Dottorato in Fisica Maggio 2005 Apparati per Fisica agli ...iaselli/Fisica dei...

Dottorato in Fisica Maggio 2005“Fisica dei rivelatori” Apparati per Fisica agli acceleratori

6 Giugno 05 M. de Palma 1

How to use single and specific How to use single and specific detection technology to build detection technology to build a general purpose apparatus a general purpose apparatus

for high energy physic for high energy physic

experiments.experiments.



Introduction (I)



Particles are detected via their interaction with matter.

Many different physical principles are involved (mainly of electromagnetic nature). Finally we will always observe ionization and excitation of matter ⇒ detectors

The classic quantities to measure are:Trajectory, Charge, Momentum, (transparent detector + Muon chamber + B)Energy (calorimeters)

In order to :identify particle, calculate mass, recover intermediate processes, decays, etc.

Introduction (II)



To do that we have to design a detector. That is exciting; one of the best part of the whole story

Important before starting: Given an accelerator (example LHC)

What we want to measure (signatures)

GammasHiggs Leptons

Hadr Jets

Sparticles → Missing energyRare mesons….Etc

How we can measure (detector)

But a lot is simply not known, therefore, stick to general assumptions and design for surprises.

Introduction (III)



Particle detection – ideal case



Particle detection – some real cases



Very good electromagnetic calorimetry for electron and photon identification

Good hadronic calorimeter jet reconstruction and missing transverse energy measurement;

Efficient and high-resolution tracking for particle momentum measurements, b-quark tagging, t tagging, vertexing (primary and secondary vertex)

Excellent muon identificationwith precise momentum reconstruction

……

fine segmentation,fast response,no dead timecoverage of full solid angle (Hermetic), no cracks but easy to dismountas less as possible material in front of the calorimeteras much as possible materialin front of the muon chambers

Pratical limitation (tecnology, space, budget):

Cost of experiment goes with~volume

+

The ‘ideal’ particle detector should provide.......



In the following, we look only collider geometry

Detector Geometry



The past…..The past - UA1



The near pastALEPH

VDET2, partially build in Bari



The present ….. or the near future

46m Long, 22m Diameter,

7’000 Ton Detector



Internation LinearCollider

The future



Magnet concept for 4π detector



Momentum measurementµ trajectory in:

a)toroidal field

b) Solenoid field



1) Check what signatures have significance (ask your preferred theoretician);2) Have a look at the interaction region and estimate your minimal δz;3) Fix your detector cell size (with precisions σφ, σz);4) Decide the magnet type;5) Place your inner tracker and muon shells in order to satisfy your min.

requests on δp/p and δz (which you can calculate);6) Decide what kind of calorimeter you need and place it;7) Calculate dose and occupancies and find your closest approach values to

the interaction region (compatible with maximum allowed dose and cellsize);

8) Go back to point 3) and re-adjust the values (if needed);9) Start your simulations and your R&D

Apologies…, I have given on following a fairly personal cut looking to the designing a detector for LHC focusing on CMS (and Atlas)

The rules for a detector designer



Lum= 1034 cm–2s–1,

Interaction Rate, R = 8⋅108HzEvents/beam crossing: ∆t= 25 nsInteractions/crossing = 20Only 2835 full out of 3564 Interactions/”active”crossing = 20 x 3564/2835

Summary):(1) A "good" event containing a Higgs decay + (2) ~ 25 extra "bad" (minimum bias) interactions

Make up for the lower production cross section. Normally, σ~1/s, so a factor x in c.m. energy needs a factor x2 in luminosity (for the samenumber of events; N=σL) ⇒ high luminosity

LHC



Momentum / charge of tracks and secondary vertices (e.g. from b-quark decays) are measured in central tracker. Energy and positions of electrons and photons measured in electromagnetic calorimeters.Energy and position of hadrons and jets measured mainly in hadroniccalorimeters. Muons identified and momentum measured in external muonspectrometer (+central tracker).Neutrinos “detected and measured” through measurement of missing transverse energy (ET

miss) in calorimeters.

Basic principle: need “general-purpose 4π ” experiments since we don’t know how New Physics will manifest itself ( →detectors must be able todetect as many particles and signatures as possible: e, µ, τ, ν, γ, jets, b-quarks, ….)



Measure Momenta of Charged Particles



Choise of magnet: Toroid



Choise of magnet: Solenoid



Tracking

CMS solution: few, very accurate pointsATLAS solution: continuous tracking

Both: add pixels for vertex tagging



CMS Tracker (SST)



SST Requirements



SST basis unit:

FE hybrid FE hybrid with FE with FE ASICSASICS

Pitch adapterPitch adapter

Silicon Silicon sensorssensors

CF frameCF frame

9’648’128 strips ≡ channels

75’376 APV chips

6’136 Thin sensors18’192 Thick sensors

440 m2 of silicon wafers 210 m2 of silicon sensors

3’112 + 2*1’512 Thin modules5’496 + 2*1’800 Thick modules

~17’000 modules

p+ strips on n-type bulk<100> crystal lattice orientation

•Polysilicon resistors to bias the strips•Strip width over pitch w/p=0.25

•Metal overhang and multiguard structure to enhance breakdown performance

2000 (+ 2000) modules are build in Bari



Tracker- b identification

3 barrel layersr = 4.1 – 4.6 cm, 7.0 – 7.6 cm, 9.9 – 10.4 cm (~ 60 x 106 pixels)

2 pairs of Forward/Backward disks–Radial coverage 6 < r < 15 cm–Average z position: 34.5 cm, 46.5 cm (~3 x 106 pixels per Disk)

⇒ 3 high resolution space points for η < 2.2

Pixel seeding fastest starting point for track reconstruction despite

the extremely high track density



Events in VDET al LEP

B+ decay in Dbar0D+K01 cm



Example: H →γγ for low mass Higgs

Higgs width is very narrow, so S/N directly ∝to signal resolution.

Moreover, initial background: x100 largerπ0 rejection: strips (ATLAS),

crystal size (isolation) (CMS);

Need excellent energy resolution of EM calorimeters

background from pp →γγH

H →γγ good resolution

H →γγ poorresolution

mγγ

eventi

Liquid argon by ATLAS. Not enough space in CMS for cryogenics ⇒ Crystal ECAL (more compact)

Optimal choice: PbWO4(Good light yield, short X0, short τ, good radiation resistance)



Hadron calorimeter



Other LCH experiments

LHCbLHCb is a dedicated experiment to study CP violation and other rare phenomena in B-meson decays.

Optimal L for LHCb ~ 2×1032cm−2 s−1: physics can be exploited from day one and β* can be tuned to run also at nominal L.Measure the CP violation in Bd and Bs systems, Search for New Physics, Determination

of the CKM

AliceAlice is a dedicated experiment to study HI collinsions to finf evidence of the quark-gluon plasma

Measure most (2π * 1.8 units η) of the hadrons (dE/dx + ToF), leptons (dE/dx) and photons (EM calorimetry) produced collisions.Track and identify from very low (< 100 MeV/c) up to fairly high pT (~100 GeV/c).……… in an environment of very high charged-particles density (dN/dη ≤ 8,000; 15,000 tracks)



LHC-b



Alice

ITS

TPCTRD

TOF PHOS

HMPID

MUON SPECTR..PMD

FMD

L3 Solenoid Magnet



Pile-up & Electronic at LHC



Example: electron reconstruction (I)

Nominal vertex (0,0,0)

B→

Predict a track

Cluster ECluster position

Propagate tothe pixel layersand look forcompatible hits

If a hit is found,estimate z vertex

Predicta new trackand propagate

Estimated vertex (0,0,z)

Pixel hit

In CMS, both tracker and ECAL are used



Example: electron reconstruction (II)

e

γsingle single electrons,electrons,pptt> 28 GeV> 28 GeV

mainmainclustersclusters

supersuper--clustersclusters

Bremsstrahlung emission could false the electron energy estimation. The 4 T field, especially a low pt, produces a large separation, in φ, between electron and γbremsstrahlung clusters

“dynamic” clusterizzation algorithms produce Supercluster = cluster of cluster



Example: electron reconstruction (III)

Combined algorithm

E = 5-10 GeV

E = 30-35 GeV

E = 80-85 GeV

Esc/Etrue Ptk/Etrue

☺

☺

Ebest/Etrue



Example: energy flow



+

SUSY

In conclusion, if everything (detector, trigger and analysis) work properly we should seen Higg

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