecage

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Old Dead Old Dead ModulesModules ““Fixed” Fixed” Modules Modules (optimizing (optimizing HELIX HELIX programprogrammming):ing): Modules noisy Modules noisy sometimes or sometimes or partially (to be partially (to be investigated)investigated) New “Noisy” New “Noisy” ModulesModules

Status of the MVD: limited number Status of the MVD: limited number of bad channels in the barrelof bad channels in the barrel

Noise in ADC counts for each strip in the barrel(one histogram per ladder)

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Characteristic noise structure:• In the wheels the strips have

different lengths • Different input C to the FE

chips, different noise

No problematic module in the wheels. Why?

• Factor 3 less channels

• In the barrel there may be one problem in the cabling

details

And much less in the wheelsAnd much less in the wheels

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Ladder cablingLadder cabling

Si planes

Hybrids

Cables

Very tight cabling

Use one side of the ladder for cabling

Use special, very thin custom cables

Minimize use of components and connectors

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Connect the hybrids via flex circuits on miniature ZIF connectors

Connectors to daisy chain the hybrids

Connectors to provide LV, HV, control signals and extract analog output

Termination resistors and filter capacitors

500 m pitch flex connection, pre-bent

Special custom multifunction (“combo”) cable

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Flex layer with stiffening to match the ZIF connector

G10 circuit layers glue

Vias between circuits and to soldering pads

Many more problems than expected:

• Very hard to cut the flex PCB with enough precision (50 m) to fit the 4 ZIFs in the 2 hybrids. Relative positions were important!

• Not easy to get the circuit of the proper thickness for the ZIF insertion (300 m)

• The conductors in the vias do not adhere to the glue, it makes a bridge between the layers (point of fragility)

• The glue is hygroscopic !• When soldering close to vias, the T increase

may create vapor that break the conductor in the via (and in extreme cases delaminate the connector)

Solutions: • Slow drying of PCBs in oven, and then store in vacuum bags

• Controlled soldering operation

• Extensive test of PCBs and of cabling at the company

• Test with (relatively) high currents at the lab

Nevertheless, some of the dead module show bad connectivity at the PCB

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On the wheels there is more space for

cabling

• Standard PCB to connect cables and put components

• Bridge between PCB and hybrids with flex jumpers, ZIFs on both sides

• Installation at the end turned out to be “easy”

• No connectivity problem so far on the wheels

• NB extra ZIFs would not have fit in the barrel

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MVD is working fine, test MVD is working fine, test tracking with cosmicstracking with cosmics

• Use the two semi-tracks as they were independent, to measure the resolution in impact parameter

• 117 um resolution, without alignment (p<1Gev tracks)

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• Alignment code is being developed and was tested on a sample of cosmics

• The results show that the module positions in each ladder are well known

•Very precise construction, markers aligned under microscope (10um)

•Very rigid ladder structure

• First iteration will need only ladder alignment (factor 5 reduction in free parameters)

• Need lot of good tracks (400K), corresponds to 2pb-1, feasible in the coming winter run despite of the bad background conditions

• A laser alignment system is present and will monitor overall rigidity

First alignments with cosmicsFirst alignments with cosmics

Alignment of each module

Module are fixed in the ladder, ladders only are aligned

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High detector occupancy with bad

background data

Question:• Is it all background, or is there a

contribution from noise?• Do we have any pick-up, coherent

noise?

Occupancy from e-p (DIS) events

Data taken is dominated by Data taken is dominated by backgroundbackground

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Clustering (performed by the ADC)•A threshold is applied to each strip

• Independent for each strip, usually set to 3 noise•A cluster is a set of consecutive strips above threshold (a single hole is allowed)

•The two “side strips” are part of the cluster•A further cluster sum threshold can be applied

•The cluster size on pedestal events is consistent with a stochastic distribution of noise in the strips

Detailed studies of noiseDetailed studies of noise

•The noise hit distribution is consistent with a stochastic 3 noise in the strips

• A noise cluster is composed by 3 strips (one above threshold)

• The number of noise hits should be 0.15% per channel per event if the threshold is set to 3 noise

• Thresholds are a little lower than 3 (truncation to integer ADC counts)

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Good events are clearly seen in the Good events are clearly seen in the MVDMVD

Cluster sums show clear Landau distribution• On average a little smaller than

in the system test with cosmics•S/N 14 instead of 16

• Likely reason: sampling a little off-time (signal rise time<40ns)

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dE/dx looks OK

Using the cluster charge, corrected for path length in Si, we get a nice dE/dx distribution from good e-p events

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We got some irradiation, but we We got some irradiation, but we monitor it properlymonitor it properly

• 16 Si PIN diodes (8 modules) with DC (current) readout to generate alarms and beam dumps (and tune beams)

• Integrating currents:• No threshold for any

background (Synchrotron light)• Need treatment of leakage

current• Use an “leaky bucket” logic (a la

Babar) to dump beams• Plan to use empty bunches to measure

the leakage currents (1.2 s available)

• 8 radfets to have a continuous monitor of the integrated dose

• Readout every 15 minutes• Very valuable to assess the overall

quality of HERA operations

• TLDs exchanged monthly to cross-check the results from radfets

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• Results from rear RADFETS in the last months of operations

• One module is at 80 Krad. This is located close to a collimator and sees the showers from low momentum leptons hitting it

• The other (also in the forward) measure doses within 20 Krad

• Doses in MVD between 20 and 80 Krad, in the most affected areas (inner layer, inside HERA ring)

Total dose received ?Total dose received ?

• MVD irradiation mostly with chips OFF

• Beam losses at injection or ramp-up (mostly e beam)

• Bad e-beam injection• Sensitivity reduced a factor 2

or more• Only marginally from normal

operations (but currents were limited so far)

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Radiation Tolerance of Radiation Tolerance of MVDMVD • The most sensitive component is

the HELIX chip• AMS 0.8 CMOS technology• Designed to be radiation

tolerant• Tested by Heidelberg (for Hera-

B) and by Nikhef (for ZEUS)• Fast decrease of S/N ratio for

the first 100 Krad• Change of shaping time and

other parameters• Helix has programmable

parameters (internal DACs) to recover the working points

• 5 Krad/yr expected from beam operations (up to 100 Krad inside on bending plane, low p leptons)

• ZEUS has set a maximum radiation budget of 300Krad in the lifetime of the detector

S/N ratio measured with chips connected to a single Si detector (input C= ½ w.r.t the actual barrel readout)

Noise increase measured at Heidelberg with 0 input C

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Stability of the HELIX working pointStability of the HELIX working point

• Study of signal shape using HELIX internal test pulse (time scans)

• No evidence of gain variations with time

• No evidence of peak time changes

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Stability of the HELIX working pointStability of the HELIX working point

• Only sign of irradiation in the chips

• Limited increase in the noise for the inner layer of the BARREL (1.5%)

Day of the year

Nois

e (

AD

C c

ounts

)

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How to recover the working pointHow to recover the working point

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• Change of gain with Ipre, for diffrerent irradiations

• Signal decreases• Can be recovered, at least

partially, with a higher Ipre current

• There is space in the cooling and LV power supplies for extra power to the chips

• Change of peak time• Signal becomes faster with

irradiation• Increase of Ipre make it

even faster• Need to recover with shaping

time

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• Changes with Vfs• Peak time can be

recovered• At the same time

also the S/N recovers

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SummarySummary

• MVD commissioning limited by backgrounds in HERA

• Number of non-working channels small after one year from the

beam startup

• The noise distributions are under control

• Data from cosmics and first events look promising, tuning

needed

• Alignment underway, need much more data. The detector is well

measured and rigid

• 20-80 Krad collected, but so far no clear evidence of damage

• “Luminosity run foreseen November ...”

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Detailed studies of noisenoise (2)

•Side strips must be sampling a noise distribution on a random noise hit

• Again, no coherent noise or cross-talk

Thresold cut

•On BG (or physics events) they must carry some induced charge information

• OK, included in the cluster

Documents

The ZEUS Micro Vertex Detector Roberto Carlin INFN – University of Padova for the ZEUS MVD Group Vertex 2002 Workshop Kailua-Kona, Hawaii 4-8 November