strawman detector

Strawman Detector

F.Forti, Università and INFN, Pisa

UK SuperB Meeting

Daresbury, April 26, 2006

http://www.unipi.it/princ.html

April 27, 2006 F.Forti - SuperB Strawman Detector 2

Experimental issues• Babar and Belle designs have proven to be

very effective for B-Factory physics– Follow the same ideas for SuperB detector– Try to reuse same components as much as

possible

• Main issues– Machine backgrounds– Beam energy asymmetry– Strong interaction with machine design

• Impact on– Detector segmentation– Radius of beam pipe and first sensitive layer– Radiation hardness


EMC6580 CsI(Tl) crystals

Instrumented Flux Returniron / RPCs&LSTs ( / neutral hadrons)

Drift Chamber40 stereo layers

1.5 T solenoid

Silicon Vertex Tracker5 layers, double sided strips

DIRC PID)144 quartz bars

11000 PMs

e+ (3.1 GeV)

e- (9 GeV)

SVT: 97% efficiency, 15 m z hit resolution (inner layers, perp. tracks)SVT+DCH:(pT)/pT = 0.13 % pT + 0.45 %, (z0) = 65 m @ 1 GeV/c

DIRC: K- separation 4.2 @ 3.0 GeV/c 3.0 @ 4.0 GeV/c EMC: E/E = 2.3 %E-1/4 1.9 %

The BABAR Detector


Machine backgrounds• In “traditional” Super BFactory designs

– Luminosity obtained with large beam currents (among other things)

• 4.1/9.4 A for SuperKEKB @ 4x1035

• 6.8/15.5 A for SuperPEP-II @ 7x1035

– Background a significant problem

• In December Linear SuperB design– Small fraction of store beam extracted from damping

ring at each collision.– Very low current at the IP make backgrounds negligible– Low collision frequency implies event pileup

• In March SuperB design – Beam currents are moderate: 1.5A @ 1036

– Background important, but should not be a huge problem (smaller than in current BFactories)

– Collision at every turn: no pileup, and continuous time-structure as in current BFactories.


Types and level of backgrounds• Extrapolations from current machines

– Full simulation is needed to completely understand backgrounds

• Beam gas• Synchroton radiation Both proportional to current

– Should not be a problem at SuperB• They become a problem at higher currents

• Luminosity sources (eg radiative Bhabhas)– Need careful IR design. – Angle crossing helps (see PEP-II/KEKPB

comparison)

87.57

6.56

5.5

4

3.532.5

21.51

0.5

4.55

HER Radiative Bhabhas

-7.5 -5 -2.5 0 2.5 5 7.5

0

10

20

30

-10

-20

-30

m

cm

M. SullivanFeb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M

3.1 G

eV

3.1 G

eV

9 GeV

9 GeV

BABAR Interaction Region

Detector

0

10

20

-10

-20

cm

0 2 4-2-4m

KEK Interaction Region

QCSL QCSR

QC1EL

QC2PL QC1ER

CSL CSR

Detector

gammas

off-energy beam particles

Radiative Bhabhas


More sources of background• Beam-beam interactions

– Potentially important, but probably under control in the low disruption regime.

• Touschek background– Intra beam scattering. Goes like 1/E2. Improves

with smaller asymmetry. Increases with beam density. Need further study

• Thermal outgassing– Due to HOM losses. Not an issue with small

currents• Injection background

– Needs further study with the 1 collision/turn scheme.

• Bursts– Due to dust. No real cure. Need robustness of

detector


Background bottom line• Probably reasonable to assume machine

background is not larger than what with have today at Babar and Belle.

• Need to design a robust detector with enough segmentation and radiation hardness to withstand surprises (x5 safety margin)– Seems within reach of current technology– There are critical points, though:

• Inner detector radius likely to be reduced more background

• Bhabha scattering at small angle can become an issue because of smaller boost more occupancy, more radiation damage

• IR design is critical– Radiative Bhabhas– Syncrotron radiation shielding– Shielding from beam-beam blow up


Beam Energy Asymmetry• Machine design prefers lower boost

– Damping rings more similar– Babar: 9 + 3.1 βγ=0.56– Belle: 8 + 3.5 βγ=0.45– SuperB?: 7 + 4 βγ=0.28

• Most obvious effect on detector Larger solid angle coverage Smaller decay vertices separation

• We can afford to have a lower boost only if the vertexing resolution is good:– small radius beam pipe– very little material in b.p. and first layer– Studies indicate a b.p. of 1cm would be OK– Need a realistic beam pipe design to confirm the viability

of the lower boost. – How much cooling is needed in the beampipe ?

• Symmetric running is also being studied– Could reduce boost-induced energy smearing in

analysis


Beam Pipe Radius• Small beam pipe radius possible because of small beam size

– Studied impact of boost on vertex separation (B)– Beampipe hypothesis (no cooling)

• 5um Au shield to protect from soft photons• 0.5cm 200um Be and 5um hit resolution (0.21% X0)• 0.5cm 300um Be and 10um hit resolution (0.24% X0)• 0.5cm 500um Be and 10um hit resolution (0.29% X0)

– Rest of tracking is Babar

Separationsignificance Proper time

differenceresolution


Beam Pipe Thickness• With 1.5A beam currents the beam pipe

will require cooling.– Beampipe design is being developed– Study effect of beampipe thickness

• Assume boost=0.28• Bdecay• 10um hit resolution 1cm beampipe

should allow good performance even with =0.28

Proper timedifferenceresolution

BaBar


Energy• Is it interesting to run at different energies ?

– Υ(5s): not an issue for the machine– oscillation of Bs rapid for TD analysis

• Required resolution very hard to obtain

• Still it might be possible to measure through time-integrated measurement branching fractions

• BsD

• BsK++0

Renga/Pierini


Energy II• Is it interesting to run at the threshold or

at the (3770) ?– Luminosity will be around 1035

– Still more than at tau-charm factories– Studies going to on on physics case

• Absolute D branching fractions, rare decays• Form factors• Unitarity tests with charm• D mixing ? Use

coherence of initial state

• CP violation

• Boosted operation– Is there something

to be gained to run at low energywith boost ?

– It might be possible to separate (a little bit) the D vertices

zzvs


Silicon Vertex Tracker• Vertexing

– Two monolithic active pixel layers glued on beam pipe• Since active region is

only ~10um, silicon can be thinned down to ~50um.

• Good resolution O(5um).• Good aspect ratio for small

radius (compared to strips)• Improves pattern recognition robustness and

safety against background • needs R&D: feasability of MAPS, overlaps,

cables, cooling

• Quite a bit of R&D going on on MAPS

x5 scale with 10mm radius BP, 6mm pixel chip


MAPS R&DCAP chip (Belle collaborators)

TSMC 0.35m Process

Column Ctrl Logic

1.8mm 132col*48row ~6 Kpixels

CAP1: simple 3-transistor cell

Pixel size:

22.5 m x 22.5 m

CAPs sample tested: all detectors (>15) function.

TESTED IN BEAM.

Source follower buffering of collected charge

Restores potential to collection electrode

Reset

Vdd Vdd

Collection Electrode

Gnd

M1

M2

M3Row Bus Output

Column Select


MAPS R&D II• SLIM chip

(Babar collabor.)

PRE SHAPER DISC LATCH

=105 mV =12 mV

Landau peak 80 mV saturation

due to low energy particle.

1250

2200 3000 (e-)

1640

threshold

threshold

90Sr electrons

Noise only (no source)

55Fe X-rays

Charge sharing

ST 0.13um triple well technologySingle pixels tested with sourceFull signal processing chain


Silicon Vertex Tracker• Intermediate silicon tracking

– More or less like the current Si strip detectors:• 5 layers of 300um Si, strip lengths 5-20cm, pitch 50-200um,

shaping time 100-400ns

– Reduction in thickness would be desirable, but not essential• Possibility of 200um Si in inner layers

– Small angle region will require special attention due to the high Bhabha rate

40 cm30 cm

20 cm


Central Tracker• Babar and Belle Drift Chambers

– Both use He based gas mixture– Cell size 12-18mm– Maximum drift time ~500ns– Resolution in the best part of the cell

~100µm– Expect that either OK.

• Solid state tracking – an all-silicon solution evaluated, but

not performant at low momentum, expensive, and not really needed with moderate backgrounds

• Need to optimize cell size against occupancy– Belle has developed a fast gas small

cell DCH, but with a degraded resolutions (5.4mm, ~150µm)

• Solutions exists, although a full design is needed

Normal cell(17.3mm)

Small cell(5.4mm)


Particle Identification• Current solutions for K identification

– Low p: • dE/dx (both Babar and Belle) • TOF (Belle only)

– High p: dedicated Cherenkov detector• DIRC (Babar) – ring imaging cherenkov counter• ACC(Belle) – aerogel threshold cherenkov counter

– Coverage: • only barrel(Babar) • barrel+endcap (Belle)

• Evolution– Ring imaging is superior to threshold counters

• Need to resolve background and mechanical issues– Forward and backward endcap coverage very

desirable to increase effective luminosity• A different kind of problem

• R&D is needed


Babar PID

• Stand-off box, filled with water expands cone on PM– Source of backgrund

• Barrel-only device• Mechanical

interference in the backward direction


Belle PID• Aerogel Cherenkov Counters, Time of Flight

– No high mom. PID for endcap

– Material (ACC+TOF ~ 0.35X0)


Evolution: Babar-Style Fast DIRC• Replace SOB with

compact readout• Tested in beam

with– Hamamatsu Multi

Anode Photo Multipliers

– Burle Micro Channel Plate PMTs


DIRC with timing: TOP • Cherenkov ring imaging

with precise time measurement– Quartz radiator (2cm-thick)

• Basic study was already done.– Photon detector (MCP-PMT)

• Good time resolution < ~40ps• Single photon sensitive under 1.5T

– Test with GaAsP photo-catode + MCP-PMT very promising

Simulation2GeV/c, =90 deg.

-ray, had. int.

K

-K separation power


Focusing Aerogel-RICH• New imaging technique by introducing multiple radiators

Focusing type Defocusing type

n1 n2n1<n2 n1>n2

Increase Cherenkov photons without loosing single angle resolution due to emission point uncertainty

Take full advantage of controllable index of aerogel

n2

n4n3n2n1n4n3n2n1

n1<n2<n3<n4 n2<n1<n4<n3


Electromagnetic calorimeter• Both Babar and Belle use CsI(Tl)

calorimeters are suitable for SuperB – signal decay time of ~.75µs (dominant) and

~3µs are OK • CsI(Tl) is too slow for endcap

– need to deal with Bhabha rate spatial and temporal overlaps.

– especially if possible to extend coverage to 100 mrad, beam line elements allowing. • Babar forward is 350 mrad, Belle forward 200 mrad,

backward 400 mrad

• Encap replacement is needed– In the case of Babar, a backward endcap needs

to be added altogether• Solutions seem to be viable with some

R&D


Candidate materials• Pure CsI

Fast (16ns) Low light yield (2500 /MeV)

• LSO or LYSO High light yield (27000 /MeV) Speed OK (47ns) Expensive


Other Detector components• Muon and KL detector

– Inside the return yoke of magnet– It doesn’t seem to be a problem– avalanche mode RPC, LST, scintillator

are all viable

• Trigger/DAQ– Not substantially different from current

schemes.– Keep open trigger scheme– Need to try vetoing Bhabhas at level 1 – Data rate seems well manageable


Reusability of Babar and Belle• Large (expensive) portions of Babar or

Belle would be reusable– Barrel calorimeter– Magnet– Barrel LSTs for Babar

• But large subsystems need to be replaced or significantly upgraded– Tracking and vertexing– Particle ID– Endcap calorimeter– Trigger/DAQ

• Babar or Belle seem good foundations for a SuperB detector– But need to look in detail at integration and

mechanical structure issues


From Hitlin’s talk at March 06 LNF


Outlook• A detector for SuperB seems to be

feasible• An R&D plan needs to be formulated

to address the remaining issues– Vertexing– Particle ID– Calorimetry

• Babar and Belle provide excellent foundations for a detector at SuperB

• More detailed studies will be possible once the machine parameters have settled.

strawman detector

Documents

superb detectortry

superb design beam currents

pisauk superb meetingdaresbury

beambeam blow upf

beam density

large beam currents

low current

radiation damageir design