forward physics with the totem cms at the lhc
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Forward Physics with the TOTEMCMS at the LHC Risto Orava
XIII ISVHECRI Pylos, Greece, 6-12 September 2004 R.Orava
Diffractive Scattering probes the hadronic vacuum
Soft diffractive scattering
Hard diffractive scattering
Valence quarks in a bag with
r 0.1fm
Baryonic charge distribution-soliton r 0.4fm
‘wee’ partons lns
Rapidity gapsurvival & ”underlying”event structures areintimately connectedwith a geometricalview of the scattering- eikonal approach!R.Orava
Longitudinal view
p
p
lns
lnMX2
jet
jet
Elastic soft SDE
hard SDE
hard CD
’Glansing’ scattering of proton fields
el - Models
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/m (m = meson mass):B 13 GeV-2
However: Scattering on a black disc: el/tot = ½, while the data (at s corresponding to B 13 GeV-2) gives el/tot = 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.
0.17
0.3 at the LHC
20 at the LHC, b2 1.6fm2
B32 at the blackdisc limit?
The black disc limitreached at 108 GeV?
tot - Models
Total cross sections show universal rise at high energies: tot s0.08
However: - Global fits cannot discriminate between Regge theory ( s) and s-channel picture leading to logs behaviour.
Total Cross Section - TOTEM
TOTEM
Diffractive Cross Sections are Large
0.375
Rel = el(s)/tot(s) Rdiff = [el(s) + SD(s) + DD(s)]/tot(s)
0.30
el 30% of tot at the LHC ? SD + DD 10% of tot (= 100-150mb) at the LHC ?
L dt = 1033 & 1037 cm2
Pomeron exchange (~exp Bt)
diffractive structure
pQCD
Photon - Pomeron interference
(* = 1540 m & 18 m)
d/
dt
(mb
/GeV
2)
Studying elastic scattering an soft diffraction requires special LHC optics. These will yield large statistics.
high-t
Additional forward coverage opens up new complementary physics program at the LHC
• Investigate QCD: tot, elastic scattering, soft & hard diffraction, multi- rapidity 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 (pp3jets+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 – spin-parity of X! (LHC as the e+e- linear collider in -mode.)
• Extension of the ‘standard’ physics reach of the CMS experiment into the forward region
• Luminosity measurement with L/L 5 %
0 0c bχ , χ
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 - background free environment (bb, WW & 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 pairs, extra dimensions
gg
TOTEM Physics ScenariosProton
* (m)
rapiditygap L(cm-2s-1)
jetinelasticactivity
,e,, , ++,...
elastic scattering
total cross section
soft diffraction
hard diffraction
1540 18
1540
1540200-400
200-400 0.5
low-x physics
exotics (DCC,...)
DPE Higgs, SUSY,...central pair
central & fwd
inelasticacceptance gap survival
jetacceptance di-jet backgr
b-tag, ,J/,...
1028 -1032
1029 -1031
1028 -1033
1031 -1033
1031 -1033
TOTEM& CMS
TOTEM& CMS
TOTEM& CMS
central& fwd jets
di-leptonsjet-
mini-jetsresolved?
± vs. o
multiplicity
leptons’s
jetanomalies?
W, Z, J/,...
, K±,,...
0.5
1031 -1033
1031 -1033
200-400 0.5
200-400 0.5
mini-jets?
R.Orava
beam halo?
trigger
Correlation with the CMS Signatures
• e, , , , and b-jets:• tracking: || < 2.5• calorimetry with fine granularity: || < 2.5• muon: || < 2.5
• Jets, ETmiss
• calorimetry extension: || < 5
• High pT Objects• Higgs, SUSY,...
• Precision physics (cross sections...)• energy scale: e & 0.1%, jets 1% • absolute luminosity vs. parton-parton luminosity via
”well known” processes such as W/Z production?
R.Orava
CMS/TOTEM
The Large Hadron Collider (LHC)
ATLAS
ALICE
LHC-B
LHC is built into 27 km the LEP tunnel
pp collisions at 14 TeV
5 experiments
25 ns bunch spacing 2835 bunches 1011 p/bunch
Design Luminosity:1033cm-2s-1 -1034cm-2s-1
100 fb-1/year
23 inelastic eventsper bunch crossing
Planned Startup on Spring 2007
The ‘Base Line’ CMS experimento Tracking
o Silicon pixelso Silicon strips
o Calorimeterso PbW04 crystals for Electro-magn.o Scintillator/steel for hadronic part
o 4T solenoido Instrumented iron for muon detection
o CoverageoTracking 0 < || < 2.7o Calorimetry 0 < || < 5
A Huge enterprise.
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.
In the forward region (| > 5): few particles with large energies/small transverse momenta.
Charge flow
Energy flow
information value low: - bulk of the particles crated late in space-time
information value high: - leading particles created early in space-time
mic
rosta
tion a
t 19m
?
RPs
Total TOTEM/CMS acceptance (*=1540m)
TOTEM + CMS
lead
ing
pro
ton
s
lead
ing
pro
ton
s
The Experimental Signatures: pp p + X + p
b-jet
CMS
- Leading protons on both sides down to 1‰- Rapidity gaps on both sides – forward activity – for || > 5- Central activity in CMS
- resolution in ?-beam energy spread?
- vertex position in the transverse plane?
-
Aim at measuring the:
Detector Detector
p2’ p1’
b-jet_
In addition: The signatures of new physics have to be normalized: The Luminosity Measurement
Luminosity relates the cross section of a given process by:L = N/
A process with well known, calculable and large (monitoring!) with a well defined signature? Need complementarity.
Measure simultaneously elastic (Nel) & inelastic rates (Ninel), extrapolate d/dt 0, assume -parameter to be known:
(1+2) (Nel + Ninel)2
16dNel/dt|t=0
L =
Ninel = ? Need a hermetic detector.
dNel/dtt=0 = ? Minimal extrapolation to t0: tmin 0.01
Relative precision on the measurement of HBR for various channels, as function of mH, at Ldt = 300 fb–1. The dominant uncertainty is from Luminosity: 10% (open symbols), 5% (solid symbols).
(ATL-TDR-15, May 1999)
Inelastic cross sectionEvent selection:• trigger from T1 or T2 (double arm o single arm)• Vertex reconstruction (to eliminate beam-gas bkg.)
Extrapolation for diffractive events needed
Lost events
Acceptance
simulated
extrapolated
detectedLoss at low masses
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
100
101
102
103
104
105
106
107
108
109
fixedtarget
HERA
x1,2
= (M/1.96 TeV) exp(y)Q = M
Tevatron parton kinematics
M = 10 GeV
M = 100 GeV
M = 1 TeV
422 04y =
Q2
(GeV
2 )
x
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
100
101
102
103
104
105
106
107
108
109
fixedtarget
HERA
x1,2
= (M/14 TeV) exp(y)Q = M
LHC parton kinematics
M = 10 GeV
M = 100 GeV
M = 1 TeV
M = 10 TeV
66y = 40 224Q
2 (G
eV2 )
x
longer Q2
extrapolation
smaller x
J. Stirling
Low-x Physics at the LHCResolving Confinement of quarks & gluons?
Puzzles in High Energy Cosmic Rays
Interpreting cosmic ray data dependson hadronic simulation programsForward region poorly knownModels differ by factor 2 or moreNeed forward particle/energy measurements e.g. dE/d…
Cosmic rayshowers:Dynamics of thehigh energy particle spectrumis crucial
How to manage with the high-pT 'bread-and-butter' signatures of the nomenclature: The “Underlying Event”
inHard Scattering Processes
Proton AntiProton
“Soft” Collision (no hard scattering)
Proton AntiProton
“Hard” Scattering
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
Proton AntiProton
“Underlying Event”
Beam-Beam Remnants Beam-Beam Remnants
Initial-State Radiation
Unavoidable background to be removed from the jets before comparing to NLO QCD predictions
LHC: most of collisions are “soft’’, outgoing particles roughly in the same direction as the initial protons.
Occasional “hard’’ interaction results in large transverse momentum outgoing partons.
The “Underlying Event’’ is everything but the two outgoing Jets, including :
initial/final gluon radiation beam-beam remnants secondary semi-hard interactions
Min-Min-BiasBiasMin-Bias
• Leading Protons
• Extended Coverage of Inelastic Activity
• CMS
To Reach the Forward Physics Goals We Need:
Need to Measure Inelastic Activity and Leading Protons over Extended Acceptance in , , and –t. Measurement stations (Roman Pots) at locations optimized vs. the LHC beam optics. Both sides of the IP.
147 m147 m 180 m180 m 220 m220 m
LP1LP1 LP2LP2 LP3LP3
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 bybeam energy spread (large ).For Higgs, SUSY etc. heavier states need LP4,5 at 300-400m!
Reduced # of bunches (43 & 156) to avoid parasitical interactions downstream.
LTOTEM = 1.6 x 1028 cm-2 s-1 & 2.4 x 1029 cm-2 s-1
For tot 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) y
* + vy(s) y*, L(s) = [s]1/2 sin (s)
x(s) = Lx(s) x* + vx(s) x* + Dx(s) ,v(s) = [(s) ]1/2 cos (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: *x,y) = / * 0.3 rad
• large beam size at IP: *x,y = * 0.4 mm
(if N = 1 m rad)
TOTEM beam optics
• more than 90% of all diffractive protons are seen!
• proton momentum can be measured with a resolution of few 10-3
Diffraction at high *: AcceptanceLuminosity 1028-1030cm-2s-1 (few days or weeks)
TOTEM ROMAN POT IN CERN TEST BEAM
Dispersion function - low * optics (CMS IR)
CMS
Disp
ersio
n in
horizo
nta
l pla
ne
(m)
x
Opti
cal fu
nct
ion
in x
and y
(m
)
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).
yDx
horizontal offset = Dx ( = momentum
loss)
Dispersion suppressor
Matching section
Separation dipoles Final focus
Potential locations for measuring the leading protons from O(100 GeV) mass DPE.
420 m 220 m CMS308/338 m
Cryogenic (”cold”) region (with main dipole magnets)
location of currently planned TOTEM pots!!
Microstation – Next Generation Roman Pot
-station concept (Helsinki proposal)
Silicon pixel detectors in vacuum (shielded)
Movable detector
Very compactA solution for 19m, 380 & 420m?
Leading Proton Detection 147m 180m 220m0m 308m 338m 420 430m
IP
Q1-3
D1
D2 Q4 Q5 Q6 Q7 B8 Q8 B9 Q9 B10 B11Q10
Jerry & Risto
= 0.02
TOTEM Detector Layout y(m
m)
y(m
m)
y(m
m)
x(mm) x(mm) x(mm)
Leading diffractive protons seen at different detector locations (* = 0.5m)
215m 300m 420m
~14 m
CMSCMS T1-CSC: 3.1 < < 4.7
T2-GEM: 5.3 < < 6.5
T3-MS: 7.0 < < 8.5 ?
10.5 mT1T1 T2T2
T3?T3?
CMS tracking is extended by forward telescopes on both sides of the IP
~19 m
- A microstation (T3) at 19m is an option.
CASTORCASTOR
Forward Tracking Stations T1,T2&T3
T1 detector
T2: 5 planes of silicon/GEM detectors
• coverage: 5.3 < < 6.7 & full azimuthal
• spatial resolution better than 20 m
0.4 m13.6 m
T1: 5 planes of CSC
• coverage: 3.1 < < 4.7 & full azimuthal
• spatial resolution better than 0.5 mm
T2
3.0 m7.5 m
HF
Castor
IP
IP
T3?
The process: pp p + H + p
p
p
b-jet
b-jet
p1
p2
p’
p”
b
b0
5
-5
10
-10
-
-0++
H
MH2 = (p1 + p2 – p’ – p”)2 12s (at the limit, where pT’ & pT” are small)
1 =p’q1/p1q1 1-p’/p1 2 = 1-p”q2/p2q2 1-p”/p2
0++
q1
q2
Leading proton studies at low *
GOAL: New particle states in Exclusive DPE
• L > few 10 32 cm2 s1 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 cm2 s1
• 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.
JPC = 0++ (2++, 4++,...)
Gap GapJet+Jet
min max
Survival of the rapidity gaps?1
1 V.A.Khoze,A.D.Martin and M.G.Ryskin, hep-ph/0007359R.Orava
Measure the parity P = (-1)J:d/d 1 + cos2
Mass resolution S/B-ratio
MX212s
Higgs Mass – New EW Fit Results
LEP Search: MH 114.4 GeV
EW fits: MH = 117 GeV
95% CL: MH < 251 GeV
+67
-45
With the new top-mass measurements, the best fit for the Higgs mass is notexcluded.
Cross Section
300fb-1
30fb-1
For a 5 signal at the LHC need:
SUSY h030fb
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?
Swamped by QCD background- have to use rare Higgs decay modes or associated production below the WW threshold.
”Base Line” Higgs Searches
Dominated by gluon fusion:
50 pb
Mass Acceptance
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.
308 m420 m
pp p + X + p
MX (GeV)
MX = 60 GeV
MX = 120 GeV
All
45%
30%
15%
All detectors combined
308m
420m
Resolution improves with increasing 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)
proton momentum loss
proton momentum loss
Momentum loss resolution at 420 m
Running Scenarios 1: High & Intemediate *
Scenario(goal)
1low |t| elastic,tot , min. bias
2diffr. phys.,
large pT phen.
3intermediate |
t|, hard diffract.
4large |t| elastic
* [m] 1540 1540 200 - 400 18
N of bunches 43 156 936 2808
Half crossing angle [rad]
0 0 100 - 200 160
Transv. norm. emitt. [m 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 [m]
454 454 880 317 - 448 95
RMS beam diverg. [rad]
0.29 0.29 0.57 1.6 - 1.1 5.28
Peak luminos. [cm-2 s-1]
1.6 x 1028 2.4 x 1029 (1 - 0.5) x 1031 3.6 x 1032
- low * physics will follow...
SUMMARY:TOTEM opens up Forward Physics to the LHC
TOTEMCMS 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