`First ep events in the Zeus micro vertex detector in 2002`i93/Jaarvergadering/2002/talks/Maddox.pdf · ZEUS 2002 HERA I (1992-2000) Lumi: 117 pb-1 e+, 17 pb-1 e-History (1): Upgrade

1NIKHEF annual meetingZEUS 2002

`First ep events in the Zeus micro vertex detector in 2002`

Erik Maddox, Zeus group

Amsterdam 18 dec 2002


ZEUS 2002

� HERA I (1992-2000)Lumi: 117 pb-1 e+, 17 pb-1 e-

History (1):

� Upgrade (2001)

� HERA II (2001-2006)Goal: 4*250pb-1 (e+/- , with longitudinal polarization)

� ZEUS UpgradeImprove tracking- Tagging of charm, beauty (also tau) with secondary vertexing

or impact parameter methods- Build and install silicon microvertex detector (impact parameter ~100 micron)--> Large NIKHEF contribution


ZEUS 2002

History (2):

� Start up 2002 difficultBeam related backgrounds much higher than expected

� Started begin Nov: `lumi-period`establish stable running (with lower beam currents)(re)comissioning of detector/trigger and new components


Introduction

Scope of the talk:

� Focus on microvertex detector- reminder of the detector- integration in data taking and event reconstruction

� Cosmic runs- estimate impact parameter resolution

� Effect of background on MVD

� 2002 nice ep events

� 2002 data studies- dE/dx of microvertex tracks- Primary and secondary vertices- K0s signal in data


Zeus microvertex detector

Geometry: (barrel)

Total 30 ladders fit in the barrelmost tracks will pass 3 cylinders,(giving 6 hits)

Ip

Elliptic beam pipe (height 5 and width 12 cm)



Geometry: (wheels)

4 wheels in the forward (proton) direction.Wheel has two layers of silicon

Total 712 silicon sensors:- 300 �m thick

- single sided 20 �m strip pitch- 120 �m read out pitch- analog read out



Cosmic runs (1):(Using the new ZEUS event display: zevis)

Energy loss in calorimeter (CAL) Cosmic muon

Measure hits and tracks in central tracker (CTD)

For vertex detector (MVD) -> zoom in



Cosmic runs (2):

Clear track inMVD is found

Also shown are noise hits and the 'ghost' hits

� MVD track fit is done using Kalman filter, developed by Nikhef group.



Cosmic runs (3):

Only the track hits are shown



Cosmic runs (4):

� ~100k clean cosmic events collected this year

- used in alignment study (in progress)

-



Cosmic runs (5):

� Plot the distribution of the difference of z

0 coordinates of

the 2 tracks.σ

CTD = 3.27 mm

σMVD

= 0.16 mm

For MVD cosmics impact parameter is then ~0.16 / sqrt(2) = 110 microns (without alignment corrections)



Impact parameter precision:

Single track MC study

� Simulation of Zeus MVD with design geometry including all detector materials

� Track fit is done using Kalman filter developed by Nikhef group.

- High p: hit precision is dominant- Low p: multiple scattering dominates (1/p)


Zeus 2002 running

Backgrounds:

Background comes from:

� Proton-beamgas

� Off-momentum positrons

� Back scattered synchroton radiation

Limiting factor:

� Currents in the central tracker become to high

� Particles backgrounds give high rates and large occupancy,leads to deadtime and bad data taking efficiency

� Effect increase with beam currents

--> What does this mean for the microvertex detecor?


Zeus 2002 running

Radiation monitoring:

I) Instantenious radiation measurement (16 Si pin diodes positioned just outside beampipe )

- generate alarms and beam dumps- used by HERA for machine optimisation

II) Integrated radiation measurement (8 radfets)

Beam loss

Increase during normal operation

Measured dose ~20 - 100 kRad

Electronics: small increase in noiseof modules close to the beam (~1%)

Silicon: small increase in leakage currents observed

Work is done to estimate the effective radiaton dose on the MVD from this

Expected dose of 300-500 kRad for 5 years


Zeus 2002 running

Example: p-gas

Large energy deposition in CAL

Many hits and tracks in CTD

Enormous number of hits in MVD

Protons, 920 GeV

Z-axis


Zeus 2002 running

Example: off-momentum e+

Electro-magnetic cluster in CAL (fakes a scattered positron)

Positron, 27.5 GeV

Many hits in +x side of MVD (particle showers inbeampipe and MVD)


Zeus 2002 running

Backgrounds and the MVD:

Z vertex [cm]

Hits in MVD

� Proton-gas background- the secondary particles hit collimator at -75 cm- large tail in number of MVD hits

� ep events (DIS) in yellow- in center of detector- MVD occupancy is small

� High data size of background events slows down data aquistion, trigger (deadtime) and event reconstruction.

--> Let's find some nice events


Zeus 2002 running

Physics events in the MVD (1):


Zeus 2002 running

Physics events in the MVD (2):


2002 data analysis

MVD dE/dx:

� Take sample of good events and good tracks

� correct measured signal in silicon for pathlength

� plot average signal vs track momentum

� pion, kaon and proton band seen!

From 2500 dis candidate events


2002 data analysis

Primary/Secondary vertexing:

� Run vertex finder without beam constraint, plot all vertices in xy-plane.

� Primary vertex and interactions in the beampipe are seen.

Nikhef vertexing package


2002 data analysis

K0 --> π+π-:

� Take all secondary 2 track vertices with opposite charged tracks.

� At least 4 MVD hits per tracks.

� Assume tracks have pion mass

� Calculate invariancemassCut on kaon Pt: >0.25

From 4400 dis candidate events

� Then require kaon to point back to 1st vertex (less background)


Summary

� Zeus microvertex detector fully integrated in data taking and event reconstruction.

� > 100K of good cosmic events recorded.

� Already good tracking precision obtained.

� Background events cause large occupancy in microvertex detecor.

� Clean ep events are found.

� No evident radiation damage observed

� `Luminosity runs` are used for detector comissioning and developing of new analysis methods for future running.

- Primary vertex/Secondary vertex- K0 peak

� Hunt for charm signal with microvertex detector has started


Click to add title

Many presentations at this meeting will be about the challenging and exciting future we have in 2007 or 2012 or whenever the future experiments start.But if you like to do physics and you are not afraid of challenges and you do not want to wait so long, why not join the Zeus experiment?

Final statement

Deze doe ik niet hoor!



Basic principle:

300 � m thick n-type Si wafers, with p-type implanted strips every 20 �m

300 �m

120 �m

Read out strips are every 120

� m. Using capacitive charge sharing the analog readout provide position resolution < 20

� m



Signal readout: (half-module)

Z coordinate

R�

coordinate (coupled to Z channel)

512 channels per sensor

4 * helix analogreadout chip

Multiplexed signal (4*) to FADC (daisy chain)then to disk/trigger

HV/LV/clock and control



Geometry: (ladder)

2 mirror imaged half-modules on top of each other form a module,inner and outer strips perpendicular. (charged track gives 2 hits)

(In reality!)

5 modules are placed on stiff carbon fiber ladder (~ 6 * 60 cm2),electronics, cooling & cabling mounted on the ladders



Geometry: (overall)

Rear: place for tubes and cables

Barrel: 30 ladders (in 3 cylinders),total 600 silicon sensors

Forward: 4 wheels (each with28 sensors)

Wheel sensors:

� same technology

� wedge shaped

� Inner and outer sensor with crossing angle of 26o

� 480 strips/sensor

� no coupling of inner and outer strips



Installation: (march 2001)

Proof it is really there!

Inside central tracker

� Large NIKHEF contribution (design,mechanics, electronics, testing, and event reconstruction) since 1997

� Detector works fine, work is now done on fine tuning

Documents

`First ep events in the Zeus micro vertex detector in 2002`i93/Jaarvergadering/2002/talks/Maddox.pdf · ZEUS 2002 HERA I (1992-2000) Lumi: 117 pb-1 e+, 17 pb-1 e-History (1): Upgrade