giornata del dipartimento di fisica

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

Siena, 21 December 2012 M. Berretti 2

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


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


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


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


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


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


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


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


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


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


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 )


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


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


(Mx2 s x)

July 2012: runs at b* = 90 m

inel = 74.7 1.7 mb


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


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


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%


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


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


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!!


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

23

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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