Transcript Document

Forward Physics with the
TOTEMCMS at the LHC
Risto Orava
XIII ISVHECRI
Pylos, Greece, 6-12 September 2004
R.Orava
Diffractive Scattering probes the hadronic vacuum
‘wee’ partons  lns
Elastic
Longitudinal view
Valence quarks
in a bag with
soft hard
SDE SDE
p
jet
lnMX2
Baryonic charge
distribution-soliton
r  0.4fm
jet
lns
h
r  0.1fm
Rapidity gap
survival & ”underlying”
event structures are
intimately connected
with a geometrical
view of the scattering
- eikonal approach!
R.Orava
p
Soft diffractive
scattering
Hard
diffractive
scattering ’Glansing’
scattering
of proton
fields
hard
CD
sel - Models
B32 at the black
disc limit?
The black disc limit
8
20 at the LHC, b2  1.6fm2 reached at 10 GeV?
Forward elastic slope shrinks
 effective interaction radius of proton
grows ( lns)
The values of the slopes agree with the
optical picture, i.e. with a fully absorbing disc
of radius R for which B = R2/4.
For a proton with R  1/mp (mp = p meson
mass):
B  13 GeV-2
0.3 at the LHC
 0.17
However: Scattering on a black disc: sel/stot =
½, while the data (at s corresponding to
B 13 GeV-2) gives sel/stot = 0.17...
 the proton is semi-transparent
 QCD colour transparency!
Mixture of scattering states with different
absorption probabilities is required for
diffractive scattering to take place.
stot - Models
Total cross sections show universal rise at high energies: stot  s0.08
However: - Global fits cannot discriminate between Regge theory ( se) and
s-channel picture leading to  logs behaviour.
Total Cross Section - TOTEM
TOTEM
Diffractive Cross Sections are Large
Rel = sel(s)/stot(s)
Rdiff = [sel(s) + sSD(s) + sDD(s)]/stot(s)
0.30
 sel  30% of stot at the LHC ?
 sSD + sDD  10% of stot (= 100-150mb) at the LHC ?
0.375
Studying elastic scattering an soft diffraction requires
special LHC optics. These will yield large statistics.
Photon - Pomeron interference r
Pomeron exchange (~exp Bt)
diffractive structure
pQCD
high-t
L dt = 1033 & 1037 cm2
(* = 1540 m & 18 m)
Additional forward coverage opens up new
complementary physics program at the LHC
•
•
•
•
Investigate QCD: stot, elastic scattering, soft & hard diffraction, multirapidity gap events (see: Hera, Tevatron, RHIC...) - confinement.
– Studies with pure gluon jets: gg/qq… - LHC as a gluon factory!
– Gluon density at small xBj (10-6 – 10-7) – “hot spots” of glue in vacuum?
– Gap survival dynamics, proton parton configurations (pp3jets+p) –
underlying event structures
– Diffractive structure: Production of jets, W, J/, b, t, hard photons,
– Parton saturation, BFKL dynamics, proton structure, multi-parton
scattering
Search for signals of new physics based on forward protons + rapidity gaps
Threshold scan for JPC = 0++ states in: pp  p+X+p χ 0c , χ 0b
– spin-parity of X! (LHC as the e+e- linear collider in gg-mode.)
Extension of the ‘standard’ physics reach of the CMS experiment into the
forward region
Luminosity measurement with DL/L 5 %
As a Gluon Factory LHC could deliver...
• О(100k) high purity (q/g = 1/3000) gluon jets with ET > 50 GeV
in 1 year; gg-events as “Pomeron-Pomeron” luminosity monitor
• Possible new resonant states, e.g. Higgs (О(100) H  bb events per
year with mH = 120 GeV, L=1034)*, glueballs, quarkonia 0++ (b ),
gluinoballs gg - background free environment (bb, WW & t+t decays)
• Invisible decay modes of Higgs (and SUSY)!
• CP-odd Higgs
• Squark & gluino thresholds well separated
- practically background free signature: multi-jets & ET
- model independence (missing mass!) [expect O(10) events for gluino/squark masses of 250 GeV]
- an interesting scenario: gluino as the LSP with mass window 25-35 GeV(S.Raby)
• O(10) events with isolated high mass gg pairs, extra dimensions
TOTEM Physics Scenarios
Proton
rapidity
gap
inelastic
activity
jet
TOTEM
& CMS
TOTEM
& CMS
g,e,m,t
L, D++,...
TOTEM
& CMS
* (m)
L(cm-2s-1)
elastic scattering
1540
18
1028 -1032
total cross section
1540
1028 -1033
inelastic
acceptance
soft diffraction
1540
200-400
1029 -1031
gap
survival
mini-jets?
L, K±,
,...
hard diffraction
200-400
0.5
1031 -1033
jet
acceptance
central
& fwd
W, Z,
J/,...
DPE Higgs, SUSY,...
200-400
0.5
1031 -1033
di-jet
backgr
central
pair
b-tag, g,
J/,...
low-x physics
200-400
0.5
1031 -1033
mini-jets
resolved?
central
& fwd jets
di-leptons
jet-g,...
0.5
1031 -1033
p± vs. po
multiplicity
jet
anomalies?
leptons
gs,...?
exotics (DCC,...)
R.Orava
beam
halo?
trigger
Correlation with the CMS Signatures
• e, g, m, t, and b-jets:
• tracking: |h| < 2.5
• calorimetry with fine granularity: |h| < 2.5
• muon: |h| < 2.5
• Jets, ETmiss
• calorimetry extension: |h| < 5
• High pT Objects
• Higgs, SUSY,...
• Precision physics (cross sections...)
• energy scale: e & m 0.1%, jets 1%
• absolute luminosity vs. parton-parton luminosity via
”well known” processes such as W/Z production?
R.Orava
The Large Hadron Collider (LHC)
pp collisions at 14 TeV
LHC is built into
27 km the LEP tunnel
5 experiments
CMS/TOTEM
25 ns bunch
spacing
 2835 bunches
1011 p/bunch
Design Luminosity:
1033cm-2s-1 1034cm-2s-1
100 fb-1/year
ALICE
ATLAS
LHC-B
23 inelastic events
per bunch crossing
Planned Startup on Spring 2007
The ‘Base Line’ CMS experiment
A Huge enterprise.
o Tracking
o Silicon pixels
o Silicon strips
o Calorimeters
o PbW04 crystals
for Electro-magn.
o Scintillator/steel
for hadronic part
o 4T solenoid
o Instrumented iron
for muon detection
o Coverage
oTracking
0 < |h| < 2.7
o Calorimetry
0 < |h| < 5
Main program: EWSB, Searches Beyond SM physics at ~90o
Important part of the phase space is not covered by
the generic designs at LHC. TOTEM  CMS Covers more
than any previous experiment at a hadron collider.
Charge flow
Total TOTEM/CMS acceptance ( *=1540m)
Energy flow
information value high:
- leading particles created early
in space-time
microstation at 19m ?
information value low:
- bulk of the particles crated late
in space-time
RPs
TOTEM + CMS
In the forward region (|h > 5): few particles with large energies/small
transverse momenta.
The Experimental Signatures:
pp  p + X + p
- vertex position in the transverse plane?
b-jet
Detector
p2’
- resolution in  ?
CMS
_b-jet
Detector
p1’
-beam energy spread?
Aim at measuring the:
- Leading protons on both sides down to D  1‰
- Rapidity gaps on both sides – forward activity – for |h| > 5
- Central activity in CMS
In addition: The signatures of new physics have to be
normalized: The Luminosity Measurement
Luminosity relates the cross section s of a
given process by: L = N/s
A process with well known, calculable and large
s (monitoring!) with a well defined signature?
Need complementarity.
Measure simultaneously elastic (Nel) & inelastic
rates (Ninel), extrapolate ds/dt  0, assume rparameter to be known:
(1+r2)
L =
Ninel = ?
16p

dNel/dtt=0 = ? 
(Nel + Ninel)2
Relative precision on the measurement of
sHBR for various channels, as function
of mH, at Ldt = 300 fb–1. The dominant
uncertainty is from Luminosity: 10%
(open symbols), 5% (solid symbols).
dNel/dt|t=0
(ATL-TDR-15, May 1999)
Need a hermetic detector.
Minimal extrapolation to t0: tmin  0.01
Inelastic cross section
Event selection:
• trigger from T1 or T2 (double arm o single arm)
• Vertex reconstruction (to eliminate beam-gas bkg.)
Lost events
Extrapolation for diffractive events needed
simulated
Loss at low
masses
Acceptance
extrapolated
detected
Low-x Physics at the LHC
Resolving Confinement of quarks & gluons?
LHC parton kinematics
Tevatron parton kinematics
9
9
10
10
8
10
x1,2 = (M/1.96 TeV) exp(y)
Q=M
8
10
10
6
5
2
Q (GeV )
10
4
M = 100 GeV
4
M = 100 GeV
10
3
3
10
10
y=
2
4
0
2
y=
4
6
4
2
0
2
4
6
2
10
M = 10 GeV
1
fixed
target
HERA
10
M = 10 GeV
1
fixed
target
HERA
10
0
0
10
-7
10
longer Q2
extrapolation
5
10
2
10
M = 1 TeV
10
2
2
Q (GeV )
6
M = 1 TeV
10
10
M = 10 TeV
7
7
10
2
x1,2 = (M/14 TeV) exp(y)
Q=M
10
-6
-5
10
10
-4
-3
10
x
10
-2
10
-1
10
0
10
-7
10
10
10
smaller
x10
-6
-5
-4
10
-3
10
-2
-1
10
x
J. Stirling
0
10
Puzzles in High Energy Cosmic Rays
Cosmic ray
showers:
Dynamics of the
high energy
particle spectrum
is crucial
Interpreting cosmic ray data depends
on hadronic simulation programs
Forward region poorly known
Models differ by factor 2 or more
Need forward particle/energy measurements
e.g. dE/dh…
How to manage with the high-pT 'bread-and-butter' signatures
of the nomenclature: The “Underlying Event” in
Hard Scattering Processes
 LHC: most of collisions are “soft’’,
outgoing particles roughly in the same
direction as the initial protons.
“Soft” Collision (no hard scattering)
Proton
 Occasional “hard’’ interaction results in
large transverse momentum
outgoing
partons.
AntiProton
“Hard” Scattering
Outgoing Parton
PT(hard)
Proton
 The “Underlying Event’’ is everything butUnderlying Event
the two outgoing Jets, including :
Final-State
Radiation
initial/final gluon radiation
Outgoing Parton
beam-beam remnants
secondary semi-hard interactions
“Underlying Event”
 Unavoidable background to be
removed from the jets before
comparing to NLO QCD predictions
Min-Bias
Min-Bias
Proton
Beam-Beam Remnants
AntiProton
Underlying Event
Initial-State
Radiation
AntiProton
Beam-Beam Remnants
Initial-State
Radiation
To Reach the Forward Physics Goals We
Need:
• Leading Protons
• Extended Coverage of Inelastic Activity
• CMS
Need to Measure Inelastic Activity and Leading Protons
over Extended Acceptance in h, ,  and –t.
Measurement stations (Roman Pots) at locations optimized
vs. the LHC beam optics. Both sides of the IP.
LP1
LP2
147 m 180 m
LP3
220 m
Measure the deviation of the leading proton location from the
nominal beam axis () and the angle between the two measurement
locations (-t) within a doublet.
Acceptance is limited by the distance of a detector to the beam.
Resolution is limited by the transverse vx location (small ) and by
beam energy spread (large ).
For Higgs, SUSY etc. heavier states need LP4,5 at 300-400m!
TOTEM beam optics
For stot need to measure elastic scattering at very small t (~ 10–3) 
measure scattering angles down to a few mrad.
Proton trajectory:
y(s) = Ly(s) qy* + vy(s) y*,
L(s) = [(s)  *]1/2 sin m(s)
x(s) = Lx(s) qx* + vx(s) x* + Dx(s) ,
v(s) = [(s) / *]1/2 cos m(s)
• Maximise Lx(s), Ly(s) at RP location
• Minimise vx(s), vy(s) at RP location (parallel-to-point focussing: v=0)
 High-* optics: for TOTEM * = 1540 m (vx  0, vy  0 at 220 m)
Consequences:
• low angular spread at IP: s(q*x,y) = e / *  0.3 mrad
(if eN = 1 mm rad)
• large beam size at IP:
s*x,y = e *  0.4 mm
 Reduced # of bunches (43 & 156) to avoid parasitical interactions
downstream.
L
TOTEM
= 1.6 x 1028 cm-2 s-1 & 2.4 x 1029 cm-2 s-1
Diffraction at high *: Acceptance
Luminosity 1028-1030cm-2s-1
(few days or weeks)
• more than 90% of all diffractive protons are seen!
• proton momentum can be measured with a resolution of few 10-3
TOTEM ROMAN POT IN CERN TEST BEAM
Dispersion function - low * optics (CMS IR)
x
y
Dx
CMS
Dispersion in horizontal plane (m)
Optical function  in x and y (m)
horizontal offset =
Dx ( = momentum loss)
For a 2.5 mm offset of
a   0.5 % proton,
need dispersion  0.5 m.
 Proton taggers to be
located at > 250 m from
the IP (i.e. in a
”cryogenic section” of
the LHC).
Potential locations for measuring the leading
protons from O(100 GeV) mass DPE.
Cryogenic (”cold”) region
(with main dipole magnets)
420 m
308/338 m
Dispersion suppressor
location of currently
planned TOTEM pots!!
220 m
Matching section
CMS
Separation dipoles
Final focus
Microstation – Next Generation Roman Pot
m-station concept
(Helsinki proposal)
Silicon pixel detectors in
vacuum (shielded)
Very compact
A solution for 19m, 380 & 420m?
Movable detector
Leading Proton Detection
0m
147m
180m
D2 Q4 Q5
IP
D1

Q1-3
 = 0.02
Jerry & Risto

220m
308m 338m
Q6
Q7


420 430m
B8 Q8 B9 Q9 B10 Q10 B11








x(mm)
300m
y(mm)
215m
y(mm)
y(mm)
TOTEM Detector Layout
x(mm)
420m
x(mm)
Leading diffractive protons seen at different detector locations (* = 0.5m)
CMS tracking is extended by forward telescopes
on both sides of the IP
CMS
T1-CSC: 3.1 < h < 4.7
T2-GEM: 5.3 < h < 6.5
T3-MS:
T1
10.5 m
T2
~14 m
7.0 < h < 8.5 ?
CASTOR
T3?
~19 m
- A microstation (T3) at 19m is an option.
Forward Tracking Stations T1,T2&T3
T1: 5 planes of CSC
• coverage: 3.1 < h < 4.7 & full azimuthal
• spatial resolution better than 0.5 mm
T2: 5 planes of silicon/GEM detectors
• coverage: 5.3 < h < 6.7 & full azimuthal
• spatial resolution better than 20 mm
3.0 m
7.5 m
T1
detector
HF
Castor
 IP
13.6 m
0.4 m
T2
T3?
IP
The process: pp  p + H + p
h
p1
p
p’
q1
0++
q2
H
0++
p2
b
b
Dh
b-jet
5
0
b-jet
p”
MH2 = (p1 + p2 – p’ – p”)2  12s
1 = 1p’q1/p1q1  1-p’/p1
10
2 = 1-p”q2/p2q2  1-p”/p2
Dh
p
-5
-10
(at the limit, where pT’ & pT” are small)
Leading proton studies at low *
GOAL: New particle states in Exclusive DPE
• L > few 10 32 cm2 s1 for cross sections of ~ fb (like Higgs)
• Measure both protons to reduce background from inclusive
• Measure jets in central detector to reduce gg background
Challenges:
• M  100 GeV  need acceptance down to ’s of a few ‰
• Pile-up events tend to destroy rapidity gaps  L < few 10 33 cm2 s1
• Pair of leading protons  central mass resolution  background
rejection
A study by the Helsinki group in TOTEM.
Central Diffraction produces two leading protons,
two rapidity gaps and a central hadronic system. In the
exclusive process, the background is suppressed and the
central system has selected quantum numbers.
Survival of the rapidity gaps?1
JPC = 0++ (2++, 4++,...)
MX212s
2p
Gap

0
R.Orava
Jet+Jet
hmin
h
hmax
Gap
Measure the parity P = (-1)J:
ds/d  1 + cos2
Mass resolution  S/B-ratio
1 V.A.Khoze,A.D.Martin
and M.G.Ryskin, hep-ph/0007359
Higgs Mass – New EW Fit Results
LEP Search: MH  114.4 GeV
+67
EW fits:
MH = 117 -45 GeV
95% CL:
MH < 251 GeV
With the new top-mass
measurements, the best fit
for the Higgs mass is not
excluded.
Cross Section
For a 5s signal at the LHC need:
30fb-1
30fb
300fb-1
SUSY h0
3fb
Relatively small cross section but clean and model independent signature
Higgs Branching Ratios
Could invisible decay modes be seen by the central diffractive process?
”Base Line” Higgs Searches
 50 pb
Dominated by gluon fusion:
Swamped by QCD background
- have to use rare Higgs decay
modes or associated
production below the WW
threshold.
Mass Acceptance
All
pp  p + X + p
308 m
420 m
MX = 120 GeV
e  45%
All detectors
combined
MX = 60 GeV
e  30%
308m
e  15%
420m
MX (GeV)
Both protons are
seen with  45 %
efficiency at
MX = 120 GeV
Some acceptance
down to:
MX = 60 GeV
308m & 420m
locations select
symmetric
proton pairs
 acceptance
decreases.
Momentum loss resolution at 420 m
Resolution
improves with
increasing
momentum loss
proton momentum loss
proton momentum loss
Dominant effect:
transverse
vertex position
(at small
momentum loss)
and beam energy
spread (at large
momentum loss,
420 m)/detector
resolution (at
large momentum
loss, 215 m &
308/338 m)
Running Scenarios 1: High & Intemediate *
(goal)
1
2
3
4
low |t| elastic,
stot , min. bias
diffr. phys.,
large pT phen.
intermediate |t|,
hard diffract.
large |t| elastic
 * [m]
1540
1540
200 - 400
18
N of bunches
43
156
936
2808
Half crossing
angle [mrad]
0
0
100 - 200
160
Transv. norm.
emitt. [mm rad]
1
1
3.75
3.75
3.75
N of part. per
bunch
0.3 x 1011
0.6 x
1011
1.15 x
1011
1.15 x 1011
1.15 x 1011
RMS beam size at
IP [mm]
454
454
880
317 - 448
95
RMS beam diverg.
[mrad]
0.29
0.29
0.57
1.6 - 1.1
5.28
Peak luminos.
[cm-2 s-1]
1.6 x 1028
(1 - 0.5) x 1031
3.6 x 1032
Scenario
2.4 x 1029
- low * physics will follow...
SUMMARY:
TOTEM opens up Forward Physics to the LHC
TOTEMCMS covers more phase space than any
previous experiment at a hadron collider.
Fundamental precision measurements on elastic scattering, total
cross section and QCD:
• non-perturbative structure of proton
• studies of pure gluon jets – LHC as a gluon factory
• gluon densities at very small xBj…
• parton configurations in proton
Searches for signals of new physics:
• Threshold scan of 0++ states in exclusive central diffraction: Higgs,
SUSY (mass resolution crucial for background rejection)
Extension of the ‘standard’ physics reach of CMS into the fwd
region & Precise luminosity measurement