p. 1Mario Deile –

TOTEM: Prospects for Total Cross-Section and Luminosity Measurements

M. Deile

(CERN)

for the TOTEM Collaboration13.01.2011

ultimate goal: ±1%

(2011: ±3%)

p. 2Mario Deile –

Luminosity-Independent Method based on the Optical Theorem

02

2

1

16

t

eltot dt

dN

L

ineleltot NN L

inelel

teltot NN

dtdN

0

2

)/(

1

16

• measure the inelastic event rate Ninel (with forward tracking chambers);• measure the elastic event rate Nel (detect surviving protons with Roman Pots) and extrapolate the cross-section dNel/dt to t = 0;• take = Re f(0) / Im f(0) [f(0) = forward elastic amplitude]

from theory, e.g. COMPETE extrapolation:

later: try to measure at km: elastic scattering in the Coulomb-nuclear interference region

Requirements for this method: • Beam optics providing proton acceptance at low |t| in the Roman Pots• Detector coverage at high ||• Trigger capability for all detector systems

0058.00025.0

.00150 1361.0

0

22

|/16

1

tel

inelel

dtdN

NN

L

p. 3Mario Deile –

The TOTEM Detector Setup

p. 3

T1 T2

installationin progress

now installed operational in 2010operational in 2010

T1 “” arm during installation

p. 4Mario Deile –

4

5

3

2

1

PHOJET

s = 7 TeV

T2

Uncertainties in inelastic cross sections large:

• non-diffractive min. bias (MB): 40 60 mb

• single diffraction (SD): 10 15 mb

• double diffraction (DD): 4 11 mb

Accepted event fractions:

T2T1 T1

Acceptance for Inelastic Events

p. 4

p. 5Mario Deile –

Measurement of the Inelastic Rate Ninel

T1/T2 trigger and selection loss

Minimum bias 50 mb 0.05 mb

Single diffractive 12.5 mb 4.83 mb

Double diffractive 7.5 mb 1.21 mb

Total 70 mb 6.1 mb

Correction for trigger losses:

• Extrapolation of the mass spectrum: fit dN/dM2 ~ 1/Mn with n ~ 2uncertainty depends on the purity of the diffractive event sample used for the extrapolation(e.g. errors from minimum bias events misidentified as diffractive events)

• Independent handle on low-mass diffraction:At * = 90 m the protons for all diffractive masses are visible (for |t| > ~10-2 GeV2).

total uncertainty on Ninel : 1.0 mb (1.4 %).

Trigger Losses at s = 7 TeV, requiring 3 tracks pointing to the IP

Acceptance single diffraction

Loss at low diffractive masses M

A [

1 / 2

Ge V

]

M [GeV]

simulated

extrapolateddetected

dN/d

( 1/M

2 ) [

1 / G

eV-2]

1/M2 [GeV-2]

M

p. 6Mario Deile –

Roman Pot System: Leading Proton Detection

p. 6

Horizontal Pot Vertical Pot BPM

scattering angle

p. 7Mario Deile –

Elastic Scattering

90m1540m

3.5m

7 TeV

squared 4-momentum transfer

t p

exponential region

RP220: detectors at 10 from beam centre

Elastic Scattering Acceptance at s = 7 TeV

|t50| = 0.0008 GeV2

|t50| = 0.024 GeV2

N = 3.75 m)

N = 1 m)

p. 8Mario Deile –

“Raw” distribution:

- No smearing corrections

- No acceptance corrections

- No background subtraction

Syst. error sources under study:

alignment, beam position and

divergence, background,

optical functions, efficiency, …

84K elastic scattering candidate events TOTEM special run (~ 9 nb-1)

s = 7 TeV

* = 3.5 m

RPs @ 7 (V) and 16 (H)

Preliminary t-distribution

0.7 GeV2

p. 9Mario Deile –

Elastic Scattering at low |t|

Exponential Slope B(t)

with detectors at* = 1540 m: |t50| = 0.0008 GeV2

* = 90 m: |t50| = 0.024 GeV2

fit interval

best parameterisation:

B(t) = B0 + B1 t + B2 t2

* = 90 m* = 1540 m

( )dd

B t tt e Cross-section

7 TeV

p. 10Mario Deile –

Extrapolation to the Optical Point (t = 0) at * = 90 m

∫ L dt = 2 nb-1

(extrapol. - model) / model in d/dt |t=0 Statistical extrapolation uncertainty

• Common bias due to beam divergence (angular spread flattens dN/dt distribution):

% @14 TeV % @7 TeV, can be corrected.

• Spread between most of the models: ±1% (Islam model needs different treatment, can be distinguished at larger |t|)

• Systematic error due to uncertainty of optical functions: ± 1.5 % , assuming L/L = 1%• Different parameterisations for extrapolation (e.g. const. B, linear continuation of B(t)): negligible impact

14 TeV 14 TeV

Study at 14 TeV, N = 3.75 m rad

upper bound:

0.25 GeV2

p. 11Mario Deile –

Acceptance versus Energy and Detector Approach

Advantage of 7 or 8 TeV w.r.t. 14 TeV: |t50| reduced shorter extrapolation

reduced model dependencereduced statistical uncertainty

x 0.6N = 3.75 m rad)

N = 1 m rad)

closer approach

lower E

x 0.4

p. 12Mario Deile –

Desired Scenario for Runs at * = 90 m

(subject to discussions with MPP and collimation expertsand to commissioning progress / surprises)

4 special runs (assuming E = 4 TeV):

n

[m rad]RP distance(window)

bunching L [cm-2 s-1]

(inelastic pileup)

|t50| [GeV2]

statistics

per 8 h

statistical uncertainty

of extrapol.

3 1b, 7 x 1010 p/b 6.9 x 1027 0.05 0.019 0.2 nb-1 ~ 1.5 %

3 1b, 7 x 1010 p/b 6.9 x 1027 0.05 0.011 0.2 nb-1 ~ 1 %

1 1b, 6 x 1010 p/b 1.5 x 1028 0.1 0.0070 0.4 nb-1 < 1 %

1 1b, 6 x 1010 p/b 1.5 x 1028 0.1 0.0043 0.4 nb-1 < 1 %

Dominated by systematics small RP distance much more important than luminosity !

Crucial: good knowledge of the optical functions

Aim: contribution from optical functions not larger than angle resolution limit from beam divergence

Ly / Ly < 1.1 % or y / y < 1.1 %

Lx / Lx < 0.2 % or x / x < 0.2 % (but our error estimates are based on 1%: sufficient)

p. 13Mario Deile –

Combined Uncertainty in tot

At * = 90 m, s = 7 TeV :

• Extrapolation of elastic cross-section to t = 0: ± 2 %

• Total elastic rate (strongly correlated with extrapolation): ± 1 %

• Total inelastic rate: ± 1.4 %

• Error contribution from (1+2) using full COMPETE error band = 33 % (very pessimistic): ± 1.2 %

Total uncertainty in tot including correlations in the error propagation: ± 3 %

Slightly worse in L (~ total rate squared!) : ± 4 %

20

1

/16 el t

elto

nt

i el

dN dt

N N

2

0

21

/16el inel

el t

N N

dN dt

L

p. 14Mario Deile –

Outlook: Extrapolation with the Ultimate Optics (* = 1540 m)

|t50| = 0.0008 GeV2 for RP window at 10 good lever arm for choosing a suitable fitting function for the extrapolation to t = 0.

Complication: Coulomb-nuclear interference must be included:

2

2

d( ) ( ) 1 ( ) ( )

d C Nf t f t i t tt sp

[Cahn, Kundrát, Lokajíček]

where and (t) is a function of fC(t) and fH(t). 2

0 1 2( )b b t b t ti

Nf t Ae e

For most models: extrapolation within ± 0.2 %.

Islam model needs different treatment; can be distinguished in the visible t-range.

1540m

7 TeV

14 TeV !!!

Difficulties: - very-high-* optics at 7 or 8 TeV still to be developed (*=1540m exists only for 14 TeV).

- additional magnet powering cables needed.

p. 15Mario Deile –

Outlook: Measurement of in the Coulomb-nuclear Interference Region?

Aim: get also the last ingredient to tot from measurement rather than theory.

might be possible at 8 TeV with RPs at 8 incentive to develop very-high-* optics before reaching 14 TeV !E.g. try to use the same optics principle as for 90m and unsqueeze further.

N = 3.75 m rad)

N = 1 m rad)

p. 16Mario Deile –

Summary

TOTEM is ready for a first tot and luminosity measurement in 2011

with * = 90m using the Optical Theorem.

Expected precision: ~3% in tot , ~4% in L

Wish: start soon with the development of the * = 90m optics to have

enough time for learning.

Desired running conditions: low beam intensity, small RP distance to the beam

Longer term:

Measurement at the 1% level with very-high-* optics (~1 km);

might give access to the parameter if the energy is still low (s ~ 8 TeV);

needs optics development work.

p. 17Mario Deile –

p. 18Mario Deile –

Backup

p. 19Mario Deile –

Preferred fit predicts:

asymptotic behaviour: 1 / ln s for s

Elastic Scattering: = f(0) / f(0)

0058.00025.0

.00150 1361.0

COMPETE [PRL 89 201801 (2002)]

=

0.1

35 ±

0.0

44

p. 20Mario Deile –

Elastic Scattering from ISR to LHC

546 GeV: CDF: 0.025 < |t| < 0.08 GeV2 : B = 15.28 ± 0.58 GeV-2 (agreement with UA4(/2))

1.8 TeV: CDF: 0.04 < |t| < 0.29 GeV2 : B = 16.98 ± 0.25 GeV-2

E710: 0.034 < |t| < 0.65 GeV2 : B = 16.3 ± 0.3 GeV-2

0.001 < |t| < 0.14 GeV2 : B = 16.99 ± 0.25 GeV-2 , = 0.140 ± 0.069 E811: 0.002 < |t| < 0.035 GeV2 : using B from CDF, E710: = 0.132 ± 0.056

1.96 TeV: D0: 0.9 < |t| < 1.35 GeV2

diffractive structure

Coulomb - nuclear interference

pQCD 1/ |t|8

pp 14 TeVBSW model

“Pomeron” exchange e– B |t|

-t [GeV2]

d/

dt [

mb

/ GeV

2 ]

UA4,

CDF

UA4

E710/811,

CDF

Block model

B(s) = Bo + 2P’ ln(s/so) 20 GeV-2 at LHC

0 1 2-t [GeV2]

p. 21Mario Deile –

Relative Luminosity Measurement

For running conditions where measurement via Optical Theorem impossible:relative measurement after a prior absolute calibration at * = 90 m or 1540 m.

Examples:

• partial inelastic rates, e.g. (T2 left) x (T2 right): robust against beam-gas background

• for running conditions with pileup: count zero-events, e.g. failing (T2 left) x (T2 right):

e.g. P(n=0) = 15 % @ L=1033 cm-2s-1 , bunches

Also usable for continuous luminosity monitoring (to be studied further).

1ln ( 0)

tot T2lxT2r

P nA t

L

p. 22Mario Deile –

Best combined fit by COMPETE:

But models vary within (at least)

Measurements of tot

4.1111.5 1.2 mb2.1tot

Conflicting Tevatron measurements

at 1.8 TeV:

E710: tot = 72.8 ± 3.1 mb

E811: tot = 71.42 ± 2.41 mb

CDF: tot = 80.03 ± 2.24 mb

Disagreement E811–CDF: 2.6

10 %.20

p. 23Mario Deile –

TOTEM Detector Configuration

RP1RP1 (RP2)(RP2) RP3RP3

220 m220 m(180 m)(180 m)147 m147 m

~14 m

T1:3.1 << 4.7

T2: 5.3 < < 6.5

10.5 m T1T1 T2T2

HF

Symmetric experiment: all detectors on both sides!

CMSCMS

p. 24Mario Deile –

Level-1 Trigger Schemes

p

Elastic Trigger: 30 mb

Single Diffractive Trigger: 14 mb

Double Diffractive Trigger: 7 mb

Central Diffractive Trigger

(Double Pomeron Exchange DPE) 1 mb

Non-diffractive Inelastic Trigger: 58 mb

tot 110 mb

pp

T1/T2

RP RPCMS

p

p

Always try to use 2-arm coincidence to suppress background.

p. 25Mario Deile –

Acceptance Losses and Selection Losses

p. 26Mario Deile –

Detection of Leading Protons

TOTEM: Proton Acceptance in (t, ):(contour lines at A = 10 %) RP220

= 0.5m - 2m

* *det yy y yy DL v y

* *det x x x xx L v x D

(x*, y*): vertex position

(x*, y

*): emission angle

= p/p

Transportequations:

10

x(mm)x [mm]

horizontal

Si detector

vertical

Si detector

vertical

Si detector

y [m

m]

Example: Hit distribution @ TOTEM RP220 with * = 90m

t ~ -p2 * 2

= 1540 m L = 1028 – 2 x 1029 95% of all p seen; all

= 90 m L = 1029 – 3 x 1030 65% of all p seen; all

= 0.5 – 2 m L = 1030 – 1034 p with seen; all t

Optics properties at RP220:

r e

solv

ed