XIV International Workshop on Deep Inelastic Scattering
April 20-24, 2006, Tsukuba (Japan)
Diffractive studies and
forward physics at CMS
Marta Ruspa, Univ. Piemonte Orientale-Novara & INFN-Torino
DIS06, 20-24/04/06, M. Ruspa
Forward detectors at CMS
CMS IP
T1/T2, Castor, BSC
ZDC RPs@150m
RPs@220m
CMS detectors along beam line:
Cal with || ≤ 3, HF with 3 ≤|| ≤ 5
Castor calorimeter, behind T2 with 5.2 ≤|| ≤ 6.5
Beam Scintillation counters BSC
Zero-degree calorimeter ZDC
420m
TOTEM detectors:
T1 (CSC) in CMS endcaps
T2 (GEM) in shielding behind HF
T1 + T2: 3 ≤ || ≤ 6.8
Roman pots with Si detectors on 2 sides at up to 220 m
Possible addition: FP420
Unprecedented rapidity coverage at a hadron collider
2
DIS06, 20-24/04/06, M. Ruspa
Roman pot acceptance
High * (1540m) @ 1028 - 1029cm-2s-1 : see J. Whitmore’s talk
90% of all diffractive protons are seen in TOTEM RPs
Low * (0.5 m) - nominal LHC beam optics @ 1033 - 1034cm-2s-1:

220 m: 0.02 <  < 0.2

420 m:
0.002 <  < 0.02
TOTEM
FP420
XL= 1 - : longitudinal momentum loss
Unprecedented ξ coverage at a hadron collider
Standard optics * = 0.5 m assumed from now on
3
CMS/TOTEM diffractive physics program


DIS06, 20-24/04/06, M. Ruspa
TOTEM and CMS pursue a common diffractive and forward physics program
to be described in a common document
A wealth of results already available
[see HERA-LHC Workshop proceedings]
Thanks to TOTEM people and to all contributors!
The results presented in the following do not depend on the specific
hardware implementation of the T1 and T2 detectors or of the roman
pots; they hold for any tracker system with the T1, T2 rapidity coverage
in conjunction with RPs at 220 m and 420 m from the IP.
4
DIS06, 20-24/04/06, M. Ruspa
Double Pomeron exchange:
Single diffraction:
X
2 gluon exchange with vacuum
quantum numbers
“Pomeron”
p p  p X
X
p p  p X p
Double diffraction:
X
p p  X Y
Y
The accessible physics is a
function of the integrated
luminosity
5
Map to diffractive/forward physics in CMS
DIS06, 20-24/04/06, M. Ruspa
Low lumi
Rapidity gap selection possible
HF, Castor, BSCs, T1, T2
Proton tag selection optional
RPs at 220m and 420 m
Diffraction is about 1/4 of tot
High cross section processes
“Soft” diffraction
Interesting for start-up running
Important for understanding pile-up
6
DIS06, 20-24/04/06, M. Ruspa
Pile-up: numbers!
PHOJET: ALL PROCESSES
NONDIF.INELASTIC
ELASTIC
DOUBLE POMERON
SINGLE DIFFR.(1)
SINGLE DIFFR.(2)
DOUBLE DIFFRACT.
110 mb
51 mb
33 mb
1.95 mb
7.66 mb
7.52 mb
9.3 mb
1 mb = 100 events/s
@ 10 29 cm-2 s-1
Number
Numberof
ofpileup
pileupevents
eventsper
perbunch
bunchcrossing
crossing==
==Lumi*
Lumi*cross
crosssection
section**bunch
bunchtime
timewidth
width**total
totallhc
lhcbunches
bunches//filled
filledbunches
bunches==
-28(m
-3 (b/mb)
-3 (b/mb)
==10
103434cm
cm-2-2ss-1-1**10
1044(cm^
(cm^22/m^
/m^22))**10
10-28
(m22//b)
b)**51
110
mbmb
* 10
* 10
* 25
* 25
(ns)
(ns)
* *
10
10-9-9(s/ns)
(s/ns)**3564
3564//2808
280817
35
Selection of diffractive events
32  0 is valid in the central detector region, but must be corrected
This
 1x10
number
with rapidity gap only possible
33 cm-2s-1,
for the elastic and diffractive cross section
in the forward
region!
at luminosities
below 10
 1x1033  3.5
where event pile-up is absent
 2x1033  7
7
Map to diffractive/forward physics in CMS
DIS06, 20-24/04/06, M. Ruspa
Low lumi
Rapidity gap selection possible
HF, Castor, BSCs, T1, T2
Proton tag selection optional
RPs at 220m and 420 m
Diffraction is about 1/4 of tot
High cross section processes
“Soft” diffraction
Interesting for start-up running
Important for understanding pile-up
QCD: SD and DPE production of vector bosons, heavy quarks, high ET jets
Diff PDFs and generalized PDFs
Low-x structure of the proton
High-density regime
γ γ and γp interactions (QED)
Forward energy flow - input to cosmics shower simulation
8
Map to diffractive/forward physics in CMS
Low lumi
Rapidity gap selection possible
HF, Castor, BSCs, T1, T2
Proton tag selection optional
RPs at 220m and 420 m
Diffraction is about 1/4 of tot
High cross section processes
“Soft” diffraction
Interesting for start-up running
Important for understanding pile-up
DIS06, 20-24/04/06, M. Ruspa
High lumi
No Rapidity gap selection possible
Proton tag selection indispensable
RPs at 220 m and 420 m
Central exclusive production
Discovery physics:
Light SM Higgs
MSSM Higgs
QCD: SD and DPE production of vector bosons, heavy quarks, high ET jets
Diff PDFs and generalized PDFs
Low-x structure of the proton
High-density regime
γ γ and γp interactions (QED)
Forward energy flow - input to cosmics shower simulation
9
The physics interest of DPE Higgs production
DIS06, 20-24/04/06, M. Ruspa
As the delivered luminosity reaches tens of fb-1 the central exclusive
production (CEP) processes become a tool to search for new physics
See B. Cox’s talk
Selection rules result in the central system
being (to good approx) JPC = 0++
shields color charge of
other two gluons
I.e. a particle produced with proton tags
has known quantum numbers
Excellent mass resolution (~GeV) from the
protons, independent of the decay products
of the central system
CP violation in the Higgs sector manifests
itself as azimuthal asymmetry of the protons
Vacuum quantum numbers
“Double Pomeron exchange”
Proton tagging may be the discovery channel
in certain regions in the MSSM
10
The physics interest of DPE Higgs production
DIS06, 20-24/04/06, M. Ruspa
As the delivered luminosity reaches tens of fb-1 the central exclusive
production (CEP) processes become a tool to search for new physics
See B. Cox’s talk
 b jets : M
H
2.5)
= 120 GeV  · BR = 2 fb (uncertainty factor ~
MH = 140 GeV  · BR = 0.7 fb
shields color charge of
other two gluons
MH = 120 GeV : 11 signal / O(10) background in 30 fb-1
after detector cuts
 WW* : M
H
= 120 GeV  · BR = 0.4 fb
MH = 140 GeV  · BR = 1 fb
MH = 140 GeV : 8 signal / O(3) background in 30 fb-1
after detector cuts
Vacuum quantum numbers
“Double Pomeron exchange”
 b-jet channel very important in “intense coupling
regime” of MSSM, cross section factor 10-20 larger,
discovery channel?
11
DPE Higgs production: necessary ingredients
beam
dipole
DIS06, 20-24/04/06, M. Ruspa
dipole
p’
roman pots
Nominal LHC beam optics @ 1033 - 1034cm-2s-1:

220 m: 0.02 <  < 0.2

420m: 0.002 <  < 0.02
p’
roman pots
1 2 s = M2
With √s = 14TeV, MH = 120 GeV
on average:
  0.009  1%
12
DIS06, 20-24/04/06, M. Ruspa
Trigger studies
“Diffractive Higgs: CMS/TOTEM level-1 trigger studies”
M. Arneodo, V. Avati, R. Croft, F. Ferro, M. Grothe, C. Hogg,
F. Oljemark, K. Osterberg, M. Ruspa
Proceedings of “ HERA and the LHC: A Workshop on the
Implications of HERA for LHC Physics",
CERN-DESY 2004/2005, p. 455-460;
hep-ph/0601013
 Semileptonic WW and tau tau decay channels
(or any final state with high-pT leptons, missing ET): trigger not a problem!
 Most challenging case is H (120 GeV)  bb
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DIS06, 20-24/04/06, M. Ruspa
Triggering jets at CMS
Calo
40 MHz
collision
HCAL
ECAL
PbWO4
crystal
Muon
Level-1 trigger
no tracking!
< 100 kHz
Trigger
tower
tveto
patterns
High-Level Trigger HLT
< 100 Hz
 4x4 trigger towers = region
 Search for jets with a
sliding 3x3 regions window
 Jet = 3x3 region with local energy
max in middle
 Reconstructed L1 jet ET on
average ~ 60% of real jet ET,
thus need for jet ET calibration
 Jet = 144 trigger towers,
with typical jet dimensions:
Dh x Df = 1 x 1
14
The difficulty of triggering on a light Higgs
DIS06, 20-24/04/06, M. Ruspa
L1 jet trigger signature for a 120 GeV Higgs: 2 jets in CMS Cal, ET < 60 GeV each




Measured L1 jet ET on average only ~60% of true jet ET
L1 trigger applies jet ET calibration and cuts on calibrated value
Thus: 40 GeV (calibrated) ~ 20 to 25 GeV measured
Cannot go much lower because of noise
while considered acceptable: O(1Khz)
 Need additional conditions in trigger
Use rate/efficiency @ L1 jet ET cutoff of 40 GeV as benchmark
15
L1 2-jet trigger +…
DIS06, 20-24/04/06, M. Ruspa
+ HT condition = isolation condition for jets:
2 jets in central Cal (|η|< 2.5) with ∑(ET 2 jets)/HT > threshold
HT = scalar sum of ET of all jets in the event with ET(jet) > threshold
 factor 2 rate reduction
16
L1 2-jet trigger +…
DIS06, 20-24/04/06, M. Ruspa
+ HT condition = isolation condition for jets:
2 jets in central Cal (|η| < 2.5) with ∑(ET 2 jets)/HT > threshold
HT = scalar sum of ET of all jets in the event with ET(jet) > threshold
 factor 2 rate reduction
+ Conditions based on TOTEM detectors T1 e T2:
• excellent suppression of QCD bacground
• useless as soon as pile-up events are present as also signal events are
vetoed (non-diff. component in pile-up events tends to quickly fill in the
rapidity gaps).
17
L1 2-jet trigger +…
DIS06, 20-24/04/06, M. Ruspa
+ HT condition = isolation condition for jets:
2 jets in central Cal (|η| < 2.5) with ∑(ET 2 jets)/HT > threshold
HT = scalar sum of ET of all jets in the event with ET(jet) > threshold
 factor 2 rate reduction
+ Conditions based on TOTEM detectors T1 e T2:
• excellent suppression of QCD background
• useless as soon as pile-up events are present as also signal events are
vetoed (non-diff. component in pile-up events tends to quickly fill in the
rapidity gaps).
+ Topological condition:
2 jets required to be in the same η hemisphere as the RP detectors that see
tthe proton
 factor 2 rate reduction
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DIS06, 20-24/04/06, M. Ruspa
+ Single-arm 220 m condition:
 mass resolution for CEP
Higgs is worst than with
420 m tag
kHz
L1 2-jet trigger +…
L=1032cm-2s-1
Integrated QCD rate for events
with at least two jets
Plot: Richard Croft
Integrated QCD rate for events
with at least two jets and
which satisfy the single-arm
220 m RP condition
19
L1 2-jet trigger +…
DIS06, 20-24/04/06, M. Ruspa
+ Single-arm 220 m condition:
 very good reduction of rate in absence of pile-up
 reduction decreases substantially in the presence of pile-up
+ Single-arm 220 m condition with  cut
TOTEM will provide implementation of a  cut at L1 (e.g.  < 0.1, recall
acceptance is 0.02 <  < 0.2). Implementation and achievable
resolution under study..
 Achievable total reduction: 10 x 2 (HT cond.) x 2 (topological cond.) = 40!
20
Triggering on a light Higgs
DIS06, 20-24/04/06, M. Ruspa
For H (120 GeV, DPE)  b bbar, adding L1 conditions on the RPs at 220m is
likely to provide a rate reduction sufficient to meet the CMS L1 bandwidth
limits at luminosities up to 2x 1033 cm-1 s-1
To go even further up in luminosity need additional handle to stay within
bandwidth limits
... So what about triggering with the 420 m RPs ?
At the current CMS L1 latency of 3.2 s they are too far away from IP
for inclusion in L1
Note: This is a hardware limit - cannot be changed without replacing
trigger pipelines of CMS tracker and preshower detectors with deeper ones
Should this however happen (under discussion for SLHC: L1 latency 6.4 s,
determined by ECAL pipeline depth) then ....
21
L1 2-jet trigger +…
DIS06, 20-24/04/06, M. Ruspa
+ Asymmetric 220 & 420 condition:
 in effect means on opposite sides events where  values of 2
protons are very different
 can be used either in L1 after increase in L1 latency or on HLT!
 Achievable total reduction: 75 x 2 (HT cond.) x 2 (topological cond.) = 300!
22
L1 efficiency – RP condition
DIS06, 20-24/04/06, M. Ruspa
How much is left of our signal?
Without RP condition
Various RP conditions
Plots: Richard Croft
23
DIS06, 20-24/04/06, M. Ruspa
L1 signal efficiency – muon condition
How many signal events are being retained by the already foreseen CMS
trigger streams, notably the muon trigger?

H  bb (120 GeV): relatively muon-rich final state from B-decays - about
20% of events have at least one muon in the final state
 Half of events with a muon in the final state can be triggered with
aa 1 muon + 1 jet trigger (to be implemented)

H  WW(140 GeV): about 23% of events have at least one muon in the final
state:
 70% of events with CMS L1 single muon trigger
Numbers: F. Oljemark
24
DIS06, 20-24/04/06, M. Ruspa
DPE processes constitute only a small part of the diffractive cross section
that can be explored by CMS and TOTEM. Exemplary of any process that
deposits low ET in the central detector.
Single diffractive
production of W, Z, dijets
25
Single diffractive production of W, Z, dijets
DIS06, 20-24/04/06, M. Ruspa
Recall:
• RP acceptances at * = 0.5 m:
220m - 0.02 <  < 0.2
420m – 0.002 <  < 0.02
• Lowest threshold for L1 jet trigger is ET > 40 GeV
• Typical loss of factor 2 in efficiency when using 220 m RP cond. (RP acceptance)
Map the parameter space (bandwidth vs efficiency) with ultimate goal
of defining a trigger table for a dedicated diffractive trigger stream with
target output rates of 1 kHz (L1) and 1 Hz (HLT)
Use POMWIG Monte Carlo
Plot: Richard Croft
26
Summary
DIS06, 20-24/04/06, M. Ruspa
 At LHC startup, where the luminosity will be low, and where no
pile-up is present, CMS can pursue a rich program of rapidity-gap based
diffractive and fwd physics
 Should the FP420 R&D project result in upgrading CMS with detectors
420 m away from the IP, proton-tag based program and discovery
physics becomes possible
 Wide proton-tag based program ranging from QCD to the low-x structure of
the proton to photon physics already possible by way of a collaboration of CMS
with TOTEM
 Key element is trigger, notably at high lumi, when amount of pile-up collisions
overlaid to the interesting hard event becomes high. Pile-up events are
themselves largely diffractive
27
Triggering diffraction at CMS: summary
DIS06, 20-24/04/06, M. Ruspa
 Triggering in absence of pile-up: no problem.

L1 2-jet rate for central with L1 jet ET cutoff of 40 GeV must be reduced to
O(1Khz) to accomplish with CMS L1 bandwith restrictions. Therefore using
L1 jet trigger alone not an option in the presence of pile-up.

Can trigger with the central detector alone by using the muon trigger
Efficiencies with already foreseen CMS L1 thresholds:
10% for H(120GeV)  bb, 20% for H(140GeV)  WW*

Can also use the L1 jet trigger when combining it with RP condition at
(rate of a few kHz achievable at 2x1033 cm-1s-1).
Requires defining a new CMS trigger stream; efficiencies around 10%.

L1 efficiencies for SD production of W’s, Z’s, die-jets available.
A dedicated trigger stream hence feasible, with output rates of O(1) kHz
L1, efficient for selecting CEP, a potential discovery channel for a light
Higgs boson, and hard single diffractive processes.
28
DIS06, 20-24/04/06, M. Ruspa
BACKUP
29
Background in RPs
DIS06, 20-24/04/06, M. Ruspa
Beam-halo/beam-gas level numbers produced by TOTEM not a problem
as soon as central CMS detector condition is used in L1
Find from PYTHIA pile-up sample:
@220m: 0.012 protons per pile-up event on average, i.e.
at 1034 cm-2s-1: 35*0.055=1.93
 @220m: In worst case on average 1.93 tracks from pile-up
in addition to track from signal event
@420m: 0.055 protons per pile-up event on average, i.e.
at 1034 cm-2s-1: 35*0.012=0.42
 @420m: In worst case on average 0.42 tracks from pile-up
in addition to track from signal event
The reduction factors in the presence of pile-up obtained by scaling
the probability per pile-up event to satisfy the relevant RP condition,
determined separately, by the average number of pile-up events at
the luminosity in question.
30
DIS06, 20-24/04/06, M. Ruspa



No problem for processes with a lepton in the final state
H (120 GeV)  bbbar
 For luminosities up to 2x1033 cm-2s-1 possible to keep a
reasonable fraction of events
 At higher luminosities ~ 10% can always be kept by
triggering on muons
MSSM scenario:
 discovery can be made with lumi at or below 1x1033 cm-2s-1
 at higher luminosities triggering on muons from b-decay
31
Other L1 conditions
DIS06, 20-24/04/06, M. Ruspa
 Effect of combining aready foreseen L1 trigger conditions with
conditions on the RP detectors
Estimated 1kHz Jet Thresholds for various Central / RP conditions
S: single-sided, D: double-sided
C: <0.1 of the leading proton
 Large rapidity gap cut at L1 (jets veto in forward calorimeter) 
Further rate reduction (approx. factor 2) at lumi where pile-up is negligible
32
L1 2-jet trigger +…
DIS06, 20-24/04/06, M. Ruspa
At 420
m&
420 m
500
150
30
10
+ Double-arm 420 condition:
 only possible after increase of L1 latency
 would allow to select events that are gold plated wrt mass resolution
 note: single-sided 220 m cond. and asymmetric cond. select events with
worst possible mass resolution
 Achievable total reduction: 30 x 2 (HT cond.) x 2 (topological cond.) = 120!
33
DIS06, 20-24/04/06, M. Ruspa
HLT studies
A) L1: 220 m single-arm condition with a  cut
B) Back-to-backness of jets (2.8 < ΔΦ< 2.48 rad) and
(E1T –E2T)/(E1T + E2T) < 0.4 and ET> 40 GeV
C)  reconstructed from jets in the central detector +(-) = s-½∑ETi exp(-(+)ηi);
cut: difference between 2  values larger than 2σ. No simulation of RP
reconstruction available so far. Assumed  resolution of 15% (20%) at 220
(420) m
Desired target output
rate; no loss in
efficiency compared to
L1
D) Either one of the 2 jets b-tagged
E) A proton seen at 420 m
No pile-up case: no QCD bgd survives selection.
HLT selection cond.
A+B+C
A+B+D
A+B+C+E
HLT rate L=1x1033cm-2s-1
15 Hz
20 Hz
< 1Hz
HLT rate L=2x1033cm-2s-1
60 Hz
80 Hz
1 Hz
Signal eff. H bb (120 GeV)
11%
7%
6%
34
Hard diffractive QCD studies
DIS06, 20-24/04/06, M. Ruspa
FAMOS (Fast CMS Simulation) + RPs acceptance tables
DPEMC MC:



tt production
 inclusive DPE for the semileptonic channel (tt  bb qq μ ν )
 good rejection of QCD background obtained
 for SD the cross section should increase by a factor 30-40
B production
 SD and DPE production of B-mesons with B J/psi μ μ
 tens of events for 10 fb-1 in DPE case and several hundreds in SD case
W and WW production
 DPE inclusive W production: abundant process can be studies at lumi
where pile up is small
 DPE exclusive WW production: 10 events in 10 fb-1
N.B.: 10 fb-1 collected in  60 days of LHC running @ 2x1033 cm-2s-1
35
Hard diffractive dijet prod.

DIS06, 20-24/04/06, M. Ruspa
Inclusive dijet production pp  pXjjp
Was used by CDF to measure diffractive structure function of the
proton: similar measurement possible at CMS, with wider kinematic
coverage ( > 0.02 (0.002) compared to  > 0.035 at CDF); statistical
accuracy of CDF measurement could be reached within a few days of
running at ~1032 cm-2 s-1
 Comparison of DPE and SD rates for dijet production would give
information on the hard diffractive factorisation breaking at the LHC


Exclusive dijet production pp  pjjp
 Cross section for central exclusive production of dijets order of 1 nb 
high rate allows precise determination of the off-diagonal un-integrated
gluon densities  uncertainties in exclusive production cross section of
Higgs to be reduced to 1% level
36
γp and γγ physics
DIS06, 20-24/04/06, M. Ruspa
Events with a fast proton in the final state can also originate from the
exchange of a vector boson. In particular, tagging one leading proton allows
the selection of photon-proton events with known photon energy; likewise
tagging two leading protons gives access to photon-photon interactions of well
known center of mass energy [PRD 63 070152, hep-ex/0201027].
p
p
 e.g.: exclusive 2- γ production of lepton pairs is an important calibration
process (forward e+e- pairs in Castor with proton tag, observed cross
section 3 pb, μ+μ- would double the statistics)
37
Light SM Higgs at the LHC (I)
DIS06, 20-24/04/06, M. Ruspa
SM Higgs with ~120 GeV:
gg  H, H  b bbar mode has highest BR
But signal swamped by gg  b bbar
Best bet with CMS: H  , where in 30 fb-1 S/√B  4.4
38
Light SM Higgs at the LHC (II)
DIS06, 20-24/04/06, M. Ruspa
Production cross section times branching ratio for CEP
From implementation of KMR model in Exhume MC
39
DIS06, 20-24/04/06, M. Ruspa
MSSM and proton tagging
Intense-coupling regime of the MSSM:
Mh~MA ~ MH ~ O(100GeV): their coupling to
, WW*, ZZ* strongly suppressed
 discovery very challenging at the LHC
100 fb
-
Cross section of two scalar (0+) Higgs bosons
enhanced compared to SM Higgs
 CEP as discovery channel
1 fb
“3-way mixing” scenario of CP-violating MSSM:
the 3 neutral Higgs bosons are nearly degenerate,
mix strongly and have masses close to 120 GeV
see Kaidalov et al
hep-ph/0307064
hep-ph/0311023
120 140
Superior mass resolution from tagged proton allows disentangling the
Higgs bosons by measuring their production line shape
Explicit CP-violation in Higgs sector visible as asymmetry in the azimuthal
distribution of tagged protons (interference of P- and P+ amplitudes) (Khoze
et al., hep-ph/0401078)
 CEP as CP and line-shape analyzer !
40
DPE Higgs production: models (I)
DIS06, 20-24/04/06, M. Ruspa
Difference between DPEMC and (EDDE/ExHuMe) is an effect of
Sudakov suppression factor growing as the available phase space for
gluon emission increases with increasing mass of the central system
Models predict different physics potentials !
41
DPE Higgs production: models (III)

DIS06, 20-24/04/06, M. Ruspa
More central rapidity in ExHuMe due to gluon distr. falling
more sharply than the Pomeron parameterisation in DPEMC
N.B: acceptance of forward proton taggers sensitive to the rapidity
distribution of central system.
Cut ξ = 0.1 applied in DPEMC as required by Bialas-Landshoff appr.
43
DIS06, 20-24/04/06, M. Ruspa
DPE Higgs event generators
1.
DPEMC 2.4 (M.Boonekamp, T.Kucs)
- Bialas-Landshof model for Pomeron flux within proton
- Rap. gap survival probability = 0.03
- HERWIG for hadronization
All three models
available in the fast
CMS simulation
2. EDDE 1.2 (V.Petrov, R.Ryutin)
- Regge-eikonal approach to calculate soft proton vertices
- Sudakov factor to suppress radiation into rap.gap
- PYTHIA for hadronization
3. ExHuMe 1.3 (J.Monk, A.Pilkington)
- Durham model for exclusive diffraction (pert. calc. by KMR)
- Improved unintegrated gluon pdfs
- Sudakov factor to suppress radiation into rap.gap + rap.gap
survival prob.= 0.03
- PYTHIA for hadronization
44
DPE Higgs production studies
DIS06, 20-24/04/06, M. Ruspa
Models: EDDE, EXHUME, DPEMC, all in FAMOS; RPs acceptance tables


H  bb in SM: back-to-backness of the jets, b-tag, two final state
protons, consistency of mass reconstruction between RPs and central
detector:
 2-4 signal events per 30 fb-1
 suppression of backgrounds rely on resolution of RP
H  WW* in SM [EPJ C45 (2006) 401]:
 1-7 events depending on mass range per 30 fb-1
 suppression of background does not rely on resolution of RPs
 irreducible backgrounds small and controllable
N.B.: 30 fb-1 collected in  30 days of LHC running @ 1034 cm-2s-1
45
DPE Higgs production studies
-
DIS06, 20-24/04/06, M. Ruspa
Recent versions of DPEMC, EDDE and ExHuMe generators as well
as new RP acceptances available in CMS fast simulation
- H->bb: Difficult channel. Cross sections, RP and b-tag efficiencies for
signal well established but the selection cuts still being tuned.
BG = ISSUE ! None of the models treats bg properly.
The bg issue needs an input from theory side.
- Comparison of generators: Rich resource in HERA-LHC proceedings
Non-negligible differences in basic quantities (ξ and yH)
influencing RP acceptances
- Comparison to data: Hard task to make a comparison to the only avail.
data (Rjj distr. from RunII). Hope to get a good
description, though.
46
DPE Higgs production studies
DIS06, 20-24/04/06, M. Ruspa
- H->WW in SM: Solid numbers for signal including L1-trigger
Bg is small and controllable
Promising channel for mh>130 GeV
- H->WW (bb,tautau) in MSSM:
Idea of Durham group (V.Khoze et al.).
In some scenarios and in some regions of (mA,tanβ)
a much higher yield than in SM case.
Especially promising for Higgs -> bb and
Higgs -> tautau channels
47
γp and γγ physics
DIS06, 20-24/04/06, M. Ruspa
Photon fluxes introduced in CALCHEP/COMPHEP,
photon events then fed to PYTHIA for decays and hadronization
CMS full detector simulation + RPs acceptance tables


γγ interactions:
 2-γ production of W pairs: studies of quartic gauge couplings
gammagamma ll
γγWW (LEP limits are weak due to limited cms energy)
 Exclusive 2- γ production of lepton pairs is an important
DY: pairs
qqbar
calibration process (forward e+ein llCastor with proton tag,
observed cross section 3 pb)
γp interactions:
 photoproduction of H: significant cross-section at LHC and good
signal-to-background ratio; low mass region with Higgs decaying
to bb, tt and W;
 W boson production at high transverse momentum, top pair
production via photon-gluon fusion, …
48
Drell-Yan
DIS06, 20-24/04/06, M. Ruspa
49
Low-x studies
DIS06, 20-24/04/06, M. Ruspa
HERA  x down to 10-5 ; LHC can probe very low x down to 10-6, 10-7
Drell-Yan: pp  qq  */Z  e+e- X
 Sensitive to very low-x partons in
the proton (x~10-6 to 10-7)
 Detect electrons in CASTOR
(5.2 < || < 6.6)
 Can enhance signal/background
ratio by requiring track in T2
50
Survey of accessible diff/fwd processes (III)
DIS06, 20-24/04/06, M. Ruspa
SD and DPE with hard scale: Production of heavy quarks
Inclusive DPE prod of t tbar: (A. Vilela Pereira)
 semileptonic decay channel:
pp  p+X+(tt)+X+p; tt  bbqq
 DPEMC and Pomwig generators
 Require 2 protons in 220m and/or
420m detectors
 Event yield 1-10 per 10fb-1, depending on
theoretical model, but taking supression
factor of 0.03 into account
DPE and SD prod of B  J/  
(D. Damiao)
DPEMC MC
Event yields per 10 pb-1:
DPE: tens of events
SD: several hundreds of events
51
Survey of accessible diff/fwd processes (IV)
DIS06, 20-24/04/06, M. Ruspa
DPE with hard scale: DPE prod of W and W-pairs (A. Loginov)
DPE pp  pYWp
 DPEMC MC
 require 2 protons, in 220m and/or 420m detectors
 several thousand events of type W  eand
W  expected per 1 fb-1
 together with SD prod of W can be used to
measure hard diffractive factorisation breaking
with LHC data alone
DPE excl prod pp  pWWp
dominated by QED
 DPE prod of W-pairs relatively rare process
 dominated by QED
 require 2 protons, in 220m and/or 420m
detectors
 expects about 1 event per fb-1
 this small SM expectation would allow
detection of anomalous WW prod, as e.g.
predicted in theory of supercritical pomeron
52