Giornata del dipartimento di Fisica
M. BerrettiSiena, 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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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)
TOTEM Physics Program Overview
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pp elastic, inelastic and total cross section
Forward multiplicitiesDiffractive processes
(SD)
Large rapidity (-ln tan /2)gap
CMSThe Compact Muon Solenoid
ATLAS A Toroidal LHC
ApparatuSLHCf
LHC forward experiment
LHCbThe Large Hadron
Collider beauty experiment
ALICEA Large Ion Collider
Experiment
TOTEMTOTal cross section, Elastic scattering and diffraction dissociation
Measurement
The TOTEM experiment at the LHC
IP5
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ATLAS A Toroidal LHC
ApparatuSLHCf
LHC forward experiment
LHCbThe Large Hadron
Collider beauty experiment
ALICEA Large Ion Collider
Experiment
TOTEM is composed by 3 different detectors:T1: CSC chambers, charged particle tracking 18<<90 mradT2: 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 diffractiveminimum bias events and ~85% of alldiffractive events have chargedparticles within the acceptance of theTOTEM detectors (T1 and T2).
The TOTEM experiment at the LHC
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The RP detector
Beam
A RP station:
Composed by 2 unitsEach one with 2 Vertical and one Horizontal PotsEach Pot is equipped with 10 “edgless” silicon planes
Phys
ical
Edg
e
10%
Effi
cien
cy
90%
Effi
cien
cy
One Roman PotSensitivity up to 50 mm thanks to the Current Terminating Structure
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T1 individual arm inelastic event reconstruction efficiency : ∼98 %
(at least one charged particle in T1 with pT >100 MeV/c)
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)
Cathode Strip Chambers
3.1 < |η| < 4.7 (h=-ln tan /2)
The T1 detector
Hit X,Y= 1mm
Installation in the CMS endcaps region
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IP5
≈40cm
≈13.8m
rmin≈4.25cm
rmax≈14.45cm
20 Triple GEM (Plus End) 20 Triple GEM (Minus End)
Δϕ=360o
min≈3mrad ≈0.2o
max≈10mrad ≈0.6o
5.3≤|h| ≤ 6.5
≈13.8m
40 Triple Gas Electron Multiplier chambers
The T2 detector
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System set-up, commissioning and software mainly developed from the Siena group
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)
40 Triple Gas Electron Multiplier chambers
Installation of 2 T2 quarters
Sensitive Area
Δϕ=192o Δϕ=192o
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)
The large occupancy and the impossibility to resolve the pile-up vertices make T2 usable only for low luminosity runs
The T2 detector
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Drift
Transit
Transit
Induction
GEM foil
GEM foil
GEM foil
Readout Plane
TOTEM Physics and results1. Measurement of the elastic scattering on a wide range of four-momentum transfer.
~ 0.7 GeV2
~ 1.7 GeV2
~1.5 GeV2
ISR
~ |t|-7.8
•Minimum moves to lower |t| with increasing CM energy
•Exponential slope grows with the CM energy
Large-t region:Important for model discrimination
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7 TeV
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.
(ρ=0.14 [COMPETE])
different bunch intensitiesand elastic acceptance !
June 2011 (EPL96): tot = (98.3 ±2.8) mbOct. 2011 (PH pre.): tot = (98.6 ±2.2) mb
tot = (99.1 ± 4.3) mb
Total cross section measurement @ 7 TeV in 3 ways
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Total cross section measurement @ 7 TeV in 3 ways
Luminosity calibration:1) L= 82/mb ± 4% L= 83.7/mb ± 3.8% 2) L= 1.65/mb ± 4% L= 1.65/mb ± 4.5 %
Estimated by CMS Estimated by TOTEM
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TOTEM Physics and results1. Measurement of the pp total cross section with 1-2% systematic error by using the luminosity independent method
EPL 96 (2011) 21002
To be published||/ tB
EL Aedtd -
dσEL
/dt
[mb/
GeV
2 ]
-t [GeV2]
Needs the extrapolation of the elastic rate to t=0 Obtained in a low luminosity run at b*=90m optics where RP edge approaches at 5 to the beam center.
A = 506 ±22.7syst±1.0stat mb/GeV2
B = 19.9±0.26syst±0.04stat GeV-2
Needs the total elastic and inelastic rate
• The visible elastic rate is 90%. The rest is extrapolated with the exponential fit
• The inelastic rate is measured triggering with T2.
inel : 72.9 ± 1.5 mb
Low mass diffraction ~ 3.7%Trigger efficiency ~2.3 % T1 only events ~2% Pile-up (m~0.03) ~ 1.5 % Track reconstruction efficiency ~1% Beam-gas background ~ 0.57%Rapidity Gap in T2 0.5%Central diffraction 0.5%
el =25.1±1.1 mb
Needs the value of r (From the COMPETE collaboration fit, r= 0.14, later with a direct measurement at b*=1Km )
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NB: Low mass diffraction cross-section can be constrainedEstimation of σinel= σtot – σel = 73.2± 1.3mb can be done with RP-only measurement (L-dependent). However, T1+T2 visible σh<6.5
inel= 70.9 ± 2.8 mb
σh>6.5inel= 3.7% σh<6.5
inel
Needs the total elastic and inelastic rate
• The visible elastic rate is 90%. The rest is extrapolated with the exponential fit
• The inelastic rate is measured triggering with T2.
inel : 72.9 ± 1.5 mb
Low mass diffraction ~ 3.7%Trigger efficiency ~2.3 % T1 only events ~2% Pile-up (m~0.03) ~ 1.5 % Track reconstruction efficiency ~1% Beam-gas background ~ 0.57%Rapidity Gap in T2 0.5%Central diffraction 0.5%
EL =25.1±1.1 mb
inel T2VIS = 95%inel
el =25.1±1.1 mb
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T1+T2 (3.1 < |h| < 6.5) give an unique forward charged particle coverage @ LHC lower Mdiff reachable:minimal model dependenceon required corrections forlow mass diffraction
Mx < 3.4 GeV = 3.1 ± 1.5 mb
MX > 3.4 GeV/c2
x/ S
D d S
D/dx
SIBYLL/PYTHIA8
QGSJET-II-4
S. OstapchenkoarXiv:1103.5684v2 [hep-ph]
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”
Low mass diffraction: T1+T2 acceptance
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(Mx2 s x)
July 2012: runs at b* = 90 m
inel = 74.7 1.7 mb
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Cross section measurements @ 8 TeV
- Nel / Ninel = 0.362 0.011
tot = 101.7 2.9 mb
Same analysis strategy as for the measurement @ 7 TeV with the luminosity independent method:
•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.
The CR connection: tuning of the MC generator used in the Extensive Air Showers simulations
Forward Physics: importance of the dN/dh measurement
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Forward Physics: importance of the dN/dh measurement Observation of the extended longitudinal scaling:
p-Gold collisions
130 GeV
19.6 GeV
200 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.
• An universally accepted theoretical description is still missing!
• The theory of the Color Glass Condensate is a promising approach
(TOTEM)Fragmentation
region
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Published: EPL 98 (2012) 31002
TOTEM measurements “combined” with the other LHC experiments
TOTEM measurementscompared 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%
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Measurement of the dNCH /dh in T2
Date, Set Trigger Inelasticevents
RPposition
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
tot, inel with CMS,soft & semi-hard diffraction,correlations
Date Trigger Inelasticevents
May 1 T2 || BX ~5 M no RP
dN/dh,correlations,underlying event
May 2012: low pileup run: b* = 0.6 m, s1/2 = 8 TeV, T1 & T2 & CMS read out
July 2012: b* = 90 m, s1/2 = 8 TeV, RP & T1 & T2 & CMS read out
2011 Ion run: proof of principle2012: 1st realization of common running
• CMS & TOTEM trigger exchange• Offline data “synchronization” (orbit and bunch #) + “merging” (n-tuple level)
Joint data taking with CMS
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TOTEM analyses in progress
• 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)
• Double Pomeron exchange cross section (soft and hard), exclusive jet production in CMS in double pomeron exchange
• Differential cross section measurement for single diffraction dSD/dt and double diffraction dDD/dhmin
Double Diffraction
SingleDiffraction
Double PomeronExchange
Multiplicities
Diffractive studies Main final state topology for inelastic events
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TOTEM analyses in progress• Elastic scattering at low-t: studied of the coulomb-nuclear interference, measurement of r
) )
) )
) )
22 4
2
2/ 2
2 2
2
ddt
4
1
16
B ttot
tot B t
c G t
t
G te
t
ec
r f
r
-
-
-
= fine structure constantf = relative Coulomb-nuclear phaseG(t) = nucleon el.-mag. form factor = (1 + |t| / 0.71)-2
Total (Coulomb & nuclear)
Nuclear scatteringdominant
Coulomb-Nuclear interference
Coulomb scattering dominant
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)Siena, 21 December 2012 M. Berretti
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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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