The CBM Experimentat FAIR

CPOD 2007GSI, 13 July 2007

Volker Friesev.friese@gsi.de

Volker Friese CPOD 2007, GSI, 13 July 2007 2

SIS100/SIS300

CBM

HESR

PANDASuper- FRS

NUSTAR

NESR

CR

GSIAcceleratorFacilities

SIS18

PP

AP

The FAIR Facility at GSI

2 x 109/s 238U 35 GeV/u(Ni: 45 GeV/u)

1013/s protons 90 GeV

Unique possibility to study extremely rare probes in heavy-ion collisions

First beam on CBM target: 2015

Volker Friese CPOD 2007, GSI, 13 July 2007 3

CBM Observables and Requirements

Strangeness

Flow

Open charm

Fluctuations

Hyperons

Dileptons

Charmonium

Hadron ID

Lepton ID

High resolution tracking

High resolution vertexing

Extreme interaction rates

Large acceptance

Radiation hardness

Fast detectorsand eletronics

Online event selection

Volker Friese CPOD 2007, GSI, 13 July 2007 4

The CBM Detector: Overview

Radiation hard Silicon Tracking System in dipole field

Electron ID in RICH+TRD+ECAL

Hadron ID in TOF (RPC)

γ, μ, π in ECAL

High-speed DAQ and trigger system

Volker Friese CPOD 2007, GSI, 13 July 2007 5

The CBM Backbone: Main Tracker (STS)

Arrangement of silicon detector stations inside magnetic dipole field

Large area coverage: strip sensors

High occupancy regions: hybrid pixel detectors /small strips

Volker Friese CPOD 2007, GSI, 13 July 2007 6

STS: Task and Challenges

UrQMD, central Au+Au @ 25 AGeV Task:• track reconstruction in high

track- density environment with high efficiency

• Momentum resolution 1 %• Acceptance coverage 2.5 – 27

degrees

Challenges:• high track density: up to 600

charges tracks per event in the acceptance

• fast sensor / readout: up to 107 events per second

• low mass detector• suitable for fast (online) event

reconstruction algorithms

Volker Friese CPOD 2007, GSI, 13 July 2007 7

STS: Conceptional Layout

target

beam

z = 50 cm – 100 cm:

double sided strip sensors, pitch 60 μm, stereo angle 15 degrees, material budget 200 – 300 μm Si

z = 20 cm – 50 cm:

hybrid pixel sensorsor small strips

other technologies under discussion

Volker Friese CPOD 2007, GSI, 13 July 2007 8

STS: Design of Si-Strip Stations

readout & cooling

readout & cooling

modular design with few (≈ 3) different wavers

connection of sensors by long-ladder technology

readout and cooling outside of acceptance

low-mass cables occupancy < 5 %

Volker Friese CPOD 2007, GSI, 13 July 2007 9

STS: Layout Studies

Ongoing layout and design

studies:

number / position of stations

pixel vs. strip sensors

strip densors: length, pitch, stereo angle

low-mass mechanical support and cabling

CAD drawing of target / STS region

Volker Friese CPOD 2007, GSI, 13 July 2007 10

STS: R&D

CIS 4"280 µm Si

GSI-01

Strip sensor development with CIS ErfurtFirst test sensor delivered July 2007

Fast self-triggered readout chip n-XYTER in collaboration with DETNIprospect: CBM-XYTER

Volker Friese CPOD 2007, GSI, 13 July 2007 11

STS: Gaining Expertise

International workshop on Silicon Detector SystemsGSI, May 2007:

o Review of detector concepto Discussion on (alternative)

technologieso Strategies for R&D and

prototyping

Volker Friese CPOD 2007, GSI, 13 July 2007 12

STS: Hit Pattern for Strip Stations

Track inpact points Occupancy Hit pattern

Large number of fake hits due to projective strip geometry:challenge for track finding

Volker Friese CPOD 2007, GSI, 13 July 2007 13

STS: Track Reconstruction

effic

ienc

y [%

]

momentum [GeV/c]

pixels + strips: 97.02 ± 0.09

only strips: 94.88 ± 0.12

pixels +strips: 92.17 ± 0.14

only strips: 90.01 ± 0.15

Track finding with Cellular Automaton method Good efficiency and performance (78 ms per event on CPU for central

Au+Au) Candidate for high level event selection (implementation in cell processors) Other algorithms (e. g. Hough Transform, suitable for FPGA) also being

developed

primary tracks all tracks

Track fit yields required momentum resolution

Volker Friese CPOD 2007, GSI, 13 July 2007 14

STS: Performance for Hyperons

Detection by weak decay topology with good acceptance and reasonable effiency: 15.8 % 6.7 % 7.7 %

Almost background-free signalsNo identification of secondaries required

Central Au+Au, 25 AGeVFull reconstruction

Volker Friese CPOD 2007, GSI, 13 July 2007 15

The Big Challenge: Open Charm

W. Cassing, E. Bratkovskaya, A. Sibirtsev, Nucl. Phys. A 691 (2001) 745 CBM measures open

charm close to threshold

extremely low multiplicity to be expected (HSD: <D0> = 2 x 10 -4 for central Au+Au @ 25 AGeV)

For discrimination from prompt background detection of the decay vertex with excellent resolution is required (D0: τ = 127 μm)

Volker Friese CPOD 2007, GSI, 13 July 2007 16

The Key to Open Charm: Vertex Detector (MVD)

Challenge: Determine secondary vertices with a precision of 50 μm or better

Requirements: very low material budget excellent coordinate resolution fast readout radiation hardness

Solution: 2 – 3 thin Si detector layers close to the target (z = 5cm or 10 cm) inside vaccuum vessel

Volker Friese CPOD 2007, GSI, 13 July 2007 17

MVD: Preferred Option MAPS

Monolithic Active Pixel Sensors

developed at IPHC Strasbourg

extremely thin (100 – 150 μm)

excellent position resolution (3 – 5 μm)

- radiation hardness- readout speed (max. 10

μs)Possible running scenario: reduced interaction rate (1 MHz) tolerable pile-up (10 – 20

events per frame) exchange first station (diameter 10 cm) periodically

Volker Friese CPOD 2007, GSI, 13 July 2007 18

MVD: Performance for D Mesons

Open charm performance is the benchmark criterion for the MVD + STS design

Study: D0 π+K-, τ=127 μm, central Au+Au @ 25 AGeV, <D0> = 2 x 10-4

First MAPS at z = 10 cm

without PID for daughterswith proton rejection

Volker Friese CPOD 2007, GSI, 13 July 2007 19

MVD: Open Charm Studies

Ongoing studies:

oD±ππK, τ = 317 μm

o D0K-π+π+π-

o Λc+pK-π+, τ = 62 μm

Preliminary: Four particle channel for D0 seems to be preferrable (stricter constraint on 4-track vertex wins over 4-particle combinatorics)

Volker Friese CPOD 2007, GSI, 13 July 2007 20

Hadrons Identified: The TOF System

Task:

Separate π-K-p over a large rapidityinterval

Requirements:

Location at z = 10 m from target

2π acceptance needed for flow and fluctuation studies large area (120 m2)

Timing resolution <≈ 80 ps

Rate capability > 20 kHz/cm2

Volker Friese CPOD 2007, GSI, 13 July 2007 21

TOF: Design and R&D

Large area requires RPC detectors

Modular design with pad (inner region) and strip (outer region) readout

R&D frontiers: uniform resolution over large

areas rate capability

R&D in close cooperation with FOPI and HADES

single gap RPC, Coimbra

Volker Friese CPOD 2007, GSI, 13 July 2007 22

TOF: Performance

Central Au+Au @ 25 AGeVFull reconstructionTime resolution 80 ps

Total efficiency vs. momentum(tracking + matching with TOF)

K / π separation up to 3.5 GeV, p / K separation up to 8 GeV at efficiencies of 80 % to 90 %

Volker Friese CPOD 2007, GSI, 13 July 2007 23

TOF: Acceptance for Hadrons

Bulk of hadrons can be identified by TOF

ycm

Volker Friese CPOD 2007, GSI, 13 July 2007 24

Electron Identification: RICH

Serves for electron identification up to 10 GeVLocated directly behind STS, outside of the fieldOptical layout: Vertically separated focal planes, shielded by magnet yokes

Volker Friese CPOD 2007, GSI, 13 July 2007 25

RICH: Ring Reconstruction

reconstructed rings in focal planecentral Au+Au @ 25 AGeV

reconstructed ring radius vs. p

Hadron blind up to 6 GeV (with N2 radiator)e / π separation up to 12 GeV

Volker Friese CPOD 2007, GSI, 13 July 2007 26

RICH: Performance

electron efficiency pion suppression

after track reconstruction, ring finding, matching and RICH quality cuts: electron efficiency 70 % - 80 % pion suppression ≈ 500 (misidentification due to false ring-track matches)

Volker Friese CPOD 2007, GSI, 13 July 2007 27

Why Electrons: Low-Mass Vector Mesons

CBM: Electron ID after spectrometer + good inv. mass resolution- opening of conversion pairs

fight electron background: γ conversion, π0 and η Dalitz decays

all identified e+e- after all cuts

ππ0 0 γγee++ee--

ππ00ee++ee--

ηη γγee++ee--

w/o pt cut on single e

ρρ ee++ee--

ee++ee--

φφ ee++ee--

Volker Friese CPOD 2007, GSI, 13 July 2007 28

LVM: Phase Space Coverage

Phase space for ρ after full reconstruction and analysis cuts

with single – e pt cutw/o single – e pt cut

Good coverage in y and pt; w/o single-e pt cut also at low pt and small minv

Volker Friese CPOD 2007, GSI, 13 July 2007 29

Further Electron ID: TRD

Tasks:electron / hadron separation for p > 1 GeVtracking (connection of STS and TOF)

Current design: 4 x 3 layers (radiator + MWPC)Pad readout

Volker Friese CPOD 2007, GSI, 13 July 2007 30

TRD: R&D

R&D frontiers: rate capability and speedPrototypes already tested at GSI

Beam test facility at GSI

Design rates (up to 100 kHz/cm2) well in reach

Volker Friese CPOD 2007, GSI, 13 July 2007 31

target 250 m

Combined RICH+TRD: Performance for J/ψ

combined pion suppression ≈ 10-

4

major background source: electrons from conversion in target; can be reduced by thinner target

J/ m = 38 MeV/c2

' m = 45 MeV/c2

target 25 m

Excellent performance for J/ψ; with thin target also ψ' in reach

Volker Friese CPOD 2007, GSI, 13 July 2007 32

CBM with Muons: MUCH

For muon measurements:RICH replaced by absorber – detector system

Challenges:first detectors in EM showertracking through absorber

TRD / TOF help to eliminate fake track matches

With removed absorber also suited for hadron measurements

Volker Friese CPOD 2007, GSI, 13 July 2007 33

MUCH Design

5 Fe absorbersinterlayed with 3 detector stations

Pad structure of detector layers

Volker Friese CPOD 2007, GSI, 13 July 2007 34

Performance for Di-Muons

Background sources:mis-identified hadrons (mostly fake matches)μ from π and K decay

J/ m = 22 MeV/c2

' m = 33 MeV/c2

Similar S/B as obtained in di-electron channels!

Volker Friese CPOD 2007, GSI, 13 July 2007 35

Summary

• Feasibility studies, including semi-realistic detector response and full event reconstruction demonstrate that the CBM detector concept is suitable for the measurement of the key observables: charm, low-mass dileptons, strangeness

• Tough detector R&D ahead to reach the design specifications

20042005

2006

Progress is fast –stay tuned:

http://www.gsi.de/fair/experiments/CBM

Volker Friese CPOD 2007, GSI, 13 July 2007 36

The CBM collaboration

Russia:IHEP ProtvinoINR TroitzkITEP MoscowKRI, St. Petersburg

China:CCNU WuhanUSTC Hefei

Croatia: RBI, Zagreb

Portugal: LIP Coimbra

Romania: NIPNE Bucharest

Poland:Krakow Univ.Warsaw Univ.Silesia Univ. KatowiceNucl. Phys. Inst. Krakow

LIT, JINR DubnaMEPHI MoscowObninsk State Univ.PNPI GatchinaSINP, Moscow State Univ. St. Petersburg Polytec. U.Ukraine: Shevchenko Univ. , Kiev

Cyprus: Nikosia Univ.

Univ. Mannheim Univ. MünsterFZ RossendorfGSI Darmstadt

Czech Republic:CAS, RezTechn. Univ. Prague

France: IPHC Strasbourg

Germany: Univ. Heidelberg, Phys. Inst.Univ. HD, Kirchhoff Inst. Univ. FrankfurtUniv. Kaiserslautern

Hungaria:KFKI BudapestEötvös Univ. Budapest

India:VECC KolkataSAHA KolkataIOP BhubaneswarUniv. ChandigarhUniv. VaranasiIlT Kharagpur

Korea:Korea Univ. SeoulPusan National Univ.

Norway:Univ. Bergen

Kurchatov Inst. MoscowLHE, JINR DubnaLPP, JINR Dubna

46 institutions

≈ 400 membersStrasbourg, September 2006