1. TOTEM early measurements
Fabrizio Ferro – INFN Genova
On behalf of TOTEM Collaboration
INFN Sezione di Bari & Politecnico di Bari, Bari, Italy
MTA KFKI RMKI, Budapest, Hungary
Case Western Reserve University, Cleveland, Ohio, USA
CERN, Geneva, Switzerland
Università di Genova & Sezione INFN, Genova, Italy
University of Helsinki & HIP, Helsinki, Finland
Penn State University, University Park, USA
Academy of Sciences, Praha, Czech Republic
Università di Siena & Sezione INFN-Pisa, Italy
Estonian Academy of Sciences, Tallinn, Estonia
2008
Fabrizio Ferro – INFN Genova

2. Fabrizio Ferro – INFN Genova
Experimental area
Leading protons detected at
-220m & -147m from IP
LHC - IP5
CMS
TOTEM
Leading protons detected at 147m and 220m from IP.
CMS coverage extended by TOTEM T1 and T2 telescopes
Leading protons detected at
+220m & +147m from IP
2008
Fabrizio Ferro – INFN Genova

3. Fabrizio Ferro – INFN Genova
Physics program
Total pp cross section
Elastic pp scattering in a wide t range 3 < -t < 10 GeV2 (-t~p2q2)
Soft diffraction
Charged multiplicity measurement in a wide  range
Study of low-xBj dynamics
Hard diffraction (single, central and with jet, W and heavy flavour production)
Exclusive particle production in central diffraction (DPE: Double Pomeron Exchange)
 and p physics
Charged particle flow
TOTEM CMS TOTEM
Energy flow 
with CMS
2008
Fabrizio Ferro – INFN Genova

4. Fabrizio Ferro – INFN Genova
Total pp cross section
Possible TOTEM measurement
Final goal: ~1 % accuracy
Early goal: ~5 % accuracy
Luminosity independent method: measurement of elastic and inelastic rate
- Fundamental ingredient in any cross section measurement
COMPETE collaboration
Fit from available data:
COMPETE Collaboration, PRL 89 (2002)
2008
Fabrizio Ferro – INFN Genova

5. Fabrizio Ferro – INFN Genova
Experimental setup
Inelastic telescopes: Tracking of charged particles & vertex reconstruction in inelastic events (main goal: measurement of Ninel)
T1: 3.1 <  < 4.7
T2: 5.3 <  < 6.5
T1: 18 – 90 mrad
T2: 3 – 10 mrad
IP5
~ 10 m T1
HF (CMS) T2
CASTOR (CMS)
~ 14 m
Roman Pots: measurement of elastic and diffractive protons near the outgoing beam
Scattering angles: 5 – 500 rad (depending on beam optics)
IP5
RP147
RP220
2008
Fabrizio Ferro – INFN Genova

6. Fabrizio Ferro – INFN Genova
T1 telescope
Cathode Strip Chambers(CSC)
3.1 < |h| < 4.7
5 planes: measurement of 3 coordinates per plane
Primary vertex reconstruction to discriminate background (not beam-beam events) for the measurement of Ninel
Vertex resolution:  ~ 2 cm, z ~ 20 cm
Trigger with anodic wires
() ~ 0.02  0.2 (depending on particle momentum)
Multiplicity measurement
CSC 3m
Spatial resolution ~1mm
2008
Fabrizio Ferro – INFN Genova

7. Fabrizio Ferro – INFN Genova
T1: preparing for installation
Support rails
Storage and cosmic tests
Status: preparing to install in 2009
¼ ofT1
2008
Fabrizio Ferro – INFN Genova

8. Fabrizio Ferro – INFN Genova
T2 telescope
3-GEM (Gas Electron Multiplier)
5.3 < |h| < 6.5
10 semi-planes which provide 2 coordinates on both beampipe sides
Primary vertex reconstruction
Trigger with pads
() ~ 0.04 – 0.1
Multiplicity measurement
65(j) x 24(h) = 1560 pads
Pads: Dh x Dj = 0.06 x 0.015p
2x2 mm2 __ 7x7 mm2
Strips: 256 (width/pitch: 80/400 mm)
Radial resolution: ~ 100 m
Azimuthal resolution: ~ 1°
2008
Fabrizio Ferro – INFN Genova

9. Fabrizio Ferro – INFN Genova
T2 installation
Test Beam
T2 and the beampipe
CMS T2
Status: ¼ of T2 installed. Complete installation in 2009
2008
Fabrizio Ferro – INFN Genova

10. Fabrizio Ferro – INFN Genova
Roman Pots
BPM fixed to RP structure  beam position
Horizontal Pot Vertical Pots BPM
RP station: 2 units, 4 m distance
1 unit: 2 vertical pots / 1 horizontal and 1 BPM
2008
Fabrizio Ferro – INFN Genova

11. Fabrizio Ferro – INFN Genova
RP installed at 147 m and 220 m on both sides of IP5
2008
Fabrizio Ferro – INFN Genova

12. Fabrizio Ferro – INFN Genova
2008
Fabrizio Ferro – INFN Genova

13. Fabrizio Ferro – INFN Genova
Roman Pot and Proton Detectors
10 planes of Si detectors
512 strips at  45°
Pitch: 66 m
Resolution: ~ 20 m
Detector overlap
Ferrite
Status: detectors installed in horizontal RPs at 220m. Complete 220m in 2009 and 147m just after.
RP vertical
RP horizontal
RP vertical
2008
Fabrizio Ferro – INFN Genova

14. Planar technology + CTS (Current Terminating Structure)
Si CTS edgeless detectors
Proton detection down to 10beam, + d (beam, = 80  600 m)
To minimize d : detectors with highly reduced inactive edge (”edgeless”)
Planar technology + CTS
(Current Terminating Structure) I2 I1 + -
biasing ring Al p+ n+
cut edge
current
terminating
ring
SiO2
n-type bulk
50µm
Micro-strip Si detectors designed to reduce the inefficiency at the edge.
Inefficient edge ~ 50 m
50 µm
2008
Fabrizio Ferro – INFN Genova

15. Optics and Beam Parameters
(standard step in LHC start-up)
= 90 m
(early TOTEM optics)
= 1540 m
(final TOTEM optics)
Crossing angle
0.0
N of bunches
156 43
N of part./bunch
(4 – 9) x 1010
3 x 1010
Emittance n [m ∙ rad]
3.75 1
10 y beam width at RP220 [mm]
~ 3
6.25
0.8
Luminosity [cm-2 s-1]
(2 – 11) x 1031
(5 – 25) x 1029
1.6 x 1028
* = 90 m ideal for early running:
fits well into the LHC start-up running scenario;
uses standard injection (b* = 11m)  easier to commission than 1540 m optics
wide beam  ideal for training the RP operation (less sensitive to alignment)
* = 90 m optics optimized both for stot and diffraction.
2008
Fabrizio Ferro – INFN Genova

16. Fabrizio Ferro – INFN Genova
TOTEM physics and LHC optics
Feasible physics depends on running scenarios:
luminosity
beam optics (β*)
acceptance of proton detectors
precision in the measurement of scattering angle (beam divergency )
stot(~1%), low t elastic, stot(~5%), low t elastic, high t elastic,
soft diffraction (semi)-hard diffraction hard diffraction
cross section luminosity
EARLY
 mb b nb
* (m)
L (cm2 s1)
TOTEM runs Standard runs
2008
Fabrizio Ferro – INFN Genova

17. Proton detected using:
Proton detection strategy
Hit distribution in the RP at 220m (diffractive scattering)
low *: 0.5  2 m
high *: 90
y(mm)
y(mm)
y ~ yscatt ~ | ty |
x ~   p/p
10
10
x(mm)
x(mm)
Proton detected using:
momentum loss (low *) or transverse momentum (high *)
2008
Fabrizio Ferro – INFN Genova

18. Fabrizio Ferro – INFN Genova
Proton Acceptance
> 10 % acceptance for RP 220 m
DPE
Measurement of cross sections for different processes (Elastic, SD, DPE, …)
Study of corresponding rapidity gaps and their suppression
2008
Fabrizio Ferro – INFN Genova

19. Fabrizio Ferro – INFN Genova
Elastic scattering
b*=90m
L=3x1030
b*=2m
L=1032
2x109 -
2.3x107 -
4000
1.2x105
500
4x104
b* = 90 m 30
3000
b* = 11 m 1
160
b* = 2 m
0.3 50
N events/day
2008
Fabrizio Ferro – INFN Genova

20. Elastic scattering at low |t|
Exponential slope B(t)
b* = 1540 m
b* = 90 m
fit interval
b* = 1540 m: |t|min = GeV2
b* = 90 m: |t|min = 0.04 GeV2
best parameterization: B(t) = B0 + B1 t + B2 t2
2008
Fabrizio Ferro – INFN Genova

21. Extrapolation to the Optical Point (t = 0) at b* = 90 m
(extrapol. - model) / model in d/dt |t= Statistical extrapolation uncertainty
∫ L dt = 2 nb-1 ( cm-2 s-1)
Common bias due to beam divergence : – 2 % (angular spread flattens dN/dt distribution)
Spread between most of the models: ±1%
Systematic error due to uncertainty of optical functions: ± 3%
Different parameterizations for extrapolation tested (e.g. const. B, linear continuation of B(t)): negligible impact
2008
Fabrizio Ferro – INFN Genova

22. Fabrizio Ferro – INFN Genova
Trigger schemes p
T1/T2 RP
CMS
Elastic Trigger
Single Diffractive Trigger
Double Diffractive Trigger
Central Diffractive Trigger
(Double Pomeron Exchange DPE)
Non-diffractive Inelastic Trigger p
Big uncertainties on expected individual cross sections p p
2008
Fabrizio Ferro – INFN Genova

23. Measurement of the inelastic rate
Inelastic double arm trigger: robust against background, inefficient at small M
Inelastic single arm trigger: suffers from beam-gas + halo background, best efficiency
Inelastic triggers and proton (SD, DPE): cleanest trigger, proton inefficiency to be extrapolated
Trigger on non-colliding bunches to determine beam-gas + halo rates.
Vertex reconstruction with T1, T2 to suppress background
Extrapolation of diffractive cross-section to large 1/M2 assuming ds/dM2 ~ 1/M2 :
- dsSD/dM can be measured with high b optics, not with low b (only for very high M)
Acceptance
single diffraction
simulated
extrapolated
detected
Loss at low diffractive masses M
s [mb]
trigger loss [mb]
systematic error after extrapolations [mb]
Non-diffractive inelastic 58
0.06
Single diffractive 14 3
0.6
Double diffractive 7
0.3
0.1
Double Pomeron 1
0.2
0.02
Total 80
3.6
0.8
2008
Fabrizio Ferro – INFN Genova

24. Fabrizio Ferro – INFN Genova
tot measurement
* = 90 m / * = 1540 m
Early
Later (asap)
Extrapolation of the elatic cross section to t = 0: ± 4 % /  0.2 %
Total elastic rate: ± 2 % /  0.1 %
Total inelastic rate: ± 1 % /  0.8 %
(error dominated by the loss of single and double diffractive events)
Contribution from (1+2) using the systematic error from COMPETE d/ = 33% ± 1.2 %
=> Total error on tot (taking into account correlations): ± 5 % /  (12) %
Error on luminosity (~ squared total rate) : ± 7 % /  2 %
A precise measurement with * = 1540 m needs:
Better knowledge of the optical functions
RP alignment precision < 50 m
2008
Fabrizio Ferro – INFN Genova

25. Very first measurements with low b* optics
Using horizontal RPs
dSD/dM (SD events with high mass)
0.02 <  < 0.18  2 < M < 6 TeV
(M)/M = 24 %
dDPE/dM
250 < M < 2500 GeV
(M)/M = 2.13.5 %
Using vertical RPs: high t elastic scattering
dElastic/dt < |t| < 10 GeV (t)  0.25|t|
 p p SD
MX2 =  s
Rapidity Gap
-ln    p X
2 p p2
1 p p1
DPE 
Rapidity Gap
-ln 1
Rapidity Gap
-ln 2 p1 X p2
MX2 = 1 2s 
2008
Fabrizio Ferro – INFN Genova

26. Soft diffraction with high b* optics
= 90 m: %
= 1540 m: 95 %
of all diffractive protons are detected, independently on their 
Reconstruction of x via protons or rapidity gap (Dh= –ln x):
= 90 m: sp(x) = 6 x (without CMS vertex knowledge)
= 1540 m: sp(x)  9 x 10-3
s(Dh) = 0.8 – 1  sDh(x) = (0.8 – 1) x
proton 2
proton 1
Dh1
Dh2 M
DPE Mass Distribution (acceptance corrected)
via rapidity gap (T1, T2)
s(x)/x = 100%
via proton (b*=90m)
via rapidity gap (CMS)
via rapidity gap (T1, T2)
proton resolution limited by
LHC energy spread
various diffractive studies (Single Diffraction and Double Pomeron Exchange)
to be extended later together with CMS.
2008
Fabrizio Ferro – INFN Genova

27. T1/T2: charged multiplicity
Measurement of charged multiplicity for different processes
Important also for cosmic ray physics (e.g. for MC generator validation)
Identification and measurement of rapidity gaps
minimum bias
Acceptance:
3.1 <  < 4.7 (T1) & 5.3 <  < 6.5 (T2)
() = 0.04  0.2, no mom. & limited  info
dNch/dh [1/unit]
Charged multiplicity
single diffractive
2008
Fabrizio Ferro – INFN Genova

28. Fabrizio Ferro – INFN Genova
Multiplicity in single diffraction
T1/T2 coverage
Multiplicity for different x ranges:
high cross sections, but
partial rapidity coverage
2008
Fabrizio Ferro – INFN Genova

29. Fabrizio Ferro – INFN Genova
Conclusions
Setup and optics
TOTEM has partially installed its detectors and will finish the installation in the first months of 2009 ready for the new LHC start-up
TOTEM measurements strongly depend on beam optics. Requested short runs at b* = 90m optics to maximize physics sensitivity.
Early measurements
With 90m optics:
5% measurement of stot
inclusive studies of the main diffractive processes
study of the elastic scattering already in a wide range of t
measurement of forward charged multiplicity
With low b* optics:
study of SD and DPE at high masses
elastic scattering at high t (t > 2 GeV2)
Later
A more precise measurement (1-2%) of stot will need the b*=1540m optics already foreseen for dedicated short TOTEM runs
An extensive program of physics together with CMS is foreseen
2008
Fabrizio Ferro – INFN Genova

30. Fabrizio Ferro – INFN Genova
Back up
2008
Fabrizio Ferro – INFN Genova

31. Fabrizio Ferro – INFN Genova
The b* = 90 m optics
Concept: Optics optimised for both elastic and diffractive scattering.
Proton coordinates w.r.t. beam in the RP at 220 m:
(x*, y*): vertex position
(x*, y*): emission angle
x = Dp/p
Ly = 265m (large)
vy = 0
Lx = 0
vx = – 2
D = 23mm
vertical parallel-to-point focussing
 optimum sensitivity to y*
and hence to t (azimuth. symmetry)
elimination of x* dependence
enhanced sensitivity to x in diffractive events,
horizontal vertex measurement in elastic events.
RP (220m) hit distribution (elastic)
x-projection
horiz. vertex distribution (shape, width)
 assuming round beams: luminosity from beam parameters
 directly: beam position measurement to ~ 1mm every minute
t ~ 10 s
2008
Fabrizio Ferro – INFN Genova