K.

1
Small X and Diffraction 2003 at
Fermilab 17-20.9.2003

The TOTEM Experiment
K. Österberg High Energy Physics Division,
Department of Physical Sciences, University of
Helsinki Helsinki Institute of Physics on
behalf of the TOTEM Collaboration http//totem.web
.cern.ch/Totem/
2
Collaboration
Università di Bari and Sezione INFN, Bari, Italy
Institut für Luft- und Kältetechnik, Dresden, Germany
CERN, Geneva, Switzerland
Università di Genova and Sezione INFN, Genova, Italy
Institut des Sciences Nucléaires, IN2P3/CNRS, Grenoble, France
University of Helsinki and Helsinki Institute of Physics, Helsinki, Finland
Warsaw University of Technology, Plock, Poland
Academy of Sciences, Praha, Czech Republic
Brunel University, Uxbridge, UK
3

• The measurement of stot

• Historical CERN tradition (PS-ISR-SPS)
• Dispersion relation (logs)? , ? ? 2.0
• Current model predictions 100-130 mb (at ?s
  14 TeV)
• Aim of TOTEM 1 accuracy
• Using the luminosity independent method
• Absolute determination of luminosity

Optical Theorem
4

• To measure the total cross section with 1
  precision
• measure elastic rate to lowest possible t (t ?
  10-3 GeV2)
  and extrapolate rate to t 0 with a precision of
  lt 0.5
• measure total inelastic rate with a precision of
  lt 1

• Roman Pot detectors to measure leading protons
  - T1 and T2 detectors to measure inelastic events

150m
215m
5
Special LHC optics for the measurement of leading
protons

• Measuring elastic protons with t ? 103 GeV2 ?
  scattering angles of a few ?rad
• At the IP small beam divergence
• sq(e / b)1/2 ? large b (b ? O(km))
• At the detector stations
• y Leff,y qy vy y
• x Leff,x qx vx x Dx x
• Optimal conditions
• parallel to point focusing planes (v 0) ?
• unique position scattering angle relation
• large Leff ? scattered proton at sizeable
• distance from the beam center ( 1 mm)
• lowest possible beam emittance (? ? 1 ?m . rad)

High ? optics lattice functions
6
b 1100 m
Elastic scattering
acceptance
? 1100 m
? 1540 m
Large t (?1-10 GeV2) elastic scattering will be
measured using injection optics (? 18 m)
7
Elastic rate at t 0 statistical and
systematical uncertainties
L 1028 cm-2 s-1 run time 4 . 104 s
10 ?m detector position uncertainty
Total systematical uncertainty lt 0.5
Systematical uncertainties beam angular
divergence and crossing angle, optical functions,
beam position, detector position and resolution,
pot alignment, effect of backgrounds (beam halo,
double Pomeron exchange).
8
t acceptance and t resolution
50 t acceptance vs detector position w.r.t.
the beam center
uncertainty on t acceptance vs uncertainty of
detector position
()
t0.004 GeV2 A44 t0.01 GeV2 A67
? 1100 m
t0.004 GeV2 A64 t0.01 GeV2 A78
? 1550 m
? (t)/t (1 arm) vs detector resolution

• smallest possible t measured when distance
  between sensitive edge of detector and bottom of
  pot is as short as possible
• detector resolution of ? 20 ?m sufficient
• detector position w.r.t. the beam center should
  be known to better than 20 ?m

total
without beam divergence
9
Leading proton detectors

• High and stable efficiency near the edge
  facing the beam, edge sharpness lt 10 ?m ?
  try to do detectors with thinner guard rings than
  present LHC technology ? 0.5 mm
• Detector size is ? 3 ? 4 cm2
• Spatial resolution ? 20 ?m
• Moderate radiation tolerance (?
  1014 1 MeV neutron / cm2 equivalent)

• Currently four different silicon based options
  are actively pursued
• cut planar strip detectors operated at cryogenic
  temperatures (cold silicon)
• development of cut planar strip detectors (for
  operation at higher temperatures)
• 3D-detectors with active edges
• planar strip detectors with active edges

10
Cut edge reconstruction (2002)
Cold silicon
Planar strip detectors without guards rings
operated at cryogenic temperatures ( 130 K).
Efficiency

• low bias voltage
• radiation hard

Z. Li et al, "Electrical and TCT characterization
of edgeless Si detector diced with different
methods", IEEE NSS Proc., San Diego, Nov. 2001
Edge at 020micron
Development of planar technology
cut edge
cut edge
Idea additional n or p ring to prevent current
C
Goal increase the operation temperature
11
3D detectors with active edges
Brunel, Hawaii, Stanford

• CERN Courier, Vol 43, Number 1, Jan 2003

• fast charge collection
• low bias voltage
• radiation hard

signal a.u.
edge sensitivity ? 5-20 ?m
position mm
Planar strip detectors with active edges
Brunel, Hawaii, Stanford
TRADITIONAL PLANAR DETECTOR DEEP ETCHED EDGE
FILLED WITH POLYSILICON
E-field
p Al
signal a.u.
n Al
position mm
edge sensitivity ? 20 ?m
n Al
12
Design of a Roman Pot
first prototype ready by end 2003

• Mechanical design of a thin window
• Secondary vacuum outgassing and RF shielding
  radiation hardness
• Integration of detectors inside the pot
  - mounting, cooling, routing
• High mechanical precision (? 20 ?m) and
  reproducibility

QRL (LHC Cryogenic Line)
Roman Pot station design and tunnel integration
4m
13
Microstation an option to Roman Pots

• A compact and light but still a robust and
  reliable system
• Integrated with the beam vacuum chamber
• Geometry and materials compatible with machine
  requirements
• Detector movement with ?m accuracy

Emergency actuator
Development in cooperation with LHC machine
groups
Inch worm motor
6cm
Space for cables and cooling link
Inner tube for rf fitting
Detector
Space for encoder
Note A secondary vacuum is an option.
M. Ryynänen, R. Orava. /Helsinki group
14
Forward inelastic detectors T1 T2

• T1 5 planes of CSC chambers/side
• coverage 3.1 lt ? lt 4.7 full azimuthal
• spatial resolution better than 0.5 mm

• T2 5 planes of silicon detectors/side
• coverage 5.3 lt ? lt 6.7 full azimuthal
• spatial resolution better than 20 ?m

IP
7.5 m
3.0 m
T1 detector
HF
Castor
? IP
13.6 m
0.4 m
T2 detector
15
Measurement of the inelastic rate

• T1, T2 and the forward leading proton
  detectors allow fully inclusive trigger
• DD, MB -- double arm inelastic trigger
• SD -- single arm inelastic single arm
  leading proton
• Elastics, DPE -- double arm leading proton
  trigger
• Vertex reconstruction necessary for disentangling
  beam-beam events from background

Event loss lt 2 Uncertainty lt 1
Diffraction
Combining TOTEM and CMS makes a large acceptance
detector.
90 of all diffractive protons detected (high ??)
Diffractive measurements at LHC energies
important for the understanding of cosmic ray
events.
16
CMS/TOTEM collaboration for high luminosity (?
0.5 m) diffraction
150 m
308 m
215 m
420 m
338 m
e.g. Double Pomeron Exchange (DPE)
M (GeV) x1 x2
xDp/p proton momentum loss
Trigger via Roman pots x gt 2.5
Trigger via rapidity gap/central system x lt 2.5

17
Exclusive DPE proton acceptance and mass
resolution (? 0.5 m)
Event fraction with both protons within
acceptance vs central system mass
Mass resolution of central system
1
pp ? p X p
0.03
pp ? p X p
all
all
215 m
? (mass)/mass
308 m
0.02
420 m
accepted fraction
0.01
0
100
300
500
700
mass of system X (GeV)
0.5
0.04
all
308 m
420 m
0.03
? (mass)/mass
0.02
0.01
0
0
60
100
140
180
60
100
140
180
mass of system X (GeV)
mass of system X (GeV)
At 120 GeV mass for central system ?50 proton
efficiency and ?2 resolution
18
Running scenario

• Total Cross Section and Elastic Scattering
• Several 1 day runs with high b
• Several 1 day runs with b 18 m for large-t
  elastic scattering
• Diffraction
• Runs with CMS with high b for L 1028cm-2 s-1
• Runs with CMS with b 0.5 m for L lt 1033cm-2
  s-1

Plans

• Test of silicon detectors (2003-04)
• Roman pot prototype by end 2003
• Technical Design Report by end 2003
• CMS/TOTEM collaboration for high luminosity
  diffraction

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20
Backup Slides
21
Elastic scattering
Coplanarity test, background rejection
azimuthal angle resolution
Detector resolution 20 mm
22
Total TOTEM/CMS acceptance (? 1540 m)
RPs
23
Elastic and total TOTEM/CMS acceptance (? 18 m)
b 18 m
b 1540 m
RPs
RPs
24
Radiation fluence in the RP silicon detectors
(N.Mokhov,I. Rakhno,Fermilab-Conf-03/086)

• Maximum fluence (1014 cm-2) for charged
  hadrons
• (Egt100 KeV , L 1033 cm-2 s-1, t107s)
• RP4 (215 m) ? Vertical 0.58, Horizontal 6.7
• Dose (104 Gy/yr)
• RP4 (215 m) ? Vertical 0.37 (max 1.9),
  Horizontal1.2 (max55)
• Main source of background pp collisions
• Tails from collimators and beam-gas scattering
  0.1-1

Radiation level manageable
25
Forward inelastic detector T1
RAILS ARE ASSEMBLED ON A TRUSS STRUCTURE, TO
WITHSTAND THE FLEXURAL LOAD THE TRUSS IS
COMPLETELY RESTRAINED ON THE OUTERMOST SPACER
RING PUSH/PULL RODS AT THE END TIE THE 2 TRUSSES
AND LIMITS THE TORSION BASIC SOLUTION STEEL
MADE, ONE TRUSS WEIGHS ROUGHLY 120 Kg PUSH ROD
COULD BE MADE OF ALUMINIUM OR FIBERGLASS (BETTER
PARTICLE TRANSPARENCY) AND/OR ARC-SHAPED
PUSH/PULL RODS
TRUSS
(In agreement with CMS)
26
Forward inelastic detector T2
Lightweight Structure
Space for services
? 470 mm
Bellow
Weight estimation 30 Kg
Thermal Insulation
400 mm
27
Trigger and event rates
Event rates at L 1028 cm-2 s-1 Elastic ( 30
mb) 300 Hz Inelastic ( 80 mb) ? 100 Hz
(suitably prescaled)
Running time per high-b? run 2104 s (10 hours,
50 efficiency) 6 106 elastic events
2 106 inelastic events

• Statistics (large-t elastic)
• t 0.5 GeV2 200 evts/bin (0.02 GeV2 bins)
• t 1.5 GeV2 80 evts/bin (0.05 GeV2 bins)

b 18 m 2800 bunches
L 1032 cm-2 s-1 for 2104 s (10 hours, 50
efficiency)

• t 6 GeV2 25 evts/bin (0.1 GeV2 bins)

28
Diffraction at high ??
-t10-2
-t10-1
log(-t) (GeV2)
90 of all diffractive protons are seen in the
Roman Pots
29
Dispersion function for LHC low ? optics (CMS IR)
horizontal offset ?x??Dx
For a diffractive proton with a 5 ? 10-3 momentum
loss to give an offset in the horizontal plane of
(at least) 5 mm ? dispersion in x ? 1 m ? need
proton detectors located gt 400 m from interaction
point.
Dx
?x
?y
Optical function ? in x and y (m)
Dispersion in horizontal plane (m)
CMS
30
Acceptance vs mass of central system
pp ? p X p

• Combined acceptance of
• all locations (dotted)
• 420 m 215 m (dashed)
• 215 m alone (solid)
• 420 m alone (dash-dotted)
• 308/338 m location brings 10-15 more
  acceptance

1
fraction of events with both protons within
acceptence
0
400
800
0
0
mass of system X (GeV)
31
Trigger timing of RP4 at 215 m
32
Case study L1 trigger for diffractive Higgs
based on decay products

• Start from diffractive Higgs sample with
  auxiliary conditions
• Both protons within acceptance of leading proton
  detectors
• Both b-jets within Silicon Tracker acceptance
  (?lt2.5) since b-tag will anyhow have to be
  required to reduce gg background.

Use 2 most energetic jets in ?lt3.
diffractive Higgs characteristics
back-to-back in azimuthal, small forward ET
(3lt?lt5) and ET sum ? MH.
diff. Higgs
diff. Higgs
azimuthal angle correlation
forward ET (3lt?lt5)
L 1033 cm-2 s-1
MH 120 GeV
inelastic
inelastic
33
Case study L1 trigger for diffractive Higgs
based on decay products
Combining 2 jet azimuthal angle sum, ET sum, ?
sum and difference forward ET
0
diffractive Higgs
inelastic bkg
-0.7
log10(efficiency)
Preliminary !!
MH 120 GeV
log10(Higgs efficiency)
-0.8
-2
L 1033 cm-2 s-1
-0.9
-1
-4
3
4
2
log10(background rate(Hz))
cut on combined likelihood
If allowed additional L1 rate from a diffractive
Higgs trigger is ?250 Hz ?
? ? 12 (includes L1
trigger efficiency, protons and b jets within
resp. detector acceptance) In addition signal
is affected by Br (H ? bb), tagging efficiency of
b-jets and HLT efficiency.