Groups Involved University of Alberta, University of Texas at Arlington, University College London. Prague, Saclay, Stoneybrook, Giessen, Manchester,

Groups Involved

University of Alberta,

University of Texas at Arlington,

University College London.

Prague, Saclay, Stoneybrook,

Giessen, Manchester, Fermilab, Louvain, Kansas

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The ATLAS Forward Detectors

AFP


The AFP Project

AFP is designed to tag forward protonsSelection rules mean that central system is (to a good approx) 0++ If you see a new particle produced exclusively with proton tags you know its QNCP violation in the Higgs sector shows up directly as azimuthal asymmetriesProton tagging may be the discovery channel in certain regions of the MSSM Tagging the protons means excellent central mass resolution (~ GeV)

Tracking detector requirementsClose to beam => edgeless detectorsHigh Luminosity => radiation hardFew micron resolution

We need to suppress pile-up (keep the rapidity gaps open)This is done by ultra-fast ToF detectors (to determine vertex)

ATLAS


Precision timing will be required to reduce pile-up background, enabling AFP to operate at design luminosity

Backgrounds are:

Three interactions, one with a central system, and two with opposite direction single diffractive protons

Two interactions, one with a central system, and the second with two opposite direction protons

Two interactions, one with a central system and a proton, the second with a proton in the opposite direction.

James L Pinfold Manchester 2007 1

[X][p][p] [X][pp] [Xp][p]

Scales with L3 Scales with L2Scales with L2

Rationale for Fast Timing Detectors (1)


For two protons coming from the same event:

Z-position = ½(Dt=tL - tR)c dZ-position = (c/√2)t

Aim for t = 10(20) ps Z ~ 2.1(4.2) mm (look for match with ATLAS/CMS main Z)

For t = 20 ps, we obtain a factor of 24 for the first two cases and 17 for the third.

Case (a) dominates at high luminosity, and in the case of t = 10 ps, we would expect a factor of nearly 50 rejection, enabling FP420 to operate at the design lumi.


Rationale for Fast Timing Detectors (2)


Baseline Plan


Two types of Cerenkov detector are employed:GASTOF – a gas Cerenkov detector that makes a single measurement

QUARTIC – two QUARTIC detectors each with 4 rows of 8 < ~90 mm long fused silica bar allowing up to a 4-fold improvement of resolution over that of a single bar

Both detectors employ Micro Channel Plate PMTs (MCP-PMTs)

30 cm

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Micro-channel Plate PMT (MCP-PMT)

We are working with 10 micronBurle tubes at present


QUARTIC- Alberta, FNAL, UTA

Each QUARTIC detector has 4 rows of 8 6mm x 6mm x ≤ ~10 cm long fused silica bars

The refractive index of fused silica is ~1.5 ( Cerenkov angle of 50o)

An array of bars is mounted at the Cerenkov angle to minimize the # reflections as the light propagates to the MCP-PMT.

The QUARTIC detectors will be positioned after the last 3D-Si tracking station because of the multiple scattering effects in the fused silica.

This arrangement is intrinsically rad hard

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A QUARTIC Prototype

1) Use short bars and reflective light guide

PRO: Less time dispersionCON: less light

OR 2) Use longer bars as the light guide

PRO: more lightCON: more time disp.


QUARTIC FE-Electronics

The readout electronics must be fast with low noise to attain the best timing resolution – a single electronics channel :

Amplifier and Constant Fraction Discriminator Louvain & Alberta have a similar CFD design designed to work with rise times as short as 150 ps and to be insensitive to amp non linearity & sat.

The TDC (for the test beam we used the Phillips 7186 25 ps TDC)The baseline solution for the final detector is the HPTDC that has a ~20ps resolution – it is radiation hard and LHC compatible (a 40 MHz clock, etc)The Alberta group has designed & built an 8 ch. HPTDC prototype board

For the GASTOF detector a single photon counter (Boston Elec. SPC-134-5ps rise time ) can replace the amp+CFD+TDC ($10K/ch.)


Combined in the ALTA approach

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QUARTIC Electronics – the CFD

Mini-module approach tuned LCFD mini-module

to Burle and Hamamatsu rise times;

12 channel NIM unit good performance : <10 ps

resolution for ≥ 4 PE’s

Remote control for threshold

ZX60 3 GHz amp


QUARTIC Electronics – the HPTDC 12 ps resolution with

pulser;

Successfully tested at UTA laser test stand with laser / 10 m tube/ZX60 amp/LCFD

13.7 ps with split CFD signal

LCFD_Ch01_No12_spe, high level light, May 6, 2009, UTA laser test RMS resolution = 13.7 ps

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A reference is obtained from the 400 MHz LHC RF converted to an optical pulse which is split and sent along fibres to both L & R detectors for each BC - pulse to pulse jitter between pulse arrival is negligible

To monitor long term drifts (e.g. T between 2 arms) the optical signal will be split at the detectors & returned to source for comparisonAt the detector stations the optical pulses are converted to electrical signals and are recorded in the detector TDCs – this conversion is envisaged to give an r.m.s (L-R) jitter of 4 ps.

Our reference timing system is designed to provide LR~5 ps

The Reference Timing System

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Testing QUARTIC

• Fermilab Test beam T958 experiment to study fast timing counters for FP420

• Used prototype detector to test concept

• Test beam at Fermilab Sep. 2006, Mar.+Jul. 2007

• CERN October 2007, June 2008

• LASER Test set up in 2009 (including 6GHz Scope)

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Timing – CERN Test-Beam 2008

Dt

56.6/1.4=40 ps/Bar including CFD!

Time difference between two 9 cm quartz bars after constant fraction discrimination is 56 ps,

implies a single bar resolution of 40 ps for about 10 PE’s (expected 10 PE’s from simulations).

Need to show improvement of resolution with # independent measurement (N)

Npe=(area/rms)2

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The √N Effect

7/14/2009 17

16.4 ps 16.6 ps 15.7 ps

10.3 ps

Measure time difference of 3 separate fibers (100 pe’s) wrt reference tube

Correct for T0 offset, average and take new time difference wrt reference tube (expect ~9.5 get 10.3 ps )

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MCP-PMT Rate & Current LimitsWe need to establish if the MCP-PMT’s are capable of coping with the large expected rates at the LHC: up to 15 MHz in a 6mm x 6mm pixel of the MCP-PMT

The limiting factor is the current in the tube given by:

I = f(p frequency) x NPE x e x G(gain)

Using 1 MHz for low lumi conditions and 15 MHz for hi-lumi, with a gain of 5x104 (!) and 10 PE’s expected for our detector, we obtain current limits of 0.24 & 3.5 A/cm2

When the tube current is too high the gain falls - saturation

– Laser test stand test at UTA show that saturation starts around 0.4 A/cm2 for the 10 m pore size Burle MCP-PMT

Luckily, we now have access to a Burle Planicon tube with 10X higher current capability – but we still need to test it

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The Lifetime Challenge

Lifetime due to photocathode damage from positive ions is proportional to extracted charge: Q/year = I*107 sec/year

Using the current limits mentioned previously we get to 35 C/ cm2 /yr (assuming 5x104 gain) at the highest lumi

This is a factor of ~50 more than the expected tube lifetime!

We are pursuing the development of a tube with a ~50 times longer lifetime, the avenues of improvement are:

Including an ion barrier – giving a factor of 5 6

Electron scrubbing gives a factor of 5 6 (Photonis tests)

Z stack design gives a factor of ~10 improvement (NIM A598,160,09)

Arradiance coating gives a factor of ~10 improvement (under study)

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Conclusion

We are on track to reach the 10 micron time resolution required

More work has to determine final parameters of the detector and electronics design

We have a R&D project to solve the lifetime problem for MCPs at the highest luminosities

We are working with three major manufacturers in this area: PHOTONIS, PHOTEK and ARRADIANCE

The way forward seems well determined!

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Last Words

Photon-photon Photo-production

Proton Proton

Pomeron-Pomeron (or g-g)

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EXTRA SLIDES

Documents

Groups Involved University of Alberta, University of Texas at Arlington, University College London. Prague, Saclay, Stoneybrook, Giessen, Manchester,