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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
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Accelerators and
Experiments
CERN
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beam
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Accelerator Complex
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CERN Experiments
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Beam Parameters
LHC
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Beam Parameters
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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
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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
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Beam Parameters
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Transfer Lines
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TED
TED
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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
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Splash Events
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Injections and Extractions
INJECTION
EXTRACTION
LHC BEAM PIPE
LHC BEAM PIPE
from SPS
To beam dump
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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
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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.
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σz is constant over the ring (~7,5 cm) σx varies and assumes its minimum in the Interaction Points
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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
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• 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
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IP Focusing
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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.
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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).
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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
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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*)
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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
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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
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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
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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
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Filling Schemes
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Filling Schemes
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_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)
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Filling Schemes
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• usually the collisions are main-main, but collisions with satellite bunches are possible
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Collision Types: Main-Main
BEAM 1
BEAM 2
S S S S M S S S S S
25 ns
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• 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
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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
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Data Taking
ALICE
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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
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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
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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
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LHC Interface
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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
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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
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Partitions
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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
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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..
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it shows who is doing what in ALICE ECS/DAQ
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ECS Status Display
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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
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Trigger
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• 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
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Cosmic Trigger with TOF
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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
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Cosmic Trigger with TOF
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PbPb collisions PID RAA multiplicity vs centrality charmonium and more…
Complex Triggers
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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
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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
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different trigger logic are possible: zero bias - minimum bias
central or semi - central events several kind of rare triggers
Trigger Classes
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the busy time is the time when detector disables triggers by raising BUSY signal; average: busy/L2a
Central Trigger Processor
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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
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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
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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
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The High Level Trigger
TPC cluster compression: a total data reduction of a factor 4-5 compared to the raw data is possible;
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Luminosity and Track Rates
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• 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.
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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
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DAQ event size per detector
Data Quality Monitoring
CTP (trigger) input rates
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HLT data size reduction TPC hit map from HLT reconstruction for A and C side
Data Quality Monitoring
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Data Quality Monitoring V0 timing ZDC timing (ION)
T0 timing
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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
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Van de Meer Scan
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Schedules and Plans
LHC
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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
28 November 2014 RC at Juniors'day - ALICE Week CERN
YETS
6.5 TeV/beam is confirmed as startup energy
57
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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
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Shifts
ALICE
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Training Management
System RC opens training
Users subscribes
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Eligibility
Training Coordinator
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TEST
T T O
5 course lines: DCS, DAQ, DQM, SL, SLI LECTURE
REAL SHIFT
“Shadows” shown on new SMS
SHADOW SHIFT
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Shift Management
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Online Crediting
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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
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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
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Backup
ALICE
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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
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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
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The High Level Trigger
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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
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Van de Meer Scan Setup in pp
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Van de Meer Scan Setup in PbPb
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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
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Tricks for Luminosity Leveling
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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)
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Lumi Tricks for 25 ns
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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