LHC Upgrade: Evaluation of monitored drift tubes inclusion into the ATLAS level 1 muon

end cap trigger

ICEPP, KEKA

Katarina Bendtz, Takayuki Kamiya, Tatsuo Kawamoto, Yoichi Ninomiya, Hiroshi Sakamoto, Takeshi DomaeA, Kunihiro NaganoA, Osamu SasakiA, Yu

SuzukiA

Outline

Introduction

- The ATLAS experiment - The trigger system - The muon system and the monitored drift tubes

LHC upgrade

- General - Level 1 Trigger - Monitored drift tubes inclusion

Methods and algorithms

- Track segment finding within the inner and middle stations

A framework for evaluating different methods

- Purpose and requested functions - Current functions and structure of the framework

Introduction

The ATLAS experiment

The ATLAS experiment is one of the detectors of the Large Hadron Collider, LHC, designed for 7TeV + 7TeV centre of mass energy proton proton collisions at a luminosity of 1034cm-2s-1.

Divided into a shell-like structure of sub detectors. From the beam axis: - Inner detector: enclosed in a 2T solenoid magnet, tracker for lighter charged particles, high resolution measurements around the interaction point - Calorimeter: measures the energy through “showering”. “Liquid argon”: charged particles (e.m interaction) and “Tile Cal” for hadrons passing the Liquid Argon (strong interaction). - Muon spectrometer: measures the momentum of the heavier muons (~100 MeV), using a bending 4 T toroidal magnet.

The Trigger system

Selects “interesting” events. Reduces event rate from 40 MHz to 200Hz

Three levels: - Level 1: Selects events at a max. 75 kHz. Info: calorimeter and muon systems.

- Level 2 & Event filter: 3.5kHz -> 200Hz by means of “Regions of interest” obtained from Level 1, and coordinated data from all detector parts

Introduction

The monitored drift tubes (MDT)

Part of the muon system

End-cap and Barrel

End-cap: Inner, middle and outer station. Between inner and middle station, is the particle bending toroidal magnetic field. Curvature - > pT.

Tracks are reconstructed using combined drift radii tangents from several stations.

Four (inner station) or three layers (middle & outer stations) = one multi layer. Two multi layers in each station.

Cylindrical tube shape: central anode wire receiving signals of electrons of gas atoms ionized by incoming particles. Radial electric field.

Middle stationOuter station Inner station

“Drift radius”

Ask Kubota for his picture

LHC Upgrade

General

Super LHC: 10 times higher luminosity: - First step: Increase statistics -> improves the precision of measurements already reachable within the standard LHC. - Later on: Opens up for interesting low cross section processes like the pair production of Higgs bosons, which may lead to the observation of the Higgs self-coupling λ, in turn giving the Higgs potential. Maintaining the present performance imposes tough upgrade requirements on all sub systems.

Level 1 Trigger

“Level 1 Accept” within 2.5 μs for triggered events, upgradable to ~ 3.2 μs.

Maximum read out rate 75 kHz, upgradable to 100 kHz.

Looks for high pT muon signatures.

Provides multiplicities of six programmable muon pT thresholds.

Level 1 Accept (latency max 2.5 μs)

datadata

Front end electronics

Read outsystem

Max75kHz

Reduced data

Level 1 Trigger

Sub detectors

LHC Upgrade

Depending on the amount of infothat can be used, the pT resolution fora certain pT threshold is different, (and the muon rate deviates from the theoretical value (straight lines)).

Maximum achievable trigger rate is ~ 5*10^4.

We want to “push down” the moment-um uncertainty for the level 1 trigger.

Monitored drift tubes inclusion

Currently only the fast response Thin gap chambers (multi-wire proportional chambers) is the only part of the muon system used in the level 1 trigger. We want to increase the performance of the trigger making minimal physical changes to the detector.

To increase the momentum resolution and reduce the number of falsely triggered low pT muons, MDT inclusion is evaluated.

The algorithms should focus on: - Looking for signatures of high (over for example 20 GeV) pT (transverse momentum) muons - Be fast (remember latency < 3.2 µs (of which ~ 1.5 µs is cables)).

Methods and algorithms

Track segment finding in the inner and middle station

First step: find a matching cluster in the second layer

Deviation of incident angle (towards station plane) from apparent track. The spread is due to inhomogeneities in the magnetic field. From Simulation. T. Domae.

Reference linesSpread

Middle station example of finding a matching cluster (not to scale).

Apparent track

dist1: difference between tangent segment 1 and tangent segment 2 at the middle line in layer 1.dist2: the same but in layer 2dist3: distance between tangent segment 2 and the apparent track at the middle line in layer 2.

Middle line

Middle line Tang.

seg. 1Tang. seg. 2

Apparent track

Second step: Two different methods of finding a track:

A). Simply draw a line between the middle positions in the two clusters.

B). Go through all pairs of tangent seg ments in the two clusters (one from each cluster), minimize with respect to the distances dist1, dist2 and dist3 (for details see figure text).

C). Any linear combination of these.

- Finding a reference line to extrapolate to the second layer-Obtain a search area by variating this

A framework for evaluating different methods

Purpose and requested functions

Monitoring of the different steps in the methods' procedures using simulated of real data.

Evaluation: - With simulated events, comparison of the candidates found by the methods to the generated particles’ features. For example: - Angle of tangents - Trigger efficiency

Current functions and structure of the framework

C++ classes for: - Physical objects: Station, chamber, tangent, track, cluster (collection of adjacent hits), tuple, hit. - Functionalities: Track segment matching, reading values from (simulated) data files, drawing.

Operation: - All stations and chambers of the MDT end caps are constructed with their individual geometrical features - Hit information (which tube, the tdc value) are retrieved from a simulated data file for all chambers.

A framework for evaluating different methods

- In each chamber and multi layer, the hits are organised into clusters.

- For each cluster, tuples (an ordered set of hits that could correspond to a muon track segment) are selected (definition of a tuple tunabe. For example: one adjacent hit from each of the 3 or 4 layers, with some angle constraint).

Figures: Cross sections of a part of a MDT chamber.

Brim of tube

Drift radius

Layer: 1 2 3 4

Second multilayer

Clusters in the “Endcap Extension” chamber located between the inner and middle stations (EEL eta=2. phi=7)

Tuples in a chamber in the inner station (EIS eta=1. phi=4)

Tuples in a chamber in the middle station (EML eta=2. phi=6)

Here a cluster in the inner station (EIL eta=4, phi=4).

A framework for evaluating different methods

- For each tuple, tangent segments are calculated (tunable method).

Tuples and corresponding tangent segments for a chamber Corresponding tdc shift registor pattern in the middle station (EML eta=1, phi=6).

- For each cluster of the first (innermost) layer of the inner station, a tangent is (if possible) calculated using cluster matching and or tangent segment matching.

Tangent segments and tangents for the inner station. The two different ways of calculating the tangents are here presented. From the right: “tangent segment method”, “cluster position method”. (EIS eta=2, phi =3).

A framework for evaluating different methods

- For each tuple, tangent segments are (if possible) calculated (tunable method).

Tuples and corresponding tangent segments for a chamber Corresponding tdc shift registor pattern in the middle station (EML eta=1, phi=6).

- For each cluster of the first (innermost) layer of the inner station, a track segment is (if possible) calculated using cluster matching and or tangent segment matching.

Tangent segments and tangents for the inner station. The two different ways of calculating the tangents are here presented. From the right: “tangent segment method”, “cluster position method”. (EIS eta=2, phi =3).

A framework for evaluating different methods

Currently working on: Evaluation methods.

These are incomplete low statistics examples for the inner station of what my framework is aiming at achieving. Used here:

-Position method for finding clusters

Katarina Bendtz

Special research student of ICEPP,ICEPP, International Center for Particle Physics, Tokyo University and M2 student of the Elementary particle Physics Group of Stockholm University, Sweden Member of the ATLAS experiment at LHC, the Large Hadron Collider bendtz@icepp.s.u-tokyo.ac.jp katarina.bendtz@cern.ch

Thank you for listening!

Methods and algoithms

Non-linearity absorption and tangent finding using shift registor pattern

The relation between the drift time (tdc) and the drift radius is unfortunately non-linear for our drift tubes.

Solution: using a row of connected “shift registors”, (buses) for each tube. The first one receives a true signal from the anode at the arrival of a drift electron. Every 25 ns, corresponding to 0.5 mm resolution, each registor passes the signal on to the next registor.

If the absolute timing from the TGC (remember: another part of the muon system already used in the level 1 trigger) is used, we can at a specific time transfer all the signals (true or false) to another row of shift registors, where the numbering is linear to the drift radii.

With this method, the pattern of the shift registors (shown later) and signals at this time, will also provide a way to find a the path of the muon (as for ex. under, over, under the tubes of the tuple) and the tangent of the drift radii.

Graph from simulation where comparison to the known drift radii have been made

The alternative linear value (for graphical comparison)

First, non-linear row of shift registors

Second, linear row of shift registors

0 1 0 0 0

Timing from tdc:

LHC clock (every 25 ns)

First non-linear shift registor row

Second linear shift registor row

Question: Since it could take 850ns for a drift electron to travel to the anode, the rate at which we can recieve signals in each tube is constraint to 850 nw by this?