# Presentation: 901729

## Exhortation*

- Albert De Roeck
- CERN
- MC4BSM 2006

-         (*)A speech or discourse that encourages, incites or earnestly advises

## Requirements for Extra DimensionAnalyses from LHC Experiments 

- Thanks to: B. Heineman, K. Matchev, F. Moortgat,L. Pape, G. Polesello, Y. Sirois, M. Spiropulu

- Talk given at Les Houches 05
-    Is still current thinking in the experiments
-    Includes some updates and additions
- While taking ED’s as an example, it does
- set the scene for BSM process generators
- in general, seen from the experiments
- Also, activity started
-   Web repository (September 05/P Skands)
-   Workshops       FNAL: MC4BSM  20-21 March
-                             LAP-LAPTH: Tools for SUSY and BSM 26-28 June
-                             CERN: MC4LHC   17-26 July

- Things are moving forward

## Large Extra Dimensions

- Large Extra dimensions (ADD)
- Gravity in bulk / flat space
- Missing energy/interference/black holes
- Warped Extra Dimensions (RS)
- Gravity in bulk / curved space
- Spin 2 resonances > TeV  range
-                                    k =  warp factor
- TeV Scale Extra Dimensions
- Gauge bosons/Higgs in the bulk
- Spin 1 resonances > TeV range
- Interference with Drell-Yan
- Special case: Universal Extra Dimensions UED
- Everybody in the bulk!
- Fake SUSY spectrum of KK states
- + many combinations/variations

## Extra Dimensions Analyses 

-                  Issues for Extra Dimension analyses for experimentalists
- Include processes on Monte Carlo Generators for LHC (Tevatron) analyses. Hence they become a ‘standard’ which can be compared in between experiments
- Include complete information into Monte Carlo Generators, such as spin correlations.  Study of measurability of spin effects (e.g. SUSYUED, Z’  KK...)
- Cross checks between codes/Monte Carlo results are important (problems have been found in the past)
- Agree on phase space available for EDs at LHC (& ILC, CLIC, Tevatron). Under which conditions do e.g. astrophysical and other limits apply. How can certain scenarios (e.g MSLED) escape these limits...? Info is scattered...
- Agree on a number of benchmark scenarios, like we have for SUSY and successfully used e.g. in LHC/ILC studies
- Time to think about K factors? See hep-ph/0411018 for ADD/RS. The K factors can be large (~1.6 in that case) and affect the search reach.
- Accuracy of the background understanding important (e.g. Drell-Yan, Z+jet, PDFs..). Important for distr. tails where statistics & experimental checks will be limited.
- Use the same formalisme in the models, e.g for the definiton of the effective M**plank**** **(see G. Landsberg efforts)

- Needed: a Forum to discuss/develop these tools & standards

## ED Monte Carlo Generators

-          Monte Carlo Generators for LHC (Tevatron) analyses
- RS included in standard working horses HERWIG and PYTHIA
- Spin correlations not complete in PYTHIA e.g. for G  ZZ, WW  (now added: Pythia version 6.226)
- ADD: several private codes for both the graviton radiation and graviton exchange processes, for PYTHIA or HERWIG
- Recently improved by SHERPA which contains complete ADD FeynmanRules (Gleisberg, Kraus, Matchev)  now used in ATLAS/CMS
- UEDs exist in a private code for COMHEP (Matchev et al.)
- Wish: have processes combinable with main working horse MCs, at present PYTHIA and HERWIG. Thanks to the Les Houches accord(*) of 2001, an agreed exchange format exists in the Monte Carlo world such that one can think of a tool kit of ED processes to be combined with these MCs for the fragmentation/ hadronization (which is done e.g. for SM and SUSY processes)

- (*) GENERIC USER PROCESS INTERFACE FOR EVENT GENERATORS.E. Boos et al. Workshop on Physics at TeV Colliders, Les Houches,  2001.  hep-ph/0109068

## Monte Carlo Generators

- Can we have a toolkit
- for ED processes?
- Needs organization
- SPA-like project?
- Les Houches 2005?
- Dedicated workshops?
- A combination of the
- above?
- Core group needed to
- take the lead/intitiative

- T. Sjostrand

- Future  ThePEG?: a toolkit/framework for HEP event generators
- Lonnblad, Gieske, Ribon, Richardson

## A Propos Les Houches Accords

-  SusyLHA1 has implemented by many spectrum calculators,
- decay packages and event generators
-                (see diagram next page)
-                  widely used by experimentalists for MSSM studies!
-  SLHA1 did not include conventions for CPV, RPV, FLV, ...
-                  SLHA2 has been defined
- Discussions on the conventions are finalizing ... have any implementations
- started? Who is planning to do so? What timescale?
-                           The experiments are eager to start testing!

## SUSY Les Houches Accord v1

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**FITTINO, SFITTER**

**FITTERS**

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## LHC Experimentalist Generator Wish List

- Have more processes available: compiled list from CMS/ATLAS
- Universal extra dimensions with KK number conservation
- Universal extra dimensions without KK number conservation
- Bulk scalars with Higgs interference
- Radions and interference with the Higgs  (now hack in HDECAY)
- Implementation of different running couplings (see hep-ph9807522)
- More flexible/complete generation of KK resonances in TeV**-1** and RS models, which include many resonances, effects of brane kinematic terms (hep-ph0212279). TeV**-1** matrix elements in ‘standard toolkit’
- Branons
- More sophisticated black hole generators...? (remnant, radiation phases, spin)
- String ball effects (black hole-like but different radiation/lower mass)
- Transplankian effects, especially high E**T** 2 jet production
- SUSY+ ED scenarios (modify the phenomenology as in )
- Thick branes, brain tension, rigid and soft branes
- Even more recent scenarios (such as intersecting branes, Higgsless EWSB)

- At this stage, for LHC: MCs of new scenarios are important if these imply new signatures and require new sorts of experimental checks

## Example: Universal Extra Dimensions

- This is a “what if?” scenario!
- What if we have a KK tower pattern from
- ED’s which look like supersymmetry:
- Can the LHC tell distinguish?

- Tools: spin of the “sparticles”/ No heavy higgses/
- mass splitting small/pattern repeates at higher
- energies...

- e.g. Cheng, Matchev, Schmaltz hep-ph/0205314

- Search: e.g
- 4 leptons +
- E**T****miss**

- Present implementation in Comphep  (Matchev et al.)
- Problem: for long decay chain e.g. up to 10 particles/partons in the final state it is difficult to compute with all the spin correlations correctly and time consuming. Some tricks to improve being explored (E. Boos)

## Is it SUSY?

- Look for variables sensitive to the particle spin eg. lepton charge asymmetries
- in squark/KKquark decay chains  Barr hep-ph/0405052; Smillie & Webber hep-ph/0507170

- KK like
- spectrum
- (small mass
- splitting)

- SPS1a benchmark
- type spectrum

- Method works better or worse depending on (s)particles spectrum

- Can the LHC distinguish?

- e.g. Cheng, Matchev, Schmaltz hep-ph/0205314

- More discriminating variables needed!! need spin in cascades of generators

## Example: UED without KK conservation

-       Add KK violating interactions mediated by gravity to allow KK excitations to decay into a SM particle + KK graviton
- Pair production
- E.g. *  + KK graviton
- Signal for LHC  2 photons + large missing ET
- Single production
- E.g. gggg*gg+KK graviton
- Signal for LHC: 2 jets + large missing ET
- Useful to check sensitivity/reach for the LHC by experiments, but generator needed to do a good job (including acceptances, smearing, trigger etc...)

- Macesanu, McMullen, Nandi

## Example: Z’/KK studies in TeV-1 EDs

- Different /Z KK resonances

-        RS S**1**/Z**2** orbifold

- Can we distinguish scenarios at the LHC? Important to have flexible
- couplings, interference effects available in the event generators etc.

- D=0

- D=R

- Private code for TeV**-1 **resonances: Polesello, Azuelos, (Rizzo)

## Example: Rigid/Soft Branes

-                                                      ADD Models
-    Rigid brane: Coupling of massive KK towers is exactly the same for less massive towers
-   Soft branes: Coupling of higher mass KK towers reduced
-           g**n****2**  g**n****2** e**-(m/********)2    **** ******** = **wall tension
-                        could have any value but expected ~ O(TeV)

- M**D**’s fixed
- to agree with
- M**D**=5 TeV, n=2

- No generator exisits, but formulae for cross sections and kinematics available

- n = 7

- n = 2

- ee  G

-   = 4 TeV

## Example: Branons

- No generator available, but formulae for cross sections and kinematics
- available

- Branons: scalar particles , associated to brane fluctuations
-               couple to SM particles by pairs.

## Example: Black Holes

| Stage | Need a Quantum Theory of Gravity? | Scale | In Event
Generators? |
| --- | --- | --- | --- |
| Production | Yes and No | >MP | πr2 |
| “Hair Loss” | No | >MP | No |
| Spin
Down | No | >MP | No |
| Hawking
Radiation | Yes and No | >MP
~MP | Yes |
| Remnant
 Decay | Yes | <MP | Many
options |

- s>> M**planck** Black Hole production

- Ch. Lester/Prague 2003

-  Several MC on the market
-  Not all radiation phases included yet
-    (important?)
-  Truenoir (Lansberg)
-  Charybdis (Harris et al.)
- “BlackHole” (Tanaka et al)

## Example: Transplanckian Effects

- Once you pass the Planck scale  ****s >> M**D**...

- Processes with small
- momentum transfer e.g. :
- Elastic transplanckian collisions:
- Study gravity propagation in ED’s
- Signal: dijets with large M**jj**

- Giudice, Rattazzi, Wells

- of the two jets

- Phenomenology (formulae) worked out but no generator available!!

## Generator Comparisons

- Eg   pp  G+   +X using Sherpa and a Pythia based version (Matchev et al)

_**X -sections: **__  _ 	    Sherpa  	                  Stagen/PYTHIA
- Version:				 1.0.6  					1.05/6.227
- PDF:					CTEQ6L				CTEQ6L
- X-sections for ADD Graviton + photon production, MD = 5000 GeV
- Cut:				PT Photon >400 GeV	      CKIN(3)>400 GeV (PT  HAT )
-        d= 2                       0.33 fb 		 	0.35 fb
-       Cut:                        P**T **Photon >100 GeV	CKIN(3)>100 GeV (PT  HAT )
-        d= 2		2.47 fb				2.78 fb

- Pythia/Sherpa

- Differences understood?

- J. Weng

## Higher QCD corrections/K factors

- D. Rainwater (TH) at Les Houches 2003:
-       Critique to the experiments:
-     “Where possible the experiments should include NLO results (if nothing better via K factors) in their experimental assessment of there sensitivity. Sometimes important effects on the sensitivity which may reclassify a process as being accessible (or vice versa)

- CMS: to be published in EPJC direct

- Shown here for Higgs ‘discovery’

## Higher QCD corrections/K-Factors

- P. Mathews, V. Ravindran, K. Shridhar, W.L. van Neerven
- NLO QCD corrections to ADD models hep-ph/0411018
-                    pp G  2 leptons

- Q= invariant mass of the
- Lepton Pair in DY production

- Note:
- K factor for gravity channel is
-   large: ~1.6
- Drell-Yan K factor is lower. Can
-  change the search sensitivity by
- ~50%

- K factors can make a difference!
- Already useful now for Tevatron
-  We encourage more K-factor
- determinations

- What about RS G 2 leptons?  same!
- What about       G ?       not same!

## Benchmarks for EDs: The SUSY example

- A number of SUSY (msugra and other) benchmark points to study LHC/LC sensitivity (Battaglia et al, Allanach et al.,...)
- Take into account direct searches at LEP and Tevatron, BR (b  s),  g-2  (E821),
- Cosmology:   0.09    h2  0.13

- Allowed regions in the M**0**-M**1/2** plane

- Very useful for comparisons of
- analyses, common studies,
- LHC/ILC studies

- We would benefit strongly from defining
- common ED benchmarks! Working group?

- ISASUGRA
- as common tool

## Constrains from other data

- It would be useful for LHC (and other studies) to know the available phase space, constrained by other data
- High energy collider data (usually known)
- Precision measurements
- Astrophysical and cosmological constraints (recent: hep-ph/0408320)
- Other experiments (gravitational measurements etc.)
- Benchmark processes need to take these into account
- Some effort in PDG. Working group?

-    Example: ADD Size of the Extra Dimensions:
-  = 1  R= 10**13** m     excluded!
-  = 2  R= 0.7 mm   essentially excluded
-          Results from SN1987A (model dependent)
-          Newtons law works down to 200m
-  = 3  R= 3 nm
-  = 4  R= 6x10**-12** m...

- Eg. LEP2 data constrains
- very strongly interacting
- gravity at the weak scale
- (Giudice, Strumia
- hep-ph/0301232)

## Formalism Unification

- G. Landsberg...

- Example: Virtual Graviton effects

- Useful to agree on a unique formalism

## Precise knowledge of the SM background

- Reduction of the
- Sensitivity due to
- PDF uncertainty
- (CTEQ6)

- Graviton exchange contributions reduce the cross section (interference)

- S. Ferrag

- Example: effect of PDFs on ADD di-jet final state sensitivity

- Other important SM background channel: Drell-Yan production

- Tev4LHC & HERA/LHC workshop

## Other requirements that came up...

- Including/keeping spin in the cascades
- Cascade decay generator implementing the full spin formalism like the one Peter Richardson has successfully implemented in Herwig.
- SusyLHA2 available? As mentioned before...
- Split Susy/Rhadrons: spectrum for large masses problematic (gluino mass > 1 TeV)
- SMadGraph/SMadEvent released and available?
- New home made models within the experiments eg.
- Excited gluons in top decays
- Jet-jet decays of virtual gravitions

## So far

- Good meeting at BNL (February) with a number of interested people (volunteers?)
- D. Bourlikov
- T. Han
- K. Matchev (+ one Florida student?)
- F. Kraus + one student?
- T. Tait
- S. Mrenna
- M. Besancon
- + a few others
- But no real work started yet before Les Houches 05
- Discussions at Les Houches & starting with the web repository
- http://www.ippp.dur.ac.uk/montecarlo/BSM/
- Useful first step/ good time to get organized now!

- 24 programs connected

## Summary: a list of wishes

- ED MC process tool box
- Complete with (many) missing processes
- Include details in the MC, eg. spin correlations. These correlations likely to become very important when LHC will discover a new object.
- In principle easy to contribute with present generator developments (Les Houches accord/ThePEG...)
- SM background processes: precision needed   (well known at this wkshop).
- Higher order QCD (EW) corrections to processes
- ED and constraints from existing data
- Start thinking of benchmark processes.
- Select a formalism, where (if) needed

- Important step forward: A forum starts to develop for these discussions
- Now we need to choose a scheme (toolkit or else) and implement it

- SUSY has the SPA project. Something similar for EDs?