Transcript Status of CMS

LHC 2006
Martignano, 12-18 June 2006
LHC Physics
Commissioning
- part 2 Roberto Tenchini
INFN - Pisa
Credits to: Roger Bailey, Tommaso Boccali, Fabiola Gianotti, Dan Green,
Fabrizio Palla, Gigi Rolandi
Trigger and DAQ
• Level 1 trigger based on muon & calorimeters ,
• then High Level trigger using reconstruction algorithms
L1 trigger
40
MHz
CMS
Yes
/No
100
kHz
High Level Trigger
(computer farm)
3.2 ms
1s
buffer
buffer
100 Hz
1 MB/event
Off-line
analysis
Level-1 Trigger
3D-EVB: scalable DAQ
DAQ unit (1/8th full system):
Data to surface:
Lv-1 max. trigger rate
RU Builder (64x64)
Event fragment size
RU/BU systems
Event filter power
Average event size
1 Mbyte
No. FED s-link64 ports > 512
DAQ links (2.5 Gb/s)
512+512
Event fragment size
2 kB
FED builders (8x8)
≈ 64+64
12.5 kHz
.125 Tbit/s
16 kB
64
≈ .5 TFlop
DAQ Scaling&Staging
HLT Trigger tables
THRESHOLD
(GeV)
RATE
(Hz)
ISOLATED MUONS
19
25
DI-MUONS
7
4
ISOLATED ELECTRONS
29
33
ISOLATED DI-ELECTRONS
17
1
ISOLATED PHOTONS
80
4
40, 25
5
SINGLE JET, 3 JET, 4 JET
657, 247, 113
9
JET + MISSING ENERGY
180,123
5
INCLUSIVE TAU JET
86
3
DI-TAU JET
59
1
ELECTRON + JET
19, 45
2
INCLUSIVE B-JET
237
5
TRIGGER OBJECT
ISOLATED DI-PHOTONS
TAU+ MISSING ENERGY
B-PHYSICS
OTHERS (pre-scales, calibration)
10
TOTAL
105
Commissioning Trigger
Example: CMS
• Test Global DAQ at Magnet Test Cosmic Challenge !
• DAQ ?
– 20XX: 100 kHz output from L1 (8 slices operational)
– 2007: only 1 slice, then 12.5kHz
– HLT output always at the maximum
( 150 Hz ?) the offline can cope with.
• Beam Crossing at 25 or 75 ns ?
– Not very different for the Trigger (quite different for physics !)
• Trigger Tables
– Calorimeter jets at high Pt
• Still uncalibrated in energy
– Muons initial alignment sufficient to see first muons
• After temporization is achieved
• Random triggers
– To study minbias
Trigger issues for CMS Pilot Run
• L1:
– Muon Ok
– Calo barrel Ok (ECAL
endcaps in 2008)
• HLT
– Initially algorithms
without pixels
(installed after Pilot Run)
• Pixels used to
– Identify primary vertex
• Irrelevant at low
luminosity no pileup
• No pile-up: less tracking
combinatorial
– Refine muon pt
• strip tracker and a bit
reconstruction time
should be enough
– Isolation
• Could use strip stracker
– Particle Id: separate e+
from e- and gamma from
jet
LHC Physics in the initial phase
• Using beam-gas and the beam halo
• Physics at the pilot run (~ 10 pb-1)
• Physics in 2008 (~ 1 fb-1)
Reminder : in most studies
•10 fb-1 is one nominal year at low luminosity
•100 fb-1 is one nominal year at high luminosity
Knowledge of SM physics on day 1 ?
W, Z cross-sections: to 3-4%
Lot of progress with NLO matrix element
MC interfaced to parton shower MC
(MC@ NLO, AlpGen,.. )
(NNLO calculation  dominated by PDF)
tt cross-section to ~7% (NLO+PDF)
<Nch> at  =0 for generic
pp collisions (minimum bias)
— AlpGen
LHC ?
Candidate to very early measurement:
few 104 events enough to get dNch/d, dNch/dpT
 tuning of MC models
 understand basics of pp collisions,
occupancy, pile-up, …
LHC start-up scenario
Stage 1
Initial commissioning
43x43 to 156x156, N=3x1010
Zero to partial squeeze
L=3x1028 - 2x1031
Stage 2
75 ns operation
936x936, N=3-4x1010
partial squeeze
L=1032 - 4x1032
Stage 3
25 ns operation
2808x2808, N=3-5x1010
partial to near full squeeze
L=7x1032 - 2x1033
Stage 4
25 ns operation
Push to nominal per bunch
partial to full squeeze
L=1034
“ Difficult to speculate further on
what the performance
might be in the first year.
As always, CERN accelerators
departments will do their best !”
Lyn Evans, LHC Project Leader
Stage 1 – pilot run luminosities
• No squeeze to start
• 43 bunches per beam
• Around 1010 per bunch
Beam energy (TeV)
6.0, 6.5 or
7.0
6.0, 6.5 or
7.0
6.0, 6.5 or
7.0
Number of bunches per
beam
43
43
156
* in IP 1, 2, 5, 8 (m)
18,10,18,10
2,10,2,10
2,10,2,10
Crossing Angle (mrad)
0
0
0
Transverse emittance
(mm rad)
3.75
3.75
3.75
Bunch spacing (ms)
2.025
2.025
0.525
Bunch Intensity
1 1010
4 1010
9 1010
Luminosity IP 1 & 5 (cm2 s-1)
~ 3 1028
~ 5 1030
~ 1 1032
Event rate / crossing IP
1&5
low
0.76
3.9
Stage 2 – 75ns luminosities
• Partial squeeze and smaller crossing angle to start
• Luminosity tuning with many bunches
• Establish routine operation
Beam energy (TeV)
6.0, 6.5 or
7.0
6.0, 6.5 or
7.0
6.0, 6.5 or
7.0
Number of bunches per
beam
936
936
936
* in IP 1, 2, 5, 8 (m)
2,10,2,10
1,10,1,10
1,10,1,10
Crossing Angle (mrad)
250
285
285
Transverse emittance
(mm rad)
3.75
3.75
3.75
Bunch Intensity
4 1010
4 1010
9 1010
Luminosity IP 1 & 5 (cm2 s-1)
~ 1 1032
~ 2 1032
~ 1 1033
Event rate / crossing IP
1&5
0.73
1.37
6.9
Stage 3 & 4 – 25ns luminosities
• Production physics running
Beam energy (TeV)
6.0, 6.5 or
7.0
6.0, 6.5 or
7.0
7.0
Number of bunches per
beam
2808
2808
2808
* in IP 1, 2, 5, 8 (m)
1,10,1,10
1,10,1,10
0.55,10,0.55,
10
Crossing Angle (mrad)
285
285
285
Transverse emittance
(mm rad)
3.75
3.75
3.75
Bunch Intensity
3 1010
5 1010
1.15 1011
Luminosity IP 1 & 5
(cm-2 s-1)
~ 4 1032
~ 1 1033
1034
Event rate / crossing IP
1&5
0.77
2.1
19.2
Long shutdown (6months)
“Pre-Collision Physics Structures”
Cosmic Muons
High energetic muons that traverse
the detector vertically
particular useful for alignment
and calibration - barrel region.
Beam
Beam Halo Muons (Hadrons)
Machine induced secondary particles that
cross the detector almost horizontally
particular useful for
alignment and calibration - endcap region.
Beam Gas Interactions
Proton-nucleon interaction in the active detector volume (7TeVEcm=115 GeV)
resemble collision events but with a rather soft pT spectrum (pT<2 GeV)
All three physics structures are interesting for alignment, calibration, gain
operational experience, dead channels, debug readout, etc …
A beam-gas event in ATLAS (full sim.)
Trigger ?
Scintillator counters inside ID cavity,
in front of end-cap cryostats
(replacing part of moderator),
covering R=15 90 cm
Provide trigger on beam-halo at low R
(TGC at large R), beam-gas, and
minimum bias for initial LHC operation
Beam-halo muons in ATLAS (full sim.)
Efficiency = 20%
PILOT RUN
1.00E+02
15 pb-1
1.00E+01
1.00E-01
1.00E-02
1.00E-03
1.00E-04
DAYS
luminosity (10**30 cm-2 sec-1)
events/crossing
integrated luminosity (pb-1)"
29
27
25
23
21
19
17
15
13
11
9
7
5
3
1
1.00E+00
Events produced Pilot Run
Eff jets =1
Eff W = 0.2
1.00E+13
1.00E+11
Eff Z = 0.2
1.00E+09
Eff ttbar = 0.015
1.00E+07
1.00E+05
min bias
1.00E+03
1.00E+01
1.00E-03
29
27
25
23
21
19
17
15
13
11
9
7
5
3
1
1.00E-01
Jet Et>25
Jet Et>140
days
Minimum bias
Jet Et>25 GeV
Jet Et>60 GeV
Jet Et>140 Gev
Gamma + Jet P0>20 GeV
W l nu
Z ll
ttbar--> l nu +X
W ->ln
Z -> ll
-
tt-> ln4q
1012
3. 1010
4. 106
40000
4000
100
Minimum Bias Events (1)
• Produced at very large rate since day1
5 kHz (0.01/beam crossing)
500 kHz (1/beam crossing)
• Almost possible to trigger random but
scintillator plane would be very useful
(also for beam halo and beam gas)
Minimum bias (2)
Low average Pt ~ 0.7 GeV/c
Low occupancy in the tracker
12 particles/event in the barrel (same number in the forward). 50% of
them curl in the Tracker and 50% reach the outermost TOB layer
Pt in Minbias - LHC
D. Green
The Pythia-Tune A predictions agree well with the
simple extrapolation for minbias data. Important to
measure and tune Pythia to represent well the minbias
background for pileup and to set trigger strategies, e.g.
isolation.
Minimum bias (3)
Need to measure charged particles in the tracker – no alignment
needed since <pt> = 0.7 GeV …. But GOOD UNDERSTANDING
OF TRACKING EFFICIENY AT LOW MOMENTA will be a
challenge (also without pixel)
Need to measure very early since very soon rate goes to 1 event per
bunch crossing
Dijets
Produced
at high rate. Physics interest is in the high
mass tail.
aaa
ds/dM (pb/GeV)= exp (- M/486 GeV)
1
10 100 pb-1
Luminosity needed for 10
events above threshold
Dijet resonances – pilot
run
Limits from CDF and D0 are
in the range 0.4 - 1 TeV
With 15 pb-1 at 14 TeV we
can extend the range
Crucial experimental
parameter is the energy
resolution in measuring jet
energy (They are narrow
resonances)
Jet Equalization with dijet balancing
•We can quickly equalize at “ low Et” and then
we run out of statistics
• One must assume equalization holds at higher
energy (but data vs MC needed for this)
Energy scale , Calibration
Processes – Jetg+qBalance
-> q +  events with the Pt of
Reach a calibration of 5%
the q and photon > 30 GeV and
the photon with |y| < 2.5 (in
ECAL) has a cross section of ~ 20
nb. At 1 nb-1 can plan to find a few
events using photon isolation cuts.
For 1 pb-1 there will be 20,000 J + 
events. Assuming the azimuthal
calibration is done using minbias
and/or dijet balance, there are then
500 jets/HCAL y “tower” (summed
over azimuth), and 100
photons/ECAL y “tower”. At
higher L the qZ and diphoton
events can be used to cross check
the HCAL and ECAL calibrations.
Dan Green
Can we discover a 1TeV dijet
resonance ?
QCD cross section
between 950 GeV and
1050 GeV is
26 pb
Excited quark cross
section is 200 pb
Can we discover a 2TeV dijet
resonance ?
QCD cross section
between 1900 GeV and
2100 GeV is
3.5 pb
Excited quark cross
section is 8 pb
But… if we do see a signal… how can we be sure about tails in the
detector energy resolution ?
What can we do with W and
Z events ?
• In 15 pb-1 we have 30K W’s and
4K Zs into leptons.
• Measure cross sections and W
and Z charge asymmetry
• Start constraining the PDF’s
• How well do we know Luminosity ?
10%
LHC Kinematic regime
Kinematic regime for LHC much broader
than currently explored
Test of QCD:
 Test DGLAP evolution at small x:
 Is NLO DGLAP evolution sufficient
at so small x ?
 Are higher orders ~  sn logm x
important?
 Improve information of high x gluon
distribution
At TeV scale New Physics cross section predictions
are dominated by high-x gluon uncertainty
(not sufficiently well constrained by PDF fits)
At the EW scale theoretical predictions for LHC
are dominated by low-x gluon uncertainty
(i.e. W and Z masses)
How can we constrain PDF’s at LHC?
x1, 2 
M
exp y 
s
QM
1  E  pz 

y  ln
2  E  p z 
Constraining PDF with early ATLAS data using W  ln angular distributions
x1, 2 
M
exp y 
s
 W production over |y|<2.5 at LHC
involves 10-4 < x1,2 < 0.1
 region dominated by g  qq
Tricoli et al., ATL-PHYS-CONF-2005-008
e- rapidity
e+ rapidity
HERWIG + NLO K-factor
generator level
CTEQ61
MRST01
ZEUS-S
y
y
detector level + cuts
y
y
Uncertainties on present PDF: 4-8%
ATLAS measurements of e angular
distributions provide discrimination
between different PDF if
experimental precision ~ 3-5%
Effect of including ATLAS data on PDF fits
Sample of 106 W en generated with CTEQ6.1 and ATLAS fast simulation
Statistics corresponds to ~ 100 pb-1
4% systematic error included by hand (statistical error negligible)
ZEUS-PDF
BEFORE including
W data
e+ CTEQ6.1
ZEUS-PDF AFTER
including W data
Tricoli et al.
e+ CTEQ6.1
pseudo-data
pseudo-data
||
||
Central value of ZEUS-PDF prediction shifts and uncertainties is reduced
Error on low-x gluon shape parameter  (xg(x) ~ x- ) reduced by 35%
Systematics (e.g. e acceptance vs ) can be controlled to few percent with Z  ee
(~ 30000 events for 100 pb-1)
Collecting luminosity after the Pilot Run
similar statistics
to Tevatron today
10 pb-1  1 month at 1030 +
< 2 weeks at 1031, =50%
 end 2007 ?
1 fb-1  6 month
at 1032, =50%
5 fb-1  3 month at 1032
+ 3 month at 1033, =50%
 end 2008 ?
Commissioning ATLAS detector and physics with top events
Can we observe an early top signal with limited detector performance ?
Can we use such a signal to understand detector and physics ?
 use simple and robust selection cuts:
pT (l) > 20 GeV
ET miss > 20 GeV
 ~ 5%
only 4 jets with pT > 40 GeV
stt (LHC)  250 pb
for gold-plated
semi-leptonic channel
W CANDIDATE
 no b-tagging required (early days …)
 m (top  jjj) from invariant mass of 3 jets
giving highest top pT
 m (Wjj) from 2 jets with highest momentum
in jjj CM frame
Total efficiency, including mjjj inside mtop
mass bin : ~ 1.5% (preliminary and conservative …)
YES !
TOP
CANDIDATE
m (topjjj)
m(Wjj)
m (topjjj)
L=300 pb-1
S
Bentvelsen at al.
|mjj-mW| < 10 GeV
S/B = 1.77
B
S/B = 0.45
S : MC @ NLO
B : AlpGen x 2 to account for W+3,5 partons (pessimistic)
Expect ~ 100 events inside mass peak for 30 pb-1
 top signal observable in early days with no b-tagging and simple analysis
W+jets background can be understood with MC+data (Z+jets)
tt is excellent sample to:
-- commission b-tagging, set jet E-scale using W  jj peak and W-mass contraint
-- understand detector performance and reconstruction tools for many physics objects
(e, m, jets, b-jets, missing ET, ..)
-- understand / tune MC generators using e.g. pT spectra
Jet energy scale calibration using
the W mass constraint in
tt  WbWb nqq' bb
CMS Note 2006/025
• Statistical
uncertainty with
500 pb-1 about 1%
• Effect of pile-up
increases
uncertainty on light
quarks jet energy
scale to 3%
Efficiency = 30%
Discoveries in Year 2008 ?
Higgs ???
Run
2008- Susy
Susy
Z’ into muons
Re-discovery of the TOP
1.00E+04
1.9 fb-1
1.00E+03
1.00E+02
1.00E+01
1.00E+00
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
1.00E-01
weeks
luminosity (10**30 cm-2 sec-1)
events/crossing
integrated luminosity (pb-1)
First LHC papers
1. Charged particle multiplicity in pp collisions at
sqrt(s)=12 TeV and sqrt(s)=14 TeV
2. Measurement of inclusive jet cross section in
pp collisions at sqrt(s)=12 TeV and sqrt(s)=14
TeV
3. Measurement of ttbar cross section at
sqrt(s)=14 TeV
4. Search of high mass particles decaying to
lepton pairs in pp collisions at sqrt(s)=14 TeV
5. Evidence for squark and gluino production in
pp collisions at sqrt(s)=14 TeV
Backup slides
Towards Physics (4): the first pp data
Starting in Summer 2007 …
Knowledge of detector on day 1 ?
Examples based on experience with test-beam and on simulation studies
Expected performance day 1
ECAL
e/
uniformity
scale
HCAL uniformity
Jet scale
Tracking alignment
~ 1%
1-2 % ?
2-3 %
< 10%
10-200 mm in R Pixels/SCT ?
Physics samples to improve (examples)
Minimum-bias, Z ee
Z  ee
Single pions, QCD jets
Z ( ll) +1j, W  jj in tt events
Generic tracks, isolated m , Z  mm
Combined test-beam, realistic simulations, cosmics and pre-collision data will help to:
 determine detector “operation” parameters: timing, voltages, relative position,
initial calibration and alignment, etc.
 classify and disentangle some systematic effects: material, B-field, intrinsic performance, …
 gain time and experience before commissioning with pp data starts