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Frigyes Nemes on behalf of the TOTEM experimentCERN*
Diffraction 2016
Acireale, Sicily, Italy
2016, September 2. – 8.
*Also at Wigner RCP, Budapest, Hungary
T1: 3.1 < |h| < 4.7, pT > 100 MeV
T2: 5.3 < |h| < 6.5, pT > 40 MeV
T1 T2 CASTOR (CMS)
10.5 m
14 m
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Only Run I
Properties:
• Installed inside CMS at 7.5 to 10.5 m from IP5
• There is one telescope on each side of IP5
• Each telescope consists of two quarters
• The quarters are formed by 5 equally spacedplanes
• The planes contain 3 trapezoidal CSC detectors, each covering 60 ̐ in azimuth
• Cathode Strip Chamber: gaseous detector with3 read-out coordinates (at 60 ̐ wrt. each other)
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Properties:
• Installed inside CMS shielding between HF and Castor calorimeters
• Centered around 13.5 m from IP5
• There is one telescope on each side of IP5
• Each telescope contains two quarters
• Quarters formed by 10 semi-circularplanes, assembled in 5 back-to-backmounted pairs
• Planes equipped with a Gas Electron Multiplierdetector
• Gaseous detector, electron multiplication by 3 perforated foils (2 mm separation)
• radial segmentation: strips (resolution ≈ 0.15 mm)
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RP stations:
• 2 units (Near, Far) at about distance
• 10 m (RP210)
• 5 m (RP220)
• Unit: 3 moveable RP to detect small proton scattering angles (few µrad)
• Overlapping detectors: relative alignment
• BPMs installed
Horizontal RP
RP unit: 2 vertical, 1 horizontal pot + BPM
BPMVertical RPs
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5
Frigyes Nemes, TOTEM
1 Roman Pot10 planes of edgeless detectors
3.5 cm
Si edgeless detector
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Proton transport description:
Transport matrix from MAD-X (ξ = Δp/p momentum loss)
*
*
*
*
*
4241
3231
2423
1413
10000 y
x
yyy
yyy
xxx
xxx
RP
y
x
y
x
DLvmm
DLvmm
DmmLv
DmmLv
y
x
Measured
Kinematics reconstruction of elastic protons per arm (arms are averaged):
*
1
xds
dvΘ
ds
dLΘ x
xx*
x
Fy
F
Ny
N*
yL
y
L
yΘ
,,2
1
2*2*2
yxpt
s: distance from IP5 (*≡IP5)
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List of TOTEM publications
http://totem.web.cern.ch/Totem/publ_new.html
Momentum conservation is required in elastic events:
• Published in EPL 95 (2011) 41001
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Horizontally… …and vertically
Spread agrees with beam divergence (17-18 μrad)
)(/)( ** sx
From Liouville’s theorem, ε: emittance
Published in EPL 95 (2011) 41001:
• |t| range spans from 0.36 to 2.5 GeV2
• Below |t| = 0.47 GeV2 exponential e-B|t| behavior
• Dip moves to lower |t|, proton becomes “larger“
• 1.5 - 2.5 GeV2 power low behavior |t|-n
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ISR
The measured dσ/dt compared with predictions of several models
Properties:• Ly ≈ 264 m• Slope B confirms that it increases with √s
• Total cross-section with optical theorem
• ρ value from COMPETE:
• Compatible results, published in:EPL 96 (2011) 21002EPL 101(2013) 21002
1
16
0
el
2
2
2
tot
tdt
dc
01.0
08.014.0
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322
min
fullsyststattot
fullsyst
statinel
syststatsyststatel
syststatsyststat
2-
0
syststatsyststat
2-
beam
105102GeV
2.26.988.22.03.98mb
26.115.736.05.73mb
07.103.043.252.12.08.24mb
239.04.5067.265.17.503GeV mb
27.003.089.19 3.02.01.20GeV
510distance RP
3.1
8.1
t
dt
d
B
t
0Im
Re
t
H
H
A
A
RP@ 10 σbeam size@RP
(RP @ 6.5, 5.5, 4.8 σbeam size@RP )
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EPL 101(2013) 21002
EPL 95 (2011) 41001 (β* = 3.5 m)
EPL 96 (2011) 21002 (β* = 90 m)
EPL 101 (2013) 2100 (β* = 90 m)
Trigger: at least one track in T2
• 95 % of inelastic events
1. Raw rate: event counting with T2
Experimental corrections: trigger and reconstruction inefficiencies,beam-gas event suppression, pile-up
2. Visible rate: visible with T2 in perfect conditions
Estimation of events with no tracks in T2: T1-only events, events withgap over T2, low-mass diffraction
3. Physics rate: true rate of inelastic events– Only one major Monte-Carlo-based correction: low-mass diffraction (which
can be constrained from data, 6.31 mb upper limit for Mx < 3.4 GeV)
4. Cross-section: uses CMS luminosity measurement
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EPL 101 (2013) 21003
inel = 73.7 ± 3.4 mb
Results:
1. Low luminosity (CMS) + Elastic d/dt + Optical th. ( EPL 96(2011) 21002 )
depends on CMS luminosity for low-L bunches, elastic efficiencies and on ρ
2. High luminosity (CMS) + Elastic + Optical theorem (EPL 101 (2013) 21002)
3. High luminosity (CMS) + Elastic + Inelastic (EPL, 101 (2013) 21004)
minimizes dependence on elastic efficiencies and no dependence on ρ
4. Elastic ratios + Inelastic ratios (T1, T2) + Optical theorem (EPL, 101 (2013) 21004)
Eliminates dependence on luminosity
tot = 98.3 ± 2.8 mb
tot = 98.6 ± 2.2 mb
tot = 99.1 ± 4.3 mb
tot = 98.0 ± 2.5 mb
1
16
0
el
2
2
2
tot
tdt
dc
ineleltot
inelel
0
el
2
2
tot1
16
NN
dt
dN
ct
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Read more:• EPL 101 (2013) 21004
• Phys. Rev. Lett. 111, 012001 (2013)
σtot
[mb]
σel
[mb]
σinel
[mb]
101.7 ± 2.9 27.1 ± 1.4 74.7 ± 1.7
Symmetries of the tagged particles’ reconstructed
kinematics:
• High statistics
• Rotational symmetry
• Left-right arm symmetry
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16
Left - right symmetry (in background estimation)
Rotational symmetry
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The observed differential cross-section w.r.t. reference exponential:• Fits with different assumptions on hadronic component
• Pure exponential excluded with more than 7σ significance !
)exp( 1tbaAN )exp( 3
3
2
21 tbtbtbaAN
Nb σtot [mb]
2 101.5 ± 2.1
3 101.9 ± 2.1
Basic properties of the data:
• RP detectors at about 3 σbeam
• |t|min = 6 10-4 GeV2
Analysis aims:
• Measure dσel/dt at the smallestpossible |t|
• AC+H= Coulomb + Hadronic +Interference terms
• Interference: the phase of hadronicamplitude appears in
• Determination of ρ became possible:
• Further improve the total cross-sectionσtot measurement
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0Im
Re
t
H
H
A
A
2
HCAdt
d
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Purely exponential hadronic amplitude:• Constant phase: excluded• Peripheral phase
o Disfavoured ρ value is not consistent with theory Theoretical arguments next to non-
exp. hadronic amplitude
Non-exponential hadronic amplitude:• Both peripheral and constant phase compatible
with datao Centrality not necessity
Nb = 1
Nb = 3
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First determination of ρ at LHC from Coulomb-hadronic interference:• Same ρ value with central and peripheral models• At s=13 TeV a ρ measurement is planned with higher statistics
Hadronic phase σtot [mb]
Central 102.9 ± 2.3
Peripheral 103.0 ± 2.3
Total cross-section measurement• Compatible with previous TOTEM measurements• About 1 mb increase due to CNI
Accepted for publication: http://cds.cern.ch/record/2114603
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Note:
• Large amount of data (trigger rate 50× w.r.t. Run I)
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Non-exponential part is visible at low-|t|
No structures at high-|t|:rules out several models
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LyLy [m]
Odderon: (hypothetical) partner of Pomeron in Regge-theory
Possible searches at the LHC:
• Structures in dσ/dt where Pomeron contribution is small
– High-t: 13 TeV TOTEM data does not show structures
– Low-t: shift in value of ρ parameter with CNI
• At 13 TeV means special optics (β* = 2500 m)
• About 1 week data taking time (approved in 2016)
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Low mass diffraction
Very high mass ( ξ > 2.5 % )
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MX2 = s
Rapidity Gap
Dh = -ln
RP RPT2 T2
IPsector 45 sector 56
=Dp/p
h
RP RPT2 T2
IPsector 45 sector 56
h
MX2 = s
Rapidity Gap
Dh = -ln
• SD events are triggered with T2, only 1 proton required in RP
• Double determination of ξ ≈ e -Δη
– From RPs (ξ ≈ x / Dx and optics non-linearity Ly(ξ), etc.)
– From rapidity gap in T1/T2
– MX 2 ≈ s · ξ
• Available data
– 7 TeV: TOTEM standalone analysis in progress
– 8 and 13 TeV: common data with CMS
Corrections included:
• Trigger efficiency
• Reconstruction efficiency
• Proton acceptance
• Background subtraction
• Extrapolation to t = 0
Missing corrections:
• ξ – resolution
• Beam divergence effects
Estimated uncertainty:
• B ~ 15 %, σ ~ 20 %
Very preliminary result:
• σSD = 6.5 ± 1.3 mb
• 3.4 < MSD < 1100 GeV
• Very-high masses: ongoing
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teCdt
d B
Event selection:
• T1 veto + 2 T2 topology
Properties:
• ηmin visible to TOTEM T2: 4.7 < |ηmin | < 6.5 ≡ 3.4 < Mdiff < 8 GeV
• Non-diff. bkg.: control sample 2 T1 + 2 T2 events
• Single diff. bkg. T1 veto + 1 T2 and proton in the RP
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CMS
Results from 7 TeV data:
• Phys. Rev. Lett. 111, 262001 (2013)
• Improvement expected with the8 TeV data, including also theCMS information
MC comparisons:
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b 25116 )5.67.4( min
h
DD
Very forward measurement with T2 :
• Published EPL, 98 (2012) 31002
• Visible cross section measured on data: ~ 94 % σinel
• Diffractive mass Mdiff > 3.4 GeV
Main contributions to the systematic uncertainty (≈ 10%)
• Subtraction of secondary particles (80 % of all tracks)
• Track efficiency
• Misalignment uncertainties
dN
ch/d
h
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29
Combined with other LHC exp.
TOTEM result with displaced vertex:
Eur. Phys. J. C (2015) 75: 126.
TOTEM + CMS result:
• Eur.Phys. J.C(2014) 74: 3053
• Both CMS and TOTEM analysisobtained triggering with T2, on thesame events
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Available data:
• 7 TeV: TOTEM only, analysis started
• 8 TeV: common data with CMS, analysis started
• 13 TeV: common data with CMS
Experimental challenge: background (pileup ES/beam halo + inelastic)
• Anti-elastic cuts: anti-collinearity, …
1=Dp1/p1
2=Dp2/p2
Correlation between leading protons and T2:
RP RPT2 T2
IPsector 45 sector 56
low ξ high ξ
1=Dp1/p1
2=Dp2/p2
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σCD estimation:
mb 1
)(
21
20 0
21
2,1
21
2
21
D
dtdt
ddtdt
eeCdtdt
d
CDCD
BtBtCD
Available data s = 7 TeV and β* = 90 m optics:
• Trigger selection: 2 × RP
• Nearly complete ξ - acceptance
• Background: elastic, beam-halo + inelastic– Elastic: anti-elastic cuts, e.g. forbidden topologies (top-top, bottom-bottom)
– Beam-halo: |y| > 11 × σbeam → halo is negligible
B = 7.8 1.4 GeV-2
Single arm CD event rate in RPintegrated , acceptance corrected
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TOTEM Preliminary
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TOTEM + CMS unprecedented properties:
• Double arm proton detection
• Mass of diffractive system X is double determined– By TOTEM Roman Pots MX
2 = s ξ1 ξ2
– By CMS
Analysis examples:
• Studies of glueball candidates
• Exclusive dijets: mainly gg (pT > 30 GeV)
• Exclusive J/ψ, Z, W production: O (10 pb – 10 nb)
• Search for missing mass signals ofO (pb) → SUSY searches
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Available data β* = 90 m:
• 8 TeV, Jul 2012, L = 1 nb-1 : proof of principle
• 13 TeV, Oct 2015, L = 0.4 pb-1 : should allow full production and decay characterisation
2015 data:
• CMS + TOTEM: trigger exchange, independent DAQ, offline data merging
• Trigger: RP double arm & T2 veto & at least one track in CMS
• Analysis strategy – verify the following glueball conditions
– Resonance enhancement with increasing collision energy
– Final states branching ratio to π π, KK, ..., with equi-flavour partitioning selection rules(or with proportionality of gluon coupling to quarks)
– Suppression of photon-photon channel (in production and final state)
• Upgrade projects: interest in lower cross-section processes
• Higher luminosity needed → Higher pile-up
– Timing: association of RP proton vertex with CMS vertex
– Pixel detectors: more tracks in RPs
CT-PPS = CMS-TOTEM Precision Proton Spectrometer
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Project CT-PPS(see F. Ferro’s talk on Wednesday)
Timing in vertical RP
Optics Low (LHC standard) β*= 0.4 m High lumi β*= 90 m
RP detectors Horizontal Vertical
Tracking Si strip in 2016 (~ 8 fb-1)3D pixel (10 μm) to be installed
Current Si strip (20 μm/RP)
Timing Diamond (100 ps/plane), installed, soon will be used
• Performance in Run II
– All detectors functional
– RPs equipped with RF shields (less impedance) close approach possible
– DAQ throughput increased 50 w.r.t. Run I (zero-suppression)
• Many analyses ongoing
– Run I and Run II
– TOTEM standalone, TOTEM + CMS
• Upgrade projects
– Timing in vertical RPs (diamonds)
– CT-PPS (pixel tracking, timing with fast silicon, diamond)
• Priorities for 2016
– Glueball analysis of 2015 data
– TOTEM special run: β* = 2.5 km, Odderon searches via CNI
– CT-PPS runs with LHC standard optics: di-photon searches with existing RPs
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Different formulations of the interference phenomenon:• Simplified West-Yennie (SWY)
o Based on QFTo Simplifications: constant slope and constant hadronic phase
• Cahn or Kundrát-Lokajicek (KL) modelo Eikonal frameworko No explicit simplifications
The t-dependence of the two considered hadronic phase model families:
Machine imperfections alter the optics:
• Strength conversion error, σ(B)/B ≈ 10-3
• Beam momentum offset, σ(p)/p ≈ 10-3
• Other factors…
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2*2*2
yxpt
→ Precise model of the LHC optics is indispensable!
Novel method from TOTEM:
• Use measured proton data from RPs
• http://iopscience.iop.org/1367-2630/16/10/103041/
Relative error distribution
before and
after optics estimation β* = 3.5 m
On the basis of constraints R1-R10 the optics can be estimated:
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RPb2,y,
RPb1,y,
RPb2,
RPb1,
2L
L
y
yR
RPb1,y,
RPb1,y,
RPb1,
RPb1,y,
3L
ds
dL
y
ΘR
/dsdL
L
Θ
xR
RPb1,x,
RPb1,x,
RPb1,x,
RPb1,
5 near_potsb1,y,
near_potsb1,14,
RPb1,
RPb1,
7L
m
y
xR
R3,4
R7,8,9,10
R5,6
2
Design LHC
10
1
2
calculated,measured,
2 ))(/)(( i
iii RRR
Measured ratiosR1-R10
Calculated ratiosR1-R10
dLx/ds, Ly
Comparison
R1
R2
Refine machine settings• 2x6 quad. magnet strength• 2x6 quad. rotation• Momentum of 2 beams