overview - analysis in alice · 2019. 10. 4. · 28 november 2014 rc at juniors'day - alice week...

the LHC beam parameters, collisions and filling scheme ALICE detector control system (DCS) and beam operations data acquisition (DAQ) and trigger (CTP) offline high level trigger (HLT) DATA TAKING rates in p, pA and AA data quality monitor (DQM) Van der Meer scan

28 November 2014 RC at Juniors'day - ALICE Week CERN 1

Overview

Accelerators and

Experiments

CERN

beam


Accelerator Complex


CERN Experiments

Beam Parameters

LHC


Beam Parameters


circumference: 26659 m injected beam energy: 450 GeV (protons) nominal beam energy in physics: 7 TeV

(protons) magnetic field at 7 TeV: 8.33 Tesla operating temperature: 1.9 K number of magnets: ~9300 number of main dipoles: 1232 number of quadrupoles: 858 number of correcting magnets: 6208 number of RF cavities: 8 per beam Field strength at top energy ≈ 5 MV/m RF frequency: 400 MHz revolution frequency: 11.2455 kHz power consumption: ~180 MW

LHC Parameters


LHC Parameters

minimum distance between bunches ~7,5 m bunch spacing 25 ns Design Luminosity 1034 cm-2 s-1 number of bunches per proton beam 2808 number of protons per bunch (at start) 1,15·1011 circulating current / beam 0,54 A number of turns per second 11245 stored beam energy 360 MJ beam lifetime 10 h (protons) – ~5h (lead) number of collisions per second 600 millions radiated power per beam (syncrotron radiation) ~ 6 kW total crossing angle (collision point) 300 μrad emittance εn 3,75 μrad beta function β* 0,55 m


Beam Parameters

Transfer Lines


TED

TED

Test during W47

• Noise from FEE, excluded from R/O and trigger during TL test

TDI 78.7m ZDC 114.6m BPTX 146.1m TI2/TED (~ 300m)

ALICE Beam systems ON continuously • BLS / BCMs Data to be analyzed No BPTX (beam stopped before) RADMON connected

BLS Pilots 5E9p/min

Splash Events


Injections and Extractions

INJECTION

EXTRACTION

LHC BEAM PIPE

LHC BEAM PIPE

from SPS

To beam dump



nRFnREV

=400 ×106[Hz]

c26659[m]

= 35640

Theoretical maximum number of RF buckets

RF 400 MHz

PS maximum RF • 40 MHz 25ns LHC RF bucket limit: 3564 In practice due to abort gaps • 2808 RF buckets • the rate of "bunches with

protons" is 2808/3564 ~ 0,8

Beam Parameters


bucket configuration determines where the protons in the two beams will cross over and collide

Longer orbit, lower revolution frequency

Shorter orbit, higher revolution frequency

• The bucket area is called longitudinal acceptance and has unites of energy x time [eV·s]

• The bunch area is called longitudinal emittance and it has also unites of energy x time [eV·s]

• Bunch area (ellipse) = π·a·b → π·(ΔE/2)·(Δt/2) = π·ΔE·Δt/4

Buckets and Bunches

synchrotron oscillations.

σz is constant over the ring (~7,5 cm) σx varies and assumes its minimum in the Interaction Points


Crossing angle: the larger is the crossing angle, θc , the smaller is the area of overlap and therefore smaller is the possibility of collision.

16 microns is the typical transversal size of the bunch at Interaction Point

Beam Parameters

• each bunch has 1,15·1011 protons as nominal value • each bunch gets squeezed down using a series of quadruples

(inner triplets) very close to the interaction point, the to 16 x16 μm2 cross section

the "volume occupied" for each proton in the interaction point is: (74800x16x16) / (1,15·1011) ~ 10-4 μm3

that’s quite bigger than an atom! so a collision is still rare


IP Focusing


Luminosity

• It´s a measurement of the number of collisions that can be produced in a detector per cm2 and per second. • The bigger is the value of L, the bigger is the number

of collisions.

• In the LHC the value of L is 100 times greater than that of LEP or Tevatron makes CERN a leader in this field.

To calculate the number of collisions we need also to

consider the cross section.


Luminosity

L can be obtained semi-qualitatively from: • N2 : number of protons, because each particle in a bunch might

collide with anyone from the bunch approaching head on. • t : time spacing between bunches. • Seff : effective section of the collision that depends on the cross

section of the bunch (“effective” because the beam profile doesn’t have a sharp edge)

the formula for this is given by : Seff =4·π·σ

2 with σ=16 microns or 16·10-4 cm (transversal size of the bunch at Interaction Point).


Luminosity

Other parameter to be considered is F, the geometric luminosity reduction factor (≤ 1), due to the crossing angle at the interaction point (IP). In 2011 F ~ 0.95 , so it can be taken as 1, So we get:

L ~ N2/(t·Seff ) with N2 = (1,15·10^11)2, t = 25·10-9 s , Seff =4·π(16·10-4)2 cm2

L ~ 10^34 cm-2·s-1


Luminosity

If we use the bunches crossing frequency (f, in this case 40·106 Hz) and Seff = 4·π·σ2,

L ~ f·N2 /(4·π·σ2)

And considering different number of protons per crossing bunches, and x and y components for σ separately:

L = f· N1N2 /(4πσx σy) We can also express the Luminosity in terms of ε (emittance) and β (amplitude function) as:

L = f·N2/ (4·ε·β*)


Luminosity

• Cross section (σ) is a measurement of the probability that an event occurs. It´s measured in “barn” 1 b = 10-24 cm2

The number of events per second (Rate) is got from:

Rate [Nevents/sec] = Luminosity · Cross Section

The total proton-proton cross section at 7 TeV is approximately 110 mbarns


Luminosity

The total of 110 mbarn can be broken down in contributions from: • inelastic = 60 mbarn • single diffractive = 12 mbarn • elastic = 40 mbarn

The cross section from elastic scattering of the protons

and diffractive events will usually not be seen by the central barrel detectors


Luminosity

it is only the inelastic scatterings that give rise to particles at sufficient high angles with respect to the beam axis.

Inelastic event rate at nominal luminosity is: R = Nevent/sec = L·σ event 10^34 x [(60x10E-3)x10E-24]= 600 million/second

With about 30 millions crosses/s: 600/30

20 inelastic events per crossing

colliding bunches

bunches only from A side bunches only from C side

trains filling scheme

• the filling scheme provides information about the number and the position inside the orbit of the colliding bunches in all the experiments

• the general scheme is _b____ 28 November 2014 RC at Juniors'day - ALICE Week CERN 25

Filling Schemes


Filling Schemes

_b____

• = single, or 2025ns, or 525ns, or 75ns, or 50ns, or 25ns; this refers to the

characteristic bunch spacing in the main injector batches used for the given filling scheme (single means that single bunches are injected into the LHC)

• = total number of bunches per beam for the given filling scheme (normally, identical for both beams)

• = expected number of colliding bunch pairs in IP1 and IP5 (ATLAS and CMS); it is always the same for both experiments

• = expected number of colliding bunch pairs in IP2 (ALICE)

• = expected number of colliding bunch pairs in IP8 (LHCb)

• = a free suffix to encode variants of a filling scheme (IONS in the previous example)


Filling Schemes

• usually the collisions are main-main, but collisions with satellite bunches are possible


Collision Types: Main-Main

BEAM 1

BEAM 2

S S S S M S S S S S

25 ns

• usually the collisions are main-main, but collisions with satellite bunches are possible

using peculiar filling schemes with time spacing higher then 25 ns it is possible to provide main-satellite collisions

if needed (in order to decrease the rate) 28 November 2014 RC at Juniors'day - ALICE Week CERN 30

Collision Types: Main Sat

BEAM 1

BEAM 2

S S S S M S S S S S

25 ns

Beam Separation

Gaussian profiles !!

Luminosity in ALICE versus total separation of the 2 beams, 6.5 TeV.

Parameters: N=1.21011 p, e = 2 mm, b* = 10 m s = 54 mm

Parameters: N=1.21011 p, e = 3.5 mm, b* = 10 m s = 71 mm

28 November 2014 RC at Juniors'day - ALICE Week CERN

31

Data Taking

ALICE


the Detector Control System (DCS) allows to perform operations with the ALICE sub-systems, such as: • set and monitor of LV, HV, cooling systems, gas systems • monitor of magnet status • monitor of beam conditions • many more tasks..

detector HV status

global ALICE status

broadcasted messages from the ARC

Detector Control and Beam

ALICE has to react in different ways to the beam operations it has to stay SAFE or SUPERSAFE during activities that could be dangerous for the detectors, such as machine development (MD), loss maps, dump tests and more.. ALICE has to stay “safe” also during the beam injection procedure and the following steps: • ramp up (magnets current ramp to • increase the beam energy from • 450 GeV to the target value) • flat top (target energy reached) • squeeze (b* optimization) • adjust (optimization of the • separation between the two beam) • during the previous steps ALICE does calibration • stable beams: ALICE becomes “ready” and starts data taking


Detector Control and Beam

READY

BEAM_TUNING

BEAM_TUNING

READY

BEAM_TUNING

BEAM_TUNING

SAFE

SAFE

SAFE

NOT SAFE

SAFE

SUPER SAFE

HV=FULL

HV=FULL

HV=FULL

EMCAL/DCAL/PHOS TPC

HV=FULL

HV=INT

HV=LOW


LHC Interface

the Experiment Control System (ECS) coordinates the other components (DCS, DAQ, Trigger...) the Data AcQuisition (DAQ) system collects the data from the different parts of the detector, converts the data in a suitable format and saves it to permanent storage:

provide online services (run control system, data flow monitoring,

detector controls, etc.) keep record of data-taking and

detector conditions avoid data corruption and data

loss, check data integrity be robust against varying data

taking conditions and detector/electronics problems

provide flexibility to record data in different configuration (commissioning, calibration, physics data-taking)

minimize dead-time 28 November 2014 RC at Juniors'day - ALICE Week CERN 36

Experiment Control System

PARTITION: part of the whole experiment that can work independently on a task each detector can be readout maximum in one partition at the time

• RUN: data taking period/session under constant conditions detectors can work as readout and/or trigger detectors

• STANDALONE RUNS: one detector running with their LTU (Local Trigger Unit) under direct control of the detector team

• GLOBAL RUNS: one or more detectors running together with CTP


Partitions

the GLOBAL RUNS can be technical or physics TECHNICAL RUNS: • one or more

detectors running for non-physics purposes

• e.g. to check that the experiment is ready to run while waiting for the beam

• detectors do not have to be necessarily in ready state


Runs

PHYSICS RUNS • data taking with real trigger with beam or without beam

(e.g. Cosmics) • all detectors must be in ready state before and after a physics run special short standalone runs are performed such as calibration, pedestal, injection..

it shows who is doing what in ALICE ECS/DAQ


ECS Status Display

the trigger of an experiment is the system that decides, in real-time, which subset of data has to be readout by the detector and archived for offline analysis

the trigger must: select with high efficiency signal(s)

of interest need to be able to precisely

calculate trigger efficiency avoid biases affecting physics

results achieve high background rejection reduce rate to match DAQ and

offline computing capabilities be affordable limited custom electronics and computing power imply that trigger algorithms must be design to have a fast execution time


Trigger

• the TOF trigger is used during cosmic data taking in ALICE at LHC: selection of cosmic muons using TOF hits

• Useful both for astrophysics studies and for commissioning • Track alignment, gaseous detectors response


Cosmic Trigger with TOF

the shaft used to lower the detectors in the pit is responsible of a difference of the cosmic muons flux in the two opposite sides of ALICE

this effect (already observed in the experiment L3 located in the same site) is clearly shown in the comparison between the site map and the muon distribution at the surface


Cosmic Trigger with TOF


PbPb collisions PID RAA multiplicity vs centrality charmonium and more…

Complex Triggers


the Central Trigger Processor (CTP) is designed to select events having a variety of different features at rates which can be scaled down to suit physics requirements and the restrictions imposed by the bandwidth of the DAQ and HLT systems the challenge for the ALICE trigger is: • to optimize the use of the detectors, • which are busy for widely different • periods following a valid trigger • to perform trigger selections in a way • which is optimized for several • running modes (AA, pp, pA), varying • by almost two orders of magnitudes • in counting rate

Central Trigger Processor

a trigger class is a combination of CTP inputs defined as follows:

C--

where name indicates the trigger logic given by the “descriptor” the collision type can be: • B = trigger fired for events with colliding bunches • A = trigger fired for events with beam coming from A side • C = trigger fired for events with beam coming from C side • E = trigger fired for “empty” events (no bunches from both sides) • S = trigger fired for “main-satellite” events example : CCUP4-B-NOPF-CENTNOTRD (trigger for Ultra-peripheral collisions) the descriptor is DCUP4 = 0OMU *0VBA *0VBC 0SM2 where: • 0OMU is TOF low multiplicity input • 0SM2 is SPD low multiplicity input • *0VBx is the veto on V0 input


different trigger logic are possible: zero bias - minimum bias

central or semi - central events several kind of rare triggers

Trigger Classes


the busy time is the time when detector disables triggers by raising BUSY signal; average: busy/L2a

Central Trigger Processor

All levels of hardware triggers (L0, L1, L2) are implemented by the CTP (Central Trigger Processor)

• The HLT decision (trigger) is based on the reconstruction of the full event and happens AFTER the read-out of the detectors.

The ALICE Trigger Schema



the Offline Project has the role to develop and operate the framework for data processing; this includes: • Simulation • Reconstruction • Calibration • Alignment • Visualization • Analysis the activities in ARC need to include also “on-line” operations from Offline in order to check that the data are correctly migrated from the DAQ to CASTOR (CERN Advanced STORage manager) facility and that all the needed steps for the reconstruction and calibration are well executed.

Offline

the ALICE detectors can read out data at much higher rate than what can be handled by the data acquisition and storage systems. • The High Level Trigger (HLT) has been designed to make use of this gap in data

bandwidth and thereby maximizing the physics output of ALICE


The High Level Trigger

TPC cluster compression: a total data reduction of a factor 4-5 compared to the raw data is possible;

Luminosity and Track Rates


• average dN/dy [pp] ~ 6 • average dN/dy [PbPb] 360 • average dN/dy [p-Pb] 21

x60 for charged tracks between pp and PbPb x3.5 for charged tracks between pp and p-Pb

Collision System

E [TeV]

L [Hz/cm2]

Interaction Rate [kHz]

Multiplicity Factor

Track Rate [kHz]

pp 2012 7 1031 700 1 700

pPb 2013 7 1029 200 3.6 720

PbPb 2015 5.2 1.2x1027 10 60 600

• 2011 HI run: 0.14 nb-1 delivered at 2.76 TeV with peak lumi of 4x1026 cm-2s-1

• we expect 0.35 nb-1 per HI period in RUN2 1 nb-1 in the 3 HI periods.


the Data Quality Monitor (DQM) has been developed to check the data online while they are being collected and the performance of all ALICE subsystems while running in physics or technical runs

the monitoring histograms have been defined by each detector and are

provided by some processes called “agents”, written in the AMORE (Automatic MOnitoRing Environment) framework it is very important to have a quick and efficient feedback about data

quality monitoring, in order to check detectors behavior and data taking configuration (DAQ, trigger…), fix problems online, don't waste precious time of data-taking

some examples of monitoring histograms are shown in the next slides

Data Quality Monitoring


DAQ event size per detector


CTP (trigger) input rates


HLT data size reduction TPC hit map from HLT reconstruction for A and C side



Data Quality Monitoring V0 timing ZDC timing (ION)

T0 timing

to measure the cross section sR for the reference process R : separate two colliding beams in transverse directions Dx,Dy by changing LHC magnet set-up measure the rate R for a reference process as a function of Dx,Dy compute shape factor (the shape is the convolution of two beam profiles) Qx,y = R(0,0) / Sx,y where Sa=SiRiDa,i is the “scan area” luminosity L = n N1N2frevQxQy the cross section will be sR = R(0,0)/L where: n = number of colliding bunches N1,2= bunch intensities


Van de Meer Scan

Schedules and Plans

LHC

Year System E [TeV] Lumi [cm-2s-1] R [kHz] LL Weeks Trig Time

2015 pp 50ns 13 1029 – 1032 10-600 YES 3 MIX pp

pp 13 5x1029 – 3x1030 50-300 YES 13.5 MIX pp

PbPb 5.1 1027 8 YES 4 MB HI

pp-ref 5.1 1029 – 2x1030 (*) 10-200 YES 1 MIX pp

2016 pp 13 1031 500 YES 22+2 MIX pp

pPb 5.1 1028 10-20 YES 4 MB HI

pp-ref 5.1 1029 – 2x1030 (*) 10-200 YES 1 MIX pp

2017/8 pp 13 1031 500 YES 22+2+N MIX pp

PbPb 5.1 1027 8 YES 4 MB HI

pp-ref 5.1 - - - 1 MIX pp

LS2 (1/7/18 18 months)

RUN2 Full Baseline

(*) preliminary


YETS

6.5 TeV/beam is confirmed as startup energy

57

ACCESS TO CAVERN POSSIBLE

• Jan- Feb: HW tests – S23 test W6

• First beams: W11 (Mar 9th )

• Re-commissioning with beam until W18 (Apr 30th)

• May 4th ALICE READY

• TS1 W22 (end of May)

• 50ns beam W23 (Jun 1st)

• 25 ns beam W28 (Jul 11th)

• TS2 W35 (Aug 24th)

• IONS W47 (Nov 16th)

28 November 2014

RC at Juniors'day - ALICE Week CERN

LHC 2015 Schedule B ON, commissioning

with cosmic and technical runs

B ON, ALICE SAFE technical runs

25ns pp

25ns pp Pb-Pb

50ns pp

58

Shifts

ALICE

Training Management

System RC opens training

Users subscribes


Eligibility

Training Coordinator


TEST

T T O

5 course lines: DCS, DAQ, DQM, SL, SLI LECTURE

REAL SHIFT

“Shadows” shown on new SMS

SHADOW SHIFT

Shift Management


Online Crediting



everything starts from:

a piece of pure lead (Pb-208) 2 cm long that weighs 500 mg

a box containing hydrogen gas surrounded with an electric field (H2 → 2H

+ + 2e-)

or

(the lead “sample” is heated to about 500°C to vaporize a small number of atoms. An electrical current is used to remove a few of the electrons from each atom, and then the newly created ions begin the ride of their life)

goes through exciting

activities in ARC

…and ends into knowledge and

papers

Conclusions

THANKS (some slides stolen to Daniele De Gruttola)

Please take part and sign up for shifts:

https://aliceglance.web.cern.ch/aliceglance/sams

https://aliceglance.web.cern.ch/aliceglance/samshttps://aliceglance.web.cern.ch/aliceglance/samshttps://aliceglance.web.cern.ch/aliceglance/sams

Backup

ALICE

New Shift Schedule: MAN • The are no “good” shifts:

all blocks are the same. • One books always 2D+2E+2N

not sub-blocks • Uniform coverage: nights

evenly distributed by design. • When the shift type changes

one gets “extra time” • Experience is diversified:

shifters get gradually used to deal with both debug (day), setup (evening) and production (nights) shifts

• We go back to 1 credit per shift, including nights

• Sync with LHC crew. Night shifts lighter (leave at 7)

• Shuttle timetable changed accordingly

7:00

15:00

23:00

28 November 2014 67 RC at Juniors'day - ALICE Week CERN

the HLT focus for 2011 has been the TPC, which is by far the largest data source in the ALICE system with up to 80 MByte for a central Pb+Pb event

1. the first step of the TPC reconstruction is calculating cluster (or hit) positions from the charge deposited by the tracks

1. the data volume of these clusters is 30% smaller than the original raw data from which

they were calculated; by saving the HLT clusters instead of the raw data, one can thus increase the event statistics on tape by a factor ~1.5

2. the most advanced feature implemented is to store not the direct cluster positions, but rather the distance to the closest TPC track; since most clusters are assigned to a track, this distribution is peaked at small distances and thus has a small entropy compared to the clusters positions which are evenly distributed

3. combining all these steps, a total data reduction of a factor 4-5 compared to the raw data is possible; which means a factor 4-5 more events for physics analysis


The High Level Trigger

motivations in pp:

measurement of the inelastic cross section luminosity normalization for all cross section measurements it is one of the main

sources of uncertainty heavy flavor production: typical theoretical uncertainties 10%÷50% aim at


Van de Meer Scan Setup in pp


Van de Meer Scan Setup in PbPb


pp Pb+Pb

pp 2.76 TeV: sV0and = 47.7 ± 0.9 mb pp 7 TeV: sV0and = 54.3 ± 0.2 (stat.) ± 1.9 (syst.) mb PbPb 2.76 TeV: sZNor = 371.4 ± 0.6 (stat.) -19+24 (syst.)

Van de Meer Scan Results

Tricks for Luminosity Leveling


1 main bunch each 50 ns

Beam 1

Beam 2

Main-Satellite collision

pp 2012

• Main-Satellite collisions

Only possible with 50 ns filling scheme With 25 ns all bunches are main!

Not applicable in RUN2 (2015-17)

Lumi Tricks for 25 ns


Beam defocussing at IP2 • Preferred method for the

other LHC experiments • Acts on b* (value of betatron

function at IP) • Range of operations is small,

reduction of factor 2-4..

Only way left for ALICE in pp is the beam separation • Can reduce by O.M. • Need protection on the experiment

side for accidental head on collisions • With 25 ns ALL BUNCHES in orbit collide

at the same time TPC BURNED 78

overview - analysis in alice · 2019. 10. 4. · 28 november 2014 rc at juniors'day - alice week...

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