Particles Multiplicity in TOTEM Giuseppe Latino (University of Siena - - PowerPoint PPT Presentation

Inelastic Cross Section and Forward Particles Multiplicity in TOTEM

Giuseppe Latino

(University of Siena & Pisa INFN)

(on behalf of the TOTEM Collaboration)

MPI 2012

CERN – December 3, 2012

1/20

TOTEM Physics Program Overview

Stand-Alone

• TOT

pp with a precision ~ 1-2%, simultaneously measuring (L ind. meth.):

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)

CMS-TOTEM (largest acceptance detector ever built at a hadron collider)

(CMS/TOTEM Physics TDR, CERN/LHCC 2006-039/G-124)

• Soft and hard diffraction in SD and DPE

(production of jets, bosons, h.f.)

• Central exclusive particle production
• Low-x physics
• Particle and energy flow in the forward region

MPI 2012 – Dec. 3, 2012

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TOTEM Detector Setup @ IP5 of LHC (Same of CMS)

CMS

HF

T1:3.1 << 4.7 T2: 5.3 <  < 6.5

Inelastic Telescopes:

reconstruction of tracks and interaction vertex; trigger capability with acceptance > 95 %

 T1: 18 - 90 mrad

T2: 3 - 10 mrad

= - log(tg(/2))



~14 m 10.5 m

T1 T2

Detectors on both sides of IP5

RP220 (RP147)

ZDC

Elastic Detectors (Roman Pots): reconstruction of elastically scattered and diff. p

Active area up 1-1.5 mm from beam: 5-10 rad

HF 3/20

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• p. 4

T1 (CSCs)

hit  1 mm

Vertical Pot Vertical Pot Vertical Pot Vertical Pot Horizontal Pots

RP 147

Package of 10 “edgeless” Si-detectors hit  10 µm

T2 (GEMs)

hit  100 µm

TOTEM Detectors

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MPI 2012 – Dec. 3, 2012

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Inelastic Cross Section @ 7 TeV

Direct T1 and T2 measurement: inel = Ninel /L (L from CMS)

T2 η

tracks

T2 η η

Inelastic events in T2: classification

• Tracks in both hemispheres: mainly non-Diffractive

minimum bias (ND) and Double Diffraction (DD)

• Tracks in a single hemisphere: mainly single

diffraction (SD) with MX > 3.4 GeV/c2  Optimized study of trigger efficiency and

beam gas background corrections

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MPI 2012 – Dec. 3, 2012

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Data sample

• Oct. 2011 run with β* = 90 m:

same data subsets used for the L-independent total cross section measurement

• T2 triggered events
• Low pile-up: (μ = 0.03)

Inelastic Cross Section @ 7 TeV: Corrections

Corrections to the “T2 visible” events ( 95%)

• Trigger Efficiency (from zero bias data, vs track multiplicity): 2.3  0.7 %
• Track reconstruction efficiency (based on MC tuned with data):

1.0  0.5 %

• Beam-gas background (from non colliding bunch data):

0.6  0.4 %

• Pile-up (μ = 0.03) (from zero bias data):

1.5  0.4 % Corrections for “missing” inelastic cross-section

• Events visible in T1 but not in T2 (from zero bias data):

1.6  0.4 %

• Rapidity gap in T2 (from T1 gap probability transferred to T2):

0.35  0.15 %

• Central Diffraction: T1 & T2 empty (based on MC):

0.0  0.35 %

• Low Mass Diffraction (based on QGSJET-II-03 MC):

4.2 %  2.1 %

(constrained by elastic scattering measurement, see later)

σinelastic = 73.7 ± 0.1stat ± 1.7syst ± 3.0lumi mb

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Compatible with

• ther similar
• meas. @ LHC

MPI 2012 – Dec. 3, 2012

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Uncertainty related to L (CMS): 4%

CERN-PH-EP-2012-352

Low-Mass Diffraction: T1+T2 Acceptance

T1+T2 (3.1 < || < 6.5) give an unique forward charged particle coverage @ LHC  lower Mdiff reachable: minimal model dependence

• n required corrections for

low mass diffraction

MPI 2012 – Dec. 3, 2012

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QGSJET-II-03: dN/dMdiff

MX > 3.4 GeV/c2 (T2 acceptance)

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

7/20

Constraint on low mass diffraction cross-section:

Use total cross-section determined from

elastic observables (via the Optical Theorem)  no assumption on low mass diffraction



inel = tot – el = 73.2  1.3 mb and the measured “visible” inelastic cross-section for || < 6.5 (T1, T2) inel, || < 6.5 = 70.5  2.9 mb to obtain the low-mass diffractive cross-section

(|| > 6.5 or MX < 3.4 GeV)



inel, || > 6.5 = inel - inel, | < 6.5 = 2.6  2.2 mb

(or < 6.3 mb @ 95% CL) [MC: 3.1  1.5 mb]

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Low-Mass Diffraction: Constraint from Nel

(I) CMS L + Elastic Scattering + Optical Theorem depends on CMS luminosity , elastic efficiencies & ρ:

no depenence on low mass diffraction

(small L bunches, * = 90 m, |t|min  210-2 GeV2): σinel = 73.5  1.6 mb (large L bunches, * = 90 m, |t|min  510-3 GeV2): σinel = 73.2  1.3 mb (II) (L L -independent): Elastic Scattering + Inelastic Scattering + Optical Theorem eliminates dependence on luminosity, depends on  & low mass diffraction models

using L- and -independent ratio:

σel / σinel = Nel / Ninel = 0.354  0.009

= 0.1410.007 (Compete)

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Inelastic Cross Section @ 7 TeV: Other Meas.

σinel = 72.9  1.5 mb CERN-PH-EP-2012-353

CERN-PH-EP-2012-239 EPL 96 (2011) 21002

inel = tot – el

(see J. Kašpar talk for σel and σtot measurements)

Inelastic Cross Section @ 7 TeV: Summary

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Excellent agreement among measurements:

• with different methods (understanding of systematic uncertainties and corrections)
• with other LHC experiments

(CERN-PH-EP-2012-353)

Same analysis strategy as for the measurement @ 7 TeV with the L L –independent “method II”:

• tot = 101.7  2.9 mb
• Nel / Ninel = 0.362  0.011

Inelastic Cross Section @ 8 TeV: Results

Paper draft approved for submission to journal

11/20

MPI 2012 – Dec. 3, 2012

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July 2012: runs at * * = 90 m

 inel = 74.7  1.7 mb

T2 alignment

• Internal alignment

two different track-based methods (HIP

and Millepede) implemented in order to resolve misalignment (x-, y-shifts) among detectors in a quarter

• Quarter-quarter alignment

using tracks in the overlap region

• Global alignment

each arm aligned (tilts and shifts) respect

to the nominal position by imposing the symmetry of the “beam pipe shadow”

• n each detector plane

Charged Particle Pseudo-Rapidity Density (dNch/d) @ 7 TeV

z

IP

x Final precision achieved: ~ 1 mm (x,y-shifts); ~ 0.4 mrad (plane tilts)

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May 2011 run, * * = 3.5 m, low pile-up (  0.03)

dNch/d in T2: Analysis Highlights

Data sample:

events at low luminosity and low pile-up, triggered with T2 (5.3 < || < 6.5)

Selection:

at least one track reconstructed in T2

Primary particle definition:

charged particle with  > 0.310-10 s, pT > 40 MeV/c

Primary particle selection:

• primary/secondary discrimination, data-driven

based on reconstructed track parameters (ZImpact)

Primary track reconstruction efficiency:

• evaluated as a function of the track  and pad multiplicity, MC-based
• efficiency of 80%
• fraction of primary tracks within the cuts of 75% – 90% ( dependent)

Un-folding of () resolution effects:

MC driven bin “migration” corrections

Systematic uncertainties (< 10%): dominated by primary track efficiency and global alignment correction uncertainty

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Track reconstruction in T2 is challenging because of the large amount of charged particles generated by the interaction with the material placed between the IP and T2 A detailed revision of the volumes and

• f the GEANT setting was necessary

Material contributing to secondary particle generation: Left: BP flange and ion-pumps. Right: BP cone at =5.53 and the lower edge of HF

Effect of the BP on the hit didtribution

IP HF HF

T2 telescope

90% (80% ) of the signal (tracks) in T2 is given by secondaries

Secondary Particles in T2

MPI 2012 – Dec. 3, 2012

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• A fit on the distribution of the track Zimpact parameter is used to separate primary

from secondary tracks

• We know from MC and data comparison the shape of the primary and secondary track

Zimpact distribution (double-gaussian for primaries, exponential for secondaries)

• A large part of the secondary contribution can be therefore extracted from the primary

region by fitting the track-ZImpact distribution. The fit is repeated for each  bin.

Track Z-Impact definition

90°

T2-track

dNch/d in T2: Primary Track Selection

One quarter distribution

Exponential secondary Double Gaussian Primary

Z-Impact distribution (one quarter, one  bin)

Z0·sign() < 13.5 m

MPI 2012 – Dec. 3, 2012

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Multiple scattering and magnetic field effects turn out to determine the primary charged particle PT acceptance of T2 At PT = 40 MeV/c the efficiency, including the Zimpact cut, is  80%. This is also the value which minimizes the inclusion of tracks with PT < 40 MeV/c and the losses on higher PT tracks

Particle PT (GeV/c)

Tracking Performance: PT Acceptance

MPI 2012 – Dec. 3, 2012

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16/20

Published: EPL 98 (2012) 31002

TOTEM measurements “combined” with the other LHC experiments TOTEM measurements compared to MC predictions

dNch/d in T2: Results

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:  95% inel

• Diffractive events with MDiff > 3.4 GeV
• ND events > 99%

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• combined dNch/d and multiplicity correlations
• hard diffraction: p + di-jets (* = 90m)

Date, Set Trigger Inelastic events RP position 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 , 2 central e/g) ~3.5 M 9.5  V, 11 H

tot, inel with CMS, soft & semi-hard diffraction, correlations

Date Trigger Inelastic events May 1 T2 || BX ~5 M no RP

dNch/d, correlations, underlying event

May 2012: low pileup run: * = 0.6 m, s = 8 TeV, T1 & T2 & CMS read out July 2012: * = 90 m, s = 8 TeV, RP & T1 & T2 & CMS read out

Joint Data Taking with CMS

Analyses ongoing:

2011 Ion run: proof of principle

2012: Ist realization of common running

• CMS  TOTEM trigger exchange
• Offline data “synchronization” (orbit and

bunch #) + “merging” (n-tuple level)

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T2 [T1]

Ongoing Activity on dNch/d Measurement

Analyses in progress:

• T1 measurement @ 7 TeV (3.1 < || < 4.7)
• Combined analysis CMS + TOTEM (0 < || < 6.5)
• n low-pileup run of May 2012 (@ 8 TeV):

common trigger (T2, bunch crossings), both experiments read out

• NEW: parasitical collision at β* = 90 m (July 2012, 8 TeV)

 vertex @ ~11m  shifted  acceptance for T2:

• extend  range up to  7.3 (under study)
• cross-check with T1 results in the 3.8-4.8  range (ongoing)

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16

 TOTEM detectors fully commissioned and operative  2011 data taking (s = 7 TeV) in special runs with different beam conditions (* = 3.5, 90 m) allowed the measurements of:

• inelastic p-p cross-section (with different methods)
• dNch/d with T2 (5.3 < || < 6.5)
• analysis ongoing for the dNch/d measurement with T1 (3.1<||<4.7)

 2012 data taking (s = 8 TeV) in special runs:

• measurement of inel with L-independent method
• first joint TOTEM/CMS data taking with common triggers and

both experiments read out: analysis ongoing on dNch/d measurement

• n the full  range (|| < 6.5)
• special run with displaced vertex @  11m: potentiality of dNch/d

measurement with T2 in the range 3.8 < || < 4.8 (and maybe up to 7.3)

 Possibility of dNch/d measurement for different inelastic topologies (ND, SD, DD) under study  Looking forward for more data a higher s

Summary & Outlook

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• u

• m

• r

• R

• u

• m

• r

• R

T1 T2

T2 T1

Leading Protons measured at +147m & +220m from IP Leading Protons measured at

• 147m & -220m from IP

TOTEM Experiment

TOTEM & CMS @ IP5 of LHC

TOTEM Collaboration: Bari, Budapest, Case Western Reserve, CERN, Genova, Helsinki, Penn U., Pisa/Siena, Prague, Tallin (~ 80 physicists)

B1

Each arm:

 5 planes with 3 coordinates/plane, each formed by 6 trapezoidal CSC detectors  3 degrees rotation and overlap between adjacent planes  Trigger with anode wires  Digital readout (VFAT) for ~ 13.5K ch.  Hit Resolution:  ~ 1 mm

T1 Telescope

1/4 of T1 Ageing studies at CERN GIF: no loss of performance during 12-month test, with ~ 0.07 C/cm accumulated charge on wires, a dose equivalent to ~ 5 years at Linst=1030 cm-2s-1

Fully commissioned and operative

B2

Each arm:

 10 planes formed by 20 triple-GEM semi-circular modules, with “back-to-back assembly and overlap between modules

Test Beam

T2 Telescope

Castor Calorimeter (CMS)

~ 0.4 m

T2: “GEM” Technology

 Double readout layer: Strips for radial position (R); Pads for R, f  Trigger from Pads (1560/chamber)  Digital readout (VFAT) for ~ 41.4K ch.  Hit Resolution: R ~ 100 m, f ~ 1o

pads strips

GEM Technology:

 Gas Detector  Rad-hard  High rate  Good spatial and timing resolution

T2 Triple GEM technology adequate to work at least 1 yr at L=1033 cm-2s-1 

Fully commissioned and operative

B3

Horizontal Pot: extend acceptance;

• verlap for relative

alignment using common track Absolute (w.r.t. beam) alignment from beam position monitor (BPM)

Beampipes

Roman Pots (I)

Each RP station has 2 units, 5m apart. Each unit has 3 insertions (‘pots’): 2 vertical and 1 horizontal

Units installed into the beam vacuum chamber allowing to put proton detectors as close as possible to the beam Protons at few rad angles detected down to  5 + d from beam (beam ~ 80m at RP)  ‘Edgeless’ detectors to minimize d

Horizontal Pot Vertical Pot BPM

B4

200m thick

beam

Roman Pots (II)

Each Pot:

 10 planes of Si detectors  512 strips at 45o orthogonal  Pitch: 66 m  Total ~ 5.1K channels  Digital readout (VFAT): trigger/tracking  Hit Resolution:  ~ 10 m

Readout chip VFAT Edgeless Si detector:

50 μm of dead area Integration of traditional Voltage Terminating Structure with the Current Terminating Structure Detectors expected to work up to Lint ~ 1 fb-1

Fully commissioned and operative

B5

CMS/TOTEM Common Physics Program

CMS + TOTEM  largest acceptance detector ever built at a hadron collider: the large  coverage and p detection on both sides allow the study of a wide range of physics processes in diffractive interactions

Charged particles Energy flux

TOTEM+CMS

dE/d dNch/d

Roman Pots T1,T2 T1,T2 Roman Pots

LHC, inelastic collisions

CMS CMS M M Double Pomeron Exchange Double Diffraction Single Diffraction Elastic Scattering

~ 60 mb 18 - 35 mb 10 - 16 mb 4 - 14 mb 0.2 - 1.5 mb << 1 mb

B6

MX > 3.4 GeV/c2 (T2 acceptance) x/SD dSD/dx

SIBYLL/PYTHIA8 QGSJET-II-4 low mass contribution

• S. Ostapchenko

arXiv:1103.5684v2 [hep-ph]

Low-Mass Diffraction: MC Predictions

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

Mx

2  s x

∆  -logx Mx

2  se-∆

B7

A = 506  23.0syst  0.9stat mb/GeV2 A = 504  26.7syst  1.5stat mb/GeV2 B = 19.9  0.27syst  0.03stat GeV-2

| | el / t B

e A dt d



  |t|dip= 0.53 GeV2

~ |t|7.8 25.4 ± 1.0lumi ± 0.3syst ± 0.03stat mb (91% directly measured) 24.8 ± 1.0lumi ± 0.7syst ± 0.2stat mb (67% directly measured)

Integrated elastic cross-section:

El = El, Meas. + El, Extr.

(L

L from CMS)

Elastic Scattering Differential Cross-Section @ 7 TeV

EPL 95 (2011) 41001 EPL 96 (2011) 21002 CERN-PH-EP-2012-239

Analysis ongoing on additional data set (2 GeV2 < |t| < 3.5 GeV2) None of the theoretical models really fit the data B8

Inelastic Cross Section @ 7 TeV: Summary

B9

CERN-PH-EP-2012-352 CERN-PH-EP-2012-353 CERN-PH-EP-2012-239 EPL 96 (2011) 21002

• 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/d measurement

B10

The Beam Pipe “Shadow” on T2

IP5

HF HF

Beam Pipe cone at  ~ 5.54 (>100 radiation lengths)

B11

|ZImpact| < 5m

Definition of the track ZImpact parameter:

T2 inelastic event detection efficiency (at least a ch. particle generated in the T2 acceptance): 99.5%

Average data APM (7 TeV)

Bin width: 0.05

APM: Average Pad-Cluster Multiplicity

T2 Tracking performance: efficiency

Event reconstruction efficiency

B12

Track ZImpact before and after the global misalignment correction in data and in a MC, where the misalignment geometry is simulated:

Maximum tilt angle measured in the data = 8mrad (T2 acceptance: 3-10 mrad !)

Tuned MC Data primaries secondaries

Primary/secondary separation is impossible without the global alignment.

Importance of Global Misalignment

B13

Resolution: RMS of the difference between the reconstructed  and the generated . Vtx smearing DZ= 5 cm, 2<E<80 GeV p-

Two estimators of  were studied: IMP and RZ

IMP = average of the  of the track hits (each one calculated with the vertex at (0,0,0)) RZ = pseudorapidity of the track calculated with the polar angle of the track in the RZ plane

 RZ  IMP

Only tracks with |ZImpact|< 5m are included IMP implicitly performs a vertex constraint. Smaller at high  because of the smaller contribution of B and Vtx smearing. RZ grows as Dη ∼ Dθ/θ, more dependent on misalignment. B14

 IMP  RZ Tracking Performance:  Resolution

• 1. Data/MC comparison of

“half quarter” trk efficiencies

• 2. Effect of wrong

misalignment parameters

• n the measured dN/d
• 3. Maximum variation of the

secondaries contamination from different MC.

Evaluation method

• 4. Fit/fitting-interval

uncertainty

• 5. MC spectrum and B

intensity variation

• 6. Different MC estimates
• 7. Data/MC discrepancy
• n the effect of the cut on

the track 2-probability. 8-9. Dedicated analysis

• n bunch-crossing

samples

(*) not all the contributions have been added in quadrature

(*)

Common to all the quarters Quarter dependent

dNch/d in T2: Systematic Errors

B15

RP insertions in normal physics runs (* = 0.6 m)

• hard diffraction together with CMS (high diffractive masses reachable)
• proton acceptance: x > 2-3 %, any t
• study of closest possible approach of the hor. RPs (i.e. acceptable beam losses)

 essential for all near-beam detector programmes at high luminosity after LS1

Collimators needed behind the RP to protect quadrupoles

Request a low-pileup run (~ 5 %) with RPs at * = 0.6 m (in May RPs not aligned)  study soft central diffraction final states with 2 leading protons defining Pomeron-Pomeron mass M2 = x1 x2 s (good x resolution at * = 0.6 m  s(M) ~ 5 GeV) Participation in the p-Pb runs with insertions of the RPs on the proton side  study diffractive/electromagnetic and quasi-elastic p-Pb scattering p-Pb test run in September with CMS was successful (T2 trigger given to CMS)

Runs Planned for 2012-13

B16

[K. Oesterberg, pA @ LHC workshop, June 2012]

pA Minimum Bias Physics

B17