Other beam-induced background at the IP B. Dalena (CEA-IRFU/SACM) Contributions from: D. Schulte and J. Esberg

Outline Beam-Beam backgrounds at CLIC 3 TeV CM energy Expected Rates Machine imperfections Machine induced backgrounds Synchrotron radiation from the final doublet 28 September 2011 B. Dalena, LCWS11

Beam-Beam interaction Particles rates produced during beam-beam interaction are expected to be high at CLIC 3 TeV CM energy They impact the interaction region design Spent beams particles Beamstrahlung photons Coherent pairs Incoherent pairs Bhabhas and radiative bhabhas Hadrons from  collisions Rates, energy and angles distributions computed with GUINEA-PIG (+ PYTHIA for hadronization) 28 September 2011 B. Dalena, LCWS11

Spent beams and beamstrahlung photons e+ e- strongly focused in the electromagnetic field of the opposite bunch emit photons Average energy loss due to the radiation ΔE/EBS ~29% Average emitted photons per beam particle n ~ 2.1 per beam particle  Long tail at low energy of the spent beam 28 September 2011 B. Dalena, LCWS11

<  > ~ 1 quantum regime Coherent processes Conversion of a beamstrahlung photon into e+e- pairs in the strong electromagnetic field of the other bunch charge distribution rate of e+e- pairs creation is small for Ecm < 1 TeV at CLIC nominal center of mass energy it is important <  > ~ 1 quantum regime conversion of virtual photon (trident cascade) are also possible at CLIC energies 28 September 2011 B. Dalena, LCWS11

Incoherent pairs & hadrons Incoherent e+e- pairs production from real-real, virtual-real and virtual-virtual photons scattering Incoherent μ+μ- pairs production, through the same processes, is also possible but much smaller rate e+ e-    hadrons (hadronization from Pythia) Cross sections increase with energy Visible in the detector 28 September 2011 B. Dalena, LCWS11

Radiative Bhabhas e+ e-  e+ e-  at lowest order and for leptons scattered at small angles the cross section can be factorized into two parts: e+ e+  equivalent photon spectrum e-   e- Compton scattering Energy of the e- and photons up to quite all the beam energy Confined at relative small angles 28 September 2011 B. Dalena, LCWS11

CLIC crossing angle c = 10 mrad A cone of half aperture of 10 mrad contains most of the particles produced after collision N.B.  is defined with respect to the beam axis in the collision reference system c = 10 mrad 28 September 2011 B. Dalena, LCWS11

Luminosity spectrum 1% single bunch energy spread due to RF structures beamstrahlung smears the center of mass energy spectrum coherent processes contribute to the low energy tail of the spectrum ~4% total (1% from e- e- or e+ e+ collisions) 28 September 2011 B. Dalena, LCWS11

Beams parameters and Luminosity Beam-Beam products per BX [*] Backgrounds rates Beams parameters and Luminosity Total Luminosity [1034 cm-2 s-1] 5.9 Peak Luminosity 2.0 fr [Hz] 50 Nb 312 t [ns] 0.5 N 0.372e+10 z [m] 44 x /y [nm]/[nm] 660/20 *x /*y 45/1 Beam-Beam products per BX [*] ΔE/EBS 29 % n 2.1 (x N) Ncoherent 66e+7 Ntrident 67e+5 Nincoh_pairs 330e+3 Nincoh_muons 12.50 NHadrons 3.2 Nrad_bhabhas 110e+3 [*] GUINEA-PIG The emittance values include the budgets for imperfections The actual values depend on the single machine and can change during operation 28 September 2011 B. Dalena, LCWS11

Beam-Beam Jitter the relative change in luminosity correspond roughly to the same change in the beam-beam background rates (except for the coherent processes with vertical offsets) B. D. and D. Schulte WEPE025, IPAC’10 28 September 2011 B. Dalena, LCWS11

Beam emittances Beam-Beam products increase/decrease together with luminosity if the emittances of the two beams decrease/increase (except for the coherent processes with vertical emittance change) B. D. and D. Schulte WEPE025, IPAC’10 28 September 2011 B. Dalena, LCWS11

Machine imperfections and corrections Due to the budget for imperfections forseen luminosity and background rate can be higher than nominal (up to 50% and 40% respectively) example: corrected machines (after BBA) ground motion following ATL low (A = 0.5×10−6 (μm)2/(ms)) applied to main LINAC only[3] luminosity and background values show a linear correlation [3] V. Shiltsev IWAA 1995, vol. 4, p 352 B. D. and D. Schulte WEPE025, IPAC’10 28 September 2011 B. Dalena, LCWS11

Machine-induced background: photon fans Spectrum of emitted photons peaks at few MeV Maximum photon cone for an envelope covering 15x and 55y arXiv:1104.2426 [physics.acc-ph] 28 September 2011 B. Dalena, LCWS11

Conclusion At CLIC 3 TeV cm energy background rates from beam-beam interaction can be high Their knowlegde is important for the interaction region design (quite important energy is deposited in the detector and extraction region) They affect the luminosity (smearing the CM distribution and adding 4% to the total luminosity) Nominal values account for imperfections  luminosity and background may increase ( up to 50% and 40% respectively) Photon fans from the final doublet are contained in the extraction cone aperture 28 September 2011 B. Dalena, LCWS11

Beam charge Perfect machines but low intensity beam 28 September 2011 B. Dalena, LCWS11

Luminosity during operation BBA FB FB FB Emittance budget: 5 nm rad (static imperfections) Emittance budget: 5 nm rad (dynamic imperfections) 28 September 2011 B. Dalena, LCWS11

Machine imperfections (static) Inputs: main LINAC “standard” magnets and cavities misalignments[1] vertical plane only Beam Based Alignment applied[2] Beam parameters: z = 44 m N = 3.72 e+09 x = 660 nm rad y = 10 nm rad Results ~30% more luminosity on average with respect to nominal luminosity ~25% more background on average with respect to nominal background fluctuation ~5% (rms/<value>) in the background values from one bunch to the other [1] BD and D. Schulte WEPE025 IPAC’10 [2] D. Schulte TH6PFP045 PAC’09 28 September 2011 B. Dalena, LCWS11