RICH : Luminosity Upgrade Neville Harnew (Oxford) Edinburgh

RICH : Luminosity Upgrade

LHCb Upgrade Meeting 11-12/01/07

Edinburgh

Neville Harnew (Oxford)

RICH : Luminosity Upgrade N. Harnew 12-01-07 LHCb Upgrade Workshop

1

Issues to address

Can the RICH survive a 2x10 33 luminosity and what is the degradation of the performance: electronics and mechanics

(rates, occupancies, radiation damage)?

What if the readout is performed at 40 MHz with a factor 40 more front-end storage, what implications this has for the detector ?

Is there manpower/money available for an upgrade - which groups are interested ?

Thanks go to Chris Jones, Jim Libby, Hans

Dijkstra, Ken Wyllie and Olav Ullaland…..

No definitive conclusions here – just a pointer to more work.


2

RICH performance at high luminosity:

First preliminary simulation studies

Generate inclusive B events with minimum bias events superimposed.

Keep the same RICH code as at 2x10 32 (no tuning of the reconstruction code for the higher luminosities except to relax the max event size).

The tracking is also not altered for the higher luminosities. If the tracking degrades then that will degrade the RICH performance (in an unknown way).

The PID results are for all forward-going tracks only.

Thanks go to Chris Jones for subsequent plots


3

Total numbers of hits in RICH-1

2x10 32

5x10 32

1x10 33

2x10 33


4

Total numbers of hits in RICH-2

2x10 32

5x10 32

1x10 33


5

2x10 33

•

Mean

•

Numbers of hits in RICH vs Luminosity


6

π

/K ID efficiencies at 2x10

32

•

“Heavy” and “light” hypotheses


7

π

/K ID efficiencies at 2x10

33

•

“Heavy” and “light” hypotheses


8

[for positive kaon ID hypothesis]

NB. DOES NOT INCLUDE ANY LOSS OF EFFICIENCY FOR HPD BUFFERING


9


10

Some preliminary remarks

1. The event occupancies increase more or less linearly as luminosity increases.

2. The event occupancies do not increase at the same rate as luminosity: factor 10 in luminosity gives factor ~2.5 in occupancy → minimum bias events are not nearly as busy as inclusive B events.

3. PID performance degrades as luminosity increases.

However, it does so smoothly and linearly. There does not appear to be a point when things just blow up.

4. RICH1 degrades faster than RICH2 (higher backgrounds and occupancies).


11

HPD pixel hit inefficiencies

But this is not the whole story → unfortunately there are pixel hit inefficiencies at high occupancy – a feature of the HPD readout architecture

:

HPD has a 16-event buffer depth.

The readout efficiency is dependent on Level-0 latency (currently 4 μ s) and the occupancy.


12

Hit-driven pixel buffering on HPD pixel chip

1 st hit

2 nd hit

Depth : 160 x 25ns clocks Ξ 4 μ s latency

Time [Delay line]

1

1

Subsequent hits are missed if buffer is filled with 16 hits (until a location is freed)

16 eventbuffer

(one per pixel)

16 th hit

•

16 deep buffer


13

Note different definitions of occupancy

Event occupancy: the fraction of pixels hit in an event on average.

Time occupancy: the fraction of time a pixel sees a hit. e.g. 10% means there is a hit every 10 bunch crossings.

A multiplicative factor – i.e. the fraction of crossings containing interactions – is required to convert event occupancy into time occupancy

1.2

1

¾

Event occupancy is relevant for ring reconstruction

0.8

0.6

¾

Time occupancy is relevant for front-end hardware buffers

0.4

0.2

0

0 5 10 15 20

•

Luminosity x 10 32

25

Thanks go to Jim Libby for subsequent plots


14

Inefficiency vs time occupancy (4

μ s latency)

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

1%

4%

8% time occupancy

This is what we have: pixel chip has buffer depth of 16

2 4 6 8 10 12 14 16

Delay unit depth

•

At 2x10 32 , 4% time occupancy ≈ 10% event occupancy (this is the very hottest region (centre of RICH1) in the worst case scenario).


15

RICH1 & 2 event occupancies at 2x10 33

Plots show average no. of pixels hit per HPD

≈

Average event occupancy/1000

•

RICH-1

•

RICH-2

HPD x,y position on HPD plane (mm) HPD x,y position on HPD plane (mm)

• Maximum average occupancy in RICH-1 is ~6%

•

Maximum average occupancy in RICH-2 is ~2.5%


16

Inefficiency vs time occupancy: 4

μ s latency

0.4

0.35

0.3

0.25

0.2

0.15

Values shown correspond to average maximum

RICH 1 occupancy

•

2x10 32 2x10 33

0.1

0.05

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

• Time

0.16

Occupancy


17

What happens if we go to 6.4

μ s latency (256 depth) ?

0.6

0.5

0.4

0.3

0.2

Values correspond to average maximum RICH 1 occupancy

•

2x10 32 2x10 33

•

6.4

μ s latency

•

4 μ s latency

0.1

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

•

Time

Occupancy

•

•

Conclusions: < 5% loss at 4 μ s latency

~15% loss at 6.4

μ s latency

Not a total disaster, but close to uncomfortable


18

What happens if the front-end readout is performed at 40 MHz with a factor

40 more front-end storage ?

Easy answer:

The readout chip is encapsulated inside the

HPD …..

 therefore all photon detectors and readout electronics will need to be replaced.


19

Radiation damage of HPDs ?

Hottest region of RICH-1: 20 krad over 10 years at 2x10 32

Possibilities of radiation damage to HPD silicon

¾

RICH-1 inner region at moment we have ~3x10 12 neutron equivalent over 10 years (worst case) - but this has a safety factor built in. Type inversion of silicon starts about 10 13 . Could be OK, but need to check it.

Need to double-check PINT chip as well.

SPECS might also have a problem.

Could be OK but certainly R&D work is necessary


20

First ideas on “Super-RICH2”

RICH-1 performance certainly degrades faster than RICH2.

Hits can be “shared” in pattern recognition, and improved granularity in RICH-1 doesn't help (since dispersion is as dominant to resolution as the 2.5mm pixel size).

However improved granularity in inner region of RICH-1 (with new photon detector) would solve the buffering problem.

Therefore, some first ideas to remove RICH-1 and have a “Super-RICH2”:

Remarks on Super-RICH2:

¾ Removing RICH-1 would help X_0

¾ New photon detectors (everywhere or just in inner regions?)

¾ Finer granularity (especially in inner region)

¾ Sub-ns timing to provide additional information? TOF also.

None of this discussed in the RICH group yet


21

Plans/aspirations of the RICH group

Most RICH groups would be interested in principle in participating, but strong priorities are with current RICH detector.

Maybe some R&D manpower from institutes in

2008.

Only CERN group has expressed possibilities of available manpower in the shorter term to start thinking and/or R&D.


22

Spare Transparencies


23

Interaction probability vs luminosity

0

1

2

3

4

5

6

7

8 9

Luminosity x10 32


24

RICH1 event occupancies at 2x10 32

Average no. of pixel hits/HPD

≈


HPD x position on HPD plane (mm)

HPD radial position (mm)

• The occupancy varies not only with R but also in azimuth.

• These are local coordinates (on HPD plane)

• Maximum average occupancy in RICH-1 is ~3.5%

• NB. maximum event occupancy in RICH-1 is ~10% (tail of the distribution)


25

RICH2 event occupancies at 2x10 32


≈


HPD x position on HPD plane (mm)

HPD radial position (mm)

• Maximum average occupancy in RICH-2 is ~0.7%


26

RICH1 Pi/K ID efficiencies at 2x10 32


27



28



29



30

Average RICH-1 event occupancies over all

HPDs in RICH1


≈


2x10 32 2x10 33

Average no. of pixel hits/HPD Average no. of pixel hits/HPD


31

RICH : Luminosity Upgrade Neville Harnew (Oxford) Edinburgh

RICH : Luminosity Upgrade

Total numbers of hits in RICH-1

Total numbers of hits in RICH-2

/K ID efficiencies at 2x10

/K ID efficiencies at 2x10

Some preliminary remarks

HPD pixel hit inefficiencies

Radiation damage of HPDs ?

First ideas on “Super-RICH2”

Plans/aspirations of the RICH group

Spare Transparencies

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RICH : Luminosity Upgrade Neville Harnew (Oxford) Edinburgh