Transcript Slide 1

Giornata del dipartimento di Fisica
M. Berretti
Siena, 21 December 2012
Latest results from the
TOTEM experiment
The TOTEM experiment
 Physics results
 Ongoing analyses and future
The TOTEM Collaboration
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TOTEM Physics Program Overview
Stand-Alone:
- TOT pp with a precision ~ 1-2% (L ind. meth.) simultaneously measuring :
Nel down to -t ~10-3 GeV2
and
Ninel with losses < 3%
- Elastic pp scattering in the range 10-3 < |t| ~ (p)2 < 10 GeV2
- Soft diffraction (SD and DPE)
- Particle flow in the forward region (cosmic ray MC validation/tuning)
pp elastic, inelastic and total
cross section
Diffractive
processes
Forward multiplicities
Large
rapidity (-ln tan /2)
gap
(SD)
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The TOTEM experiment at the LHC
TOTEM
IP5
TOTal cross section, Elastic
scattering and diffraction
dissociation Measurement
CMS
The Compact Muon Solenoid
ALICE
A Large Ion Collider
Experiment
LHCb
ATLAS
LHCf
The Large Hadron Collider
beauty experiment
A Toroidal LHC ApparatuS
LHC forward experiment
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The TOTEM experiment at the LHC
TOTEM is composed by 3 different detectors:
T1: CSC chambers, charged particle tracking 18<<90 mrad
T2: GEM chambers, charged particle tracking 3<<10 mrad
RP: movable silicon detector: elastic and diffractive proton
measurement (optics-dependent acceptance)
About 99.5% of all non diffractive
minimum bias events and ~85% of all
diffractive events have charged
particles within the acceptance of the
TOTEM detectors (T1 and T2).
ALICE
LHCb
A Large Ion Collider
Experiment
ATLAS
LHCf
A Toroidal LHC ApparatuS
LHC forward experiment
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The Large Hadron Collider
beauty experiment
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The RP detector
One Roman Pot
Sensitivity up to 50 mm
thanks to the Current
Terminating Structure
Beam
90% Efficiency
10% Efficiency
Physical Edge
A RP station:
Composed by 2 units
Each one with 2 Vertical and one Horizontal Pots
Each Pot is equipped with 10 “edgless” silicon planes
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Installation in the CMS endcaps region
The T1 detector
3.1 < |η| < 4.7 (h=-ln tan /2)
Cathode Strip Chambers
 No loss of performance after a total
charge integrated on the anode wires
of 0.065 C/cm
(5 years at a luminosity of 1030 cm−2s−1)
 Hit X,Y= 1mm
T1 individual arm inelastic event reconstruction efficiency : ∼98 %
(at least one charged particle in T1 with pT >100 MeV/c)
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System set-up, commissioning and
software mainly developed from the
Siena group
The T2 detector
40 Triple Gas Electron Multiplier chambers
rmax≈14.45cm
rmin≈4.25cm
Δϕ=360o
IP5
min≈3mrad ≈0.2o
max≈10mrad ≈0.6o
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 Hit R,f= 0.1mm, 1o
T2 inelastic event reconstruction
efficiency : ∼99.5 % (at least one
charged particle in T2 with pT
>40 MeV/c)
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The T2 detector
40 Triple Gas Electron Multiplier chambers
Drift
Installation of 2 T2 quarters
GEM foil
Transit
GEM foil
Δϕ=192o
Transit
Δϕ=192o
GEM foil
Induction
Sensitive
Area
Readout Plane
Advantage of a GEM plane :
High tolerance to radiation (> 50 Mrad)
High rate capability (> 10 MHz/cm2)
Low material budget (10 planes: 0.07 X0)
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The large occupancy and the impossibility
to resolve the pile-up vertices make T2
usable only for low luminosity runs
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TOTEM Physics and results
1. Measurement of the elastic scattering on a wide range of
four-momentum transfer.
~ 1.7 GeV2
7 TeV
ISR
Large-t region:
Important for
model
discrimination
~ 0.7 GeV2
~ |t|-7.8
•Minimum moves to lower |t|
with increasing CM energy
~1.5 GeV2
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•Exponential slope grows with
the CM energy
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Total cross section measurement @ 7 TeV in 3 ways
(ρ=0.14 [COMPETE])
June 2011 (EPL96): tot = (98.3 ±2.8) mb
Oct. 2011 (PH pre.): tot = (98.6 ±2.2) mb
different bunch intensities
and elastic acceptance !
tot = (99.1 ± 4.3) mb
tot = (98.0 ± 2.5) mb
Excellent agreement between cross-section measurements at 7 TeV using
- runs with different bunch intensities and RP acceptances.
- different methods.
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Total cross section measurement @ 7 TeV in 3 ways
Luminosity calibration:
Estimated by CMS
1) L= 82/mb ± 4%
2) L= 1.65/mb ± 4%
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Estimated by TOTEM
L= 83.7/mb ± 3.8%
L= 1.65/mb ± 4.5 %
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TOTEM Physics and results
1. Measurement of the pp total cross section with 1-2%
systematic error by using the luminosity independent method
dσEL/dt [mb/GeV2]
 Needs the total elastic and inelastic rate
 Needs the extrapolation of the elastic rate to t=0
• The visible elastic rate is 90%. The rest is
Obtained
in awith
low luminosity
run atfitb*=90m optics where
RP edge mb
extrapolated
the exponential
el =25.1±1.1
approaches at 5 to the beam center.
• The inelastic rate is measured triggering with T2.
EPL 96 (2011) 21002
Low mass diffractionTo be published
~ 3.7% A = 506 ±22.7syst±1.0stat mb/GeV2
Trigger efficiency
d EL / dt  ~2.3
Ae- B%|t|
B = 19.9±0.26syst±0.04stat GeV-2
T1 only events
~2%
inel : 72.9 ± 1.5 mb
Pile-up (m~0.03)
~ 1.5 %
Track reconstruction efficiency ~1%
Beam-gas background
~-t 0.57%
[GeV2]
Rapidity Gap in T2
0.5%
 Needs the Central
value of diffraction
r (From the COMPETE collaboration
0.5% fit, r= 0.14, later with a
direct measurement at b*=1Km )
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NB: Low mass diffraction cross-section can be constrained
Estimation of σinel= σtot – σel = 73.2± 1.3mb can be done with RP-only
measurement (L-dependent). However, T1+T2 visible σh<6.5inel= 70.9 ± 2.8 mb
σh>6.5inel= 3.7% σh<6.5inel
 Needs the total elastic and inelastic rate
• The visible elastic rate is 90%. The rest is
extrapolated with the exponential fit

=25.1±1.1
mb
 el
=25.1±1.1
mb
EL
• The inelastic rate is measured triggering with T2.
Low mass diffraction
Trigger efficiency
T1 only events
Pile-up (m~0.03)
Track reconstruction efficiency
Beam-gas background
Rapidity Gap in T2
Central diffraction
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~ 3.7%
~2.3 %
~2%
~ 1.5 %
~1%
~ 0.57%
0.5%
0.5%
inel : 72.9 ± 1.5 mb
inel T2VIS = 95%inel
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T1+T2 (3.1 < |h| < 6.5) give
an unique forward charged
particle coverage @ LHC
 lower Mdiff reachable:
minimal model dependence
on required corrections for
low mass diffraction
x/SD dSD/dx
Low mass diffraction: T1+T2 acceptance
MX > 3.4 GeV/c2
S. Ostapchenko
arXiv:1103.5684v2 [hep-ph]
QGSJET-II-4
SIBYLL/PYTHI
A8
(Mx2  s x)
Several models studied: correction for low mass single diffractive cross-section based on
QGSJET-II-03 (well describing low mass diffraction at lower energies), imposing observed
2hemisphere/1hemisphere event ratio and the effect of “secondaries”
Mx < 3.4 GeV = 3.1 ± 1.5 mb
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Cross section measurements @ 8 TeV
July 2012: runs at b* = 90 m
 tot = 101.7  2.9 mb
 inel = 74.7  1.7 mb
Same analysis strategy as
for the measurement @ 7
TeV with the luminosity
independent method:
- Nel / Ninel = 0.362  0.011
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Forward Physics: importance of the dN/dh measurement
 The CR connection: tuning of the MC generator used in the Extensive
Air Showers simulations
•A good description of the forward particle
multiplicity and density produced in p-Air
collision is important for the analysis of the
Extensive Air Shower produced when a High
Energy CR interacts in the athmosphere.
•The energy and mass of the primary CR can be
understood from measurement on Earth thanks to
MCs which simulate the air shower.
•7 TeV pp collisions at LHC correspond to pCR-pAIR
collisions with pCR of ~25 PeV.
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Forward Physics: importance of the dN/dh measurement
 Observation of the extended longitudinal scaling:
p-Gold collisions
200 GeV
130 GeV
For very high energy collisions in the reference
system with the target at rest, particles produced
in the fragmentation region approach to a limiting
distribution which doesn’t depend anymore on
the collision center of mass energy.
19.6 GeV
• An universally
accepted theoretical
description is still
missing!
(TOTEM)
Fragmentation
region
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• The theory of the
Color Glass
Condensate is a
promising approach
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Measurement of the dNCH /dh in T2
TOTEM measurements “combined”
with the other LHC experiments
TOTEM measurements
compared to MC predictions
None theoretical model fully describes the data.
Cosmic Ray (CR) MCs show a better agreement
for the slope:
- SYBILL (CR): 4–16% lower
- QGSJET-II (CR): 18-30% higher
High “visible” fraction of inelastic cross section:
inel 95% inel
- Diffractive events with MDiff > 3.4 GeV
- ND events > 99%
Published: EPL 98 (2012) 31002
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Joint data taking with CMS
2012:
1st
2011 Ion run:
proof of principle
realization of common running
• CMS & TOTEM trigger exchange
• Offline data “synchronization” (orbit and
bunch #) + “merging” (n-tuple level)
May 2012: low pileup run: b* = 0.6 m, s1/2 = 8 TeV, T1 & T2 & CMS read out
Date
Trigger
Inelastic
events
May 1
T2 || BX
~5 M
no RP
dN/dh,
correlations,
underlying event
July 2012: b* = 90 m, s1/2 = 8 TeV, RP & T1 & T2 & CMS read out
Date, Set
Trigger
July 7, DS 2
T2 || RP2arms || BX
~2 M
6
July 12-13, DS 3a
T2 || RP2arms || BX
~10 M
9.5  V, 11 H
July 12-13, DS 3b
T2 || RP2arms || CMS
(CMS = 2 jets @ pT > 20GeV,
2 m, 2 central e/g )
~3.5 M
9.5  V, 11 H
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Inelastic
events
RP
position
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tot, inel with CMS,
soft & semi-hard diffraction,
correlations
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TOTEM analyses in progress
Multiplicities
• Inelastic dNCH /dh @ 8 TeV CMS + T2 (0 < |h| < 6.5)
• Inelastic dNCH /dh T1 measurement @ 7 TeV (3.1 < |h| < 4.7)
• Inelastic dNCH /dh @ 8 TeV with the displaced vertex (11m)
Diffractive studies
• Differential cross section
measurement for single diffraction
dSD/dt and double diffraction
dDD/dhmin
• Double Pomeron exchange cross
section (soft and hard), exclusive jet
production in CMS in double
pomeron exchange
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Main final state topology for inelastic events
Single
Diffraction
Double
Diffraction
Double
Pomeron
Exchange
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TOTEM analyses in progress
• Elastic scattering at low-t: studied of the coulomb-nuclear interference, measurement of r
Coulomb scattering dominant
d

dt
4 2  c ) G 4  t )
2
Total (Coulomb & nuclear)
Coulomb-Nuclear
interference
Nuclear scattering
dominant
 = fine structure constant
f
= relative Coulombnuclear phase
G(t) = nucleon el.-mag. form
factor = (1 + |t| / 0.71)-2
t
2

  r - f )  tot G 2  t )
t
 tot 2 1  r 2 )
16  c )
2
e
e
-B t / 2

-B t
First (preliminary)
measurement
in the interference region!!
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Near future (during LS1):
 Extend the multiplicity analyses for each event class (ND,SD, events with Jets in
CMS) . Charged particle correlations.
 Data taking p-Pb runs in Jan-Feb 2013 with CMS (s1/2NN=5 TeV).
 Multiplicity(T1+T2) and Energy flow (CASTOR & HF) in pp and pPb
After LS1(2014/2015) :
Repeat the stand-alone TOTEM program at the higher LHC energy
Installation/Development of RP-like timing detectors (< 10 ps resolution,
Cherenkow light from Quartz + SiPm) + tracking detector (pixels) : this will allow
the study of the hard diffraction with CMS (combining the RP protons to the
reconstructed CMS vertices)
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Conclusions
 The TOTEM experiment at LHC is fully operative.
 7 analysis-papers have been published/submitted (on the elastic,
inelastic, total pp cross section @7 and 8 TeV and on the T2 dN/dh
measurement @ 7 TeV)
 Fundamental contribution of the Siena University to this
success (installation and commissioning of T2, TOTEM-trigger,
T2 offline and online software...).
 Sevaral analyses are ongoing:
Large amount of work done (to do) on analysis of the multiplicties,
correlations, diffractive cross sections both in pp and pA runs.
 Common runs already collecte with a common CMS/TOTEM trigger.
Possibility to repeat the multiplicty and diffractive cross section
measurements when central jets are produced.
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