LHC Detectors (ATLAS)

Shlomit TaremTechnion, Israel Inst. of Tech.

The LHC and its detectors

The LHC, a pp collider with 14 TeV pp cm energy will start operation in 2008

4 experiments are working to finish assembly and commissioning ATLAS – general purpose – discovery of new particles CMS – general purpose – discovery of new particles LHCB – B Physics – forward ALICE – heavy ion physics

LHC collisions are a difficult experimental ground We won’t know the cm energy of each collision There will be many pp collisions on top of each other Most of the collisions are due to uninteresting physics There will be too much data to collect

LHC Design Parameters

Energy at collision 14 TeV

Luminosity 1034/cm²/s

Bunch spacing 7.48 m

25 ns

Particles/bunch 1011

Collisions per BC 23

Luminosity lifetime 10 h

ATLAS and CMS will start operation at the LHC at the end of 2007

Higgs bosons or alternatives for SSB

CP-violation with high precision

Rare B decays Top mass SUSY particles? Beyond the SM

The ATLAS and CMS Experiments

The ATLAS detector

First conclusive Higgs search

Particle detection basics

Fast particles created in LHC collisions will interact with the detector in various ways and leave signals in it Charged particles will ionize it Electrons will radiate in it Photons will produce e+e- pairs Hadrons will interact with nuclei

We use these interactions to build detectors The different interaction of different particle types

with the detector help us distinguish between them Different technologies help distinguish between

different particle types Stable particle types which leave signals in the

detector include , e, , , k, p, n and hypothetical exotics

A modern detector is like an onion The collision point is surrounded by a magnetic

field to bend charged particles according to their momentum In the field region is a tracking detector to measure particle

trajectories and bending Next are Electromagnetic calorimeters which utilize EM

showers to stop electrons and photons and measure/sample their energy

Then there are Hadronic Calorimeters which utilize nuclear interactions with detector material to create and measure hadron showers and stop hadrons

Outside are muon detectors – another tracking detector for the only known charged particle type which is not stopped in the calorimeter

The muon detector may have it’s own magnets – then it’s a muon spectrometer

ATLAS has such a magnet for muons CMS has all detectors inside one big magnet

Particle detection basics

Ionization energy loss Relativistic particles lose energy by ionizing atoms of

the material they pass Ionization occurs randomly at points along the particle path We detect the ionization positions to find the particle

trajectory The amount of energy loss per unit path length, dE/dx,

depends on the particle charge and velocity and atomic properties of the medium

For a known medium, and since most stable particles have 0 or unit charge, dE/dx is a tool to find the particle velocity

Knowing the momentum and velocity we can obtain the particle mass

Tracking detectors aredesigned to measure energyloss positions

Electromagnetic showers Relativistic electrons lose energy primarily via

Bremsstrahlung radiation due to acceleration by multiple scattering Energy loss by Brem is proportional to E Energy loss by ionization is proportional to ln(E)

Photons create e+e- pairs The distance over which these

happen is characterized by a “radiation length” A characteristic of the medium The distance over which an

electron is left with 1/e of it’s energy The average path length for pair

creation The repeated occurrence of

Brem and pair production create an EM shower

EM showers

The number of particles at each stage is N(t)=2t

The energy per particle is E(t)=E02-t

The process continues until the electrons go below the Brem threshold Ec

The total number of electrons in a shower is proportional to the initial particle energy

EM showers are narrow and well contained A shower of a 100 GeV

electron in lead is 4 cm wide and 16 cm long

EM calorimeters

A calorimeter creates a shower and measures the number of secondary electrons produced in it

A radiator is a heavy material with short radiation length, which advances the shower process

Between radiators we place measurement layers to measure how many electrons pass each layer

The measurement is either via ionization energy loss or via scintillation

Some materials can radiate and measure (lead glass) To measure correctly the electron/photon energy the

calorimeter has to be deep enough to stop the whole shower

Muons and hadrons leave an ionization trail in the EM calo

Hadronic showers

Hadron have strong interactions with the detector nuclei New particles, mostly pions, are produced and continue to

interact The differences from EM showers:

Greater distance between collisions More than 2 particles produced per

interaction Particles stopped at ~200 MeV Larger scattering angles – wider

shower If a 0 is produced it’ll start an EM shower Large statistical differences in measured energy between

showers from similar particles This is the only way to detect neutral hadrons Both EM and hadronic showers are detected via ionization

losses of the resulting particles The EM calorimeter is the first layer of the Hadronic

calorimeter

Other interactions with matter

Scintillation In some materials 1-3% of the ionization e-loss goes into

optic or near optic photons The light can be collected – very fast detectors Used in the ATLAS tile calorimeter

Cerenkov radiation Radiation created when the passing

particle is faster than the speed of light in the medium

Can help distinguish between particle types in energy ranges depending on radiator

Transition radiation Radiation induced when a particle passes between two

media Also used to distinguish between particle types Used in ATLAS tracking

Reconstructing an energetic collision

In order to understand a collision we need to know When did the collision happen The directions of final state particles

Ionization trajectories of charged particles Shower position center for neutrals

The momenta and energy of final state particles Charged particle momenta from bending in B field Neutral energy from EM or hadronic energy deposition Velocity from TOF, dE/dx or Cerenkov angle Energy and momenta of unstable particles from conservation

laws What type of particle?

Specific interaction – EM shower for electrons, lack of it for muons

Mass calculation from momentum and velocity Particle spin? From decay angular distribution Lifetime? Secondary vertex and proper decay time

reconstruction

Important detector characteristics Time resolution t Spatial resolution x Energy resolution E Detection efficiency Misidentification probability Two track resolution x

Detector characteristics derived from the above

Momentum resolution from x and the B field integral Velocity measurement resolution

From t if by TOF From E if by dE/dx From x if by Cerenkov

Cost, stability (aging) and longevity are also important for detectors

Gas wire chambers

Detection of ionization on a particle trajectory by electrons drifting to a wire at high potential is known since Rutherford built a gas tube with a central wire in 1900

At a high potentials the drifting electrons are accelerated and ionize additional atoms in their path

An avalanche is formed, creating amplification >105

In MWPCs (G. Charpak, Nobel prize 1992) a plane of anode wires at high potential is arranged between two cathodes with amplifying gas between.

MWPC and TGC

A particle passing in gas will leave a trail of electron clusters (+ ionized gas atoms). The electrons will drift in the E field towards the closest wire, and will create an avalanche and charge on the wire. The charge is read by readout electronics.

Since the signal arrives from the closest wire to the particle passage, the “hit” resolution is the distance between wires.

Parallel to the wire direction the position can be obtained by Charge division between the wire ends (resolution 1% of wire length) Difference in time of arrival on the 2 sides (resolution ~3 cm) Measuring the induced charge on pick-up strips on the cathode

(resolution 30-100 m) With the last method there may be

ambiguities In ATLAS the end-cap muon trigger (TGC) is made this way

Drift chambers

In drift chambers we measure the time between the passage of the energetic particle and the signal arrival to the wire.

This allows to estimate the distance from the wire where the cluster was produced, providing an accurate hit position measurement

The electron drift velocities is ~50 m/ns with little dependence on the field – the position resolution is 50-200 m

Traditionally large drift chambers surrounded the IP, now largely replaced by semi-conductor trackers

The ATLAS Monitored Drift Tube (MDT), the precision muon chambers, are a kind of drift chamber

Semiconductor trackers

Charged particles produce electron-hole pairs in O(nm) thin reverse bias junctions – ionization again The high electron density and low ionization potential (3 eV

compared to 30 in gas) result in large signals in thin sensors without the need for multiplication

The electrons/holes are collected on electrodes subdivided in thin micro-strips or pixels of 20-100 m

The detectors are fast because of the short distances The charge is collected via tiny bump bonds connected to

the readout electronics

Basic particle identification

Advanced particle identification

dE/dx

Threshold CerenkovRing Imaging Cherenkov

Comments on measurement accuracy Measuring a charged particle trajectory in a magnetic

field is an accurate way to measure momentum and direction Charged particles are easier to detect accurately This affects which decay channels to measure

At low energy, an EM calorimeter is less accurate At high energies the EM calorimeter is competitive, but

since it’s far from the interaction point, the creation vertex of the particle is unknown

Semiconductor trackers are very accurate but expensive Readout is an issue, especially for pixel detectors Many dense readout channels required Very fine connection of readout to sensor - difficult

Silicon detectors used together with coarser measurements In ATLAS with transition radiation tracker

EEE %10

Reconstructing short lived particles Reconstruct from decay products

Identify possible decay products Calculate invariant mass Reconstruct secondary decay vertex

Need decay channels with easily identified final state

Background Combinatorial background from unrelated tracks falling

randomly in the mass window Particle misidentification (fake muons or electrons) Misaligned detector causes widening of invariant mass –

more background

Secondary vertex reconstruction for Ks, , b-hadrons

Impact parameter cuts in reconstruction may reduce efficiency for Ks,

b from D0

The ATLAS detector

η

We work in the coordinate system , , z

Inner Detector

The ATLAS Inner Detector (ID) is inside a 2T solenoid magnet

There are 3 detector types: semi-conductor pixel semi-conductor strips transition radiation

tracker The pixel and SCT will

provide a few very accurate points

The TRT will providecontinuous tracking –36 points

Each contributes similarlyto the resolution

Pixel detector

3 barrel and 8 disk layers of 140 MILLION pixels on 2228 Silicon semiconductor modules

The 140 MILLION channels are read out providing a resolution of 10 in r- and 50 in z

SCT

SCT is designed to provide eight precision measurements per track in the intermediate radial range

contributing to measurement of Momentum Impact parameter Vertex position

In the barrel SCT eight layers of silicon microstrip detectors

The end-cap modules use tapered strips with one set aligned radially.

TRT

The Transition radiation Tracker is based on the use of straw drift detectors – like miniature MDTs can operate at high rates due to their small diameter

and the isolation of the sense wires within individual gas volumes

Electron identification capability is added by employing Xenon gas to detect transition radiation photons created in a radiator between the straws.

Each straw is 4 mm in diameter and equipped with a 30 µm diameter gold-plated W-Re wire The barrel has ~50,000 straws The endcaps have 320 000 straws

Calorimeter

The EM calorimeter, and part of the Hadron calorimeter are made of an accordion like arrangement of lead radiator and liquid argon measurement medium

There are over 100000 channels in the barrel and 70000 in the endcap

The calorimeter takes part in the level 1 trigger

H Why is this channel so difficult? The final state is 2 neutral particles

No momentum and direction measurements in the tracking detector are available

Photons shower in the EM calo, with energy resolution

The invariant mass of a pair of photons has to be calculated – mass resolution is related to the single particle momentum resolution

We expect a wide distribution Almost every 0 decays into 2 photons

There are many 0 produced in each collision Highly boosted 0 produce very close to each other The calorimeter has to be highly segmented to tell one from 2 0 is a big combinatorial background under the H peak.

This channel dictated the design of the EM calo

EEE %10

H

Signal and background After background subtraction

Tile hadronic calorimeter

In the central region <1.3 there is also a scintillating tile hadronic calorimeter Steel is the absorber material (radiator) causing showers Particle showers are sampled by tiles of scintillating

plastic which emit light when charged particles go through them.

The light pulses are carried by wavelength shifting optical fibers and converted to electronic signals

The tile calorimeter is highly segmented 0.1x0.1 in , 3 radial segments

Can help identifying Narrow (ionization)

signal continuinginto the outer layer

Jet energy scale

The signal in the calorimeter requires translation into the energy of the particle

This translation is particle type and detector region dependent Pions leave a different signal than electrons for the same

energy loss Different sampling depths result in different calibration

Jets are more complicated still 0 and charged , but also muons/electrons/neutrino

These calibrations are started at test-beams Continue using simulation Will continue using well understood samples

Z+jets

“Missing energy”

The total cm energy will be 14 TeV Most final state energy will go down the beam-pipe

unmeasured Hard interaction energy unknown and differs by

event Products characterized by momentum transverse to the

beam-line pT

No way to measure “missing energy” out of unknown total

What we measure is the pT imbalance in the final state

sddsZs

uuR

01

01

01

~~~

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eeZ 0

Measured as vector sum of energy deposition in calo cells

Characterizes events with particles that leave the detector unobserved

No missing ET Missing ET

Missing ET continued

What particles result in missing ET? Neutrinos The SUSY LSP or neutral stable NLSP Muons?

They leave little energy in the calorimeter, so if not accounted for, will produce fake missing ET

They are not accounted for in the calorimeter trigger so high pT muons can produce a missing ET trigger

This should be corrected at Event Filter or offline Charged stable NLSP?

Like muons No other source of missing ET in event

Detector malfunction can fake missing ET

A “hot” or “dead” area in the calorimeter willchange the ET balance artificially

Particles going through cracks also createfake missing ET

Fake missing ET

eeH

Missing ET resolution

A lot of work on understanding missing ET and its dependence on topologies jet energy calibration

e// energy corrections crack and dead areas Jet punch through seen as muon

The ATLAS detector – The Muon spectrometer

Trigger chambers

Precision chambers

Trigger chambers RPC and TGC are

used for triggering, measure 2 coordinates, and

Precision chambers The MDT are used

for precision measurement and measure only

The CSC measures precisely and coarsely

Tracking requires combining the information from all sub-detectors

Monitored Drift Tube chambers

Precision measurements in the muon spectrometer are performed by chambers of Monitored Drift Tubes (MDT) The basic elements are aluminum tubes with a 3 cm

diameter and a wire at HV in the middle The basic measurement is the drift time of ionized

electrons to the wire The measurement resolution is ~80 m Each chamber has 2 superlayers, each with 3 or 4 layers

of tubes

The radius from which the electrons drift to the wire is calculated from the time measurement

These R-T relations have to be calibrated constantly to maintain the resolution

The segment is tangent to the radii

To maintain resolution we also need to know exactly where each tube is alignment is a big issue

Hit radius reconstruction in the MDT

t0t=t0+tdrift

R=R(t-t0) =R(tdrift)

tdrift

Segment reconstruction in MDT

Reconstructing muons in ATLAS

Muons appear in many heavy particle decays this makes them interesting

They are by far the easiest to identify Just look for energetic particles outside the calorimeter

Their momentum may be measured in the muon spectrometer outside of the mess of tracks in the inner detector

The experiment output is a list of hitchannels and some information on thehit For MDT – drift time For trigger chambers – Beam Crossing ID For CSC – pulse height distribution

Noise hits too…(MDT)

MDT RPC/TGC

Muon reconstruction in ATLAS detector

End Cap

Toroid

Barrel Toroid

Calorimeter

Inner

Detector

MDT RPC/TGC

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Muon reconstruction in ATLAS detector

Track reconstruction in the Muon Spectrometer is done with MOORE or MuonBoy

Large volume toroidal field – bending in η direction

Low detector occupancy Accurate high momentum

measurements

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In ATLAS, muon tracks can be reconstructed independently in the muon spectrometer. A search for all is performed

Muon reconstruction

Short segments of the trajectory are found is the MS stations

The segments are then connected into tracks We know the B field

and thus the trajectory of a of a given momentum

The momentum isobtained from the track fit

Muon reconstruction in ATLAS detector

Similar programs reconstruct tracks in the Inner Detector

Reconstruction of all charged particles is done in the Inner Detector

High track multiplicity Bending in φ direction

Muon reconstruction in ATLAS detector

Following this, muon tracks or segments are combined with inner detector tracks to obtain the muon momentum at the interaction point

MuId/Staco Extrapolate muon tracks

back to the primary vertex region

Combines them with Inner detector tracks

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Muon Reconstruction

A different program, MuGirl, identifies muons by associating muon hits and segments to an inner detector track in order to flag the track as a muon[1] Initialize Muon candidate from ID track parameters [2] Extrapolate track to Muon Spectrometer chambers [3] Look for hits in a road around the track extrapolation [4] Make segments from hits [5] Improve extrapolation by

using segment information [6] Collect hit & segment

information to identify muon[8] Select “muon like” candidates

This method works betterfor low pT muons

H4, 22e

Best channels for finding the Higgs Good trigger with high pT muons

Low pT muon reconstruction an issue for low mass Higgs Lowest pT muon under 10 GeV for many events

Could require 2 high pT muons w Z mass and collect additional ones

Triggering at the LHC

Object What physics?

eHiggs, new gauge bosons, extra dimensions, SUSY, W, top, B-physics,

Higgs, extra dimensions, SUSY, B-physics

Higgs, new gauge bosons, extra dimensions, SUSY, W, top, B-physics

Jets SUSY, compositeness, resonances, B-physics

The LHC event rate is too high to collect

Selection of physics signals by identification of objects that can be isolated from the high particle density environment.

Event rateEvent rate

Level-2Level-2

Level-1Level-1

Offline AnalysesOffline Analyses

The ATLAS Trigger

The 3-level trigger selects interesting events at an output rate of 100 Hz from the input rate of 40 MHz The Level-1 (LVL1) trigger – 40 MHz to 75 KHz

Uses custom electronics to make the decision in hardware Uses low granularity data from a subset of trigger detectors Identifies Regions of Interest Identifies bunch crossing of interest Has 2 sec to complete each selection

The Level-2 (LVL2) trigger – 75 KHz to 5-10 KHz Uses the full granularity data Starts from Regions of Interests flagged by LVL1 Only data requested by the algorithms are read out. The average time budget ~10 ms.

The Event Filter (EF) – 10 KHz to 100 Hz Uses complete event information Time budget of a few seconds. Accepted events are written to mass storage

hard

war

eso

ftw

ar

e

Goal of the level 1 muon trigger

Select from b, t, W, Z, H Low pT for b pT>6 GeV

High pT for Higgs pT>20 GeV

Look for muons from the interaction point Eliminate cavern

background Eliminate beam halo and

cosmic muons Reduce background

from decay in flight of /K

pT of muons from different processes

Trigger scheme

In passing the b field Awill bend up Awill bend down The window between

them contains all with pT>threshold

For large pT the window becomes small, and we need a longer lever-arm to resolve it – add another station

Endcap muon trigger – more detail

Windows

pT thresholds are determined from the maximal acceptable rate Each trigger type gets a

bandwidth Flexibility is required

Window sizes for each pT/η/φ are found from simulation

The actual selection is done in hardware

The charge created in the chamber is digitized by an ASD

The digital signal passes in cables 2-10 meters long

They are received at the trigger electronics PS-Pack ladder on the TGC sector

Endcap muon trigger – the electronic implementation

There is 1 PS-Pack ladder for each 1/24 triplet and doublet-pair

electronic path scheme

triplet

triplet

innerdoublet

innerdoublet

pivot doublet

pivot doublet

wiretriplet

Slave boards

striptriplet

wire

wire doublet

stripdoublet

strip

High pT

boardswire

strip

sector

logic

pp

Level-1: Calorimeter

Calorimeter Trigger looking for e/ + Jets + t

objects Using trigger towers of

Hadronic and Electromagnetic calorimeters

The requirement for a trigger object: The RoI cluster is a local

maximum The most energetic cluster > ET

Total ET in EM isolation < EM Isolation Threshold

Total ET in Hadron < Hadronic isolation threshold

Example of e/ trigger algorithm:

Missing ET trigger

At level 1 – jet energy sum processor computes total scalar ET, Ex and Ey

Missing ET not an inclusive trigger but combined with single jet or electron/photon or hadron/ triggers which may not pass level 1 by themselves

Envisioned missing ET thresholds could start ~70 GeV Does not fit the RoI mechanism – global by definition At level 2 unpacking the data from 200,000

calorimeter cells is prohibitive corrections for known level1 deficiencies calculating missing ET from jet RoIs

It may be too slow even for the EF, in this case the missing ET may be calculated from jets rather than calo cells

The CMS trigger

CMS has a 2 level trigger LVL1

Uses muon chambers and calorimeter Finds e, jet, candidates above thresholds 40 MHz 100 KHz

HLT Uses algorithms similar to offline 100 KHz 100 Hz Inclusive b,c, trigger (high pT jet) Partial reconstruction of exclusive decays around μ ROI

The ROI mechanism

At level 2 the processors run algorithms seeded by level 1 Regions of Interest (RoI)

For each RoI the algorithm fetches the relevant data from subdetectors which did not participate in the level 1 decision

Level 2 algorithms are run in a sequence, refining the decision in stages

They create new seeds for the Event Filter

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1 in 5 000 000 events is kept

Trigger issues for b-physics performance

LHC is geared towards “Discovery Physics” B physics is a side show

B-physics performance is impacted strongly by trigger menus Characteristic B-physics triggers are at low pT

The experiments have multilevel triggers Level-1 is in hardware – designed for 40MHz100KHz The level-1 trigger for B-physics is based on one or more muons

Acceptable trigger rates in ATLAS and CMS have been reduced due to “staging” of high level trigger processing power Envisioned trigger menus include 2 low pT or one higher pT Algorithms are developed for recovery of events at level-2

First luminosity is expected to be lower and that will enable collecting 6 GeV single muons at the beginning

Detector calibration depends on channels that are also good for B Physics - J/ and

Algorithms to recover events at level-2

The level 1 trigger output of is ~20 KHz of events with at least one muon with pT > 6 GeV 4 KHz from b events Most triggers from cavern background or muons from K/

decays, At the level 2 trigger this rate must be reduced by x100

This may be achieved by confirming a muon in the Inner Detector in addition to confirming it in the Muon Spectrometer

Then cutting harder on pT

This selection criterion removes many interesting b events We would like to achieve

higher efficiency for the “gold” channels (J/) at level 2 After

Level-2

Example of level 2 algorithm

The rate of J/ and +– events is low enough for the second level trigger

A di-muon trigger will allow an effective selection of channels with J/ +– and rare di– b decays

One way is dimuon trigger at level 2 based on a single muon trigger at level1

The second muon, usually lower pT, is found by searching in an extended region of interest around the level 1 RoI

single-muon

di-muon

all

all

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h

b

b

c

c

J/

@1033cm-2s-1

Cro

ss s

ecti

on

, (n

b)

μμ

RoI ( φ, η )

Create the pair of tracks with

opposite charge

Dimuonrecovery at level 2

MDT RPC/TGCLVL1 pT() > 6GeV

Results from this algorithm

level 1 muon RoI

Enlarged muon RoI

level 1 muon RoI

Enlarged muon RoI

J/ψμ(pT>6GeV)μ(pT>3GeV)J/ψμ(pT>2.5GeV)μ(pT>4GeV)

J/ψμ(pT>6GeV)μ(pT>3GeV)J/ψμ(pT>2.5GeV)μ(pT>4GeV)

J/ψμ(pT>6GeV)μ(pT>3GeV)J/ψμ(pT>2.5GeV)μ(pT>4GeV)

The efficiency of J/ψ identification vs. pT of the lower pT muon

Efficiency of J/ψ (relative to level 1) vs. fake rate for different cuts

The efficiency to find J/ψ vs. the size of window opened around the level 1 μ RoI

Detector issues for new Physics The case of a new long lived particle

Heavy charged long lived particles exist in many theories beyond the standard model A case in point is GMSB where the stau is the NLSP and

couples weakly to the gravitino. The signal we look for is a charged particle with low

hence referred to as stau Any slepton would have the same signature R Hadrons also have strong interactions

An existing lower limit gives the stau M>100 GeV/c2

Imagine a 100 GeV/c2 stable charged particle going through a detector with pT of 100 GeV/c

This cannon-ball should be easily visible – we can’t miss it…

Think again!!

How would the look in ATLAS

A very slow stau would lose a lot of energy by ionization A 100 GeV/c2 stau with pT < 25 GeV at eta=0.1, would be

absorbed in the calorimeter. Likewise, a 200 GeV/c2 central stau with pT < 35 GeV

BUT A particle with >0.5 would lose less than 7 GeV A particle with >0.8 is almost minimum ionizing

Particles with <0.6-0.7 will arrive in the muon spectrometer with a different beam crossing

Signals in the ID and Muon Spectrometer may be modified due to higher ionization

~

The following study was done for a stau with a mass of 100GeV/c2 as introduced in GMSB point 1 of

CERN-TH/2000-206

ATLAS length > 20m & Collision period = 25 ns 3 events coexist in the detector at the same time

To match correctly event fragments from different sub-detectors BCID is crucial

BCID is based on time measurements, each detector unit is calibrated with respect to particles which move almost at the speed of light ( =1)

(stau)<1 so it may be marked with the wrong BCID

Timing issues for a heavy charged particle

Delay in arriving to the muon spectrometer wrt a muon in units of BC

The stau data is associated with event N+2

and LVL1 - the case of a “normal trigger”

Assuming a non stau trigger on event number N

A with pT > 75 GeV can give a missing ET trigger The resulting readout requirements are the same as above

The stau data is associated with event N+1

Muon trigger chambers (TGC and RPC) should read out BCs N, N+1, N+2.

The MDT always reads out many BCs.

~

The case of a calorimeter trigger~

calorimeters

The muons were here in event N-2

and LVL1 - The case of a muon stau trigger

A with pT > 30 GeV can give a high pT muon trigger. Assuming the triggered event number N.

All sub detectors have to read events number N, N-1, N-2

All particles were here in event N-2

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Different trigger scenarios result in different readout requirements

The different sub-detectors have the ability to acquire data from different (more than one) BCs.

BUT

Readout programming can not be changed by trigger type.

Moreover, it can not be changed during ATLAS run time

the decision of which events are to be read by each sub detector will have a dramatic effect on ATLAS’s ability to discover the

and LVL1 - conclusion~

~

Possible data taking mode

Muon spectrometer collects data from events N, N+1 and N+2 Inner Detector collects data from events N, N-1 and N-2 Calorimeter collects data from events N, (N-1 and N+1)

Lost Data

If the stau produced a muon trigger, and there was also a muon in the event (that didn’t trigger), then the muon spectrometer data related to that muon is lost

Open questions Is it possible to acquire data from more events at all levels? What needs to be done to actually do it? How does this data taking mode effect the data size ?

Identification of the in RPC The RPC chambers have great time resolution -

3.125ns The BC and the time within the BC are known it is

possible to calculate the Time Of Flight (TOF) from the interaction point

Apply the TOF calculation to the barrel LVL2 algorithm muFast to get initial estimation of the particle’s speed

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Estimation in muFast for Different generated

The RPC TOF can be estimated at the level 2 trigger

An event identified at LVL2 as containing a slow high pT particle could be moved directly to a rapid analysis track

reject ~80% of the muons

reject ~97% of the muons

Hit radius reconstruction in the MDT

The long time window of the MDT guarantees that data of low particles will be saved.

The measured hit radius is incorrect

The segment is tangent to the radii Larger radii result in

Badly fitted segment Wrong direction segment

t0t=t0+tdrift

R=R(t-t0) =R(tdrift)

t0+ttstau=t0+t+tdrift

Rstau=R(tstau-t0) = R(tdrift+t)>R

tdrift

Segment reconstruction in the MDT

A reconstruction algorithm Relies on long time window of MDT and BCID from ID Identify penetrating particle by associating muon hits and

segments with extrapolated ID track Loop over possible t0s

Change MDT digits’ time and hence radii. Create MDT segments from the re-timed digits.

Choose the segment with the best 2. Obtain the real t0 (TOF) as the one

that minimizes the 2

Calculate

GMSB – Example points Background

Main background is from muons with pT>40

(>40)/(stau point 1) ~ 25

distribution not from model

Mass reconstruction

Offline analysis – Signal and Background Preliminary Results Minimal cuts

<0.99 Reasonable 2 Segments in all the 3 stations

Background will be reduced by better reconstruction

No cuts With cuts

Heavy charged particle summary

If nature cooperates, we have a chance to find such a particle

However, this requires paying attention to details of detector and trigger operation

Some modifications are needed to previously envisioned operation

Summary

We expect/hope the LHC will be an exciting place to do physics – the new energy gives space for discoveries

Detector knowledge was required to design a detector (two) which can find the interesting physics

Understanding the detector will help us in our analysis

Theorists should understand what measurements are more/less possible as a guide to choosing the channels they calculate

Theorist could use this info to understand how to assess experimental measurements